In the present study, we consider the air entrainment into a suction pipe which is vertically inserted down into a suction sump across a mean free-water surface. This configuration is often referred to as the "vertical wet-pit pump", and has many practical advantages in construction, maintenance and operation. In particular, we focus our concern upon the critical submergence depth S c , which is one of the prime and conventional indicators for the air-entrainment occurrence. By a systematic approach, we experimentally investigate the influences of kinetic and geometric parameters upon S c. As the kinetic parameters, we consider the Reynolds number Re and the Weber number We, in addition to the Froude number Fr, on such a basis as Fr is not much larger than unity in many actual cases. As the geometric parameters, we consider back clearance X, sump breadth B and bottom clearance Z. Here, all parameters are non-dimensionalised by the outside diameter D and the intake velocity V i of the suction pipe. As a result, we reveal the effects of such six parameters upon S c. The We effect, namely, the surface-tension effect can be ignored at We > 12. And, the Re effect, namely, the viscous effect becomes negligibly small at Re > 3×10 4. Under such conditions for We and Re, we could consider only the Fr effect, namely, the gravitational effect. Concerning the X/D and B/D effects, S c /D attains the maximum at a certain X/D or B/D. On the other hand, the Z/D effect is monotonic, and becomes small at Z/D > 2.5. Some aspects of these geometric effects can be evaluated by a local-Froude-number effect on the basis of the global relation between S c /D and Fr. And, the other aspects is necessarily considered to be related with the flow structure in the suction sump.

A confined jet sometimes causes a self-exited oscillation due to the existence of a downstream target. In this work, the authors study this phenomenon. More specifically, the authors deal with a simple fluidic oscillator; namely, a two-dimensional confined jet into an abruptly-expanding channel with a downstream target of a square cylinder. The authors conduct the velocity measurements by an UVP (ultrasonic velocity profiler). Besides, the flow patterns in the fluidic oscillator are observed by a PIV (particle image velocimetry). As a result, the authors reveal the geometrical effects upon the range of stable jet's oscillation, such as the aspect-ratio effect, the channel-breadth effect, the cylinder-size effect and the cylinder-distance effect, together with the Re effect.

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In this study, we deal with the tumbling, which is a rotating motion with the axis perpendicular to the falling direction. Our purpose is to reveal the fundamental aerodynamic characteristics of the tumbling, experimentally. Regarding a test plate, we consider a prism with a rectangular cross section with a depth-to-width ratio λ of 0.3. The results are as follows. The reduced terminal rotating rate Ω * , the lift coefficient C L , the drag coefficient C D and the lift-to-drag ratio C L /C D are independent of the aspect ratio AR, when AR is greater than 10. As the inertia moment ratio I * increases from zero to 50, Ω * , C L and C D increase. However, Ω * , C L and C D become almost constant, at I * greater than 50. We propose the empirical formulae to predict them. At low I * , the tumbling shows a dominant periodicity of 360 deg.

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