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

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：International Symposium on Turbulence and Shear Flow Phenomena, TSFP10  

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

DOI： 10.1016/j.proci.2016.08.033

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DOI： 10.1007/s10494-016-9770-1

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DOI： 10.1007/s10494-016-9756-z

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

DOI： 10.1016/j.ijhydene.2016.04.006

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DOI： 10.1007/s00348-016-2146-4

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DOI： 10.1080/00102202.2016.1195820

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Other Link： https://projects.repo.nii.ac.jp/?action=repository_uri&item_id=377692

Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SAE International  

DOI： 10.4271/2015-01-1910

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：SAE International  

DOI： 10.4271/2015-01-1909

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

DOI： 10.1017/jfm.2015.158

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Simultaneous CH-OH planar laser induced fluorescence (PLIF) and stereoscopic particle image velocimetry (SPIV) measurements at 10 kHz have been conducted in a methane-air turbulent jet premixed flame. Around the flame tip in the high Reynolds number condition, the fine scale unburned mixture islands are ejected downstream. The enhancement of the turbulent burning velocity is statistically analyzed by the local consumption rate, which is estimated from the OH and CH PLIF images with the assumption of the spherical and pillar shapes of the unburned mixture. The most probable consumption rates with different methods give significantly higher burning velocity than the laminar.

DOI： 10.1299/jsmefed.2015._1027-1_

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To investigate propagation characteristics of methane-air premixed flames at high pressure, constant volume vessel which can control turbulence characteristics, initial pressure and equivalence ratio has been developed, and high repletion rate OH planar laser induced fluorescence (PLIF) and CH chemiluminescence measurements are performed in the combustion field. The flame front and radius of flame are evaluated from OH PLIF and CH chemiluminescence independently. When radius of flame is large, flame speed becomes constant in laminar flame but increases in turbulent flame. Flame speed which is evaluated from OH PLIF images fluctuates significantly because of local turbulence characteristics and flame structure.

DOI： 10.1299/jsmeted.2015._f133-1_

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

It is known that Taylor-Couette flow shows a transition in the Reynolds number dependency of the mean torque near Re 〜 10000. To investigate the turbulent vortical structures in the transition state, direct numerical simulations of Taylor-Couette flow with fixed outer cylinder have been conducted in the different Reynolds numbers from Re = 8000 to 25000. As the Reynolds number increases, the fine scale eddies are more populated in a large part of the domain and they tend to take more various angles. The joint probability functions of the tilting angles of eddies with respect to the tangential direction and their radial positions exhibit preferential distributions, which is due to the shear layer between the large scale Taylor vortex motions. The present results suggest that the distribution and the orientation of the fine scale eddies in this Reynolds number range are greatly affected by the Taylor vortex structure.

DOI： 10.1299/jsmemecj.2015._j0550301-

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Three-dimensional direct numerical simulation of methane-air turbulent premixed planar flame propagating in homogenous isotropic turbulence is conducted to investigate local flame structure in thin reaction zones. GRI-Mech 3.0 is used to represent methane-air reactions. For a better understanding of the local flame structure in thin reaction zones, distributions of mass fractions of major species, heat release rate and temperature are investigated. The results show that in thin reaction zones, pixel by pixel product of CH_2O-OH or CH_2O-H images have good correlation with heat release rate and is more accurate to discern local flame structures than single OH images. The correlation between heat release rate, principal curvature and tangential strain rate are investigated.

DOI： 10.1299/jsmeted.2015._f144-1_

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Direct numerical simulations of Taylor-Couette flow from Re = 8000 to 25 000 have been performed to understand the spectral characteristics of turbulence in the transition of the Reynolds number dependency of the mean torque near Re = 10 000. The velocity fluctuations are decomposed into the wavenumber components, and their contributions in the radial profiles of the Reynolds stress and the transmission of the mean torque are evaluated. In the net mean torque, the contribution of the azimuthally averaged component overtakes that of the remaining turbulent counterparts around Re = 15 000. Therefore, the torque transition can be explained by the competition between the contributions of azimuthally averaged Taylor vortex and the remaining turbulent fluctuations.

DOI： 10.1299/jsmefed.2015._1514-1_

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TSFP-9  

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

DOI： 10.1016/j.proci.2014.09.007

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

DOI： 10.1016/j.proci.2014.10.003

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

DOI： 10.1016/j.proci.2014.07.059

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

DOI： 10.1016/j.proci.2014.07.057

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

DOI： 10.1007/s00348-014-1731-7

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

Direct numerical simulation (DNS) has been carried out to clarify the characteristics of turbulent statistics of Taylor-Couette flow in high Reynolds number around Re ≈ 10000. Reynolds number, Re, which is defined by the differences of inner-wall and outer-wall and rotating speed of inner cylinder, is set in the range from 8000 to 20000, where the turbulent characteristics are expected to change referring to Wendt's empirical formula. In this study, turbulent statistics are obtained by averaging in azimuthal direction, axial direction and time in fully developed state, and their characteristics are discussed with budgets of the transport equation for each Reynolds stress component. As a result, the intensity of diagonal component of Reynolds stress do not show monotonic increase in wall units when Reynolds number rise. The reason of large Reynolds stress in axial direction at Re = 20000 is also discussed using contributions of each term in the transport equation.

DOI： 10.1299/jsmekanto.2014.20._20306-1_

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

To investigate fractal characteristics of turbulent premixed flames with mean shear, direct numerical simulations of hydrogen-air turbulent jet and V-shape premixed flames are conducted. From fractal analysis with box-counting methods, it is revealed that fractal dimensions of flame surfaces of jet and V-shape flames increase in streamwise direction. The fractal dimensions calculated with a three dimensional box-counting method reach about 2.52-2.57 in downstream region where turbulence is fully developed by mean shear. An expression proposed by Shim et al. gives good predictions for inner cutoffs of turbulent premixed flames with mean shear and in a high pressure condition when flame surfaces are sufficiently distorted by turbulence.

DOI： 10.1299/jsmeted.2014._i123-1_

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Language：English   Publishing type：Research paper (international conference proceedings)  

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

DOI： 10.1103/PhysRevLett.107.194502

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Language：English   Publishing type：Research paper (international conference proceedings)  

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

DOI： 10.1016/j.ijheatfluidflow.2011.03.001

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

DOI： 10.1017/jfm.2011.32

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

DOI： 10.1007/s10494-010-9258-3

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

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

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

We have performed experiments in a turbulent mixing layer with periodic forcing introduced by a Piezo Film Actuator (PFA). Three different lengths of PFAs have been used, and the effects of various combinations of forcing amplitudes and frequencies are investigated. The forcing at the first and second sub-harmonic frequencies against the natural frequency enhances the development of the thickness of the mixing layer: the mixing layer spreads due to the forcing. On the other hand, the forcing near the natural frequency suppresses the development: the mean velocity gradient becomes steeper than the no control case. The vector pattern of the periodic velocity components indicated the formation of the vortical structure. By forcing at the natural and its first sub-harmonic frequencies, two counter-rotating vortices are clearly observed in one period of forcing. By forcing at second sub-harmonic frequency, the vortical structure is found only in the downstream region. The distribution of the periodic Reynolds shear stress significantly varies with the forcing frequency and it takes a positive value when forcing occurs near the natural frequency. However, the total value of the Reynolds shear stress remains negative due to the contribution of the turbulent components.

DOI： 10.1299/jfst.5.156

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

DOI： 10.1016/j.ijheatfluidflow.2009.01.002

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Language：English   Publisher：The Japan Society of Mechanical Engineers  

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, the time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of the vortex is evident from both velocity and pressure measurements: The power spectral density (PSD) of the transverse velocity fluctuation increases in the lower frequency range, and the distribution of the pressure fluctuation exhibits an elongated shape in the <i>z</i> direction as well as two peaks slightly off from the vortex center. The distribution of the measured velocity-pressure correlation varies significantly near the center of the vortex especially in downstream locations.

DOI： 10.1299/jfst.4.107

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Language：Japanese   Publisher：The Japan Society of Mechanical Engineers  

In this paper, an experimental study is performed to reveal the effects of flow pulsation on vortex structure in a rectangular jet. A hydrogen bubble technique is used to observe the vortex structure from rectangular cross section nozzle of an aspect ratio of 5. The flow pulsation is generated by superimposing large amplitude and low frequency pulsation on the steady flow. The difference of the vortex deformation process is discussed in relation to pulsating conditions. Obtained results are as follows: the pulsation leads to the formation of vortices at regular intervals, which are larger than those occurring in a steady jet. The vortex ring generated, then changed the own shape three-dimensionally with increasing time. The pulsating jet expanded sharply very near the nozzle exit. The merging process of vortices is especially sensitive to the pulsating frequency.

DOI： 10.1299/jsmefed.2007._313-1_

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

DOI： 10.1016/j.ijheatfluidflow.2006.02.023

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Language：English   Publishing type：Research paper (international conference proceedings)  

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Event date： 2015.1

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Event date： 2015

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Event date： 2014.11

Language：Japanese  

To investigate fractal characteristics of turbulent premixed flames with mean shear, direct numerical simulations of hydrogen-air turbulent jet and V-shape premixed flames are conducted. From fractal analysis with box-counting methods, it is revealed that fractal dimensions of flame surfaces of jet and V-shape flames increase in streamwise direction. The fractal dimensions calculated with a three dimensional box-counting method reach about 2.52-2.57 in downstream region where turbulence is fully developed by mean shear. An expression proposed by Shim et al. gives good predictions for inner cutoffs of turbulent premixed flames with mean shear and in a high pressure condition when flame surfaces are sufficiently distorted by turbulence.

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Event date： 2014.3

Language：Japanese  

Direct numerical simulation (DNS) has been carried out to clarify the characteristics of turbulent statistics of Taylor-Couette flow in high Reynolds number around Re &ap; 10000. Reynolds number, Re, which is defined by the differences of inner-wall and outer-wall and rotating speed of inner cylinder, is set in the range from 8000 to 20000, where the turbulent characteristics are expected to change referring to Wendt's empirical formula. In this study, turbulent statistics are obtained by averaging in azimuthal direction, axial direction and time in fully developed state, and their characteristics are discussed with budgets of the transport equation for each Reynolds stress component. As a result, the intensity of diagonal component of Reynolds stress do not show monotonic increase in wall units when Reynolds number rise. The reason of large Reynolds stress in axial direction at Re = 20000 is also discussed using contributions of each term in the transport equation.

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Event date： 2014.3

Language：Japanese  

To investigate thermoacoustic instability and dynamic modes of turbulent swirling premixed flame, dynamic mode decomposition (DMD) is applied to results of direct numerical simulation (DNS) of hydrogen-air turbulent swirling premixed flame in a cuboid combustor. DMD of pressure field reveals that the quarter-wave mode in longitudinal acoustics has the largest energy and that there is differences between dominant frequencies in spectral analysis of time-series pressure data at one point on a wall and DMD of time-series pressure field data. DMD of heat release rate field reveals that the quarter-wave mode in longitudinal acoustics is not a dominant mode in heat release rate field and oscillation mode caused by large scale vortical motions has large energy not only in pressure field but also in heat release rate field. Interactions between dynamic modes of pressure and heat release rate are also discussed.

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Event date： 2014

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Event date： 2013.9

Language：English  

Simultaneous measurement of fluctuating velocity and pressure is conducted in a wake of circular cylinder with the Reynolds number of 3900. and the measured velocity-pressure correlation is compared with the computational reference data obtained by a large-eddy simulation in order to validate the measurement results. It is shown that the experimental and computational resuits of correlation between the streamwise velocity component and pressure, up, are in good agreement, while there was certain disagreement between the profiles of up, the correlation between the transverse velocity component and pressure. It is found in the further investigation that up is extremely sensitive to a small time lag between the velocity and pressure signals whist up is insensitive, and the experimental results with correction of the time lag is in acceptable agreement with the computational result.

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Event date： 2013.1

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Event date： 2010.7

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Event date： 2010

Language：Japanese  

Effect of periodic forcing by piezo-film actuators on the mixing layer development is investigated by means of wind-tunnel experiment. In addition to the two-dimensional forcing studied by Naka et al. (2010), we also investigate three-dimensional forcings with varying the spanwise wavelength. The wind-tunnel is operated at 6.8m/s and 3.8m/s on the high-speed and low-speed sides, respectively. The frequency of forcing is 30Hz and the displacement of actuator is measured to be 1.3mm. Momentum thickness is found to develop faster due to forcing as compared to the uncontrolled case. Mixing enhancement in the upstream region is found to be greater with three-dimensional forcing than that with two-dimensional one.

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Event date： 2010

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Event date： 2009.9

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Event date： 2009

Language：Japanese  

We experimentally investigate the effect of the control of a flow around a circular cylinder using plasma actuators. Against conventional two dimensional actuation for boundary layer of a circular cylinder, we apply three dimentional disturbance by using four rows of plasma actuator. This experiment is performed at the Reynolds number of Re&sime;5000 and the wake of a circular cylinder is investigated by means of PIV measurement. The time-mean and instantaneous results show that the three dimensional disturbance causes the global instability of separated shear layers in the downstream of the actuator locations.

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Event date： 2009

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Event date： 2009

Language：Japanese  

We study the influence of the flow induced by a plasma actuator on the wing-tip vortex generation. A wing model with the plasma actuator is set inside the wind tunnel and the velocity components are measured by using a PIV system. The plasma actuator is set on the suction side of the wing model. By changing the induced flow direction, i.e., either blowing or suction, the starting position of the wing-tip vortex generation and the position of the vortex core are changed. Especially, in the case of blowing, the plasma actuator has a significant impact on the wing-tip vortex generation: its starting position is shifted downstream.

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Event date： 2008

Language：Japanese  

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of vortex is quantitatively evaluated from both velocity and pressure measurements. The pressure-diffusion term of the transport equation of turbulent kinetic energy is compared with the turbulent-diffusion term. The magnitude of these terms are compareble and the pressure-diffusion was the widely distributed than the turbulent-diffusion.

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Event date： 2008

Language：Japanese  

We experimentally investigate the effects of periodic perturbation in a plane turbulent mixing layer. A piezo-film actuator is used for generating the perturbation. The local velocity and pressure in the downstream regions are measured simultaneously by using a combined hot-wire/pressure probe. Enhancement of mixing by the actuator is confirmd by the increase of mixing-layer thickness and velocitiy fluctuations. Analysis of the phase-averaged quantities obtained by the simultasous measurement of velocity and pressure reveals that the flow structure is modified in the upstream region, directly influenced by the motion of actuator, and grows as it is convected toward the downstream region.

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Event date： 2007.11

Language：Japanese  

A novel technique to evaluate velocity-pressure correlation is proposed. Static pressure fluctuation is indirectly calculated from fluctuating total and dynamic pressure. The applicability is examined by the measurement in a turbulent mixing layer as well as in a wake of circular cylinder. The result is compared with directly measured fluctuating static pressure. Several statistical procedures are introduced to improve the estimated fluctuating static pressure, and it is confirmed that the correction practices is partly effective. Estimated velocity-pressure correlation with the correction practice has a similar profile to directly measured one. To obtain the quantitatively reasonable data, however, further improvement is still necessary.

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Event date： 2007.11

Language：Japanese  

Development of the flow in the near wake region of a NACA0012 wing has been investigated. The profiles of three components of mean velocity, time-averaged vorticity and turbulent kinetic energy are evaluated by multi-position technique with an X-type hotwire probe at three different streamwise locations. The existence of an wing tip vortex is apparent in the profile of tangential velocity, and the axial velocity dificit is also clearly observed. As measurement location goes toward downstream, streamwise velocity deficit recovers, the peak value of vorticity decreases, and the turbulent kinetic energy at the center of the vortex increases. These results indicate the wing tip vortex begins to attenuate in the very near wake region of the wing, and this might be caused by the effect of low Reynolds number and high free stream turbulence.

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Event date： 2007

Language：Japanese  

A novel experimental technique for simultaneous measurement of fluctuating velocity and pressure is tested in a turbulent mixing layer. The fluctuating total pressure and velocity are simultaneously measured and fluctuating static pressure is calculated from them. Fundamental characteristics of the present technique are demonstrated and their effects are taken into account; e.g., the effect of angle of attack, frequency response, phase delay between velocity and pressure signals. The RMS value of fluctuating static pressure obtained by the present method is significantly greater than that of directly measured fluctuating static pressure. The velocity-pressure correlation is also far from that measured by another method. These inconsistencies may be related to imbalance between dynamics pressure included in total pressure and that calculated from velocity. Further improvements are still necessary to obtain accurate time-series of fluctuating static pressure.

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Event date： 2006.3

Language：Japanese  

Simultaneous measurements of fluctuating velocity and pressure were carried out in developing region of a turbulent mixing layer. A miniature probe for fluctuating static pressure was combined with X-wires hot-wire anemometer to evaluate velocity-pressure correlation at arbitrary location. To capture the contribution of largest motion of the flow, the spatial resolution, which is actually the distance between velocity- and pressure- probes, is required to be the same as integral length scale of the flow. It is also valid to check cross-spectrum coherence and phase at the dominant frequency of large scale motion. It is found that the results which satisfy the criteria coincide well with the DNS result.

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Event date： 2006

Language：Japanese  

The technique to measure velocity-pressure correlation is examined in terms of dependence of the distance between pressure- and velocity-probes. The distance, which actually determines spatial resolution, is fixed to 2.0mm in order to minimize the probe interference. Judging from our spectral analysis, it is fair to say that spatial resolution is enough to estimate velocity-pressure correlation in a plane turbulent mixing layer out of equilibrium state.

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Event date： 2005.12

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Language：Japanese   Presentation type：Oral presentation (general)  

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