Linear stability of optimal streaks in the log-layer of turbulent channel flows
Linear stability of optimal streaks in the log-layer of turbulent channel flows
复制标题
湍流河道流对数层最佳条纹的线性稳定性
DOI：
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发表时间：
2015
期刊：
影响因子：
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通讯作者：
F. Alizard
中科院分区：
文献类型：
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作者：
F. Alizard
研究了湍流通道对数区条纹二次不稳定性对附壁涡结构产生的重要性。条纹和它们的线性不稳定性通过求解与有组织的运动相关联的方程来计算，所述有组织的运动包括对非相干波动的影响进行建模的涡流粘度。研究了三种摩擦雷诺数Reτ = 2000、3000和5000。对于所有流动情况，最佳流向涡（即，具有线性瞬态能量放大的最高潜力）被用作初始条件。由于提升机制，这些最佳扰动导致条纹的非线性增长。基于沿着展向的Floquet理论，当条纹振幅超过一个临界值时，我们观察到条纹二次不稳定性的发生。结果表明，在中性条件下，条纹不稳定模的能量主要集中在中心区。
The importance of secondary instability of streaks for the generation of vortical structures attached to the wall in the logarithmic region of turbulent channels is studied. The streaks and their linear instability are computed by solving equations associated with the organized motion that include an eddy-viscosity modeling the effect of incoherent fluctuations. Three friction Reynolds numbers, Reτ = 2000, 3000, and 5000, are investigated. For all flow cases, optimal streamwise vortices (i.e., having the highest potential for linear transient energy amplification) are used as initial conditions. Due to the lift-up mechanism, these optimal perturbations lead to the nonlinear growth of streaks. Based on a Floquet theory along the spanwise direction, we observe the onset of streak secondary instability for a wide range of spanwise wavelengths when the streak amplitude exceeds a critical value. Under neutral conditions, it is shown that streak instability modes have their energy mainly concentrated in the ove...