高速平板边界层中定常条带的前缘感受性

Leading-edge receptivity of steady streaks in a hypersonic flat-plate boundary layer

来流湍流度较高时,自由流涡波可在边界层内激发流向条带结构,并引起边界层的旁路(bypass)转捩。本文采用调和线性化Navier-Stokes方程(harmonic linearized Navier-Stokes,HLNS)方法模拟平板边界层条带对自由流涡波的前缘感受性,并通过直接数值模拟验证了HLNS方法的可靠性。针对马赫数4.8的高速平板边界层,分析了零频涡波激发定常条带的前缘感受性过程及定常条带的演化规律。研究结果表明,边界层外的自由流涡扰动对边界层条带的发展存在持续的激励作用;对于固定展向波数的自由流涡波,法向波数为0时激发的条带幅值最大;自由流涡波的法向波数在小于临界角度时仅影响条带的幅值,而不影响条带扰动的形函数剖面。随着当地雷诺数的增加,条带的幅值演化和形函数剖面呈现出很好的相似性;当地无量纲展向波数β=0.18时,归一化幅值最大。

Free-stream vortical waves can excite streamwise streaks and trigger the bypass transition of boundary layers subjected to a large magnitude of free-stream turbulence.In this paper,the harmonic linearized Navier-Stokes(HLNS)method is applied to simulate the leading-edge receptivity of streaks to free-stream vortical waves,and its reliability is validated by direct numerical simulations.For a supersonic flat-plate boundary layer in the condition of Mach number 4.8,a systematic analysis was conducted on the leading-edge receptivity process of steady streaks excited by zero-frequency vortical waves and the evolution of these steady streaks.Results suggest that the development of streaks is forced continuously by free-stream vortical waves outside the boundary layer.The amplitude of the generated streak reaches the maximum when the vertical wavenumber is zero for free-stream vortical waves with specified spanwise wavenumbers.When the vertical wavenumber is less than the critical angle,it affects the amplitudes but not the shape functions of streaks.As the local Reynolds number increases,the streaks'amplitude evolutions and the shape functions exhibit strong similarity.The peak normalized amplitude of the streaks occurs at a local non-dimensional spanwise wave number of about 0.18.