The pre-transitional Klebanoff modes and other boundary-layer disturbances induced by small-wavelength free-stream vorticity
The pre-transitional Klebanoff modes and other boundary-layer disturbances induced by small-wavelength free-stream vorticity
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小波长自由流涡引起的过渡前克莱巴诺夫模式和其他边界层扰动
DOI：
10.1017/s0022112009990838
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发表时间：
2009
影响因子：
3.7
通讯作者：
P. Ricco
中科院分区：
文献类型：
--
作者：
P. Ricco
本文研究了Blasius边界层对对流阵风型自由流涡扰动的响应。边界层的涡量特征通过边界区域方程计算，边界区域方程是低频扰动的Navier-Stokes方程的严格渐近极限。采用匹配渐近展开法得到了初始边界条件和外边界条件。对于二维阵风强迫的情况，考虑了与边界层厚度相当的壁面法向波长的影响。阵风粘性耗散和平均边界层引起的上升位移对粘性区域内的脉动产生了显著的影响。同样的分析也证明，对于由展向波长与边界层厚度相当的三维阵风引起的边界层响应的二阶精度计算是有用的。它还遵循的流向速度的边界层波动匹配相应的自由流速度分量。速度分布与实验数据进行了比较，取得了良好的协议。Tollmien-Schlichting波的产生之间的非线性混合的二维非定常涡量波动和平均流畸变引起的局部壁面粗糙度和吸力也进行了研究。小的壁正常波长的阵风产生显着不同的振幅的不稳定波的强迫频率的选定范围。这主要是由于自由流中和边界层内的流向速度波动之间的差异造成的。
The response of the Blasius boundary layer to free-stream vortical disturbances of the convected gust type is studied. The vorticity signature of the boundary layer is computed through the boundary-region equations, which are the rigorous asymptotic limit of the Navier–Stokes equations for low-frequency disturbances. The method of matched asymptotic expansion is employed to obtain the initial and outer boundary conditions. For the case of forcing by a two-dimensional gust, the effect of a wall-normal wavelength comparable with the boundary-layer thickness is taken into account. The gust viscous dissipation and upward displacement due to the mean boundary layer produce significant changes on the fluctuations within the viscous region. The same analysis also proves useful for computing to second-order accuracy the boundary-layer response induced by a three-dimensional gust with spanwise wavelength comparable with the boundary-layer thickness. It also follows that the boundary-layer fluctuations of the streamwise velocity match the corresponding free-stream velocity component. The velocity profiles are compared with experimental data, and good agreement is attained. The generation of Tollmien–Schlichting waves by the nonlinear mixing between the two-dimensional unsteady vorticity fluctuations and the mean flow distortion induced by localized wall roughness and suction is also investigated. Gusts with small wall-normal wavelengths generate significantly different amplitudes of the instability waves for a selected range of forcing frequencies. This is primarily due to the disparity between the streamwise velocity fluctuations in the free stream and within the boundary layer.