Numerical Investigation of Transition Mechanisms in Hypersonic Boundary Layers of Generic Reentry Geometries

本提案的总体目标是确定在扰动自由流条件和各种粗糙度分布下导致钝再入飞行器前体层流-湍流过渡的基本影响和机制。为了实现这一目标，将改进基于TP2-BS实验数据和TP1直接数值模拟结果的高超声速路德维格管布伦瑞克（HLB）风洞流微扰的测定方法，采用停滞点探针。这是第一个资助期的结果，在这个资助期中，锥探头对所测隧道噪声的模态分解具有不利的特性。将风洞的扰动数据与HLB中的新型转捩实验相结合，将与确定的风洞噪声联系起来，并用于改善转捩和风洞噪声的相关性。在第二个资助期的数值研究中，将分析确定的隧道噪声与钝式再入飞行器前体分布粗糙度的相互作用。由于在TP2-GÖ中表明，在HLB的当前雷诺数范围内，再入飞行器不能预期模态增长，因此研究了粗糙度尾迹中的非模态瞬态增长。因此，要分析在一定条件下隧道噪声如何激发稳定边界层模式，并对瞬态生长产生影响。其次，研究了确定性分布粗糙度的各种排列方式对结构的影响，以了解粗糙度的排列方式是否具有根本性的影响。如果情况并非如此，则可以在未来的数值和实验研究中使用易于参数化的确定性分布粗糙度来模拟更现实的随机分布粗糙表面。

The overall objective of this proposal is the identification of essential effects and mechanisms that lead under perturbed freestream conditions and various types of roughness distributions to laminar-turbulent transition on the frontbody of blunt reentry vehicles. To satisfy this objective the determination of the pertubations in the wind tunnel flow of the Hypersonic Ludwieg Tube Braunschweig (HLB), which is based on experimental data from TP2-BS and direct numerical simulation results from TP1 , will be improved by using a stagnation-point probe. This is a consequent result of the first funding period in which it was shown that the cone probe has unfavorable properties for the modal decomposition of the measured tunnel noise. The pertubation data of the wind tunnel in conjunction with novel transition experiments in the HLB will be linked to the determined tunnel noise and used to improve correlations of transition and tunnel noise. In the numerical investigations in the second funding period, the interaction of the determined tunnel noise and distributed roughness on the forebody of a blunt reentry vehicle will be analyzed. Since it was shown in TP2-GÖ that modal growth can not be expected for the reentry vehicle in the current Reynolds number range of the HLB, non-modal transient growth is investigated in the wake of the roughness. Therefore, it is to be analyzed how tunnel noise under certain conditions excites stable boundary layer modes and such influences transient growth. Next, the influence of various arrangements of deterministic distributed roughness is investigated to understand whether or not the roughness arrangement has a fundamental impact. If this is not the case, easily parameterizable deterministic distributed roughness can be used in future numerical and experimental investigations to mimic more realistic stochastically distributed rough surfaces.