円柱後流の不安定性と振動源(安定性(3),一般講演)

概要

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The mechanism of sustained oscillation in the flow past a circular cylinder is investigated numerically, in which impulsive force is given at a certain point in the flow and subsequent spatio-temporal development of induced disturbance is observed. Extending the conventional notions of convective and absolute instabilities established on the parallel flow approximation to non-parallel flows, we evaluate the growth rate of each instability mode. We found that the oscillation is sustained by superiority of the growth due to the convective instability over the decrease due to advection of the packet. It is concluded that the entire flow field is absolutely stable below the critical Reynolds number although some extent of the flow behind the cylinder is convectively unstable, while the flow becomes absolutely unstable everywhere behind the cylinder simultaneously when the Reynolds number exceeds the critical value.
2010-09-09