高雷诺数下马赫6边界层转捩拉格朗日结构演化过程研究

Spatial-temporal evolution of Lagrangian structures in a transitional Mach 6 boundary layer at high Reynolds number

本文实验研究了单位雷诺数为9.7×10^(6)/m、马赫数6条件下边界层转捩中的拉格朗日结构演化过程。实验首先使用红外摄像机测量了不稳定波的发展及其对壁面温度分布的影响;接着采用超快流动显示技术和粒子图像测速技术观测了湍流产生过程。结果表明,在转捩后期,第二模态波被长波长的低频波调制并形成一个波包。基于速度场计算的拉格朗日物质线演化结果显示,该波包演化过程依次包括:1)边界层下层流体抬升运动形成孤子状波包;2)边界层上层流体越过鼓包下扫,并形成局部强剪切层;3)剪切层演化为涡旋。

This paper presents an experimental investigation of the spatial-temporal evolution of Lagrangian structures in the transition process of a boundary layer with a unit Reynolds number of 9.7×106/m and Mach number of 6.The development of unstable waves and the associated wall temperature distribution are measured by an infrared camera;the turbulence generation process is observed by utilizing state-of-the-art ultrafast flow visualization methods and particle image velocimetry.The results show that the second mode waves are modulated by long-wavelength and low-frequency waves,forming wave packets at the late transition stage.The evolution of Lagrangian material lines,based on the velocity fields derived from particle image velocimetry,demonstrates that the wave packets undergo three steps.Firstly,near-wall fluids are lifted upward to be solitonlike waves;secondly,the fluids away from the wall are swept down over the bulge,yielding a localized strong shear layer;finally,the shear layer eventually evolves into vortical structures.