具有大后掠角马赫数的高超音速附着线不稳定性
Hypersonic attachment-line instabilities with large sweep Mach numbers
摘要：
本研究的目的是揭示高超声速大后掠角马赫数的附着线不稳定性。本文研究了引起大后掠角马赫数的大后掠角冷圆柱绕流。采用高阶激波拟合方法求解全纳维-斯托克斯方程，得到了高精度的底部流场。利用局部和整体稳定性理论，发现沿前缘层流-湍流转捩的附着线模态占主导地位，这与实验观测结果Gaillard 1999吻合得很好。这种模态的行为解释了为什么当后掠马赫数大于5时转捩发生得更早。而且，如果用边界层假设计算底流，则不存在这种附着线模式，这表明边界层外无粘流的影响不能象通常那样忽略。它清楚地表明，全球模式显示的附着线模式的功能，如在扫Hiemenz流，和横流的模式沿表面进一步下游。与不可压缩流相反，该模式被证明是无粘的性质。此外，前缘曲率对大展向波数的附着线模态有失稳作用，但对小展向波数的附着线模态有稳定作用。
英文摘要：
This study aims to shed light on hypersonic attachment-line instabilities with large sweep Mach numbers. Highly swept flows over a cold cylinder that give rise to large sweep Mach numbers are studied. High fidelity base flows are obtained by solving full Navier-Stokes equations with a high-order shock-fitting method. Using local and global stability theories, an attachment-line mode is found to be dominant for the laminar-turbulent transition along the leading edge that agrees well with experimental observations Gaillard1999. The behavior of this mode explains the reason why the transition occurs earlier as the sweep Mach number is above 5. Also, this attachment-line mode is absent if the base flow is calculated with boundary-layer assumptions, indicating that the influence of inviscid flow outside the boundary layer can not be ignored as is normally done. It is clearly demonstrated that the global modes display the features of both attachment-line modes, as in sweep Hiemenz flow, and cross-flow-like modes further downstream along the surface. In contrast to incompressible flows, the mode is shown to be of inviscid nature. Moreover, the leading-edge curvature has a destabilizing effect on the attachment-line mode for large spanwise wave numbers but a stabilizing effect for small spanwise wave numbers.
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