超声速/高超声速边界层转捩后期流场的模态分析

摘要

将动力模态分解(DMD)方法应用到超声速和高超声速边界层转捩后期的流场分析中,通过获得流场主要的相干结构和对模态的重构,研究了相干结构与壁面阻力和热流的关系.结果表明超声速和高超声速边界层转捩的流场结构存在明显差别.超声速转捩流场由低频流向涡的模态主导,这些模态对转捩后期的壁面阻力和热流有重要贡献;高超声速转捩流场中存在多个不同量级频率的模态,在DMD频谱上表现为多个不同的分支,通过对不同分支能量最高的模态进行考察,我们发现低频模态的结构为流向条带,高频模态的结构为二维扰动波,这些模态对壁面阻力和热流的影响与模态的结构形式类似.%Dynamic mode decomposition (DMD) is applied to the analysis of supersonic and hypersonic boundary layer late transitional flow.The primary coherent structures are obtained and modal reconstruction is performed.The relation is studied between the coherent structures,the skin friction and the heat flux.Significant difference can be found between supersonic and hypersonic transitional flow.Streamwise vortex of low-frequency modes plays dominant roles in supersonic transitional flow.These modes contribute to the skin friction and heat flux.In hypersonic boundary layer,there exist modes with several different orders of frequencies,and they're shown as several different branches in DMD frequency spectrum.By the analysis of the modes with the highest energy of each branch,we find that the structures of low-frequency modes are streamwise streaks,while for high frequency modes the structure is two-dimensional disturbance waves.The influence of skin friction and heat flux on the wall is similar to the structure of the modes.