壁面扰动对超声速湍流边界层拟序结构的影响研究

Influences of wall disturbances on coherent structures in supersonic turbulent boundary layers

本文研究了壁面扰动对来流马赫数为2.0的超声速湍流边界层中相干结构和湍流输运的影响.通过对直接数值模拟数据的分析,本文讨论了与动量和热传输相关的物理量的瞬时分布和谱特性.研究发现,壁面扰动在增强动量和热传输方面发挥重要作用,其在近壁区域引起了与壁面扰动波长及其谐波长度尺度的能量湍流脉动.同时,壁面扰动也激发了大尺度运动,其长度尺度为湍流边界层厚度,这是由壁面扰动和某些尺度的湍流运动之间的非线性相互作用所致.壁面扰动还引起了较强的密度和压力脉动,通过改变声速面而穿透边界层,保持等熵的特性向自由流辐射.在此过程中,稳态壁面扰动被湍流扭曲,从而具有了多尺度和多频率的特征.

In the present study,the influences of wall disturbances on coherent structures and the corresponding turbulent transport in supersonic turbulent boundary layers are investigated.The free-stream Mach number is set as 2.0.The database is scrutinized to present the instantaneous distributions and spectral properties of momentum and heat transfer related flow quantities.In their important roles in enhancing the momentum and heat transfer,the wall disturbances lead to the energetic turbulent fluctuations with the length scales of the wall disturbance wavelength and its harmonics in the near-wall region.The large-scale motions are also excited with the spanwise length scales of the turbulent boundary layer thicknesses,which,by reasoning,is caused by nonlinear interactions between wall disturbances and turbulent motions at some certain scales.They also produce intense density and pressure fluctuations that penetrate the boundary layer by deforming the sonic surfaces and radiate towards the free stream,where the fluctuations remain isentropic processes in nature.During this process,the steady wall disturbances are distorted by the turbulence,therefore endued with the features of multi-scale and multi-frequency instead of remaining energetic at a single wavelength or frequency.