超音速マイクロエジェクタを用いて速度が数十m/sの気流を制御する手法の開発を行う．

Outcome：

2022
超音速マイクロエジェクタにより転向する流れの転向角を決定するパラメータを明らかにした．

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Publishing type：Research paper (scientific journal)   Publisher：The Japan Society for Aeronautical and Space Sciences  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Last author   Publishing type：Research paper (scientific journal)  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：Springer  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Berlin Heidelberg  

Authorship：Last author   Publishing type：Research paper (scientific journal)   Publisher：Springer Nature  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Inc.  

Authorship：Lead author   Publishing type：Research paper (international conference proceedings)   Publisher：IOP (Institute of Physics) Publishing  

Publishing type：Research paper (scientific journal)   Publisher：Green Asia Education Center, Kyushu University, Research and Education Center of Carbon Resources, Kyushu University, and Research and Education Center for Advanced Energy Materials, Devices, and Systems, Kyushu University  

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer  

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

Particle image velocimetry (PIV) has become a powerful tool for flow velocity measurements in wind tunnel testing. However, it is generally difficult to apply the PIV technique to supersonic flows because of unreliable particle traceability. In the present study, the PIV and MTV (molecular tagging velocimetry) techniques are applied to transonic and supersonic flows, in which a normal shock wave appears, to evaluate particle traceability. Based on this work, it is found that the PIV data largely deviate from the MTV data behind a normal shock wave for both flows. The drag coefficient is also estimated for a particle from the velocity data measured by the two techniques. Its value is then compared to the drag coefficient value calculated from an empirical formula for particle Mach numbers ranging between 0.1 and 0.9. Based on the results, it is found that the experimental data can be reproduced reasonably well by the formula for particle Reynolds numbers higher than similar to 1. However, the data associated with particle Reynolds numbers lower than similar to 1 deviate largely from the formula.

DOI： 10.1007/s12650-015-0286-x

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

In this study, a feedback mechanism for supersonic deep-cavity flows is modeled. The model is developed on the basis of previous flow visualization results. In this model, two pressure waves play an important role in the feedback mechanism; one wave is generated at the trailing edge of the cavity owing to the motion of the shear layer, and the other wave is generated as a result of the third reflection of the former wave at the cavity bottom. The constants in the model are determined using the flow visualization results. The frequencies calculated in the model agree well with the dominant frequencies observed in experiments; in particular, the feedback mechanism responsible for deep-cavity-induced pressure oscillation is successfully clarified.

DOI： 10.2514/1.J053184

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORP  

A supersonic flow over a rectangular cavity is known to oscillate at certain predominant frequencies. The present study focuses on the effect of the cavity length-to-depth (L/D) ratio on the frequency for a free-stream Mach number of 1.7. The pressure oscillations are measured by changing the L/D ratio from 0.5 to 3.0, and the power spectral density is calculated from the temporal pressure signals for each L/D ratio. The results demonstrate that the spectral peaks for an L/D ratio of less than similar to 1 and greater than similar to 2 are accounted for by the feedback mechanisms of the transverse and longitudinal oscillations, respectively. The results also demonstrate that the spectral peaks in the transition (1 <similar to L/D <similar to 2) are accounted for by either of the two feedback mechanisms of transverse and longitudinal oscillations; that is, the flows under the transition regime oscillate both transversely and longitudinally.

DOI： 10.1155/2015/751029

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

In this study, a novel wall-mounted cavity having a three-dimensional shape is proposed for enhancing supersonic mixing. This device induces an oscillatory secondary flow that effectively enhances mixing. To demonstrate the device performance, we experimentally compare supersonic mixing fields in three ducts without any devices, with a rectangular cavity, and with the newly proposed cavity (new device). In the experiments, time-dependent pressure measurements and oil-flow surface visualization are carried out. The experimental results show that the newly proposed cavity induces not only self-sustained flow oscillation but also secondary flow, both of which effectively enhance mixing. The jet issuing from the injector is also visualized for each duct by a planar laser-induced fluorescence (PLIF) technique. The PLIF visualizations reveal that mixing is enhanced far more rapidly in the duct with the newly proposed cavity than in the other ducts and that the jet penetration in the duct with the newly proposed cavity is much higher. These results are attributed to the large-amplitude jet fluctuation due to the oscillatory secondary flows induced by the newly proposed cavity.

DOI： 10.1007/s00348-014-1711-y

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

The 3D flow structure induced by a normal shock-wave/boundary-layer interaction in a transonic diffuser is experimentally and computationally investigated. In the diffuser, the shock wave is located in the diverging section. The experiments are done with wall pressure measurements, oil-flow surface visualization, and Mach number measurements with a laser-induced fluorescence (LIF) method. In the computational work, the Reynolds-averaged Navier-Stokes equations are numerically solved with the k-omega two-equation turbulence model. The numerical solution agrees reasonably well with the experiment and clarifies the vortex structure in the interaction zone along with the 3D behavior of the boundary layer downstream of the shock wave. A careful investigation of the calculated flow reveals that the vortices are generated at the foot of the shock wave. It is also found that a complicated wave configuration is formed near the diffuser corner. A flow model is constructed by considering this wave configuration. This model explains the 3D flow characteristics in the transonic diffuser very well.

DOI： 10.1115/1.4023657

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The mechanism behind cavity-induced pressure oscillations in supersonic flows past a deep rectangular cavity is not well understood despite several investigations having been carried out. In particular, the process by which the pressure wave is generated and the path of the pressure wave propagating inside the cavity remains unclear. In the present study, the pressure waves around a deep rectangular cavity over which nitrogen gas flows at a Mach number of 1.7 are visualized using the schlieren method. The length of the cavity is 14.0 mm. The depths of the cavity are selected as 20.0 and 11.7 mm, corresponding to length-to-depth ratios of 0.70 and 1.2, respectively. The pressure waves propagating inside as well as outside the cavity have been successfully visualized using a high-speed camera, and the propagation pattern of these waves is found to be different from that previously predicted by numerical simulation and from those expected in previous oscillation models. In addition, the pressure oscillation near the trailing edge of the cavity is also measured using semiconductor-type pressure transducers simultaneously with the capture of the schlieren images. As a result, the relationship between the shear-layer motion, pressure-wave generation, and pressure oscillation at the trailing edge of the cavity is clarified experimentally.

DOI： 10.1007/s00348-012-1400-7

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)  

The oscillatory behaviors in a supersonic cavity flow are visualized by LIF (Laser-Induced Fluorescence) and schlieren methods. In the LIF method, an argon-ion laser is used as a light source to excite the iodine molecules seeded into the working gas. The iodine fluorescence, whose intensity is known to be a function of temperature, is detected by the photomultiplier. The pressure oscillation on the bottom wall of the cavity is also measured simultaneously with the fluorescence detection. The phase of fluorescence-intensity oscillation is corrected on the basis of the cavity-bottom pressure oscillation and the correction is performed at every fluorescence detection point. As a result, the temperature oscillations inside and outside the cavity are qualitatively visualized in two-dimensional sense. In the schlieren method, the light source is controlled so as to flash responding to a specific phase of the periodic pressure signal and the oscillatory motion of the shear layer developing along the cavity span is captured. By carefully observing both of the visualization results, the relation between the temperature oscillation and shear-layer motion is clarified. © 2012 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.78.1318

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

A method that is based on laser-induced fluorescence (LIF) and that involves the use of acetone as a seed can be utilized for measurement of supersonic flows with high temporal and spatial resolutions. In the present study, the feasibility of using this method to measure the number density in supersonic flows at temperatures lower than the atmospheric temperature is investigated. An experiment in which low-temperature conditions are created by supersonic isentropic flows in a convergent-divergent nozzle is carried out. LIF is realized by exciting acetone with the fourth harmonic of a Nd:YAG laser, and the LIF signal is detected by a CCD camera with an image intensifier. In order to theoretically determine the LIF characteristics, a multistep decay model that can be used for temperatures of 300-900 K is extended so that it can be used in the low-temperature regime. The constant included in the model is redetermined by fitting the model to the present experimental data. The LIF calculated by using this extended model is found to agree very well with the experimental data. The model also indicates that the number density measured by the LIF method in the temperature range 170-290 K is insensitive to temperature.

DOI： 10.1007/s00348-010-1029-3

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 日本機械学会  

DOI： 10.1299/kikaib.73.1002

Authorship：Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Visualization Society of Japan  

Three-dimensional flow oscillations in a supersonic cavity are investigated by the numerical simulation based on the Navier-Stokes equations. The dominant frequencies of the pressure fluctuation calculated by this simulation agree very well with those measured in the previous experiments. In order to extract the fluctuating components of the dominant frequency, time-dependent solutions are phase-averaged. With this method, three-dimensional behaviors of the oscillating cavity flow are clearly visualized. The visualization result reveals that the unsteady motion of the shear layer is not uniform along the duct span due to the existence of two sidewalls. This non-uniformity makes acoustic wave generation localized on the cavity trailing edge in the vicinity of the duct center, and consequently produces the highly three-dimensional pattern of the standing wave in the cavity.<br>

DOI： 10.3154/tvsj.26.74

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Aeronautics and Astronautics Inc.  

The three-dimensional flow structure induced by normal shock-wave/turbulent boundary-layer interaction in a constant-area rectangular duct is investigated by a laser-induced-fluorescence method. This diagnostic system uses an argon-ion laser as a light source, and the target gas is dry nitrogen with iodine seeded as a fluorescence material. The Mach-number distributions in the duct are obtained from the measured fluorescence intensity, and the three-dimensional flow pattern in the expansion region downstream of the initial shock wave is clarified. In addition to this, the region having locally higher Mach number near the duct corners is observed immediately behind the shock wave, and the three-dimensional shape of the boundary layers is found. These flow characteristics are reproduced by solving the Navier-Stokes equations numerically. The calculated result reveals that the complicated shock-wave configuration is formed at the duct corner because of the interaction of two bifurcated shock waves developed on the two perpendicularly adjacent walls. The simple flow model is also constructed by considering this interaction. This model can explain very well the three-dimensional flow characteristics. Copyright © 2005 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.

DOI： 10.2514/1.12976

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

The three-dimensional flow structure induced by normal shock wave/ turbulent boundary-layer interaction in a constant area rectangular duct is investigated by a laser-induced fluorescence method. This diagnostic system uses an argon-ion laser as a light source, and the target gas is dry nitrogen with iodine seeded as a fluorescence material. The Mach number distributions in the duct are obtained from the measured fluorescence intensity, and the three-dimensional flow pattern in the expansion region downstream of the initial shock wave is clarified. In addition to this, the region having locally higher Mach number at the duct corners is observed just behind the shock wave, and the three-dimensional shape of the boundary layers induced by the shock wave is found. These flow characteristics are explained with the simple flow model constructed by considering the interaction between two bifurcated shock waves developed on the two perpendicularly adjacent walls.

DOI： 10.1299/kikaib.70.1687

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER INST AERONAUT ASTRONAUT  

Self-excited shock wave oscillation in a two-dimensional transonic diffuser is investigated experimentally and analytically. In the experiments, the temporal position of a shock wave is recorded by a high-speed charge-coupled device camera combined with a schlieren system, simultaneously measuring the fluctuation of the static pressure on the diffuser wall. The temporal variation of the static pressure is also measured to obtain the propagation of pressure disturbances. The results show that a pressure disturbance is generated near the stem of the shock wave and is convected in the downstream direction. In the downstream region where the boundary layer becomes highly turbulent, another disturbance is generated that propagates upstream and causes the shock wave to oscillate. One-dimensional Euler equations are solved numerically, and the power spectral density distribution of the shock wave oscillation is calculated. The numerical results agree very well with the experiments. It is also shown that the present calculation can explain the shock wave oscillation in the diffusers reported so far.

DOI： 10.2514/2.1914

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER-VERLAG  

Multiple shocklets are frequently generated in transonic diffuser flows. The present paper investigates the formation of these shocklets with a high-speed CCD camera combined with the schlieren method. It is observed that compression waves steepen while propagating upstream, and eventually become new shock waves. The ordinary shock wave is found to move upstream beyond the nozzle throat or to disappear while moving downstream depending on the pressure ratio across the nozzle. This phenomenon is also analyzed with the one-dimensional Euler equations by assuming a pressure disturbance given by the sine function at the channel exit. The calculated results are found to reproduce quite well the experimental behavior of the shocklets. The effect of the frequency of disturbance is also studied numerically, and it is shown that the multiple shocklet pattern appears when the amplitude of disturbance is not large and the diverging part of the channel downstream of the ordinary shock wave is long.

DOI： 10.1007/s001930200123

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

To obtain the time-response and the effect of temperature of the pressure sensitive paints (PSPs), the luminescence intensity of the PSPs is measured in the pressure and wall temperature range of 1∼101.3 kPa and 263∼303 K, respectively. The PSPs studied in the present works are PtOEP, PtTFPP, H2TFPP, H2TCPP, H2TSPP, and H2TTMAPP
they are painted on a commercially-available porous silica thin-layer chromatography (TLC) plate. The effect of the plate temperature on the pressure measurements is examined, and it is found that H2TFPP has the smallest temperature sensitivity of 3.5 kPa/K among the paints tested. The time-response of the paints is also investigated by using a shock tube. The change in luminescence caused by the sudden pressure rise due to an incident shock wave is detected by a photomultiplier. Results indicate that the response time is on the order of 20∼40 microseconds. In addition, the contact surface in the shock tube flow provides a method of checking the effect of the sudden change in gas temperature, and it is found that the luminescence intensity is insensitive to this effect.

DOI： 10.1299/kikaib.68.1384

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

The effects of Reynolds number on pilot-pressure distributions were studied for the underexpanded free jets. The hot-wire probe experiments were conducted for the axisymmetry supersonic nozzels with a Mach number of 2.0. The pilot-pressure for laminar and turbulent flows was found to recover downstream of the Mach disk. This recovery was attributed to the viscous effect that gradually transfered momentum from high pressure peripheral to the low pressure central region of the jet. The recovery was significant for turbulent flow while slow and gradual for laminar flow.

DOI： 10.2514/2.5829

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

Concerning the self-excited shock oscillation in a transonic diffuser flow, the response of a normal shock wave to a "white" pressure disturbance, that is, a small pressure disturbance having the same power spectral density over every frequency, is analyzed by solving the equation representing shock displacement due to the disturbance. According to the present analysis, the spectral density distribution and peak frequency of the shock oscillation depend on Mach number just upstream of the shock wave and a non-dimensional parameter determined from the diffuser geometry at the time- mean shock location. The shock displacement power spectral density distributions obtained by the analysis agree very well with those measured in our experiment. A non-dimensional relationship between the peak frequency of the shock oscillation and diffuser geometry at the shock location, Eq. (18), is obtained, and this equation agrees well with the present and previous experimental results.

DOI： 10.1299/kikaib.66.1345

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Mechanical Engineers  

Mechanism of self-excited shock oscillation in two-dimensional transonic diffuser flow is investigated experimentally. The diffuser used in this work is composed of the flat top wall and the curved bottom wall. Time-sequence of shock location is recorded by the high speed CCD camera combined with schlieren system, together with simultaneous measurements of static pressure fluctuations along the top wall. The pressure fluctuations at many locations on the side wall are also measured simultaneously. As a result, it is found that disturbances which induce shock oscillation are propagating upstream from downstream portion of the shock wave where the boundary layer behaves unsteadily and the most violently. Furthermore, vortices generated by the shock oscillation are observed to be convected downstream. The shock oscillation is explained to be sustained by the upstream-propagating disturbances and the downstream-convected vortices.

DOI： 10.1299/kikaib.66.1337

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：一般社団法人 日本機械学会  

Constant-temperature hot-wire anemometer is calibrated in a nozzle through which air is sucked from the atmosphere, and the heat transfer characteristic of the hot-wire at low Reynolds numbers is investigated from low subsonic to supersonic range. As a result, it is shown that the Nusselt number Nu which represents the heat transfer characteristic of the hot-wire is a function of both Mach number M and Reynolds number Re when M is in the range from about 0.3 to 1.1,although it depends only on Re in the cases of M<0.3 and M>1.1. It is also shown that Nu becomes maximum when M is about 0.6,which should be noted in measurement of mass flux by means of hot-wire anemometers.

DOI： 10.1299/kikaib.64.1385

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

Event date： 2023.7

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Event date： 2023.7

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Event date： 2023.7

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Measuring pressure or temperature in microflows is usually considered challenging. Nevertheless, with its gradual development, pressure-sensitive paint (PSP) shows more and more satisfying capability in surveying pressure in microflows. In the present study, we fabricate a paintable PSP based on polymer particles, i.e. (pp-)PSP, and paint it onto the sidewall of a microduct whose exit height is 500 μm, length is 10 mm. With appropriate calibration, not only the temperature distribution is revealed by virtue of the high temperature-sensitivity of the paint, but also the pressure variation is disclosed through oxygen quenching and the acquired temperature data. The experimental results of PSP are validated by numerical computation that has 3-D Reynolds-averaged Navier-Stokes (RANS) governing equations, indicating feasible application of (pp-)PSP in measuring pressure of temperature of microflows.

Presentation type：Oral presentation (general)  

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The number density distribution along flow passage in a microduct is measured by adopting laser-induced fluorescence (LIF) technique. Initially, acetone molecules are seeded into the flow from the upstream region, then are excited by a Nd:YAG laser. The light emission from the excited acetone molecules is detected by a CCD camera via image intensifier as LIF signals that are further converted to number density. Numerical computation is executed by solving 3-D Reynolds-averaged Navier-Stokes equations, and is compared with the experimental results. The LIF technique is considered capable of detecting the number density in microflows with accuracy.

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Language：Japanese   Presentation type：Oral presentation (general)  

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