Shinichi Tashiro

Phase Averaging Analysis of the Unsteady Velocity Profiles in a Separated Flow

By using phase averaging technique, turbulent structure in a flow was studied. For the phase angle of the time dependent signal modulated in frequency, data acquisition is difficult. This study proposed a new method of phase averaging by wavelet transformation. The purpose of the present study is to compare the results of the phase averaging by wavelet transformation with those by the traditional phase averaging technique. These two phase averaging techniques were applied to the experimental data of the velocities in a separated flow with periodical fluctuation. Between the results by these techniques, noticeable differences were shown. If the velocity signals include the frequency modulation, the profiles of phase-averaged velocity by the traditional technique will have nearly the same shapes and be similar to those of time-averaged velocity. On the other hand, the profiles by wavelet transformation showed the clear differences at each phase angle even for the velocity signals with modulated frequencies.Copyright

Phase Averaging by Wavelet Transformation and the Application to Periodically Fluctuated Separation Flow

The vortex structures in a separated region are generated by the motion of the separated shear layer caused by the introduction of periodic fluctuation. The main cause of the motion of the separated shear layer is the external fluctuation with the characteristic frequency. In order to investigate the principal motion of the velocity field, phase averaging was conducted to the velocity signals obtained by single hot-wire measurement. In phase averaging, wavelet analysis was applied to obtain the dominant frequency and the characteristic phase in the fluctuation. The profiles and the contours of the phase-averaged velocity could be found and discussed. The profiles vary dynamically at each phase and show the periodic motion of the shear layer. The separated shear layer flutters with the external fluctuation in the mean flow. If the suitable frequency is selected in the external fluctuation, the separated region disappears in almost all each phases owing to the depression of the shear layer near the wall.Copyright

Micro Rod Mixer Using AC Electric Field Induced Flow

A novel rod mixer, using a micro-scale flow structure induced with electrokinetics under an AC electric field, is proposed for three-dimensional micro-scale processing of biological applications. Flow structures around the micro-rod mixer are demonstrated using the micro-particle image velocimetry method and the particle-tracking velocimetry method. Characteristics of the flow structure and mixing property are investigated for several electric field intensities and frequencies. It is observed that the micro-mixing flow structures induced with an AC electric field at the appropriate intensity and frequency conditions which are intermediate conditions between a dielectrophoresis and an electrolysis. A source-type three-dimensional flow structure is generated around the tip of the micro-rod electrode installed in the sample liquid. Furthermore it is possible to control the scale of the flow structure by adjusting the supplied AC electric field intensity and frequency. The mixing characteristics are also discussed.Copyright

Analysis based on Phase Averaging of the Unsteady Velocity Profiles in the Separated Flow

The vortex structures in a separated flow region are generated by the motion of the separated shear layer caused by the introduction of periodic fluctuation. In order to investigate the principle motion of the velocity field, phase averaging was conducted to the velocity signals obtained by single hot-wire measurement. In phase averaging, Wavelet transformation was applied to obtained the dominant frequency and the characteristic phase angle in the fluctuation. It was found that the phase averaging technique by using Wavelet transformation is more useful in the process of averaging the data which include frequency modulation than the traditional phase averaging technique. The profiles of the phase-averaged velocity could be found and discussed. The profiles vary dynamically at each phase angle and show the periodic motion of the shear layer. The separated shear layer flutters with the external fluctuation in the mean flow. If the suitable frequency is selected in the external fluctuation, the separated flow region disappears in almost all phase angles owing to the depression of the shear layer near the wall.

Phase Averaging Analysis of Periodically Fluctuated Separated Shear Layer

The vortex structures in a separated flow region are generated by the motion of the separated shear layer caused by the introduction of periodic fluctuation. The main cause of the motion of the separated shear layer is the external fluctuation with the characteristic frequency. In order to investigate the principle motion of the velocity field, phase averaging was conducted to the velocity signals obtained by single hot-wire measurement. In phase averaging, wavelet transformation was applied to obtained the dominant frequency and the characteristic phase angle in the fluctuation. The profiles of the averaged velocity could be found and discussed. The profiles vary dynamically at each phase angle and show the periodic motion of the shear layer. The separated shear layer flutters with the external fluctuation in the mean flow. If the suitable frequency is selected in the external fluctuation, the separated flow region disappears in almost all phase angles owing to the depression of the shear layer near the wall.

A Study on the Effect of Periodic Wake on a Separation Flow. On the Changes of the Fluctuation Frequency of Separation Flow.

Te vortex structure within a separated flow region changes when the disturbance is introduced in a mean-flow. This change was investigated by numerical simulation. The periodic velocity fluctuation introduced into the mean-flow at the upstream of separation shear layer, and its amplitude is 30% of the mean-flow velocity. By this periodic fluctuation, the shear layer is flapped to make vortices be shed with the frequency of fluctuation. For making the separation region narrow, it is found that the most effective frequency is about twice of the frequency which is dominant in the separation flow without fluctuation. Furthermore, first sub and super harmonics of that frequency make the flow be periodic. These resonance are explained by using the wave number which is equivalent to the vortex scale.