Local boundary-layer receptivity to a convected free-stream disturbance
Local boundary-layer receptivity to a convected free-stream disturbance
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DOI：
10.1017/s0022112098003243
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发表时间：
1999-01
影响因子：
3.7
通讯作者：
A. Dietz
中科院分区：
文献类型：
--
作者：
A. Dietz
研究了Blasius边界层对谐波涡旋扰动的局部可接受性，作为理解边界层对自由流湍流可接受性的一步。虽然已经对描述边界层声接受度的线性理论进行了扎实的实验验证，但这是第一次对局部对流扰动接受度背后的机制进行实验验证。位于平板上游的振动带的谐波尾迹提供了自由流扰动。板表面的二维粗糙度单元作为局部接受点。在粗糙度下游边界层的热线测量证实了长波长对流扰动与粗糙度引起的短尺度平均流畸变在外层相互作用下产生的TS不稳定波。对不稳定波的特征进行了仔细测量，以确保它们的行为是线性稳定理论的正确模型。这一理论随后被用来确定由接受过程产生的不可测量的小的初始波幅，从下游测量的波幅。进行测试以确定当前接受性理论中线性假设的有效性范围。通过将实验数据以与自由流振幅、粗糙度高度和粗糙度几何无关的效率函数的形式表示，将在线性条件下得到的实验数据与其他作者的理论结果进行比较。在一定的频率和雷诺数范围内，得到了实验和理论效率函数的合理一致。
An investigation of the local receptivity of a Blasius boundary layer to a harmonic vortical disturbance is presented as a step towards understanding boundary-layer receptivity to free-stream turbulence. Although there has been solid experimental verification of the linear theory describing acoustic receptivity of boundary layers, this was the first experimental verification of the mechanism behind local receptivity to a convected disturbance. The harmonic wake from a vibrating ribbon positioned upstream of a flat plate provided the free-stream disturbance. Two-dimensional roughness elements on the surface of the plate acted as a local receptivity site. Hot-wire measurements in the boundary layer downstream of the roughness confirmed the generation of Tollmien–Schlichting (TS) instability waves by an outer-layer interaction between the long-wavelength convected disturbance and the short-scale mean-flow distortion due to the roughness. The characteristics of the instability waves were carefully measured to ensure that their behaviour was correctly modelled by linear stability theory. This theory was then used to determine the immeasurably small initial wave amplitudes resulting from the receptivity process, from wave amplitudes measured downstream. Tests were performed to determine the range of validity of the linear assumptions made in current receptivity theories. Experimental data obtained in the linear regime were then compared to theoretical results of other authors by expressing the experimental data in the form of an efficiency function which is independent of the free-stream amplitude, roughness height and roughness geometry. Reasonable agreement between the experimental and theoretical efficiency functions was obtained over a range of frequencies and Reynolds numbers.