Turbulence is an eternal target of fluid mechanics. In the end of 20th century, numerical study of turbulence was initiated. The famous milestone was Stanford Conference held in 1980-1981. In 21th century, the popularization of turbulence calculation has occurred because of spreading of low coat but high performance PC and CFD tools in which turbulence models are implemented. Turbulence of functional fluids has attracting much interest because of its utility in engineering applications. Among them turbulence including microbubbles has a lot of physically unique properties. Recently Kolmogorov's inertial subrange needs reconsideration on its existence condition and ubiquitousness. Finally, the applicability of the probability theory is addressed. In spite of the fact that turbulence is probabilistic phenomena, the application of probability theory has not been made much progress these decades. However this way of study is most likely to proceed with cutting edge technologies of measurement and advanced mathematics.

A pulsating flow has been studied experimentally, because of its practical importance in the mechanical engineering (e.g.,intake-exhaust systems of the engine and the industrial piping). It is very useful to investigate such an unsteady flow experimentally for improvement of mechanical efficiency. The present experiment is conducted to clarify a flow state of the pulsating flow with a period T=0.2sec in the 180° curved pipe. We measured the wall static pressure, wall shear stress and distributions of axial flow velocity respectively. The pressure gradient shows favorite pressure gradient during the acceleration to the deceleration phase and it forms the adverse pressure gradient near the phase of valve closing. The wall shear stress shows a spiking peak just after opening the valve. The distribution of the axial flow velocity shows the flow maintained constant, and then the fast flow is shifted to the outside which is affected by the centrifugal force.

In this study, an experimental study is performed for multiple-passage duct flows. The multiple-passage is a reverse flow type, and consists of the five branch ducts. The duct flows are investigated from the view point of flow uniformity and pressure loss. Experiments are performed for the Reynolds number based on the bulk velocity and hydraulic diameter at the inlet duct from 6.0×10² to 1.5×10³ . Aspect ratio (i.e., the ratio between the height and width of the branch duct) is changed into 0.6, 1.0 and 20. The wall static pressure is measured, and the pressure loss and flow rate are evaluated. The results show that the pressure loss decreases and the flow rate in each branch passage improves by increasing the aspect ratio. The uniform flow distribution is realized by increasing the volume of the outlet chamber.

This paper presents the measurements of flows in the upper human airways consisting of the trachea down to the third generation of the bronchial tree using particle image velocimetry (PIV). This study utilized realistic transparent human bronchus model in order to improve understanding of mechanisms in chronic obstructive pulmonary disease (COPD) and Bronchial stenosis. The transparent silicon model of human bronchus was fabricated from CT images. These results showed that velocity distributions were divided into three locations in human bronchus. Mean velocity were calculated by time average. Reynolds number was calculated from the averaged-velocity and compared with that of Weibel's report.

Chaotic mixing in three different types of curved-square channel flow has been studied experimentally and numerically. The wall of channel rotates around the center of curvature and a pressure gradient is imposed in the direction toward the exit of the channel. This flow is a kind of Taylor-Dean flow. Effects of three different types of moving walls, top and inner walls (B.C.1; Boundary Condition 1), an inner wall (B.C.2; Boundary Condition 2), and a top wall (B.C.3; Boundary Condition 3) on chaotic mixing, have been investigated experimentally and numerically. The secondary flow is measured using PIV (Particle Image Velocimetry) and LIF (Laser Induced Fluorescence) methods to examine secondary flow characteristics. Also we performed three-dimensional numerical simulations for the exactly same configuration as the experimental system to study the mechanism of chaotic mixing. It is found that good mixing performance is obtained in the case of B.C.1.

It is known that the critical Reynolds number of turbulent transition in the straight-pipe flow is about 2300. However, it is reported that turbulent transition is delayed when there are micro-bubbles in water. And the drag was reduced in same Reynolds number range. To confirm the effect of the drag reduction, it is important to make a laminar flow at the entrance of the test section. To keep flow stable, we ensure the long entrance section of about 4 m. Then we measured the differential pressure and calculated friction factor in the straight pipe with circular cross section. The inner diameter of the pipe is 20 mm. In this experiment, turbulent transition took place at the same Reynolds number range when we use water with micro-bubbles and without micro-bubbles.

The micromixer, which has a rotor with a curved channel, is studied experimentally. The Taylor-Dean flow in a curved channel of square cross-section is investigated using PIV (Particle Image Velocimetry) and LIF (Laser Induced Fluorescence) methods. Two walls of the channel (the inner and top walls) rotate around the center of curvature and a pressure gradient is imposed in the direction of the exit of the channel. The non-dimensional parameters concerned are the Dean number De and the Taylor number Tr. Photographs of the flow in a cross-section at 180° downstream from the curved channel entrance are taken by changing the flux (De) at a constant rotational speed (Tr) of the channel walls. It is found that good mixing performance is obtained in the case of De ≤ 0.1Tr. This tendency appears more strongly if curvature is large. And we have confirmed the curvature effect of the channel on the mixing.

In semiconductor production, efficiency and precision of the cleaning process is important. In this study, we handle “Single Wafer Cleaner” that is one of the washing methods in the way of blowing air to a wafer with a turning disk at a high speed. However, the flow in the device becomes turbulence, which causes a problem that water drops and dusts re-attach to the wafer. It is necessary to understand the flow in the device. In previous investigations, we were able to get knowledge of the detection of vortices using numerical computation and Particle Image Velocimetry analysis in using the simplified experiment model. Therefore, we tried to understand the detection of large-scale vortices combining speed data and the unsteady pressure data. We measure pressure using microphones and perform the frequency analysis and cross correlation of the data. In doing so, we have get the knowledge of the vortical structure.

The existing vacuum handling device has some problems because the work becomes dirty and broken. Therefore, now a day the noncontact Bernoulli handling device becomes mainly. However, this device too has also some problems. For example, this device adsorption power is weak. Thus requires large power and flow rate. Hence this research will focus on the noncontact handling device with a swirling flow. The aim of this research is to verify the effect of parameter on the performance of the device.

Three-dimensional numerical predictions are presented for a laminar flow through a square channel with a sudden expansion of area ratio 4：1 in the range of Reynolds numbers Re = 20 to 1,900, using an Open Source CFD Toolbox (OpenFOAM). In particular, the effect of pressure gradient on the secondary flow, shear layer and the bifurcation of flow structure downstream of the sudden expansion was investigated. The results showed that the secondary flow induced by the pressure gradient existed along the shear layer upstream of the area of the disordered motion, and the secondary flow made the stream-wise vortex in the shear layer. So that, the high value of stream-wise fluctuating velocity also distributed in the shear layer.

Recently, the choice of power sources in industrial vehicles has tended to shift from internal combustion engines to electric motors. Consequently, contribution of noise emitted from a hydraulic system is becoming relatively prominent. It is, therefore, more than ever important to take care of the hydraulic noise in the industrial vehicles. It is known that speed of sound in hydraulic oil has an effect on pressure ripples which can be source of the noise. Therefore, it is important to understand behavior of the speed of sound reasonably in design of quiet hydraulic systems. However, relationship between operating conditions and the speed of sound has not been revealed up to now. In this study, the speed of sound has been investigated at the operating conditions for typical agricultural machines and construction machinery.

Pulsatile exhaust flow from an automotive engine is studied to investigate the correlation between the flow field and pressure characteristics. In our experiments, the exhaust flow is generated by a four-cylinder gasoline engine in a S-shaped duct, which consists of two bends and straight part, and time fluctuations of velocity and pressure of the flow are measured by hot wire anemometry and pressure sensor, respectively. Numerical simulations are also performed with RNG k-ε model. It is shown that time fluctuations of velocity and pressure are waves which have 8 peaks and we found that the fluctuation of velocity influences on differential pressure at both bends. In present work, the relation between velocity and wall pressure in S-shaped duct is discussed.

The objective of this research is to asses the periodicity in pulsating-arterial-flow with non-uniform rational B-spline (NURBS) representation of aorta. We compare wall shear stress (WSS) and the second invariant of the velocity gradient tensor to evaluate the periodicity. We also compute flow with aortic valve, and show the impact in the aortic arch due to the leaflets motion.

Noise suppression is of importance for jet engines. Acoustic panels installed in the fan duct can reduce the noise emission while it induces the pressure loss. In order to achieve the suppression of the noise emission and the low duct loss simultaneously, we have designed new acoustic panel and conducted implicit large eddy simulations of the duct flow with the panel in this study. Since the Mach numbers in the duct and the hole of the cavity are extremely different, we have employed an all speed Roe scheme for compressible flow solvers. The turbulence is induced by a roughness block. We have found that the turbulent boundary layer becomes thinner just downstream of the hole in the duct since a part of the turbulence goes into the cavity.

Particles transport in an unsteady flow is of great interest in physical or engineering subjects. In the present report, we consider particle deposition on the channel wall induced by a sudden deceleration, namely, rapid closure of the end of channel. For such case, the induced flow by the sudden suspension of inlet flow in a pipe was simulated, and particles transport was considered. Suspension of the inlet flow provides impulsive pressure gradient through the pipe. The impulsive pressure gradient plays a role of velocity potential reversively. The sudden stop of inlet and outlet generates a counter flow depending on velocity profile in Poiseuille flow. The counter flow provided vortex streets, then a breakdown of vortex has possibility to make particle deposit to the wall. So, we discussed the mechanisms of the flow induced by the sudden stop of the inlet flow and particles transport whom the breakdown of vortex may drive.

A typical exhaust system includes Diesel oxidation catalyst (DOC), which is for oxidizing the gas, and Diesel particulate filter (DPF), which is mainly for trapping the PM. Because these processes involve chemical reactions, the temperature inside the system is significant. Our objective here is to estimate the fluid temperature by thermo-fluid analysis. Here we use the space–time isogeometric analysis (ST-IGA).

In this research, three-dimensional separated flows around a rotating disk in uniform flow are experimentally examined to understand the flow mechanism around an automobile tire. Experiments are performed with a circular disk supported at the center of the test section of water circuit and velocity vectors around the disk are measured by using particle image velocimetry (PIV). The velocity of bulk flow is 250 mm/s and the Reynolds number based on the disk diameter is 1.25×10⁴ . Three-dimensional vector field is reconstructed from two sets of time-averaged distributions of two-dimensional vectors independently measured from two different directions. The reconstructed results successfully represent the structure of longitudinal vortex in the wake.

The purpose of this examination is evaluate usefulness of microbubble for PIV. It is necessary to compare microbubble and solid particle because specific gravity of them are different. Mean diameter of microbubbles are around 40μm. Investigations has been done using backward-facing step flow (Re=11000). The channel has an aspect ratio of 6 and expansion ratio is 2. This investigations show distribution of mean velocity and Reynolds stress. The result using microbubbles generally consisted with that of solid particles. On the other hand, difference of result near the peel sheering layer is larger than that of lower Reynolds number, therefore, there is a possibility that the difference cause measurement error for PIV using flow of high Reynolds number with peeling.

Through the simultaneous measurement of the pressure and strain-velocity, the role of Pressure-Strain Correlation, which appears in Reynolds stress transport equation, is investigated in a turbulent planar jet. We use a constant-temperature hot-wire anemometry system and a miniature pressure probe for velocity measurement and fluctuating pressure measurement, respectively. Two types of the combined probe are introduced for acquiring the Pressure-Strain Correlation. One consists of a X-type hot-wire probe and a pressure probe and the other consists of two I-type hot-wire probes arranged in vertical direction and a pressure probe. The measurements were well-performed in the present planar jet expect for the location where the mean streamwise velocity is small. The acquired signal and the result of the cross-wavelet analysis show the intermittency of the Reynolds stress and the Pressure-Strain Correlation, which indicate that the Reynolds stress transport phenomena occurs locally in space and time in a turbulent planar jet.

When the vortex ring moves to some extent, circumferential waves occur in vortex ring and the amplitude of wave becomes big gradually. At last vortex ring deform and disappear. Study of vortex ring has been experimented by technique of the visualization. In the case of visualization, it is necessary to use the tracer. However, the tracer may influence something to vortex ring disappearance. Therefore this study measure the vortex ring without the tracer using hot wire anemometer. We produce the hot wire anemometer and device to measure circumferential waves. As the result, we were able to check the operation of hot wire anemometer and device.

In the separated and reattachment flow, unsteady heat transfer, which is relative to the flow behavior, is observed near the reattachment point. To clarify the thermal fluctuation, it is necessary to measure simultaneously thermal and flow fields using the measurement techniques with the high sensitivity and fast response. The aim of this paper is to construct the simultaneous measurement system, which is able to measure unsteady heat transfer and flow behavior using dynamic PIV and high-speed infrared thermography, and to discuss the fluctuations of thermal and flow behavior in the separated and reattachment flow over a backward facing step.

The effect of the disturbance on the laminar-turbulent transition of the mixing layer is experimentally investigated. So far, two kinds of experiments were conducted with the Reynolds number of 5000; in one, the plates at the nozzle exit do not protrude into the nozzle section and remain in a 'stationary state' and in the other, 'anti-symmetrical oscillating state', the plates oscillate perpendicularly to the flow and anti-symmetrically with each other in relation to the flow. In the present study, the Reynolds number was decreased to 3000 and this flow field was visualized by smoke wire method. The effect of the Reynolds number was examined with aid of the visualized flow field image.

Mixing phenomena, induced by a jet issued diagonally upward into a two-layer densitystratified fluid in a cylindrical tank, are numerically simulated. The upper and lower fluids are water and a NaCl aqueous solution, respectively. The mass concentration of the NaCl-water solution is 0.02. The lower fluid is issued from a nozzle mounted on the tank bottom. The angle of the nozzle to the tank bottom is 60 degree, and the Reynolds number defined by the jet velocity and the nozzle diameter ranges from 475 to 3089. The simulation highlights the jet behavior relative to the density interface and the resultant mixing phenomena.

The purpose of this study is to investigate the effect of turbulence properties on turbulent diffusion phenomena. Various turbulent flow fields mixed stretched and unstretched turbulence were made by changing the type of turbulence generator set in inlet and outlet positions of the contraction unit of a wind tunnel. As the result, it was found that the highest diffusion factor was in the case that turbulence generator was set in the inlet position of the contraction, namely, stretched turbulence only. This result means that stretched longitudinal vortex contributes greatly to turbulent diffusion and longitudinal vortex is broken down by the turbulence generator when it is set in the outlet position of the contraction.

It is thought that local absolute instability by jet fluid with low density and Widnall instability of a vortex ring are related with side-jets formation in a round jet with low-density. If the density of the jet fluid is sufficiently lower than that of the ambient fluid, an initial region in a two-dimensional jet becomes locally absolute unstable. Side jets are formed in the rectangular jet as similar to a round jet, when the density of jet fluid is sufficiently lower than that of ambient fluid. Relationship between streamwise vortexes and side-jets is discussed from a result of three-dimensional imaging for the rectangular jet.

When a low density fluid, such as hot air and helium gas, is discharged from a round nozzle, side jets are generated in the initial region of the jet. These radial ejections of the jet fluid are called side jets. It is thought that the side jets are generated by self-excited oscillations in the jet column. The self-excited oscillations are caused by the local absolute instability. We think that the absolute instability is generated in the jet column by a feedback effect generated by an external counter flow. It was confirmed that the side jet is formed in a round jet with an external counter flow, using flow visualization by a planar laser Mie scattering.

The article describes a review of the researches on the separating shear layer over the backward-facing step and its control since 1960. The separating shear layer over the step is one of the typical flows which involves the vortex evolution and reattachment process after the boundary layer separate at the step. There are many papers on the flow control techniques and devices in the backward-facing step flow, since it is easy to evaluate the effect of flow control method quantitatively by comparing the reattachment length under the different control conditions. The recent trend on the flow control is also discussed.

A small centrifugal compressor with a high rotation speed is necessary for the 100-kW class gas turbine, and variable inlet guide vanes (IGVs) should be installed at the inlet of such a compressor. Under lower flow rates, the vane angle (β₂) is set smaller in order to align the flow with the compressor blade motion, and flow instabilities having specific frequency characteristics appear and the performance of the compressor degrades. On the other hand, it is known that the periodic oscillation occurs in a suction pipe with swirling flow. This phenomenon is induced by spiral vortices. In this study, an attempt is made to clarify the relation between the flow instabilities downstream of annular inlet guide vanes and the swirling flow in a strait suction pipe. The influence of the suction pipe length on the oscillating characteristics of the flow downstream of IGVs is discussed based on the measured pressure fluctuation.

This paper presents a three-dimensional flow around NACA0012 in a periodic flow with a sinusoidal velocity profile in the streamwise direction. The measurement is conducted in a water tunnel under Reynolds number Re=3000, reduced frequency k = 2.3 and angle of attack 15° . The phase-averaged velocity field is measured by using Particle Image Velocimetry (PIV). Three dimensional phase-averaged u − v vector field is reconstructed by twenty-one x − y vector fields. Proper Orthogonal Decomposition (POD) is applied to identify dynamic structure at each phase. It is shown that low-order mode functions have large contribution when periodic velocity is maximum velcity.

Many researchers have experimentally and numerically investigated the flow field around an unsteady airfoil, which is a common unsteady flow. In particular, there have been a number of studies on the flow field around a pitching airfoil, a heaving airfoil and a combination airfoil with combined pitching and heaving motions. In recent years, the flow field in the vicinity of moving airfoils capable of flexible elastic deformation has become a focus of attention. Flow in the vicinity of an elastically deforming airfoil may be understood as a fluid-structure interaction (FSI) problem, and the motion and deformation of elastic airfoils, as well as the associated vortex flow phenomena in their vicinity, are complicated. In this study, we investigate the dynamic behavior of vortices on elastic heaving airfoil in a separation region, at 16 degree of attack angle, by fluid structure interaction simulation using ANSYS 16.1/ANSYS CFX 16.1.

Detailed experiments have been made for effect of the favorable pressure gradients on the law of the wall in a turbulent boundary layer. The local wall shear stress was measured with a direct measurement device. Mean and turbulent velocity profiles were measured with a hot wire anemometer. The effect of the gap between a surrounding plate and floating element will be reduced by using an appropriate floating element size. The mean velocity profile under the favorable pressure gradient is likely to be consistent with a modified log-law.

In this paper, the effect of leading edge shape on developing of the boundary layer on a flat plate have been investigated by the measurement of boundary layer velocity distribution at the mainstream velocity 5m/s and 14m/s. The leading edge shapes are elliptical shapes (2:1, 4:1, 8:1), sharp edge (30 deg.) and right angle. As the result, the elliptical shapes (4:1, 8:1) produced the laminar boundary layer. In addition, sharp edge formed the turbulent boundary layer, regardless of the mainstream velocity. On the other hand, the elliptical shape (2:1) took the different boundary layer by the mainstream velocity.

Effect of apex angle 2α has been investigated on the behavior of the arch vortex generated from a circular cone placed in a thin laminar boundary layer. The apex angle of circular cone is in the range of 15°<2α<90°and the height H is 50mm. Then, the Reynolds number based on the height of the circular cone is 1000 and the relative boundary layer height δ/H is 0.42. The flow fields were visualized using the PIV (Particle Imaging Velocimetry). Conventional time averaged and phase averaged vector fields were obtained behind the cone. Some quantitative properties such as maximum vorticity, frequency and radius of the unsteady vortex were defined and discussed on dependence of the vortex structure on the apex angle.

Effect of setting and apex angles on the flow drag acting on a pyramid placed in boundary layers has been investigated experimentally. Flow drag was measured by drag balance and flow patterns were examined by oil film method. Drag coefficient takes minimum value for certain range of setting angle. Some characteristic lengths were defined based on oil film observations. Possible behavior of vortical motion and separation or reattachment flows are correlated with the variation of drag coefficient due to setting and apex angles.

In the present study in order to investigate the possibility of flow control for multiple cylinders using elastic cylinder, we conduct a simulation of finite-length multiple cylinders being installed in turbulent channel flow. For a elastic cylinder, the rigorous equation of motion for elastic continuum is solved with a finite volume method; the effect of existence of cylinder in the flow computation is taken into account using the immersed boundary method. From time averaged quantities, we demonstrate that multiple cylinders included elastic cylinder markedly modulates the wake structure depending on the separation between cylinders.

The mean flow properties of the multiple circular jets issuing from circular nozzles in a line were investigated experimentally. The aim of this study is to clarify an effect of the arrangement pitch of the circular nozzles on the mixing and the development processes of the jets. In this study, the nozzle arrangement pitch (S/d) was set to 4.2, 2.8 and 1.4. S/d indicates a nozzle arrangement pitch which is normalized with nozzle diameter d. Reynolds number was kept constant at 25000 throughout the present experiment. The experiments were made using an X-type hot wire probe and the linearized constant temperature anemometers to measure the longitudinal mean velocity. From this experiment, it is revealed that the section of which U_ox/U_e on the x axis shows the decreasing rate of the two dimensional jet (U_ox ∝ (x/d) ^-0.5), moves toward the upstream region as decreasing with S/d.

The mean velocity field of turbulent free jet issuing from the multiple rectangular nozzles which are arranged in line has been investigated, experimentally. The aim of this study is to examine characteristics of the mean velocity field of the multiple rectangular jets with constant nozzle pitch aspect ratio S/L (=1.00) which is the ratio of the nozzle arrangement pitch S/d to the nozzle aspect ratio L/d. Four nozzle arrangement pitches used in this study were 6.25, 12.50, 18.75 and 25.00. The Reynolds number based on the nozzle width d and the exit mean velocity U_e was kept constant 25000, throughout this experiment.

Velocity fields of circular jets issued from circular orifices arrayed at an equal interval in a line, were studied with a central focus on the relation between the velocity and vortex motions. The interval of the circular orifices, which was the distance between jet exit centers, was 1.5 times greater than the diameter of the jet exit, and Reynolds number of the jets was 2500. In order to reveal the vortex motions and explore means of flow control, the jets were excited by a loudspeaker placed near the jet exit. Velocity was measured by a single normal hot wire probe, and mean velocity and turbulence intensity of the circular jets were examined. From the experimental results, the effect of the excitation appeared on the three-dimensional deformation and interaction of vortex rings, and the excitation frequency related to the instability of the shear layer near the jet exit was effective for increasing the jet cross-sectional area.

The effects of tabs at the flow characteristics of a plane jet at low Reynolds number was investigated. The flow visualization and velocity measurements were carried out using particle image velocimetry (PIV). In addition, three-dimensional plane jet numerical simulations were performed using ANSYS Fluent to investigate the vorticity and the vortical structures. We found that a plane jet with square tabs had the smallest jet spread downstream, and the jet's centerline velocity was larger than those of jets perturbed by the other tabs at Re = 2,000. It was also observed that the spanwise vortical structure of a plane jet disappeared completely if square tabs or delta tabs were attached. Good agreement was found between the experimental and numerical simulation velocity profiles when large eddy simulation (LES) with Dynamic Smagorinsky-Lilly (DSL) model was employed. The development of streamwise vortices in the shear layers that were produced behind the square or delta tabs could prevent the jet from spreading.

As a part of study on the diffusion control of jet flow, the purpose of this study is to control the jet diffusion by using the deforming nozzle. The shape of polypropylene nozzle can change from square shape into cruciform one smoothly. The velocity measurement of the jet flow was performed using a hot-wire sensors, by changing the shape of nozzle exit variously. The basic characteristics of the jet flow, such as velocity distributions and half value widths have been obtained. As a result, it has been clarified that the jet width of the deforming nozzle is suppressed in the downstream location from the nozzle exit to the 8 times the characteristic length. And the jet width of the deforming nozzle in xOy'-plane is small, comparing with that in xOz-plane. Moreover it has been also found that the diffusion of the deforming nozzle is same level in both planes in the downstream location more than 10 times of the characteristic length. Furthermore, in the in the downstream location more than 13 times of the characteristic length, in the case of the shape of the nozzle is a square, the diffusion of the jet is suppressed and the jet diffusion in the case of changing the shape of the nozzle continually periodically is promoted.

It is well known that longitudinal vortex appears in two-dimensional vortex street wake. The purpose of this study is to clarify about details of formation process of this longitudinal vortex and interaction between longitudinal vortex and two-dimensional vortex street wake by using flow visualization. As the result , it was found that the formation process of longitudinal vortex and the interaction mechanism depend on Reynolds number.

We have investigated the influence of flow velocity on the fiber distribution of a wood pulp suspension in wake region behind a flat plate inserted in a channel. This study was considered to understand the behavior of the pulp fibers in the hydraulic headbox of papermaking machines. The wake flow of pulp suspension was firstly visualized, and then the distribution of pulp fibers was obtained by optical techniques. The time-averaged and fluctuating fiber concentrations exhibit a complicated distribution that depends on the thin water layer formed on the flat plate and the shear layer generated at the trailing edge of the plate. The partition plate is slightly effective for obtaining a uniform time-averaged fiber concentration distribution and for making the fluctuating fiber concentration lower.

An experimental investigation has been made on the separated flow region behind a long flat plate with a blunt trailing edge. The flow was controlled by an additional corrugated sheet (CS) fitted to the trailing edge along the wake center line. The length of CS was adjusted 10, 20 and 60 mm. The instantaneous streamwise velocity of the wake with CS was measured by a single-hot-wire probe. 3D structure of the dominant shedding frequency just behind the trailing edge of the test flat plate, varying according to the length and shape of CS, was detected. Moreover, the change of flow pattern with CS, suggesting 3D structure, was visualized by using smoke-wire method. The results imply the three-dimensionality of the separated flow caused by the installation of CS.

Standard ‘ static ’ square grid is incapable of producing intense turbulence , while active grid produces large deviation isotropy isotropy . In this study , we investigated a method to generate the relatively strong and near-isotropic turbulence ‘ passively ’ by tethering a small object such as sphere and cylinder with a string. Turbulence is found to be intensified by oscillation of the small objects and there is clear difference in the manner of oscillation.

Laboratory experiments on atomization of shear thinning fluids (Xanthan gum solution in water) using airless sprayer were conducted in order to understand the hydrodynamic instability of the liquid sheet, which leads to droplet formation for ship hull coating. Flow visualization by backlight method reveals that the spatio-temporal behavior of the liquid sheet strongly depends on both the fluid rheology (concentration of the xanthan gum) and the spray pressure. The quantitative DFT analysis of the high speed video images shows that the high frequency modes of the liquid sheet instability are viscously damped for the high concentration fluids at low pressure atomization; the collapse distance of the liquid sheet at the spray axis increases with the concentration while it slightly depends on the angle from the axis. Our experimental results provide fruitful information to improve the efficiency and the quality in the spray painting for the ship hull.

Aquatic animals shed the vortex by oscillating their fins. The propulsive forces of these animals are related to unsteady fluid forces accompanied with the movement of vortices. The aim of this study is to clarify the relationship between the unsteady fluid force and the vortex behavior. Experiments using a mechanically controlled monofin were carried out in a water flume. The effect of the vortex dynamics on the propulsive force was investigated by calculating the forces acting on the monofin from the momentum of vortex. The propulsive force during one oscillating cycle estimated from the vortex attached to the monofin surface has the same tendency of propulsive force measured by a load cell.

In order to improve the performance of heat transfer with multiple impinging jets(MIJ), we investigate the DNS (direct numerical simulation) of single and two round impinging jets arranged at an inflow of flow field. In addition we introduce the intermittent control of inflow velocity as the new control method. As some parameters of intermittent control, both the period and phase difference between two jets are varied. From the view of timeaveraged velocity distribution of MIJ, it reveals that the generation of flow phemonomena such as up-wash due to the interaction between two jets are reduced through the intermittent control, and that the heat transfer performance i.e. Nusselt number on the impinging plate in both single and multiple cases are improved than that of uncontrolled cases.

We study effects of the divergence of the viscous terms on the incompressible flow. Here the set of the exact solution, of which the flow has global anisotropy, is applied to specify the effects. The anisotropy of the exact solution could be controlled by using a parameter. Firstly, the present framework of the simulation is verified. Then the numerical results are shown. The divergence of the viscous term reduces decreasing kinetic energy of the flow. The effects on the kinetic energy are hardly affected by the initial anisotropy. However, a temporal evolution of the anisotropy is produced due to the divergence of the viscous terms, which should be constant in the exact solution without the divergence. The divergence of the viscous terms increases the anisotropy of the flow field.