[in Japanese]

View full abstract

Shape and stability of a bubble embedded in a Rankine's combined vortex is investigated theoretically. Assuming that the gas inside the bubble changes polytropically, we introduce a variational function with a Lagrangian multiplier. Steady solutions are obtained from the condition of vanishing first variation and their stability is studied by looking at the sign of second variation. In general, a bubble stretches axially as the vortex becomes stronger, but a further increase of vortex strength makes the bubble to shrink to a small sphere, if the pressure inside the bubble is constant and its radius is small compared with the vortex radius. Any bubble is stable against asymmetric disturbances. Stability against axisymmetric disturbances depends, mainly, on the value of the polytropic exponent. Bubbles that are filled with a gas of constant temperature is stable, whereas those filled by a constant pressure gas are unstable irrespective of the vortex strength.

View full abstract

The pressure distributions of the flow through a two-dimensional channel with oscillating wall were measured experimentally. In this study, our attention was paid to the steady components of pressure distributions and the experiments were carried out in the vicinity of transitional flow region. The experimental results showed that the oscillation of wall had a strong effect on the steady components of pressure distribution when the oscillational frequency of wall lay in the vicinity of 30Hz. Moreover, it was found that this effect became clear with decreasing Reynolds number of the bulk flow.

View full abstract