以下の論文に対して，平成28年4月に日本機械学会賞（論文）を受賞したものである．
草野 和也, 古川 雅人, 山田 和豊, “半開放形プロペラファンにおける翼端渦の三次元構造”, 日本機械学会論文集, Vol. 80, No. 810, DOI: 10.1299/transjsme.2014fe0024, 2014.

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1088/1742-6596/1909/1/012007

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (other academic)  

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DOI： https://doi.org/10.1115/GT2020-15426

Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： https://doi.org/10.1115/FEDSM2020-20344

Language：English   Publishing type：Research paper (scientific journal)  

Water refrigerant heat pump system with a water vapour turbo compressor is developed. Water (R718) is an ideal refrigerant that is considered perfectly environment friendly. Although water refrigerant heat pump is studied extensively, the development of turbo compressors of high pressure ratio is still a technical challenge, in terms of both aerodynamics of the impellers and high-speed rotordynamics. In this study, the high-speed rotor is supported by journal bearings lubricated with water refrigerant. Additionally, other system components such as sprayed direct intercooler heat exchanger and anti-cavitation flow control valve have to be designed and developed with the new requirements as well. An experimental test rig of closed-loop heat pump is constructed which achieves the cooling capacity of 100 kW on the rated condition with COP = 5. The experimental results and the experienced challenges and their undertaken solutions are discussed in terms of the efficiency and the vibrations of the turbo compressor and the heat pump system.

DOI： https://doi.org/10.1177/0954408920938197

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.38036/JGPP.11.2_38

Language：English   Publishing type：Research paper (scientific journal)  

The present paper demonstrates the capability of a numerical method based on the lattice Boltzmann method (LBM) with wall-resolved grid to predict the broadband sound generated from the turbulent boundary layer at low Mach numbers. The present method is based on the lattice BGK equation with the D2Q9 and D3Q15 models, and a multi-scale approach using hierarchically refined grids is proposed to efficiently and simultaneously capture the multi-scale phenomena of turbulent eddies near walls and far-field sound waves. Numerical instabilities caused by the lack of grid resolution are suppressed with a fourth-order implicit filtering scheme. This numerical method is discussed in two benchmark problems and an application to the prediction of the broadband sound generated from the turbulent boundary layer. First, the computational accuracy and speed of the LBM scheme are assessed with a pulse-propagating problem. The results indicate that the LBM can achieve accuracy comparable to the fourth-order central scheme with the four-stage Runge-Kutta method for the compressible Navier-Stokes (N-S) equations and compute 12.3 times faster. These findings suggest that the LBM is an efficient computational method for aeroacoustic simulations. Second, the proposed method is validated by simulating the Aeolian tone generated by the flow past a circular cylinder at Reynolds number of 150 and Mach number of 0.2. The present simulation is compared with a compressible N-S simulation using a high-order finite difference scheme in terms of the wave profile and the propagation speed of the tonal sound. This validation result suggests that the present method is available for direct aeroacoustic simulations of low-Mach-number flows. Finally, the capability of the present method to predict the broadband sound is demonstrated by conducting a wall-resolved simulation for the turbulent flow generated by a short separation bubble over an isolated airfoil at Reynolds number of 2.0×10⁵ and Mach number of 0.058. This simulation shows a good agreement with measurements of the surface pressure distributions, the wake velocity profiles, and the far-field sound spectrum. In contrast to hybrid approaches based on the incompressible N-S equations, the present method can accurately predict the broadband sound in the high-frequency range by simulating the acoustic scattering on the airfoil.

DOI： 10.1016/j.jsv.2019.115044

Repository Public URL： http://hdl.handle.net/2324/4481545

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DOI： 10.1088/1757-899X/604/1/011010

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Secondary flows in transonic centrifugal compressor impellers affect their aerodynamic performance. In open-type impellers, low energy fluids can accumulate on the suction surfaces near the trailing edge tip side since the secondary flows and tip leakage flows interfere each other and complex flow phenomena can be generated around the impellers. Therefore, designers must consider the effect of secondary flows to avoid the aerodynamic performance degradation while designing compressor impellers. In this paper, a novel design concept about suppression of secondary flows in centrifugal compressor impellers to improve their aerodynamic performance. A transonic centrifugal compressor impeller was redesigned with the present design concept by a two-dimensional inverse method based on a meridional viscous flow calculation in this study. A design concept was introduced in above calculation process. As the design concept, by bending vortex filaments with controlling peak positions of the blade loading distributions, induced velocity due to bound vortices at the blades was generated in radial opposite direction of the secondary flows on the suction surface. Due to investigate the effect of the design concept in this paper, three-dimensional Reynolds Averaged Navier-Stokes simulations were carried out, and the vortex cores were visualized by a critical point theory and colored by non-dimensional helicity. In the conventional transonic centrifugal compressor impeller, the secondary flow vortices were confirmed and one of the vortices was broken down. In the redesigned impeller, the breakdown of the secondary flow vortices was not observed and the accumulation of the low energy fluids was suppressed compared with the conventional impeller. The total pressure ratio and adiabatic efficiency of the redesign impeller were higher than that of the conventional impeller, and the secondary flows were successfully suppressed in this research.

DOI： 10.1115/AJKFluids2019-5319

Language：English   Publishing type：Research paper (international conference proceedings)  

The present optimum design method has been advanced for simultaneous optimization of impeller blade loading distribution and meridional geometry. This is based on an aerodynamic design method and a genetic algorithm. The aerodynamic design method consists of two parts: a meridional viscous flow analysis and a two-dimensional inverse blade design procedure. In the meridional viscous flow analysis, an axisymmetric viscous flow is numerically analyzed on a two-dimensional grid to determine the flow distribution around the impeller and diffuser. Effects of blades onto the axisymmetric flow field are considered by a blade force modeling. In the inverse blade design procedure, 3-D impeller geometry can be obtained from the result of meridional viscous flow analysis and the predetermined blade loading distribution. In the optimization procedure, the total pressure ratio and adiabatic efficiency obtained from the meridional viscous flow analysis are employed as objective functions. As a constraint of the optimization, mass flux distribution at the impeller trailing edge is introduced in the evaluation procedure, in order to suppress the boundary layer development near the shroud, especially under low flow rate condition. Total performances and three-dimensional flow fields of centrifugal compressors have been analyzed by 3D-RANS simulations to certify effectiveness of the present design method. The 3D-RANS simulations and the flow visualization have been applied to a conventional centrifugal compressor and optimized design cases. From the analysis results, the performance enhancement of optimized designs is confirmed under low flow rate condition including design point. In addition to that, it is revealed that the constraint works effectively on the performance improvement. As a result, construction of the simultaneous optimization using the aerodynamic design method and the genetic algorithm is successfully achieved.

DOI： 10.1115/AJKFluids2019-5358

Language：English   Publishing type：Research paper (other academic)  

This paper describes the influence of a bent inlet pipe installed immediately upstream of a transonic centrifugal compressor on the aerodynamic performance and the stability. In order to clarify the influence of the bent inlet pipe, the internal flow fields in the inlet pipe, the impeller, and the diffuser of the compressor have been numerically investigated by a DES (Detached Eddy Simulation). For the purpose of comparison, the simulation was also conducted for the case of uniform axial inflow using a straight pipe. In order to make clear the influence of non-uniform flow with a bent pipe as far as possible, a 90-degree bent pipe was installed immediately upstream of the compressor, that is 0.86 times the inlet inner diameter. In the case of installing the bent pipe on the upstream of the compressor, the pressure ratio decreased on the high flow rate side in the compressor performance characteristic, whereas it increased at the low flow rate side. At the low flow rate operating point, there is a reversed flow occurring in the compressor impeller on the shroud side near the blade leading-edge. Installation of the bent pipe promotes mixing between the reversed flow and the main flow at the inlet of the compressor thanks to occurrence of a secondary flow. Since the reversed flow comes out from inside of the impeller, it has a high circumferential velocity. Therefore, the mixing of the reversed flow makes the compressor inlet flow a pre-swirl flow, and thereby the incidence decreases. As a result, leading-edge separation on the blade tip side of the impeller is suppressed, and the flow field inside the impeller is improved. In the diffuser section, when the bent pipe is installed, the circumferential velocity of the impeller exit flow increases on the hub side, whereas the radial velocity decreases. As a result, the diffuser performance is deteriorated and the diffuser stall tends to occur.

DOI： 10.1115/GT2019-90794

Language：English   Publishing type：Research paper (other academic)  

DOI： 10.1115/GT2019-90791

Language：English   Publishing type：Research paper (other academic)  

Flow structure and flow loss generation in a transonic axial compressor has been numerically investigated by using a large-scale detached eddy simulation (DES). The data mining techniques, which include a vortex identification based on the critical point theory and a limiting streamline visualization with the line integral convolution (LIC) method, were applied to the DES result in order to analyze the complicated flow field in compressor. The flow loss in unsteady flow field was evaluated by entropy production rate, and the loss mechanism and the loss amount of each flow phenomenon were investigated for the first rotor and the first stator. In the first rotor, a shock-induced separation is caused by the detached shock wave and the passage shock wave. On the hub side, a hub-corner separation occurs due to the secondary flow on the hub surface, and a hub-corner separation vortex is clearly formed. The flow loss is mainly caused by the blade boundary layer and wake, and the loss due to the shock wave is very small, only about 1 percent of the total loss amount in the first rotor. However, the shock/boundary layer interaction causes an additional loss in the blade boundary layer and the wake, which amount reaches to about 30 percent of the total. In the first stator, the hub-corner separation occurs on the suction side. Although only one hub-corner separation vortex is formed in the averaged flow field, the hub-corner separation vortex is generated in multiple pieces and those pieces interfere with each other in an instantaneous flow field. The hub-corner separation generates huge loss over a wide range, however, the loss generation around the hub-corner separation vortex is not so large, and the flow loss is mainly produced in the shear layer between the mainstream region and the separation region. The main factors of loss generation are the boundary layer, wake and hub-corner separation, which account for about 80 percent of the total loss amount in the first stator.

DOI： 10.1115/GT2019-90439

Language：English   Publishing type：Research paper (scientific journal)  

Recently, the application field of the pressure measurement technique using pressure sensitive paint (PSP) has been expanding. However, the temperature dependence of PSP is a serious obstacle to accurate pressure measurement in low gauge pressure conditions because PSP is an absolute pressure sensor. Therefore, the temperature information of PSP is indispensably required for accurate pressure measurement, especially in low gauge pressure conditions. As a result, both temperature information and pressure information with a function of temperature are required simultaneously to use the PSP in low gauge pressure conditions. Dual-layer PSP/temperature sensitive paint (TSP) (DL-PTSP) is one solution, but simultaneous measurement of pressure and temperature requires two optical filters to separate the luminescence of PSP and TSP, resulting in complex equipment and additional error caused by parallax. To solve the problem, we introduce a lifetime-based method for DL-PTSP that allows simultaneous measurement of pressure and temperature. It is a method which separates each component of luminescence with different lifetimes. Firstly, the DL-PTSP developed in this study was optimized by reducing the luminescence intensity of the PSP with a longer lifetime while maintaining the luminescence intensity of the TSP with a shorter lifetime, considering the lifetime measurement method. Secondly, we have clarified the optimum time conditions of the monolayer TSP and the monolayer PSP by analysing their luminescence decay process, by controlling the irradiation delay of the light source relative to the camera shutter. Thirdly, the sensitivity of the DL-PTSP was examined using conditions optimized for mono-layer TSP and PSP. The luminescence decay of the TSP component shows sufficient temperature dependence, while the pressure dependence is very small. On the other hand, the dependence of the luminescence decay of the PSP component on the temperature and pressure is almost equal to that of the mono-layer PSP. The results confirm the feasibility of the simultaneous measurement of pressure and temperature using DL-PTSP.

DOI： 10.1088/1361-6501/aae408

Language：English   Publishing type：Research paper (international conference proceedings)  

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Higher aerodynamic performance of turbochargers has been demanded because of vehicle engine down-sizing. Centrifugal compressors for automotive turbochargers require higher efficiency and wider operating range. Meridional geometry of the centrifugal compressors is one of their design specifications and it drastically affects the aerodynamic performance of the compressors. In this study, we designed the meridional geometry by using the aerodynamic design method based on a meridional viscous flow analysis and investigated the relation between the meridional geometry and the aerodynamic performance by analyzing meridional viscous flow calculation results and three-dimensional RANS calculation results. As a result, the relation between the boundary layer development near the shroud and the mass flux at the trailing edge was found out according to the meridional viscous flow calculation results. In addition, the relation and the performance improvement were confirmed according to experimental results.

DOI： 10.1115/FEDSM2018-83398

Language：English   Publishing type：Research paper (other academic)  

This paper describes unsteady flow phenomena of a two-stage transonic axial compressor, especially the flow field in the first stator. The stator blade with highly loaded is likely to cause a flow separation on the hub, so-called hub-corner separation. The flow mechanism of the hub-corner separation in the first stator is investigated in detail using a large-scale detached eddy simulation (DES) conducted for its full-annulus and full-stage with approximately 4.5 hundred million computational cells. The detailed analysis of complicated flow fields in the compressor is supported by data mining techniques. The data mining techniques applied in the present study include vortex identification based on the critical point theory and topological analysis of the limiting streamline pattern. The simulation results show that the flow field in the hub-corner separation is dominated by a tornado-type separation vortex. In the time averaged flow field, the hub-corner separation vortex rolls up from the hub wall, which is generated by the interaction between the mainstream flow, the leakage flow from the front partial clearance and the secondary flow across the blade passage toward the stator blade suction side. The hub-corner separation vortex suffers a vortex breakdown near the mid chord, where the high loss region due to the hub-corner separation expands drastically. In the rear part of the stator passage, a high loss region is migrated radially outward by the induced velocity of the hub-corner separation vortex. The flow field in the stator is influenced by the upstream and downstream rotors, which makes it difficult to understand the unsteady effects. The unsteady flow fields are analyzed by applying the phase-locked ensemble averaging technique. It is found from the phase-locked flow fields that the wake interaction from the upstream rotor has more influence on the stator flow field than the shock wave interaction from the downstream rotor. In the unsteady flow field, a focal-type separation also emerges on the blade suction surface, but it is periodically swept away by the wake passing of the upstream rotor. The separation vortex on the hub wall connects with the one on the blade suction surface, forming an arch-like vortex.

DOI： 10.1115/GT201876480

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (scientific journal)  

Flow fields in 2-blade and 4-blade half-ducted propeller fans for the outdoor units of air-conditioners were calculated with large eddy simulation based on finite element method with the aim of investigating the influence of blade number on aerodynamic noise. We confirmed that the tip vortex had a great influence on aerodynamic noise in half-ducted propeller fans. The length of the tip vortex trajectory and the blade pitch for the 2-blade propeller fan were longer than those for the 4-blade propeller fan. These were suppressed the interaction between the tip vortex and the adjacent blade in the 2-blade propeller fan. The 2-blade propeller fan was therefore more silent than the 4-blade propeller fan.

DOI： 10.5293/IJFMS.2017.10.4.318

Language：English   Publishing type：Research paper (international conference proceedings)  

In this study, the hub-corner separation in a multi-stage transonic axial compressor has been investigated using a largescale detached eddy simulation (DES) with about 4.5 hundred million computational cells. The complicated flow field near the hub wall in a stator with partial tip clearances was analyzed by data mining techniques extracting important flow phenomena from the DES results. The data mining techniques applied in the present study include vortex identification based on the critical point theory and topological data analysis of the limiting streamline pattern visualized by the line integral convolution (LIC) method. It is found from the time-averaged flow field in the first stator that the hub-corner separation vortex formed near the solid part of the stator tip interacts with the leakage flow and secondary flow on the hub wall, resulting in a complicated vortical flow field. Near the leading edge of the stator, the leakage flow from the front partial clearance generates the tip leakage vortex, which produces loss from the leading edge to 10 percent chord position. At the mid-chord, the hub-corner separation vortex suffers a breakdown, resulting in the widespread huge loss production. It is shown from limiting streamlines on the suction surface of the stator that a reverse flow region expands radially from the solid part of the stator tip toward the downstream. From 50 percent chord position to the trailing edge of the stator, the leakage flow through the rear partial clearance interacts with the secondary flow on the hub wall. The leakage vortex generated along the rear partial clearance becomes a major loss factor there.

DOI： 10.1115/FEDSM2017-69116

Language：English   Publishing type：Research paper (scientific journal)  

This paper describes the flow mechanisms of rotating stall inception in a multistage axial flow compressor of an actual gas turbine. Large-scale numerical simulations of the unsteady have been conducted. The compressor investigated is a test rig compressor that was used in the development of the Kawasaki L30A industrial gas turbine. While the compressor consists of a total of 14 stages, only the front stages of the compressor were analyzed in the present study. The test data show that the fifth or sixth stages of the machine are most likely the ones leading to stall. To model the precise flow physics leading to stall inception, the flow was modeled using a very dense computational mesh, with several million cells in each passage. A total of 2×109 cells were used for the first seven stages (3×108 cells in each stage). Since the mesh was still not fine enough for large-eddy simulation (LES), a detached-eddy simulation (DES) was used. Using DES, a flow field is calculated using LES except in the near-wall where the turbulent eddies are modeled by Reynolds-averaged Navier-Stokes. The computational resources required for such largescale simulations were still quite large, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena at the stall inception were analyzed using data mining techniques such as vortex identification and limiting streamline drawing with line integral convolution (LIC) techniques. In the compressor studied, stall started from a separation on the hub side rather than the commonly observed leading-edge separation near the tip. The flow phenomenon first observed in the stalling process is the hub corner separation, which appears in a passage of the sixth stator when approaching the stall point. This hub corner separation grows with time, and eventually leads to a leading-edge separation on the hub side of the stator. Once the leading-edge separation occurs, it rapidly develops into a rotating stall, causing another leading-edge separation of the neighboring blade. Finally, the rotating stall spreads to the upstream and downstream blade rows due to its large blockage effect.

DOI： 10.1115/1.4035519

Language：English   Publishing type：Research paper (international conference proceedings)  

In process centrifugal compressors used in various types of plants, the compressor is the heart of a plant, and it requires high reliability. Therefore, prediction of the surge is important for centrifugal compressors. There have been numerous researches on the surge: study on improvement of surge margin, and study on the rotating stall, which is recognized as a precursor to surge, in impeller or diffuser of the compressor. However, the researches have not focused on the surge inception flow phenomena, namely detailed flow mechanism leading to the surge, although understanding of such flow phenomena is important for prediction of the surge. The paper describes in detail unsteady flow fields in a transonic centrifugal compressor at near-surge conditions. The flow fields have been investigated by detached eddy simulations (DES) using 400 million grid points. The simulation results show that the huge reverse flow region occupies the flow field near the shroud in the impeller at off-design condition, triggered by the blade stall at the tip of impeller full-blade, and it drastically develops at near-surge. It is also found that the rotating disturbance with reversed flow appears in the diffuser near the endwall at around peak pressure-rise point, and it eventually evolves into the rotating stall cell with a large reverse flow, blocking the flow inside the diffuser at near-surge.

DOI： 10.1115/GT2017-63568

Language：English   Publishing type：Research paper (international conference proceedings)  

An optimum aerodynamic design method for centrifugal compressor impeller has been developed. The present optimum design method is using a genetic algorithm (GA) and a two-dimensional inverse blade design method based on a meridional viscous flow analysis. In the meridional viscous flow analysis, an axisymmetric viscous flow is numerically analyzed on a two-dimensional meridional grid to determine the flow distribution around the impeller. Full and splitter blade effects to the flow field are successfully evaluated in the meridional viscous flow analysis by a blade force modeling. In the inverse blade design procedure, blade loading distribution is given as the design variable. In the optimization procedure, the total pressure rise and adiabatic efficiency obtained from the meridional viscous flow analysis are employed as objective functions. Aerodynamic performance and three-dimensional flow fields in the Pareto-optimum design and conventional design cases have been investigated by three-dimensional Reynolds averaged Navier-Stokes (3D-RANS) and experimental analyses. The analyses results show performance improvements and suppressions of flow separations on the suction surfaces in the optimum design cases. Therefore, the present aerodynamic optimization using the inverse method based on the meridional viscous flow analysis is successfully achieved.

DOI： 10.1115/GT2017-63539

Language：English   Publishing type：Research paper (scientific journal)  

The paper presents the results of large-scale numerical simulations which were conducted for better understanding of unsteady flow phenomena in a multi-stage axial flow compressor at near-stall condition. The compressor is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. The compressor consists of 14 stages, the front two stages and the front half stages of which were investigated in the present study. According to the test data, it is considered that the 2nd stage and the 5th or 6th stage are suspected of leading to the stall. The final goal of this study is to elucidate the flow mechanism of the rotating stall inception in the multi-stage axial compressor for actual gas turbines. In order to capture precise flow physics in the compressor, a computational mesh for the simulation was generated to have at least several million cells per passage, which amounted to 650 million cells for the front 2-stage simulation and two billion cells for the front 7-stage simulation (three hundred million cells for each stage). Since these were still not enough for the large-eddy simulation (LES), the detached-eddy simulation (DES) was employed, which can calculate flow fields except near-wall region by LES. The required computational resources were quite large for such simulations, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena in the present compressor at near-stall condition were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method. The simulation showed that the stall in the present compressor could be related to the corner separation on the hub side.

Language：English   Publishing type：Research paper (international conference proceedings)  

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DOI： 10.1299/jfst.2016jfst0011

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Three-dimensional structure of tip vortex in a half-ducted propeller fan

DOI： 10.1299/transjsme.2014fe0024

Repository Public URL： http://hdl.handle.net/2324/4481542

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1115/1.4007894

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Effects of Tip Clearance Flow on Rotating Stall Inception Process in an Axial Compressor Rotor

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DOI： 10.1115/1.4007570

Language：English   Publishing type：Research paper (international conference proceedings)  

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Vortical and Separated Flow Structures in a Centrifugal Compressor Impeller with Splitter Blades at Off-Design Condition

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DOI： 10.1299/jsmeb.46.163

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DOI： 10.1115/1.1412565

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DOI： 10.1115/1.1412566

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DOI： 10.1299/jsmeb.44.748

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Anomalous Flow Phenomena Due to Breakdown of Tip Leakage Vortex in an Axial Compressor Rotor at Near-Stall Contition

Language：English   Publishing type：Research paper (scientific journal)  

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The paper presents a result of the direct numerical simulation with the lattice Boltzmann method which was conducted for quantitative prediction of turbulent broadband noise. For better prediction of broadband noise with high frequency, which is generally generated in high Reynolds number flows, not only high grid resolution is required for a flow simulation to capture very small eddies of the sound source inside the turbulent boundary layer, but also the computation of acoustic field is often needed. In such case, the direct simulation of flow field and acoustic field is straightforward and effective. In this study, the direct simulation with the lattice Boltzmann method was conducted for a flow around the NACA0012 airfoil with the Reynolds number of two hundred thousand. In order to efficiently simulate this high Reynolds number flow with the LBM, the multi-scale approach was introduced in conjunction with the Building-cube method, while keeping the advantage of the LBM with the Cartesian mesh. At the condition with angle-of-attack of 9 degrees, a laminar separation bubble arises on the suction surface near the leading-edge and the suction boundary layer downstream of it is turbulent due to the separated-flow transition. As a result, turbulent broadband noise is generated from the boundary layer over the airfoil with the separated-flow transition. In the paper, as for prediction of such broadband noise, the computed frequency spectrum of far-field sound is validated to agree with the experimental result. In addition, through the detailed analyses of turbulent properties of the turbulent boundary layer on the suction surface, the validity of the present direct numerical simulation is demonstrated.

DOI： 10.1115/FEDSM2016-7585

Language：English   Publishing type：Research paper (other academic)  

The paper describes the flow mechanism of the rotating stall inception in a multi-stage axial flow compressor for an actual gas turbine. Large-scale numerical simulations have been conducted. The compressor investigated is a test rig compressor which was used for development of the industrial gas turbine, Kawasaki L30A. While the compressor consists of 14 stages, the front half stages of the compressor were analyzed in the present study. According to the test data, it is considered that the 5th or 6th stage is the one most suspected of leading to the stall. In order to capture precise flow physics that could happen at stall inception, a computational mesh was made dense, giving at least several million cells to each passage. It amounted to about two billion cells for the first 7 stages (three hundred million cells in each stage). Since the mesh was still not enough for the largeeddy simulation (LES), the detached-eddy simulation (DES) was employed. In the DES, a flow field is calculated by LES except near-wall and near-wall turbulent eddies are modeled by RANS. The computational resource required for such large-scale simulation was still quite large, so the computations were conducted on the K computer (RIKEN AICS in Japan). Unsteady flow phenomena at the stall inception were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method. The present compressor has stall started from the separation on the hub side instead of the commonly observed leading-edge separation near the tip. The flow phenomenon first observed in the stalling process is the hub corner separation, which appears in some passage of the 6th stator when approaching the stall point. This hub corner separation expands with time, and eventually leads to the leading-edge separation on the hub side for the stator. Once the leading-edge separation happens, it rapidly develops into the rotating stall, causing another leading-edge separation for the neighboring blade in sequence. Finally, the rotating stall spreads to the upstream and downstream bladerows due to its large blockage effect.

DOI： 10.1115/GT2016-57104

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： DOI:10.1299/transjsme.15-00058

Language：English   Publishing type：Research paper (other academic)  

The new type of shrouded wind turbine called "wind-lens turbine" has been developed. The wind-lens turbine has a brimmed diffuser called "wind-lens", by which the wind concentration on the turbine blade and the significant enhancement of the turbine output can be achieved. A simultaneous optimization method for the aerodynamic design of rotor blade and wind-lens has been developed. The present optimal design method is based on a genetic algorithm (GA) which enables multi objective aerodynamic optimization. In the present study, aerodynamic performances and flow fields of the Pareto optimal solutions of wind-lens turbines designed by the present optimal design method have been investigated by windtunnel tests and three-dimensional Reynolds averaged Navier-Stokes (RANS) analyses. Output power coefficients obtained from the wind-tunnel tests in the optimal wind-lens turbine exceeded the Betz limit, which is the performance limitation for bare wind turbines. The numerical results and the experimental results show that the suppression of flow separations in the diffuser is important to achieve significant improvement in aerodynamic performances. As a result, it is found that the aerodynamic performance of wind-lens turbine is significantly affected by the interrelationship between the internal and external flow fields around the wind-lens.

DOI： 10.1115/GT2015-43619

Language：English   Publishing type：Research paper (other academic)  

The present paper provides validation results of the lattice Boltzmann method (LBM) for the simulation of a complicated flow field around a propeller fan. In the present numerical simulation, solid boundaries of the rotor and the shroud were calculated by a simple immersed boundary scheme. The computational grid around the propeller fan was generated by the Building-Cube Method (BCM). Furthermore, the multi-scale model was introduced into the LBM to allow the calculation with such grids. The LBM result agreed well with the experimental result and the result of detached eddy simulation (DES) which solved the Navier-Stokes equations. It confirmed that the present approach was effective for flow simulations of propeller fans using LBM.

Language：English   Publishing type：Research paper (other academic)  

The paper presents the results of large-scale numerical simulations which were conducted for better understanding of unsteady flow phenomena in a multi-stage axial flow compreßor at off-design condition. The compreßor is a test rig compreßor which was used for development of the industrial gas turbine, Kawasaki L30A. The compreßor consists of 14 stages, the front two stages and the front half stages of which were investigated in the present study. The final goal of this study is to elucidate the flow mechanism of the rotating stall inception in the multi-stage axial compreßor for actual gas turbines, and according to the test data it is considered that the 2nd stage and the 5th or 6th stage are suspected of leading to the stall. In order to capture precise flow physics in the compreßor, a computational mesh for the simulation was generated to have at least several million cells per paßage, which amounted to 650 million cells for the front 2-stage simulation and two billion cells for the front 7-stage simulation (about three hundred million cells for each stage). Since these were still not enough for the largeeddy simulation (LES), the detached-eddy simulation (DES) was employed, which can calculate flow fields except near-wall region by LES. The required computational resources were quite large for such simulations, so the computations were conducted on the K computer (RIKEN AICS in Japan). The simulations were well validated, showing good agreement with the measurement results obtained in the test. In the validation, the effect of the boundary condition for the casing wall was also investigated by comparing the results between the adiabatic boundary condition and the isothermal boundary condition. As for the unsteady effect, the wake/blade interaction was investigated in detail. In addition, unsteady flow phenomena in the present compreßor at off-design condition were analyzed by using data mining techniques such as vortex identification and limiting streamline drawing with the LIC (line integral convolution) method. The simulation showed that they could be caused by the corner separation on the hub side.

DOI： 10.1115/GT2015-42648

Language：English   Publishing type：Research paper (other academic)  

Today turbocharging has become a fundamental technology to realize engine downsizing, which is an attractive strategy for low carbon emissions. High efficiency and wide operating range are strongly required for the automotive turbochargers. Especially centrifugal compressors for automotive turbochargers are requested to operate with high efficiency from the surge limit to the choke limit. The internal flow in a centrifugal compressor is however three dimensional and shows very complex unsteady flow phenomena like a rotating stall and a surging, which have yet to be elucidated fully. In this study the effect of flow path height of impeller and diffuser on flow fields in a transonic centrifugal compressor has been investigated both numerically and experimentally. Detached Eddy Simulation (DES) has been applied and revealed the reduction of impeller exit flow path affects the accumulation of low momentum flow at impeller inlet as well as impeller exit. Also it has been confirmed experimentally the 15% reduction of the impeller exit flow path height can halve the surging flow rate with same choking capacity at pressure ratio of 2.6.

DOI： 10.1115/GT2015-43271

Language：English   Publishing type：Research paper (other academic)  

An optimum aerodynamic design method for the new type of wind turbine called "wind-lens turbine" has been developed. The wind-lens turbine has a diffuser with brim called "wind-lens", by which the wind concentration on the turbine rotor and the significant enhancement of the turbine output can be achieved. In order to design efficient wind-lens turbines, an aerodynamic design method for the simultaneous optimization of rotor blade and wind-lens has been developed. The present optimum design method is based on a genetic algorithm (GA) and a quasi-three-dimensional design of turbine rotor. In the GA procedure, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used as evaluation and selection model. The Real-coded Ensemble Crossover (REX) is used as crossover model. The quasi-three-dimensional design consists of two parts: meridional viscous flow calculation and two-dimensional blade element design. In the meridional viscous flow calculation, an axisymmetric viscous flow is numerically analyzed on a meridional plane to determine the wind flow rate through the wind-lens and the spanwise distribution of the rotor inlet flow. In the two-dimensional rotor blade element design, the turbine rotor blade profile is determined by a one-dimensional through flow modeling for the wind-lens turbine and a two-dimensional blade element theory based on the momentum theorem of the ducted turbine. Total performances and three-dimensional flow fields of the optimized wind-lens turbines have been investigated by Reynolds averaged Navier-Stokes (RANS) simulations, in order to verify the present design method. The RANS simulations and the flow visualization have been applied to conventional and optimum design cases of the wind-lens turbine, in order to elucidate the relation between their aerodynamic performances and the flow fields around them. The numerical results show that separation vortices behind the wind-lens brim play a major role in the wind concentration and the diffuser performance of the wind-lens. As a result, it is found that the aerodynamic performance of wind-lens turbine is significantly affected by the interrelationship between the internal and external flow fields around the wind-lens.

DOI： 10.1115/GT2014-25770

Language：English   Publishing type：Research paper (other academic)  

This paper presents a novel blade design concept about control of the secondary flow in axial turbines to improve the internal efficiency. A rotor blade for the high and intermediate pressure stage of a steam turbine was designed by one-dimensional inverse method incorporated with throughflow calculation. In the throughflow calculation, the axisymmetric Navier-Stokes equations are solved, assuming that the meridional flow is axisymmetric and viscous. To take into account the blade loading, a blade force is introduced as a body force to the governing equations. The blade force contains the inviscid blade effect only, namely, the pressure difference across a blade. The blade force acts in the direction perpendicular to a three-dimensional blade camber surface, which is constructed from camber lines stacked in blade height direction, so that the flow convects along the surface. The camber line is calculated by one-dimensional inverse method, based on a given blade loading distribution and the meridional velocity distribution from the throughflow calculation. The present throughflow calculation method was validated for a direct problem, using blade geometry of existing turbine rotor. The blade force with the camber surface in the present method was able to express the secondary flow inside the turbine by modifying the camber surface appropriately. As a result, the calculation result showed good agreement with the experimental result. The turbine rotor blade was redesigned with the present method, modifying the chord-wise blade loading distribution so as to suppress the development of the secondary flow. The way of modifying the chord-wise blade loading distribution is based on a new idea, which can be actualized by the present design method. It was confirmed that the secondary flow was successfully suppressed as intended in the designed rotor.

DOI： 10.1115/GT2014-25630

Language：English   Publishing type：Research paper (other academic)  

An optimum aerodynamic design method has been developed for the new type of wind turbine called "wind-lens turbine". The wind-lens turbine has a diffuser with brim called "wind-lens", by which the wind concentration on the turbine rotor and the significant enhancement of the turbine output can be achieved. The present design method is based on a genetic algorithm (GA) and a quasi-three-dimensional design of turbine rotor. The quasi-three-dimensional design consists of two parts: meridional viscous flow calculation and two-dimensional blade element design. In the meridional viscous flow calculation, an axisymmetric viscous flow is numerically analyzed on a meridional plane to determine the wind flow rate through the wind-lens and the spanwise distribution of the rotor inlet flow. In the two-dimensional rotor blade element design, the turbine rotor blade profile is determined by a one-dimensional through flow modeling for the wind-lens turbine and a two-dimensional blade element theory based on the momentum theorem of the ducted turbine. In the present optimization method, the Non-dominated Sorting Genetic Algorithm II (NSGA-II) is used as evaluation and selection model. The Real-coded Ensemble Crossover (REX) is used as crossover model. The present aerodynamic design method has been applied to the coupled design of turbine rotor and wind-lens. Total performances and flow fields of the wind-lens turbines designed have been investigated by Reynolds averaged Navier-Stokes simulations, in order to verify the present design method.

DOI： 10.1115/FEDSM2013-16569

Language：English   Publishing type：Research paper (other academic)  

Lattice Boltzmann method (LBM) has a potential to simulate airfoil self-noise with low Mach number flow including turbulent flow and aerodynamic feedback loops. In this study, the computational techniques concerning LBM were developed toward direct numerical simulation of aeroacoustic fields with low Mach number. For applications of multi-scale phenomena such as flow and acoustic fields, multi-scale model was introduced, which enables to use locally refined grids. The grids were efficiently arranged using the Building-Cube Method (BCM) by dividing the computational domain into multiple blocks with various grid sizes. Furthermore, the zonal DNS and LES approach was adopted to suppress the numerical instability in the region of coarse grids. The grid dependency of the results provided by the present numerical method was investigated by two-dimensional simulations of flow fields around a NACA0012 airfoil using four different grids. Furthermore, a three-dimensional simulation of flow around a NACA0018 airfoil with moderate Reynolds number was conducted. The computational results were compared and have a good agreement with the experimental ones. The present method can simulate flow around airfoil with moderate Reynolds number involving the laminar-to-turbulent transition.

DOI： 10.1115/FEDSM2013-16526

Language：English   Publishing type：Research paper (other academic)  

The paper presents experimental and numerical studies on the effects of tip clearance on the stall inception process in a low-speed axial compressor rotor with a large tip clearance. It has been revealed that in the small tip clearance case, shortly after the spike disturbance which results from the leading-edge separation near the rotor tip appears, the tornado-like vortex is generated by the separation, and soon the compressor falls into stall. In the large tip clearance case, the experiment showed that the performance characteristic differs from that in the small tip clearance case at near-stall conditions. This implies that the stall inception process differs with the tip clearance size. The flow phenomenon in the stall inception leading to such difference has been investigated in this study. Pressure and velocity fields which were ensemble-averaged and phase-locked by the periodic multi-sampling technique were measured on the casing wall and downstream of the rotor, respectively. In addition, to capture the unsteady flow phenomena inside the rotor, "Instantaneous Casing Pressure Field Measurement "was carried out: instantaneous casing pressure fields in one rotor passage region were measured by 30 high response pressure transducers mounted on the casing wall. In order to investigate further details of near-stall flow field for the large tip clearance, DES (Detached Eddy Simulation) has been conducted using a computational mesh with 120 million points. The results are compared with those from previous studies for the small tip clearance. As expected, the measurement results show notable differences in the near-stall flow field between the two tip clearance cases. The results from the casing pressure measurement show that high pressure fluctuation appears on the pressure side near the rotor leading-edge in the large tip clearance case. In the result of the velocity field measurement downstream of the rotor, high turbulence intensity is found near the casing in the large tip clearance case. The numerical results reveal that the vortex breakdown occurs in the tip leakage vortex and induces the oscillation of the tip leakage vortex with its unsteady nature. The flow phenomena confirmed in the experimental results are clearly explained by considering the breakdown of the tip leakage vortex. The vortex breakdown gives rise to not only large blockage but also the rotating disturbance through the interaction of the fluctuating tip leakage vortex with the pressure surface of the adjacent blade, and governs the stall inception process.

DOI： 10.1115/GT2013-95479

Language：English   Publishing type：Research paper (scientific journal)  

Flow fields near rotating stall inception in a low-speed axial compressor rotor with two different tip clearances have been investigated by instantaneous measurements of casing wall pressure distributions using 30 high response pressure transducers and by detached eddy simulations (DES) using 120 million grid points. It is found that the stall inception process in the large tip clearance case is dominated by the breakdown of the rotor tip leakage vortex, in contrast to the spike-type stall inception in the small tip clearance case which is dominated by the leading-edge separation near the rotor tip. The vortex breakdown induces the large oscillation of the tip leakage vortex with its unsteady nature, resulting in the low-pressure regions in the instantaneous casing wall pressure field and the high pressure fluctuation region on the pressure side of the adjacent blade tip in the ensemble-averaged casing wall pressure field. The large blockage effect due to the tip leakage vortex breakdown causes the rotating disturbance propagating in the circumferential direction, which can appear and disappear with a slight change in the flow rate.

DOI： 10.1299/kikaib.79.900

Language：English   Publishing type：Research paper (other academic)  

The unsteady behavior and three-dimensional flow structure of spike-type stall inception in an axial compressor rotor have been investigated by experimental and numerical analyses. Previous studies have revealed that the test compressor falls into a mild stall after emergence of a spike, in which multiple stall cells, each consisting of a tornado-like vortex, are rotating. However, the flow mechanism from the spike onset to the mild stall remains unexplained. The purpose of this study is to describe the flow mechanism of a spike stall inception in a compressor. In order to capture the transient phenomena of spike-type stall inception experimentally, an instantaneous casing pressure field measurement technique was developed, in which 30 pressure transducers measure an instantaneous casing pressure distribution inside the passage for one blade pitch at a rate of 25 samplings per blade passing period. This technique was applied to obtain the unsteady and transient pressure fields on the casing wall during the inception process of the spike stall. In addition, the details of the three-dimensional flow structure at the spike stall inception have been analyzed by a numerical approach using the detached-eddy simulation (DES). The instantaneous casing pressure field measurement results at the stall inception show that a low-pressure region starts traveling near the leading edge in the circumferential direction just after the spiky wave was detected in the casing wall pressure trace measured near the rotor leading edge. The DES results reveal the vortical flow structure behind the low-pressure region on the casing wall at the stall inception, showing that the lowpressure region is caused by a tornado-like separation vortex resulting from a leading-edge separation near the rotor tip. A leading-edge separation occurs near the tip at the onset of the spike stall and grows to form the tornado-like vortex connecting the blade suction surface and the casing wall. The casing-side leg of the tornado-like vortex generating the low-pressure region circumferentially moves around the leading-edge line. When the vortex grows large enough to interact with the leading edge of the next blade, the leading-edge separation begins to propagate, and then, the compressor falls into a stall with decreasing performance.

DOI： 10.1115/GT2012-69186

Language：English   Publishing type：Research paper (other academic)  

Recently, the application of turbochargers is increasing because they are effective in improving fuel consumption of engines. One of the most important turbocharger characteristics is compressor operating range, since it has been used in various driving patterns with the advent of variable geometry turbochargers. Owing to the complicated phenomena such as rotating stall occurring at low flow rate condition, flow analysis is very difficult and details of flow structure have not been fully understood for a long time since the early 1970's. In this study, two compressors with different operating range width were investigated with experimental and computational flow analysis. In the compressor with narrow operating range, the amplitude of blade passing pressure fluctuation decreases rapidly and rotating stall occurs near surging. On the other hand, in the compressor with wide operating range, the blockage by the tip leakage vortex breakdown play a role in stabilizing the flow filed and keeping up a high performance even at low flow rates.

DOI： 10.1115/GT2012-68947

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (other academic)  

In order to comply with recent legislations against exhaust gas emission and vehicle fuel consumption, demands on improvement of turbocharger performance are increasing. The demands of compressor performance for a wider range and higher efficiency are especially strong, while the control of complicated inner flow is important to improve such performance. At the same time, the growth of computing capacity has made a large-scale computing possible, not only in academic study but also in commercial development. The improved computational fluid dynamics method combined with the experimental fluid dynamics made it possible to understand and control unsteady and asymmetric aerodynamic phenomena that can be applied on the improvement of compressor performance. This paper describes an example of performance improvement activity in controlling "tip leakage vortex," which has strong unsteady and asymmetric characteristics.

DOI： 10.1533/9780857096135.3a.135

Language：English   Publishing type：Research paper (other academic)  

In order to use vortex rings for mass and momentum transport, the relationship between the circulation of vortex rings generated continuously by a pulsating jet flow, which are referred to herein as 'cyclic vortex rings', and the conditions of jet flow are investigated experimentally. The results indicate that the formation time at which the cyclic vortex rings reach maximum circulation, i.e., become optimal vortex rings, can be estimated using the concept proposed by Gharib et al. Based on their concept, the optimal vortex rings are formed when the translation velocity of the vortex core becomes equal to the convection velocity of the shear layer of the jet. The translation velocity of vortex rings and the convection velocity of shear layers can be estimated by empirical equations under pulsating jet conditions. Therefore, the formation time of the optimal vortex rings can be estimated from the pulsating jet conditions, when the circulation of vortex rings stop growing and the vortex rings start to become disconnected from the shear layers. The circulation of vortex rings estimated using this method is in good agreement with the measurement data within the measurement error. There exists a specific Strouhal number at which the circulation of the vortex rings reaches the maximum value. This Strouhal number is expected to be the optimal generating condition of cyclic vortex rings for using transportation.

DOI： 10.1115/AJK2011-16015

Language：English   Publishing type：Research paper (other academic)  

The unsteady behaviors and three-dimensional flow structure of the spike-type stall inception in an axial flow compressor rotor have been investigated by experimental and numerical analyses. In order to capture the transient phenomena of spiketype stall inception experimentally, "SFMT (Simultaneous Field Measurement Technique)", by which instantaneous pressure distributions on the casing wall were acquired, was developed. By applying this technique, the unsteady flow pattern on the casing wall was extracted for each phase of development process of the stall inception. The details of three-dimensional flow structure in the stall inception process were revealed by the numerical analysis using a detached-eddy simulation (DES). At the stall inception, the characteristic patterns of the casing wall pressure distributions are observed in the experimental results: the low pressure regions moving in the circumferential direction and the variations of the low pressure regions at the leading edge. Considering the results of DES, these patterns are made by the vortices fragmented from the deformed tip leakage vortex or the tornado-type separation vortex and also are made by the tornado-type separation vortex itself, as well. The vortical flow structures have been elucidated. These vortices actually result from the leading edge separation at the blade tip. Therefore, it has been found that spike-type stall inception is dominated by the leading edge separation at the rotor blade tip.

DOI： 10.1115/AJK2011-22079

Language：English   Publishing type：Research paper (other academic)  

This paper describes the experimental and numerical investigationson unsteady three-dimensional flow fields in two types of transonic centrifugal compressor impellers with different aerodynamic characteristics. In the experimental results, the frequency spectra of the pressure fluctuations, which were measured with the high-response pressure transducers mounted on the casing wall just upstream of the impeller, turned out to be quite different between the compressor impellers at stall condition. 0The simulation results also showed different stall pattern for each compressor impeller. In the compressor impeller with a better performance at off-design condition, the stall cell was never formed despite decreasing flow rate and instead all the passages were covered with a reverse flow near the tip, where the vortex breakdown happened in the tip leakage vortex of full blade and led to the unsteadiness in the impeller. The vortex breakdown happened in all the passages prior to the stall and generated a blockage near the tip. This means that even with the advent of rotating stall the flow could not return to a normal undistorted condition in unstalled region, because all the passages are already occupied by the blockage due to the vortex breakdown. As a result, the rotating stall cell could not appear in the impeller. In the other compressor impeller, the rotating stall cell was formed at stall inception without the vortex breakdown in the tip leakage vortex of full blade, and developed with decreased flow rate.

DOI： 10.1115/GT2011-46253

Language：English   Publishing type：Research paper (scientific journal)  

Influence of interaction with a tangential lean blade and a box type casing on blade passing frequency (BPF) noise level in small axial-flow fans was investigated by measurement and computational fluid dynamics (CFD). Noise level of five fans having different tangential lean angles was measured. By increasing tangential lean angle, BPF noise level and broadband noise level reduced. An unsteady CFD simulation of tangential lean angle 31-degrees and 63-degrees was conducted to analyze the cause of BPF noise reduction. By increasing tangential lean angle, the inward blade force of the 63-degrees blade was increased compared to the 31-degrees blade. The increase of the inward blade force decreased centrifugal flow in radial direction at the exit of casing, because the inward blade force gave a momentum to the flow in radial inward direction. The decrease of the centrifugal flow suppressed interaction of the flow with the casing wall. The suppression of the interaction reduced static pressure fluctuation for BPF of the casing wall. The reduction of static pressure fluctuation for BPF was found to have a great influence on the BPF noise reduction. It is therefore clarified that increasing tangential lean angle was effective in reduction of the BPF noise.

DOI： 10.1299/kikaib.77.1620

Language：English   Publishing type：Research paper (scientific journal)  

The formation process of a vortex ring generated by a pulsating jet flow, which is called the cyclic vortex ring, is investigated experimentally with PIV measurement. The waveform of the jet flow is conducted using sine curves by changing the amplitude of Reynolds' numbers Re ₀ of 1200∼5040 and Womersley numbers a of 12.5∼24.4. The results indicate that the formation process of the cyclic vortex ring is different from the laminar vortex ring Another vortex ring which is formed from separated wall boundary layers in the nozzle during the suction period, which is called the separation vortex ring, is transported toward the nozzle exit during the discharge period. This separation vortex ring interferes with the formation process of the cyclic vortex ring at the nozzle exit plane. The circulation of the separation vortex ring depends on the pulsating conditions of the jet flow. Distribution of the vorticity around the core center of the cyclic vortex ring is in good agreement with the Oseen vortex model. The formation process of the cyclic vortex ring is classified into three categories, depending on Strouhal number.

DOI： 10.1299/kikaib.77.546

Language：English   Publishing type：Research paper (other academic)  

Three-dimensional structures and unsteady nature of vortical flow fields in a half ducted propeller fan have been investigated by a detached eddy simulation (DES) based on k-ω two-equation turbulence model. The validity of the numerical simulation performed in the present study was demonstrated by the comparison to LDV measurement results. The simulation shows the tip vortex is so strong that it dominates the flow field near the rotor tip. The tip vortex does not impinge on the pressure surface of the adjacent blade directly, however it interacts with the shroud surface and induces a separation vortex on the shroud. Furthermore, this separation vortex interacts with the pressure surface of the adjacent blade. These flow structures cause high pressure fluctuation on the shroud surface and the blade pressure surface. Besides, sound pressure levels were predicted by Ffowcs William-Hawkings equation based on Lighthill's acoustic analogy using the unsteady surface pressure data obtained by DES. As a result, the degree of contribution by each flow structure to overall sound has been estimated quantitatively.

DOI： 10.1115/AJK2011-22048

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Formation Process of Vortex Ring Generated by a Pulsating Jet Flow

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：Japanese   Publishing type：Research paper (scientific journal)  

Formation Process of Vortex Ring Generated by a Pulsating Jet Flow

Language：English   Publishing type：Research paper (other academic)  

Two types of transonic centrifugal compressor impeller with splitter blades, which are different in blade count, have been investigated in this study. RANS (Reynolds-Averaged Navier-Stokes) simulations were carried out for several operating conditions to clarify differences in aerodynamic performance characteristic and tip clearance flow field between the two compressors. The simulation shows that basically similar flow events happen in both compressors. A low velocity region is generated near the tip at low flow rate conditions, which results from an expansion of the tip leakage vortex. The low velocity region expands as the flow rate is decreased, and interacts with the pressure surface of the splitter blade near the leading edge. This causes a descent of the blade loading near the tip of the leading edge, and an accumulation of high entropy fluid near the casing-suction corner. Moreover, the tip clearance flow spills ahead of the leading edge of the splitter blade at near stall condition, and eventually the spillage happens at the full blade at stall condition. However, the major difference in solidity influences tip clearance flow/blade interaction, which leads to changes in the performance characteristics. In the impeller with low solidity, the tip leakage vortex breaks down with a large blockage effect because of high blade loading at the tip, which decreases the pressure ratio. The impeller with high solidity is subject to the spillage, which results in an early and large-scale stall that decreases the efficiency.

DOI： 10.1115/GT2010-23345

Language：English   Publishing type：Research paper (other academic)  

This paper presents a combined experimental and numerical analysis of rotating stall in a transonic centrifugal compressor impeller for automotive turbochargers. Stall characteristics of the compressor were examined by two high-response pressure transducers mounted on the casing wall near the impeller inlet. The pressure traces were analyzed by wavelet transforms to estimate the disturbance waves quantitatively. Three-dimensional unsteady internal flow fields were simulated numerically by Detached Eddy Simulation (DES) coupled LES-RANS approach. The analysis results show good agreements on both compressor performance characteristics and the unsteady flow features at the rotating stall. At stall inception, spiral-type breakdown of the full-blade tip leakage vortex was found out at some passages and the brokendown regions propagated against the impeller rotation. This phenomenon changed with throttling, and tornado-type separation vortex caused by the full-blade leading edge separation dominated the flow field at developed stall condition. It is similar to the flow model of short-length scale rotating stall established in an axial compressor rotor.

DOI： 10.1115/GT2009-59516

Language：English   Publishing type：Research paper (other academic)  

Three-Dimensional Inverse Design Method, where the 3-D blade profile is designed for a specified blade loading distribution, has been applied for designing a propeller fan rotor with high efficiency and low noise. A variety of the blade loading distributions (pressure jump across the blade), vortex pattern (forced vortex, free vortex, and compound vortex) and the stacking conditions (sweep angles) were specified and the corresponding 3-D blade configurations were obtained. Among the 22 different designs, 14 propeller fan rotors including the reproduced baseline fan were manufactured by a rapid prototyping based on a selective laser sintering system (SLS) and tested. It was confirmed experimentally that the best design achieved about 5.7 points improvement in the peak total-to-static efficiency and the 2.6dB(A) reduction in aerodynamic noise. The flow mechanisms leading to the higher efficiency and lower aerodynamic noise were discussed based on experiments and the RANS steady flow simulations. Based on these investigations, design guidelines for the inverse design of propeller fan rotors with higher efficiency and lower aerodynamic noise were proposed.

DOI： 10.1115/FEDSM2009-78454

Language：English   Publishing type：Research paper (scientific journal)  

The authors have reported that a minichannel flow system had a high heat transfer coefficient. We investigated the heat transfer and flow structure of single and array minichannels combined with an impingement flow system experimentally and numerically. The diameter D of the channel was 1.27 mm, and length to diameter ratio L/D was 5. The minichannel array was so-called shower head, which was constructed by 19 minichannels located at the apex of equilateral triangle, the side length S of which was 4 mm a single stage block was used to investigate the heat transfer without impinging flow system. Two stage blocks were combined in series to compose an impingement heat transfer system with an impingement distance of H. H/D ranged from 1.97 to 7.87. The dimensionless temperature increased as the impingement distance became short. A comparison of heat transfer performance was made between minichannel flow and impingement jet by comparing the single- and two-stage heat transfer experiments. It was found that dimensionless temperature of the minichannel exceeded that of the impingement jet. The mechanism of high heat transfer was studied numerically by the Reynolds-averaged Navier-Stokes equation and k-ω turbulence model. The limiting streamline pattern was correlated well to the surface heat flux distribution. The high heat transfer was achieved by suppressing the development of boundary layer under strong pressure gradient near the channel inlet. This heat transfer mechanisms became dominant when the channel size fell into the region of the minichannel.

DOI： 10.1115/1.2751146

Language：English   Publishing type：Research paper (other academic)  

Three-dimensional structure of separated and vortical flow field has been investigated by numerical analysis on a half-ducted propeller fan. Complicated flow phenomena in the fan were captured by the Reynolds-averaged Navier-Stokes flow simulation (RANS) and a vortex structure identification technique based on the critical point theory. The flow field around the fan rotor is dominated by the tip leakage vortex. The tip leakage vortex starts to be formed near the blade mid-chord and grows nearly in the tangential direction without vortex breakdown. In the rotor passage, the high vorticity flow around the tip leakage vortex core is impinging on the pressure surface of the adjacent blade. It is expected that the behavior of the tip leakage vortex plays a major role in characteristics of the fan noise.

DOI： 10.1115/FEDSM2007-37607

Language：English   Publishing type：Research paper (scientific journal)  

A flow modeling for the meridional flow calculation in the aerodynamic design of the half-ducted turbomachinery blade rows has been presented. It is assumed that the meridional flow is axisymmetric and viscous one. To take into account the blade loading, a blade force is introduced as a body force to the axisymmeric Navier-Stokes equations. The blade force contains the inviscid blade effect only, namely, the pressure difference across a blade. Numerical examples have been presented for a wind-lens turbine and a half-ducted propeller fan in order to demonstrate the validity of the present flow modeling. For the wind-lens turbine, the present flow modeling can predict non-uniform flow distributions at the inlet and outlet of the turbine rotor. For the half-ducted propeller fan, however, the formation of the several separated and vortical flow structures results in the well prediction of the inlet flow angle only. It is found that the present flow modeling is useful to the blade row design tool.

Language：English   Publishing type：Research paper (other academic)  

It is known that the tip clearance flow is dominant and very important flow phenomena in axial compressor aerodynamics because the tip clearance flow has a great influence on the stability as well as aerodynamic loss of compressors. Our goal is to clarify the behavior of tip clearance flow at near-stall condition in a transonic axial compressor rotor (NASA Rotor 37). In the present work, steady and unsteady RANS simulations were performed to investigate vortical flow structures and separated flow field near the tip for several different clearance cases. Boundary layer separation on the casing wall and blade suction surface was investigated in detail for near-stall and stall condition. In order to understand such complicated flow field, vortex cores were identified using the critical point theory and a topology of the three-dimensional separated and vortical flows was analyzed. In the nominal clearance case, the breakdown of tip leakage vortex has occurred at a near-stall operating condition because of the interaction of the vortex with the shock wave, leading to a large blockage and unsteadiness in the rotor tip. On the other hand, the calculation with no clearance suggested that the separation on the suction surface was different from that with the nominal clearance. Since the shock wave induced the boundary layer separation on the blade suction surface in the transonic axial compressor rotor, focal-type critical points appeared on the suction surface near the tip at near-stall condition.

DOI： 10.1115/GT2007-27725

Language：English   Publishing type：Research paper (other academic)  

Transonic centrifugal compressors are used in turbochargers and turboshaft engines because of their small dimensions, relatively high efficiency and wide operating range. The flow field of the transonic centrifugal compressor impeller is highly three dimensional, and is complicated by shock waves, tip leakage vortices, secondary flows and the interactions among them. In order to improve the performance, it is indispensable to understand these complicated flow phenomena in the impeller. Although experimental and numerical research on transonic impeller flow has been reported, thus providing important flow physics, some undetected flow phenomena remain. The authors of the present report carried out detailed Navier-Stokes computations of a transonic impeller flow measured by Laser Doppler Velocimetry (LDV) in previous work. The highly complicated vortical flow structure and the mechanism of loss generation were revealed by a visual data mining technique, namely vortex identification based on the critical point theory and limiting streamline mapping by means of line integral convolution. As a result, it was found that the tip leakage vortices have a significant impact on the flow field and vortex breakdowns that increase the blockage of the flow passage, and that these were caused by shock wave interaction.

DOI： 10.1115/GT2007-27791

Language：English   Publishing type：Research paper (other academic)  

The authors have reported that minichannel flow system had high heat transfer coefficient, the reason of which was investigated experimentally and numerically for single and array minichannels combined with impingement flow system. The diameter D of the channel was 1.27 mm and length to diameter ratio L/D was 5. The minichannel array was so called shower head which was constructed by 19 minichannels located at the apex of equilateral triangle, the side length S of which was 4 mm. Single stage block was used to investigate the heat transfer without impinging flow system. Two stage blocks were used to compose an impingement heat exchanger system with an impingement distance of H. H/D ranged from 1.97 to 7.87. A comparison of heat transfer performance was made between minichannel flow system and impingement jet using the single and two stage heat transfer experimental data. It was found that heat transfer performance of the minichannel was equivalent to that of impingement jet. The mechanism of high heat transfer was studied numerically by the Reynolds averaged Navier-Stokes equation and k-ω turbulence model. The limiting stream-line pattern was correlated well to the surface heat flux distribution. The high heat transfer in the single minichannel was achieved by suppressing the development of boundary layer under strong pressure gradient near the channel inlet and by the formation of large recirculating flow system in the downstream plenum of the minichannel exit. These heat transfer mechanisms became dominant when the channel size fallen into the regime of minichannel. For the array of 19 minichannels, the high heat transfer around the channel inlet was also observed clearly in the target plate of the impingement jet where minichannels of second stage were bored to exhaust the fluid of impingement jet.

DOI： 10.1115/icnmm2006-96213

Language：English   Publishing type：Research paper (scientific journal)  

Heat transfer was investigated for high pressure ratio air flow in square minichannels, which were machined on the oxygen free copper block. The size of the channels were 0.3, 0.6, 1.0 and 2.0 mm, and the length were 10, 20, 50 and 100 mm. The pressure ratio was changed widely up to the flow choked at the exit. It was found that the heat transfer coefficient was about 7.3 times greater than fully developed turbulent pipe flow. Experimental result showed that 75 percent of the total heat transfer was achieved in 10 percent inlet portion of the whole channel.

DOI： 10.1299/kikaib.71.1005

Language：English   Publishing type：Research paper (other academic)  

This paper investigates the heat transfer of airflow in square and circular minichannels. The square channels were machined on the oxygen free copper blocks. The width of them were 0.3, 0.6, 1.0 and 2.0 mm, and the lengths were 10, 20, 50 and 100 mm. The circular channels were drilled in oxygen free copper disks. The diameters of them were 1.0, 1.27, 2.0 and 2.8 mm and the length to diameter ratios were 5 and 10. The mean heat transfer coefficient included the transferee heat upstream of the channel inlet cross-section, since the inlet was not thermally insulated. The pressure ratio of the inlet and outlet plenum was increased up to the flow choked at the channel exit. The square channel showed 7.3 times greater mean heat transfer coefficient than fully developed turbulent pipe flow for width of 2 mm and length of 10 mm channel. The so-called tube cutting method was employed to investigate the sectional heat transfer rate of the square channel. About 75 percent of the total heat transfer was completed in 10 percent inlet portion of the channel. The Stanton number was found to be principally the function of length to diameter ratio. The circular channel showed 6.79 times greater mean heat transfer coefficient than fully developed turbulent pipe flow for diameter of 1.27 mm and length of 6.35 mm channel. The heat transfer coefficient increased as the channel size (width or diameter) became smaller for constant length to diameter ratio. It implied that the result of high heat transfer coefficient had a possibility to be limited to the minichannel. Heat transfer of gas turbine film cooling hole has a possibility to be larger than ever thought.

DOI： 10.1115/icmm2005-75184

Language：English   Publishing type：Research paper (scientific journal)  

The experimental studies on active control of vortex shedding frequency were conducted to suppress fluid-dynamic forces of a square cylinder. Each sidewall of the cylinder consists of four vibrating side-plates equipped with piezoelectric actuators. The vortex shedding frequency was controlled by means of a lock-in phenomenon that was caused by vibrating the side-plates transversely with amplitude less than 100 μm. The results are summarized as follows: (1) the spanwise synchronous excitation brings about reduction of the time-averaged drag coefficient C_d. It is reduced by approximately 20% of the natural condition. (2) When a half span of sidewall surface is vibrated with 180 degrees differential phase against the other half span, the vortices shed from each half span in the reversal phase mode. The fluctuating lift coefficient C_i' is reduced by approximately 70% of the natural condition with the reversal phase mode.

DOI： 10.1299/kikaib.70.579

Language：English   Publishing type：Research paper (scientific journal)  

A control of periodic vortex shedding behind a cylindrical bluff body has been made experimentally by vibrating side-plates with piezoelectric actuators. Entrainment of the vortex shedding frequency occurs by the vibration with amplitude of 20≈65 μm. The entrainment effect is evaluated quantitatively by introducing an integral scale of the frequency in the power spectral density distribution. When the side-plates are vibrated with an opposite phase in a half span of the body, the vortex shedding follows up the vibration. In the mid span, a switching phenomenon of the vortex shedding is observed.

DOI： 10.1299/kikaib.69.2030

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1299/jsmeb.46.356

Language：English   Publishing type：Research paper (scientific journal)  

The effect of tip clearance on the transient process of rotating stall evolution in the axial compressor stage with three stator-rotor gaps was investigated experimentally by the pressure traces on the casing wall. The measurement of the pressure field on the casing wall covering the rotor and the velocity distribution behind the rotor with a slanted hot wire were performed near the stall point to clarify the effect of the rotor tip clearance on the flow field. In the case of small clearance, the stall evolution depends on the stator-rotor gap. However, in the case of large clearance, there is little difference of the stall evolution among three gaps. From the measurement of the pressure and velocity field near the stall point, it seems that breakdown of tip leakage vortex occurs in the case of large clearance for three different gaps. It is supported from the axial velocity distribution at the rotor exit. From the pressure field traces just before the stall, we can find the distinctive flow phenomenon like rotating instability which was found previously by März, et al. The tip vortex plays a very important role for stall inception.

DOI： 10.1299/kikaib.69.1155

Language：English   Publishing type：Research paper (scientific journal)  

Three-dimensional vortical flow structures and velocity fluctuation near the rotor tip in an axial flow fan have been investigated by experimental analysis using a rotating hot wire probe and a numerical simulation. Both the experimental and the numerical analysis have been performed in the relative frame of reference rotating with the rotor. It is found that a tip leakage vortex is observed in the blade passage, which has a major role near the rotor tip. The tip leakage vortex formed close to the leading edge of the blade tip on suction side grows in the streamwise direction, and forms a local recirculation region resulting from a vortex breakdown inside the blade passage. It causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and large total pressure loss. High velocity fluctuation is observed in the interference region between the tip leakage vortex and the main flow. Near the casing wall, a discrete frequency is formed between tip leakage vortex center and rotor trailing edge.

DOI： 10.1299/kikaib.68.2460

Language：English   Publishing type：Research paper (scientific journal)  

The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at eight circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator-rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They become the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with "high-frequency stall inception." For the small stator-rotor gap, the stalling process is identified with "long wavelength stall inception" and supported the recent computational model for the short wavelength stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been developed that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

DOI： 10.1115/1.1458022

Language：English   Publishing type：Research paper (scientific journal)  

The transient processes of rotating stall evolution were investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at 8 circumferential locations on the casing wall near the rotor leading edge were analyzed by the wavelet transforms, which is useful to look into the behavior of disturbances with various length scales. In addition to this, the pressure field traces on the casing wall covering the rotor region were examined to imagine the transient event in the stalling process. The experimental results show that the evolution process of these disturbances depends on the stator-rotor gap. For the large and middle gap, the stall is initiated by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. These high frequency waves become the short length-scale cells for large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. For the small stator-rotor gap, the stalling process is identified with 'long wave-length stall inception'.

DOI： 10.1299/kikaib.68.108

Language：English   Publishing type：Research paper (scientific journal)  

Three-dimensional structures of the vortical flow field in a propeller fan with a shroud covering only the rear region of its rotor tip have been investigated by experimental analysis using laser Doppler velocimetry (LDV) measurements and by numerical analysis using a large eddy simulation (LES) in Part I of the present study. The propeller fan has a very complicated vortical flow field near the rotor tip compared with axial fan and compressor rotors. It is found that three vortex structures are formed near the rotor tip: the tip vortex, the leading edge separation vortex, and the tip leakage vortex. The tip vortex is so strong that it dominates the flow field near the tip. Its formation starts from the blade lip suction side near the midchord. Even at the design condition the tip vortex convects nearly in the tangential direction, thus impinging on the pressure surface of the adjacent blade. The leading edge separation vortex develops close along the tip suction surface and disappears in the rear region of the rotor passage. The tip leakage vortex is so weak that it does not affect the flow field in the rotor.

Language：English   Publishing type：Research paper (scientific journal)  

In a low-speed compressor test rig at Kyushu University, multiple short length-scale stall cells appeared under a mild stall condition and turned into a long length-scale cell under a deep stall condition. Then, for the two types of stall cell, the pressure distribution on the casing wall and the velocity distributions upstream and downstream of the rotor have been measured by high-response pressure transducers and a slanted hot-wire, respectively. The time-dependent ensemble-averages of these distributions have been obtained phase-locked to both the rotor and the stall cell rotation using a "double phase-locked averaging technique" developed by the authors. The structures of the two stall cells are compared: The short length-scale stall cell is characterized by a concentrated vortex spanning from the casing wall ahead of the rotor to the blade suction surface. In the long length-scale stall cell, the separation vortices go upstream irregularly when blade separation develops in the front half of the cell, and re-enter the rotor on the hub side in the rear half of it. The unsteady aerodynamic force and torsional moment acting on the blade tip section have been evaluated from the time-dependent ensemble-averages of the casing wall pressure distribution. The force fluctuation due to the short length-scale cells is somewhat smaller than that for the long length-scale cell. The blade suffers two peaks of the force during a period of the short length-scale cells passing through it. The moment fluctuation for the short length-scale cells is considerably larger than that for the long length-scale cell.

DOI： 10.1115/1.1326085

Language：English   Publishing type：Research paper (other academic)  

The transient processes of rotating stall evolution have been investigated experimentally in a low-speed axial compressor stage with three stator-rotor gaps. The pressure traces at 8 circumferential locations on the casing wall near the rotor leading edge have been analyzed by the wavelet transforms. With the appropriate mother wavelets, the evolution of short and long length-scale disturbances leading to the stall can be captured clearly. Behavior of these disturbances is different depending on the stator- rotor gap. For the large and middle gap, the stall inception is detected by a spiky short length-scale disturbance, and the number of spiky waves increases to generate the high frequency waves. They becomes the short length-scale part-span stall cells at the mild stall for the large gap, while they turn into a big stall cell with growth of a long length-scale disturbance for the middle gap. In the latter case, therefore, the stalling process was identified with 'high frequency stall inception'. For the small stator-rotor gap, the stalling process is identified with 'long wave-length stall inception', and supported the recent computational model for the short wave-length stall inception by showing that closing the rotor-stator gaps suppressed the growth of short length-scale disturbances. From the measurement of the pressure field traces on the casing wall, a hypothesis has been built up that the short length-scale disturbance should result from a separation vortex from a blade surface to reduce circulation. The processes of the stall evolution are discussed on this hypothesis.

DOI： 10.1115/2001-GT-0341

Language：English   Publishing type：Research paper (scientific journal)  

Behavior of multiple stall cells with short length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, the multiple short length-scale stall cells appeared under a mild stall condition. In order to capture the short length-scale cells in the mild stall state, a so-called 'double phase-locked averaging technique' has been developed, by which the flow field can be measured phase locked to both of the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the 3 D velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high response pressure transducers. From the experimental results, the flow mechanism of the short length-scale stall cell has been clarified. The distinctive feature of the stall cell structure is a tornado-like separation vortex which spans from the casing wall ahead of the rotor to the blade suction surface and travels with changing the blade in turn on which the vortex leg stands.

DOI： 10.1299/kikaib.66.804

Language：English   Publishing type：Research paper (scientific journal)  

Anomalous flow phenomena in an axial compressor rotor at near-stall conditions have been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulations show-that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists and turns violently with time, thus interacting with the pressure surface of the adjacent blade. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the tip leakage flow field at the near-stall conditions: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the blade pressure surface. As the flow rate is decreased from the near-stall conditions, the movement of the tip leakage vortex due to the vortex breakdown becomes so larger that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction gives rise to the three-dimensional separation of the suction surface boundary-layer.

DOI： 10.1299/kikaib.66.1029

Language：English   Publishing type：Research paper (other academic)  

The unsteady flow nature caused by the breakdown of the tip leakage vortex in an axial compressor rotor at near-stall conditions has been investigated by unsteady three-dimensional Navier-Stokes flow simulations. The simulations show that the spiral-type breakdown of the tip leakage vortex occurs inside the rotor passage at the near-stall conditions. Downstream of the breakdown onset, the tip leakage vortex twists and turns violently with time, thus interacting with the pressure surface of the adjacent blade. The motion of the vortex and its interaction with the pressure surface are cyclic. The vortex breakdown causes significant changes in the nature of the tip leakage vortex, which result in the anomalous phenomena in the time-averaged flow fields near the tip at the near-stall conditions: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing wall pressure trough corresponding to the leakage vortex, large spread of the low-energy fluid accumulating on the pressure side, and large pressure fluctuation on the pressure side. As the flow rate is decreased, the movement of the tip leakage vortex due to its breakdown becomes so large that the leakage vortex interacts with the suction surface as well as the pressure one. The interaction with the suction surface gives rise to the three-dimensional separation of the suction surface boundary layer.

DOI： 10.1115/2000-GT-0666

Language：English   Publishing type：Research paper (scientific journal)  

Evolution and structure of multiple stall cells with short-length-scale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, a short-length-scale stall cell appeared at first, but did not grow rapidly in size, unlike a so-called 'spike-type stall inception' observed in many multistage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, the size of which was on the same order of the inception cell (a few blade spacings), were rotating at 72 percent of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long-length-scale wave appeared overlapping the multiple short-length-scale waves, then developed to a deep stall state with a large cell. In order to capture the short-length-scale cells in the mild stall state, a so-called 'double phase-locked averaging technique' has been developed, by which the flow field can be measured phase locked to both the rotor and the stall cell rotation. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high-response pressure transducers. By a physically plausible explanation for the experimental results, a model for the flow mechanism of the short-length-scale stall cell has been presented. The distinctive feature of the stall cell structure is on the separation vortex bubble with a leg traveling ahead of the rotor, with changing the blade in turn on which the vortex leg stands.

DOI： 10.1115/1.555426

Language：English   Publishing type：Research paper (other academic)  

In a low-speed compressor test rig at Kyushu University, multiple short length-scale stall cells appeared under a mild stall condition and turned into a long length-scale cell under a deep stall condition. Then, for the both types of stall cell, the pressure distribution on the casing wall and the velocity distributions upstream and downstream of the rotor have been measured by high response pressure transducers and a slanted hot-wire, respectively. The time-dependent ensemble averages of these distributions have been obtained phase-locking to both of the rotor and the stall cell rotation by using a so-called 'double phase-locked averaging technique' developed by the authors. Structure of the two stall cells are compared with each other: The short length-scale stall cell is characterized by a concentrated vortex spanning from the casing wall ahead of the rotor to the blade suction surface. In the long length-scale stall cell, the separation vortices go upstream irregularly when blade separation develops in the front half of the cell, and reenter the rotor on the hub side in the rear half of it. The unsteady aerodynamic force and torsional moment acting on the blade tip section have been evaluated from the time-dependent ensemble averages of the casing wall pressure distribution. The force fluctuation due to the short length-scale cells is somewhat smaller than that for the long length-scale cell. The blade suffers two peaks of the force during a period of the short length-scale cells passing through it. The moment fluctuation for the short length-scale cells is considerably larger than that for the long length-scale cell.

DOI： 10.1115/2000-GT-0425

Language：English   Publishing type：Research paper (scientific journal)  

Evolution of multiple stall cells with short length-scale in an axial compressor rotor was investigated experimentally. In a low-speed research compressor rotor tested, a short length-scale stall cell appeared at first, but did not grow rapidly in size unlike a so-called "spike-type stall inception" observed in many multi-stage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, size of which was on the same order of the inception cell (of a few blade spacings), were rotating at 72% of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long length-scale wave appeared overlapping the multiple short length-scale waves, then developed to a deep stall state with a big cell. The ensemble averages of the axial velocity components upstream and downstream of the rotor, which were obtained phase-locked to the cell rotation, showed that the stall cells were of a part-span type.

DOI： 10.1299/kikaib.65.4021

Language：English  

This paper describes visualization of multiple stall cells propagating in an axial compressor rotor. The multiple stall cells have appeared at equal intervals under a mild stall condition of the compressor test rig in Kyushu University. Then, time-dependent ensemble averages of the three-dimensional velocity components upstream and downstream of the rotor, and the pressure distributions on the casing wall have been obtained by a so-called 'double phase-locked averaging technique' in which the outputs of a hot-wire and high response pressure transducers are averaged phase-locked to both of the rotor and the cell rotation. On the basis of the 25 time dependent averaged flow fields, the animations have been made to visualize the flow behavior of the stall cell propagation. The structure of the stall cell is characterized by the length-scale of a few blade spacing and a part-span type. It consists of the separation vortex bubble with a leg travelling ahead of the rotor, changing the blade in turn on which the vortex leg stands. The reverse flows appeared upstream and downstream of the rotor are resulted from this vortical flow.

Language：English  

Structure and unsteady behavior of the vortical flow in a half-ducted propeller fan, in which only a rear part of a rotor is covered by a shroud, have been investigated by a large eddy simulation (LES) with a subgrid-scale model of Smagorinsky. The vortical flow structure is visualized by a semi-analytic method for identifying vortex cores based on the critical-point theory. The simulation shows that the tip vortex plays a major role in the structure and unsteady behavior of the vortical flow in the half-ducted propeller fan. The tip vortex starts to be formed on the blade tip suction side near the midchord and grows nearly in the tangential direction, thus impinging on the pressure surface near the tip of the adjacent blade. The spiral-type breakdown of the tip vortex occurs near the midpitch, so that the tip vortex twists and turns violently with time. The very large movement of the tip vortex causes the high pressure fluctuation in the interference region between the tip vortex and the main stream.

Language：English   Publishing type：Research paper (scientific journal)  

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubblelike recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow, resulting from the contraction of the bubblelike structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at near-stall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise, and pitchwise directions. The growth of the breakdown causes the blockage and the loss to Increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

DOI： 10.1115/1.2841339

Language：English   Publishing type：Research paper (scientific journal)  

A method for measuring propagation of disturbance in a high-speed flow has been developed by using a laser-induced fluorescence (LIF) technique. A cross-correlation function between the time- dependent LIF signal and a pressure sensor signal at a reference point enables to measure a propagation speed of disturbance. Through a bandpass filter, the speed of disturbance with a particular frequency can be obtained. A feature of disturbance propagation can be grasped by drawing maps for the cross-correlation coefficients on a space at successive delay-times and making an animation. The method was applied to a supersonic flow over a rectangular cavity with length to depth ratio of 2, to elucidate feedback mechanisms of self-sustaining flow oscillation with several dominant frequencies.

DOI： 10.1299/kikaib.65.948

Language：English   Publishing type：Research paper (other academic)  

Evolution and structure of multiple stall cells with short lengthscale in an axial compressor rotor have been investigated experimentally. In a low-speed research compressor rotor tested, a short lengthscale stall cell appeared at first, but did not grow rapidly in size unlike a so-called "spike-type stall inception" observed in many multi-stage compressors. Alternatively, the number of cells increased to a certain stable state (a mild stall state) under a fixed throttle condition. In the mild stall state the multiple stall cells, size of which was on the same order of the inception cell (a few blade spacings), were rotating at 72 % of rotor speed and at intervals of 4.8 blade spacings. With further throttling, a long length-scale wave appeared overlapping the multiple short length-scale waves, then developed to a deep stall state with a big cell. In order to capture the short length-scale cells in the mild stall state, a so-called 'double phase-locked averaging technique' has been developed, by which the flow field can be measured phase locked to both of the rotor and the stall cell rotation. Then, lime-dependent ensemble averages of the 3D velocity components upstream and downstream of the rotor have been obtained with a slanted hot-wire, and the pressure distributions on the casing wall with high response pressure transducers. By a physically plausible explanation for the experimental results, a model for the flow mechanism of the short length-scale stall cell has been presented. The distinctive feature of the stall cell structure is on the separation vortex bubble with a leg traveling ahead of the rotor, with changing the blade in turn on which the vortex leg stands.

DOI： 10.1115/99-GT-097

Language：English   Publishing type：Research paper (scientific journal)  

The flow model and loss model in the rectangular scrolls constructed from the main flow with free vortex flow, the 3D equilibrium boundary layer on the side walls and the 2D boundary layer on the inner and outer walls, and the equation to estimate the loss in it were made in this research. The model is based on the theory of the 3D equilibrium boundary layer". The calculated results of it are shown good coincidence with test results^2'3'. The flow equations are made from the 3D boundary layer equation with 1/n multiplier law and Mager's equation", and main flow with free vortex flow. Those equations have three unknown variables which are n, boundary layer thickness and radial velocity parameter. The mean outlet flow angles are estimated by using the values of those three variables decided by the measured volocity distributions^2'3'. It is made clear that the flow rate of main flow is reduced by the flow through the 3D equilibrium boundary layer and the outlet flow angle become small at the main flow, and the loss less main flow is sustained for being main flow.

DOI： 10.1299/kikaib.65.247

Language：English   Publishing type：Research paper (scientific journal)  

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 deg and 45 deg, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that “breakdown” of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The “vortex breakdown” causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in a behavior of the tip leakage flow that is substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

DOI： 10.1115/1.2841777

Language：English   Publishing type：Research paper (international conference proceedings)  

Language：English   Publishing type：Research paper (other academic)  

Structure of a tip leakage flow field in an axial compressor rotor has been investigated by detailed numerical simulations and appropriate post-processing. Physical explanations of the structure are made in terms of vortex-core identification, normalized helicity, vortex-lines, limiting streamlines, etc. The onset of the discrete tip leakage vortex is located on the suction surface at some distance from the leading edge. The vortex core with high vorticity is generated from a shear layer between the leakage jet flow and the main flow. The streamlines in the leakage flow are coiling around the vortex core. All the vortex-lines in the tip leakage vortex core link to ones in the suction surface boundary layer. The other vortex-lines in the suction surface boundary layer link to the vortex-lines in the pressure surface boundary layer and in the casing wall boundary layer. There are two mechanisms to reduce intensity of the tip leakage vortex: one is reduction of discharged vorticity caused by the linkage of vortex-lines between the suction surface and casing wall boundary layers, and another is diffusion of vorticity from the tip leakage vortex. Relative motion of the endwall has a substantial influence on the structure of the leakage flow field. In the case of a compressor rotor, it intensifies streamwise vorticity of the leakage vortex but reduces leakage flow loss.

DOI： 10.1115/98-GT-091

Language：English   Publishing type：Research paper (other academic)  

The breakdown of tip leakage vortex has been investigated on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics are elucidated by Navier-Stokes flow simulations and visualization techniques for identifying the breakdown. The simulations show that the leakage vortex breakdown occurs inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown is characterized by the existence of the stagnation point followed by a bubble-like recirculation region. The onset of breakdown causes significant changes in the nature of the tip leakage vortex: large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex. The expansion has an extremely large blockage effect extending to the upstream of the leading edge. The disappearance of the concentrated vorticity results in no rolling-up of the vortex downstream of the rotor and the disappearance of the pressure trough on the casing. The leakage flow field downstream of the rotor is dominated by the outward radial flow resulting from the contraction of the bubble-like structure of the breakdown region. It is found that the leakage vortex breakdown plays a major role in characteristic of rotor performance at nearstall conditions. As the flow rate is decreased from the peak pressure rise operating condition, the breakdown region grows rapidly in the streamwise, spanwise and pitchwise directions. The growth of the breakdown causes the blockage and the loss to increase drastically. Then, the interaction of the breakdown region with the blade suction surface gives rise to the three-dimensional separation of the suction surface boundary layer, thus leading to a sudden drop in the total pressure rise across the rotor.

DOI： 10.1115/98-GT-239

Language：English   Publishing type：Research paper (scientific journal)  

The breakdown of tip leakage vortex was examined on a low-speed axial compressor rotor with moderate blade loading. Effects of the breakdown on the rotor aerodynamics were elucidated by Navier-Stokes flow simulations and visualization techniques. The leakage vortex breakdown were observed inside the rotor at a lower flow rate than the peak pressure rise operating condition. The breakdown was characterized by the existence of the stagnation point followed by a bubble-like recirculating region. The onset of breakdown resulted to large expansion of the vortex and disappearance of the streamwise vorticity concentrated in the vortex.

Language：English   Publishing type：Research paper (scientific journal)  

Structure of a tip leakage flow field in an axial compressor rotor has been investigated by detailed numerical simulations and appropriate post-processing. Physical explanations of the structure are made in terms of vortex-core identification, normalized helicity, vortex-lines, limiting streamlines, etc. The onset of the discrete tip leakage vortex is located on the suction surface at some distance from the leading edge. The vortex core with high vorticity is generated from a shear layer between the leakage jet flow and the main flow. The streamlines in the leakage flow are coiling around the vortex core. All the vortex-lines in the tip leakage vortex core link to ones in the suction surface boundary layer. The other vortex-lines in the suction surface boundary layer link to the vortex-lines in the pressure surface boundary layer and in the casing wall boundary layer. There are two mechanisms to reduce intensity of the tip leakage vortex: one is reduction of discharged vorticity caused by the linkage of vortex-lines between the suction surface and casing wall boundary layers, and another is diffusion of vorticity from the tip leakage vortex. Relative motion of the endwall has a substantial influence on the structure of the leakage flow field. In the case of a compressor rotor, it intensifies streamwise vorticity of the leakage vortex but reduces leakage flow loss.

Language：English   Publishing type：Research paper (scientific journal)  

This research aims to develop an advanced technology of highly loaded axial compressor stages with high efficiency and sufficient surge margin. To improve endwall boundary layer flows which lead to energy loss and instability at an operation of low flow rate, the Controlled-Endwall-Flow (CEF) rotor blades were designed and tested in the low speed rotating cascade facility of Kyushu University. The CEF rotor blades have three distinctive features: the leading-edge sweep near hub and casing wall, the leading-edge bend near the casing, and the same exit metal angle of blade evaluated by a conventional design method. Mechanical strength of the blade was verified by a numerical simulation at a high speed condition. The baseline rotor blades were designed under the same design condition and tested to compare with the CEF rotor. The results showed that the maximum stage efficiency of the CEF rotor was higher by 0.7 percent and the increase in surge margin was more than 20 percent in comparison with the baseline rotor. The results of both internal flow survey and 3D Navier-Stokes analysis showed that improvement of the overall stage performance resulted from activation of the endwall boundary layers, and suggested that further improvement might be expected by combination of end-bend stator blades and a highly loaded axial compressor stage could be developed by use of the CEF rotor.

Language：English   Publishing type：Research paper (other academic)  

This research aims to develop an advanced technology of highly loaded axial compressor stages with high efficiency and sufficient surge margin. To improve endwall boundary layer flows which lead to energy loss and instability at an operation of low flow rate, the Controlled-Endwall-Flow (CEF) rotor blades were designed and tested in the low speed rotating cascade facility of Kyushu University. The CEF rotor blades have three distinctive features: The leading-edge sweep near hub and casing wall, the leading-edge bend near the casing, and the same exit metal angle of blade evaluated by a conventional design method. Mechanical strength of the blade was verified by a numerical simulation at a high speed condition. The baseline rotor blades were designed under the same design condition and tested to compare with the CEF rotor. The results showed that. the maximum stage efficiency of the CEF rotor was higher by 0.7 percent and the increase in surge margin was more than 20 percent in comparison with the baseline rotor. The results of both internal flow survey and 3D Navier-Stokes analysis showed that improvement of the overall stage performance resulted from activation of the endwall boundary layers, and suggested that further improvement might be expected by combination of end-bend stator blades and a highly loaded axial compressor stage could be developed by use of the CEF rotor.

DOI： 10.1115/97-GT-248

Language：English   Publishing type：Research paper (scientific journal)  

The 'lock-in' phenomenon has been investigated experimentally by vibrating cylindrical bluff body surfaces locally using piezoelectric actuators. The maximum amplitude of oscillation is of the order of 20 μm (nearly 1.0 × 10^-3 times the body thickness), and the excitation frequency covers below and above a natural vortex shedding frequency from the body. The Reynolds number ranges from 5.25 × 10³ to 2.31 × 10⁴. Substantial entrainment of vortex shedding frequency has been observed by exciting the upstream surface of sidewalls, where a short laminar separation bubble exists. Vortex shedding becomes more periodical and the total pressure in the wake becomes high by the local excitation of body surfaces. Possibilities for application to the active control of vibration and noise due to vortex shedding, as well as to drag reduction are discussed.

DOI： 10.1299/kikaib.63.605_69

Language：English   Publishing type：Research paper (scientific journal)  

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in an axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 degrees and 45 degrees, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that `breakdown' of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The `vortex breakdown' causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in the behavior of the tip leakage flow substantially different from that in the axial flow rotor: no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

Language：English   Publishing type：Research paper (other academic)  

Experimental and computational results of tip leakage flow fields in a diagonal flow rotor at the design flow rate are compared with those in on axial flow rotor. In the diagonal flow rotor, the casing and hub walls are inclined at 25 degrees and 45 degrees, respectively, to the axis of rotation, and the blade has airfoil sections with almost the same tip solidity as that of the axial flow rotor. It is found out that "breakdown" of the tip leakage vortex occurs at the aft part of the passage in the diagonal flow rotor. The "vortex breakdown" causes significant changes in the nature of the tip leakage vortex: disappearance of the vortex core, large expansion of the vortex, and appearance of low relative velocity region in the vortex. These changes result in the behavior of the tip leakage flow substantially different from that in the axial flow rotor; no rolling-up of the leakage vortex downstream of the rotor, disappearance of the casing pressure trough at the aft part of the rotor passage, large spread of the low-energy fluid due to the leakage flow, much larger growth of the casing wall boundary layer, and considerable increase in the absolute tangential velocity in the casing wall boundary layer. The vortex breakdown influences the overall performance, also: large reduction of efficiency with the tip clearance, and low level of noise.

DOI： 10.1115/97-GT-043

Language：English   Publishing type：Research paper (scientific journal)  

The authors developed a method to estimate nozzle-wake exciting forces (NEF) using Fourier series development of angular momentum flux (AMF) at the blade inlet of radial turbines. The NEF is strongly affected by the nozzle profiles. Application of this method to the evaluation of the NEF and AMF resulted in fundamental standards for selection of the number of nozzle blades and the profiles. The values of each order of NEF are obtained from Fourier series development of AMF. There is an increasing region of NEF to the distance from a nozzle trailing edge. The maximum estimation error of the blade vibration stress, which is calculated using the values of the first order of NEF and the coefficients of effective exciting force, is 10%. The coefficient of effective exciting force is 1/3 in the first and second modes, and 1/2 in third mode. Those coefficients are evaluated as the ratio of NEF and equivalent exiting forces calculated using the measured data of vibration stresses at two different points on the blade.

DOI： 10.1299/kikaib.62.3635

Language：English   Publishing type：Research paper (scientific journal)  

A laser-induced fluorescence technique to diagnose a three-dimensional transonic flow with complicated shock wave-boundary layer interaction is presented. The diagnostic system consists of an argonion laser sheet traversing laterally in the flow field with seeded iodine as fluorescence material, a CCD camera with an image intensifier and a microcomputer for image processing. The temperature distributions in a rectangular duct with a swept-back bump are investigated by this system, and the structure of the flow field is clarified including the curved shock waves and the boundary-layer separation.

DOI： 10.1299/kikaib.61.3230

Language：English   Publishing type：Research paper (other academic)  

A laser-induced fluorescence (LIF) method is developed to investigate the three-dimensional transonic flow with complicated shock-wave/boundary-layer interaction. This diagnostic system uses an argon-ion laser with iodine seeded as fluorescence material, and is applied to a rectangular duct with a swept-back bump. The temperature distributions in the duct are obtained, and the structure of the flow field is clarified including the curved shock wave and the boundary-layer separation. The measured temperature distributions are compared with those obtained by a Navier-Stokes flow simulation to investigate the reliability of temperature measurement by the present LIF method.

Language：English   Publishing type：Research paper (scientific journal)  

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to have a skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to one third of the scroll circumference, the secondary flow grows so strongly that most of the low-momentum fluid in the incoming boundary layer is transported to the nozzle region. The succeeding elimination of the lowmomentum fluid in the boundary layer suppresses growth of the boundary layer farther downstream, where the boundary layer shows a similar velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.

DOI： 10.1115/1.2929431

Language：English   Publishing type：Research paper (scientific journal)  

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to assume a skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to one-third of the scroll circumference, the secondary flow increases largely that most of the low-momentum fluid in the incoming boundary layer is transported to the nozzle region. The succeeding elimination of the low-momentum fluid in the boundary layer suppresses growth of the boundary layer further downstream, where the boundary layer shows a self-similar velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.

DOI： 10.1299/kikaib.60.766

Language：English   Publishing type：Research paper (scientific journal)  

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to have the skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to the one third of the scroll circumference, the secondary flow grows so strongly that the most of the low momentum fluid in the incoming boundary layer are transported to the nozzle region.

Language：English   Publishing type：Research paper (other academic)  

A detailed experimental investigation was carried out to examine the three-dimensional boundary layer characteristics in a radial inflow turbine scroll. Some basic flow phenomena and growth of secondary flow were also investigated. In the inlet region of the scroll, the incoming boundary layer begins to have the skewed nature, namely the radially inward secondary flow caused by the radial pressure gradient. From the inlet region to the one third of the scroll circumference, the secondary flow grows so strongly that the most of the low momentum fluid in the incoming boundary layer are transported to the nozzle region. The succeeding elimination of the low momentum fluid in the boundary layer suppresses growth of the boundary layer further downstream, where the boundary layer shows a similarity of velocity profile. The distributions of the boundary layer properties in the scroll correspond well to those of the flow properties at the nozzle. The behavior of the boundary layer in the scroll is found to affect the circumferential nonuniformity of the nozzle flow field.

DOI： 10.1115/93GT138

Language：English  

The measurements of flow fields have been performed by changing tip clearance and flow rate for two diagonal flow impellers with different vortex types, a free vortex type and a vortex type of constant tangential velocity. This paper presents overall behaviors of the secondary flow in the diagonal flow impellers to offer available data for modeling of spanwise mixing due to the secondary flow. The characteristics of the secondary flow are that, in comparison with axial flow impellers, the leakage vortex roll-ups are not seen clearly and the low energy region caused by the tip leakage flow is larger. As the tip clearance increases, the low energy region near the casing becomes larger and shifts toward the suction side of the blade. The low energy region tends to move from the pressure side to the suction side with decrease of the flow rate. For the impeller with a vortex type of constant tangential velocity, there exists a strong secondary flow due to the spanwise loading distribution.

Language：English   Publishing type：Research paper (scientific journal)  

An implicit upwind scheme has been developed for Navier-Stokes simulations of unsteady flows in transonic cascades. The two-dimensional, Reynolds-averaged Navier-Stokes equations are discretized in space using a cell-centered finite volume formulation and in time using the Euler implicit method. The inviscid fluxes are evaluated using a highly accurate upwind scheme based on a TVD formulation with the Roe’s approximate Riemann solver, and the viscous fluxes are determined in a central differencing manner. The algebraic turbulence model of Baldwin andLomax is employed. To simplify grid generations, a zonal approach with a composite zonal grid system is implemented, in which periodic boundaries are treated as zonal boundaries. A new time linearization of the inviscid fluxes evaluated by Roe’s approximate Riemann solver is presented in detail. No approximate factorization is introduced, and unfactored equations are solved by a pointwise relaxation method. To obtain time-accurate solutions, 30 linear iterations are performed at each time step. Numerical examples are presented for unsteady flows in a transonic turbine cascade where periodic unsteadiness is caused by the trailing edge vortex shedding.

DOI： 10.1115/1.2929184

Language：English   Publishing type：Research paper (scientific journal)  

A new zonal approach for computation of compressible viscous flows in cascades has been developed. The two-dimensional, Reynolds-averaged Navier-Stokes equations are discretized spatially by a cell-centered finite volume formulation. In order to make the present approach robust, the inviscid fluxes at cell interfaces are evaluated using a highly accurate TVD scheme based on the MUSCL-type approach with the Roe’s approximate Riemann solver. The viscous fluxes are determined in a central differencing manner. To simplify the grid generation, a composite zonal grid system is adopted, in which the computational domain is divided into nonoverlapping zones, and structured grids are generated independently in each zone. The zonal boundary between two zones is uniquely defined by cell interfaces of one zone, which ensures the uniqueness of the zonal boundary. Communication from one zone to the other is accomplished by numerical fluxes across the zonal boundary. It should be noted that the complete conservation of the numerical fluxes across the zonal boundary can be satisfied by directly evaluating the numerical fluxes using the finite volume method and by ensuring the uniqueness of the zonal boundary. In order to demonstrate the versatility of the present zonal approach, numerical examples are presented for viscous flows through a transonic turbine cascade.

DOI： 10.1115/1.2929118

Language：English   Publishing type：Research paper (scientific journal)  

An implicit upwind scheme has been developed for Navier-Stokes simulations of unsteady flows in transonic cascades. The two-dimensional, Reynolds-averaged Navier-Stokes equations are discretized in space using a cell-centered finite volume formulation and in time using the Euler implicit method. The inviscid fluxes are evaluated using a highly accurate upwind scheme based on a TVD formulation with the Roe's approximate Riemann solver, and the viscous fluxes are determined in a central differencing manner. The algebraic turbulence model of Baldwin and Lomax is employed. To simplify grid generations, a zonal approach with a composite zonal grid system is implemented, in which periodic boundaries are treated as zonal boundaries. A new time-linearization of the inviscid fluxes evaluated by the Roe's approximate Riemann solver is presented in detail. No approximate factorization is introduced, and unfactored equations are solved by a pointwise relaxation method. To obtain time-accurate solutions, 30 inner iterations are performed at each time step. Numerical examples are presented for unsteady flows in a transonic turbine cascade where periodic unsteadiness is caused by the trailing edge vortex shedding.

Language：English   Publishing type：Research paper (other academic)  

An implicit upwind scheme has been developed for Navier-Stokes simulations of unsteady flows in transonic cascades. The two-dimensional, Reynoldsaveraged Navier-Stokes equations are discretized in space using a cell-centered finite volume formulation and in time using the Euler implicit method. The inviscid fluxes are evaluated using a highly accurate upwind scheme based on a TVD formulation with the Roe's approximate Riemann solver, and the viscous fluxes are determined in a central differencing manner. The algebraic turbulence model of Baldwin and Lomax is employed. To simplify grid generations, a zonal approach with a composite zonal grid system is implemented, in which periodic boundaries are treated as zonal boundaries. A new time-linearization of the inviscid fluxes evaluated by the Roe's approximate Riemann solver is presented in detail. No approximate factorization is introduced, and unfactored equations are solved by a pointwise relaxation method. To obtain time-accurate solutions, 30 inner iterations are performed at each time step. Numerical examples are presented for unsteady flows in a transonic turbine cascade where periodic unsteadiness is caused by the trailing edge vortex shedding.

DOI： 10.1115/91-GT-223

Language：English   Publishing type：Research paper (scientific journal)  

A new zonal approach for compressible viscous flow computations using a TVD finite volume method has been developed. The two-dimensional. Reynolds-averaged NavierStokes equations are discretized spatially by the finite volume formulation. The inviscid fluxes at the cell interfaces are evaluated through the MUSCLtype approach of an upwind scheme. In the present approach, the computational domain is divided into non-overlapping zones. The zonal boundaries are constructed from the cell interfaces, since the finite volume formulation with the cell-centered control volumes is used. Consequently communication from one zone to another is accomplished by the numerical fluxes through the zonal boundaries. The use of the finite volume formulation can ensure the unity of zonal boundaries and the complete conservation of numerical fluxes at the zonal boundaries, which results in a high-accuracy zonal approach. In order to demonstrate the versatility of the present zonal approach, numerical results are presented for viscous flows through a transonic turbine cascade.

DOI： 10.1299/kikaib.56.609

Language：English   Publishing type：Research paper (scientific journal)  

A new zonal approach for computation of compressible viscous flows in cascades has been developed. The two-dimensional, Reynolds-averaged Navier-Stokes equations are discretized spatially by a cell-centered finite volume formulation. In order to make the present approach robust, the inviscid fluxes at cell interfaces are evaluated using a highly accurate TVD scheme based on the MUSCL-type approach with the Roe's approximate Riemann solver. The viscous fluxes are determined in a central differencing manner. To simplify the grid generation, a composite zonal grid system is adopted, in which the computational domain is divided into non-overlapping zones, and structured grids are generated independently in each zone. The zonal boundary between two zones is uniquely defined by cell interfaces of one zone, which ensures the uniqueness of the zonal boundary.

Language：English   Publishing type：Research paper (other academic)  

A new zonal approach for computation of compressible viscous flows in cascades has been developed. The two-dimensional, Reynolds-Averaged Navier-Stokes equations are discretized spatially by a cell-centered finite volume formulation. In order to make the present approach robust, the inviscid fluxes at cell interfaces are evaluated using a highly accurate TVD scheme based on the MUSCL-Type approach with the Roe's approximate Riemann solver. The viscous fluxes are determined in a central differencing manner. To simplify the grid generation, a composite zonal grid system is adopted, in which the computational domain is divided into non-overlapping zones, and structured grids are generated independently in each zone. The zonal boundary between two zones is uniquely defined by cell interfaces of one zone, which ensures the uniqueness of the zonal boundary. The communication from one zone to the other is accomplished by numerical fluxes across the zonal boundary. It should be noted that the complete conservation of the numerical fluxes across the zonal boundary can be satisfied by directly evaluating the numerical fluxes using the finite volume method and by ensuring the uniqueness of the zonal boundary. In order to demonstrate the versatility of the present zonal approach, numerical examples are presented for viscous flows through a transonic turbine cascade.

DOI： 10.1115/90-GT-260

Language：English   Publishing type：Research paper (scientific journal)  

The behavior of secondary flows in a turbine scroll has been investigated experimentally. Detailed flow measurements, using a five-hole probe, were made at sixteen cross sections. Considering the effect of nozzle sink flows, the secondary flows were defined by the velocity components perpendicular to the local flow directions of the axisymmetric potential flow solutions in each measuring plane. This secondary flow field was found to correspond well to the distribution of streamwise vorticity and to be dominated by two passage vortices. The secondary flows associated with the passage vortices increase rapidly downstream of the scroll inlet section. As the secondary flows increase, inward radial flows of low energy fluids on the walls are so strong that the low energy fluids flow out into the nozzle. The discharge of low energy fluids results in the decrease in the secondary flows at the downstream part in the scroll.

DOI： 10.1299/kikaib.55.3370

Language：English   Publishing type：Research paper (scientific journal)  

This report presents a method for meridional through-flow calculations in turbomachines which is available to the quasi-three-dimensional design problem. An equilibrium equation along an arbitrary quasi-orthogonal is formulated by exactly averaging the equations of continuity, momentum and energy in the circumferential direction. In the present method the assumption of S2-surface is unnecessary, and the effect of blade force due to the pressure difference across a blade and the effect of non-axisymmetricity due to finiteness of the number of blades can be rigorously taken into account.

Language：English   Publishing type：Research paper (scientific journal)  

A test apparatus of turbine scroll has been devised to investigate the secondary flow phenomena in a scroll. The scroll is of parallel end wall type and based on a logarithmic spiral. The three-dimensional flow field survey can be taken in arbitrary cross sections with a probe traverse mechanism newly developed. Distributions of total pressure and three velocity components have been measured in detail, using a five-hole probe. The secondary flow field is to be dominated by passage vortices on end walls and low energy fluid accumulating on a tongue. The favorable pressure gradient and the inward secondary flow on end walls suppress an extreme growth of wall boundary layer. However, the secondary flow affects the distribution of exit flow angle in the direction of passage height.

DOI： 10.1299/kikaib.52.4001

Language：English   Publishing type：Research paper (scientific journal)  

The four stage Runge-Kutta(4SRK) and two stage Rational Runge-Kutta(2SRRK) schemes have been applied to solve the compressible Navier-Stokes equations, in order to develop a fast, accurate explicit time-marching technique suitable for vectorization. On a supercomputer, a problem of shock-boundary layer interaction is calculated by use of these schemes combined with local timestepping. It is shown that the 4SRK scheme with the fourth-order central differencing of convective terms is stable out to a Courant number of 2.06 according to Neumann's stability criterion. The practical limit of Courant number has been very close to the theoretical limit. At a high Reynolds number, the Courant number limit of 2SRRK scheme is significantly less than that of conventional explicit methods. Both the 4SRK and 2SRRK schemes are readily vectorizable. The use of implicit residual averaging reduces iterations, but is not suitable for vectorization.

DOI： 10.1299/kikaib.52.3874

Language：English   Publishing type：Research paper (scientific journal)  

In order to develop a diagonal inflow gas turbine with a three-dimensional airfoil impeller, an experimental investigation was carried out. For that purpose, an airfoil impeller was made on the basis of a quasi-three-dimensional design, and the internal flow field was measured in detail. It was found that the diagonal inflow turbine with a three-dimensional airfoil impeller can be operated efficiently at high specific speed, and that the velocity coefficient of the impeller is as high as that for an axial flow turbine. But the turbine performance is strongly affected by the secondary flow in the impeller, which is so strong that the low energy fluid is accumulated near the tip of impeller. It is necessary to study on determination of the optimum incidence angle by considering this secondary flow.

DOI： 10.1299/kikaib.50.459_2843

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：Japan  

Event date： 2021.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：Japan  

Event date： 2021.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：United States  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：United States  

Event date： 2020.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：United States  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：United Kingdom  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Online conference   Country：United States  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2019.9

Language：English   Presentation type：Oral presentation (general)  

Venue：London   Country：United Kingdom  

Event date： 2019.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：秋田市   Country：Japan  

Event date： 2019.7 - 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2019.7 - 2019.8

Language：English   Presentation type：Oral presentation (general)  

Venue：San Francisco   Country：United States  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Phoenix   Country：United States  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Phoenix   Country：United States  

This paper describes the influence of a bent inlet pipe installed immediately upstream of a transonic centrifugal compressor on the aerodynamic performance and the stability. In order to clarify the influence of the bent inlet pipe, the internal flow fields in the inlet pipe, the impeller, and the diffuser of the compressor have been numerically investigated by a DES (Detached Eddy Simulation). For the purpose of comparison, the simulation was also conducted for the case of uniform axial inflow using a straight pipe. In order to make clear the influence of non-uniform flow with a bent pipe as far as possible, a 90-degree bent pipe was installed immediately upstream of the compressor, that is 0.86 times the inlet inner diameter. In the case of installing the bent pipe on the upstream of the compressor, the pressure ratio decreased on the high flow rate side in the compressor performance characteristic, whereas it increased at the low flow rate side. At the low flow rate operating point, there is a reversed flow occurring in the compressor impeller on the shroud side near the blade leading-edge. Installation of the bent pipe promotes mixing between the reversed flow and the main flow at the inlet of the compressor thanks to occurrence of a secondary flow. Since the reversed flow comes out from inside of the impeller, it has a high circumferential velocity. Therefore, the mixing of the reversed flow makes the compressor inlet flow a pre-swirl flow, and thereby the incidence decreases. As a result, leading-edge separation on the blade tip side of the impeller is suppressed, and the flow field inside the impeller is improved. In the diffuser section, when the bent pipe is installed, the circumferential velocity of the impeller exit flow increases on the hub side, whereas the radial velocity decreases. As a result, the diffuser performance is deteriorated and the diffuser stall tends to occur.

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Phoenix   Country：United States  

Flow structure and flow loss generation in a transonic axial compressor has been numerically investigated by using a large-scale detached eddy simulation (DES). The data mining techniques, which include a vortex identification based on the critical point theory and a limiting streamline visualization with the line integral convolution (LIC) method, were applied to the DES result in order to analyze the complicated flow field in compressor. The flow loss in unsteady flow field was evaluated by entropy production rate, and the loss mechanism and the loss amount of each flow phenomenon were investigated for the first rotor and the first stator. In the first rotor, a shock-induced separation is caused by the detached shock wave and the passage shock wave. On the hub side, a hub-corner separation occurs due to the secondary flow on the hub surface, and a hub-corner separation vortex is clearly formed. The flow loss is mainly caused by the blade boundary layer and wake, and the loss due to the shock wave is very small, only about 1 percent of the total loss amount in the first rotor. However, the shock/boundary layer interaction causes an additional loss in the blade boundary layer and the wake, which amount reaches to about 30 percent of the total. In the first stator, the hub-corner separation occurs on the suction side. Although only one hub-corner separation vortex is formed in the averaged flow field, the hub-corner separation vortex is generated in multiple pieces and those pieces interfere with each other in an instantaneous flow field. The hub-corner separation generates huge loss over a wide range, however, the loss generation around the hub-corner separation vortex is not so large, and the flow loss is mainly produced in the shear layer between the mainstream region and the separation region. The main factors of loss generation are the boundary layer, wake and hub-corner separation, which account for about 80 percent of the total loss amount in the first stator.

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岐阜市   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：室蘭市   Country：Japan  

Event date： 2018.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台市   Country：Japan  

Event date： 2018.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島市   Country：Japan  

Event date： 2018.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：鹿児島市   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：吹田市   Country：Japan  

Event date： 2018.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：吹田市   Country：Japan  

Event date： 2018.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Morioka   Country：Japan  

Event date： 2018.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Montreal   Country：Canada  

Event date： 2018.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Oslo   Country：Norway  

Event date： 2018.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2018.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2017.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Maui, Hawaii   Country：United States  

Event date： 2017.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Okinawa   Country：Japan  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：久留米   Country：Japan  

Event date： 2017.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：松山   Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山   Country：Japan  

Event date： 2017.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：埼玉   Country：Japan  

Event date： 2017.7 - 2017.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Waikoloa, Hawaii   Country：United States  

Event date： 2017.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Charlotte   Country：United States  

Event date： 2017.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Charlotte   Country：United States  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2016.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2016.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2016.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：酒田   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Event date： 2016.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Washington, DC   Country：United States  

Event date： 2016.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul   Country：Korea, Republic of  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2015.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2015.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2015.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：札幌   Country：Japan  

Event date： 2015.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：米子   Country：Japan  

Event date： 2015.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2015.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Seoul   Country：Korea, Republic of  

Event date： 2015.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Montréal   Country：Canada  

Event date： 2015.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Montréal   Country：Canada  

Event date： 2015.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Montréal   Country：Canada  

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2015.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2015.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Lyon   Country：France  

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市   Country：Japan  

Event date： 2014.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市   Country：Japan  

Event date： 2014.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山市   Country：Japan  

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：富山市   Country：Japan  

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市   Country：Japan  

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市   Country：Japan  

Event date： 2014.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分   Country：Japan  

Event date： 2014.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagasaki   Country：Japan  

Event date： 2014.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2014.7 - 2014.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Event date： 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Düsseldorf   Country：Germany  

Event date： 2014.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Düsseldorf   Country：Germany  

Event date： 2014.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Barcelona   Country：Spain  

Event date： 2013.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋市   Country：Japan  

Event date： 2013.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：調布市   Country：Japan  

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya   Country：Japan  

Event date： 2013.9

Language：English   Presentation type：Oral presentation (general)  

Venue：Nagoya   Country：Japan  

Event date： 2013.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山   Country：Japan  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Incline Village   Country：United States  

Event date： 2013.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Incline Village   Country：United States  

Event date： 2013.6

Language：English   Presentation type：Oral presentation (general)  

Venue：San Antonio   Country：United States  

Event date： 2013.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2012.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：釧路   Country：Japan  

Event date： 2012.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：金沢市   Country：Japan  

Event date： 2012.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Copenhagen   Country：Denmark  

Event date： 2012.6

Language：English   Presentation type：Oral presentation (general)  

Venue：Copenhagen   Country：Denmark  

Event date： 2012.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2011.12

Presentation type：Oral presentation (general)  

Venue：吹田市   Country：Japan  

Event date： 2011.12

Presentation type：Oral presentation (general)  

Venue：横浜市   Country：Japan  

Event date： 2011.11

Presentation type：Oral presentation (general)  

Venue：Osaka   Country：Japan  

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：浜松市   Country：Japan  

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：Hamamatsu   Country：Japan  

Event date： 2011.6

Presentation type：Oral presentation (general)  

Venue：Vancouver   Country：Canada  

Event date： 2011.5

Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Limerick   Country：Ireland  

Presentation type：Oral presentation (invited, special)  

Venue：福岡市   Country：Japan  

Shift from Vector-Parallel to Scalar-Parallel Computers?

Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Numerical Analysis of Separated and Vortical Flow Field in Propeller Fans

Presentation type：Oral presentation (general)  

Venue：福岡   Country：Japan  

Quasi-Three-Dimensional Aerodynamics Design of Wind Turbine With Brimmed Diffuser

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Three-Dimensional Aerodynamic Design of Wind Turbine with Brimmed Diffuser Using Inverse Design Method

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Three-Dimensional Structure of Vortical Flow Field in a Half-Ducted Propeller Fan

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Effect of Tip Clearance on Structure of Rotating Stall Cell in an Axial Flow Compressor Rotor

Presentation type：Oral presentation (general)  

Venue：熊本   Country：Japan  

Three Dimensional Flow Mechanism of Rotating Stall in an Axial Flow Compressor

Presentation type：Oral presentation (general)  

Venue：川越市   Country：Japan  

Unsteady Three Dimensional Flow Behavior of Separated Flow in an Axial Flow Compressor Rotor at Rotating Stall

Presentation type：Oral presentation (general)  

Venue：川越市   Country：Japan  

Experimental and Numerical Investigation of Minichannel Heat Transfer Phenomenon

Presentation type：Oral presentation (general)  

Venue：名古屋市   Country：Japan  

Numerical Analysis of Complex Flow Fields in a Centrifugal Compressor with Vaneless Diffuser

Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Numerical Analysis of Internal Flow in Ultrasonic Flowmeter for Gaseous Hydrogen

Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

LES Analysis of Complex Flow Fields in a Centrifugal Compressor with Vaneless Diffuser

Presentation type：Oral presentation (general)  

Venue：北九州市   Country：Japan  

Numerical Analysis of Internal Flow in Ultrasonic Flowmeter for Gaseous Hydrogen

Presentation type：Oral presentation (general)  

Venue：北九州市   Country：Japan  

Quasi-Three-Dimensional Blade Design of Wind Turbine with Brimmed Diffuser

Presentation type：Oral presentation (general)  

Venue：北九州市   Country：Japan  

Complex Vortical Flow Structure in a Propeller Fan

Presentation type：Oral presentation (general)  

Venue：Montreal   Country：Canada  

Presentation type：Oral presentation (general)  

Venue：San Diegol   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Presentation type：Oral presentation (general)  

Venue：Jeju   Country：Korea, Republic of  

Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Sapporo   Country：Japan  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Olando   Country：United States  

Presentation type：Oral presentation (general)  

Venue：Vail   Country：United States  

Presentation type：Oral presentation (general)  

Country：Japan  

Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Glasgow   Country：United Kingdom  

Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：東京   Country：Japan  

Presentation type：Symposium, workshop panel (public)  

Venue：東京   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：東京   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Public lecture, seminar, tutorial, course, or other speech  

Venue：東京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2012.4

Language：English   Presentation type：Oral presentation (general)  

Venue：Senlis   Country：France  

Event date： 2011.11

Presentation type：Oral presentation (general)  

Venue：Osaka   Country：Japan  

Event date： 2011.7

Presentation type：Oral presentation (general)  

Venue：Hamamatsu   Country：Japan  

Presentation type：Oral presentation (general)  

Venue：東京  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

EFD/CFD Analyses of Unsteady Flow Phenomena in Axial and Centrifugal Compressors

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Aerodynamic Design for Wind-Lens Turbine

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Prediction of Surge in Centrifugal Compressor

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Behavior of Tip Vortex in a Half-Ducted Propeller Fan

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Clarification of Rotating Stall Inception Phenomena in a Multi-Stage Axial Compressor

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Applications of Visualization Techniques to Unsteady Flow Phenomena in Compressors

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Effects of Tip Leakage Vortex Breakdown on Internal Flows and Performance Characteristics of Compressors

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Unsteady Flow Phenomena Related to Rotating Stall Inception in Axial Flow Compressors

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Development of New Type Wind Turbine Originated from University

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Unsteady Flow Phenomena in a Centrifugal Compressor Impeller at Rotating Stall

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Challenge to Prediction of Unsteady Flow Phenomena in Decelerating Cascades Near Stall

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Extraction of Flow Phenomena in Turbomachinery Using Visual Data Mining

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Applications of CFD Analysis to Aerodynamic Noise Prediction for Propeller Fans

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Analysis of Vortical Flow Structure in Cascades

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)