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由大粗糙元引起的高超声速边界层强制转捩在航天技术中有实际应用,因而近年来受到人们的广泛关注.虽然目前导致该转捩过程的内在机理尚不完全清楚,但有一点是明确的,即粗糙元的尾迹流场中存在强对流不稳定性.文章的出发点是研究这种对流不稳定模态是如何触发转捩的.首先通过CFD方法,计算出高超声速边界层中粗糙元的尾迹流场,并对其进行二维稳定性分析.结果发现,在传统不稳定Tollmien-Schlichting(T-S)模态出现的临界Reynolds数之前,存在高增长率的无黏不稳定模态,表现为对称的余弦模态和反对称的正弦模态.然后对该不稳定模态在粗糙元尾迹流中的演化进行了模拟,验证了二维稳定性分析的结果,并考察了非平行性效应的影响.最后通过直接数值模拟,研究由这些不稳定模态触发转捩的全过程.结果表明,对流不稳定模态确实是导致边界层转捩的关键机制.该转捩过程的特点是,局部湍斑首先在不稳定模态特征函数的峰值附近出现,然后向全流场扩散.就文章研究的工况而言,余弦和正弦模态的相互作用对转捩的影响并不明显,且后者在转捩过程中起主导作用.
Due to the practical application of hypersonic boundary layer caused by large coarse elements in space technology, it has drawn much attention in recent years. Although the underlying mechanism underlying the transition is not fully understood yet, it is clear that That is, the convectional instability of the wakes in the wakes of the rough elements.The starting point of the paper is to study how the convective instability mode triggers the transition.Firstly, by using the CFD method, the roughness The results show that there exists a high growth rate non-viscous unstable mode before the critical Reynolds number appears in the traditional unstable Tollmien-Schlichting (TS) Symmetrical cosine mode and antisymmetric sinusoidal mode.And then the evolution of the unstable mode in the wake flow of rough wakes was simulated and the results of two-dimensional stability analysis were verified and the effects of nonparallel effect Finally, the whole process of the transition from these unstable modes is investigated by direct numerical simulation.The results show that the convective instability mode is indeed the key mechanism leading to the transition of the boundary layer. The transition process is characterized by local turbulent spot first appearing around the peak of the eigenstablishment of the unstable mode, and then spreading to the full flow field. In terms of the working conditions of the article, the interaction of cosine and sine modal transitions The impact is not obvious, and the latter play a leading role in the transition process.