The formation and development of oblique Tollmien-Schlichting waves around a turbulence wedge have been investigated in a radial liquid film flow. The liquid film flow was formed of water discharged to the atmosphere from a narrow cylindrical gap between the end of a pipe and a smooth surface of a disk. The turbulence wedge was generated artificially by a water jet injection into the laminar region of the liquid film flow through a small hole in the disk. The behavior of oblique T-S waves around the turbulence wedge was observed by means of high-speed photography. In addition to the observation, downstream development of the oblique T-S waves was calculated on the basis of a linear stability theory. For both the shape of the oblique T-S waves and the manner of the oblique T-S waves spreading outward on the way downstream, the calculation gave a good agreement with the experimentally observed result.

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[in Japanese]

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Our experimental study is devoted to the analysis of the flow past wto tandem circular cylinders near the vortex shedding threshold. A recent two-dimentional numerical analysis of this flow, Mizushima & Suehiro (2005), has predicted that the bifurcation diagram should becomes complex in the vicinity of the instability threshould. subcritical and saddle node bifurcation that lead to hysteretic exchanges between two different modes of vortex shedding were detected for particular distance of separation of the cylinders. We present here visualization and velocity profile measurement of this flow in a water channel to prove the robustness of the complexity of the bifurcation diagram in real flows and to clarify the three-dimentional effect due to finit length of the cylinders.

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Vortical structures were experimentally investigated in the wake of a sphere by multi-hotwire measurements and flow visualizations. Two kinds of the Strouhal numbers were observed in the range of Re=800〜7000: the low mode St number kept almost constant of St_L≒0.2 and the high mode St number increased discontinuously with increasing the Re number. A helical-type low mode structure composed of 2〜3 high mode vortices was observed for Re〓2000. A staggered-type I structure with 2〜6 high mode vortices existed for Re=1700〜3800. A staggered-type II structure containing of 4〜8 high mode vortices for Re=2400〜7000. For Re〓7000, the inside of the low mode structure became turbulent due to the interaction between the high mode vortices, then the low mode structure was basically staggered-type. Wavelet analyses showed that the whole number of the high mode vortices contained in the low mode structure increased with the Re number.

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This paper describes that an experimental study is performed to reveal the effects of an acoustic forcing frequency on flow characteristics in a plane jet. Active control of a planar jet has been attempt using a sinusoidal excitation blowing and sucking at the nozzle exit. The turbulent intensity of excitation is set at 2% of the jet velocity, the frequency of excitation is changed from 50 to 900 Hz and jet velocity is changed from 10 to 30 m/s. The hot-wire measurements directly provide phase averaged flow fields and they illustrate appearance of the jet fluttering.

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The purpose of this investigation is to clarify the production mechanism of Reynolds shear stress in the vortex street wake. The space distributions of velocity fluctuation were shown by using ensemble average technique based on angular direction of velocity fluctuation vector at reference point where is maximum production point of Reynolds shear stress. As the result of this study, the relation between the space structure produced Reynolds shear stress and the angular direction of velocity fluctuation vector was revealed.

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An experimental study has been performed on the similarity of the Reynolds stress profiles for smooth- and rough-wall turbulent boundary layers under zero-pressure-gradient. The new scale of turbulent momentum flux was defined with considering both wall shear stress and mean flow momentum flux coming from the slope of mean streamline. Then, the wall shear stress was determined by direct measurement with a floating element device. The Reynolds stress profiles, normalized with the new scale, for the smooth- and rough-wall turbulent boundary layer at high Reynolds number almost collapse on a single curve.

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The local isotropy hypothesis presented by Kolmogorov seems to work well as a good approximation depending on the nature of large-scale anisotropy. We discuss how the large-scale anisotropy penetrates the small scales by investigating the anisotropic spectrum measured in the rough wall boundary layers and also the pressure spectra.

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The local isotropy hypothesis presented by Kolmogorov seems to work well as a good approximation depending on the nature of large-scale anisotropy. We discuss how the large-scale anisotropy penetrates the small scales by investigating the anisotropic spectrum measured in the rough wall boundary layers and also the pressure spectra.

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Detailed experiments have been made for the effect of the adverse pressure gradients on the log-law in turbulent boundary layers. The wall shear stress was measured by a direct measurement device and scaling law of the mean velocity was discussed with high accuracy experimental data. By considering significant contribution of the inertia term in the equations of motion, a new velocity scale is defined and a similarity law was yielded for the mean velocity profile subjected to the adverse pressure gradient.

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As a preliminary experiment, the motion of Vibrio is observed by use of dark field microscope with CCD camera and its image is recorded to video recorder, By using NIHImage, the video image is digitized and the position as well as inclined angle of bacterial cell is obtained numerically. It is shown that variations of the speed and the frequency of wobbling motion of the bacterium can be obtained. In the analytical study, a computational procedure is developed to simulate wobbling motion of bacteria with single helical flagellum, the axis of which is inclined to major axis of the bacterial cell. The resistance force theory is employed to estimated force exerted on rotating flagellum.

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Fluid structure interaction of a circular cylinder is simulated by the coupling of a Vortex Element Method and Boundary Element Method. Both methods are volume-mesh-free, and thus alleviates the burden on handeling moving boundary problems in general. The rigid vibration of the cylinder is examined first, and compared with experimental studies. Then, the elastic deformation is considered.

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The purpose of this study is to investigate the wake structure and drag characteristics of a living tree as fundamental researches of windbreak forests and roadside trees. We used a conifer and a broadleaf tree as test pieces in the wind tunnel experiment. The wake profiles behind the conifer and broadleaf tree were almost same as that of a permeable cylinder which has flow permeability. It found that a wake profile of a living tree is influenced by density of a leaf and shape of a tree canopy.

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In this paper, we simulated a motion of soft-matter body in consideration of fluid motions inside and outside the body. This is important to investigate a motion of an amoeba or an earthworm regarded as a soft-matter robot. There are many researches and developments of the bipedal walking robot or the portable mechanism by using a wheel. However, some reports paid attention to the displacement technique by peristalses, such as ameboid movement of a protozoan, and earthworm, as a robot which can move in the inside of fluid or slight space. We used the model of a circular flexible object including the internal fluid which has a different quality from external fluid. We report the result of the simulation

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A series of wind tunnel tests were conducted on the vibration and scattering behavior of full-sized model of roof tiles, which were used widely for roofings of Japanese wooden dwellings. The 100 roof tiles were set up on 10 lines and 10 lows on the pitched roof in the downstream of the flow from the wind tunnel. This study has investigated the nature and source of the vibrating and scattering behavior of roof tiles with the aim of providing a better insight to the mechanism.

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An experimental investigation into the aerodynamics of a ring wing has been carried out in an low speed wind tunnel, at a Reynolds number of 215,000. A flying toy that has a rim on their outer edge was selected as a model of the ring wing to examine the effect of rim on the aerodynamic performances when the flow comes from the trailing edge of the airfoil. The lift and drag coefficients shows that the ring wing with the rim has a good performance in the reversed flow, resulting low drag characteristics at a flight angle of attack. CFD analysis revealed that the separated vortex from the rim makes the streamline smooth and thereby set their drag lower than the case without rim at the same airfoil.

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Aiming at providing instructive aerodynamic principles for the MAV (Micro Air Vehicle) design of a mini-helicopter, aerodynamic characteristics of rotary wings of insect and bird sizes were studied numerically using a biology-inspire dynamic flight simulator. A geometrical model was built based on a realistic insect body and wings; a rotating angular velocity for the rotary wing is defined to be identical with that of a flapping insect wing; and an angle of attack is taken to be equal to the mean angle of attack of the flapping wing. Computations of hovering aerodynamics of the insect-type, mini-helicopter were conducted with a specific focus on the effects of the size which varied over a wide range of 1〜10000, and the reduced frequency at 0.382, 0.764 and 1.146. Our results indicate that the LEV (leading-edge vortex) is observed at all the Re numbers detached onto the upper surface of the wing and is responsible for the lift generating as seen in a flapping wing of insect flight. Furthermore, the computed CT/CQ is clearly sensitive to the Reynolds number rather than the reduced frequency.

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A multi-block-and overset grid-based computational fluid dynamic (CFD) study was implemented for the unsteady flows surrounding a hovering hawkmoth with the realistic body-wing geometrical and kinematic models. The computed results show that downwash produced by a flapping hawkmoth has time dependency fairly. In particular, weak downwash is detected during downstroke, in contrast; strong downwash is predicted during upstroke. The reason the strong downwash is produced is that the combination of leading-edge vortex, shedding trailing-edge vortex and wing tip vortex forms a ring-shaped vortex characterized by strong downward-flows in the center of it during downstroke. The remarkable downward-flows travel to bottom area of a flapping insect during upstroke when the ring-shaped vortex is shed by wing rotation and flapping wings push it downward. Moreover downwash distribution does not exhibit a circle shape that has been explained by the Rankin-Fluid momentum theory.

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The purpose of the present study is to clarify the dynamic behaviors of butterfly wings, such as the trajectory of butterfly wings and flapping angle of butterfly by flight observation. Moreover, we visualize flow around the butterfly with particles, process images and clarify the vortex flow structure on the butterfly wings. In particular, we draw attention to the tip vortices rolled up from the wing tip and discuss on the three-dimensional vortex flow structure on the butterfly wing. Cynthia cardui wings have elastic behaviors not only in the wing chord direction but also in the wing span direction. The flapping angle of the Cynthia cardui wing showed triangular wave and the time ratio for moving upward and downward of the flapping wing was approximately 1:1.25. The vortex flow called "delayed stall" which is important for insect flight, grew in the wing chord direction of the Cynthia cardui. A pair of vortices rolled up from vortex tip was formed not only in the chord center of the wing but also in the leading and trailing edge when the downstroke of the wing started from the top dead-center position. Therefore, it is considered that a cylindrical vortex rolled up from the vortex tip at downstroke in the flapping motion.

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The purpose of our study is to develop a takeoff system for a Micro Air Vehicle (MAV). We observed the takeoff sequence of a butterfly from ground, that is, motion of wings and body, taken by a high speed camera. The acceleration in the x and y direction became the maximum when the angle of a butterfly was 60 degrees in the down-stroke phase. Whereas, the acceleration in the x direction became the maximum in the up-stroke phase. We described the relation among flapping and angles of attack of the body in this paper. We indicated the down-stroke vortex is important for lift and impellent force and up-stroke vortex for impellent force.

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We have developed an insect-size flapping Micro Air Vehicle (MAV) with hovering ability, having a wing length of 5 cm and a total weight of 2.35 g. It can be remote controlled by infrared transmitter. Intersecting 4 wings, which consist of 2 pairs of wings, showing X-like front view, were driven by a pager motor of 4 mm in diameter. The static thrusts obtained by 4 wings was 30 % lager than the doubled value of those obtained by 2 wings for the same flapping frequencies. It can be considered to be due to the "clapping" effects of the butterfly. The electric energy to obtain the thrust of 2.35 g was 0.60 W, which is much lager than the theoretical value calculated by momentum jet theory.

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The governing equations for high-speed lateral atomizing injector nozzle flow based on the LES-VOF model in conjunction with the CSF model are presented, and then an integrated parallel computation are performed to clarify the detailed atomization process of a high speed nozzle flow and to acquire data which is difficult to confirm by experiment such as atomization length, liquid core shapes, droplets size distributions, spray angle and droplets velocity profiles. According to the present analysis, it is found that the atomization rate and the droplets-gas two-phase flow characteristics are controlled by the turbulence perturbation upstream of the injector nozzle, hydrodynamic instabilities at the gas-liquid interface, shear stresses between liquid core and periphery of the jet. Furthermore, stable and a high-resolution computation can be attained in the high density ratio (ρ_l/ρ_g=554) conditions conditions by using our numerical method.

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For quality keeping of the beverage, we usually exchange the air in head space of the PET bottle for non-activate gas, such as N_2 gas or CO_2 gas. We try to confirm the CFD result by Mach Zender interferometer's image and gas exchange effect is checked the CFD result by experimental result.

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In this study, a numerical simulation of clear air turbulence (CAT) was carried out by an large eddy simulation (LES). Measurement-integrated simulation based on four-dimensional variational method (4D-Var) was introduced because it is difficult to determine initial and boundary condition for CAT. The 4D-Var is formulated as a minimization problem of a cost function of initial flow variables, thus an adjoint code was developed to obtain gradient of the cost function at one time. The 4D-Var was applied to the flight data obtained when an aircraft encountered CAT. Characteristic vortices which correspond to CAT was reproduced by the 4D-Var. And then, power spectrum density of reproduced flow field was investigated.

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Numerical simulation and experiment are important tools in flow analysis, but they have advantages and disadvantages. We have proposed Measurement-Integrated simulation that integrates numerical simulation and measurement to reproduce the real flows. This new methodology reproduced the velocity field of Karman vortex street behind a square cylinder in far better agreement with the real flow than the ordinary simulation. In this paper, the pressure field obtained by the MI simulation is validated in comparison with pressure measurement on the sidewall of the wind tunnel. Results show the MI simulation successfully reproduces the pressure oscillation near the cylinder although the root-mean-square pressure is degraded in the downstream region. In addition, the pressure field of Karman vortex street is analyzed and visualized in real-time using the hybrid wind tunnel.

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A measurement-integrated simulation (MI simulation) is a SIMPLER-based flow simulation scheme modified by adding a feedback signal proportional to the difference between the simulation and the real flow. MI simulation has been in practical use, however, a general theory of MI simulation has not been established. In this study, numerical experiment was performed for MI simulation of turbulent flow in a square duct to obtain fundamental knowledge in constructing a general theory. MI simulation applying feedback at one grid point revealed that the effect of feedback propagates sharply in the downstream direction. As a result, MI simulation applying feedback at the grid points on every twentieth plane in the x_1 direction still reduces the error by a factor on the order of 10^<-4> at some feedback gain, while MI simulation with the feedback on the planes skipped in the x_2 direction requires ten times more planes to achieve the same reduction rate.

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Circulatory diseases have relations to the hemodynamics, and therefore, detailed and accurate information of blood flow field is essential for advanced diagnosis or treatment of them. Hence, we have developed Ultrasonic-Measurement-Integrated (UMI) simulation. This methodology adds feedback signals derived from the differences between measured and computed Doppler velocities to the numerical simulation, and makes the computational result converge to the real blood flow field as time progresses. In this study, we performed the numerical experiment of the UMI simulation to reproduce the standard numerical solution of the three-dimensional unsteady flow or the model of a real blood flow. The UMI simulations effectively reduced the error due to the boundary conditions in and after the feedback domain, and reproduced the blood flow field in the aneurysm, especially in the case of using two ultrasound proves. Consequently, we confirmed the effectiveness of the UMI simulation in a real blood flow condition.

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