高超声速进气道强制转捩流动的大涡模拟

吸气式高超声速飞行器常在进气道边界层内布置粗糙颗粒或涡流发生器强制流动转捩为湍流以确保发动机正常启动。为了清晰认识强制转捩过程，采用隐式大涡模拟方法，对强制转捩问题开展了数值模拟研究。针对钻石形和斜坡形涡流发生器，计算得到涡流发生器诱导的流动结构，显示出强制转捩流动由涡流发生器产生的反向旋转流向涡对主导。扰动沿流向增长和发展，导致流向涡对以偶模式或奇模式失稳，偶模式失稳产生对称形式的涡对破碎，而奇模式失稳则导致非对称（弯曲）形式的涡对破碎。流向涡对破碎后产生一系列发卡涡并最终促使边界层转捩为湍流。最后就计算网格和数值耗散对隐式大涡模拟结果的影响以及计算的收敛性进行了讨论。

Large eddy simulation for forced transition flow at hypersonic inlet

Forced transition is commonly used for a hypersonic air breathing vehicle to ensure its scramjet's normal start by placing roughness elements or vortex generators in the inlet boundary layer. To get a clear image of forced transition process, an implicit large eddy simulation method is used for laminar-turbulent forced transition flows in the boundary layer of a hypersonic inlet configuration. Main structures are obtained for the forced transition flows induced by the vortex generators shaped of diamonds and ramps, which show that the flows are dominated by stream-wise counter-rotating vortices. Fluctuations grow in the stream-wise direction and cause instabilities. Two fundamental modes of the instabilities are found in the simulations, the even mode and the odd one. The even mode leads to a varicose way of breaking down of the counter-rotating vortices, while the odd one leads to a sinuous way. Strings of hairpin vortices are generated after the breaking down and finally cause the transition. A discussion is carried out on the computation convergence together with the influence of the grids and numerical dissipation.