高超声速轴对称压缩斜板流转捩方案
Transition scenario in hypersonic axisymmetrical compression ramp flow
摘要：
在自由飞行马赫数为5、过渡雷诺数为1的条件下，对15 °轴对称压缩斜面引起的激波/过渡边界层干扰进行了高保真模拟。为了激发对流不稳定性，用白噪声扰动计算域的入口。相干结构提取使用频谱本征正交分解（SPOD），它给出了一个数学上的最佳分解的时空相关的结构内的流。平均流被用来进行预解式分析，以研究非正态线性放大机制。预解式分析和SPOD结果之间的比较提供了对流动中起作用的线性和非线性机制的见解。为了进行分析，将流动分成三个主要的感兴趣区域：附着边界层、混合层和再附着区域。所观察到的过渡过程是依赖于在边界层在很宽的频率范围内的斜模式的线性放大。这些模式非线性地相互作用以产生细长的流向结构，然后在域的其余部分中通过线性机制放大，直到它们在再附着区域中预锻。早期的非线性相互作用被发现是必不可少的过渡过程。
英文摘要：
A high-fidelity simulation of the shock/transitional boundary layer interaction caused by a 15-degrees axisymmetrical compression ramp is performed at a freestream Mach number of 5 and a transitional Reynolds number. The inlet of the computational domain is perturbed with a white noise in order to excite convective instabilities. Coherent structures are extracted using Spectral Proper Orthogonal Decomposition (SPOD), which gives a mathematically optimal decomposition of spatio-temporally correlated structures within the flow. The mean flow is used to perform a resolvent analysis in order to study non-normal linear amplification mechanisms. The comparison between the resolvent analysis and the SPOD results provides insight on both the linear and non-linear mechanisms at play in the flow. To carry out the analysis, the flow is separated into three main regions of interest: the attached boundary layer, the mixing layer and the reattachment region. The observed transition process is dependent on the linear amplification of oblique modes in the boundary layer over a broad range of frequencies. These modes interact nonlinearly to create elongated streamwise structures which are then amplified by a linear mechanism in the rest of the domain until they break down in the reattachment region. The early nonlinear interaction is found to be essential for the transition process.
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