Direct Numerical Simulation of boundary-layer transitionunder consideration of chemical and thermal non-equilibrium at a generic capsule geometry with smooth and rough surfaces.

本文采用直接数值模拟的方法，研究了化学平衡和非平衡条件下高焓流动的层流-湍流转变演化过程。阿波罗太空舱形状的一般几何形状被使用，包括高温气体效应。研究了离解和非平衡效应对不稳定边界层扰动发展的影响。特别是在大气再入飞行任务中，化学平衡和非平衡条件下的粗糙度诱导跃迁是研究的重点。这些调查是对其他PAK 742合作伙伴的理想气体调查(HLB的冷风洞条件)的补充。研究了分布粗糙度的瞬时增长机制和离散粗糙度尾迹流的二次失稳机制对扰动的放大作用。二次不稳定是由局部速度和温度梯度驱动的，这在化学(非)平衡流动中会更加明显，在这些情况下会导致更早的转变。然后将模拟扩展到在风洞中加入干扰背景(“风洞重建”)，以更好地预测实验中的过渡。将这些结果外推到高焓的自由飞行条件是特别有趣的。

In the proposed project, direct numerical simulations are used to investigate the laminar-turbulent transition evolution in a high-enthalpy flow under chemical equilibrium and non-equilibrium conditions. A generic geometry of the Apollo-capsule shape is used including high-temperature gas effects. The effect of dissociation and non-equilibrium effects on the disturbance development in the boundary layer subject to instabilities shall be investigated. Especially, roughness induced transition under chemical equilibrium and non-equilibrium conditions as for atmospheric re-entry missions is the main focus of the investigations. These investigations complement the ideal-gas investigations (cold wind-tunnel conditions at HLB) of the other PAK 742 partners. Disturbance amplification through the so-called transient growth mechanism for distributed roughnesses as well as secondary instability mechanisms for the discrete roughness wake flow are examined. Secondary instabilities are driven by local velocity and temperature gradients, which can be more pronounced in chemical (non-)equilibrium flows, leading to earlier transition in these cases. The simulations are then extended to incorporate the disturbance background in the wind tunnel ("wind-tunnel rebuilding") to better predict transition in experiments. Extrapolation of these results to high-enthalpy free-flight conditions are of particular interest.