| 1. |
Akihisa YAMADA, Takeshi INO, Shin-ichi TSUDA, Satoshi WATANABE and Taiki TAKAMINE
, Numerical prediction of cavitation in centrifugal pump using multi-process cavitation model, Journal of Fluid Science and Technology, 10.1299/jfst.2024jfst0011, 19, 2, 2024.03. |
| 2. |
Koki SUGAYA, Yoshiki ODAIRA, Satoshi WATANABE, Junnosuke OKAJIMA, Yuka IGA, Experimental study on the boundary layer of the NACA16-012 hydrofoil during the cavitation disappearance phenomenon, Journal of Fluid Science and Technology, 10.1299/jfst.2022jfst0005, 17, 2, 2022.07. |
| 3. |
De ZHANG, Yusuke KATAYAMA, Satoshi WATANABE, Shin-Ichi TSUDA, Akinori FURUKAWA, Performance prediction model of contra-rotating axial flow pump with separate rotational speed of front and rear rotors and its application for energy saving operation, Journal of Fluid Science and Technology, 10.1299/jfst.2020jfst0015, 2020.07. |
| 4. |
De Zhang, Yusuke Katayama, Satoshi Watanabe, Shin Ichi Tsuda, Akinori Furukawa, Numerical study on loss mechanism in rear rotor of contra-rotating axial flow pump, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2020.13.1.241, 13, 1, 241-252, 2020.01, It is known that higher efficiency can be achieved with reduced specific speed design of rear rotor in contra-rotating axial flow pump. To investigate the mechanism of increased efficiency with the reduced specific speed of rear rotor, three models with different specific-speed rear rotors are designed with the conventional method, and the flow fields are simulated by unsteady RANS simulation. To analyze the loss generation mechanism, two loss evaluation methods based on the entropy production rate and the material-derivative of rothalpy are employed. It is found that, although the both methods qualitatively estimate the total loss through the rear rotor, the derivative of rothalpy can give much better quantitative prediction of the losses. Two distinct flow features are observed in the rear rotor, the corner separation at the hub corner of blades and the tip leakage vortex, both of which are responsible for the loss generation. With the evaluation of local loss generation based on the material derivative of rothalpy, the loss contribution of corner separation is found to be very small compared with that due to the tip leakage vortex. The tip leakage vortex structure in high specific speed rear rotor shows the strong interaction with the leading edge of adjacent blade, which seems to strengthen the blockage effect in the tip region. This is relieved in the lower specific speed rear rotor, resulting in the achievement of higher efficiency with it.. |
| 5. |
Tatsuya Morii, Yohei Tanaka, Satoshi Watanabe, Satoru Ohashi, Yasushi Matsunaga, Suction performance and cavitation instabilities of turbopumps with three different inducer design, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2019.12.2.128, 12, 2, 128-135, 2019.04, In the present study, the suction performance and the cavitation instabilities in turbo-pumps with three different inducers designed with different design incidence angle are experimentally investigated in the wide range of operating flow rate. Three inducers L with the lowest design incidence angle, M with the moderate one and H with the largest one are used in combination with identical main impeller. As a result, the total head of pump with inducer H is confirmed to be the largest especially at large flow rates, while the shaft power is almost the same, resulting in the best efficiency with the inducer H. The suction performance is the best with inducer H at large flow rates and is the best with inducer L at low flow rates. Two kinds of instabilities, the cavitating whirling vortex and the surges are mainly observed for the all both inducers, but they are limited at low flow rates. The occurrence ranges of these instabilities in terms of the operating flow rate is the widest with inducer H. However, those in terms of the shockless flow rate ratio is similar for the all three inducers: This fact can contribute to establish some guideline to the pump operation avoiding serious flow instabilities.. |
| 6. |
Y. Suzuki, Y. Katayama, S. Watanabe, S. Tsuda, A. Furukawa, A study on performance prediction of Darrieus-type hydroturbine operated in open channels using CFD with actuator disk method, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/240/4/042020, 240, 4, 2019.03, A performance of Darrieus-type hydroturbine is strongly influenced by the channel and flow condition. These flow conditions are different from place to place and also dependent upon the seasons, therefore it is difficult to study these influences only by experiments. On the other hand, numerical simulation can be adopted for various flow conditions. However, calculation costs are very expensive since fully unsteady simulation taking account of free surface of water should be conducted for this turbine as a cross-flow type. Then, in this paper, a simple numerical model is developed. In this model, instead of solving the complex flow field around the turbine, it is modeled by an actuator disk which imposes the total pressure difference consumed by the rotating turbine. Our previous study suggested that the head coefficient defined as the total pressure difference across the runner normalized by the dynamic pressure with area averaged flow velocity into the turbine seemed to well represent the specific performance of Darrieus-type hydroturbine. In this paper, the specific performance is determined from the experiment in one channel, and the corresponding total pressure change is locally applied to the actuator disk as a function of local inflow velocity. The predicted overall head coefficient, which is defined as the total pressure difference between far upstream and downstream normalized by area averaged velocity downstream of the turbine, is compared with experiment. As a result, when the flow velocity or depth decreases, the overall head coefficient increases. The proposed model can qualitatively reflect this influence of flow velocity and depth on the turbine performance in most cases, while quantitatively the predicted overall head coefficient is different from that in the experiments, indicating the necessity of further modification of the model for quantitative prediction.. |
| 7. |
T. Morii, Y. Tanaka, S. Watanabe, S. Ohashi, Y. Matsunaga, Experimental investigation on suction performance and cavitation instabilities of turbopumps with two different inducers, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/240/3/032041, 240, 3, 2019.03, In the present study, the suction performance and the cavitation instabilities in turbo-pumps with two different inducers designed with different design incidence angle are experimentally investigated in the wide range of operating flow rate. Compared to the Inducer A, Inducer B is designed with larger incidence angle, therefore it has slightly larger inlet and outlet angles. The identical centrifugal impeller is used as a main impeller. As a result, the total head of pump with inducer B is confirmed to be larger than that with inducer B especially at large flow rates, while the shaft power is almost the same, resulting in the better efficiency with the inducer B. The suction performance is better with inducer B at large flow rates. Two kinds of instabilities, the cavitating whirling vortex and the surges are mainly observed for the both inducers, but they are limited at low flow rates. The occurrence ranges of these cavitation instabilities are wider with inducer B.. |
| 8. |
Yushin Ehara, Soichiro Kitamura, Wakana Tsuru, Satoshi Watanabe, Shin Ichi Tsuda, Unsteady forces and moments acting on a cantilevered rectangular hydrofoil with tip clearance in cavitating conditions, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/240/6/062054, 240, 6, 2019.03, It is known that the lift and drag forces of hydrofoil increase then decrease with the decrease of cavitation number, i.e. the development of cavitation, in many cases. In our previous study, the measurement of lift and drag forces of cavitating Clark Y-11.7% hydrofoil was conducted under the assumption of two-dimensional flow, which showed the similar tendency to above common knowledge. However, since there was a tip clearance, the bending moment should present to some content due to the flow asymmetry. In the present study, by using hydrofoil supported by a cantilever equipped with totally 8 strain gauges, the lift and drag forces and their moments are separately measured. It is found that the time-averaged moments around midspan due to lift and drag forces change with the decrease of cavitation number as well as the lift and drag forces change. This means that the working points of lift and drag forces move in the spanwise direction, indicating the importance of the three-dimensionality of cavitation development including that due to tip clearance flow. Unsteady lift and drag forces and their moments also show the significant fluctuations due to periodic behaviour of cavitation instabilities.. |
| 9. |
D. Zhang, T. Tsuneda, Y. Katayama, S. Watanabe, S. I. Tsuda, A. Furukawa, Backflow vortex behaviours in contra-rotating axial flow pump at low flow rates, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/163/1/012036, 163, 1, 2018.07, Backflow usually exists at the inlet of rotors of many turbomachines at low flow rates. In counter-rotating rotors applied for the axial flow pump, such vortical structures are also able to form. In our previous researches, some broad-banded pressure fluctuations in low frequency range have been observed between front and rear rotors, but we have not yet been able to explain what causes such phenomenon. In this study, in order to find out the causes of low frequency components at low flow rates, unsteady numerical simulations for the whole front and rear rotors are conducted, and casing pressure is experimentally measured at the inlet and outlet of front rotor and the inlet of rear rotor. It is found that vortical structures exist between front and rear rotors at below 40% of design flow rate. These vortices seem to be the result of shear layer instability at the impingement location of the exiting flow from front rotor to the backflow of rear rotor. The behaviours of these backflow vortices and their interaction with front rotor contribute the low frequency components in pressure fluctuations observed at low flow rates.. |
| 10. |
Taiki Takamine, Daichi Furukawa, Satoshi Watanabe, Hiroyoshi Watanabe, Kazuyoshi Miyagawa, Experimental analysis of diffuser rotating stall in a three-stage centrifugal pump, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2018.11.1.077, 11, 1, 77-84, 2018.01, Rotating stall phenomenon limits the operation range of turbomacnines, therefore it is important to understand the crucial parameters of this phenomenon. In the present study, the diffuser rotating stall in a three-stage centrifugal pump was experimentally studied. Examined main parameter was an axial offset of rotor against the stationary part, which might be unavoidable due to accumulation of geometrical tolerances and assembling errors. The effect of leakage flow rate at the balance drum section employed as a thrust balancing device, which increases the thru-flow rate at the first and second stages diffusers. was also studied. The effect of rotor axial offset was clearly observed and, with the rotor axial offset to the suction side, the rotating stall appeared only at the third stage diffuser. By setting the balance flow rate set to zero, the onset range of rotating stall became wider m the first and second stage diffusers, which was well explained by the decrease of the thru-flow rate.. |
| 11. |
Masashi Yasuda, Satoshi Watanabe, How to avoid severe incidents at hydropower plants, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2017.10.3.296, 10, 3, 296-306, 2017.07, Hydropower is now changing its role from the energy generator into the most powerful and reliable tool for stabilizing the electrical network, especially under the increase of intermittent power sources like wind-power and solar-power. Although the hydropower plants are the most robust generating facilities, they are not immune from unexpected severe incidents having long downtime, considerable restoration cost and sometimes fatalities. The present paper provides some study results about severe incidents in the conventional hydropower plants, mainly about the flood, fire and electromechanical troubles, except for the incidents of civil facilities. It also provides some possible scenarios which may lead some measures how to avoid such incidents. Finally, it provides some comprehensible recommendations to avoid severe incidents based on experiences.. |
| 12. |
Wakana Tsuru, Takafumi Konishi, Satoshi Watanabe, Shin ichi Tsuda, Observation of inception of sheet cavitation from free nuclei, Journal of Thermal Science, 10.1007/s11630-017-0933-8, 26, 3, 223-228, 2017.06, Prediction of inception of sheet cavitation on solid walls has been recognized to be very difficult, since it is significantly affected by the boundary layer flow characteristics, the population of free nuclei, the nuclei held in the wall roughness, the amount of dissolved air in liquid and so on. It has not sufficiently been made clear how the inception is affected by the conditions of water qualities and background flow characteristics. In this study, high speed observation of inception of sheet cavity from free nuclei is conducted for a two-dimensional convergent- divergent nozzle flow, where the sheet cavity forms just downstream of the nozzle throat. The effects of the amount of dissolved air and the free stream velocity on the inception process of sheet cavitation is examined. In addition, the bubble nuclei density, which is well known to be important factor for cavitation inception, is passively controlled by the filter installed in the tunnel. From the observations, it is confirmed that the nuclei number density significantly affects the formation of sheet cavity rather than the other two parameters. In conditions with large nuclei number density, the sheet cavity does not form, and bubbly cavitation appears instead. In the case with small nuclei number density, the sheet cavity forms from a single flowing nucleus and develops streamwisely and spanwisely. In the conditions with medium nuclei number density, the sheet cavity also forms but is shorter/ narrower streamwisely/spanwisely, due to interaction of other nuclei flowing near the formed sheet cavity.. |
| 13. |
Keisuke Tsutsumi, Satoshi Watanabe, Shin ichi Tsuda, Takeshi Yamaguchi, Cavitation simulation of automotive torque converter using a homogeneous cavitation model, European Journal of Mechanics, B/Fluids, 10.1016/j.euromechflu.2016.09.001, 61, 263-270, 2017.01, To understand the flow mechanism of cavitation and its effect on the performance of automotive torque converter, numerical simulation considering cavitation is carried out at various turbine–pump speed ratios from 0 to 0.8. Since the cavitation in working fluid of torque converter is rather gaseous than vaporous, the partial pressure of air is applied to the cavity pressure in the simplified Rayleigh–Plesset cavitation model used in the present simulations. It is found that, for the lower speed ratios (0.6), the cavitation occurs at the pump inlet simultaneously or earlier than that at the stator. Once the cavitation occurs at the pump, the pump torque seems to drop suddenly.. |
| 14. |
Taiki Takamine, Satoshi Watanabe, Daichi Furukawa, Hiroyoshi Watanabe, Kazuyoshi Miyagawa, Experimental investigation on diffuser rotating stall in a three-stage centrifugal pump, ASME 2017 Fluids Engineering Division Summer Meeting, FEDSM 2017
Symposia
Keynotes; Advances in Numerical Modeling for Turbomachinery Flow Optimization; Fluid Machinery; Industrial and Environmental Applications of Fluid Mechanics; Pumping Machinery, 10.1115/FEDSM2017-69386, 2017.01, Rotating stall phenomenon frequently causes the troubles such as vibrations acting on the shaft system and reduces the reliability of turbomachines. In the present study, the diffuser rotating stall in a three-stage centrifugal pump was experimentally studied. Special emphasises were placed on the geometrical conditions; an axial offset of rotor against the stationary part, which might be unavoidable due to accumulation of geometrical tolerances and assembling errors., and the radial clearances of annular leakage paths which increases the thru-flow rate at the impellers and the first and second stage diffusers. As a result, with the rotor axial offset to the suction side, the rotating stall appeared only at the third stage diffuser, while with that to the discharge side, the rotating stall was more significant. By enlarging the leakage flow passages at the inter-stage bush and the balancing flow channel, the onset range of rotating stall became narrower in the first and second stage diffusers, which was well explained by the increase of the thru-flow rate. On the other hand, with the enlarged leakage passage at the liner ring, the onset range. |
| 15. |
Masashi Yasuda, Satoshi Watanabe, How to Avoid Severe Incidents at Pumped Storage Power Plants, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/49/11/112002, 49, 11, 2016.12, Pumped storage is now increasing its importance as the most powerful and reliable tool for stabilizing the electrical network, especially under the increase of intermittent power sources like wind-power and solar-power. However, pumped storage power plants have generally more machinery troubles than the conventional hydropower plants and sometimes they encountered unexpected severe incidents having long-term outage and a considerable restoration cost. The present paper provides some study results about general tendencies of machinery troubles in pumped storage, some examples of severe incidents mainly about the electro-mechanical troubles but also about the flood and fire, and possible scenarios which may lead into a severe result. Finally, it provides lessons learned and some recommendations to avoid severe incidents based on experiences.. |
| 16. |
K. Nakashima, S. Watanabe, D. Matsushita, S. Tsuda, A. Furukawa, Performance Prediction of Darrieus-Type Hydroturbine with Inlet Nozzle Operated in Open Water Channels, IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/49/10/102011, 49, 10, 2016.12, Small hydropower is one of the renewable energies and is expected to be effectively used for local supply of electricity. We have developed Darrieus-type hydro-turbine systems, and among them, the Darrieus-turbine with a weir and a nozzle installed upstream of turbine is, so far, in success to obtain more output power by gathering all water into the turbine. However, there can several cases exist, in which installing the weir covering all the flow channel width is unrealistic, and in such cases, the turbine should be put alone in open channels without upstream weir. Since the output power is very small in such a utilization of small hydropower, it is important to derive more power for the cost reduction. In the present study, we parametrically investigate the preferable shape of the inlet nozzle for the Darrieus-type hydroturbine operated in an open flow channel. Experimental investigation is carried out in the open channel in our lab. Tested inlet nozzles are composed of two flat plates with the various nozzle converging angles and nozzle outlet (runner inlet) widths with the nozzle inlet width kept constant. As a result, the turbine with the nozzles having large converging angle and wide outlet width generates higher power. Two-dimensional unsteady numerical simulation is also carried out to qualitatively understand the flow mechanism leading to the better performance of turbine. Since the depth, the width and the flow rate in the real open flow channels are different from place to place and, in some cases from time to time, it is also important to predict the onsite performance of the hydroturbine from the lab experiment at planning stage. One-dimensional stream-tube model is developed for this purpose, in which the Darrieus-type hydroturbine with the inlet nozzle is considered as an actuator-disk modelled based on our experimental and numerical results.. |
| 17. |
Shin Ichi Tsuda, H. Hyodo, S. Watanabe, Validation of Bubble Dynamics Equation for a Nano-scale Bubble via Molecular Dynamics Simulation, Journal of Physics: Conference Series, 10.1088/1742-6596/656/1/012039, 656, 1, 2015.12, For a validation of the application of conventional bubble dynamics to a nano-scale bubble behaviour, we simulated a nano-scale bubble collapsing or vibration by Molecular Dynamics (MD) method and compared the result with the solution of Rayleigh-Plesset (RP) equation and that of Confined RP (CRP) equation, whose boundary condition was corrected to be consistent with that of MD simulation. As a result, a good coincidence was obtained between MD, RP, and CRP in the case of one-component fluid. In addition, also a good correspondence was obtained particularly in the comparison between MD and CRP in the case of two-component fluid containing non-condensable gas. The present results indicate that conventional bubble dynamics equation can be applied even to a nano-scale tiny bubble.. |
| 18. |
Y. Yamamoto, Satoshi Watanabe, Shinichi Tsuda, A simple cavitation model for unsteady simulation and its application to cavitating flow in two-dimensional convergent-divergent nozzle, International Symposium of Cavitation and Multiphase Flow, ISCM 2014
IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899X/72/2/022009, 72, Forum 2, 2015.01, In this paper, a simple cavitation model is developed under the framework of homogeneousone-fluid model, in which the perfect mixture of liquid and vapor phases is assumed. In most of conventional models, the vapor phase is considered as a dispersed phase against the liquid phase as a continuous phase, while in the present model, two extreme conditions are considered: for low void fraction, dispersed vapor bubbles in continuous liquid phase, while for high void fraction, dispersed droplets in continuous vapor phase. The growth of bubbles and droplets are taken into account in the mass transfer between vapor and liquid phases, and are switched according to the local void fraction. The model is applied for the simulation of cavitating flow in a two-dimensional convergent-divergent nozzle, and the result is compared with that using a conventional model. To enhance the unsteadiness of cavitation due to the instability at the cavity interphase, the turbulent shear stress is modified depending upon the continuous phases in combination with the proposed cavitation model, which drastically reduces the turbulent viscosity for high void fraction region. As a result, the unsteadiness of cavitation observed in experiments is well reproduced.. |
| 19. |
Linlin Cao, Satoshi Watanabe, Akinori Furukawa, Dazhuan Wu, Numerical investigation of influence of rotor-rotor gap on performances of contra-rotating axial flow pump, ASME/JSME/KSME 2015 Joint Fluids Engineering Conference, AJKFluids 2015
Symposia, 10.1115/AJKFluids201533053, 1, 2015.01, As a high specific speed pump, the contra-rotating axial flow pump with two rotors rotating reversely has been proved with higher hydraulic and cavitation performances. However, while compared with the traditional rotor-stator combination, it suffers from more significant potential interactions between two rotating blade rows, and the gap between two rotors has to be kept large with accepting the small deterioration of head performance. In our previous studies, the different speed design was confirmed effective to weaken the blade rows interactions, and therefore indicated the possibility to pertinently reduce the gap between two rotors as well as improve the hydraulic performances of the contra-rotating axial flow pump. The present paper majorly discuss the possibility to further improve the hydraulic performances of contra-rotating axial flow pump by reducing the gap between two blade rows. The cases with original gap, increased gap and reduced gap were studied by the numerical approach. The internal flow structures between two blade rows were concentrated, and a simplified method for the pressure fluctuations investigation was applied. This study is supposed to offer more understanding about the internal flow properties and give more guidelines to determine the related parameters for contra-rotating rotor-rotor combination.. |
| 20. |
Daisuke Matsushita, Kei Tanaka, Satoshi Watanabe, Kusuo OKuma, Akinori Furukawa, Experimental and numerical investigations on performances of Darriues-type hydro turbine with inlet nozzle, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2014.7.4.151, 7, 4, 151-159, 2014.01, Low head hydropower is one of realistic renewable energies. The Darrieus-type hydro turbine with an inlet nozzle is available for such low head conditions because of its simple structure with easy maintenance. Experimental and numerical studies are carried out in order to examine the effects of gap distances between the runner pitch circle and two edges of inlet nozzle on turbine performances. By selecting narrower gaps of left and right edges, the performance could be improved. From the results of two dimensional numerical simulations, the relation between the performance and flow behaviors around the Darrieus blade are discussed to obtain the guideline of appropriate inlet nozzle design.. |
| 21. |
Linlin Cao, Hironori Honda, Hiroaki Yoshimura, Satoshi Watanabe, Akinori Furukawa, Experimental investigation of blade rows interactions in contrarotating axial flow pump, ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels
Symposia
Fluid Machinery; Fluid-Structure Interaction and Flow-Induced Noise in Industrial Applications; Flow Applications in Aerospace; Flow Manipulation and Active Control: Theory, Experiments and Implementation; Multiscale Methods for Multiphase Flow; Noninvasive Measurements in Single and Multiphase Flows, 10.1115/FEDSM2014-21901, 2014.01, As a high specific speed pump, the contra-rotating axial flow pump with two rotors rotating reversely has been proved with higher hydraulic and cavitation performance, while in our previous researches, our prototype rotors designed with equal rotational speeds for both the front and the rear rotors was also confirmed with the strong potential interaction between two blade rows. In the present study, the experimental investigations were focused on the rotor-rotor interactions in the contra-rotating rotors under two rotational speed combinations, an equal speed and a different speed ones with the lower speed of rear rotor; the latter is determined aiming at relieved rotor-rotor interaction. As the major experimental approach, casing wall static pressure measurements were conducted at pressure taps covering from upstream to downstream of the both rotors, and the pressure fluctuation modes were investigated by the FFT analyses. By series of pressure taps with different peripheral locations prepared at several axial locations, the pressure fluctuation modes with frequencies non-synchronous to the BPF (blade passing frequency) components were recognized, and confirmed to be related to the rotor-rotor interaction on the basis of theoretical analyses on the rotor-stator interaction in conventional rotorstator types.. |
| 22. |
Linlin Cao, Satoshi Watanabe, Hironori Honda, Hiroaki Yoshimura, Akinori Furukawa, Experimental investigation of blade-to-blade pressure distribution in contra-rotating axial flow pump, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2014.7.4.130, 7, 4, 130-141, 2014.01, As a high specific speed pump, the contra-rotating axial flow pump with two rotors rotating reversely has been proved with higher hydraulic and cavitation performance, while in our previous researches, the potential interaction between two blade rows was distinctly observed for our prototype rotors designed with equal rotational speed for both front and rear rotors. Based on the theoretical and experimental evidences, a rotational speed optimization methodology was proposed and applied in the design of a new combination of contra-rotating rotors, primarily in expectation of the optimized blade pressure distributions as well as pertinently improved hydraulic performances including cavitation performance. In the present study, given one stationary and two rotating frames in the contra-rotating rotors case, a pressure measurement concept taking account of the revolutions of both front and rear rotors simultaneously was adopted. The casing wall pressure data sampled in time domain was successfully transferred into space domain, by which the ensemble averaged blade-to-blade pressure distributions at the blade tip of two contra-rotating rotors under different operation conditions were studied. It could be seen that the rotor pair with the optimized rotational speed combination as well as work division, shows more reasonable blade-to-blade pressure distribution and well weakened potential interaction. Moreover, combining the loading curves estimated by the measured casing wall pressure, the cavitation performance of the rotor pairs with new rotational speed combination were proved to be superior to those of the prototype pairs.. |
| 23. |
D. Matsushita, R. Moriyama, K. Nakashima, Satoshi Watanabe, K. Okuma, A. Furukawa, Tentative study on performance of darriues-type hydroturbine operated in small open water channel, 27th IAHR Symposium on Hydraulic Machinery and Systems, IAHR 2014
IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/22/6/062007, 22, 2014.01, The development of small hydropower is one of the realistic and preferable utilizations of renewable energy, but the extra-low head hydropower less than 2 m is almost undeveloped yet for some reasons. The authors have developed several types of Darrieus-type hydro-turbine system, and among them, the Darrieus-turbine with a wear and a nozzle installed upstream of turbine is so far in success to obtain more output power, i.e. more shaft torque, by gathering all water into the turbine. However, there can several cases exist, in which installing the wear covering all the flow channel width is unrealistic. Then, in the present study, the hydraulic performances of Darrieus-type hydro-turbine with the inlet nozzle is investigated, putting alone in a small open channel without upstream wear. In the experiment, the five-bladed Darrieus-type runner with the pitch-circle diameter of 300 mm and the blade span of 300 mm is vertically installed in the open channel with the width of 1,200 mm. The effectiveness of the shape of the inlet nozzle is also examined using two types of two-dimensional symmetric nozzle, the straight line nozzle (SL nozzle) with the converging angle of 45 degrees and the half diameter curved nozzle (HD nozzle) whose radius is a half diameter of runner pitch circle. Inlet and outlet nozzle widths are in common for the both nozzles, which are 540 mm and 240 mm respectively. All the experiments are carried out under the conditions with constant flow rate and downstream water level, and performances are evaluated by measured output torque and the measured head difference between the water levels upstream and downstream of the turbine. As a result, it is found that the output power is remarkably increased by installing the inlet nozzle, and the turbine with SL nozzle produces larger power than that with HD nozzle. However, the peak efficiency is deteriorated in both cases. The speed ratio defined by the rotor speed divided by the downstream water velocity at the peak efficiency is larger in both cases with the inlet nozzle, partly due to the increase of inflow velocity into the turbine. In order to understand the cause of the differences of power, i.e. torque characteristics of the turbine with SL and HD nozzles, twodimensional CFD simulation is carried out. It is found that the instantaneous torque variation is important for the overall turbine performances, indicating the possibility of further performance improvement through the optimization of nozzle geometry.. |
| 24. |
Satoshi Watanabe, Keisuke Enomoto, Yuya Yamamoto, Yoshinori Hara, Thermal and dissolved gas effects on cavitation in a 2-D convergent-divergent nozzle flow, ASME 2014 4th Joint US-European Fluids Engineering Division Summer Meeting, FEDSM 2014, Collocated with the ASME 2014 12th International Conference on Nanochannels, Microchannels, and Minichannels
Fora
Cavitation and Multiphase Flow; Fluid Measurements and Instrumentation; Microfluidics; Multiphase Flows: Work in Progress; Fluid-Particle Interactions in Turbulence, 10.1115/FEDSM2014-21902, 2014.01, It is well known that the thermal effect of cavitation suppresses the development of cavity with the decreased local temperature due to the latent heat of evaporation. In the present study, to obtain the fundamental knowledge of thermal effect of cavitation, an experimental study of cavitation in a simple convergent-divergent nozzle was carried out using hydrofluoro- ether (HFE) as a working fluid. HFE was expected to reveal the thermal effect at room temperature, which enabled us to simply neglect the heat flux between the test section and outside, and to roughly keep adiabatic conditions on nozzle wall surfaces. It was found that the cavitation in HFE was a foam-like sheet cavity, which was different from a film like cavity in cold water. The temperature depression, near the leading edge of cavitation, was confirmed especially in more developed cavitation cases, revealing the existence of thermal effect of cavitation. However, in lower velocity cases, the measured cavity length was apparently longer in HFE despite of the expected thermal effect. The measured pressures inside the cavity were found to be apparently larger than the vapor pressure, indicating the possible separation of dissolved air into the cavity. Then, the cavitation number based on the measured cavity pressure instead of vapor pressure was proposed, and by using the proposed cavitation number, the thermal effect was clearly confirmed in terms of the cavity development. Frequency characteristics of measured pressure fluctuations were qualitatively similar regardless of the species of working fluid.. |
| 25. |
S. Watanabe, W. Yamaoka, A. Furukawa, Unsteady lift and drag characteristics of cavitating Clark Y-11.7% hydrofoil, 27th IAHR Symposium on Hydraulic Machinery and Systems, IAHR 2014
IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/22/5/052009, 22, 2014.01, Unsteady cavitating flow and lift/drag characteristics of a two-dimensional Clark Y- 11.7% hydrofoil are experimentally investigated in order to clarify the relation between the lift drop mechanism and the unsteady cavity behavior. Unsteady lift and drag forces are measured by strain gauges attached on the cantilever supporting the hydrofoil, assuming the negligible bending moment. In combination with the above force measurements, the cavitating flow is filmed from both top and side simultaneously using two high speed video cameras. It is clearly observed that, in larger attack angle conditions (4-10 degrees), the time-averaged lift coefficient slightly increases from that in the non-cavitating condition. After the slight increase, the lift gradually decreases then its steep decrease starts to occur. On the other hand, in a small attack angle case (2 degrees), little increase of the lift is observed, and just after that the sudden lift drop occurs. From the instantaneous frequency spectra of the lift, the followings are found; during the slight increase of the lift, the cavity is being a partial cavity in almost steady state, but during the subsequent gradual lift decrease, the partial cavity oscillates with cloud cavity shedding, in other word, the partial cavity oscillation occurs, whose frequency decreases with the growth of the cavity. During the sudden lift drop, the low frequency transitional cavity oscillation occurs, in which the cavity dramatically changes between partial and super cavities. The typical events of cavity behavior during the cavitation instabilities are found to be able to be related with the behavior of instantaneous lift force and pressure.. |
| 26. |
L. L. Cao, Satoshi Watanabe, T. Imanishi, H. Yoshimura, A. Furukawa, Blade rows interaction in contra-rotating axial flow pump designed with different rotational speed concept, 6th International Conference on Pumps and Fans with Compressors and Wind Turbines, ICPF 2013
IOP Conference Series: Materials Science and Engineering, 10.1088/1757-899X/52/2/022004, 52, TOPIC 2, 2013.12, The contra-rotating axial flow pump consisiting of counter-rotating tandem rotors has been expermentally confirmed with better performances than the conventional axial flow pump, but it is known to suffer from the significant potential interaction between the counter-rotating blade rows, which is responsible for the repetitive stresses and unfavourable to the reliable operation. Consequently, to improve the realiability of contra-rotating axial flow pump including the reduction of the blade rows interaction, a new type of rear rotor was designed in the previous study by the rotational speed optimization methodology with some additional considerations. In the present study, to understand the effectiveness of the new design method, instantaneous static pressure fluctuations on the casing wall under the design and off design conditions are investigated by means of experimental and numerical simulation methods. The Fourier analysis is employed to process the data obtained from experiments and numerical simulations, and the axial distribution of the Blade Passing Frequency (BPF) amplitude is obtained. The new rear rotor shows weakened BPF amplitude both upstream and downstream especially at the positions between the two blade rows in both CFD and EFD analyses, implying the reduced blade rows interaction with the new rear rotor.. |
| 27. |
Kei Tanaka, Kotaro Hirowatari, Kai Shimokawa, Satoshi Watanabe, Daisuke Matsushita, Akinori Furukawa, A study on Darrieus-type hydroturbine toward utilization of extra-low head natural flow streams, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2013.6.3.152, 6, 3, 152-159, 2013.10, A two-dimensional Darrieus-type hydroturbine system, installed with a wear for flow streams such as small rivers and waterways, has been developed for hydropower utilization of extra-low head less than 2m. There are several problems such as flow rate change and flowing wastes to be solved for its practical use in natural flow streams. In the present study, at first, a design guideline in the case of overflow or bypass flow is shown by using simple flow model. Next, in order to avoid the unexpected obstacles flowing into the hydroturbine, an installation of waste screening system is examined. It is confirmed that the screen is effective with some amount of bypass flow rate, however the output power is remarkably deteriorated.. |
| 28. |
S. Watanabe, Y. Uchinono, K. Ishizaka, A. Furukawa, J. H. Kim, Suction performance and internal flow of a 2-bladed helical inducer with inlet asymmetric plate, Journal of Thermal Science, 10.1007/s11630-013-0641-y, 22, 5, 395-403, 2013.10, It has been found in our past studies that the installation of asymmetric plate at the inlet of inducer is effective for the suppression of cavitation surge phenomenon. In the present study, the suction performance of 2-bladed helical inducer with an inlet asymmetric plate is experimentally investigated. It is observed that the suction performance in large flow rate conditions is not significantly influenced by the asymmetric plate, whereas the head of inducer with the asymmetric plate increases just before the head breakdown in partial flow conditions. To understand the mechanism of this additional head, the flow measurements and the numerical simulations are carried out. It is found that the circumferential component of absolute velocity at the exit of inducer slightly increases with the development of cavitation in both cases with and without the inlet asymmetric plate, indicating the increase of the theoretical head. The theoretical head increase with the inlet asymmetric plate is also confirmed by the unsteady numerical simulations, suggesting that the additional head is achieved through the increase of the theoretical head with the change of the exiting flow from the inducer associated with some amount of cavitation. © 2013 Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg.. |
| 29. |
Linlin Cao, Satoshi Watanabe, Toshiki Imanishi, Hiroaki Yoshimura, Akinori Furukawa, Experimental Analysis of Flow Structure in Contra-Rotating Axial Flow Pump Designed with Different Rotational Speed Concept, Journal of Thermal Science, 22, 4, 345-351, 2013.08. |
| 30. |
Linlin Cao, Satoshi Watanabe, Toshiki Imanishi, Hiroaki Yoshimura, Akinori Furukawa, Experimental analysis of flow structure in contra-rotating axial flow pump designed with different rotational speed concept, Journal of Thermal Science, 10.1007/s11630-013-0634-x, 22, 4, 345-351, 2013.08, As a high specific speed pump, the contra-rotating axial flow pump distinguishes itself in a rear rotor rotating in the opposite direction of the front rotor, which remarkably contributes to the energy conversion, the reduction of the pump size, better hydraulic and cavitation performances. However, with two rotors rotating reversely, the significant interaction between blade rows was observed in our prototype contra-rotating rotors, which highly affected the pump performance compared with the conventional axial flow pumps. Consequently, a new type of rear rotor was designed by the rotational speed optimization methodology with some additional considerations, aiming at better cavitation performance, the reduction of blade rows interaction and the secondary flow suppression. The new rear rotor showed a satisfactory performance at the design flow rate but an unfavorable positive slope of the head - flow rate curve in the partial flow rate range less than 40% of the design flow rate, which should be avoided for the reliability of pump-pipe systems. In the present research, to understand the internal flow field of new rear rotor and its relation to the performances at the partial flow rates, the velocity distributions at the inlets and outlets of the rotors are firstly investigated. Then, the boundary layer flows on rotor surfaces, which clearly reflect the secondary flow inside the rotors, are analyzed through the limiting streamline observations using the multi-color oil-film method. Finally, the unsteady numerical simulations are carried out to understand the complicated internal flow structures in the rotors. © 2013 Science Press, Institute of Engineering Thermophysics, CAS and Springer-Verlag Berlin Heidelberg.. |
| 31. |
Kei Tanaka, Kotaro Hirowatari, Kai Shimokawa, Satoshi Watanabe, Daisuke Matsushita and Akinori Furukawa, A Study on Darrieus-type Hydroturbine toward Utilization of Extra-Low Head Natural Flow Streams, International Journal of Fluid Machinery and Systems, 6, 3, 152-159, 2013.07. |
| 32. |
Lift and drag characteristics of a Clark-Y 11.7% hydrofoil. |
| 33. |
Linlin Cao, Satoshi Watanabe, Simpei Momosaki,
Toshiki Imanishi, Akinori Furukawa, Low Speed Design of Rear Rotor in Contra-Rotating Axial Flow Pump, International Journal of Fluid Machinery and Systems, 6, 2, 105-112, 2013.04. |
| 34. |
Experimental study on destruction mechanism of ceramic bearing and some important consideration in design. |
| 35. |
Linlin Cao, Satoshi Watanabe, Simpei Momosaki, Toshiki Imanishi, Akinori Furukawa, Low speed design of rear rotor in contra-rotating axial flow pump, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2013.6.2.105, 6, 2, 105-112, 2013.02, The application of contra-rotating rotors for higher specific speed pump has been proposed in our studies, which is in principle effective for reducing the rotational speed and/or the pump size under the same specification of conventional axial flow pump. In the previous experiments of our prototype, the cavitation inception at the tip region of the rear rotor rather than that of the front rotor and the strong potential interaction from the suction surface of the rear rotor blade to the pressure surface of the front one were observed, indicating the possibility to further improve the pump performance by optimizing rotational speed combination between the two rotors. The present research aims at the design of rear rotor with lower rotational speed. Considering the fact that the incoming flow velocity defects at the tip region of the rear rotor, an integrated inflow model of 'forced vortex' and 'free vortex' is employed. The variation of maximum camber location from hub to tip as well as other related considerations are also taken into account for further performance improvement. The ideas cited above are separately or comprehensively applied in the design of three types of rear rotor, which are subsequently simulated in ANSYS CFX to evaluate the related pump performance and therefore the whole low speed design idea. Finally, the experimental validation is carried out on one type to offer further proofs for the availability of the whole design method.. |
| 36. |
L. L. Cao, S. Watanabe, T. Imanishi, S. Momosaki, A. Furukawa, On high efficiency operation of contra-rotating axial flow pump with rotational speed control toward effective energy saving, 26th IAHR Symposium on Hydraulic Machinery and Systems
IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/15/4/042027, 15, PART 4, 2012.12, For high specific speed pump with high performance operation, a contra-rotating axial flow pump has been proposed and the effectiveness of rotational speed control of front and rear rotors has been demonstrated experimentally. In the present paper, a prediction method of pump characteristics under the condition of optimized rotational speed control is proposed, based on consideration of flow mechanism in both front and rear rotors. The accuracy of prediction is examined for two combinations of front and rear rotors. Then, the amount of energy saving by application of rotational speed control method for the contra-rotating axial flow pump is demonstrated and an advantage of usage of contra-rotating pump is discussed.. |
| 37. |
A. Furukawa, Satoshi Watanabe, K. Okuma, Research on Darrieus-type hydraulic turbine for extra-low head hydropower utilization, 26th IAHR Symposium on Hydraulic Machinery and Systems
IOP Conference Series: Earth and Environmental Science, 10.1088/1755-1315/15/1/012003, 15, PART 1, 2012.12, A Darrieus-type turbine has been investigated for extra-low head hydropower utilization. In the present paper, authors'research on Darrieus-type hydraulic turbine is briefly reviewed. The working principle of Darrieus turbine is explained with advantage of its simple structure, at first. Then the fluid-dynamic difference between rotating and linear motions of a blade in a uniform flow is clarified with guiding principle of high performance design of Darrieus turbine. Cavitation problem is also described. Next, effects of duct-casing, consisting of an intake, runner section and draft tube, are discussed and a simplified structure of Darrieus turbine is shown by installing the inlet nozzle. Finally, in the practical use, an adjustment of inlet nozzle section by lowering the inlet nozzle height is proposed when flow rate is varied temporally and seasonally.. |
| 38. |
Yoshiki Yoshida, Kengo Kikuta, Kazuki Niiyama, Satoshi Watanabe, Thermodynamic parameter on cavitation in space inducer, ASME 2012 Fluids Engineering Division Summer Meeting, FEDSM 2012 Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and M, FEDSM 2012
ASME 2012 Fluids Engineering Division Summer Meeting Collocated with the ASME 2012 Heat Transfer Summer Conference and the ASME 2012 10th Int. Conference on Nanochannels, Microchannels, and M, FEDSM 2, 10.1115/FEDSM2012-72212, 203-213, 2012.12, Cavitation is physically "a vaporization of liquid" which needs latent heat for phase change. A cavity grows in the liquid, so the latent heat of vaporization can only be supplied by the liquid surrounding the cavity. Thus, the liquid close to the interface region of the cavity is cooled down. In general, cryogenic liquids are very thermosensitive. For liquid hydrogen and oxygen used in rocket propulsion, the temperature in the cavity, i.e., the vapor pressure in the cavity, is lower than those of the liquid bulk. Thanks to this thermal effect, cavitation in cryogenic liquids is less developed than that in water at room temperature. This thermal effect on cavitation is beneficial in that it improves cavitation performance and alleviates cavitation instability in space inducers. In previous works, we investigated the relationship between the thermodynamic effect and the cavitation instabilities, e.g., rotating cavitation and cavitation surge, with a focus on the cavity length as an indication of cavitation. In the present work, first, aspects of cavitation in the inducer were observed by direct optical visualization in liquid nitrogen. Second, joint experiments in liquid nitrogen and cold water were conducted on a cavitaing inducer. In nitrogen experiments, operating conditions, i.e., rotational speed and liquid temperature, were varied to determine the cavitation scaling law. Through these experimental results, characteristic times, namely, the transit time for bubble growth and the characteristic thermal time introduced from the thermal property, were investigated as a cavitation thermodynamic parameter. It was found out that the adjustment of cavitation number has a good correlation with the ratio of the transit time and the characteristic thermal time.. |
| 39. |
Satoshi Watanabe, Ryosuke Otani, Shun Kunimoto, Yoshinori Hara, Akinori Furukawa, Takeshi Yamaguchi, Vibration characteristics due to cavitation in stator element of automotive torque converter at stall condition, ASME 2012 Fluids Engineering Division Summer Meeting, FEDSM 2012 Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 10th International Conference on Nanochannels, Microchannels, and M, FEDSM 2012
ASME 2012 Fluids Engineering Division Summer Meeting Collocated with the ASME 2012 Heat Transfer Summer Conf. and the ASME 2012 10th Int. Conf. on Nanochannels, Microchannels, and M, FEDSM 2012, 10.1115/FEDSM2012-72418, 1, 535-541, 2012.12, Cavitation behaviors in an automotive torque converter at pump speed of 600, 700 and 800 min-1 at the stall condition are investigated by means of the transparent model. At the same time, the influences of cavitation on mechanical vibration are studied. As a result, at the onset of cavitation, the longitudinal corner vortex cavitation is formed at the corner between outer wall and either suction or pressure surface of stator blades. After the further decrease of charge pressure, the cavitation bubbles are observed in the flow separation region formed at the leading edge on the suction surface of stator blades. Vibration spectrum peaks are found in the wide range of frequency, which increase with the development of cavitation but then decrease with its excessive development. Discussions are made for higher and lower frequency ranges separately to understand the relation between mechanical vibrations and cavitation.. |
| 40. |
Kai Shimokawa, Akinori Furukawa, Kusuo Okuma, Daisuke Matsushita, Satoshi Watanabe, Experimental study on simplification of Darrieus-type hydro turbine with inlet nozzle for extra-low head hydropower utilization, Renewable Energy, 10.1016/j.renene.2011.09.017, 41, 376-382, 2012.05, A ducted Darrieus-type hydro turbine has been proposed for utilization of extra-low head hydropower less than 2 m. In general, the low head hydro turbine system demands the simple structure to reduce the cost of power generation. The Darrieus-type hydro turbine is cross flow type and takes larger values of generated torque with higher efficiency on the upstream path of the Darrieus blades passing in one revolution. Based on this reason, when a narrow intake at the upstream of the runner, called as "inlet nozzle", is installed, the performance of Darrieus-type hydro turbine becomes higher than that without one. In addition, it is possible to remove the draft tube and side-walls of the runner casing keeping the turbine efficiency high. In the present paper, more simplified runner casing, composed of only the inlet nozzle and the small upper-casing, is proposed and the experimental results are shown. © 2011 Elsevier Ltd.. |
| 41. |
Satoshi Watanabe, Kai Shimokawa, Akinori Furukawa, Kusuo Okuma, Daisuke Matsushita, Experimental study on adjustment of inlet nozzle section to flow rate variation for darrieus-type hydro-turbine, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2012.5.1.030, 5, 1, 30-37, 2012.03, A two dimensional Darrieus-type turbine has been proposed for the hydropower utilization of extra-low head less than 2m. In a practical use of Darrieus-type hydro-turbine, head and flow rate may be varied temporally and seasonally. Considering that the cost advantage is required for the low head hydro turbine system, the Darrieus turbine should be operated with high efficiency in the wider range of flow rate possibly by using an additional device with simpler mechanism. In the present paper, an adjustment of inlet nozzle section by lowering the inlet nozzle height is proposed to obtain the preferable inlet velocity in low flow rate conditions. Effects of resulting spanwise partial inlet flow are investigated. Finally, an effective modification of inlet nozzle height over flow rate variation is shown.. |
| 42. |
Satoshi Watanabe, Kai Shimokawa, Akinori Furukawa, Kusuo Okuma, Daisuke Matsushita, Experimental study on adjustment of inlet nozzle section to flow rate variation for darrieus-type hydro-turbine, International Journal of Fluid Machinery and Systems, 10.5293/IJFMS.2012.5.1.030, 5, 1, 30-37, 2012.03, A two dimensional Darrieus-type turbine has been proposed for the hydropower utilization of extra-low head less than 2m. In a practical use of Darrieus-type hydro-turbine, head and flow rate may be varied temporally and seasonally. Considering that the cost advantage is required for the low head hydro turbine system, the Darrieus turbine should be operated with high efficiency in the wider range of flow rate possibly by using an additional device with simpler mechanism. In the present paper, an adjustment of inlet nozzle section by lowering the inlet nozzle height is proposed to obtain the preferable inlet velocity in low flow rate conditions. Effects of resulting spanwise partial inlet flow are investigated. Finally, an effective modification of inlet nozzle height over flow rate variation is shown.. |
| 43. |
Satoshi WATANABE, Simpei MOMOSAKI, Satoshi USAMI and Akinori FURUKAWA, Internal Flow and Limiting Streamlines Observations of Contra-Rotating Axial Flow Pump at Partial Flow Rate, Int. J. of Fluid Machinery and Systems, 4, 2, 235-242, 2011.04. |
| 44. |
Jun-Ho KIM, Takashi ATONO, Koichi ISHIZAKA, Satoshi WATANABE, Akinori FURUKAWA, Cavitation in Pump Inducer with Axi-asymmetrical Inlet Plate Observed by Multi-cameras, Int. J. of Fluid Machinery and Systems, Vol.3, No.2 pp.122-128, 2010.06. |
| 45. |
Satoshi WATANABE, Naoki INOUE, Koichi ISHIZAKA, Akinori FURUKAWA, Jun-Ho KIM, Internal Flow of a Two-Bladed Helical Inducer at an Extremely Low Flow Rate, Int. J. of Fluid Machinery and Systems, Vol.3, No.2 pp.129-136, 2010.06. |
| 46. |
Akinori Furukawa, Satoshi Watanabe, Daisuke Matsushita, Kusuo Okuma, Development of ducted Darrieus turbine for low head hydropower utilization, Current Applied Physics, 10.1016/j.cap.2009.11.005, 10, 2 SUPPL., S128-S132, pp.S128-S132, 2010.03, It is mentioned in front part of the present paper that how to extract an extra-low head power is one of key-solutions for problems on exhaustion of fossil fuels and greenhouse gas emissions, after explaining the present situation of micro-hydropower utilization in Japan. Since extra-low head sites of rivers are available near urban-sides with high population, where there is a demand for electricity, an appearance of suitable turbine, which has high cost-effectiveness, maximum reliability, easy maintenance and little environmental impact, is required. In rear part of the present paper, a guiding principle of design parameters of a ducted Darrieus-type water turbine for high performance is shown, based on authors' experimental results. Then the advantage and disadvantage of Darrieus turbine are reviewed and the key problems, which are settled as urgent works in future in order to diffuse the utilization of extra-low head hydropower, are finally suggested. © 2009 Elsevier B.V. All rights reserved.. |
| 47. |
Jun-Ho KIM, Koichi ISHIZAKA, Satoshi WATANABE, Akinori FURUKAWA, Cavitation Surge Suppression of Pump Inducer with Axi-asymmetrical Inlet Plate, Int. J. of Fluid Machinery and Systems, Vol.3, No.1 pp.50-57, 2010.02. |
| 48. |
Daisuke Matsushita, Hikaru Matsumiya, Yoshinori Hara, Satoshi Watanabe, Akinori Furukawa, Studies on numerical site calibration over complex terrain for wind turbines, Science China Technological Sciences, 10.1007/s11431-010-0027-2, 53, 1, 8-12, Vol.53, No.1, pp.8-12, 2010.01, The estimation of wind turbine performance over complex terrain is very difficult because of the document of standard IEC61400-12 is adapted for flat or slightly complex topography. And the cost of constructing a meteorological mast is higher with scaling wind turbine up. We have proposed a numerical site calibration (NSC) technique in order to estimate the inflow velocity at the position of wind turbine by using CFD tool to calculate the flow field around the site. The present paper shows the problems for the procedure of NSC in which a commercial nonlinear CFD tool and the improvement method are used to gain a more accurate result. It is clarified that the wind turbine performance which is estimated by using the wind speed on the meteorological mast has a good result for annual energy production. © 2010 Science in China Press and Springer Berlin Heidelberg.. |
| 49. |
Kai Shimokawa, Akinori Furukawa, Kusuo Okuma, Daisuke Matsushita, Satoshi Watanabe, Side-wall effect of runner casing on performance of Darrieus-type hydro turbine with inlet nozzle for extra-low head utilization, Science China Technological Sciences, 10.1007/s11431-010-0014-7, 53, 1, 93-99, Vol.53, No.1, pp.93-99, 2010.01, A ducted Darrieus-type turbine has been proposed for hydropower utilization of extra-low head less than 2 m. Though the hydro turbine system, in general, might consist of an intake, runner casing section and a draft tube for higher efficiency operation, it was clarified in previous experiment that there was no need of the side-walls of runner casing section and a draft-tube for keeping the efficiency high in the case of duct with an inlet nozzle. This would yield a simplification of the structure of the turbine system. In order to reconfirm this result for large-sized turbine with 560 mm×300 mm duct, instead of small-sized one with 400 mm×200 mm duct, the side-wall effect on turbine performance was experimentally investigated for three- or four-bladed runner. In the present paper, the experimental results are shown with considering flow behaviors in the runner section. © 2010 Science in China Press and Springer Berlin Heidelberg.. |
| 50. |
Internal Flow of a Flat Plate Helical Inducer at an Extremely Low Flow Rate. |
| 51. |
Naoki MATSUSHITA, Akinori FURUKAWA, Satoshi WATANABE, Kusuo OKUMA, Study on Design of Air-water Two-phase Flow Centrifugal Pump Based on Similarity Law, Int. J. of Fluid Machinery and Systems, Vol.2, No.21, pp.127-135, 2009.05. |
| 52. |
Effects of Side-Wall Gaps of Runner Pitch Circle and Runner Blade Number on Performance of Darrieus-Type Hydro-Turbine with Inlet Nozzle. |
| 53. |
Cavitation Surge Suppression of Pump Inducer with Axi-asymmetrical Inlet Plate. |
| 54. |
Jun-Ho KIM, Takashi ATONO, Koichi ISHIZAKA, Satoshi WATANABE, Akinori FURUKAWA, Rotating Behavior Observation of Cavitation in Inducer with Suction Axi-asymmetrical Plate, Journal of Fluids Science and Technology, Vol.3, No.6, pp.744-753, 2008.09. |
| 55. |
Study on Design of Air-water Two-phase Flow Centrifugal Pump Based on Similarity Law. |
| 56. |
Cavitation in Pump Inducer with Axi-asymmetrical Inlet Plate Observed by Multi-cameras. |
| 57. |
Satoshi WATANABE, Akinori FURUKAWA, Yoshiki YOSHIDA, Theoretical Analysis of Thermodynamic Effect of Cavitation in Cryogenic Inducer Using Singularity Method, International Journal of Rotating Machinery, Vol. 2008, Article ID 125678, 2008.06. |
| 58. |
Daisuke MATSUSHITA, Kusuo OKUMA, Satoshi WATANABE, Akinori FURUKAWA, Simplified Structure of Ducted Darrieus-type Hydro Turbine with Narrow Intake foe Extra-low Head hydropower Utilization, Journal of Fluids Science and Technology, Vol.3, No.3, pp.387-397, 2008.06. |
| 59. |
Internal flow measurement with LDV at design point of contra-rotating axial flow pump
The adoption of the contra-rotating rotor has been proposed in response to a demand for the axial flow pump with higher specific speed. The internal flow field and blade rows interactions between the front and rear rotors should be considered in the design for higher performance and more stable operation, but has not been clarified yet. The flow field in contra-rotating axial flow pump was measured at various flow rates with the LDV and wall pressure measurements. In the present paper, the experimental and numerical results in the flow field between front and rear rotors are shown at the design flow rate and the flow behaviors are discussed, related on blade loading, blade tip leakage flow, wake and blade rows interaction.. |
| 60. |
Flow measurement with LDV around rear rotor of contra-rotating axial flow pump at partial flow rate
An application of contra-rotating rotors, in which a rear rotor is employed in tandem with a front one and these rotors rotate in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump. The most important feature of contra-rotating axial flow pump is that the rear rotor, installed instead of the stator of conventional type, plays a role not only to recover the static head but also to give the energy to the fluid directly. Then, the rotational speed or the pump size could be reduced with the same design specifications of pump head and flow rate as those of the conventional type. As another advantage, contra-rotating rotor theoretically yields a stable head-characteristic curve with a negative slope. In actual performance test of contra-rotating axial flow pump, a positive slope of head-characteristic curve, however, appears at the partial flow rate, which seems to be in the same manner to conventional type, depending on the rotors design. In the present study, in order to investigate the flow mechanism of head deterioration at the partial flow rate, blade-to-blade velocity distributions around the rear rotor have been measured with Laser Doppler Velocimetry (LDV) in the partial flow rate conditions by ensemble averaging technique with the rotating position of the rear rotor. Flow distributions in the tip region of rear rotor at flow rates just before and after the head deterioration are compared and the flow mechanism of head deterioration is discussed with the help of static head distribution on the casing wall.. |
| 61. |
Jun-Ho KIM, Masao ISHIZAKI, Naoki ENOMOTO, Koichi ISHIZAKA, Satoshi WATANABE,
Akinori FURUKAWA, Suppression Effect of Upstream Installed Ring-shaped Obstacle Plate on Cavitation Surge in Pump Inducers, Journal of Fluids Science and Technology, Vol.3, No.1, pp.1-10, 2008.01. |
| 62. |
oshinobu Tsujimoto, Satoshi Watanabe, Hironori Horiguchi, Cavitation Instabilities of Hydrofoils and Cascades, Proceedings of the 9th Asian International Conference on Fluid Machinery (AICFM-9), 13-21, 2007.10. |
| 63. |
Satoshi Watanabe, Tatsuva Hidaka, Hironori Horiguchi, Akinori Furukawa, Yoshinobu Tsujimoto, Analysis of thermodynamic effects on cavitation instabilities, Journal of Fluids Engineering, Transactions of the ASME, 10.1115/1.2754326, 129, 9, 1123-1130, Vol.129, pp.1123〜1130, 2007.09, The suction performance of turbopumps in cryogenic fluids is basically much better than that in cold water because of the thermodynamic effect of cavitation. However, it is not still clear how the thermodynamic effect works on cavitation instabilities, such as rotating cavitation and cavitation surge. In the present study, the unsteady heat exchange between the cavity and the surrounding liquid is taken into account in a stability analysis using a singularity method. The results are qualitatively compared to existing experi ments to clarify the research needs for deeper understanding. Copyright © 2007 by ASME.. |
| 64. |
Mizuho MATSUBARA, Masao WATANABE, Satoshi WATANABE, Kozo KONISHI, Shohei YAMAGUCHI and Makoto HASHIZUME, Fluid Dynamic Study on Budd-Chiari Syndrome: Sensitivity Study of Vessel Reconstruction on Image-Based Simulation, Journal of Biomechanical Science and Engineering, Vol. 2, pp. 69-80, 2007.05. |
| 65. |
Akinori Furukawa, Toru Shigemitsu, Satoshi Watanabe, Performance test and flow measurement of contra-rotating axial flow pump, Journal of Thermal Science, 10.1007/s11630-007-0007-4, 16, 1, 7-13, Vol.16, No.1, pp. 7-13, 2007.03, An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. In the present paper, the advantage and disadvantage of using contra-rotating rotors are described in comparison with conventional type of rotor-stator, based on theoretical and experimental investigations. The advantages are as follows: (1) The pump is inherently designed as smaller sized and at lower rotational speed. (2) A stable head-characteristic curve for flow rate with negative slope appears. (3) As the rear rotor rotational speed is varied as independent control of front rotor, the wider range of high performance operation is obtained by rear rotor speed control in addition to front rotor speed control. The disadvantages are as follows: (1) The structure of double shaft system becomes complex. (2) The pump performance is inferior at over flow rate as the rear rotor loading is weakened. (3) The blade rows interaction from rear rotor to front rotor more strongly appears. Then the rear rotor design is a key to achieve higher pump performance. Some methods to overcome these disadvantages will be discussed in more details toward wider usage of contra-rotating axial flow pump in various industrial fields. © 2007 Science Press.. |
| 66. |
Satoshi Watanabe, Tatsuya Hidaka, Hironori Horiguchi, Akinori Furukawa, Yoshinobu Tsujimoto, Steady analysis of the thermodynamic effect of partial cavitation using the singularity method, Journal of Fluids Engineering, Transactions of the ASME, 10.1115/1.2409333, 129, 2, 121-127, Vol.129, No.1, pp.121-127, 2007.02, It is well known that the suction performance of turbopumps in cryogenic fluids is much better than that in cold water because of the thermodynamic effect of cavitation. In the present study, an analytical method to simulate partially cavitating flow with the thermodynamic effect in a cascade is proposed; heat transfer between the cavity and the ambient fluid is modeled by a one-dimensional unsteady heat conduction model under the slender body approximation and is coupled with a flow analysis using singularity methods. In this report, the steady analysis is performed and the results are compared with those of experiments to validate the model of the present analysis. This analysis can be easily extended into unsteady stability analysis for cavitation instabilities such as rotating cavitation and cavitation surge. Copyright © 2007 by ASME.. |
| 67. |
Suppression effect of cavitation surge of pump inducer by installing ring-shaped obstacle plate upstream of inducer
The attachment of an inducer upstream of the main impeller is a powerful method to improve the cavitation performance. It is known, however, that the cavitation surge oscillation, which is focused in the present paper, occurs under operation condition of partial flow rate and low suction pressure. The attempts to suppress the cavitation surge were made by installing a ring-shaped obstacle plate just upstream of inducer. The ring-shaped inlet plates with various blockage rates of 14%, 27% and 39% were tested to examine the effect of blockage rates on the suppression of cavitation surge for two kinds of inducers having two blades with the solidity of 2.0 and the different blade angle of 14° and 8° at the blade tip. In the present paper, the changes of the onset region of cavitation surge are clarified and the mechanism of cavitation surge suppression is discussed with casing wall pressure distribution and inlet velocity distribution.. |
| 68. |
Akinori FURUKAWA, Tomoya TAKANO, Toru SHIGEMITSU, Kusuo OKUMA, Satoshi WATANABE, Blade Rows Interaction of Contra-Rotating Axial Flow Pump in Pressure Field on Casing Wall, JSME International Journal, Series B, Vol. 49, No. 3, pp. 670-677, 2006.08. |
| 69. |
Blade rows interaction of contra-rotating axial flow pump in pressure field on casing wall
An application of contra-rotating rotors, consisting of front and rear rotors rotating in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump with more compact structure, higher efficiency and higher cavitation performance. The blade rows interaction between front and rear rotors should be clarified for stable operation and reduction of unsteady losses. In the present paper, static pressure distributions on casing wall are shown at two flow rates by measuring with phase locked sampling method, where double trigger signals from rotation pick-ups equipped on both front and rear rotor shafts are used. From the comparison between experimental results of two types of the rear rotors, one of which has three blades with long chord length and the other has five blades with short length, the difference of the rear blade interaction and the unsteady pressure fluctuation are identified. The pressure fluctuations by rear rotor were observed even upstream of the front rotor and upstream flow field changed due to the pressure fluctuation in the former case. The effect of pressure fluctuation to the flow field will be discussed in more details and the guideline of rear rotor design will be considered.. |
| 70. |
Analysis of partial cavitation on cascade blades considering thermodynamic effect (2nd report, linear analysis of rotating cavitation)
The suction performance of turbopumps in cryogenic fluids is basically much better than that in cold water because of thermodynamic effect of cavitation. However, it is not still clear how the thermodynamic effect works on cavitation instabilities such as rotating cavitation and cavitation surge. In the present study, the singularity method is combined with an unsteady heat transfer model to examine the thirmodynamic effects on rotating cavitation. The results are qualitatively compared with existing experiments to clarify the research needs for deeper understanding.. |
| 71. |
Air/water two-phase flow performance of contra-rotating axial flow pump and rotational speed control of rear rotor
An application of contra-rotating rotors, consisting of front and rear rotors rotating in the opposite direction each other, has been proposed against a demand for developing higher specific speed axial flow pump with more compact structure, higher efficiency and better cavitation performance. Air/water two-phase flow performance of contra-rotating pump has to be, also, investigated as axial flow pumps are used for standby operations of air-lock and air/water mixing discharge to prevent floods. In the present paper, experimental results on air/water two-phase flow performance of test pump of contra-rotating rotors (RR1 Type) are shown and compared with those of conventional axial flow pump, consisting of a front rotor and a rear stator. Effects of changes of rear rotor rotational speed, which is an advantage of contra-rotating axial flow pump, on two-phase flow performance of RR1 type are discussed. It is shown that air/water two-phase flow performance of contra-rotating axial flow pump is capable to be improved by this control procedure for rear rotor rotational speed.. |
| 72. |
Toru Shigemitsu, Tomoya Takano, Akinori Furukawa, Kusuo Okuma, Satoshi Watanabe, Pressure measurement on casing wall and blade rows interaction of contra-rotating axial flow pump, Journal of Thermal Science, 10.1007/s11630-005-0025-z, 14, 2, 142-149, Vol.14, No.2, pp. 142-149, 2005.06, An application of contra-rotating rotors has been proposed against a demand for developing higher specific speed axial flow pump. The blade rows interaction between front and rear rotors should be clarified for its stable operation and reduction of unsteady losses. In this paper, the static pressure distributions on casing wall are provided by measuring with the phase locked sampling method. The measurements are carried out for two types of the rear rotors with different blade number and chord length, and it is found that, for both types of rotors, the unsteady pressure fluctuations are more remarkable in the front rotor than in the rear rotor and they are caused by the rear rotor pressure field. The effects of pressure fluctuations will be discussed in more details toward understanding the blade rows interaction in the contra-rotating axial flow pump.. |
| 73. |
Development of air-water two-phase flow centrifugal pump and its operating characteristics
A design concept of two-phase flow centrifugal impeller is described with experimental results. The short bladed forward impeller with high outlet blade angle is recommended to keep theoretical head higher even in two-phase flow condition and to disperse the air accumulating region on the suction blade surface by the water jet flow coming along the pressure blade surface. Furthermore, tandem arrangement of outer and inner rotating cascades with the same blade numbers was adopted to suppress the rotating stall phenomena appearing in the case of a single stage of outer cascade. Then how to evaluate the impossibility of pumping due to two-phase flow is shown from a relation between the two-phase flow head characteristic curve and the resistance curve of piping system.. |
| 74. |
Analysis of partial cavitation on cascade blades considering thermodynamic effect (1st report, steady analysis using singularity method)
It is well known that the suction performance of turbopumps in cryogenic fluids is much better than that in cold water because of thermodynamic effect of cavitation. In the present study, an analytical method to simulate partial cavitating flow with the thermodynamic effect in a cascade is proposed : heat transfer between the cavity and the ambient fluid is modeled by one-dimensional unsteady heat conduction model under the slender body approximation and is coupled with flow analysis using a singularity method. In this report, the steady analysis is performed and the results are compared with those of experiments to validate the model of the present analysis. This analysis can be easily extended into unsteady stability analysis for cavitation instabilities such as rotating cavitation and cavitation surge.. |
| 75. |
Hirokazu YAKUSHIJIN, Satoshi WATANABE, Hisasada TAKAHARA and Akinori FURUKAWA, Experimental Study of Stall Behavior in Radial Vaneless Diffuser of Centrifugal Pump, Memoirs of the Faculty of Engineering Kyushu University, Vol. 64, No.3, pp.185〜196, 2004.09. |
| 76. |
Experimental study of cavitation induced oscillation in flat plate helical inducer with various blade angles
Cavitation test has been carried out for flat plate helical inducer with various blade angles. Effects of inducer blade angles on head characteristics and cavitation induced oscillation phenomena are described in the present paper. Head characteristics, head breakdown point due to cavitation and the range of cavitation induced oscillation occurring are correlated as guiding principles for inducer design. Then measured casing wall pressure distributions and observed cavitation behaviors are discussed from the aspect of advance detection of cavitation surge oscillation.. |
| 77. |
Akira FUJII, Seiji AZUMA, Yoshiki YOSHIDA, Yoshinobu TSUJIMOTO, Hironori HORIGUCHI and Satoshi WATANABE, Higher Order Rotating Cavitation in an Inducer, International Journal of Rotating Machinery, Vol. 10, No. 4, pp. 241-251, 2004.07. |
| 78. |
Takashi EGUCHI, Satoshi WATANABE, Hisasada TAKAKARA, Akinori FURUKAWA, Development of Pusatile Flow Experiment System and PIV Measurement in an Elastic Tube, Memoirs of the Faculty of Engineering Kyushu University, Vol.63, No.3, pp.161-172, 2003.09. |
| 79. |
Satoshi WATANABE and Christopher BRENNEN, Dynamics of Cavitating Propeller in a Water Tunnel, Transactions of ASME, Journal of Fluids Engineering, Vol. 125, No. 2, pp.283-292, 2003.03. |
| 80. |
Experimental Study on Rear Rotor Design in Contra-rotating Axial Flow Pump. |
| 81. |
Akinori FURUKAWA, Koichi ISHIZAKA and Satoshi WATANABE, Flow Measurement in Helical Inducer and Estimate of Fluctuating Blade Force in Cavitation Surge Phenomena, JSME International Journal, 10.1299/jsmeb.45.672, 45, 3, 672-677, Vol.43，No.3，pp.672〜677, 2002.08. |
| 82. |
Higher order rotating cavitation in an inducer
In the present study, a higher order rotating cavitation predicted by the stability analysis was identified through the measurements of inlet pressure fluctuations and blade stress fluctuations. The propagation speed ratio of the higher order rotating cavitation is about 5, and the amplitude of the blade stress fluctuation at the root of leading edge caused by the rotating cavitation is the same level as the conventional rotating cavitation. The higher order rotating cavitation occurred at higher cavitation number compared with that of conventional rotating cavitation. A higher order cavitation surge was also observed at the transition point from the conventional to the higher order rotating cavitation. It was clarified that these cavitation instabilities can be suppressed by modifying the shape of the inlet casing.. |
| 83. |
On suppressing cavitation surge by using tandem bladed helical inducer with low solidity front blades
A cavitation surge oscillation in the range of partial flow rate and low NPSH hinders the wide operation of an inducer for industrial turbo-pumps, though it is very effective to improve the cavitation performance. The harmful oscillation of cavitation surge occurs in the case of inducers with high solidity more than 1.0. This oscillation might be suppressed if a tandem bladed inducer, having a front inducer with low solidity less than 1.0, would be employed. Experiment tests to examine its effect are described in the present paper. Results show that the amplitude of the oscillation takes almost zero when a relative peripheral or axial position between the front and rear blades is properly chosen. The reasons are discussed with measured casing wall pressure distributions and observed cavitation behaviors.. |
| 84. |
Experimental study of cavitation induced oscillation in helical inducer with various blade lengths
Cavitation tests have been carried out for helical inducer with various blade lengths. Effects of inducer blade lengths on head characteristics and cavitation induced oscillation phenomena are described in the present paper. The oscillation occurring in the case of inducers with lower solidity less than 1.0 differs from that with the solidity of 2.0. Change of the flow distributions during the oscillation is measured from by using a single hole yawmcter with the phase locked sampling method to the oscillation. By compared with the results for higher solidity inducer, the behaviors of cavitation induced oscillation are clarified.. |
| 85. |
Flow measurement in helical inducer and estimate of fluctuating blade force in cavitation surge phenomena
An attachment of inducer is a powerful method to improve the cavitation performance of a turbo-pump. Cavitation surge phenomena, occurring under the severe suction pressure at partial flow rate, is focused in the present paper. Flow measurements were carried out at the inlet and outlet sections of a flat-plate helical inducer with the solidity of 2.0 and tip blade angle of 11 degrees byusing a total-head yawmeter with a phase locked sampling method to the cavitation oscillation. Change of the flow distributions during the oscillation is clarified with observed cavitation behaviors. After the results are compared with those at conditions just before and after the oscillation, the fluctuating blade forces are estimated from the blade to blade distributions of casing wall pressures measured at these conditions.. |
| 86. |
Satoshi WATANABE，Yoshinobu TSUJIMOTO, Akinori FURUKAWA, Theoretical Analysis of Transitional and Partial Cavity Instabilities, Transactions of ASME, Journal of Fluids Engineering, 10.1115/1.1378295, 123, 3, 692-697, Vol.123, No.3, pp.692-697, 2001.09. |
| 87. |
Basic and experimental study of contra-rotating axial flow pump
Demands for higher performance of axial flow pumps have led pump designers to consider the creative strategies for the new type. As a solution, contra-rotating rotors might be applied to a pump. Comparative experiments were conducted for two types, consisting of contra-rotating rotors and a rotor and a stator respectively, which were designed under the same specifications of pump head, flow rate and rotor specific speed. The measured pump performances and flow distributions are shown and the advantages of using contra-rotating type are clarified as follows. Contra-rotating type is superior in-pump efficiency and cavitation performance in range of partial flow rates to conventional one though the specified pump head and maximum efficiency were not satisfied at design point in the case of contra-rotating test rotors. Kesults demonstrate that the rear rotor design is important to improve the pump efficiency.. |
| 88. |
Hironori Horiguchi, Satoshi Watanabe, Yoshinobu Tsujimoto, Theoretical analysis of cavitation in inducers with unequal blades with alternate leading edge cutback: Part II - Effects of the amount of cutback, Journal of Fluids Engineering, Transactions of the ASME, 10.1115/1.483272, 122, 2, 419-424, 2000.06, In Part I, it was found that the alternate blade cutback of the leading edge causes a peculiar behavior in the development of steady cavitation. A stability analysis showed that the alternate blade cutback can reduce the onset region of rotating cavitation by enhancing the stability of alternate blade cavitation. In this report, we examine the effects of the amount of cutback. It was found that the development of steady cavity is significantly different depending on the amount of cutback. Those steady cavity developments are explained by the interaction of local flow near the cavity closure with the leading edge of the opposing blade just in the same way as for the development of alternate blade cavitation. It is also shown that the range of cavitation number with stable cavitation can be increased by increasing the amount of cutback.. |
| 89. |
Yoshinobu Tsujimoto, Satoshi Watanabe, Hironori Horiguchi, Linear Analyses of Cavitation Instabilities of Hydrofoils and Cascades, Proceedings of the Abnormal Flow Phenomena in Turbomachinery, US-Japan Seminar, 1-12, 1998.11. |
| 90. |
Hironori Horiguchi, Satoshi Watanabe, Yoshinobu Tsujimoto, Masanori Aoki, A Theoretical Analysis of Alternate Blade Cavitation in Inducers, Proceedings of the Cavitation and Multiphase Flow Forum, ASME 1998 Fluids Engineering Division Summer Meeting, FEDSM98-5057, 1-6, 1998.06. |
