Title: Transition mechanisms in hypersonic wind-tunnel nozzles: a methodological approach using global linear stability analysis Show Chinese title

Title: 高超声速风洞喷管中的过渡机制：基于全局线性稳定性分析的方法学方法

Abstract: Base-flow computations and stability analyses are performed for a hypersonic wind tunnel nozzle at a Mach number of 6. Isothermal and adiabatic wall boundary conditions are investigated, and moderate stagnation conditions are used to provide representative scenarios to study the transition in quiet hypersonic wind tunnel facilities. Under these conditions, the studied nozzle shows a small flow separation at the convergent inlet. Global stability analysis reveals that this recirculation bubble may trigger a classical three-dimensional stationary unstable global mode. Resolvent analysis reveals G\"ortler, first and second Mack modes affecting the divergent part of the nozzle, along with a Kelvin-Helmholtz instability induced by the bubble. The present study also highlights the key impact of perturbations located in the convergent inlet on the development of instabilities further downstream in the divergent outlet, helping understand the need and efficacy of a suction lip upstream of the nozzle throat to mitigate instabilities in the divergent nozzle. Detailed knowledge of all these mechanisms is essential for understanding flows in quiet hypersonic wind tunnel nozzles and, consequently, represents a key step toward the optimisation of such nozzles. Show Chinese abstract

Abstract: 针对马赫数为6的高超声速风洞喷管进行了基流计算和稳定性分析。研究了等温壁面条件和绝热壁面条件，并采用适度的滞止条件提供代表性场景以研究安静高超声速风洞设施中的过渡现象。在这些条件下，所研究的喷管在收敛段入口处显示出轻微的流动分离。全局稳定性分析表明，这种回流泡可能触发经典的三维稳态不稳定全局模态。分辨率分析揭示了Görtler模态、第一和第二Mack模态影响喷管发散部分，以及由气泡引起的Kelvin-Helmholtz不稳定性。本研究还强调了位于收敛段入口的扰动对下游发散段不稳定性发展的重要影响，有助于理解在喷管喉部上游设置吸力唇以减轻发散段不稳定的必要性和有效性。详细了解所有这些机制对于理解安静高超声速风洞喷管中的流动至关重要，因此代表了优化此类喷管的关键步骤。