線香花火の火花が何度も枝分かれする機構を科学的に解明した研究業績が評価された。

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

DOI： https://doi.org/10.1016/j.flowmeasinst.2023.102361

Other Link： https://doi.org/10.1016/j.flowmeasinst.2023.102361

Repository Public URL： https://hdl.handle.net/2324/6791119

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Flow Measurement and Instrumentation  

This paper describes the use of a high-speed streaming camera combined with in-house image processing for real-time particle tracking velocimetry (PTV) above 1 kHz. The proposed system is evaluated by measuring the diameter and velocity of multiple free-falling droplets in a simultaneous manner. Two existing particle tracking methods are examined: median flow (MF) and four-frame best estimate (4BE). Area-limiting processing is newly added to MF and 4BE to reduce the region of interest (ROI) in which particles are detected in the next image, resulting in area-limiting MF (AMF) and area-limiting 4BE (A4BE). Except for MF, the rest three methods of AMF, 4BE, and A4BE are capable of 1-kHz real-time PTV for 1246 pixel × 600 pixel images, with 4BE and A4BE achieving even at 10 kHz for 1246 pixel × 100 pixel images. The processing times for tracking and image preparation are measured, and the bottleneck is found to be the image acquisition and preparation, rather than the tracking. AMF achieves faster processing times than MF in all conditions, showing the effectiveness of the limited ROI, while 4BE and A4BE exhibit comparable performance. The measurement error is confirmed to be approximately 1% for droplet velocity and diameter, demonstrating the high accuracy of the first in-situ real-time PTV exceeding 1 kHz.

DOI： 10.1016/j.flowmeasinst.2023.102361

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

ロケットエンジンの間欠作動時の性能予測モデルを新たに構築した．

DOI： https://doi.org/10.2514/1.B38793

Other Link： https://doi.org/10.2514/1.B38793

Repository Public URL： http://hdl.handle.net/2324/4793654

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

高品質な金属粉末を実現するために重要な，粉末製造プロセスを可視化し，数理モデルを構築した．

DOI： https://doi.org/10.1016/j.powtec.2022.117778

Repository Public URL： http://hdl.handle.net/2324/4822538

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

To elucidate from a thermo-fluid perspective the fragmentation and solidification processes that occur during the production of a metal powder, we conducted experiments to visualize the water atomization of molten 42Sn–58Bi fusible alloy and made measurements of the circularity of the resulting metal powder. The fragmentation process inside a fully developed fast water spray with a pressure up to 5 MPa was clearly captured. The time-resolved images revealed fragmentation patterns involving extending molten ligaments resulting from splashing, vapor explosions, and splitting. The time variation of the thinning of the neck diameter of the ligaments revealed that the fragmentation is rate-controlled by the capillarity of the molten drop itself, and solidification and viscosity have no influence on the pinching-point dynamics. The produced metal powder displayed size-dependent circularity, and larger particles tended to be less spherical than small particles. The mechanism is attributed to non-uniform solidification, which is enhanced at the pinching part of a droplet, consistent well with the images obtained.

DOI： 10.1016/j.powtec.2022.117778

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

高温の燃焼ガスによる強制対流熱伝達からロケットエンジン燃焼室を保護するために，冷却液膜が使用される．液膜のドライアウト点の予測は設計開発上重要であるが，困難な課題であった．本研究では，液膜のドライアウト点の理論的予測に初めて成功し，実機エンジン燃焼試験との比較を通じて，その妥当性を検証した．

DOI： https://doi.org/10.2514/1.J061381

Other Link： https://doi.org/10.2514/1.J061381

Repository Public URL： http://hdl.handle.net/2324/4793656

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Propulsion and Power  

We propose a theoretical model for predicting the impulse bit of bipropellant thrusters under pulse-firing operations. The present theoretical model, which considers the nonuniformity of the mixture ratios created inside the thrust chamber, extends the stream-tube approach, which is limited to the prediction of the steady performance. In pulse-firing operation, the fuel or the oxidizer alone can be injected in isolation due to the mismatched injection timing before the rated injection, which leads to the deterioration of performance as compared with the steady operation. The present approach (the unsteady stream-tube model) successfully implements a time-dependent stream-tube structure inside the thrust chamber, allowing for the prediction of the impulse bit as a straightforward function of the injection conditions. Three different pulse-firing tests using distinct hypergolic propellants demonstrate the validity of this model, typically reproducing the notable trend of deterioration in the impulse bit in the short-pulsed mode. We also examine the time-averaged specific impulse and mass flow rate to improve the impulse bit during short-pulsed operations.

DOI： 10.2514/1.B38793

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Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST AERONAUTICS ASTRONAUTICS  

A film cooling technique using a liquid film subjected to a hot gas flow in a turbulent condition is theoretically investigated. We successfully incorporate the two essential factors for the evaporating liquid film, droplet entrainment and three-dimensional film architecture, allowing for the physically-consistent straightforward formulation. The validity of the present model is convinced by reproducing combustion test results conducted for two types flightmodel bipropellant thrusters, in which the film length or dryout point shortens approximately inversely proportional to the combustion pressure. The underlying scenario to determine the film length is revealed. The gas flow initiates the originally smooth liquid film to be destabilized by Kelvin-Helmholtz instability in the axial direction and accelerates the wave crests leading to Rayleigh-Taylor instability in the transverse direction. Superposing the two types of waves produces three-dimensional cusps on the film as roots of entrained droplets. The convective heat transfer evaporating the liquid film is enhanced by the entrainment, reducing the net film flow rate, and by the cusp structure, enlarging the area of liquid/gas interface along the transverse direction in particular.

DOI： 10.2514/1.j061381

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

DOI： https://doi.org/10.1103/PhysRevE.104.L053101

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

DOI： https://doi.org/10.2514/1.B38421

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

金属積層技術が広く使用される昨今の状況にあって，金属粉末の製造技術の高度化が強く期待されている．本研究は，溶融金属に高速の水噴霧を衝突させる水アトマイズ法を対象に，高速度カメラを用いて金属粉末の生成プロセスを明らかにすることに初めて成功した．

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

DOI： https://doi.org/10.2514/1.B38310

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

DOI： 10.1016/j.ijmultiphaseflow.2021.103580

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

DOI： doi: 10.1063/5.0038399

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

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

A traditional hand-held firework generates light streaks similar to branched pine needles, with ever smaller ramifications. These streaks are the trajectories of incandescent reactive liquid droplets bursting from a melted powder. We have uncovered the detailed sequence of events, which involve a chemical reaction with the oxygen of air, thermal decomposition of metastable compounds in the melt, gas bubble nucleation and bursting, liquid ligaments and droplets formation, all occurring in a sequential fashion. We have also evidenced a rare instance in nature of a spontaneous fragmentation process involving a direct cascade from big to smaller droplets. Here, the self-sustained direct cascade is shown to proceed over up to eight generations, with well-defined time and length scales, thus answering a century old question, and enriching, with a new example, the phenomenology of comminution.

DOI： 10.1103/PhysRevLett.118.074502

Publisher：Journal of Engineering for Gas Turbines and Power  

Erosion of steam turbine blades due to coarse droplet impingement is a serious problem. The physical relationship is still elusive between the dynamics of wavy liquid film on a wall and the droplet dispersion from the trailing edge. In this study, we experimentally and theoretically investigate the liquid film subjected to the turbulent airflow and following fragmentation process under well-controlled flow conditions, where the airflow velocity is up to 100 m/s, and initial liquid film velocity is 0.06 and 0.10 m/s, and trailing edge thicknesses are 0.5, 1.0, and 2.0 mm. By applying the developed planar laser-induced fluorescence (PLIF)-based method with no use of artificial threshold of brightness, we quantify the film thickness and interfacial friction factor. As the airflow velocity increases, the liquid film instability promotes and the interfacial friction factor increases, much exceeding the Blasius correlation. When the liquid film reaches the trailing edge, several liquid columns extend by the Rayleigh-Taylor instability. We identify that the interfacial friction factor to accelerate the ligament corresponds to the Blasius correlation, distinct from the one on the wavy liquid film upstream. Incorporating the identified two interfacial friction factors, we successfully formulate the diameter of ligament as the characteristic lengthscale of the spreading droplet downstream. Derived formulation for the droplet statistics is well validated by the experimental results of mean and maximum diameters and size distribution.

DOI： 10.1115/1.4066375

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Publisher：Experiments in Fluids  

The planar laser-induced fluorescence (PLIF) method has been widely applied for measuring the thickness of liquid films. To identify the liquid–gas interface, however, PLIF-based methods require an artificial threshold value of brightness or a calibration curve between the thickness and the brightness, limiting its application in measuring unknown film thickness. To overcome the drawbacks, we propose a new method, time-variant PLIF (T-PLIF), which employs an index of time variance of brightness to detect the interface. We first establish the mathematical principle of T-PLIF, wherein the time variance of a phase-dependent variable becomes the maximum exactly at the time-averaged position of the wavy interface. We then perform experiments for a well-controlled downward annular liquid film flow to test the reliability of T-PLIF. We demonstrate that T-PLIF measures liquid film thickness of h>0.2mm with the accuracy of ε≤10% to the theoretical reference and h≤0.2mm with ε=20%. T-PLIF is able to quantify the film thickness with no need for any pre-/post-calibration or artificial threshold values. We further confirm the applicability of T-PLIF to the wavy film flow sheared by an airflow up to 30m/s by measuring the phase velocity and wavelength, which well matches the theoretical results.

DOI： 10.1007/s00348-025-03989-z

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Repository Public URL： https://hdl.handle.net/2324/7347392

Publishing type：Research paper (scientific journal)   Publisher：International Journal of Heat and Mass Transfer  

For producing fine metal powders, the critical step is ligament dynamics of molten metal, while the thinning and breakup processes subjected to the interfacial heat and mass transfer are elusive. Here, we conduct high-speed visualization and infrared pyrometry on a single tin ligament that enable us to distinguish the effects of surface oxidation and cooling. On the tin ligament, a thin oxide layer grows according to the molecular diffusion of ambient oxygen, leading to the significant increase of viscosity coefficient at the interface. The capillary destabilization is then suppressed by the surface oxidation. We discover that the tin ligament thins initially following the capillary timescale, while the necking is accelerated to obey the viscous-capillary timescale as the oxide layer becomes one-tenth of the neck radius, corresponding to the Ohnesorge number of larger than unity. Simultaneously, the neck is cooled by the ambient. The accelerated thinning due to the viscous effect leads to the prompt decrease of heat capacity. We successfully formulate the rapid temperature drop at the neck based on the interfacial heat transfer coupled with the viscous-capillary necking dynamics in a consistent manner.

DOI： 10.1016/j.ijheatmasstransfer.2024.126043

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Publishing type：Research paper (scientific journal)   Publisher：Materials and Design  

Fine metal particles produced by gas atomization are recognized as an essential material for additive manufacturing. However, spatio-temporally resolved images for the atomization process are still lacking. In the present study, we apply a high-speed Schlieren optical system synchronized with a pulse light source with flashing period of 30 ns to a simple atomization setup, consisting of a single supersonic [Formula presented] jet at Mach number of 1.5 and free-falling tin droplets. Covering the tin droplets by Ar gas, we generate spherical droplets by minimizing the initial oxidation from the ambient. Impinging on the large-momentum gas jet, the tin droplet largely deforms to be shaved the bottom end and bounced above the jet with partially penetrating inside the gas core. The spreading ligaments above the jet thins at first along with the capillary timescale. As the surface oxidation proceeds, the neck transitionally shrinks according to the viscous-capillary timescale, which evidences the direct observation of gas atomization process superposed by the molecular diffusion across the interface. Statistics of collected metal particles demonstrate a bimodal distribution for the diameter, originated from the distinct atomization mechanisms of aerodynamic dominant breakup inside the gas jet and of capillary dominant breakup spreading above the jet.

DOI： 10.1016/j.matdes.2024.113413

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Publishing type：Research paper (scientific journal)   Publisher：Experimental Thermal and Fluid Science  

For the thermal management of industrial devices, a reduction in the net coolant flow rate by droplet dispersion from a liquid film is important because it can cause unexpected thermal failure. To understand the process of droplet dispersion from a liquid film better, we experimentally and theoretically evaluated the characteristics of boiling-induced atomization in a liquid film formed by oblique jet impingement on a superheated wall. Atomization processes were visualized using magnified high-speed imaging using a backlight technique. In this study, two types of droplets were observed using high-speed-magnification imaging. These were large droplets that disintegrated from the ligament formed on a relatively high-temperature wall, and small droplets from the ligament formed via bubble bursting in the nucleate boiling regime. For the atomization induced by nucleate boiling, larger droplets were produced via bubble bursting further downstream from the impingement point because the bubble size and liquid film thickness increased. Finally, the total volume of the droplets produced by nucleate boiling was estimated from the frequency of bubble bursting and droplet size measured from the visualization results. The estimation results suggest that the ratio of the total volume flow rate of the ejected droplets to the injection flow rate of the liquid was negligible (2%). Thus, most of the injected liquid eventually reached the wetting front of the sheet, separating it from the wall before drying out.

DOI： 10.1016/j.expthermflusci.2024.111262

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Language：Japanese   Publisher：THE JAPANESE SOCIETY FOR MULTIPHASE FLOW  

<p>From the Edo-period, a unique fragmentation cascade, the successive bursting of droplets, draws the ramifying sparks in a Japanese traditional sparkler, Senko-hanabi, depicting the fragile beauty. Involved potassium-salt droplets demonstrate nucleation without evaporation, while the thermal-decomposition supplies gas into a bubble following the thermal diffusion timescale. We specify the distinctions of Senko-hanabi from puffing/micro-explosion of multi-components volatile droplets and from bursting metal sparks rate-controlled by mass diffusion. But in the end, beyond the differences, we generally understand the underlying process of bursting droplet driven by a growth of internal bubble.</p>

DOI： 10.3811/jjmf.2024.t012

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Propulsion and Power  

We perform physics-based theoretical analyses on the tradeoff between the overall performance of specific impulse and the thermal protection ability of a coolant liquid film to identify the optimal configuration of a liquid rocket engine. A bipropellant thruster is set as the target, which uses a hypergolic propellant mixture of nitrogen tetroxide as the oxidant and monomethyl hydrazine as the fuel. By considering the practical nonuniform distribution of the local mixture ratio produced in the thrust chamber, the maximum specific impulse is achieved when the fuel and oxidizer spray widths become identical, allowing for the specification of the diameter of the impinging-type injector. The heat balance between the convective heat transfer from the combustion gas and the latent heat of the three-dimensionally wavy liquid film provides the optimal diameter of the combustion chamber. The longest liquid film is found to be achieved when half of the initial film is entrained by the fast gas, correspondingly mitigating the heat transfer area due to the liquid film waviness. We successfully demonstrate the optimal architecture of the liquid engine based on the tradeoff, in which an improvement of specific impulse by 1 s shortens the film length by 2 mm.

DOI： 10.2514/1.B39409

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Publishing type：Research paper (scientific journal)   Publisher：Journal of Fluid Mechanics  

Droplet spreading is ubiquitous and plays a significant role in liquid-based energy systems, thermal management devices and microfluidics. While the spreading of non-volatile droplets is quantitatively understood, the spreading and flow transition in volatile droplets remains elusive due to the complexity added by interfacial phase change and non-equilibrium thermal transport. Here we show, using both mathematical modelling and experiments, that the wetting dynamics of volatile droplets can be scaled by the spatial-temporal interplay between capillary, evaporation and thermal Marangoni effects. We elucidate and quantify these complex interactions using phase diagrams based on systematic theoretical and experimental investigations. A spreading law of evaporative droplets is derived by extending Tanner's law (valid for non-volatile liquids) to a full range of liquids with saturation vapour pressure spanning from to Pa and on substrates with thermal conductivity from to. In addition to its importance in fluid-based industries, the conclusions also enable a unifying explanation to a series of individual works including the criterion of flow reversal and the state of dynamic wetting, making it possible to control liquid transport in diverse application scenarios. The Author(s), 2024.

DOI： 10.1017/jfm.2024.385

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Publisher：AIAA SciTech Forum and Exposition, 2024  

To reduce the probability of unstable ignition during vacuum startup of bipropellant thrusters using hypergolic propellants, it is essential to comprehend the propellant jet within the combustion chamber from startup to ignition, in addition to the spray conditions of heterogeneous impingement. Particularly for new thruster design, understanding the atomization and mixing state and being capable of predicting ignition from cold flow tests are of utmost importance. In this research, the propellant flow during simulated thruster vacuum startup transient was visualized to clarify the mechanism of ignition delay. Moreover, the nondimensional injection condition Λ, which serves as a mixing condition index during steadystate combustion, is extended to the vacuum startup transient. As the process transitions from a vacuum to oxidizer vapor pressure, the oxidizer jet morphs into a spray condition due to flash boiling. A scenario is developed where the oxidizer sprays exacerbate the spray atomization and mixing of heterogeneous impingement as a result of interactions with the fuel, leading to ignition failure. Furthermore, by extending the nondimensional injection condition Λ into two dimensions and evaluating the correlation between the propellant distribution and Λ, it is demonstrated that the spray mixing of heterogeneous collisions can be predicted, even during the vacuum startup transient.

DOI： 10.2514/6.2024-1396

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Authorship：Corresponding author   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the ASME Turbo Expo  

Erosion of steam turbine blades due to coarse droplet impingement is a serious problem. The physical relationship is still elusive between the dynamics of wavy liquid film on a wall and the droplet dispersion from the trailing edge. In this study, we experimentally and theoretically investigate the liquid film subjected to the turbulent airflow and following fragmentation process under well-controlled flow conditions, where the airflow velocity is up to 100 m/s, and initial liquid film velocity is 0.06 and 0.10 m/s, and trailing edge thicknesses are 0.5, 1.0, and 2.0 mm. By applying the developed PLIF based method with no use of artificial threshold of brightness, we quantify the film thickness and interfacial friction factor. As the airflow velocity increases, the liquid film instability promotes and the interfacial friction factor increases, much exceeding the Blasius correlation. When the liquid film reaches the trailing edge, several liquid columns extend by the Rayleigh-Taylor instability. We identify that the interfacial friction factor to accelerate the ligament corresponds to the Blasius correlation, distinct from the one on the wavy liquid film upstream. Incorporating the identified two interfacial friction factors, we successfully formulate the diameter of ligament as the characteristic lengthscale of the spreading droplet downstream. Derived formulation for the droplet statistics is well validated by the experimental results of mean and maximum diameters and size distribution.

DOI： 10.1115/GT2024-124848

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Language：English   Publisher：International Journal of Gas Turbine, Propulsion and Power Systems  

Water droplet impingement on a low-pressure steam turbine blade causing erosion has been recognized as a crucial issue. It is essential to elucidate a comprehensive droplet detachment mechanism, not only from the trailing edge but also from the liquid film surface. In the present paper, we investigate the influence of interfacial friction factor against liquid film dynamics on a wall sheared by a turbulent gas flow, including the liquid film thickness, liquid film velocity and entrained droplet detached from liquid surface for both pipe flow and plate flow conditions. We conduct the analyses by using a liquid film dynamics model, recently established, considering the three-dimensional destabilized waves and droplet entrainment from the liquid surface. As a result, the film thickness and velocity greatly depends on the interfacial friction factor. Interestingly, the rate of entrained droplet to initial liquid film has a minimum value when the interfacial friction factor equals to the inverse of the liquid film Reynolds number, while the remaining liquid film flow rate becomes maximum.

DOI： 10.38036/jgpp.13.3_1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Explosives Society  

A metal spark generated by grinding carbon steel has been recognized proceeding multiple bursting events, akin to the luminous branching fireworks. The mechanism of successive fragmentation observed in carbon steel spark, however, has not been elucidated yet. In the present study, we develop a new comprehensive analytical framework for estimating the droplet size of carbon steel sparks, time of flight, and time-variant temperature, combined with high-speed images of the spreading sparks, for the quantitative discussion of the timescale of bursting metal sparks. We find that the flight time to burst for a mother droplet is independent of the content of carbon, corresponding to the Fourier number for the molecular diffusion of unity. The successive fragmentation of carbon steel sparks is rate-controlled by the molecular diffusion of ambient oxygen inside the droplet. Since the measured temperature indicates that the heat is produced by the oxidation of iron, the successive fragmentation stops when the iron in the spark is fully oxidized, immediately becoming a solid particle.

DOI： 10.34571/stem.83.3_95

CiNii Research

Publisher：Journal of Propulsion and Power  

We conduct a high-speed visualization of coolant liquid film dynamics inside a 10N-class bipropellant thruster using monomethylhydrazine and a mixture of nitrogen tetroxide with approximately 3% nitric oxide as propellants at equivalent conditions with the flight model. The direct visualization of the liquid film inside a quartz glass chamber demonstrates the transient dynamics of film flow from ignition to cutoff for the first time. The scenario for the life of the film flow is found as follows: the coolant fuel jet impinges on the chamber wall being the liquid film; the friction force from the chamber wall rapidly decelerates the film as one-tenth of the injection velocity; next, the film moves sheared by the fast combustion gas downstream; and eventually the film completely evaporates by heat transfer from the hot combustion gas. The liquid film presents the typical ripple wave structure, covered by the velocity and thermal boundary layers. The effect of the mixture ratio is significant as the film flow rate increases at a small mixture ratio, leading to the longer film length.

DOI： 10.2514/1.B38421

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Language：English  

3台の高速度カメラを同期させて画像再構成することで，連鎖的な液滴分裂現象を観察できる線香花火の3次元構造を世界で初めて明らかにするとともに，そのカスケードを定式化することに成功した．

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Non-uniform distribution of interfacial mass flux across an evaporating droplet will subsequently induce a temperature gradient across the liquid-air interface, and result in thermal Marangoni stress that reforms the flow field inside the droplet. Recent study (Shiri, et al. Phys. Rev. Lett. 2021, Yang, et al. Langmuir 2022) confirmed the role of thermal Marangoni effect on the shape of evaporating single component droplets on completely wetting substrates. Nevertheless, a comprehensive evaluation of the interacting mechanisms is still lacking due to the intrinsic limitation of experimental techniques to decompose the different influence factors. To this end, we formulate a mathematical model to simulate the evaporation of volatile droplets on completely wetting substrates based on the lubrication theory. With this model, we elucidate the interacting physical mechanisms that governs the droplet kinetics during phase change, which includes the capillary effect, the thermal Marangoni effect, the interface motion due to evaporation, as well as the removal of energy barriers by precursor film. A phase diagram is summarized in terms of the Knudsen number and liquid-to-solid Biot number, which quantifies the prevalence of the interacting effects.</p>

DOI： 10.1299/jsmefed.2022.os06-26

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>In recent years, Additive Manufacturing (AM) technology such as 3D printing has attracted much attention. In order to produce high-quality metal powders as printing materials, it is necessary to elucidate the phenomena of liquid metal splitting accompanied by solidification, which is manifested in the powder manufacturing process. So far, various experiments have been conducted on the atomization method, but the mechanism for determining powder properties has not been clarified. In particular, there is insufficient knowledge about the phenomenon of molten metal splitting along with solidification. Therefore, in this study, we investigate the breakup process of a single ligament of 42Sn-58Bi, which is a kind of fusible alloy with a melting point of 139 ℃. A high-speed camera is used to visualize the pinch-off process of the ligament. The variation of the neck diameter of the ligament is traced during the fragmentation process. When the initial temperature is high, we found that the neck diameter thins down following a power law of 2/3, corresponding to the trend derived from capillary time scale. On the other hand, as the initial temperature gets lower, the neck diameter becomes thinner than that predicted by the capillary time scale just before breaking up, which is attributed to the influence of solidification.</p>

DOI： 10.1299/jsmefed.2022.os06-24

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

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

DOI： https://doi.org/10.34571/stem.82.2_50

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

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

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

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

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

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

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

In bi-propellant thrusters, impinging type injectors are widely used to deliver propellants to a combustion chamber. By impinging the jet streams of fuel and oxidizer, the spray spreads while the two liquids mix. To design the injectors, several correlations related to injection conditions have been proposed (e.g., Rupe factor), and practically utilized over the last half-century. However, the physical meanings of the past correlations are not well understood, because the essential scale of the spray structure is elusive. In this paper, we derive the global length scale of the spray produced by impinging injectors of unlike doublet, fuel-oxidizer-fuel triplet, and oxidizer-fuel-oxidizer triplet in a consistent manner. The unified length scale is found representing the spray width ratio of oxidizer to fuel evidenced by comprehensive cold-flow tests including several past studies, covering various parameters such as injector types, nozzle diameters, physical properties of working liquids, and injection velocities. Finally, we clearly provide the physical meaning based on practical correlations in a phenomenological sense.

DOI： 10.2322/tjsass.62.213

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

A fast-response pressure-sensitive paint (PSP) technique was applied to the measurement of unsteady surface pressure of an oscillating cascade blade in a transonic flow. A linear cascade was used, and its central blade was oscillated in a translational manner. The unsteady pressure distributions of the oscillating blade and two stationary neighbors were measured using the fast-response PSP technique, and the unsteady aerodynamic force on the blade was obtained by integrating the data obtained on the pressures. The measurements made with the PSP technique were compared with those obtained by conventional methods for the purpose of validation. From the results, the PSP technique was revealed to be capable of measuring the unsteady surface pressure, which is used for flutter analysis in transonic conditions.

DOI： 10.1115/1.4039180

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

For the prediction of heat transfer coupled with sloshing phenomena in the propellant tanks of reusable launch vehicle for sounding mission, the pressure drop induced by heat transfer and the dynamic motion of liquid in sub-scale vessels were experimentally investigated. The correlation between the pressure drop and liquid motion was confirmed in the experiment. It was suggested that splash and wavy surface induced by violent motion of liquid cause the pressure drop in the closed vessel. In addition, as the preliminary investigation, non-isothermal sloshing of liquid nitrogen and liquid hydrogen were successfully visualized and pressure drop depending on the gaseous species was discussed.

DOI： 10.2514/6.2018-4755

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

Bi-propellant thrusters in space propulsion systems often utilize unlike-doublet or triplet injectors as the hypergolic propellant injection device. The impingement of liquid jet streams of fuel and oxidizer involves sheet expansion, droplet fragmentation, mixing, evaporation, and chemical reactions in liquid and gas phases. In the sequential reactive, multiphase, thermo-fluid dynamics, the rate controlling phenomenon is the mixing step. In this study, a defined length scale demonstrates the distribution of fuel and oxidizer and thus represents their mixing states, facilitating the straightforward formulation of characteristic velocity in a consistent manner for doublet and triplet injectors as a function of propellant injection conditions with a film cooling effect. The validity of the present modeling framework is confirmed by a good agreement with characteristic velocity measured by hot firing tests covering a wide range of the mixture ratio. We also clarify the meaning of a widely accepted practical indicator, the so-called Rupe factor, over half a century of injector design history.

DOI： 10.1615/IntJEnergeticMaterialsChemProp.2018025085

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

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

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

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

A simple method of determining normalizing spray flux distribution was demonstrated applying flow visualization and the measurement of droplet distribution using a patternator. Two reservoirs are used to contain the working fluid (water) under pressure. This liquid is injected into still air from two nozzles. The nozzles are adjustable to eliminate any misalignment of the water jets. The surface tension coefficient was measured using an automatic surface tensiometer employing the plate method. The atomization process was visualized using a high-speed video camera in conjunction with a backlighting technique. The 3D-printed patternator was demonstrated to be useful for the 2D measurement of spray mass flux distributions. The spray mass flux distribution was normalized as a function of normalized distance after atomization was complete. The flux distribution at any location could be calculated from the normalized distribution convergence considering the spread of the spray.

DOI： 10.2322/tjsass.60.255

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

In liquid-propellant chemical propulsion systems, the liquid fuel and oxidizer are atomized by impinging jet atomization, mixed and combustions will occur due to auto-ignition inside a chamber. It is important for a performance prediction to simulate the primary atomization phenomenon; especially, the local mixture ratio can be used as indicator of thrust performance, so it is useful to evaluate it from numerical simulations. In this research, to predict local mixture ratio distribution downstream from an impingement point, we propose a numerical method for considering bi-liquid and the mixture and install it to CIP-LSM which is a two-phase flow simulation solver with level-set and MARS method as an interfacial tracking method. A new parameter, β, which is defined as the volume fraction of one liquid in the mixed liquid within a cell is introduced and the solver calculates the advection of β, inflow and outflow flux of β to a cell. SMART method is used for the interpolating value in a cell. By validating this solver, we conducted a simple experiment and the same simulation. From the result, the solver can predict the penetrating length of a liquid jet correctly and it is confirmed that the solver can simulate the mixing of liquids. Then we apply this solver to the numerical simulation of impinging jet atomization. From the result, the inclination angle of fan after the impingement in the bi-liquid condition reasonably agrees with the theoretical value. Also, it is seen that the mixture of liquids can be simulated in this result. We validate the numerical method by comparing numerical results with the experimental results with local mass flux and mixture ratio distributions.

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

In liquid-propellant chemical propulsion systems, the liquid fuel and oxidizer are atomized by impinging jet atomization, mixed and combustions will occur due to auto-ignition inside a chamber. It is important for a performance prediction to simulate the primary atomization phenomenon; especially, the local mixture ratio can be used as indicator of thrust performance, so it is useful to evaluate it from numerical simulations. In this research, to predict local mixture ratio distribution downstream from an impingement point, we propose a numerical method for considering bi-liquid and the mixture and install it to CIP-LSM which is a two-phase flow simulation solver with level-set and MARS method as an interfacial tracking method. A new parameter, β, which is defined as the volume fraction of one liquid in the mixed liquid within a cell is introduced and the solver calculates the advection of β, inflow and outflow flux of β to a cell. SMART method is used for the interpolating value in a cell. By validating this solver, we conducted a simple experiment and the same simulation. From the result, the solver can predict the penetrating length of a liquid jet correctly and it is confirmed that the solver can simulate the mixing of liquids. Then we apply this solver to the numerical simulation of impinging jet atomization. From the result, the inclination angle of fan after the impingement in the bi-liquid condition reasonably agrees with the theoretical value. Also, it is seen that the mixture of liquids can be simulated in this result. We validate the numerical method by comparing numerical results with the experimental results with local mass flux and mixture ratio distributions.

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

Sparkling firework, which is a Japanese sparker called Senko-hanabi, is composed of black powder containing no metal wrapped in a twisted paper. The firework has a unique beauty with streaks of light similar to the pine needles. For over 300 years, however, physics behind the beauty of the firework is hidden mystery. In this study, detailed high-speed visualization measurements are conducted to quantify the individual stages in the life of sparkling firework. It is confirmed that the droplets, which will be the streaks of light, are formed from liquid atomization induced by bursting of the fireball itself or the bubbles on the surface. The rupture process of non-evaporative droplets is successfully captured, and it is determined that the bursting of a droplet is caused by microexplosion, which is the sudden expansion of gas produced inside the droplet.

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

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

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

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

Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design conditions, an effective technique is verified utilizing small amount of gas (microjet) injection. The microjet is supplied from a pressurized reservoir and is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effect, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD by the microjet injection with the amount of only 1% of liquid mass flow rate. The dominant non-dimensional number is found to be the ratio of the dynamic pressure (microjet/liquid jet) at the impingement point. The optimized atomization efficiency is achieved when the dynamic pressure ratio is approximately two.

DOI： 10.2514/6.2013-3705

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

This paper describes the results obtained by free surface analysis of impinging jet nozzles for a wide range of orifice diameter and jet momentum under non-reactive conditions. The numerical results are compared with experimental results under some conditions. Capability of the present simulation method CIP-LSM to impinging jet atomization is confirmed by comparing the fan-shaped liquid condition after impingement. As a consequence, the present method can simulate the angle of the liquid after the impingement and the impinging modes approximately. The numerical analysis for three sector of simulant thruster is conducted and it is confirmed that interactions between fans are demonstrated.

DOI： 10.2514/6.2013-4069

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

For the prediction of heat transfer coupled with sloshing in the propellant tanks of launch vehicle, the pressure drop induced by liquid motion in a sub-scale vessel excited in vertical direction was experimentally investigated. The strong correlation between the pressure drop and liquid motion was confirmed in the experiment. The mechanisms enhancing heat transfer were discussed based on the visualization. It was suggested that shear flow and vortices induced by violent motion of liquid should cause the pressure drop in the closed vessel.

DOI： 10.2514/6.2013-3906

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

Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, however, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design operation, an effective technique is verified utilizing small amount of gas injection. The gas jet is supplied from a pressurized reservoir independent of the liquid supply system, and it is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effectivity, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that atomization is drastically promoted when the dynamic pressure of gas overcomes that of liquid at the impingement point. By the gas injection with the amount of only 1% of liquid mass flow rate, Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD. In addition, the optimized atomization efficiency is achieved when the gas dynamic pressure is twice as much as the liquid at the impingement point.

DOI： 10.1299/kikaib.78.1990

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

Aimingatelucidating the relationship between a liquid sheet atomization and the detailedflowfield inside the sheet produced by an impingement-type injector, numerical computation, experimental observation, and theoretical analysis were performed. A numerical method was developed to examine atomization phenomena. First, the method was verified through quantitative comparison with a corresponding experiment of pinch off. Then, experimental and theoretical analyses were conducted on the atomization of an axisymmetric liquid sheet through Kelvin-Helmholtztype instability, which was produced by two opposing watexr jets. The numerical results showed qualitative resemblance to the corresponding experimental and theoretical analyses. Finally, it was clarified that a nonuniform injection velocity profile resulted in a velocity distribution with an inflection point inside the sheet. As a result, the sheet tended to be unstable and enhanced atomization.

DOI： 10.2514/1.B34392

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

An analytical method was proposed and validated for droplet diameters and size distributions. The method was developed based on the energy conservation law including surface free energy and Laplace pressure. Under several hypotheses, the law derived an equation indicating that atomization resulted from a kinetic energy loss. Thus, once the amount of loss was obtained, the droplet diameter was able to be calculated without any experimental parameters. When the effects of ambient gas were ignorable, injection velocity profiles of liquid jets were the essential factor for the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization was inversely proportional to the injection Weber number under the conditions of injection velocity profiles with laminar or turbulent. By applying the mean diameter model, a non dimensional distribution function was also derived assuming Nukiyama-Tanasawa's function. The validity of these estimation methods were favorably confirmed by comparisons with corresponding mean diameters and the size distributions, which were experimentally measured under atmospheric pressure.

DOI： 10.1299/kikaib.78.850

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

With the progress of human activities in space, the occasion to handle liquids in no-uniform acceleration or low-gravity is now growing. On the launch vehicles with liquid propulsion system, the dynamic acceleration during its powered ascent or ballistic flight makes it very difficult to control the position of propellants in the tanks. For the establishment of the technology for the management of liquid propellant in space vehicles, a numerical method, called 'CIP-LSM' (CIP based Level Set & MARS), was developed to simulate three-dimensional free-surface flows under various gravity conditions, which has been applied to clarify the dynamic behavior of liquid propellant in the tanks of launch vehicles.

DOI： 10.1299/kikaib.76.765_778

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

Aiming at elucidating the relationship between injector internal flow, especially injection velocity profiles, and atomization characteristics of liquid sheet, experimental measurement, numerical and theoretical analyses were carried out. Liquid space distribution produced by atomization of axisymmetric sheet, which was created by collision of two water jets in opposite direction, was experimentally obtained utilizing paternator. The amplitude of the liquid sheet oscillation was developed based on linear stability analysis. The numerical results of atomization process through Kelvin-Helmholtz type instability showed qualitative resemblance with corresponding experimental results and theoretical analyses. It was clarified that non-uniform injection velocity profile resulted in velocity distribution with inflection point inside the sheet, thus the sheet became unstable and enhanced atomization. The effect of injection velocity profile on atomization at impingement type injector was also clearly represented.

DOI： 10.1299/kikaib.76.765_755

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

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

In order to obtain fundamental knowledge of liquid breakup phenomena, the three dimensional flow field of oscillatory liquid jet in pinch off was numerically studied by the developed method, CIP-LSM. In the present paper, not only the liquid jet shape but also its inner structure was investigated. The numerical results of liquid shapes and velocity distributions were compared with the corresponding experimental ones. From the results, CIP-LSM was confirmed to have potential to simulate liquid breakup phenomena in which surface tension was predominant. It was revealed that inner structures of the liquid jet were constructed due to the surface tension at the nozzle exit. The jet breakup was demonstrated to occur at the fluid element injected with the minimum acceleration.

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

In a preburner of liquid rocket engines, some liquid-oxygen (LOX) posts, which introduced oxygen into combustion chamber, experienced severe flow-induced vibration due to unsteady cryogenic hydrogen flow. The mechanism of the vibration has not been fully understood because of the complexity of the flow field. In the present study, a new numerical method was developed to analyze the flow field of hydrogen, whose characteristic properties lie in its non-idealness and compressibility. The unsteady hydrogen flow inside the preburner unit was analyzed to investigate the details of hydrogen flow field as well as the mechanism of LOX post vibration. It was clarified that hydrogen flow inside the manifold and fluid dynamic forces on LOX posts were strongly affected by vortices shed from the junction at the upstream of the inlet. A baffle plate put inside the manifold was shown to reduce unsteady fluid forces on the LOX posts.

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

In liquid-propellant chemical propulsion systems, the liquid fuel and oxidizer are atomized by impinging jet atomization, mixed and combustions will occur due to auto-ignition inside a chamber. It is important for a performance prediction to simulate the primary atomization phenomenon; especially, the local mixture ratio can be used as indicator of thrust performance, so it is useful to evaluate it from numerical simulations. In this research, to predict local mixture ratio distribution downstream from an impingement point, we propose a numerical method for considering bi-liquid and the mixture and install it to CIP-LSM which is a two-phase flow simulation solver with level-set and MARS method as an interfacial tracking method. A new parameter, β, which is defined as the volume fraction of one liquid in the mixed liquid within a cell is introduced and the solver calculates the advection of β, inflow and outflow flux of β to a cell. SMART method is used for the interpolating value in a cell. By validating this solver, we conducted a simple experiment and the same simulation. From the result, the solver can predict the penetrating length of a liquid jet correctly and it is confirmed that the solver can simulate the mixing of liquids. Then we apply this solver to the numerical simulation of impinging jet atomization. From the result, the inclination angle of fan after the impingement in the bi-liquid condition reasonably agrees with the theoretical value. Also, it is seen that the mixture of liquids can be simulated in this result. We validate the numerical method by comparing numerical results with the experimental results with local mass flux and mixture ratio distributions.

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

In order to reveal the nozzle scaling law of a Repetitive Pulsed (RP) laser thruster, momentum-coupling coefficients of several conical nozzles were investigated by means of experiment and numerical analysis. In the experiment, a pendulum method was used to measure an impulse imparted to a conical nozzle by a laser-driven blast wave. A propagation of the blast wave in a conical nozzle and an exhaust-refill process were analyzed by CFD. The calculated C_m agreed with the experimental data. The processes until a critical time are qualitatively the same regardless of a divergence angle, but quantitatively different. As a result, the nozzle of a small apex angle enhances the performance of a RP laser thruster when only a single pulse is input.

Language：Japanese   Book type：General book, introductory book for general audience

Event date： 2022.2 - 2022.3

Language：English  

Venue：Online   Country：Japan  

researchmap

Event date： 2022.2 - 2022.3

Language：English  

Venue：Online   Country：Japan  

researchmap

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.11

Language：English   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： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.1

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： 2020.12

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： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2020.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Event date： 2020.8

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京   Country：Japan  

Event date： 2020.2

Language：English   Presentation type：Oral presentation (general)  

Venue：BORDEAUX, FRANCE   Country：France  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2019.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇部   Country：Japan  

Event date： 2019.12

Language：English   Presentation type：Oral presentation (general)  

Venue：Fukuoka, Japan   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大分   Country：Japan  

Event date： 2019.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo, Japan   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：名古屋   Country：Japan  

Event date： 2019.6

Language：English   Presentation type：Oral presentation (general)  

Venue：AOSSA and Happiring Fukui, Japan   Country：Japan  

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：機械振興会館   Country：Japan  

Event date： 2019.5

Language：Japanese   Presentation type：Oral presentation (invited, special)  

Venue：機械振興会館   Country：Japan  

Event date： 2019.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Puerto Vallarta, Mexico   Country：Mexico  

Event date： 2018.12

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：岡山市   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Event date： 2018.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：倉敷市   Country：Japan  

Event date： 2018.10 - 2019.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：久留米市   Country：Japan  

Event date： 2018.5

Language：English   Presentation type：Oral presentation (general)  

Venue：Seville   Country：Spain  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Denver, Colorado   Country：United States  

Event date： 2017.11

Language：English   Presentation type：Oral presentation (general)  

Venue：Sendai   Country：Japan  

Event date： 2017.8

Language：English  

Venue：Atlanta   Country：Georgia  

We demonstrate an environmentally friendly and easily handling cold flow diagnostics to determine the value of exhaust velocity c^∗ in bi-propellant thrusters, practically useful prior to the hot firing tests. We employ only water as the simulant liquid, and directly measure the local ratios of mixture and flow rate using a conventional patternator with an absorbance spectrometer. The density ratio mismatching to the real propellants of MON/MMH is able to be reasonably compensated. Combining with the chemical equilibrium analysis, we calculate c^∗ at wide range of injection mixture ratio under several injector configurations. The validity of the framework is quantitatively evidenced by comparing with corresponding hot firing tests. This fact deduces that the mixing states of MON/MMH at firing condition is reproducible by water flow diagnostics under the appropriate conversion technique. We also investigate the c^∗ trend resulting from injection conditions by flow visualizations.

Event date： 2017.6

Language：English  

Venue：Charlotte   Country：United States  

A fast-response pressure-sensitive paint (PSP) technique was applied to the measurement of unsteady surface pressure of an oscillating cascade blade in a transonic flow. A linear cascade was used, and its central blade was oscillated in a translational manner. The unsteady pressure distributions of the oscillating blade and two stationary neighbors were measured using the fast-response PSP technique, and the unsteady aerodynamic force on the blade was obtained by integrating the data obtained on the pressures. The measurements made with the PSP technique were compared with those obtained by conventional methods for the purpose of validation. From the results, the PSP technique was revealed to be capable of measuring the unsteady surface pressure, which is used for flutter analysis in transonic conditions.

Event date： 2016.12

Language：English  

Venue：Perth   Country：Australia  

In liquid-propellant chemical propulsion systems, the liquid fuel and oxidizer are atomized by impinging jet atomization, mixed and combustions will occur due to auto-ignition inside a chamber. It is important for a performance prediction to simulate the primary atomization phenomenon; especially, the local mixture ratio can be used as indicator of thrust performance, so it is useful to evaluate it from numerical simulations. In this research, to predict local mixture ratio distribution downstream from an impingement point, we propose a numerical method for considering bi-liquid and the mixture and install it to CIP-LSM which is a two-phase flow simulation solver with level-set and MARS method as an interfacial tracking method. A new parameter, β, which is defined as the volume fraction of one liquid in the mixed liquid within a cell is introduced and the solver calculates the advection of β, inflow and outflow flux of β to a cell. SMART method is used for the interpolating value in a cell. By validating this solver, we conducted a simple experiment and the same simulation. From the result, the solver can predict the penetrating length of a liquid jet correctly and it is confirmed that the solver can simulate the mixing of liquids. Then we apply this solver to the numerical simulation of impinging jet atomization. From the result, the inclination angle of fan after the impingement in the bi-liquid condition reasonably agrees with the theoretical value. Also, it is seen that the mixture of liquids can be simulated in this result. We validate the numerical method by comparing numerical results with the experimental results with local mass flux and mixture ratio distributions.

Event date： 2015.6

Language：English  

Venue：Montreal   Country：Canada  

Eulerian-Lagrangian hybrid method is implemented for the prediction of liquid atomization phenomena produced by 2 liquid water jets impinging by an angle of 40 deg. in quiet ambient air. To calculate the flow fields with liquid/gas interface, Eulerian analyses are conducted inside a fixed computational grid system. After the atomization occurs, every droplet is converted to a spherical particle. The motion of particles are tracked in Lagrangian form. For the validation of the developed Eulerian-Lagrangian hybrid method, flow visualization by using a high-speed video camera is carried out. To obtain quantitative values of spray characteristics, the liquid mass flux distribution in space is measured by utilizing a patternator. Numerical and experimental results of atomization process and mass flux distribution of spray show a similarity, and thus the developed method is evaluated that it has potential to predict spray characteristics produced by liquid sheet atomization. The developed numerical method can calculate unsteady spray distributions not only at the plane close to the injector but also far downstream. The spray mass flux distribution in the transient state, which is hard to measure by experiment, is demonstrated.

Event date： 2015.6

Language：English  

Venue：Montreal   Country：Canada  

Leading edge separation of thin airfoil cascade in subsonic flow at large angle of incidence was simulated by implicit large eddy simulation (ILES) and Reynolds averaged Navier-Stokes (RANS) simulations with various turbulence models. In the ILES simulations with fine grids, the timeaveraged surface pressure qualitatively agreed with the experimental data. The RANS and ILES simulations on the coarse mesh failed to capture a peak of pressure near the leading edge. From spectrum analysis, it was observed that the flow-field was turbulent in the separation bubble. In the failed RANS simulations, the separation bubble was much longer and the turbulence energy near the leading edge was much lower than those in the ILES results. The development of lambdashaped vortex structures and their sudden weakening near the reattachment point was observed in the unsteady simulations. Two possible modifications to existing turbulence models in RANS simulations were proposed based on the comparison of turbulence energy between the ILES and RANS results. It is shown that these modifications improve the bubble length and C_p distributions of RANS simulations, though further validation and modeling are needed for the application to realistic cases.

Event date： 2014.6

Language：English  

Venue：Dusseldorf   Country：Germany  

Fully coupled steady fluid-solid interaction (FSI) and flutter simulations were conducted on a NASA Rotor 67 transonic experimental fan to demonstrate the capability of application for capturing various aeroelastic phenomena in turbomachinery. The effect of blade deformation on the aerodynamic performance was investigated by steady FSI. Aeroelastic modes were determined using the modal identification technique for the vibration of the cascade. The proposed identification method successfully estimated aeroelastic modes without significant uncertainty. Aeroelastic eigenvalues were localized around the structural modes in vacuum forming the "mode family", and there was negligible change in their frequency. The calculated aerodynamic coupling between the structural modes was small. Based on the reconstructed local unsteady aerodynamic force, the major damping sources in the 1F mode family were determined to be the shock motion and supersonic region near the leading edge. From these results, it was confirmed that the developed FSI method was applicable to the analysis of unsteady characteristics of blades in multimode oscillation.

Event date： 2013.7

Language：English  

Venue：San Jose, CA   Country：United States  

For the prediction of heat transfer coupled with sloshing in the propellant tanks of launch vehicle, the pressure drop induced by liquid motion in a sub-scale vessel excited in vertical direction was experimentally investigated. The strong correlation between the pressure drop and liquid motion was confirmed in the experiment. The mechanisms enhancing heat transfer were discussed based on the visualization. It was suggested that shear flow and vortices induced by violent motion of liquid should cause the pressure drop in the closed vessel.

Event date： 2013.7

Language：English  

Venue：San Jose, CA   Country：United States  

Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design conditions, an effective technique is verified utilizing small amount of gas (microjet) injection. The microjet is supplied from a pressurized reservoir and is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effect, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD by the microjet injection with the amount of only 1% of liquid mass flow rate. The dominant non-dimensional number is found to be the ratio of the dynamic pressure (microjet/liquid jet) at the impingement point. The optimized atomization efficiency is achieved when the dynamic pressure ratio is approximately two.

Event date： 2013.7

Language：English  

Venue：San Jose, CA   Country：United States  

This paper describes the results obtained by free surface analysis of impinging jet nozzles for a wide range of orifice diameter and jet momentum under non-reactive conditions. The numerical results are compared with experimental results under some conditions. Capability of the present simulation method CIP-LSM to impinging jet atomization is confirmed by comparing the fan-shaped liquid condition after impingement. As a consequence, the present method can simulate the angle of the liquid after the impingement and the impinging modes approximately. The numerical analysis for three sector of simulant thruster is conducted and it is confirmed that interactions between fans are demonstrated.

Event date： 2013.6

Language：English  

Venue：San Antonio, Tx   Country：United States  

With increasing focus on environmental effects and the need for fuel diversity in gas turbines, good liquid atomization is increasingly important. It is known that impinging atomization is able to produce fine drops by impingement of fast liquid jets. However, the atomization characteristics deteriorate at lower injection velocities. In this study, for improving atomization characteristics under a wide range of injection velocity, an effective technique is verified utilizing a small amount of gas (microjet) injection. The microjet is supplied from a pressurized reservoir independent of the liquid supply system, and it is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effectiveness, experimental visualizations and drop size measurements are carried out. It is found that atomization is remarkably promoted when the dynamic pressure of microjet overcomes that of the liquid at the impingement point. By the microjet injection with only 1% of liquid mass flow rate, Sauter mean diameter (SMD) becomes one-tenth of the original SMD. In addition, optimized atomization efficiency is successfully achieved when the dynamic pressure of the microjet is two times that of the liquid at the impingement point.

Event date： 2012.7 - 2012.8

Language：English  

Venue：Atlanta, GA   Country：United States  

Pressure drops in the non-isothermal sloshing of liquid nitrogen and liquid hydrogen were experimentally investigated. Heat and mass transfer indicated by the pressure change induced by violent sloshing in the cryostat driven by the mechanical exciter were successfully obtained. Based on the visualized image of liquid motion, it was found that splash and wavy surface induced by violent sloshing of liquid should enhance heat transfer around liquid surface and result in pressure drop. It was also suggested that the instability of singlecomponent system with different temperature between the gaseous and liquid phase could make the pressure control more difficult.

Event date： 2012.7 - 2012.8

Language：English  

Venue：Atlanta, GA   Country：United States  

A theoretical model is proposed and validated for calculating droplet diameters and size distributions. The model is derived based on the energy conservation law including the surface free energy and the Laplace pressure. Under several hypotheses, the law derives an equation indicating that atomization results from kinetic energy loss. Thus, once the amount of loss is determined, the droplet diameter is able to be calculated without the use of experimental parameters. When the effects of ambient gas are negligible, injection velocity profiles of liquid jets are the essential cause of the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization is inversely proportional to the injection Weber number when the injection velocity profiles are laminar or turbulent. A non-dimensional distribution function is also derived from the mean diameter model and Nukiyama-Tanasawa's function. The new estimation methods are favorably validated by comparing with corresponding mean diameters and the size distributions, which are experimentally measured under atmospheric pressure.

Event date： 2012.6

Language：English  

Venue：Copenhagen   Country：Denmark  

A consistent theoretical model is proposed and validated for calculating droplet diameters and size distributions. The model is derived based on the energy conservation law including the surface free energy and the Laplace pressure. Under several hypotheses, the law derives an equation indicating that atomization results from kinetic energy loss. Thus, once the amount of loss is determined, the droplet diameter is able to be calculated without the use of experimental parameters. When the effects of ambient gas are negligible, injection velocity profiles of liquid jets are the essential cause of the reduction of kinetic energy. The minimum Sauter mean diameter produced by liquid sheet atomization is inversely proportional to the injection Weber number when the injection velocity profiles are laminar or turbulent. A non-dimensional distribution function is also derived from the mean diameter model and Nukiyama- Tanasawa's function. The new estimation methods are favorably validated by comparing with corresponding mean diameters and the size distributions, which are experimentally measured under atmospheric pressure.

Event date： 2011.7 - 2011.8

Language：English  

Venue：San Diego, CA   Country：United States  

For the prediction of heat transfer coupled with sloshing phenomena in the propellant tanks of reusable launch vehicle, the pressure drop induced by heat transfer and the dynamic motion of liquid in sub-scale vessels were experimentally observed and numerically investigated. The correlation between the pressure drop and liquid motion was confirmed in the experiment. The mechanisms enhancing heat transfer were discussed based on the computation. It was suggested that splash and wavy surface induced by violent motion of liquid cause the pressure drop in the closed vessel. In addition, as the preliminary investigation, non-isothermal sloshing of liquid nitrogen and liquid hydrogen were successfully visualized and pressure drop depending on the gaseous species was discussed.

Event date： 2011.7 - 2011.8

Language：English  

Venue：San Diego, CA   Country：United States  

Aiming at elucidating the flow characteristics of liquid jet at a coaxial type injector, experimental visualization and theoretical analysis as well as numerical simulation were carried out. For computing atomization phenomena, a numerical method has been developed, and it was firstly verified through quantitative comparisons with corresponding experiment of pinch off. It was confirmed that the method can compute inertia force, interfacial tension, viscous force and gravity force adequately, all of which generally affect atomization phenomena. Then, it was experimentally confirmed that fast gas flow enhanced atomization of liquid jet. Numerical analysis showed satisfactorily good agreement with corresponding experimental results. When the gaseous injection velocity became slow at constant mass flow rate, the atomization was suppressed, which was coincident with linear stability analysis of two dimensional liquid/gas parallel flow. It was clearly represented that installation of recess enhanced atomization due to straight gas flow guided by the recess. When the fast gas blew close to liquid jet, the amplitude of instability wave grew, and, additionally, impact of gas on liquid resulted in promotion of atomization.

Event date： 2010.4

Language：English  

Venue：Honolulu, HI   Country：United States  

Aiming at elucidating the relationship between injector inner flow, especially injection velocity profiles, and atomization characteristics of liquid sheet, experimental measurement, numerical and theoretical analysis were carried out. Liquid spacial distribution produced by atomization of axisymmetric sheet, which was created by collision of two water jets in opposite direction, was experimentally obtained utilizing paternator. The amplitude of the liquid sheet oscillation was theoretically developed. The numerical results of three dimensional unsteady atomization process through Kelvin-Helmholtz type instability showed qualitative resemblance with corresponding experimental results and theoretical analyses. It was clarified that non-uniform injection velocity profile resulted in velocity distribution with inflection point inside the sheet, thus the sheet became unstable and enhanced atomization. The effect of injection velocity profile on atomization of two dimensional plane jet was also clearly represented.

Event date： 2009.8

Language：English  

Venue：Denver, CO   Country：United States  

Aiming at elucidating the relationship between injection conditions, especially injection velocity profiles, and atomization characteristics of liquid sheet at the impingement type of injector, numerical analysis, experimental observation and theoretical analysis were carried out. For computing atomization phenomena, a numerical method has been developed. The method was verified through quantitative comparisons with corresponding experiment of pinch off. Then experimental and theoretical studies were performed on atomization of axisymmetric liquid sheet, which was produced by collision of two water jets in opposite direction. The numerical results of the atomization process through Kelvin-Helmholtz type of instability showed qualitative resemblance with corresponding theoretical analyses. It was clarified that non-uniform injection velocity profile resulted in velocity distribution with inflection point inside the sheet. Thus the sheet with non-uniform injection velocity profile tended to be unstable and enhanced atomization. The effect of injection velocity profile on atomization at the impingement type injector was also represented.

Event date： 2008.7

Language：English  

Venue：Hartford, CT   Country：United States  

Aiming at clarifying and quantifying atomization characteristics at impinging jet injector, numerical analysis, experimental observation and theoretical analysis were conducted. For computing atomization phenomena, a numerical method was developed. The method was verified through quantitative comparisons with corresponding experiment of pinch off. Then experimental and theoretical studies were performed on atomization of axisymmetric liquid sheet, which was produced by collision of two water jets in opposite direction, as well as numerical analysis. The numerical results of the atomization process through Kelvin-Helmholtz type of instability showed qualitative resemblance with experimental visualization and theoretical analysis. Finally, atomization characteristics at impinging jet injector were numerically analyzed. Liquid distributions from the injector face plate were quantified, and the dynamic behavior of the liquid sheet was found to affect strongly on liquid distributions at downstream.

Event date： 2007.7

Language：English  

Venue：Cincinnati, OH   Country：United States  

In order to obtain fundamental knowledge of atomization, the three dimensional unsteady phenomena of pinch off were numerically studied by developed method. The numerical results of liquid shapes and velocity distributions were compared with the corresponding experimental ones. They showed satisfactorily good agreement in a qualitative sense. The liquid jet shape, the pressure and velocity distributions, and the inner flow structure were clarified through the comparisons of distinctly different flow fields due to presence or absence of surface tension. The condition of pinch off, which had close correlation with fluid acceleration at injection, was clearly specified. It was observed that the satellite drops were suppressed by large perturbation amplitude.

Event date： 2006.7

Language：English  

Venue：Sacramento, CA   Country：United States  

In a preburner of liquid rocket engines, some liquid-oxygen (LOX) posts, which introduced oxygen and hydrogen into combustion chamber, experienced severe flow-induced vibration in unsteady hydrogen flow. The mechanism of the vibration has not been fully understood because of the complexity of the flow field. In the present study, a new numerical method was developed to analyze the flow field of hydrogen, whose characteristic properties lie in its non-idealness and compressibility. The unsteady hydrogen flow inside the preburner unit was analyzed to investigate the details of hydrogen flow field as well as the mechanism of LOX post vibration. It was clarified that hydrogen flow inside the manifold was strongly affected by the upstream condition.

Language：English   Presentation type：Oral presentation (general)  

Venue：Tokyo   Country：Japan  

Other Link： https://psfvip13.org/index.html

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡市   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：熊本市   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：オンライン   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Kobe   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Valletta   Country：Malta  

拡散に律速された液滴の連鎖分裂機構を国際会議で解説した．

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：仙台市   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Kyoto   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：京都   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長崎   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：長崎   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：大阪   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Florida   Country：United States  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北九州   Country：Japan  

Language：Japanese  

Venue：東京都   Country：Japan  

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Language：Japanese  

Venue：熊本市   Country：Japan  

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Language：Japanese  

Venue：東京都   Country：Japan  

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Language：Japanese  

Venue：オンライン   Country：Japan  

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Language：Japanese  

Venue：オンライン   Country：Japan  

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Language：Japanese  

Venue：Online   Country：Japan  

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Language：Japanese  

Venue：オンライン   Country：Japan  

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Venue：オンライン   Country：Japan  

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Venue：福岡市   Country：Japan  

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Venue：Tokyo   Country：Japan  

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Venue：Kobe   Country：Japan  

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Venue：Valletta   Country：Malta  

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Venue：Boston   Country：United States  

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Venue：東京都   Country：Japan  

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Venue：仙台市   Country：Japan  

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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  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Language：Japanese  

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Academic society, research group, etc. 

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線香花火をの科学を解説

線香花火の火花の枝分かれを高速度カメラで鮮明にとらえた世界初の映像を提供

線香花火の火花の枝分かれを高速度カメラで鮮明にとらえた世界初の映像を提供

線香花火の火花の枝分かれを高速度カメラで鮮明にとらえた世界初の映像を提供

線香花火の火花の枝分かれを高速度カメラで鮮明にとらえた世界初の映像を提供

線香花火の火花の枝分かれを高速度カメラで鮮明にとらえた世界初の映像を提供

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明

線香花火の科学の解明