角柱後流の対流不安定性から絶対不安定性への交替(安定性(1),一般講演)

概要

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Transition of convectively unstable flow past a rectangular cylinder to an absolutely unstable state is investigated numerically, in which a localized disturbance is added at a certain point in the flow field and the subsequent spatiotemporal development of the disturbance is observed. We found that the added localized disturbance propagates immediately to an absolutely unstable region just behind the cylinder, and then, it is convected downstream after growing in the absolutely unstable region if the flow is globally unstable (at supercritical Reynolds numbers). The boundary separating the absolutely unstable and convectively stable regions is estimated in numerical simulations for the non-parallel two-dimensional flow in which the flow is approximated by the parallel flow field in the upstream region than a prescribed distance behind the cylinder. We conclude that existence of even a very small absolutely unstable region causes the global instability of the flow and that the theory of stability for parallel flow is insufficient to determine whether the flow is absolutely or convectively unstable.
日本流体力学会の論文
2008-09-04