局部凹槽对高超声速边界层中第二模态扰动演化的影响

采用直接数值模拟方法研究了局部矩形凹槽对来流马赫数为6.0的高超声速平板边界层中第二模态扰动演化的影响。引入了透射系数(定义为凹槽下游与上游扰动渐近幅值的比率)来量化凹槽的局部散射效应。数值结果表明:对于较浅的凹槽,频率较低的第二模态扰动被促进,而高频扰动的规律相反。对于大多数情况,凹槽深度的增加使得透射系数减小,这表明凹槽对扰动的促进作用减弱或抑制作用增强。当凹槽的深度超过某一临界值时,透射系数与凹槽深度的关系变为正相关,这表明了另一机制的出现。临界深度受扰动的频率影响:频率越低,临界深度越大。 

Impact of local cavities on evolution of the second-mode disturbances in hypersonic boundary layers

The influence of local rectangular cavities on the evolution of the second-mode disturbances in a incoming Mach number 6.0 hypersonic boundary layer over a flat plate was investigated by using direct umerical simulation. The local scattering effect was quantified by a transmission coefficient defined as the ratio of perturbation amplitude downstream cavity to upstream cavity. It was found from the numerical results that, for a shallow cavity, thesecond-mode disturbance with a relatively low frequency was enhanced by the cavity, while the opposite was true when the frequency was high. In most of the cases, the transmission coefficient reduced with the increase of the cavity depth, implying a weaker enhancement or a stronger suppression effect. When the cavity depth exceeded a critical value, the dependence of the transmission coefficient on cavity depth was changed to a positive correlation, implying the emergence of a new regime. The critical depth relies on the disturbance frequency: it is larger for a lower frequency.