直接数值模拟揭示的超临界翼型跨声速抖振机制
Mechanisms of transonic buffet over supercritical airfoils revealed by direct numerical simulations
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中文总结 AI 辅助
通过直接数值模拟揭示超临界翼型跨声速抖振机制：识别出单一主导全局模态，并阐明激波-声波反馈回路（含两条传播路径）如何维持抖振周期，统一了抖振的物理图景。
中文摘要 AI 辅助
我们采用直接数值模拟研究了超临界翼型上的湍流跨声速流动，涵盖了从稳定状态到完全发展的抖振的转变过程，基于弦长的雷诺数为$3\ imes10^5$和$6\ imes10^5$。雷诺数决定了来流边界层状态，从而影响分离行为。谱本征正交分解揭示了一个单一的主导模态，该模态在抖振起始之前出现，并在向抖振转变的过程中持续存在。该模态的能量随攻角增加而增加，而其空间结构和基频几乎保持不变，这与全局不稳定性饱和为非线性的极限环相一致。几何声学提供了全局模态传播的一阶描述，并识别出两条连接声源（位于近尾流中）与激波的路径。较短的路径从后方冲击激波，而较长的路径绕过激波尖端，然后从前方到达激波。线性化的激波-声波相互作用理论预测，激波对低频、前向入射的声波扰动响应更强。时空相关性将下游路径的建立与完全边界层分离联系起来，这种分离是由激波的向上游运动间歇性地诱发的。沿前向入射路径的上游声学时间与下游对流时间之和，在两种雷诺数下均与测量的抖振周期相符。综合来看，这些结果与抖振的统一图景一致，其中气动声学反馈机制提供了扰动能够维持全局动力学的物理路径。
英文摘要
We use direct numerical simulations to study the turbulent transonic flow over a supercritical airfoil, spanning the transition from stable conditions to fully developed buffet at chord-based Reynolds numbers of $3\times10^5$ and $6\times10^5$. The Reynolds number determines the incoming boundary-layer state, thereby affecting the separation behaviour. Spectral proper orthogonal decomposition reveals a single dominant mode that emerges below onset and persists across the transition to buffet. The energy of this mode increases with the angle of attack while its spatial structure and fundamental frequency remain nearly unchanged, consistent with a global instability that saturates into a nonlinear limit cycle. Geometrical acoustics provides a first-order description of the global mode propagation and identifies two paths connecting the acoustic source, located in the near wake, to the shock. A shorter path impinges on the shock from behind, while a longer one circumvents the shock tip before reaching it from the front. Linearised shock--acoustic interaction theory predicts a stronger shock response to low-frequency, front-impinging acoustic disturbances. Space--time correlations link the establishment of a downstream path to complete boundary-layer separation, which is induced intermittently by the upstream motion of the shock. The sum of the upstream acoustic time along the front-impinging path and the downstream convective time is compatible with the measured buffet period at both Reynolds numbers. Together, these results are consistent with a unified picture of buffet, where an aeroacoustic feedback mechanism provides the physical pathways through which perturbations can sustain the global dynamics.
