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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。
Aspirated hypersonic vehicles often have coarse particles or vortex generators in the inlet boundary layer that force the flow to turbulent flow to ensure proper engine start-up. In order to clearly understand the compulsory transfer process, implicit large eddy simulation method was used to simulate the forced transfer problem. For the diamond-shaped and ramp-shaped vortex generators, the flow structure induced by the vortex generators is calculated and shows that the forced swirling flow is dominated by the counter-rotating vortices generated by the vortex generators. The turbulence increases and develops along the flow direction, resulting in the vortices on the even mode or odd mode instability, the even mode instability produces symmetrical eddy-vortex crushing, while the odd mode instability leads to the asymmetric (curved) vortex on the crushing. The vortex eddy produced a series of card-induced vortices after crushing and finally caused the boundary layer to turn into turbulent flow. Finally, the influence of computational grid and numerical dissipation on the results of implicit large eddy simulation and the convergence of the computation are discussed.