过膨胀平面喷管中跨声速激波/湍流边界层相互作用的时空动力学
Spatiotemporal dynamics of transonic shock-wave/turbulent-boundary-layer interactions in an overexpanded planar nozzle
AI总结：
本文结合实验与三维DDES数值模拟，研究过膨胀平面喷管中弱跨声速激波/湍流边界层相互作用的时空动力学，揭示分离泡下游扰动通过气动声学反馈回路维持低频激波非定常性的机制。
摘要：
我们开展了一项数值与实验相结合的研究，以探究激波诱导分离的缩比平面喷管中的跨声速激波/湍流边界层相互作用（STBLI），该喷管的全膨胀马赫数为 $M_j = 1.05$，射流雷诺数为 $Re \sim 10^5$。喷管构型通过时间分辨纹影可视化进行测试。尽管已有大量研究针对高雷诺数分离流场，但对低喷管压比（NPR）跨声速喷管中存在的弱激波非定常性知之甚少。因此，采用高分辨率三维延迟分离涡模拟（DDES）进行数值仿真，以研究壁面压力信号和非定常激波相互作用的时空动力学。所考虑的瞬态统计包括基于谱傅里叶和小波的分析以及动态模态分解（DMD）。谱分析揭示了与激波非定常性的分级行为相对应的能量低频模态，以及与下游湍流混合层中开尔文-亥姆霍兹不稳定性特征相关的高频模态。低频非定常性的机制通过模态分解和谱分析加以推演，其中发现分离泡内的下游扰动不仅在闭合气动声学反馈回路方面起主要作用，而且允许低频非定常性的持续演化和维持。还通过涡片方法进行了分析，以表征啸音的产生，假设存在向上游传播的导引射流模态。
英文摘要：
We perform a combined numerical and experimental study to investigate the transonic shock-wave/turbulent-boundary-layer interactions (STBLI) in a shock-induced separated subscale planar nozzle with fully-expanded Mach number,$M_j = 1.05$ and jet Reynolds number $Re \sim 10^5$. The nozzle configuration is tested via time-resolved schlieren visualisation. While numerous studies have been conducted on the high Reynolds number separated flowfields, little is known on the weak shock wave unsteadiness present in low nozzle pressure ratio (NPR) transonic nozzles. Therefore, numerical simulations are carried out with high resolution three-dimensional delayed detached eddy simulation (DDES), to study the spatiotemporal dynamics of wall pressure signals and unsteady shock interactions. The transient statistics considered include spectral Fourier and wavelet-based analysis and dynamic mode decomposition (DMD). The spectral analyses reveal energetic low frequency modes corresponding to the staging behaviour of shock unsteadiness, and high frequencies linked to the characteristics of the Kelvin-Helmholtz instabilities in the downstream turbulent mixing layer. The mechanisms for the low frequency unsteadiness is educed through modal decomposition and spectral analysis, wherein it is found that the downstream perturbations within the separation bubble play a major role in not only closing the aeroacoustic feedback loop, but allowing the continual evolution and sustainment of low frequency unsteadiness. An analysis via the vortex sheet method is also carried out to characterise the screech production, by assuming an upstream propagating guided jet mode
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