The effect of confinement on the stability of two-dimensional shear flows
The effect of confinement on the stability of two-dimensional shear flows
复制标题
约束对二维剪切流稳定性的影响
DOI：
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发表时间：
2006
影响因子：
3.7
通讯作者：
M. Juniper
中科院分区：
文献类型：
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作者：
M. Juniper
最近的研究表明，当二维尾迹被两个平板约束在横向时，它的不稳定性增加。约束导致在较低的剪切值时发生从对流到绝对不稳定的转变。本文综合分析了这一效应，认为这是由于尾迹(或喷流)和周围流动中群速度为零的模式的结构性相互作用所致。当尾迹(或喷流)中基模的波数与周围流动中基模的波数相匹配时，出现最大不稳定性。当一种模式的谐波与另一种模式的基波相互作用时，就会出现其他高度不稳定的区域。在密度比从0.001到1,000的情况下检查这种效果。在每个密度比下，可以预测导致最大绝对不稳定性的约束。这项研究还表明，为了避免过度预测绝对不稳定，检查绝对不稳定模的波数是至关重要的。在某些情况下，这个波数非常小，必须根据实际情况对模式进行折现。
It has been shown recently that the instability of a two-dimensional wake increases when it is confined in the transverse direction by two flat plates. Confinement causes the transition from convective to absolute instability to occur at lower values of shear. This paper examines this effect comprehensively and concludes that it is due to the constructive interaction of modes with zero group velocity in the wake (or jet) and in the surrounding flow. Maximum instability occurs when the wavenumber of the fundamental mode in the wake (or jet) matches that of the fundamental mode in the surrounding flow. Other regions of high instability occur when the harmonics of one mode interact with the fundamental of the other. This effect is examined at density ratios from 0.001 to 1000. At each density ratio, the confinement which causes maximum absolute instability can be predicted. This study also shows that it is vital to examine the wavenumber of absolutely unstable modes in order to avoid over-predicting the absolute instability. In some situations this wavenumber is vanishingly small and the mode must be discounted on physical grounds.