掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Fluids  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Sensors Journal  

The randomized group-greedy (RGG) method and its customized method for large-scale sensor selection problems are proposed. The randomized greedy sensor selection algorithm is applied straightforwardly to the group-greedy (GG) method, and a customized method is also considered. In the customized method, a part of the compressed sensor candidates is selected using the common greedy method or other low-cost methods. This strategy compensates for the deterioration of the solution due to compressed sensor candidates. The proposed methods are implemented based on the D-and E-optimal design of experiments, and numerical experiments are conducted using randomly generated sensor candidate matrices with potential sensor locations of 10000-1000000. The proposed method can provide better optimization results than those obtained by the original GG method when a similar computational cost is spent as for the original GG method. This is because the group size for the GG method can be increased as a result of the compressed sensor candidates by the randomized algorithm. Similar results were also obtained in the real dataset. The proposed method is effective for the E-optimality criterion, in which the objective function that the optimization by the common greedy method is difficult due to the absence of submodularity of the objective function. The idea of the present method can improve the performance of all optimizations using a greedy algorithm.

DOI： 10.1109/JSEN.2023.3258223

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Experiments in Fluids  

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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掲載種別：研究論文（学術雑誌）   出版者・発行元：Geophysical Journal International  

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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その他リンク： https://academic.oup.com/gji/article-pdf/234/3/1786/50241650/ggad165.pdf

Web of Science

掲載種別：研究論文（学術雑誌）   出版者・発行元：Institute of Electrical and Electronics Engineers (IEEE)  

DOI： 10.1109/jsen.2023.3328005

掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Access  

Objective functions for sensor selection are investigated in linear time-invariant systems with a large number of sensor candidates. This study compared the performance of sensor sets obtained using three types of D-optimality-based indices as objective functions for sensor selection based on the greedy method. The compared indices are computed based on the snapshot-to-snapshot Fisher information matrix, the observability Gramian and the Kalman filter-based matrix. Both random systems and systems with eigenmodes are considered, indices for selecting the best-performing sensor set for each are identified, as well as computational complexity and corresponding wall clock times. The sensor optimized for each index works best for that index, as expected. We also clarified the trend of the sensor sets selected by the greedy method based on each objective function in terms of the other objective function.

DOI： 10.1109/ACCESS.2023.3291415

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掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Visualization  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Physics of Fluids  

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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掲載種別：研究論文（学術雑誌）   出版者・発行元：Measurement Science and Technology  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIAA Journal  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Sensors  

We developed and evaluated an anodized-aluminum pressure-sensitive paint (AA-PSP) with new formulations of free-base porphyrin, (Formula presented.), as an optical unsteady pressure sensor. The luminophore (Formula presented.) 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 (Formula presented.) 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

掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Wind Engineering and Industrial Aerodynamics  

This study proposes a method for predicting the wind direction against the simple automobile model (Ahmed model) and the surface pressure distributions on it by using data-driven optimized sparse pressure sensors. Positions of sparse pressure sensor pairs on the Ahmed model were selected for estimation of the yaw angle and reconstruction of pressure distributions based on the time-averaged surface pressure distributions database of various yaw angles, whereas the symmetric sensors in the left and right sides of the model were assumed. The surface pressure distributions were obtained by pressure-sensitive paint measurements. Three algorithms for sparse sensor selection based on the greedy algorithm were applied, and the sensor positions were optimized. The sensor positions and estimation accuracy of yaw angle and pressure distributions of three algorithms were compared and evaluated. The results show that a few optimized sensors can accurately predict the yaw angle and the pressure distributions.

DOI： 10.1016/j.jweia.2022.105043

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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Visualization  

Abstract: 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. Graphical abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s12650-022-00829-8

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掲載種別：研究論文（学術雑誌）   出版者・発行元：AIAA Journal  

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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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AIAA AVIATION 2022 Forum  

The present study proposes a method for estimating the wind direction against a simple automobile model (Ahmed model) and reconstructing surface pressure distribution on it by the sparse pressure sensors. The sparse pressure sensor placement was optimized by the three algorithms based on data-driven sparse sampling using the time-averaged surface pressure distributions as the training data. The surface pressure distributions were obtained by pressure-sensitive paint (PSP) measurements. The estimation models were constructed based on the training data, and then, the estimation accuracy of yaw angles and pressure distributions was compared and evaluated.

DOI： 10.2514/6.2022-3606

Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Sensors  

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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PubMed

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmefed.2022.os03-48

CiNii Research

掲載種別：研究論文（学術雑誌）  

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

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：28th AIAA/CEAS Aeroacoustics Conference, 2022  

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

掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Access  

In the present study, we organize the existing sparsity-promoting dynamic mode decomposition (DMDsp) in terms of noise robustness, propose faster optimization algorithm for DMDsp, and evaluate its characteristics. Two kinds of DMDsp, namely system-based DMDsp (sDMDsp) and observation-based DMDsp (oDMDsp), combined with three kinds of optimization algorithm, namely the fast iterative shrinkage thresholding algorithm (FISTA), the alternating direction method of multipliers (ADMM), and a greedy algorithm, are investigated. For both sDMDsp and oDMDsp, FISTA yields the shortest processing time. The processing time for sDMDsp with FISTA is shorter than that for oDMDsp with FISTA. The original data reconstruction errors for sDMDsp and oDMDsp are similar among the three optimization algorithms. The noise robustness for sDMDsp and oDMDsp is evaluated. sDMDsp and oDMDsp have similar robustness to observation noise, except for a system with large system and observation noise, for which oDMDsp outperforms sDMDsp.

DOI： 10.1109/ACCESS.2022.3193157

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：28th AIAA/CEAS Aeroacoustics Conference, 2022  

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

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AIAA AVIATION 2022 Forum  

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

掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Signal Processing  

In this study, a nondominated-solution-based multi-objective greedy method is proposed and applied to a sensor selection problem based on the multiple indices of the optimal design of experiments. The proposed method simultaneously considers multiple set functions and applies the idea of Pareto ranking for the selection of sets. Specifically, a new index is iteratively added to the nondominated solutions of sets, and the multi-objective functions are evaluated for new sets. The nondominated solutions are selected from the examined solutions, and the next sets are then considered. With this procedure, the multi-objective optimization of multiple set functions can be conducted with reasonable computational costs. This paper defines a new class of greedy algorithms which includes the proposed nondominated-solution-based multi-objective greedy algorithm and the group greedy algorithm, and the characteristics of those algorithms are theoretically discussed. Then, the proposed method is applied to the sensor selection problem and its performance is evaluated. The results of the test case show that the proposed method not only gives the Pareto-optimal front of the multi-objective optimization problem but also produces sets of sensors in terms of D-, A-, and E-optimality, that are superior to the sets selected by pure greedy methods that consider only a single objective function.

DOI： 10.1109/TSP.2022.3224643

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掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AIAA AVIATION 2022 Forum  

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

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：一般社団法人 日本航空宇宙学会  

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 (M) and Reynolds number (Re) based on the relative velocity between the particle and the quantities behind the planar shock wave were 0.46 ¯ M ¯ 1.24 and 3500 ¯ Re ¯ 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 ¯ Re ¯ 9800 and M = 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.

DOI： 10.2322/tjsass.65.185

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CiNii Research

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：28th AIAA/CEAS Aeroacoustics Conference, 2022  

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

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmefed.2022.os03-04

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmekanto.2022.28.15f10

CiNii Research

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmemecj.2022.j025-05

CiNii Research

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Transactions on Signal Processing  

The present paper proposes a data-driven sensor selection method for a high-dimensional nondynamical system with strongly correlated measurement noise. The proposed method is based on proximal optimization and determines sensor locations by minimizing the trace of the inverse of the Fisher information matrix under a block-sparsity hard constraint. The proposed method can avoid the difficulty of sensor selection with strongly correlated measurement noise, in which the possible sensor locations must be known in advance for calculating the precision matrix for selecting sensor locations. The problem can be efficiently solved by the alternating direction method of multipliers, and the computational complexity of the proposed method is proportional to the number of potential sensor locations when it is used in combination with a low-rank expression of the measurement noise model. The advantage of the proposed method over existing sensor selection methods is demonstrated through experiments using artificial and real datasets.

DOI： 10.1109/TSP.2022.3212150

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Scopus

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：AIAA Journal  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Sensors Journal  

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 the A-optimality criterion and reconstruction error.

DOI： 10.1109/JSEN.2021.3073978

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Web of Science

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Sensors  

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)3 ), 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)3, 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)3 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.

DOI： 10.3390/s21093187

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PubMed

掲載種別：研究論文（学術雑誌）   出版者・発行元：Experiments in Fluids  

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

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その他リンク： https://link.springer.com/article/10.1007/s00348-021-03164-0/fulltext.html

担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Fluid Dynamics Research  

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

その他リンク： https://iopscience.iop.org/article/10.1088/1873-7005/abe04c/pdf

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Sensors (Switzerland)  

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 (Pref) was set to 0.5–140 kPa. Localized Stern–Volmer coefficient Blocal increased and then decreased with increasing oxygen mole fraction. Although Blocal 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, Blocal peaks at PO2 ref < 12 kPa. In contrast, for PC-PSP, which is an atmospheric-pressure-type PSP in the investigated range, Blocal does not have a peak. Blocal 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 SPR, which is the emission intensity change with respect to normalized pressure fluctuation, appears at a lower partial pressure of oxygen than that of Blocal. This is because the intensity of PSP becomes quite low at a high partial pressure of oxygen even if Blocal 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.

DOI： 10.3390/s21041062

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PubMed

出版者・発行元：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

掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Access  

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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掲載種別：研究論文（学術雑誌）   出版者・発行元：IEEE Access  

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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arXiv

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：AIAA Aviation and Aeronautics Forum and Exposition, AIAA AVIATION Forum 2021  

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

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmekanto.2021.27.10d14

CiNii Research

掲載種別：研究論文（学術雑誌）   出版者・発行元：CMES - Computer Modeling in Engineering and Sciences  

A vector-measurement-sensor-selection problem in the undersampled and oversampled cases is considered by extending the previous novel approaches: a greedy method based on D-optimality and a noise-robust greedy method in this paper. Extensions of the vector-measurement-sensor selection of the greedy algorithms are proposed and applied to randomly generated systems and practical datasets of flowfields around the airfoil and global climates to reconstruct the full state given by the vector-sensor measurement.

DOI： 10.32604/cmes.2021.016603

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Scopus

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Fluid Mechanics  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal for Numerical Methods in Fluids  

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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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Measurement Science and Technology  

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

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担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Fluid Mechanics  

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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記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：Sensors (Switzerland)  

A temperature-sensitive paint (TSP) using a chameleon luminophore [Tb0.99Eu0.01 (hfa)3 (dpbp)]n 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, TbIII and EuIII . The temperature sensitivity when using the ratio of the emission intensities at 616 nm derived from EuIII and at 545 nm derived from TbIII 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 × 10−2%/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 TbIII and EuIII .

DOI： 10.3390/s20092623

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PubMed

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Shock Waves  

In this study, free-flight tests of a sphere for Reynolds numbers between 3.9 × 103 and 3.8 × 105 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 103–105 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.

DOI： 10.1007/s00193-019-00924-0

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記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmefed.2019.os9-09

CiNii Research

担当区分：筆頭著者   掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019  

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

掲載種別：研究論文（国際会議プロシーディングス）   出版者・発行元：ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019  

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

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：Journal of Fluid Mechanics  

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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担当区分：筆頭著者   記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：International Journal of Heat and Mass Transfer  

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

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

DOI： 10.2495/CMEM-V6-N1-162-175

Scopus

担当区分：筆頭著者   掲載種別：研究論文（学術雑誌）   出版者・発行元：{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

記述言語：英語   掲載種別：研究論文（学術雑誌）   出版者・発行元：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

記述言語：日本語   出版者・発行元：(一社)日本泌尿器科学会総会事務局  

J-GLOBAL

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人 日本機械学会  

DOI： 10.1299/jsmecmd.2016.29.4_176

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語  

J-GLOBAL

記述言語：日本語   出版者・発行元：一般社団法人日本物理学会  

CiNii Books

開催年月日： 2018年

© 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.

開催年月日： 2018年

記述言語：日本語  

開催年月日： 2018年

記述言語：日本語  

開催年月日： 2018年

記述言語：日本語  

開催年月日： 2017年12月

記述言語：日本語  

開催年月日： 2017年12月

記述言語：日本語  

開催年月日： 2017年

記述言語：日本語  

開催年月日： 2016年9月

記述言語：日本語  

開催年月日： 2016年

© 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.

開催年月日： 2016年

© 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.

開催年月日： 2015年4月

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.

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：英語  

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.

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

開催年月日： 2015年

記述言語：日本語  

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.

開催年月日： 2015年

記述言語：日本語  

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.