In this article, we are interested in the wake downstream a horizontal axis wind turbine. The velocity field explorations are carried out using PIV. An optical sensor is used to provide a signal in order to ensure synchronization between a digital camera, lasers and the angular position of the blade. This signal then passed by a delay circuit so that acquisition takes place according to desired azimuth angles. Exploration was carried out in planes with the angles 0, 30, 60 and 90°. Because of the resolution of camera CCD and the large dimensions of the field studied, each plane was divided into 6 windows. For each window, the velocity field was obtained by averaging the results of 95 pairs of images. Thus, the 3D velocity field was reconstituted by treating the results of images resulting from the explored azimuth planes. These results will be very useful to validate the various numerical models.

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The wake of Horizontal Axis Wind Turbine rotor was studied with both wind tunnel and field measurements. The detail measurements were carried out in the wind tunnel with Pitot tube array, and particle image velocimetry (PIV). The field measurements were carried out with cup anemometers and wind vane for 10-m diameter rotor. From the wind tunnel measurement, the wake was expanded from the position where the tip vortex was dissipated. The wake velocity behind field wind turbine was recovered in shorter distance than that for the wind tunnel measurement. The wake area was shifted toward radial direction in rotational plane related to wind turbine rotational direction. The wake velocity below rotor axis was not much recovered by the effect of tower compared to those above rotor axis.

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Turbulent flow measurements were conducted in the region between a pair of square cylinders set in uniform flow in tandem. The velocity data obtained with a PIV were averaged with respect to the pressure oscillation induced by vortex shedding from the cylinder to realize the three-level decomposition. The Reynolds stress related to the periodic fluid motion was found excessively large compared to those due to turbulent fluctuation. The correlation between the fluctuating pressure gradient and velocity was evaluated. The effect of organized vortex motion was recognized as the strong correlation between velocity and pressure gradient, which could explain the poor performance of RANS turbulence models in predicting this kind of flows.

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In this study, The Flow characteristics around a rotating circular cylinder with grooves are investigated. Thirty-two arc grooves are set to cylinder surface. The surface pressure of rotating circular cylinder with grooves is measured by transducer. In smooth cylinder, the lift coefficient shows negative value as spin rate ratio (rotating speed of cylinder surface/uniform flow) increases in Re ≥1.0×10^5. However, the lift coefficient of cylinder with grooves increases monotonically with the increase in spin rate ratio.

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An experimental study is performed to determine the flow characteristics inside diamond-shaped cylinder bundles by means of two-dimensional particle image velocimetry (PIV) and two-dimensional laser Doppler velocimetry (LDV). Flow cross-sectional areas and flow rates are varied to change the Reynolds number on the flip-flop flows in the bundles. By means of PIV measurements, the velocity contours in divergent-region inside diamond-shaped cylinder bundles are disclosed to be symmetrical with respect the central, longitudinal dividing line, and the exsistence of "energy source point" is also disclosed from results of the equi-dU/dx distribution. The LDV is employed to measure velocity fluctuations in the flip-flop flow, while power spectra representing its oscillating characteristics are determined from LDV data. It is disclosed that the oscillation ratio of flip-flop flow and von Karman vortex street is about 1/20.

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In the present paper the attention is focused on the vortex shedding in normal triangular tube arrays with closely mounted twist serrated fin. We measured the spectrum of velocity fluctuation, the phase delay and the gap velocity in the simulated tube arrays. We found two types of vortex shedding with different Strouhal number of 0.40 and 0.20 in the case of Reynolds number R_e, based on the equivalent diameter and the measured gap velocity, between 6.2×10^4 and 9.6×10^4. The vortex shedding of S_t=0.40 mainly formed within the fin-tube arrays and the other vortex of S_t=0.20 was in the wake of the fin-tube arrays. Strouhal number of vortex shedding within the fin-tube arrays changed from 0.40 to 0.32 between R_e=6.2×10^4 and 7.7×10^4. Strouhal number 0.32 agreed well with Strouhal number 0.30 obtained from Fitz-hugh's map for bare tube arrays and other Strouhal number of 0.20 is similar to the vortex shedding from a circular cylinder.

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This study investigates active control of self-sustained oscillating flow past an open cavity by a moving bottom wall. The incompressible Navier-Stokes equations are solved using finite difference methods for the two-dimensional cavity with laminar boundary layer upstream. We move the cavity bottom wall tangentially with nondimensional velocity ranging from -0.2 to +0.2. The computational results show that the effect of wall velocity changes the characteristics of recirculating flow in the cavity and that the modification of recirculating flow plays an important role in changing the oscillation characteristics of the separated shear layer. When the wall velocity is less than -0.1, two recirculating vortices change to one clockwise recirculating vortex in the cavity, so that the self-excited shear layer oscillations are completely suppressed. When the wall velocity is more than +0.19, the two stationary vortices exist in the upper side and lower side of cavity respectively and the self-excited oscillations are suppressed.

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Suppression of an aerodynamic noise generated by a laminar separating flow over a cavity is attempted experimentally and numerically, using a thin plate inserted in to the cavity as a passive flow-controlling device. As a result, it is shown that the noise suppressing effect is present when the plate is inserted near the center of the cavity. The results of a numerical simulation partly coincide with the experiment, however there are some discrepancies.

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A method for controlling the position of an oscillatory jet cavity flow is demonstrated. The method involves secondary injection of a lower mass flow control jet into the cross-flow region of the primary jet. The primary jet in this case is a turbulent jet (Re=55000) which when injected into the rectangular cavity with no secondary control, attains a stable oscillation with a characteristic Strouhal number of S_<t,W>=0.013. The secondary injection control method is investigated using a combined experimental and numerical approach with a water model test rig and a 2D and 3D computational fluid dynamics (CFD) model. Based on previous work, a baseline cavity, with a depth to width ratio of H/W=0.16 and entry nozzle submergence of S/W=0.38, is used to study the effect of secondary jet injection parameters on deflection angle (δ). These secondary jet control parameters include mass flow ratio (α), momentum ratio (β) and injection position (Y_i).

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Investigations of time-dependent laminar and transitional flows need accurate and reproducible generation of the flow as a function of time. For this purpose, an electronically controlled air valve, with which the mass flow rate is controlled, was designed and built. The working principle and lay-out of the valve are explained and the performance of the valve is demonstrated. It was found that with the present equipment one can study any nonperiodic and periodic flow and the flow can be adjusted to be laminar, transitional and turbulent. The investigations on laminar and transitional time-dependent flows are reported. Laminar flow investigations showed that the generated sinusoidal mass flow rates agree well with that of analytical solution. Non-periodic transient and periodic sinusoidal pulsatile transitional flows were investigated. It was shown that elucidation of the transition in non-periodic transient flows may help in understanding the transition in periodic flows.

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A NACA0012 airfoil undergoing pitching and plunging motion at Reynolds number Re=40,000 was simulated using a 2D Navier Stokes flow solver. These results are compared to experimental measurements in the literature and those from an inviscid analytical method and an unsteady panel method code. While the peak in efficiency with Strouhal number demonstrated in the experimental results was predicted by the inviscid methods, it was found to be significantly modified by leading-edge vortex shedding and viscous drag at low Strouhal number. The occurrence and influence of vortex shedding decreased as Strouhal number increased, corresponding to increased flapping motion frequency.

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Aerodynamic forces and moments of a flexible delta wing in its pitching motion were experimentally studied in a low-speed wind tunnel. Three types of flexible delta wings were investigated, the flexible parts of which were 44, 70 and 99% of the delta wing. The pitching motion of the delta wing was changed smoothly and periodically by means of a manipulator equipped with six stepping motors, which were controlled by a microcomputer. Since it had six degrees of freedom, the delta wing could move arbitrarily not only in pitching motion but also yawing, rolling, translation motions, and their combinations. The objective of the research is to analyze dynamic characteristics of the flexible pitching delta wing with comparison to a fully hard delta wing made of metal alloy without its deformation in the motion. A developed compact force balance with the weight of 5.6 grams was used to measure lift, drag and pitching moments. Aerodynamic characteristics were different among the three flexible and hard delta wings, and it was found that the winding-up of the leading edge of the delta wing is a key factor which decides the leading edge vortex on the upside of the wing and the pressure distribution on the windward side. Lift, Cl, drag, Cd and pitching moment, Cpm, made a hysteresis loops with an angle of attack during the pitching motion, especially in the region of a high attack angle accompanied by the leading edge vortex breakdown. Flow visualization for the leading edge vortices were also carried out to explain the dynamic characteristics of the delta wings.

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A studies on the unsteady flow at the low Reynolds number region have been catalyzed in recent years by an interest in the Micro-Electro-Mechanical-Systems based on the concept of flow control, Micro-Air-Vehicle and micro flight robot. In order to clarify the detailed vortex structure and vortex scale on an unsteady airfoil, such as a pitching airfoil and a heaving airfoil, at low Reynolds number region. We have carried out the flow visualization around unsteady airfoils at Re=4000 using three visualization techniques, such as schlieren visualization, dye flow visualization and PIV measurement. Especially, we report the dynamic behavior of vortices shed from the leading edge, the number of vortex shedding and its scale. The small discrete vortices shed from the leading edge one after another in a pitching airfoil and a heaving airfoil at low Reynolds number region. When the non-dimensional pitching rate in a pitching airfoil and the non-dimensional heaving velocity become high, the clear discrete vortices were visualized. The number of vortex shedding from the leading edge during one pitching cycle on a pitching airfoil was strongly depends on the non-dimensional pitching rate and independent of the airfoil configuration, mean angle of attack and pitching amplitude. At the low non-dimensional pitching rate in a pitching airfoil, a lot of discrete vortices shed from the leading edge and its scale was very small. At the high non-dimensional pitching rate in a pitching airfoil and the high non-dimensional heaving velocity in a heaving airfoil, on the other hand, the number of vortex shedding from the leading edge during one cycle was low. However, its scale was about one fourth of the chord length and it did not depend on the airfoil configuration. Moreover, these vortices consisted of the re-circulation region on the suction surface.

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Aerodynamic characteristics of pantographs for high-speed trains are critical to steady current collection. We introduce a new panhead in which air is taken in at the leading edge and ejected around the trailing edge to control the lift force. We estimate aerodynamic characteristics of this panhead by CFD and a wind tunnel experiment. The results show that the lift force can be controlled effectively by this panhead.

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The paper describes results of a numerical and experimental study of pressure and velocity fields arising during normal injection of a radial slot jet into ducted flow. The studies were carried out for injection parameters varying in a broad range. In this paper, the jet exit has two types of shape: sharp and round edge (α). The pressure profile along the duct length plotted in generalized coordinates was found to be quite a universal distribution. The distribution of the longitudinal velocity in the tube under different blowing parameters m is also given. Results of measurements of local hydraulic losses are presented for the duct section where the normal injection of the slot jet was organized. The numerical and experimental data are shown to be underestimated compared with the results predicted by the theory of perfect mixing for a ducted flow with mass supply. The possible reasons of hydraulic losses coefficient behavior are discussed.

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Experimental study was conducted on turbulent mixing of hot and cold airflows in a T-junction with rectangular cross sections, which simulates the HVAC (Heating, Ventilating, Air-Conditioning) unit used for an automobile air conditioning system. The flow entering the main channel from the branch is separated at the edge of the T-junction and forms a large separation bubble. Longitudinal vortices are formed around this separation bubble, and thus the flow field shows a complex three-dimensional structure. In spite of such a complex flow field, the mean temperature of the mixed flow shows quite uniform distributions in the spanwise direction of the channel.

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The piping systems in buildings often have a main duct, junction and branch. The flow at the T-junction is very complex and various problems have resulted from the mixture of the main duct and branch fluids. In particular, thermal fatigue failure accidents at the T-junction in fast breeder reactors (FBRs) have occurred because of thermal fluctuations called "thermal striping." We installed a turbulence promoter at a T-junction and investigated its effect on the flow in T-junction piping systems. An experiment was carried out using a visualization test by dye injection and a velocity measurement by laser Doppler velocimetry (LDV). As a result, we clarified that the secondary flow in pipe sections becomes stronger and the diffusion of momentum increases with the turbulence promoter. The peculiar reverse flow generated by the turbulence promoter can be controlled by adjusting the shape of the turbulence promoter.

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T-junction piping system is used to mix the fluids in different temperature. If the temperature fluctuation generated in the mixing process is transmitted to the structure, it may bring thermal fatigue in the structure. Here, "Turbulence promoter" was considered to reduce the amplitude and the low frequency component of the temperature fluctuation. In this study, numerical simulation under iso-thermal condition is conducted to clarify the change of the flow pattern and the mixing mechanism due to the promoter and to optimize the promoter configuration. As the result, we clarified that the horseshoe eddy can be controlled by the promoter and appropriate height of the promoter was found to reduce the horseshoe eddy.

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The agitators are used in various industrial fields where it is necessary to mix two reactants in a short period of time. However, despite their widespread use, complex mixing flow characteristics of industrial agitators have not investigated systematically. The present research aimed to measure the unsteady mixing flow by dynamic stereo PIV. In this research, axial and radial types of impellers were used. Two high resolutions, high-speed digital cameras (1280pixel×1024pixel) were used to allow the time-resolved animation work. The rotating speed of mixing impellers is 100rpm respectively. The present dynamic stereo PIV represents the complicated velocity fields, especially, in terms of time-dependent characteristics of the velocity fields at given measuring sections. Quantities such as three velocity vector components, vortices distributions and other related flow information can be easily visualized by means of the 3D time-resolved postprocessing software to make the easy understanding of the unsteady mixing flow characteristics in the field of industrial agitators.

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The Dynamic PIV system (Time-resolved PIV) has been applied to the high-speed mist flow with edge obstacle in a narrow channel. The boundary layer has been clearly visualized with the high-speed camera and high repetition double-pulse laser. The target area is 10mm with 10m/s, i.e. Re=10,000. The flow from edge is captured to evaluate the detail flow structure of the boundary layer.

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This paper tries to employ ultrasonic CT to obtain temperature distributions of a hot jet. In regard with CT reconstruction, ART (Algebraic Reconstruction Technique) is suggested to deal with the problems of limited projection by using the good initial distribution instead of zero initial distribution. CT reconstruction simulation is carried out to demonstrate the advantages of the suggested method by evaluating an error function. Temperature measurement of the hot jet is conducted for the experimental verification. With the CFD-based numerical calculation results as the initial distribution for ART reconstruction, it is found that good agreement between CT-reconstructed values and those obtained by thermocouple is confirmed even the projection angle is limited..

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Particles concentration on a cross section in a fluidized bed has been qualitatively visualized by a capacitance CT during the drug coating and drying processes. As a result, the high concentration is located near the tube wall at the drug coating process. However, the concentration tends to be uniform on the cross section. The originality of the present study lies in the application of capacitance CT to particles movement in a fluidized bed in jet coating as a first step of active control of drug production in order to prevent agglomeration of cohesion particles in pharmaceutical industry. Finally, the CT image is compared with the DEM simulation qualitatively to discuss the availability.

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In the present paper a method to measure the instantaneous mass flow rates of fuel passing through fast operating injection nozzles is described. The flow rate information is deduced from instantaneous pressure gradient measurements. Through a Fourier transformation Fourier-coefficients of the pressure gradient are determined, which are used for the calculation of the transient mass flow rate of fuel through injection nozzles, utilizing a special reconstruction algorithm. In the paper the theoretical background of the measuring method is provided and the entire development work is summarized as car-ried out by the authors to yield a practically applicable measuring system. The latter is used for verification experiments providing time resolved flow rates for a magnetically driven injection valve operating at a pressure of approximately 6 bars. The authors stress that on-line measurements of the injection mass flow rates can be presented with their developed measuring system.

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Symmetric and Asymmetric vortices were captured on the leeside of a conical shape forebody at high angle of attack, without perturbing the flow by sideslip angle or geometric perturbation. On the basis of RANS, two different Turbulence models have been analysed to access their ability to predict the onset of flow separation and the quantity of flow separation. Extensive simulations and analysis have given into the behavior of the flow field and the onset of vortex asymmetry. Silent features of the flow at high angle of attack were highlighted. Co-efficient of pressure plot obtained by using SST k-ω model exhibit adequate agreement with experimental data. It was concluded that asymmetry in flow in numerical simulation is basically due to truncation error which is random in nature and there is a need to predict the asymmetry of flow and unsteadiness by using the latest approach in CFD i.e. DBS.

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The effect of the heterogeneous condensation on the characteristics of axisymmetric under-expanded jet is investigated numerically. The governing equations are unsteady, axisymmetric, compressible Navier-Stokes equations with a rate equation of liquid-phase production. As the results, the condensation with the heterogeneous nucleation has a strong effect on the jet structure. Furthermore, it is shown that the condensing flow field with the heterogeneous nucleation is dependent largely on the concentration of solid particles in moist air.

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When the high pressure gas is exhausted to the rest gas through the nozzle, the supersonic jet including the Mach disk is generated. Supersonic jet has many potential applications for aeronautical and mechanical industries such as the laser cutting and the HVOF thermal splay. The final object of this study is to clear the characteristics of supersonic air jet exhaust to rest gas including the geometry effect of nozzle and the real gas effect such as the moist air including the condensation. As the first step of study, a computational analysis for perfect gas is done to clarify the effect of nozzle geometry on the sonic line and characteristics of Mach disk of under-expanded supersonic jet in the present paper.

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An experimental program has been undertaken to simulate the impingement of an under-expanded supersonic jet, resulting from the failure of the wall of an aero-engine combustion chamber, onto an adjacent surface. Experiments were performed for a range of nozzle pressure ratios from 10 to 60 for an axisymmetric sonic nozzle and a rectangular sonic nozzle. The impingement plate was placed 17 nozzle exit diameters downstream. Schlieren images of the flow structure are presented and discussed. In the case of the rectangular nozzle, flow field asymmetry is observed to persist well downstream of the nozzle exit to the point of impingement.

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The intermolecular collision scheme is developed to obtain an excellent result even if cells are lengthened (more than the local mean free path) in the direct simulation Monte Carlo (DSMC) calculation. In the new scheme, the velocity of one molecule of a collision pair is modified before and after the substantial collision calculation (the core of the collision calculation), assuming that velocity distributions in all flowfield are in local equilibrium with some temperature and flow velocity (local Maxwellian distribution). The new collision scheme is applied to three-dimensional supersonic free jets for a steady problem and a two-dimensional vortex shedding behind a flat plate for an unsteady problem, respectively, and its effect on them is confirmed.

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When gas was injected into a cylindrical bath through a centered bottom nozzle, a bubbling jet was formed above the nozzle. It swirled around the bath axis under a certain condition. The liquid in the bath also swirled in phase with the swirl motion of the bubbling jet. Such a swirl motion of the bubbling jet has a high mixing ability. A similar swirl motion appeared when a liquid or a mixture of gas and liquid was injected in a cylindrical bath. The occurrence conditions of these swirling jets were experimentally investigated in addition to their basic characteristics such as the period and amplitude.

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Swirling jets generated in a cylindrical bath have high mixing ability and find their wide applications in a variety of engineering fields such as materials, chemical, environmental, and mechanical engineering. They are applicable to the food industry, as well, because any mechanical devices are not present in the bath. Some examples of their applications in the environmental engineering were introduced in this paper; degradation of organic wastewater, degradation of dioxins, sludge treatment, and snow melting.

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The effect of pressurized air inlets in the reservoir upstream of the annular slit on characteristics of the axial and tangential velocity components is investigated numerically, and the mechanism of occurrence of spiral nozzle flow is clarified. In simulations, UPACS is used, and the results obtained are compared with velocity distributions measured by the two-component laser doppler velocimeter system.

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The objective of the present paper is to investigate Reynolds number dependence of separation and reattachment process over a backward-facing step in a low Reynolds number range. A study on low Reynolds number flow such as the flow around the micro device is strongly required in MEMS development. The Reynolds number based on step height is set at 130 to 3700 in the micro sensing wind tunnel. The reattachment and separation points are measured by Micro Flow Sensor (MFS), and the flow field is visualized with a high-speed video camera. The results show a strong dependence of Reynolds number on the flow behavior on the step and opposite-side wall downstream of the step.

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Free surface flow has been the subject of numerous research efforts in industrial fields like power engineering, chemical engineering, civil engineering and environmental studies. Free surface flow has been studied from a numerical investigation point. In the SP-VOF model, interface-tracking calculation has been simplified by approximating cubic cells to spherical ones. Free surface flow in a channel with both open and closed sections was calculated by using the present method. The calculated results provided reliable liquid velocities compared with observed velocity distribution. The present method was applied to simulation of a three-dimensional dam break. It can calculate the complex free surface flow of water jumping over a barrage and scattering blobs from break waves.

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In the present study, we perform large eddy simulations of a circular jet up to Re=10^5 based on the jet-exit velocity and jet diameter (D). We investigate the effect of the momentum thickness (θ) of initial shear layer because it is known to be one of the important parameters governing the jet characteristics. Four different initial momentum thicknesses, i.e. D/θ=50, 80, 120 and 180, are considered, and background disturbances are imposed on the jet-exit velocity to provide a more realistic inflow condition. The results show that the vortical structures significantly change with the Reynolds number and initial momentum thickness.

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To develop efficient method of jet mixing, direct numerical simulations of combined jets are carried out. The Reynolds number is defined with a nozzle diameter, is Re=1500. The spatial discretization is performed with hybrid scheme in which sixth order compact scheme in streamwise direction and Fourier series in cross section are adopted. The distance between two jets is fixed at 6 times jet diameter, and the inclination angle of jet is changed from 45 to 70 deg. As a results, it reveals that the turbulence intensity is strengthened with decreasing inclination angle, and that the jet width increases via the excitation of jets. These findings suggest that the combination of jets flexibly meet the diversified needs of jet mixing control.

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This paper presents the performance of a new non-linear k-ω model for computations of turbulent flows and heat transfer in several different flow types. This model is developed by incorporating cubic terms that take into account the anisotropy of the Reynolds stresses, and the effects of extra strain rates due to a streamline curvature and the rotation of the flow passages. Five cases of turbulent flows are numerically simulated: fully developed turbulent flows in a channel without rotation, in a curved channel, in a rotating channel, and the flow over a two-dimensional blunt rectangular section. Both flow and heat transfer characteristics were examined for the above mentioned flow passages. The governing equations are discretized using a non-staggered finite-volume formulation employing a bounded higher-order differencing scheme. The comparisons are made among the experimental data and the results obtained by DNS, linear and non-linear k-ω models. It is shown that the non-linear k-ω model generally gives superior results over the existing linear k-ω model by demonstrating better agreement with the data for both flow and heat transfer computations.

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For the flow around a rectangular cylinder, fluid-dynamic characteristics change according to the side ratio D/H, where the height of cylinder is defined as Hand the depth as D, and Reynolds number Re=U_∞H/v, where U_∞ is uniform flow velocity and v is kinetic viscous coefficient. In the present study we carried out a three-dimensional turbulent flow calculation, using the large eddy simulation (LES) with the standard Smagorinsky model, to solve the flow around rectangular cylinders with side ratios D/H of 0.6, 1, 2.5, 3 and 6. We then quantitatively predicted sound generated from dipoles involved in pressure fluctuations on the cylinder surface, and studied the variation of sound level affected with the side ratios.

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An axisymmetric numerical simulation approach to the hole-tone feedback problem is presented. It is based on the discrete vortex method and an 'acoustic analogy' representation of flow noise sources. The shear layer of the jet is represented by 'free' discrete vortex rings, and the jet nozzle and end plate by bound vortex rings. This model is capable of predicting the sound-generating unsteady jet flow with good accuracy. In the acoustic model, a monopole source term alone is capable of predicting the correct frequency spectrum, and the correct sound pressure level of the dominating frequency component (the hole tone) in the acoustic near field. The last part of the paper presents several case studies on suppression of the hole tone by forced acoustic excitation of the shear layer near the nozzle exit.

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Aerodynamic sound generated from a separated turbulent shear flow was studied experimentally with measurements of emitted sound, velocity, fluctuating static-pressure and flow visualization. Each velocity and fluctuating static-pressure was measured simultaneously with emitted sound to study relations between aerodynamic sound and vortex motions with spectrum, waveforms, coherence and COP (Coherent Output Power). Ajet was issued from a squared nozzle (0.1m×0.1m) along the flat wall and a two-dimensional sharp-edged fence with a height h of 7mm was placed on the wall to generate the separated turbulent shear flow. The aerodynamic sound generated from the shear flow was measured by a microphone fixed near the fence outside the flow. A velocity at jet center Ue was 35m/s and Reynolds number Re (=Ue h/v) was 1.6×10^4. The present study suggests that the measurements of fluctuating static-pressure give us useful information to study relations between sound source caused by vortex motion and aerodynamic sound.

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The purpose of this study is to investigate flow around of a living tree as the basic research of the windbreak forest. A conifer which name is "goldcrest", a kind of garden plant, was used as test piece in the wind tunnel experiment. Drag of a living tree was directory measured by the 6-axis force torque sensor. Drag coefficient of a living tree was less than that of two-dimensional circular cylinder and rectangular plate in the range of mean flow velocity of 5〜15m/s. Because a living tree has two aerodynamics characteristic, the flexibility and the permeability. Branches and leaves of a living tree have a permeability to pass through a wind to reduce the drag. Moreover, the flexibility is that the bole of a living tree bends itself so as to decrease the projected frontal area in the wind. This also plays an important role in drag reduction. Effect of bending of the bole and the permeability of branches and leaves in tree's crown was estimated using visualization technique. The wake profile behind a living tree was also measured by means of the wind tunnel experiment. The reverse flow was found at further downstream region behind a living tree. Because flow passes through the tree crown consisted of branches and leaves, flow velocity was decreased calmly. In being decreased, it makes to retard the development of shear layer vortices.

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A loach has unique propulsion technique by bending its long body and using its tail fin. Its motion and flow around it have been experimentally visualized by particle image velocimetry (PIV). Vortices around a loach and the interactions between the loach motion and water flow are analyzed. Generating and growing vortices by bending its body, it pushes water backward to gain repulsing force, at the same time it moves through vortices reducing the resistance force. When a vortex reaches to the tail fin, it accelerates both sides of the vortex pushing water back and gaining propulsion utilizing the tail fin. After moving forward it leaves a vortex street like reverse Karman vortices which means loach gains propulsion. The role of tail fin and vortex structure was studied in detail by both of horizontal and vertical views (two 2D2v PIV). Flows with and without tail fin, different species of loach were also studied.

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