Boundary-layer receptivity to unsteady pressure gradients: experiments and overview
Boundary-layer receptivity to unsteady pressure gradients: experiments and overview
复制标题
边界层对不稳定压力梯度的感受性：实验和概述
DOI：
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发表时间：
1986
影响因子：
3.7
通讯作者：
Morkovin
中科院分区：
文献类型：
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作者：
By M. Nishioka;M.;v.;Morkovin
对圆频率为ω、波长为λTS的不稳定涡量波（Tollmien-Schlichting-Schubauer波或TS波）在壁层中受振幅为A、频率为ω的非定常压力梯度作用机理的实验证据进行了回顾，发现它们是混乱和矛盾的。有人提出，一个可能有效的接受机制取决于这样一个事实，即在现实条件下，a沿着任何有限厚度的物体a (x)随距离x变化，从而引入了可以匹配λTS的额外特征长度。探索性论证表明，压力梯度通过A(x)注入壁面涡度，并以与ΔAF（κTS）实部成正比的速率迫使TS均方涡度$在{zeta^2}$上的空间增长，在x−1 / 2 λTS和x + 1 / 2 λTS之间的A(x)对傅里叶变换AF（κ）在κ = κTS处的贡献。$overline{zeta^2_{
m TS}}$ growth的第二个输入对应于通过强迫场的法向速度vf的作用，将稳定边界层涡度转换为不稳定的ζTS。该比率由$int_0^{delta}overline{v_{
m f}zeta_{
m TS}}U^{primeprime}(y),{
m d}y $给出，并与κTSΔAF（KTS）的虚部成正比。这个命题在所有目前可验证的方面都与一个数值和一系列实验室实验相一致。在室内实验中，自由流中不同配置的脉动压力源和屏蔽板为附近的平壁面边界层提供了变幅压力梯度。本文给出的三个例子表明，定常非定常压力场在边界层稳定时诱发斯托克斯样亚层，在边界层不稳定时诱发自激涡量波。第四次实验的结果表明，靠近边界层的尾迹中的非定常压力源可以迫使不稳定壁波在尾迹频率上生长，即使它们的传播速度不同。材料也提出了关键的苏联实验和观点的接受。最后，对这些实验和我们的实验进行了一致性和互补性的检验。
The experimental evidence on the mechanisms of forcing of unstable vorticity waves (the Tollmien–Schlichting–Schubauer or TS waves) of circular frequency ω and wavelength λTS in wall layers by unsteady pressure gradients of amplitude A and frequency ω is reviewed and found to be confused and contradictory. It is proposed that a likely effective receptivity mechanism rests on the fact that under realistic conditions A varies with distance x along any body of finite thickness, A(x), and introduces thereby additional characteristic lengths which can match λTS. Heuristic arguments suggest that through A(x) the pressure gradient infuses vorticity at the wall and forces spatial growth of the TS mean-square vorticity $overline{zeta^2}$, at a rate proportional to the real part of ΔAF(κTS), the contribution of A(x) between x−½λTS and x + ½λTS to the Fourier transform AF(κ) at κ = κTS. A second input into $overline{zeta^2_{
m TS}}$ growth corresponds to the conversion of the steady boundary-layer vorticity into unsteady ζTS, through the action of vf, the normal velocity of the forcing field. The rate is given by $int_0^{delta}overline{v_{
m f}zeta_{
m TS}}U^{primeprime}(y),{
m d}y $ and is proportional to the imaginary part of κTSΔAF(KTS). The proposition is consistent in all currently verifiable respects with one numerical and a series of laboratory experiments. In the laboratory experiments, various configurations of a pulsating pressure source and shielding plates located in the free stream supplied the variable-amplitude pressure gradients over the nearby flat-wall boundary layer. Three of the cases presented here demonstrate that stationary unsteady pressure fields induce Stokes-like sublayers when the boundary layer is stable and self-excited vorticity waves when it is unstable. The results of a fourth experiment suggest that unsteady pressure sources in wakes near the boundary layer can force the growth of unstable wall waves at the wake frequencies even though their propagation speeds differ. Material is also presented on key Soviet experiments and views on receptivity. Finally, these experiments and ours are examined for consistency and complementarity.