Publishing type：Research paper (scientific journal)  

The present study proposes a reservoir computing reduced-order model (RCROM) of the post-stall flow around the National Advisory Committee for Aeronautics 0015 airfoil based on the time series velocity field, and the estimation accuracy of the RCROM is evaluated compared to that of a linear reduced-order model (LROM). The data were experimentally obtained by particle image velocimetry at a chord Reynolds number of 6.4 × 104 and an angle of attack of 18°. The low-dimensional description of the velocity field can be obtained by decomposing the velocity field with a proper orthogonal decomposition (POD) technique and by employing the leading POD mode coefficients as temporal variables of the data instead of the velocity field. Reservoir computing (RC) is adopted as a nonlinear function that predicts several steps ahead of the leading POD mode coefficients. The hyperparameters of RC are tuned by Bayesian optimization, and the optimized RCROM outperforms the LROM in terms of estimation accuracy. The estimation accuracy of the RCROM can be investigated under different numbers of the predicted dominant POD modes and prediction step conditions. As a result, the RCROM shows higher estimation accuracy than the LROM.

DOI： 10.1063/5.0150947

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Scopus

Publishing type：Research paper (scientific journal)  

The estimation of time-resolved three-dimensional (3D) density fields of an underexpanded jet at the nozzle pressure ratio of 2.42, a so-called "spatiotemporal super-resolution"was conducted using non-time-resolved three-dimensional background-oriented schlieren (3D-BOS) and time-resolved microphone measurements. This approach aims to reconstruct three-dimensional density fields associated with the intermittent and switching behavior of the B mode of a screeching jet from the microphone data by constructing a linear regression model. An azimuthal Fourier decomposition is applied to the 3D-BOS and microphone data, and the proper orthogonal decomposition (POD) is performed for each of their azimuthal Fourier modes. The m = 1 azimuthal Fourier mode is dominant in both cases, and the leading two POD modes in the m = 1 azimuthal mode of the microphone data are associated with the B mode. The linear regression model is constructed from the POD modes of the m = 1 azimuthal 3D-BOS data and the first two microphone POD modes of the m = 1 azimuthal mode of the microphone data. The three-dimensional density fields reconstructed from each POD mode of the m = 1 azimuthal mode of the microphone data have helical structures with opposite rotation directions. The amplitudes of those POD modes change with time, and the azimuthal structure associated with the B mode is determined depending on those amplitudes. The present result showed that intermittency in the flapping to helical structures and their strength can be interpreted by the temporal changes in the strengths of two rotating helical structures with opposite rotation directions.

DOI： 10.1063/5.0149809

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Scopus

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/JSEN.2023.3258223

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Scopus

Publishing type：Research paper (scientific journal)  

A pressure distribution inside a two-dimensional rectangular cavity with a ratio L/ D= 5.0 of the cavity length L to the depth D over a supersonic flow was obtained using an improved fast anodized-aluminum pressure-sensitive paint (AA-PSP). The freestream Mach number was M∞= 1.9 and the frequencies of the dominant cavity modal phenomena, called “Rossiter” modes, were on the order of 1–10 kHz. The fast AA-PSP using a free-based porphyrin luminophore and a high-frequency-repetition double-pulsed laser were applied, and instantaneous pressure fields were captured. This measurement system has a 60 kHz sampling rate and is suitable for the purpose of a direct measurement of the Rossiter mode phenomena. The result of the power spectral density (PSD) of the PSP measurement showed that this measurement system is capable of observing phenomena of approximately 18 kHz. Time-resolved pressure transducer measurement was also employed, and PSD obtained by the PSP measurement was validated. The frequency spectra and the amplitudes of PSD obtained by the PSP measurement were in good agreement with those obtained by the pressure transducer data. A spectral proper orthogonal decomposition (SPOD) analysis was also conducted, and the symmetric and asymmetric spatial modes were extracted at each peak frequency. In this analysis, the seventh Rossiter mode phenomena of approximately 21 kHz were visualized. The peak frequencies of symmetric modes were in good agreement with those of the Rossiter mode, and lower than that of asymmetric modes. The energy of the symmetric modes at each peak frequency was several times higher than that of the asymmetric mode. The phase of the SPOD mode revealed the propagation direction of the pressure waves. It showed the existence of the upstream propagation waves and standing waves inside the cavity.

DOI： 10.1007/s00348-023-03648-1

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：Oxford University Press (OUP)  

SUMMARY

The ‘big’ seismic data not only acquired by seismometers but also acquired by vibrometers installed in buildings and infrastructure and accelerometers installed in smartphones will be certainly utilized for seismic research in the near future. Since it is impractical to utilize all the seismic big data in terms of the computational cost, methods which can select observation sites depending on the purpose are indispensable. We propose an observation site selection method for the accurate reconstruction of the seismic wavefield by process-driven approaches. The proposed method selects observation sites suitable for accurately estimating physical model parameters such as subsurface structures and source information to be input into a numerical simulation of the seismic wavefield. The seismic wavefield is reconstructed by the numerical simulation using the parameters estimated based on the observed signals at only observation sites selected by the proposed method. The observation site selection in the proposed method is based on the sensitivity of each observation site candidate to the physical model parameters; the matrix corresponding to the sensitivity is constructed by approximately calculating the derivatives based on the simulations, and then, observation sites are selected by evaluating the quantity of the sensitivity matrix based on the D-optimality criterion proposed in the optimal design of experiments. In this study, physical knowledge on the sensitivity to the parameters such as seismic velocity, layer thickness, and hypocentre location was obtained by investigating the characteristics of the sensitivity matrix. Furthermore, the effectiveness of the proposed method was shown by verifying the accuracy of seismic wavefield reconstruction using the observation sites selected by the proposed method.

DOI： 10.1093/gji/ggad165

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Scopus

Other Link： https://academic.oup.com/gji/article-pdf/234/3/1786/50241650/ggad165.pdf

Web of Science

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/ACCESS.2023.3291415

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Scopus

Publishing type：Research paper (scientific journal)  

The present study proposed the framework of the spatiotemporal superresolution measurement based on the sparse regression with dimensionality reduction using the proper orthogonal decomposition (POD). The non-time-resolved particle image velocimetry (PIV) and the time-resolved near-field acoustic measurements using microphones were simultaneously performed for a Mach 1.35 supersonic jet. POD is applied to PIV and microphone data matrices, and the sparse linear regression model of the reduced-order data is calculated using the least absolute shrinkage and selection operator regression. The effects of the hyperparameters of the superresolution measurement were quantitatively evaluated through randomized cross-validation. The superresolved velocity field indicated the smooth convection of the velocity fluctuations associated with the screech tone, while the convection of the large-scale structures at the downstream side was not observed. The proposed framework can reconstruct the unsteady fluctuation with multiple frequency phenomena, although the reconstruction is limited to the phenomena that are associated with the microphone output. Graphical Abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s12650-022-00855-6

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Scopus

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

Unsteady drag, unsteady lift, and movement of one or two moving particles caused by the passage of a planar shock wave are investigated using particle-resolved simulations of viscous flows. The particle motion analysis is carried out based on particle-resolved simulations for one or two particles under a shock Mach number of 1.22 and a particle Reynolds number of 49, and the particle migration and fluid forces are investigated. The unsteady drag, unsteady lift, and particle behavior are investigated for different densities and particle configurations. The time evolution of the unsteady drag and lift is changed by interference by the planar shock wave, Mach stem convergence, and the shock wave reflected from the other particle. These two particles become closer after the shock wave passes than in the initial state under most conditions. Two particles placed in an in-line arrangement approach each other very closely due to the passage of a shock wave. On the other hand, two particles placed in a side-by-side arrangement are only slightly closer to each other after the shock wave passes between them. The pressure waves resulting from Mach stem convergence of the upstream particle and the reflected shock waves from the downstream particle are the main factors responsible for the force in the direction that pushes the particles apart. The wide distance between the two particles attenuates these pressure waves, and the particles reduce their motion away from each other.

DOI： 10.1063/5.0101365

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Abstract

In this study, a new method that optimizes a measurement condition in a lifetime-based simultaneous measurement of a pressure-sensitive paint (PSP) and a temperature-sensitive paint (TSP) is proposed for the improvement of the accuracy of the pressure measurement. An optimal gate is selected based on a pressure measurement error when calculating the pressure and the temperature simultaneously from measurement values of a PSP and a TSP. A shot noise of a PSP, a temperature error, and a fluctuation in an emission intensity ratio due to blurring were considered error factors of the PSP measurement. The pressure measurement error propagated from each error source was considered as an evaluation index in an optimization of a measurement condition. We evaluated 17 types of TSP characteristics and selected an optimal TSP and a measurement condition for the PSP measurement. Further, the optimized measurement condition was evaluated in a PSP/TSP simultaneous measurement using a coupon-based test. The optimal measurement condition obtained based on the proposed method and an empirical selection method were compared by a PSP/TSP simultaneous measurement using a coupon-based test. A small-pressure measurement error, i.e. high pressure-measurement accuracy, was realized by the proposed method in the simultaneous lifetime-based method of a PSP and a TSP. In addition to the analyses above, the blurring effects were found to be minor and briefly summarized in appendices.

DOI： 10.1088/1361-6501/ac769b

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：American Institute of Aeronautics and Astronautics ({AIAA})  

Distributions of the pressure and mass transfer coefficient on rotating blades under low-pressure (low-Reynoldsnumber) conditions were visualized, whereas the latter is closely related to the skin-friction distribution. Two types of optical measurement techniques, lifetime-based pressure-sensitive paint (PSP) measurements and sublimation visualization, were implemented for the experiment inside a low-pressure chamber. For the lifetime-based PSP measurement, different types of PSP were compared, and the one most suitable in low-pressure applications was selected. In addition, the gate time setting for the low-pressure condition was determined. For the sublimation method, naphthalene was selected as the sublimation surface based on previous studies. The rotating blade test model was a 0.3-m-diam rotor system with two rectangular blades with an aspect ratio of two. The experiments were carried out at a rotational speed of 2400 rpm and at an ambient pressure of 10 kPa. The three-fourth-span Reynolds number was 9000. The pitch angle of the blades was set to 0–20 deg. Both methods successfully illustrated clear images of the distribution of pressure and mass transfer coefficients on the upper surface of the blade, and the measurement in the low-pressure environment was successful.

DOI： 10.2514/1.J061638

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Scopus

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

We developed and evaluated an anodized-aluminum pressure-sensitive paint (AA-PSP) with new formulations of free-base porphyrin, H2TCPP, as an optical unsteady pressure sensor. The luminophore H2TCPP has quite a short fluorescent lifetime (2.4 ns on the condition of the AA-PSP). The fluorescence spectroscopy result shows that the excitation wavelength of H2TCPP corresponds to violet-colored (425 nm) and green-colored (longer than 520 nm) lights. The pressure sensitivity is sufficiently high for the pressure sensor (0.33-0.51%/kPa) and the temperature sensitivity is very low (0.07-1.46%/K). The photodegradation of the AA-PSPs is not severe in both excitation light sources of the green LED and the Nd:YAG laser. The resonance tube experiment result shows the cut-off frequency of the AA-PSPs is over 9.0 kHz, and the results of the shock tube experiment show the 10 µs order time constant of the normal shock wave.

DOI： 10.3390/s22176401

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PubMed

Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.jweia.2022.105043

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Scopus

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

Signal processing methods that remove noise due to atmospheric fluctuation and image sensors and extract fluid phenomena from schlieren images obtained in the low-density wind tunnel test were developed together with the highly sensitive schlieren measurement setup. Time-series schlieren images of the flow around a triangular airfoil were analyzed, and the effectiveness of noise reduction methods using the randomized singular value decomposition and band-pass filtering using the fast Fourier transform (FFT) and the inverse FFT were investigated. The proposed method succeeded in removing noise by taking advantage of the frequency difference between the noise and fluid phenomena, and the fluid phenomena around the airfoil were clearly visualized at a Reynolds number of 3000 and a Mach number of 0.15.

DOI： 10.1007/s12650-022-00829-8

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Publishing type：Research paper (scientific journal)   Publisher：American Institute of Aeronautics and Astronautics ({AIAA})  

Martian conditions present various challenges when designing rotorcraft. Specifically, the thin atmosphere and low sound speed require Martian rotor blades to operate in a low-Reynolds-number (1000–10,000) compressible regime, for which conventional airfoils are not designed. Here, we use PyFR to undertake high-order direct numerical simulations (DNS) of flow over a triangular airfoil at a Mach number of 0.15 and Reynolds number of 3000. Initially, spanwise periodic DNS are undertaken. Extending the domain-span-to-chord ratio from 0.3 to 0.6 leads to better agreement with wind-tunnel data at higher angles of attack, when the flow is separated. This is because smaller domain spans artificially suppress three-dimensional breakdown of coherent structures above the suction surface of the airfoil. Subsequently, full-span DNS in a virtual wind tunnel are undertaken, including all wind-tunnel walls. These capture blockage and wall boundary-layer effects, leading to better agreement with wind-tunnel data for all angles of attack compared to spanwise periodic DNS. The results are important in terms of understanding discrepancies between previous spanwise periodic DNS and wind-tunnel data. They also demonstrate the utility of high-order DNS as a tool for accurately resolving flow over triangular airfoils under Martian conditions.

DOI： 10.2514/1.J061454

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Scopus

Publishing type：Research paper (international conference proceedings)   Publisher：American Institute of Aeronautics and Astronautics  

DOI： 10.2514/6.2022-3606

Scopus

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

We propose a markerless image alignment method for pressure-sensitive paint measurement data replacing the time-consuming conventional alignment method in which the black markers are placed on the model and are detected manually. In the proposed method, feature points are detected by a boundary detection method, in which the PSP boundary is detected using the Moore-Neighbor tracing algorithm. The performance of the proposed method is compared with the conventional method based on black markers, the difference of Gaussian (DoG) detector, and the Hessian corner detector. The results by the proposed method and the DoG detector are equivalent to each other. On the other hand, the performances of the image alignment using the black marker and the Hessian corner detector are slightly worse compared with the DoG and the proposed method. The computational cost of the proposed method is half of that of the DoG method. The proposed method is a promising for the image alignment in the PSP application in the viewpoint of the alignment precision and computational cost.

DOI： 10.3390/s22020453

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Scopus

PubMed

Publishing type：Research paper (international conference proceedings)  

This study proposes a reservoir computing reduced-order model (RCROM) of the post-stall flow around NACA0015 airfoil based on the time series velocity field, and the estimation accuracy of RCROM is evaluated compared to that of a linear reduced-order model (LROM). The data is experimentally obtained by the particle image velocimetry measurement with the chord Reynolds number of 6.4 × 104, and the angle of attack of 18 deg. The low-dimensional description of the velocity field can be obtained by decomposing the velocity field with a proper orthogonal decomposition (POD) technique and treating the dominant POD modes amplitude as temporal variables. The nonlinear function that estimates one step ahead of the POD modes amplitude is obtained by the reservoir computing. Similarly, the linear function is calculated by postulating the linear development of the POD modes amplitudes. The hyper parameters of RCROM are tuned by the Bayesian optimization. The results show that the estimation accuracy of RCROM is better than that of LROM under the condition that the number of target POD modes is one, three, and five.

DOI： 10.2514/6.2022-3242

Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES  

<p>In the present study, the visualization of compressible flow around a particle/particles including wake vortices and drag estimation were conducted through shock-particle interaction experiments. An experimental method that can investigate flow over isolated and clustered particle(s) (with a minimum diameter of 0.3 mm) interacting with a planar shock was established. For flow visualization, the Mach number (<i>M</i>) and Reynolds number (<i>Re</i>) based on the relative velocity between the particle and the quantities behind the planar shock wave were 0.46 ≤ <i>M</i> ≤ 1.24 and 3500 ≤ <i>Re</i> ≤ 9800, respectively. The present measurement system succeeded in visualizing flow structures not only for shock waves, but also wake structures formed behind the particle(s) under subsonic and transonic conditions, and the Mach number effect was provided. The mean drag coefficient was estimated from the time-position data of the particle at 3100 ≤ <i>Re</i> ≤ 9800 and <i>M</i> = 0.46. The estimated drag coefficient was close to that of the value estimated by the drag model and previous experiments. The flowfield around clustered particles was visualized and its breakdown process was observed. The particle cluster dispersed due to aerodynamic interference. Particularly, the particles located on the upper side of the particle cluster moved upward against the gravitational force.</p>

DOI： 10.2322/tjsass.65.185

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CiNii Research

Publishing type：Research paper (international conference proceedings)  

The method for estimating time-resolved three-dimensional velocity field is developed to investigate the high spatial and temporal flow structures of the supersonic jet with the Mach number of 1.35. The supersonic jet were measured by non-time-resolved particle image velocimetry (PIV) measurement and time-resolved near-field acoustic measurement. The multi-time-delay modified linear stochastic estimation (MTD-mLSE) was applied into the reduced-order velocity data and the Fourier coefficient acoustic data which is decomposed by the complex Fourier expansion series. The four azimuhal modes were reconstructed from the developed method. The azimuthal mode 0 is the axisymmetric mode, the azimuthal mode 1 and 3 are helical mode and the azimuthal mode 2 is the helical and the lateral modes. The dominant azimuthal mode of the Mach number of 1.35 can be identified from time-resolved three-dimensional velocity fields which are the sum of the mean and the fluctuations components.

DOI： 10.2514/6.2022-3024

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>In this study, steady drag force measurements and time-resolved schlieren visualization were conducted for subsonic compressible flows around a rectangular cylinder with a side length ratio from 0.5 to 1.2. The effect of the compressibility on the critical geometry was evaluated based on the drag coefficient using a low-density wind tunnel in the Mach number range from 0.1 to 0.6 at the Reynolds number of <i>O</i>(10³). In addition, the relationship between the change in the drag coefficient and the flow field was discussed. The side length ratio that the drag coefficient takes the maximum was confirmed to change with the Mach numbers. Remarkably, the peak drag coefficient at the Mach number of 0.6 appears at the side length ratio of 1.0, even though the side length ratio of the critical geometry at the incompressible flow is approximately 0.65. However, the sharp peak in the drag coefficient which is observed in the previous incompressible studies could not be reproduced even at the Mach number of 0.2. This is considered to be due to the lack of the spanwise length of the model or the Reynolds number effects. The schlieren images showed the influence of the Mach number on the location of the vortex formation, and the location moves downstream as the Mach number increases. The change in the flow fields behind rectangular cylinders causes a change in the back pressure, and it might result in a sudden change in the drag coefficient.</p>

DOI： 10.1299/jsmefed.2022.os03-04

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Urolithiasis is a disease in which calcium oxalate crystallizes in the urinary tract, and has a high recurrence rate. It is necessary to consider the burden on the body by surgical treatment, therefore, treatment methods that effectively promote spontaneous stone passage are required. In this study, to develop a working accelerated renal pelvis and calyx simulator, we visualized the orbit of a renal callus model by using a physiological 3D renal pelvis and calyx model and an acceleration motion experiment system. According to analysis from experiments, it was confirmed that the simulator is able to reproduce spontaneous stone passage similar to our experiment results. By establishing a spontaneous stone passage prediction simulator, it will be possible to devise a method to effectively promote spontaneous stone passage in patients. By reducing the morbidity of urinary lithiasis that requires surgery, it is expected to reduce the burden on patients and medical sites.</p>

DOI： 10.1299/jsmekanto.2022.28.15f10

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Urolithiasis is a disease in which calcium oxalate crystallizes in the urinary tract, and has a high recurrence rate. It is necessary to consider the burden on the body by surgical treatment, therefore, treatment methods that effectively promote spontaneous stone passage are required. In this study, we investigated the effects of angular velocity on spontaneous stone passage and established the parameters needed to develop a working accelerated renal pelvis and calyx simulator. According to analysis from experiments, it was confirmed that the simulator using our established parameters is able to reproduce spontaneous stone passage similar to our experiment results. By establishing a spontaneous stone passage prediction simulator, it will be possible to devise a method to effectively promote spontaneous stone passage in patients. By reducing the morbidity of urinary lithiasis that requires surgery, it is expected to reduce the burden on patients and medical sites.</p>

DOI： 10.1299/jsmemecj.2022.j025-05

CiNii Research

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>The time-resolved three-dimensional velocity measurement of an underexpanded jet is performed using time-resolved microphone and non-time-resolved particle image velocimetry (PIV) measurements. Flapping screech jets at the nozzle pressure ratio (NPR) of 2.97 was measured and analyzed using the proposed approach. It was found that the dominant azimuthal mode at the present case is flapping mode. The screech tones are strongly associated with the first two proper orthogonal decomposition modes of the dominant azimuthal modes of the microphone data. The azimuthal characteristics of these modes are helical mode, and the rotation direction is opposite. These findings are qualitatively consistent with the previous results. The flapping structure rotates over a wide range of temporal scales, with random changes in direction of rotation.</p>

DOI： 10.1299/jsmefed.2022.os03-48

CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/TSP.2022.3224643

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Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/TSP.2022.3212150

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Scopus

Publishing type：Research paper (scientific journal)  

The exact dynamic mode decomposition (DMD) was applied to the nonsequential image dataset obtained by the double-pulsed schlieren measurement of a supersonic impinging jet, and the effect of the dataset length on the obtained spatial modes and estimated frequencies of the aeroacoustic fields was investigated. The Mach number of the jet was 2.0, the Reynolds number based on the diameter of the nozzle exit was 1.0 × 10 6 and the distance between the nozzle exit and the flat plate was four times the nozzle diameter long. The DMD modes extract the characteristic pattern and its frequency that relate to the aeroacoustic fields. The estimated frequencies of DMD modes were compared with the acoustic spectra measured using microphones. The estimated frequency of the DMD mode that has the largest amplitude approximately coincides with that of the highest peak in the acoustic spectra regardless of the dataset length. However, the variation in the estimated frequencies of the high-order DMD modes increases when the dataset length is short. Although the estimated frequencies of the second and third DMD modes did not match the peak frequencies of the acoustic spectra, the estimation accuracy of the frequency of the modes can be improved by recalculating the frequency based on the wavelength of the corresponding spatial mode. The order of the amplitude of DMD modes did not agree with the order of the peak magnitude in the acoustic spectra, except for the first mode. This is because the schlieren method visualizes the density gradient resulting in emphasizing the high-frequency fluctuations. This mismatch was mitigated by correcting the acoustic spectrum considering the first derivative of the acoustic spectrum. Therefore, the verification of the estimation accuracy considering the data characteristics is important when the exact DMD analysis is applied to the noisy experimental data. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s12650-022-00836-9

Scopus

Publishing type：Research paper (international conference proceedings)  

The present study proposes a framework of the superresolution measurement based on the dynamic mode decomposition (DMD) with the Kalman filter and Rauch–Tung–Striebel smoother. The dual-planar particle image velocimetry (PIV) systems were constructed to acquire the paired velocity fields of a Mach 1.1 supersonic jet. The acoustic measurement was simultaneously performed, and the velocity and acoustic data are used for the superresolution. Although the dual PIV system measures the basic characteristics of the velocity fields, all the DMD modes calculated by the exact DMD are decay modes due to the measurement noise. The superresolved velocity field shows smooth convection of the large-scale structures at the downstream side. Therefore, the proposed method is effective to reconstruct the entire flow fluctuation because the DMD modes express the linear dynamical system of the velocity fields.

DOI： 10.2514/6.2022-3065

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/ACCESS.2022.3193157

Web of Science

Scopus

Publishing type：Research paper (international conference proceedings)  

In this study, a pressure distribution inside a two-dimensional rectangular cavity with a ratio L/D= 5.0 of the cavity length L to the depth D over supersonic flow was obtained using anodized-aluminum pressure-sensitivity paint (AA-PSP). The freestream Mach number was M = 1.85 and the frequencies of the dominant cavity modal phenomena called a Rossiter mode were on the order of 10 kHz. Fast-responding AA-PSP using free-based porphyrin luminophore and a high-frequency-repetition pulse laser were applied, and instantaneous pressure fields were measured. This measurement system has a 60 kHz sampling rate and is suitable for the purpose of a direct measurement of the Rossiter mode phenomena. The result of the power spectral density (PSD) of the PSP measurement showed that this measurement system is capable of observing phenomena of approximately 18 kHz. Time-resolved schlieren and dynamic pressure transducer measurements were employed and PSD obtained by the PSP measurement was validated. The frequency spectra and amplitudes of PSD obtained by the PSP measurement were in good agreement with those obtained by the schlieren and dynamic pressure transducer data. A dynamic mode decomposition analysis was also conducted for sequential data of PSP, and the frequency and the energy distribution at the peak frequency could be extracted.

DOI： 10.2514/6.2022-2959

Scopus

Publishing type：Research paper (international conference proceedings)  

The objective of this study is to develop digital signal processing methods that reduce noise caused by atmospheric fluctuation and image sensors and extract signal of fluid phenomena from data obtained by the highly sensitive schlieren measurement in the low-density wind tunnel. Time-series schlieren images of the flow around a triangular airfoil were used for analysis, and the effectiveness of noise reduction methods based on the randomized singular value decomposition (RSVD). In the proposed method, noise and signal of fluid phenomena were separated by frequency components using fast Fourier transform (FFT) and inverse FFT in advance, and the flow was visualized at Re= 3000 and M = 0.15, where the signal-to-noise ratio was particularly low.

DOI： 10.2514/6.2022-4166

Scopus

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

A comprehensive review of all relevant experimental data was completed, including recent data for the drag coefficient for a sphere in supersonic and hypersonic flows. The primary characterization parameter included the relative Mach, Knudsen, and Reynolds numbers based on the relative velocity, the sphere diameter, and other parameters. This review of data showed that the previously proposed nexus at a Reynolds number below 45 was not strictly met, and it instead included a weak transonic bump, which was identified numerically for the first time with the present simulations. New continuum-gas and rarefied-gas simulations were conducted and were combined with the expanded experimental dataset to improve the quantitative description of the drag coefficient in this region. The results indicated that a quasi nexus bridges the rarefaction regime and the compressible flow regimes. The comprehensive dataset was then used to develop new empirical models for the drag coefficient that showed improved robustness and accuracy as compared to previous models. These models are limited by the critical Reynolds number associated with boundary-layer transition on the sphere, which was found to increase substantially with the sphere Mach number.

DOI： 10.2514/1.J060153

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Scopus

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

The present study proposes a sensor selection method based on the proximal splitting algorithm and the A-optimal design of experiment using the alternating direction method of multipliers (ADMM) algorithm. The performance of the proposed method was evaluated with a random sensor problem and compared with previously proposed methods, such as the greedy and convex relaxation methods. The performance of the proposed method is better than the existing greedy and convex relaxation methods in terms of the A-optimality criterion. Although, the proposed method requires a longer computational time than the greedy method, it is quite shorter than that of convex relaxation method in large-scale problems. Then the proposed method was applied to the data-driven sparse-sensor-selection problem. The dataset adopted was the National Oceanic and Atmospheric Administration optimum interpolation sea surface temperature dataset. At a number of sensors larger than that of the latent variables, the proposed method showed similar and better performance compared with previously proposed methods in terms of.

DOI： 10.1109/JSEN.2021.3073978

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Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

The characteristics of fast-response pressure-sensitive paints (PSPs) in low-pressure conditions were evaluated. Three representative porous binders were investigated: polymer-ceramic PSP (PC-PSP), anodized-aluminum PSP (AA-PSP), and thin-layer chromatography PSP (TLC-PSP). For each PSP, two types of luminophores, Pt(II) meso-tetra (pentafluorophenyl) porphine (PtTFPP) and tris(bathophenanthroline) ruthenium dichloride (Ru(dpp) ), were used as sensor molecules. Pressure sensitivities, temperature sensitivities, and photodegradation rates were measured and evaluated using a pressure chamber. The effect of ambient pressure on the frequency response was investigated using an acoustic resonance tube. The diffusivity coefficients of PSPs were estimated from the measured frequency response and luminescent lifetime, and the governing factor of the frequency response under low-pressure conditions was identified. The results of static calibration show that PC-PSP/PtTFPP, AA-PSP/Ru(dpp) , and TLC-PSP/PtTFPP have high pressure sensitivities that exceed 4%/kPa under low-pressure conditions and that temperature sensitivity and photodegradation rates become lower as the ambient pressure decreases. Dynamic calibration results show that the dynamic characteristics of PSPs with PtTFPP are dependent on the ambient pressure, whereas those of PSPs with Ru(dpp) are not influenced by the ambient pressure. This observation indicates that the governing factor in the frequency response under low-pressure conditions is the lifetime for PC-PSP and TLC-PSP, whereas the governing factor for AA-PSP is diffusion. 3 3 3

DOI： 10.3390/s21093187

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Scopus

PubMed

Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract: This study aims to isolate and evaluate the influence of a corrugation on flow structures and aerodynamics under compressible low Reynolds number conditions, and to compare it to simpler but well-known model: the flat plate. The simplified corrugated model was made by a flat surface with only two corrugations on the leading edge. The models only differ for the corrugations on the leading edge. Force values were measured at a Reynolds number ranging from 10,000 to 25,000 and at a Mach number from 0.2 to 0.6. Pressure sensitive paint was used at the same flow conditions and the pressure distribution over the models was obtained. Schlieren visualization was also conducted and flow characteristics were observed. Detailed analysis showed that the corrugated model experiences strong depression on the leading edge caused by the separation of the boundary layer. Because of the presence of the corrugation, the shear layer transitions to turbulent rapidly and reattaches to the surface before reaching the summit of the first corrugation, separating again at its peak. Instabilities in the shear layer were dissipated thanks to the shape of the corrugation allowing pressure recovery and discouraging flow separation. The flow reattaches before reaching the trailing edge. The results showed that the transition of the boundary layer was accelerated as the Reynolds number increases on corrugated model, leading to a stronger negative pressure zone in the leading edge. Due to pressure recovery being less effective, lead to similar performances for the range of studied Reynolds numbers. The compressibility effects resulted in a delay on the transition of the instability of the shear layer, negatively affecting the intensity of the pressure gradients as well as pressure recovery. This contributed to the variation in the performance of the wing. As a result, the corrugated model has a better aerodynamic performance compared to the flat plate at low Reynolds numbers, but not for higher Mach numbers. Graphic abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s00348-021-03164-0

Web of Science

Scopus

Other Link： https://link.springer.com/article/10.1007/s00348-021-03164-0/fulltext.html

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

Flow over a flat plate with a 5% thickness ratio is investigated by schlieren visualization in compressible low-Reynolds-number conditions. The results show that flow separates at the leading-edge and laminar separation-bubble forms. The position of the maximum root mean square of the schlieren image which is related to the position of the vortex shedding moves downstream as a Mach number increases. Furthermore, the two-dimensional structure of generated vortices is maintained up to the trailing edge at the Mach number of 0.66. The frequency analysis of the time-series intensity value of the schlieren images also shows that the flow is stabilized with increasing the Mach number. The position of the end of the pressure plateau region matches the position where the root-mean-square value of the intensity image becomes a maximum due to vortex shedding.

DOI： 10.1088/1873-7005/abe04c

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Scopus

Other Link： https://iopscience.iop.org/article/10.1088/1873-7005/abe04c/pdf

Language：English   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

The effects of the oxygen mole fraction on the static properties of pressure-sensitive paint (PSP) were investigated. Sample coupon tests using a calibration chamber were conducted for poly(hexafluoroisopropyl methacrylate)-based PSP (PHFIPM-PSP), polymer/ceramic PSP (PC-PSP), and anodized aluminum PSP (AA-PSP). The oxygen mole fraction was set to 0.1–100%, and the ambient pressure (P ) was set to 0.5–140 kPa. Localized Stern–Volmer coefficient B increased and then decreased with increasing oxygen mole fraction. Although B depends on both ambient pressure and the oxygen mole fraction, its effect can be characterized as a function of the partial pressure of oxygen. For AA-PSP and PHFIPM-PSP, which are low-pressure-and relatively low-pressure-type PSPs, respectively, B peaks at P ref < 12 kPa. In contrast, for PC-PSP, which is an atmospheric-pressure-type PSP in the investigated range, B does not have a peak. B has a peak at a relatively high partial pressure of oxygen due to the oxygen permeability of the polymer used in the binder. The peak of S , which is the emission intensity change with respect to normalized pressure fluctuation, appears at a lower partial pressure of oxygen than that of B . This is because the intensity of PSP becomes quite low at a high partial pressure of oxygen even if B is high. Hence, the optimal oxygen mole fraction depends on the type of PSP and the ambient pressure range of the experiment. This optimal value can be found on the basis of the partial pressure of oxygen. ref local local local O2 local local PR local local

DOI： 10.3390/s21041062

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Scopus

PubMed

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Urolithiasis is a disease in which calcium oxalate crystallizes in the urinary tract, and has a high recurrence rate. It is necessary to consider the burden on the body by surgical treatment, therefore, treatment methods that effectively promote spontaneous stone passage are required. In this study, we verified the results of the drainage orbit visualization using a 3D kidney calix model and an acceleration motion experiment system to identify the parameters necessary for an accelerated kidney calix simulator. From analysis and experiments, it was confirmed that this simulator can reproduce spontaneous stone passage similar to the experiment in a kidney calix for each angular velocity. By establishing a spontaneous stone passage prediction simulator, it will be possible to devise a method to effectively promote spontaneous stone passage. By reducing the morbidity of urinary olithiasis that requires surgery, it is expected to reduce the burden on patients and medical sites.</p>

DOI： 10.1299/jsmekanto.2021.27.10d14

CiNii Research

Publishing type：Research paper (international conference proceedings)  

Supersonic jets of M=1.35 and 2.0 were measured by time-resolved near-field acoustic measurement and non-time-resolved particle image velocimetry (PIV). The multi-time-delay modified linear stochastic estimation (MTD-mLSE) was applied to the reduced-order acoustic and velocity field data based on the proper orthogonal decomposition (POD) coefficients. Time-resolved snapshots of the velocity field reconstructed by MTD-mLSE show the smooth convection of the velocity fluctuations. The fluctuations of the shock cell structure that seems to be the noise source of the screech tone were observed.

DOI： 10.2514/6.2021-2106

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Computers, Materials and Continua (Tech Science Press)  

DOI： 10.32604/cmes.2021.016603

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Scopus

Publisher：AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2021  

Applicability of exact dynamic mode decomposition (DMD) for the evaluation of the aeroacoustic field was investigated on the nonsequential data obtained by the double-pulsed schlieren measurement of the supersonic impinging jet. The Mach number of the jet was 2.0, the Reynolds number based on the diameter of the nozzle exit was 1.0×106, and the distance between the nozzle exit and the flat plate was 4 times the nozzle diameter. The effect of the length of a dataset on the obtained spatial modes and estimated frequencies of the acoustic field was provided. The estimated frequencies were compared with the result of microphone measurements. As a result, a non-time-resolved measurement system was demonstrated to be capable of clarifying physical phenomena and estimating the characteristic frequencies by applying DMD to paired images with a short time interval. In addition, the dataset length used affects the estimation accuracy, and its evaluation is important for discussion.

DOI： 10.2514/6.2021-2217

Scopus

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

In this paper, the sparse sensor placement problem for least-squares estimation is considered, and the previous novel approach of the sparse sensor selection algorithm is extended. The maximization of the determinant of the matrix which appears in pseudo-inverse matrix operations is employed as an objective function of the problem in the present extended approach. The procedure for the maximization of the determinant of the corresponding matrix is proved to be mathematically the same as that of the previously proposed QR method when the number of sensors is less than that of state variables (undersampling). On the other hand, the authors have developed a new algorithm for when the number of sensors is greater than that of state variables (oversampling). Then, a unified formulation of the two algorithms is derived, and the lower bound of the objective function given by this algorithm is shown using the monotone submodularity of the objective function. The effectiveness of the proposed algorithm on the problem using real datasets is demonstrated by comparing with the results of other algorithms. The numerical results show that the proposed algorithm improves the estimation error by approximately 10% compared with the conventional methods in the oversampling case, where the estimation error is defined as the ratio of the difference between the reconstructed data and the full observation data to the full observation. For the NOAA-SST sensor problem, which has more than ten thousand sensor candidate points, the proposed algorithm selects the sensor positions in few seconds, which required several hours with the other algorithms in the oversampling case on a 3.40 GHz computer.

DOI： 10.1109/ACCESS.2021.3076186

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Scopus

Publishing type：Research paper (scientific journal)   Publisher：Institute of Electrical and Electronics Engineers ({IEEE})  

The problem of selecting an optimal set of sensors estimating a high-dimensional data is considered. Objective functions based on D-, A-, and E-optimality criteria of optimal design are adopted to greedy methods, that maximize the determinant, minimize the trace of the inverse, and maximize the minimum eigenvalue of the Fisher information matrix, respectively. First, the Fisher information matrix is derived depending on the numbers of latent state variables and sensors. Then, a unified formulation of the objective function based on A-optimality is introduced and proved to be submodular, which provides the lower bound on the performance of the greedy method. Next, greedy methods based on D-, A-, and E-optimality are applied to randomly generated systems and a practical dataset concerning the global climate; these correspond to an almost ideal and a practical case in terms of statistics, respectively. The D- and A-optimality-based greedy methods select better sensors. The E-optimality-based greedy method does not select better sensors in terms of the index of E-optimality in the oversample case, while the A-optimality-based greedy method unexpectedly does so in terms of the index of E-optimality. The poor performance of the E-optimality-based greedy method is due to the lack of submodularity in the E-optimality index and the better performance of the A-optimality-based greedy method is due to the relation between A- and E-optimality. Indices of D- and A-optimality seem to be important in the ideal case where the statistics for the system are well known, and therefore, the D- and A-optimality-based greedy methods are suitable for accurate reconstruction. On the other hand, the index of E-optimality seems to be critical in the more practical case where the statistics for the system are not well known, and therefore, the A-optimality-based greedy method performs best because of its superiority in terms of the index of E-optimality.

DOI： 10.1109/ACCESS.2021.3067712

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Scopus

arXiv

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Cambridge University Press ({CUP})  

In the present study, compressible low-Reynolds-number flow past a stationary isolated sphere was investigated by direct numerical simulations of the Navier-Stokes equations using a body-fitted grid with high-order schemes. The Reynolds number based on free-stream quantities and the diameter of the sphere was set to be between 250 and 1000, and the free-stream Mach number was set to be between 0.3 and 2.0. As a result, it was clarified that the wake of the sphere is significantly stabilized as the Mach number increases, particularly at the Mach number greater than or equal to 0.95, but turbulent kinetic energy at the higher Mach numbers conditions is higher than that at the lower Mach numbers conditions of similar flow regimes. A rapid extension of the length of the recirculation region was observed under the transitional condition between the steady and unsteady flows. The drag coefficient increases as the Mach number increases mainly in the transonic regime and its increment is almost due to the increment in the pressure component. In addition, the increment in the drag coefficient is approximately a function of the Mach number and independent of the Reynolds number in the continuum regime. Moreover, the effect of the Mach and Reynolds numbers on the flow properties such as the drag coefficient and flow regime can approximately be characterized by the position of the separation point.

DOI： 10.1017/jfm.2020.629

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Scopus

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

In the present study, we proposed a simple collision algorithm, which can be handled arbitrarily shaped objects, for flow solvers using the immersed boundary method (IBM) based on the level set and ghost cell methods. The proposed algorithm can handle the collision of the arbitrarily shaped object with little additional computational costs for the collision calculation because collision detection and calculation are performed using the level set function and image point, which are incorporated into the original IBM solver. The proposed algorithm was implemented on the solid-liquid IBM flow solver and validated by simulations of the flow over an isolated cylinder and sphere. Also, grid and time step size sensitivity on the total energy conservation of objects were investigated in cylinder-cylinder, cylinder-red-blood-cells-shaped (RBC-shaped) objects, sphere-sphere, and sphere-flat plate interaction problems. Through validation, good agreement with previous studies, grid and time step size convergence, and sufficient total energy conservation were confirmed. As a demonstration, the drafting, kissing, and tumbling processes were computed, and it was confirmed that the present result by the proposed method is similar to the previous computations. In addition, particle-laden flow in a channel including obstacles with collision and adhesion phenomena and the interaction of cylinders and wavy-wall were computed. The results of these simulations reveal the capability of solving a flow containing arbitrarily shaped moving objects with collision phenomena by a simple proposed method.

DOI： 10.1002/fld.4826

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Scopus

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：{IOP} Publishing  

In the present study, new performance evaluation parameters for pressure-sensitive paint (PSP) were proposed, and the effects of ambient pressure on the characteristics of the PSP were evaluated. The proposed parameters allow us to determine the optimal pressure range on the basis of the following quantities: (1) the Stern-Volmer coefficient, (2) the normalized pressure sensitivity to intensity changes due to flow-induced pressure fluctuations, (3) the change in the intensity of PSP emissions in response to the given change in pressure, and (4) the signal-to-noise ratio of the change in the PSP emission intensity due to flow-induced pressure fluctuations. The characteristics of several types of PSP were evaluated using the proposed parameters. It was demonstrated that the proposed parameters enable a comparison of the effects of ambient pressure on the characteristics of PSP, and the optimal pressure range for aerodynamic measurements could be successfully identified for the different PSP.

DOI： 10.1088/1361-6501/ab81bb

Web of Science

Scopus

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

In the present study, a compressible low-Reynolds-number flow over a circular cylinder was investigated using a low-density wind tunnel with time-resolved schlieren visualizations and pressure and force measurements. The Reynolds number based on freestream quantities and the diameter of a circular cylinder was set to be between 1000 and 5000, and the freestream Mach number between 0.1 and 0.5. As a result, we have clarified the effect of on the aerodynamic characteristics of flow over a circular cylinder at. The results of the schlieren visualization showed that the trend of effect on the flow field, that are the release location of the Kármán vortices, the Strouhal number of vortex shedding and the maximum width of the recirculation, is changed at approximately. In addition, the spanwise phase difference of the surface pressure fluctuation was captured by the measurement using pressure-sensitive paint at approximately of higher- cases. The observed spanwise phase difference is considered to relate to the spanwise phase difference of the vortex shedding due to the oblique instability wave on the separated shear layer caused by the compressibility effects. The Strouhal number of the vortex shedding is influenced by and , and those effects are nonlinear. However, the effects of and can approximately be characterized by the maximum width of the recirculation. In addition, the effect on the drag coefficient can be characterized by the maximum width of the recirculation region and the Prandtl-Glauert transformation.

DOI： 10.1017/jfm.2020.221

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：{MDPI} {AG}  

A temperature-sensitive paint (TSP) using a chameleon luminophore [Tb Eu (hfa) (dpbp)] is proposed. The chameleon luminophore was dispersed in isobutyl methacrylate polymer in a toluene solvent to fix it on a sample coupon. Temperature and pressure sensitivities of the chameleon luminophore-based TSP were measured using a spectrofluorophotometer. The emission for each wavelength was confirmed to be dependent on the temperature and pressure. The temperature and pressure sensitivities of the TSP were 0.81–2.8%/K and 0.08–0.12%/kPa, respectively. Higher temperature sensitivity can be obtained using the ratio of emissions from the two lanthanide ions, Tb and Eu . The temperature sensitivity when using the ratio of the emission intensities at 616 nm derived from Eu and at 545 nm derived from Tb was 3.2%/K, which was the highest value in the present study. In addition, the pressure sensitivity for the case using the ratio of the emission intensities at 616 and 545 nm was 4.8 × 10 %/kPa. Higher temperature sensitivity and lower pressure sensitivity than that with a single wavelength can be achieved using the ratio of the emission intensities at the two peak wavelengths derived from Tb and Eu . 0.99 0.01 3 n III III III III −2 III III

DOI： 10.3390/s20092623

Web of Science

Scopus

PubMed

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media {LLC}  

In this study, free-flight tests of a sphere for Reynolds numbers between 3.9 × 10 and 3.8 × 10 and free-flight Mach numbers between 0.9 and 1.6 were conducted using a ballistic range, and compressible low-Reynolds-number flows over an isolated sphere were investigated with the schlieren technique. The flow visualization was carried out under low-pressure conditions with a small sphere (minimum diameter of 1.5 mm) to produce compressible low-Reynolds-number flow. Also, time-averaged images of the flow near the sphere were obtained and compared to previous numerical results for Reynolds numbers between 50 and 1000. The experimental results clarified the structure of shock waves, recirculation region, and wake structures at the Reynolds number of 10 –10 under transonic and supersonic flows. As a result, the following characteristics were clarified: (1) the amplitude of the wake oscillation was attenuated as the free-flight Mach number increased; (2) use of singular value decomposition permitted extraction of the mode of the wake structure even when schlieren images were unclear due to severe condition, and different modes in the wake structure were identified; (3) the Reynolds number had little effect on the separation point, but the length of the recirculation region increased as the Reynolds number decreased; and (4) the wake diameter at the end of the recirculation region decreased as the Mach number increased. 3 5 3 5

DOI： 10.1007/s00193-019-00924-0

Web of Science

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

<p>Urinary stones are calcium oxalate stones in the urinary tract. According to the 2005 national survey, the lifetime prevalence of urinary stones is 15.1% for Japanese men and 6.8% for women. In addition, 96% of the whole are upper urinary tract stones such as kidney stones. Small stones are excreted in the urine without feeling great pain in the process of excreting, but when they become large, natural excretory becomes difficult and it causes severe pain when it descends into a narrow ureter. Therefore, it is desirable to establish a treatment that can be discharged before growing. However, the mechanism of the flow around kidney stones from the upper urinary tract has not been fully investigated, and confirmation by follow-up observation is also difficult. Furthermore, the natural excretion can be difficult from the lower kidney calix because of the gravity. We analyzed flows around a stone by numerical simulation using immersed boundary method. First, the numerical results and the actual experiment were compared with the free fall sphere. As a result, accuracy of the numerical simulation was confirmed. Furthermore, the lower kidney calix model was created based on medical computed tomography images, and the flow of stones was analyzed by numerical simulation.</p>

DOI： 10.1299/jsmefed.2019.os9-09

CiNii Research

Publishing type：Research paper (international conference proceedings)  

In this study, a compressible low-Reynolds number flow over a circular cylinder was investigated by schlieren visualization and the force measurement. A Reynolds number based on freestream quantities and a diameter of a cylinder is set to be 1000 = Re = 5000 and a Mach number is set to be 0.1 = M = 0.5 by using the low-pressure wind tunnel. From the schlieren visualization, frequency of the vortex shedding was obtained by performing frequency analysis on the time series schlieren images. Near wake structure by the circular cylinder is measured by time-averaged schlieren image. Even though M is less than 0.5, the structure of the flow fields changes depending on M. The effect of M on the scale of wake structure depends on Re. Under the condition at Re of 1000-3000, the scale becomes large as M increases more than 0.2. On the other hand, under the condition that Re is 4000-5000, it becomes small as M increase 0.3 or more St is revealed to be decrease for Re of 2000-3000 with increasing M, and St increases at Re of 4000-5000. From the force measurement, drag coefficient (Cd) and pressure distribution on a circular cylinder (Cp) obtained. The effect of M on Cd does not depend on Re, and Cd also increases as M increases. The effect of Re on Cd is also observed that Cd increases as Re increases and this trend doesn’t depend on M. The Cp decrease with Re increase. The M effect on Cp is that the range of Cp is enlarged with M increase.

DOI： 10.1115/AJKFluids2019-5164

Scopus

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

In this study, flow over a pair of vane-type vortex generator is investigated by solving the Navier–Stokes equation. A pair of the vane-type vortex generator implemented on a slip wall in laminar flow is considered so that the problem setting could be simple. The Reynolds number based on freestream quantities and the height of the vanes is set to be 500. The effect of the arrangement and geometry of vanes on the circulation coefficients, induced flow velocities, and aerodynamic force coefficients of VGs are investigated. In addition, a new non-dimensional circulation coefficient, normalized by freestream velocity and the height of the vortex core was introduced and its effectiveness is examined. This new parameter, Ct´, include the height of the vortex core, so that appears to be a better measure of VG effectiveness on momentum exchange. From the computational results, the wider arrangement can introduce the effective vortices with small drag. Also, the longer vanes can introduce strong and effective vortices with smaller drag coefficient.

DOI： 10.1115/AJKFluids2019-5312

Scopus

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

In this study, direct numerical simulation of the flow around a rotating sphere at high Mach and low Reynolds numbers is conducted to investigate the effects of rotation rate and Mach number upon aerodynamic force coefficients and wake structures. The simulation is carried out by solving the three-dimensional compressible Navier-Stokes equations. A free-stream Reynolds number (based on the free-stream velocity, density and viscosity coefficient and the diameter of the sphere) is set to be between 100 and 300, the free-stream Mach number is set to be between 0.2 and 2.0, and the dimensionless rotation rate defined by the ratio of the free-stream and surface velocities above the equator is set between 0.0 and 1.0. Thus, we have clarified the following points: (1) as free-stream Mach number increased, the increment of the lift coefficient due to rotation was reduced; (2) under subsonic conditions, the drag coefficient increased with increase of the rotation rate, whereas under supersonic conditions, the increment of the drag coefficient was reduced with increasing Mach number; and (3) the mode of the wake structure becomes low-Reynolds-number-like as the Mach number is increased.

DOI： 10.1017/jfm.2018.756

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Scopus

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier {BV}  

In this study, an analysis of the flow properties around an isolated sphere under isothermal conditions for flows with high Mach numbers and low Reynolds numbers is conducted via direct numerical simulation (DNS) of the three-dimensional compressible Navier–Stokes equations. The calculations are performed with a boundary-fitted coordinate system. The Reynolds number based on the diameter of the sphere and the freestream quantities is varied from 100 to 300, the freestream Mach number is varied between 0.3 and 2.0, and the temperature ratio between the sphere surface and the freestream is varied between 0.5 and 2.0. We focus on the effects of the Mach number and the temperature ratio on the flow properties. The results show the following characteristics: (1) unsteady vortex shedding from the sphere is promoted (suppressed) when the temperature ratio is less (greater) than unity; (2) the drag coefficient increases with the temperature ratio, but previous drag relations give poor prediction on effect of the temperature ratio on the drag coefficient in the continuum regime; (3) Nusselt number relations proposed in previous studies can be applied if the temperature ratio is close to unity under subsonic conditions; (4) the changes in several flow properties can be characterized by a separation point in the range investigated.

DOI： 10.1016/j.ijheatmasstransfer.2017.12.042

Web of Science

Scopus

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

This study was devoted to investigate the interaction between platelets and blood cells in a blood plasma by using computational fluid dynamics (CFD). In this study, we developed a flow solver to solve the two-dimensional incompressible solid–liquid multiphase flow including collision and adhesion effects. This solver is based on equally-spaced Cartesian mesh and immersed boundary method (IBM) to represent the platelets and red blood cells including the interaction. We proposed a new adhesion algorithm to simulate the collision and interaction of the platelet–platelet and platelet–blood vessel. This adhesive strength determined by Kelvin Voigt model is enforced on the immersed boundary. In addition, we introduced a collision algorithm for complex-shaped object to analyze the flow including real blood cells. In the previous study by Kamada et al. [1], the moving particle semi-implicit (MPS) method was adopted to simulate the behaviour of blood plasma, platelets and red blood cells. From this study, it was confirmed that the number of adhesion platelet increases with the value of shear rate at the wall. Then, in this study, we analyzed the solid–liquid multiphase channel flow to confirm the deposit of the platelet. The channel flow including an obstacle of a medical stent and the moving cylinders of platelets was investigated for the comparison with the previous study. The Reynolds number based on the channel height was set to be between 5 and 50. As results, we confirmed that the platelets adhere to the wall due to the separation and vortex generation behind the obstacle. The influence of the vortex became more effective with increasing the Reynolds number.

DOI： 10.2495/CMEM-V6-N1-162-175

Scopus

Authorship：Lead author   Publishing type：Research paper (scientific journal)   Publisher：{AIP} Publishing  

In this study, analysis of flow properties around a sphere and its aerodynamic coefficients in the high-Mach-and-low-Reynolds-numbers conditions is carried out by direct numerical simulations solving the three-dimensional compressible NavierStokes equations. The calculation is performed on a boundary-fitted coordinate system with a high-order scheme of sufficient accuracy. The analysis is conducted by assuming a rigid sphere with a Reynolds number of between 50 and 300, based on the diameter of the sphere and the freestream velocity and a freestream Mach number of between 0.3 and 2.0, together with the adiabatic wall boundary condition. The calculation shows the following yields: (1) unsteady fluctuation of hydrodynamic forces become smaller as the Mach number increases under the same Reynolds number condition, (2) the drag coefficient increases with the Mach number due to an increase in the pressure drag by the shock wave, and (3) an accurate prediction of the drag coefficient in the supersonic regime using traditional models might be difficult.

DOI： 10.1063/1.4947244

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：HINDAWI PUBLISHING CORP  

This study is devoted to investigating a flow around a stationary or moving sphere by using direct numerical simulation with immersed boundary method (IBM) for the three-dimensional compressible Navier-Stokes equations. A hybrid scheme developed to solve both shocks and turbulent flows is employed to solve the flow around a sphere in the equally spaced Cartesian mesh. Drag coefficients of the spheres are compared with reliable values obtained from highly accurate boundary-fitted coordinate (BFC) flow solver to clarify the applicability of the present method. As a result, good agreement was obtained between the present results and those from the BFC flow solver. Moreover, the effectiveness of the hybrid scheme was demonstrated to capture the wake structure of a sphere. Both advantages and disadvantages of the simple IBM were investigated in detail.

DOI： 10.1155/2015/438086

Web of Science

Scopus

J-GLOBAL

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J-GLOBAL

J-GLOBAL

J-GLOBAL

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J-GLOBAL

Language：Japanese  

J-GLOBAL

The present study proposes a sensor selection method based on the proximal
splitting algorithm and the A-optimal design of experiment using the
alternating direction method of multipliers (ADMM) algorithm. The performance
of the proposed method was evaluated with a random sensor problem and compared
with the previously proposed methods such as the greedy method and the convex
relaxation. The performance of the proposed method is better than an existing
method in terms of the A-optimality criterion. In addition, the proposed method
requires longer computational time than the greedy method but it is quite
shorter than the convex relaxation in large-scale problems. The proposed method
was applied to the data-driven sparse-sensor-selection problem. A data set
adopted is the NOAA OISST V2 mean sea surface temperature set. At the number of
sensors larger than that of the latent state variables, the proposed method
showed similar and better performances compared with previously proposed
methods in terms of the A-optimality criterion and reconstruction error.

arXiv

Other Link： http://arxiv.org/pdf/2010.09329v1

J-GLOBAL

J-GLOBAL

Language：Japanese  

J-GLOBAL

In this study, free-flight tests of a sphere at a Reynolds number between 5.7 × 10 and 3.1 × 10 under transonic to supersonic condition is conducted using ballistic range and investigate the flow over a sphere under compressible low-Reynolds number conditions. The flow visualization is carried out by schlieren technique. A free-flight Reynolds number is between 5.7 × 10 and 3.1 × 10 and a free-flight Mach number is between 0.9 and 1.6. To realize the compressible low-Reynolds number flow, the flow visualization is carried out under low-pressure conditions with a small sphere (minimum diameter is 2.0 mm). in addition, the time-averaged images around a sphere are obtained and compared with previous numerical results for the Reynolds number between 50 and 1000. From the experimental results, the near field and far field flow structure at the Reynolds number of between 5.7 × 10 and 3.1 × 10 under supersonic conditions are visualized. As a result, following characteristics are clarified: 1) the perturbation amplitude of wake vortex is attenuated as a free-flight Mach number increases, 2) mode of wake structure is changed by changing the free-flight Mach number, 3) there is no Reynolds number dependences on the separation point, but a length of the recirculation region is influenced by the Reynolds number. 3 5 3 5 3 5

DOI： 10.2514/6.2019-2156

Scopus

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

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J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebio.2018.30.1F12

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmebio.2018.30.2H02

In this study, flow over an isolated sphere for a Reynolds number (Re) between 500 and 1000 and a Mach number (M) between 0.8 and 2.0 is investigated via direct numerical simulation (DNS) of three-dimensional compressible Navier–Stokes equations. We focused on the Mach and Reynolds numbers effect on the flow geometry, the flow regime, and the drag coefficient. The results show the following characteristics: 1) for previous studies, the flow field is axisymmetric for Re ≤ 300 and 1.2 ≤ M, but asymmetry and unsteadiness appears at Re = 750 and 1000, respectively, 2) the drag coefficient by DNS indicate different trends to the previous drag models.

DOI： 10.2514/6.2018-0381

Scopus

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmeth.2018.53.51

Language：Japanese  

J-GLOBAL

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J-GLOBAL

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J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmemecj.2016.S0550104

J-GLOBAL

A flow containing multiple particles and the shock wave is investigated by the direct numerical simulation with immersed boundary method. The shock Mach number and the Reynolds numbers of particle behind the shock wave are set to be 1.5 to 2.0 and 300 to 600, respectively. The comparison of the present results with one-dimensional simulation results, shows good agreement. From the results, we clarified characteristic flow structure at different shock Mach and Reynolds number. The turbulence kinetic energy was enhanced from the vortex structure in the wake of particles for the high Reynolds number case. The drag coefficient from the present simulation and the previous prediction models shows almost the same values at Mach number 1.5. At Mach number 2.0, however, discrepancy is obtained for the drag coefficient between the present flow simulation and the previous prediction models.

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecmd.2016.29.4_176

J-GLOBAL

In this study, direct numerical simulation of the flow around a sphere at the high Mach number and the low Reynolds number condition is carried out in order to investigate the flow properties. The three-dimensional compressible Navier-Stokes equations are solved on boundary fitted coordinate system. It is confirmed to have sufficient accuracy from the results of the previous study. Analyses are performed at the Reynolds number of between 50 and 300, the freestream Mach number of between 0.3 and 2.0, and the temperature ratio of the sphere surface and freestream of between 0.5 and 2.0. As the results, we clarified the following points: 1) the freestream Reynolds number and the temperature ratio influence the flow properties, 2) the effect of the temperature ratio can be summarized by the effective Reynolds number that is a newly proposed parameter.

DOI： 10.2514/6.2016-1251

Scopus

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, a direct numerical simulation is carried out for the flow that the particle passes a shock wave to investigate interference between the particles and shock wave. The flow simulation based on three-dimensional compressible Navier-Stokes equations is conducted by Cartesian mesh method with immersed boundary method to deal with multiple moving boundaries by Euler-Euler approach. This flow solver is developed for the purpose of accurate prediction of the acoustic field around a rocket launch site. The objective of this study is to investigate a flow containing shock waves and moving multiple particles. The shock Mach numbers are 1.2, 1.5, 2.0, and 2.5. When multiple particles pass the shock wave, characteristic vortex structure is formed in the wake. The vortex structure may be a key factor of the interference.

DOI： 10.1299/jsmefed.2015._0802-1_

CiNii Books

Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this study, DNS of flow around a stationary sphere under the isothermal conditions with the high Mach numbers and low Reynolds numbers flow were conducted by solving three-dimensional compressible Navier-Stokes equations for investigation of the influence of the Mach number and temperature ratio on the vortex structures. From calculation result, we clarified the following facts that the Mach number and temperature ratio effect on the wake of the sphere: (1 the vortex shedding is decreases in the case of high Mach number or high temperature ratio, (2 the sphere releases strong vortex in the case of high Mach number or low temperature ratio and (3 turbulent kinetic energy at the wake of the sphere increases in the case of high Mach number or low temperature ratio.

DOI： 10.1299/jsmefed.2015._0704-1_

CiNii Books

Language：English   Publisher：INT CENTER NUMERICAL METHODS ENGINEERING  

In this work, direct numerical analyses for flow around particles passing a shock wave was carried out to predict effects of small particles in rocket plumes. A flow solver based on three-dimensional compressible Navier-Stokes equations is developed for the purpose of high accurate prediction of the acoustic field around rocket plumes. This flow solver is capable of analysing a flow around moving multiple particles and motion equations was introduced. The flow field and the drag coefficient after the shock wave passage were validated by comparing with the drag models at shock Mach number 1.2-2.8. The result was in good agreement with the drag models. In the flow around multiple particles, the interference between particles was confirmed.

Web of Science

Scopus

This study analyses gas particle flow around a sphere under an adiabatic condition at high Mach number and low Reynolds number by direct numerical simulation of the three- dimensional compressible Navier-Stokes equation to investigate flow properties. The calculation was performed on a boundary-fitted coordinate system with a high-order scheme of sufficient accuracy. Analysis is conducted by assuming a rigid sphere with a Reynolds number based on the diameter of the sphere, and the free-stream velocity set between 50 and 300 and a free-stream Mach number set between 0.3 and 2.0. The effect of the Mach number on the flow properties and drag coefficient are discussed. The calculation shows the following results: 1) unsteady fluctuation of the hydrodynamic force becomes smaller as the Mach number increases, 2) the drag coefficient increases along with the Mach number due to an increase in the pressure drag by the shock-wave, and 3) an accurate prediction of the drag coefficient in the supersonic regime using traditional models might be difficult.

Web of Science

Scopus

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese  

J-GLOBAL

Language：Japanese   Publisher：一般社団法人日本物理学会  

CiNii Books

Event date： 2018

Language：Japanese  

Event date： 2018

Language：Japanese  

Event date： 2018

Language：Japanese  

Event date： 2018

Language：Japanese  

Event date： 2018

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. In this study, flow over an isolated sphere for a Reynolds number (Re) between 500 and 1000 and a Mach number (M) between 0.8 and 2.0 is investigated via direct numerical simulation (DNS) of three-dimensional compressible Navier–Stokes equations. We focused on the Mach and Reynolds numbers effect on the flow geometry, the flow regime, and the drag coefficient. The results show the following characteristics: 1) for previous studies, the flow field is axisymmetric for Re ≤ 300 and 1.2 ≤ M, but asymmetry and unsteadiness appears at Re = 750 and 1000, respectively, 2) the drag coefficient by DNS indicate different trends to the previous drag models.

Event date： 2018

Language：Japanese  

Event date： 2018

Language：Japanese  

Event date： 2017.12

Language：Japanese  

Event date： 2017.12

Language：Japanese  

Event date： 2017

Language：Japanese  

Event date： 2016.9

Language：Japanese  

Event date： 2016.9

Language：Japanese  

Event date： 2016

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All Rights Reserved. A flow containing multiple particles and the shock wave is investigated by the direct numerical simulation with immersed boundary method. The shock Mach number and the Reynolds numbers of particle behind the shock wave are set to be 1.5 to 2.0 and 300 to 600, respectively. The comparison of the present results with one-dimensional simulation results, shows good agreement. From the results, we clarified characteristic flow structure at different shock Mach and Reynolds number. The turbulence kinetic energy was enhanced from the vortex structure in the wake of particles for the high Reynolds number case. The drag coefficient from the present simulation and the previous prediction models shows almost the same values at Mach number 1.5. At Mach number 2.0, however, discrepancy is obtained for the drag coefficient between the present flow simulation and the previous prediction models.

Event date： 2016

© 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All Rights Reserved. In this study, direct numerical simulation of the flow around a sphere at the high Mach number and the low Reynolds number condition is carried out in order to investigate the flow properties. The three-dimensional compressible Navier-Stokes equations are solved on boundary fitted coordinate system. It is confirmed to have sufficient accuracy from the results of the previous study. Analyses are performed at the Reynolds number of between 50 and 300, the freestream Mach number of between 0.3 and 2.0, and the temperature ratio of the sphere surface and freestream of between 0.5 and 2.0. As the results, we clarified the following points: 1) the freestream Reynolds number and the temperature ratio influence the flow properties, 2) the effect of the temperature ratio can be summarized by the effective Reynolds number that is a newly proposed parameter.

Event date： 2015.4

This study analyses gas particle flow around a sphere under an adiabatic condition at high Mach number and low Reynolds number by direct numerical simulation of the three- dimensional compressible Navier-Stokes equation to investigate flow properties. The calculation was performed on a boundary-fitted coordinate system with a high-order scheme of sufficient accuracy. Analysis is conducted by assuming a rigid sphere with a Reynolds number based on the diameter of the sphere, and the free-stream velocity set between 50 and 300 and a free-stream Mach number set between 0.3 and 2.0. The effect of the Mach number on the flow properties and drag coefficient are discussed. The calculation shows the following results: 1) unsteady fluctuation of the hydrodynamic force becomes smaller as the Mach number increases, 2) the drag coefficient increases along with the Mach number due to an increase in the pressure drag by the shock-wave, and 3) an accurate prediction of the drag coefficient in the supersonic regime using traditional models might be difficult.

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

In this study, DNS of flow around a stationary sphere under the isothermal conditions with the high Mach numbers and low Reynolds numbers flow were conducted by solving three-dimensional compressible Navier-Stokes equations for investigation of the influence of the Mach number and temperature ratio on the vortex structures. From calculation result, we clarified the following facts that the Mach number and temperature ratio effect on the wake of the sphere: (1 the vortex shedding is decreases in the case of high Mach number or high temperature ratio, (2 the sphere releases strong vortex in the case of high Mach number or low temperature ratio and (3 turbulent kinetic energy at the wake of the sphere increases in the case of high Mach number or low temperature ratio.

Event date： 2015

Language：Japanese  

In this study, a direct numerical simulation is carried out for the flow that the particle passes a shock wave to investigate interference between the particles and shock wave. The flow simulation based on three-dimensional compressible Navier-Stokes equations is conducted by Cartesian mesh method with immersed boundary method to deal with multiple moving boundaries by Euler-Euler approach. This flow solver is developed for the purpose of accurate prediction of the acoustic field around a rocket launch site. The objective of this study is to investigate a flow containing shock waves and moving multiple particles. The shock Mach numbers are 1.2, 1.5, 2.0, and 2.5. When multiple particles pass the shock wave, characteristic vortex structure is formed in the wake. The vortex structure may be a key factor of the interference.

Event date： 2015

Language：English  

In this work, direct numerical analyses for flow around particles passing a shock wave was carried out to predict effects of small particles in rocket plumes. A flow solver based on three-dimensional compressible Navier-Stokes equations is developed for the purpose of high accurate prediction of the acoustic field around rocket plumes. This flow solver is capable of analysing a flow around moving multiple particles and motion equations was introduced. The flow field and the drag coefficient after the shock wave passage were validated by comparing with the drag models at shock Mach number 1.2-2.8. The result was in good agreement with the drag models. In the flow around multiple particles, the interference between particles was confirmed.

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2015

Language：Japanese  

Event date： 2014

Language：Japanese