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首页> 外文期刊>Journal of Fluid Mechanics >Relevance of local parallel theory to the linear stability of laminar separation bubbles
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Relevance of local parallel theory to the linear stability of laminar separation bubbles

机译：局部平行理论与层流分离气泡线性稳定性的关系

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摘要

Laminar separation bubbles are thought to be highly non-parallel, and hence global stability studies start from this premise. However, experimentalists have always realized that the flow is more parallel than is commonly believed, for pressure-gradient-induced bubbles, and this is why linear parallel stability theory has been successful in describing their early stages of transition. The present experimentalumerical study re-examines this important issue and finds that the base flow in such a separation bubble becomes nearly parallel due to a strong-interaction process between the separated boundary layer and the outer potential flow. The so-called dead-air region or the region of constant pressure is a simple consequence of this strong interaction. We use triple-deck theory to qualitatively explain these features. Next, the implications of global analysis for the linear stability of separation bubbles are considered. In particular we show that in the initial portion of the bubble, where the flow is nearly parallel, local stability analysis is sufficient to capture the essential physics. It appears that the real utility of the global analysis is perhaps in the rear portion of the bubble, where the flow is highly non-parallel, and where the secondaryonlinear instability stages are likely to dominate the dynamics.
机译：层流分离气泡被认为是高度不平行的，因此全局稳定性研究就是从这个前提开始的。但是，实验人员始终意识到，对于压力梯度引起的气泡，流动比通常认为的更为平行，这就是为什么线性平行稳定性理论已成功地描述了其过渡的早期阶段。当前的实验/数值研究重新审查了这一重要问题，并发现由于分离的边界层与外部势流之间的强相互作用过程，这种分离气泡中的基本流动变得几乎平行。所谓的死空气区域或恒压区域是这种强相互作用的简单结果。我们使用三层理论对这些特征进行定性解释。接下来，考虑整体分析对分离气泡的线性稳定性的影响。特别是，我们表明，在气泡接近流动平行的初始部分，局部稳定性分析足以捕获基本物理原理。似乎全局分析的真正用途可能是在气泡的后部，那里的流动高度不平行，并且次级/非线性不稳定阶段很可能主导动力学。

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