Measurements of wall shear stress of a turbulent boundary layer in the channel flow were carried out using MEMS (Micro-Electro-Mechanical-Systems) -based micro shear stress imaging chip. The chip is designed and fabricated by surface micromachining technology which is compatible with IC technology. One array of 25 micro shear stress sensors in the chip that covers a distance of 7.5 mm is used to measure the instantaneous spanwise distribution of the surface shear stress. The characteristics of high shear stress streaks were described with statistics. Based on the measurement, the physical quantities associated with the high shear-stress streaks, such as their length, width and peak shear-stress level, were obtained. We found out that a high correlation exists between the peak shear-stress level and front-end shear-stress gradient of a high shear-stress streak. This important property is currently being applied to the design of real-time flow control logic.

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Noise generated by the annular film-flow plunging into a water surface in a vertical drain-pipe was investigated experimentally to obtain a basic idea to suppress noises related to a bubble entrainment. The correlation among the noise level, entrainment of bubbles and state of film-flow when it plunged into a water surface was observed. It was found that when the turbulent film-flow plunged into the water surface, the sound pressure level of the noise increased abruptly, and the number and size of bubbles also increased. The major frequency of the noise was explained by bubble-cloud oscillation rather than an oscillation of a single bubble. The bubbles regarded as a noise source were in the recirculating region near the water surface. The recirculating region found to become larger when the plunging velocity of the film-flow increased.

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A series of experiment has been carried out by the use of a conventional shock tube to investigate the unsteady behavior of shock reflection. Especially, attention is focused on the phenomenon in the vicinity of the transition wedge angle for a specified incident shock Mach number. Although models used in the experiment are ordinary plane wedges, a transition phenomenon from regular to Mach reflection has taken place during the shock propagation. In other words, the phenomenon cannot be regarded steady with respect to some fixed point on the incident shock. The discrepancy between theory and experiment is ascribed to this unsteadiness (non-selfsimilarity). The behavior of incidence and reflection angles suggests that the so-called von Neumann paradox might be resolved as the incident shock proceeds. It is concluded that the cause of unsteadiness lies in the transport properties of the medium.

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The surface pressure change during a pitching motion of an airfoil was measured, and was analyzed to obtain a precursor of separation. A pitching airfoil was adopted to produce a predictable separation, because it is necessary to know a precise time to start separation to distinguish the precursor from other signals. The sinusoidal wave amplified exponentially in time was found to appear just before separation. This fluctuation is regarded as an instability wave of boundary layer based on the velocity profile with an inflection point.

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The unsteady flow structures around a square cylinder are examined numerically. The non-linear k-ε model with the effect of the strain parameter and the rotation parameter is adopted as the turbulence model. Applicability of the model to the Karman vortex shedding in the 2-D flow field is firstly investigated through the comparison of the calculated results with the experimental ones conducted in closed water section by Lyn (1992) and the model constants are adjusted. Then, the 3-D computations of unsteady flows in open channels are carried out focusing on the Karman vortex and the horseshoe vortex.

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Measurement of the acoustic intensity (Al) flux is made in the neighborhood of a circular cylinder set normal into a circular jet flow. Results for Al flux show acceptable features only when the sensors are well out of the acoustic near-field of the sound source, that is, the cylinder. Although it can be shown analytically that Al measurement with two microphones should work well even in the near-field, measured results there show totally unacceptable features. The inevitable conclusion is that microphones inside the near-field scatter the near-field into real sound wave, and then measure it.

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The present paper is concerned with the behavior of single streamwise vortex embedded in Blasius boundary layer. Our main aim is to study the subcritical transition caused by single streamwise vortex. It is interesting to see how the vortex can trigger a sequence of events leading to the transition. In the present study we observed the flow at the momentum thickness Reynolds number R_θ=160 to 180. We found that a streamwise vortex with Γ/v= 72 can disturb the Blasius flow such that the local flow surrounding the vortex core exhibits inflectional instabilities and amplifies small disturbances. It should be emphasized that the inflectional instabilities undergo synchronizing with the instability of the vortex core itself.

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The aerodynamic shape of a wing for a SST has been designed by a supersonic inverse method. This method handles a wing-fuselage configuration and provides the section geometry at every span station of the wing. The design system consists of an inverse problem solver and a Navier-Stokes simulation code. The design procedure is based on the iterative residual correction concept with which a baseline shape is successively modified. The inverse problem solver determines the geometrical correction value for the current wing to be updated. The simulation provides the pressure distribution along the updated current wing surface. The residual is defined as the difference between the target and the current pressure distributions. The process is iterated until the pressure distribution of the modified wing geometry converges to a specified target pressure distribution. By means of the present design method, a better wing for the SST has been designed than that by the traditional linear theory.

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Time-evolutions of decaying turbulence in two-dimensional non-divergent fluid on a rotating sphere were conducted with high-resolution numerical model to examine what stream pattern appears finally.
To investigate the condition needed for each pattern to appear in detail, higher-resolution model are used and wider parameter range of initial condition or angular velocity of sphere rotation are swept than other past researches on the same subject.
As a result, it is confirmed that the appearance of easterly polar vortex when the angular velocity of sphere rotation is rapid is a robust feature. Furthermore, it turned out to be necessary for band structure of zonal flow to appear in middle and low latitudes that initial energy must be injected into small scale enough as well as the angular velocity of sphere rotation is rapid.

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Friction coefficient of a rigid body sliding on a powder layer was measured. This is a model to explain the small apparent friction coefficient exhibited debris avalanches. In experiment, flour was mainly used as the powder material and metal disks used as the rigid body that slides a powder layer.As a result, it was found that friction coefficient became small at a higher speed than critical value. The obtained friction coefficient was smaller than the normal friction coefficient between rigid bodies. In addition it was confirmed disk was floating over that speed from observation of sliding marks.
“Dynamic pressure model” is proposed as the mechanism providing force to float a disk. The critical speed derived from this model is consistent with experimental results.

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Efficiency of ensemble experiment is examined for the purpose of describing the time development of tropical atmospheric response to a sea surface temperature (SST) anomaly. An ensemble experiment with the test cases of 200 is carried out by the use of a simplified atmospheric general circulation model (AGCM). The surface boundary condition is idealized to have a local warm SST area placed on the equator of a sphere covered with an SST distribution symmetric around the equator and zonally uniform (“aqua-planet”).
It is shown that the ensemble mean operation effectively reduce the small-scale random noise caused by precipitation activity and the noise known as intraseasonal oscillation. It is demonstrated that the time-development of planetary scale responce to the warm SST area can be clearly extracted by the enesemble mean operation. It is found that the ensemble size of at least 64 is required to extract the time-development of pressure field.

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