The effect of a spanwise traveling wave motion on a turbulent boundary layer over a flexible sheet was investigated. The test plate placed in wind tunnel had a flexible sheet section, where the traveling wave motion was generated by the vibration device. It enables the measurements for the higher amplitude and frequency compared to our previous measurements due to the loudspeaker. Velocity profile was measured with a hot-wire anemometry. Amplitude and frequency of the traveling wave motion were measured using two laser displacement sensors. The drag reduction ratio was estimated from the development of momentum thickness of the turbulent boundary layer over the flexible sheet section. The maximum drag reduction with the spanwise traveling wave motion could be obtained T^+=95 and a^+=27.

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We have conducted the velocity measurements for turbulent water flow over an angled wavy plate on the bottom wall in an open channel. The plate is a model of deformed skin of a swiftly swimming dolphin. The friction drag acting on the plate is estimated from the mean velocity profile. The total drag acting on the plate has also been measured from the strain of thin-metal supports of the plate. The experimental results show 4% reduction of friction drag and 58% increase in the total drag for the wavy plate compared with those in the case of flat wall.

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Direct numerical simulation (DNS) of a channel flow with an anisotropic compliant surface is performed in order to investigate its drag reduction effect in a fully developed turbulent flow. The surface is passively driven by the pressure and wall-shear stress fluctuations, and the surface velocity provides a boundary condition for the fluid velocity field. A stochastic optimization method (CMA-ES) is used to optimize the parameters of the anisotropic compliant surface. The optimization identifies several sets of parameters that result in a reduction of the friction drag with a maximum reduction rate of 8%. The primary mechanism for drag reduction is attributed to the decrease of the Reynolds Shear Stress (RSS) near the wall induced by the anisotropic structure and kinematics of the surface. The resultant wall motion is a uniform wave traveling downstream.

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Direct numerical simulation has been conducted for turbulent water flow around a deforming film covered with polysaccharide in order to examine whether or not large blades of algae reduce the friction drag. We consider that polysaccharide layers can be models with beads, spring and dashpots model to the film surface. It is found that the film deformation and polysaccharide layers modify the coherent structures and thin reduce the friction drag. In addition, we clarified the change of wall shear stress and of turbulent flow structure depend on the polymer and polysaccharide's action on the flow field.

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The effect of external disturbances on the transition of a flat plate boundary layer is studied by introducing external disturbances using a turbulence generator located behind the leading edge of the plate. The results indicate the existence of the process, where low-frequency components of the external disturbances influence the boundary layer, generating low-frequency velocity fluctuations inside the boundary layer, prior to the high-frequency components directly reaching the boundary layer.

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We have clarified that an incipient spot generated by a small jet, we called it a laminar spot, is still laminar during the initial stage of its downstream development and developed into a turbulent spot at far downstream. However, we have not ascertained the influence of the Reynolds number on the downstream development of a spot. To clarify this question, we investigated experimentally the downstream development of a spot under various displacement thickness-Reynolds numbers. The purpose of this study was to clarify this question using CFD. From results obtained, we found that development of a spot is caused by the inflexion-point instability of the velocity profile.

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Spectral direct numerical simulations of fully developed turbulent flow in a straight square duct were performed in order to investigate flow structures at low Reynolds numbers. It was found that turbulence can be maintained for values of the bulk Reynolds number above approximately 1100, and the minimum value for the streamwise period of the computational domain is around 190 wall units, which is roughly independent of the Reynolds number. The flow state at marginal Reynolds numbers exhibits a 4-vortex secondary flow structure alternating in time, whereas the fully turbulent one presents the usual 8-vortex pattern. It is shown that buffer layer coherent structures play a crucial role in the appearance of secondary flow of Prandtl's second kind at the marginal Reynolds numbers. The coherent structures are observed to affect the mean primary and secondary flow even at higher Reynolds numbers.

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Static pressure fluctuations are an important ingredient in turbulence, but little is known about it. We have developed the accurate pressure measurement technique. The results were carefully compared with DNS results. In this study this technique is extended into the pressure gradient measurement and two point correlation measurement. Also, new idea to correct the HR resonance and low frequency fluctuation is presented. The acceleration vector is given by N.S. equation as follows; a^^→=-∇(p/ρ)+v∇^2u^^→. In a fully developed turbulence, the viscous damping term is small compared with the pressure gradient term, therefore, the acceleration is closely related to the pressure gradient, and particle acceleration is evaluated by measuring the instantaneous pressure fluctuations.

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Reynolds shear stress profile has been discussed on roughness effect for the turbulent boundary layer over a rough wall under a zero pressure gradient. The value of Reynolds shear stress normalized with friction velocity is lower than that of smooth wall turbulent boundary layer. The value in the logarithmic layer can be represented with the sum of both the wall shear stress and integral of correlations value between velocities and vorticities fluctuations in the roughness sub-layer by analyzing the x-direction Reynolds equation. From the results of the correlations, it is indicated that the Reynolds shear stress in the logarithmic layer has a lower value than the wall shear stress.

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The turbulent flow over a wavy wall was visualized and quantitatively measured with a PIV. The flow in a channel with a flat top wall and a sinusoidal bottom wall were examined. The wave length and the amplitude of the wavy wall were 32 mm and 4.5 mm, respectively. The Reynolds numbers, defined with the half channel height, was varied from 1100 to 3300. The flow separates from the wavy wall at the downstream of the crest and a recirculation region appears in the trough of the wavy wall. A large scale bursting motion out of the trough is observed. The differences of velocity profiles depending on the Reynolds number are clarified. The experimental results were compared with the previous DNS results with a wavy wall having a different wavelength-to-amplitude ratio.

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Laminar-turbulent transition of the boundary layer in an inlet region of a circular pipe is experimentally investigated. The pipe is 6238mm long and 60mm in diameter. As a disturbance, a jet is introduced vertically from the pipe wall periodically. The period and the flow rate of the jet were varied. A single hot-wire probe whose sensing element is 5μm in diameter and 1mm long was used. The phase of the jet issue is recognized by the output signal of a photo sensor. An isolated turbulent patch was formed by the issue of the jet. The qualitative property of the patch does not change with the frequency nor flow rate of the jet.

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This study is concerned with the turbulent structure of a three-dimensional boundary layer on a thin cylinder rotating in a uniform stream at the velocity ratio of Ω_m=0 - 1. Measurements were made by using a single hot-wire probe, which was fixed in the axial direction and rotated around the y-axis. Boundary layer thickness was increased with increasing the velocity ratio, and its thickening rate was extreme at Ω_m=0.4. Mean and fluctuating velocity profiles in the axial and peripheral directions were examined in inner scaling and outer scaling, and then the statistical properties of the axial fluctuation were represented by the power spectrum. It is shown that an energy bump appears in the lower frequency range of spectra in the rotating cases.

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Effects of winglet are experimentally studied on the flow behavior and the wall shear stress in three types of the swirling pipe flow. The circumferential and axial velocity is reduced near the pipe wall by the winglet, and also its corresponding wall shear stress is affected so that the circumferential stress can be reduced remarkably by the high winglet in the strong swirl. Especially, the flow resistance seems to be reduced by the low winglet in the weak swirling flow with the forced vortex.

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The periodic behavior of the horseshoe vortex interacting with a pair of longitudinal vortices by Active Vortex Generators (AVG) was discussed in the paper. The horseshoe vortex was generated at the base of NACA0024 and the longitudinal vortices were produced by AVG with the controlled yaw angle. The velocity was measured by using a rotary x-array hot-wire anemometer with a stepping motor. The objective is to clarify experimentally the phase-averaged characteristics of the velocity and the vorticity in the interference field between horseshoe vortex and longitudinal vortices. The Reynolds number Re_θ based on the momentum thickness was 1670. It was found that the horseshoe vortex was shifted by longitudinal vortex pair. The longitudinal vortices in Common Flow Up Case make the horseshoe vortex move forward the corner of the wing and has the effect of attenuate as to the vorticity in the downstream. In Common Flow Down Case, they merge into one vortex and their vorticity is decreased.

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In order to clarify the relationship between the flow around passenger vehicle body and the high speed stability, the pressure affecting vehicle body and its influence for vehicle behavior was studied through wind tunnel experiment and on-road driving. As these test object, two kind of passenger vehicles were applied that one is the two-dimensional flow structure on trunk deck and the another one is the three-dimensional flow structure. During on-road driving, the variation was measured for the unsteady pressure on trunk deck and the vertical motion of vehicle body. These test result shows that the pressure fluctuation restrained vertical motion of vehicle body is occurred for the vehicle provided two-dimensional flow structure on trunk deck.

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The relation between pressure distribution on the rear deck of vibrating vehicle and the vehicle shape is not clarified. To clarify the relation, two vehicle models were used in experiments. One is easy to entrain side flow to the rear deck, another is difficult to do so. Pressure fluctuation on the rear deck was measured with the pressure sensor. The models were pushed up sinusoidally. In the model easy to entrain side flow, the pressure fluctuation on the rear deck was small. The pressure fluctuation on the rear deck center was correlated inversely well with the model height. On the other hand, in the difficult model, the pressure fluctuation was large. It on the rear deck center was slightly correlated inversely with the model height. The model easy to entrain side flow is less stable when the model is vibrated.

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This study is concerned with the flow around a triangular cylinder in the uniform flow exposed to a simple and high frequency acoustic excitation as the periodic disturbance. The mean pressure field on the cylinder surface and the velocity field around it are carefully investigated. When the disturbance related to the separated shear layer instability is added, the diffusion of the shear layer is changed and the vortex shedding characteristics are affected.

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The fluttering characteristics of a multi-articulated flat plate were investigated experimentally in a wind tunnel. An articulated flat plate oscillates itself in a mean flow, and it has steady oscillating mode. The flow structures around an articulated plate were visualized by using the smoke wire method. From the results of visualization, it was found that the separated flow region formed on the concave side of the articles of the plate. Also the tip vortices were formed from both of the side edges of the plate. These separated regions and tip vortices formed around the articulated plate synchronized with the periodic movement of the plate. Furthermore, the results of the visualization showed that the separated region formed behind the articulated plate was disappeared when the tip vortices were growth. It is because that the tip vortices induce the flow behind the plate to the surface of the flat plate.

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In this study, we studied flow around a freely falling flat plate, especially focusing on the autorotating motion, by experiment using high speed camera and numerical simulation by discrete vortex method. The computed result agree well with the experiment and it was found that the trajectory of the plate is almost linear but fluctuate, especially, in the region where the plate turn around. Experimental result show that the effect of the aspect ratio L/W becomes large in the region L/W<4.2 and in this region, the rotation frequency increases as L/W increases. The computed result show the relation between flow pattern and fluid dynamic forces and the comparison with calculation of the falling plate with forced rotation founds that the interaction between plate motion and fluid dynamic force appear in the region θ=0°〜θ=90°.

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In this study, the interaction vortex flow features around a pair of parallel arranged bluff cylinders were observed by visualizing water flow experiment at the range of the gap ratio G/d=0〜3. It was obtained that the result of established wind tunnel test and the result of this water tank test agreed about the characteristics of vortex shedding when varying the distance of circular cylinder gap. The flow pattern and vortex shedding frequency of another type bluff cylinder (triangular and square cylinder) were also investigated. As a result of the experiment, it was shown that the flow pattern of wake flow was divided into three kinds (coupled vortex streets, biased gap flow and single vortex street) regardless of the cylinder section shape and the cylinder size. Then, the region of the appearance of flow pattern was shown about each case.

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The purpose of this study is to understand the effects of the 3-dimensional disturbance in the 2-dimensional vortex street wake, which is produced by a zigzag circular cylinder, on the wake characteristics and the breakdown process of the vortex street. As a result, it was found that the longitudinal vortex structures are formed in the narrow region around the top of zigzag, and that these longitudinal vortex produce high Reynolds shear stress.

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A new spectral method is proposed for the analysis of cylinder wakes by use of the Chebyshev-Fourier spectral method. It has not been often used in the cylinder-wake problems due to its difficulty of giving the boundary conditions at the downstream direction, however this difficulty is removed by applying of the boundary condition approaching a uniform flow at infinity.

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It was reported that the galloping of square cylinder can be suppressed by a downstream strip-plate in cruciform arrangement. The purpose of this study is to investigate the effect of the downstream strip-late for various dimension system. It is shown downstream strip-plates with a width of w=0.5d〜1.0d suppress the galloping of square cylinders with side length d=26, 32, 40mm when the gap s is smaller than certain values depending on the system dimensions. For the system with w/d=1.0, the trailing vortex excitation is induced over the range of s/d=1.0〜1.6.

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Particle image velocimetry (PIV) is applied to measurement of airflows around permeable circular cylinders. The aim of this study is to understand the wake structure of a permeable object subjected to uniform flow, such as buildings under construction, steel tower frames, and natural trees. The experimental model of the permeable cylinder is made of squared meshed sheet with a mesh number 32 and an opening ratio of 0.54. The following points are newly found when the flow field is compared to that of a solid cylinder. 1: In case of the permeable cylinder, the turbulence peak appears in a downstream region relative to the solid cylinder, because generation of vortex street is delayed significantly. 2: The drag is not simply estimated only by the opening ratio of the permeable cylinder. 3: The permeable cylinder has non-periodical vortex shedding. This has been confirmed from the correlation coefficient between the enstrophy and the turbulence intensity, which is greater than the solid one.

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The purpose of this study is to investigate drag characteristics of a living tree as fundamental research of roadside trees and windbreak forests. We used living conifers, broadleaf trees and a bamboo, as test pieces of the wind tunnel experiment. Reynolds number based on tree's maximum crown width is in the range of 2.0×10^4-1.3×10^6. Change of drag was influenced by swaying of tree's trunk and deformation of tree's crown. Drag of trees was increased and drag coefficients were decreased as Reynolds number was increased. However, the tendency of drag characteristics depends on the swaying motion of tree's individual difference.

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The drag coefficient of solid particles falling in the air has been investigated experimentally. Small spherical particles free-fall through quiescent or turbulent flow in which the turbulent level is kept constant with rotating grids as a turbulent generator. Averaged flow property that is changed depending on the charge of the particles is measured by means of LDV. Particle velocity is measured by means of 2D-PTV with laser sheet and CMOS camera. In still flow, by increasing particle volume fraction (up to O(10^<-3>)) the drag force for each particle changes, while in the turbulent flow the drag force for each particle is changed with the change of volume fraction but is relatively insensitive to turbulent intensity. Consequently, the existing empirical drag coefficient for solid particle, which depends only on the particle Reynolds number, is insufficient and it depends on the volume fraction of solid particles and ambient turbulent statistics.

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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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A number of studies on unsteady flow at low Reynolds number regions have been performed in recent years since the Micro-Electro-Mechanical-Systems (MEMS) is developed with the aim of flow control and micro flight robot. The flow field above has also attracted significant attentions in bio-hydrodynamics due to the need to understand the propulsion mechanisms of aquatic animals, birds and insects. In this study, we have measured detailed vortex flow structures behind a elastic flat plate airfoil undergoing heaving motion at low Reynolds number regions by PIV measurement. We have clarified the vortex flow patterns, vorticity contours and jet velocity behind the elastic flat plate. Moreover, the detailed vortex flow structures behind the heaving elastic flat plate were compared with those of heaving flat plate and heaving NACA0010. The thrust producing vortex street was formed easily behind the elastic flat plate undergoing heaving motion. The jet velocity behind heaving elastic flat plate increases as Strouhal number increases. In particular, jet flow becomes over 3.0 at St=0.43 and the values are greater than those of the heaving NACA0010.

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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.

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The vortex rings generated in non-circular jets are deformed and interacted three-dimensionally owing to self-induced velocity, and the vortex motion enhances mixing. To understand the mechanism of the mixing enhancement, it is crucial to make clear the three-dimensional vortical structure caused by the interaction of non-circular vortices. In the present study, the details of three-dimensional vortical structure of a rectangular jet of aspect ratio 4 is clarified using Large Eddy Simulation (LES), and the interaction mechanism of rectangular vortices is discussed, focusing the deformation of vortices. The simulation results reveal the details of the vortex interaction in the rectangular jet: the vortices deform owing to the non-uniform curvature effect, and the interaction of vortices generates hairpin vortices via vortex stretching.

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A numerical simulation of two-dimensional jets was carried out by the SOLA methods. The two-dimensional jets were discharged from a slit in a wall at Reynolds numbers less than 50. The difference between the calculated flow fields and those of the Bickley jet is due to the non-uniformity of pressure field near the jet exit of the wall. The jet spreads faster than the Bickley jet. The decay of streamwise velocity on the center-plane is more rapid than that of the Bickley jet. The streamwise velocity profile is different from that of the Bickley jet, and a reversed flow is generated in the outer part of the jet. Integrals of momentum and pressure were calculated on a control surface to confirm the momentum conservation law. The integral of momentum is not constant, and balances to the integral of pressure, in the streamewise direction.

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Structure of roll vortices was examined in the transition region of a parabolic plane jet of Re=3850. Their pairing process were controlled by acoustical bimodal excitation and small tabs attached around a jet exhaust. Conditional sampling gave the phase-averaged maps of turbulence quantities; vorticity, Reynolds stresses and production terms. At pairing enhancing mode for the case of symmetrical vortex arrangement, the weaker trailing vortex shifted inward and entangled toward the downstream stronger leading vortex at the height of the tabs. Large amounts of coherent and incoherent Reynolds stresses became distributed widely through their mutual interaction, stretching of the trailing vortex or fragmentation by the breakdown of coherent vortices. Negative energy transfer from the incoherent to coherent components was observed, being caused by the excessive enhancement of the vertical structure. At the pairing redarding mode, two adjacent vortices were observed seldom to merge each other.

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As a result of the characteristics of the flow structure of plane jet from push-pull local ventilation systems, we reached the conclusion as follows. At first, in the region close to the nozzle, the maximum value of the mean velocity of jet goes down with downstream distance and the distribution spread upward and downward. The distribution profile of velocity u^^- and v^^- develops forming similar figure when X_1/L=0.34. The relative turbulence intensity profile of u' and v' shows the similar tendency and the position of the peak value moves from y_1/b_<1/2>=1 to y_1/b_<1/2>=0.8 with down stream distance. Secondary, in the region close to the exhaust hood, the mean velocity distribution in the axial direction is almost identical to the gauss distribution when y_1/b_<1/2><1. However, when y_1/b_<1/2>>1, the distribution moves upward from the gauss distribution. When it comes to the relation turbulence intensity profile, the value is lower than the results by Gutmark et al. As it gets close to the exhaust hood, the relative value of u^^-/u^^-_m increases because the value u^^-_m goes down, resulting in unclear peak point. Thirdly, the maximum value of mean velocity on the central axis goes down with downstream distance. That result is almost identical to that by V.W. goldschmidt et al. When the half-velocity points are almost identical to the relation expressions by Gutmark et al. until X_1/2B_1=8, however, when it comes to the downstream below that, the value increases under the influence of the exhaust.

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It is possible to control the spread of a plane jet passively by the vortices from a two-dimensional cylinder installed in the nozzle contraction. In this passive control method, two remarkable conditions to enhance the jet diffusion were found. One is the harmonic excitation and another one is the inharmonic excitation where the two distinctive spectral peaks at frequencies f1, f2 and low frequency f3. It is also known that the jet exhibits flapping motion at the low frequency f3. In this study, in order to compare the controlling effect of the jet diffusion by the wake from a small circular cylinder installed in the nozzle. As the results, the jet spread was found to be enhanced only by flapping motion of the jet in multiple control conditions in which diameter and location of the cylinder differed. However, the Strouhal frequency of the vortex in the cylinder wake in these enhancing conditions to was almost equal, and it became a value which was similar to the Strouhal frequency St_H≒0.45 of shear-layer mode.

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A planar liquid sheet jetting from a thin nozzle slot starts two-dimensional flutter in the direction normal to the sheet at a certain distance downstream from the slot. Further downstream amplitude of the flutter exceeds in the order of its wavelength and then the sheet breaks down to droplets. Recent linear stability theory suggests that viscosity of circumambient gas is one of fundamental factors of the sheet flutter. In this study, in order to control the streamwise velocity of the circumambient gas around the sheet, homogenous jets from air nozzles mounted in both sides of the water nozzle were supplied. Flow images show obvious suppression of the sheet flutter in the case where the gas velocity is equivalent to the velocity of the sheet, suggesting that the circumambient gas essentially affects growth of the flutter of the liquid sheet.

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Jet flows generated by a circular synthetic jet actuator were investigated experimentally by using a hot-wire anemometer. The mean and turbulent velocity profiles were measured for two forcing conditions of alternating flow in an orifice nozzle. An equivalent jet velocity is defined based on the measured momentum of synthetic jets to compare with the velocity profiles in a circular jet. The results indicate that the synthetic jets show the larger spreading rate in jet width and the higher decay rate in velocity than those of a circular jet. This wider spreading can be caused by the stronger turbulent motions in the synthetic jets. Two synthetic jets whose momentum is similar but forced by different frequencies show the different jet evolutions. This difference is attributed to the change in lifetime of vortex rings emitted from the orifice nozzle.

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In the present paper, a new type of oscillatory device is proposed. This device is excited by one-degree-of-freedom flutter which does not occur in the uniform flow. As for the characteristics of oscillation, the dependence of pitching amplitude and Strouhal number(St) was measured vs. Reynolds number(Re) on L/c. As for the characteristics of mixing, the time-averaged velocity distributions were measured, and the effect of mixing enhancement was evaluated from the extension of the half-velocity width and the decay of maximum mean velocity. Oscillation characteristics shows that St was almost constant in Re>1.0×10^5. Pitching amplitude was constant when flow velocity is the critical flutter speed. Mixing characteristics shows, the half-velocity width and the decay of maximum mean velocity were found to be greater for the oscillating flat plate than for the without flat plate.

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An abrasive water suspension jet(AWSJ) has a greater capacity for drilling and cutting than a conventional abrasive water injection jet (AWIJ). However, the drilling capability of the AWSJ under submerged condition decreases steeply with the increase of the standoff distance. In order to expand the effective standoff distance of the AWSJ under submerged condition, a sheathed AWSJ nozzle was proposed in the previous paper. In the present paper, observations of the jet issuing from the sheathed nozzle are conducted without addition of abrasive. The injection pressure of the jet is 5 to 10 MPa and the cavitation number is in the range from 0.01 to 0.05. Observations of the flow in the sheath are carried out with a sheath made of transparent acrylic resin pipes. A void filled with vapor is formed in the root part of the sheath. The jet expands fully out to the sheath inner diameter in the region near the sheath exit and a bubbly mixture zone is formed. A cavitation cloud extending from the bubbly mixture zone appears to be continuous near the sheath exit but separates and develops into lumps of cavitation bubbles. The bubbly mixture zone in the sheath fluctuates with time but the frequency of the fluctuation is much smaller than that of the evolution of the lumps of cavitation bubbles outside the sheath.

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In order to study on the jet diffusion control, the jet flow issuing from the circular pipe with fluttering fins has been investigated. It has been already recognized from previous studies that the jet diffusion was promoted by attaching fins to the circular pipe and there exists more effective fin length to the jet diffusion. In this paper, the turbulent properties were investigated from the velocity information obtained by the PIV method. This experiment has been carried out in the cases without fins and with fins having the length L/d=1.5 and 2.5. As a result, it has been found that the turbulent intensity is supplied by the fin vibration and a large fluctuating component appears with the increase of the fin length. Moreover, from the results of the auto-correlation, it has been clarified that the turbulent structure contained in the jet flow is destroyed by attaching fins.

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The relationship between flutter phenomena of a flexible thin sheet on a lip of jet outlet swept by a plane air jet flow and the enhancement of jet diffusion is examined under a backward facing step. The investigation is based on an experiment where the mean velocity of the jet, the step heights and the length of the flexible thin sheet are varied. The comparison of the velocity distribution of the jet between with the fluttering flexible thin sheet and without it. As a result, it has been clarified that the jet with the fluttering flexible thin sheet enhances the jet diffusion.

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When we input momentum to the circular jet by the mini jet that is about 1/100 size and set on edge of the circular jet the cross section of the circular jet is deformed to elliptically. And diffusion of the circular jet is prompted. In this case suitable position of the mini jet is considered. Around the position initial mechanism of vortex ring is seen. Momentum or materials input into the circular jet due to the mini jet are took in the circular jet and mixed immediately. Operation of the mini jet prompts the diffusion of the circular jet and mixes the materials introducing by the mini jet with the circular jet. And this shows possibility the control of products in combustion gas etc.

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In order to develop a new mixing procedure, we conduct DNS (direct numerical simulation) of a combined jet, in which four jets are placed on one plane and each jet is directed for a impinging point. Three configuration are examined for several inclination angle of jet, in particular in two of three cases, a swirl motion is produced by adjusting the meeting position. From view of coherent structures, it is found that the impingement enhances the occurence of small scale vortices, while that of large-scale structures does not definitely appear. Also to compare the mixing efficiency, a statistical entropy is calculated for all cases. As a result, the swirl motion contributes to the increase of mixing efficiency, however, because of the lack of large-sale structures, the jet expansion of all cases are suppressed.

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A development process of a low-density jet, such as a helium gas and a hot air jets, is different from that of a constant-density jet. Side jets, which are radial ejections, are formed at vicinity of the nozzle exit and mixing of fluids between the jet and the surroundings is enhanced. Helium gas jets were discharged from a round nozzle upward and visualized by planar laser Mie scattering (PLMS). A configuration of the side jets varies with Reynolds number. Side jets at low Reynolds number are similar to a bifurcation. A flow structure of the side jets at low Reynolds number was mainly investigated. The visualized side jet was recorded using a high-speed video camera. The velocity field involving the side jet was visualized by PIV. The instantaneous velocity in the potential core was measured by a hot-film anemometer. The velocity in the potential core periodically fluctuates, and lamps with high speed and low speed are alternately passing the inside of the potential core. The potential core is pulsating radially, and the side jets at the low Reynolds number is generated periodically.

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Active control is applied on a circular jet using secondary film flow, with and without acoustic excitation. The velocity ratio of the film flow to the main stream and/or acoustic excitation frequency is changed. This active control method is applied on a circular jet buoyant jet (Carbon dioxide or Helium gas). The jet structure is visualized with laser light sheet in the plane including jet axis. It is described qualitatively the process of vortex ring growth and outbreak that it is generated in the shear layer of jet.

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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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In order to investigate the sustaining mechanism of the large-scale streamwise vortical structures in a turbulent Couette flow, a vorticity-probe consisted of 4-X type hotwire has been developed. The effects of the probe-size and mean-shear on the probe-performance as well as effectiveness of the temperature compensation scheme developed are discussed. The final probe performance was estimated by measuring the fluctuating velocity and vorticity components in turbulent Poiseuille flow and comparing them with DNS and/or LDV measurements. Contributions to Dω^^-_1/Dt from various terms of ω^^-_1 (streamwise vorticity) transport equation in Poiseuille flow and Couette flow are estimated using data obtained from vorticity-probe experiment. In Poiseuille flow the total of these terms weaken the streamwise vortex, while these in Couette flow have no such tendency. These results are consistent with the decaying or sustaining properties of the streamwise vortex in Poiseuille or Couette flow.

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The objective of this study is to control the reattachment process of the separating flow over a backward facing step in a low Reynolds number range by synthetic jet. The Reynolds number based on the step height ranges from 301 to 908. The synthetic jet has a frequency of 36Hz. In order to investigate the effect of periodic disturbance on the reattachment process, Micro Flow Sensor was used for measurement of forward flow fraction and frequency analysis. The experimental results show that synthetic jet is effective for flow control. The reattachment process strongly depends on Reynolds number and velocity ratio.

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Numerical simulations of relaminarization from turbulence in two-dimensional channel flow are carried out using the lattice kinetic scheme, which is an improved method of the original lattice Boltzmann method. Calculated turbulent energy in the relaminarization shows an exponential decay for 600〓Re〓900, where Re is the Reynolds number based on the streamwise velocity at the centerline and the half width of the channel. Also, the half-life time of turbulence is investigated in these cases and the critical Reynolds number of the relaminarization is estimated as around 1165. In addition, these results indicate that the present numerical method can be useful for microscopic investigation of such transition problems.

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In this research, we educed organized vortex structures from numerical data of the supersonic mixing layer (Watanabe and Maekawa, 2004) using Proper Orthogonal Decomposition (POD). Lambda-shaped vortices were founded as organized structure which has high energy contribution in supersonic mixing layer. The pressure-strain correlation term is responsible for the energy exchange among three components of turbulent energy. POD results remarkably showed energy flow described by pressure-strain correlation term.

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Underexpanded jet which exhausts from a circular nozzle and impinges on a flat plate is studied experimentally and numerically. The flow field is visualized by shadowgraph method and the shlieren method, and the frequency of oscillation is measured. Three-dimensional Euler equations are solved using symmetric TVD scheme. The oscillatory phenomena mainly in the helical mode which are considered to be caused by the vortices moving around the jet are shown. These vortices are generated on the jet boundary near the nozzle exit and become larger as they move downstream. In case of the impinging jet, they affect the comparatively low-speed flow such as the wall jet and the separation bubble with small nozzle-plate spacing. The jet strongly oscillates with larger nozzle-plate spacing.

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