Optimal excitation of three‐dimensional perturbations in viscous constant shear flow
Optimal excitation of three‐dimensional perturbations in viscous constant shear flow
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DOI：
10.1063/1.858574
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发表时间：
1993-06
影响因子：
4.6
通讯作者：
B. Farrell;P. Ioannou
中科院分区：
文献类型：
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作者：
B. Farrell;P. Ioannou
通过对完整的解析解集进行优化，可以得到在选定的时间间隔内能量增加最大的粘性常剪切流的三维扰动。这些最佳的扰动本质上是三维的，受限制的形态，并表现出大的能量增长的平流时间尺度上，尽管没有指数正常模式的不稳定性，在恒定的剪切流。最佳结构可以解释为与两种可区分的增长机制相关的两种基本运动类型的组合：流向涡通过平均流向速度的平流增长以形成流向条纹，以及上游倾斜波通过二维剪切不稳定的下梯度雷诺应力机制增长。在选定的时间间隔内的最佳激励包括这两种机制的组合，其特征是产生具有大大放大的扰动能量的倾斜滚转涡。有人建议...
The three‐dimensional perturbations to viscous constant shear flow that increase maximally in energy over a chosen time interval are obtained by optimizing over the complete set of analytic solutions. These optimal perturbations are intrinsically three dimensional, of restricted morphology, and exhibit large energy growth on the advective time scale, despite the absence of exponential normal modal instability in constant shear flow. The optimal structures can be interpreted as combinations of two fundamental types of motion associated with two distinguishable growth mechanisms: streamwise vortices growing by advection of mean streamwise velocity to form streamwise streaks, and upstream tilting waves growing by the down gradient Reynolds stress mechanism of two‐dimensional shear instability. The optimal excitation over a chosen interval of time comprises a combination of these two mechanisms, characteristically giving rise to tilted roll vortices with greatly amplified perturbation energy. It is suggested ...