Drag reduction and transient growth of a streak in a spanwise wall-oscillatory turbulent channel flow
Drag reduction and transient growth of a streak in a spanwise wall-oscillatory turbulent channel flow
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DOI：
10.1063/5.0050547
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发表时间：
2021-06
影响因子：
4.6
通讯作者：
A. Yakeno
中科院分区：
文献类型：
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作者：
A. Yakeno
作为 Yakeno 等人工作的延伸，研究了湍流通道中展向壁振荡的减阻机制。 [“具有展向壁振荡的减阻湍流通道流中准流向涡旋结构的修改”，Phys。 Fluids 26, 085109 (2014)] 低雷诺数。通过计算振荡基流下的瞬态能量增长来评估流动不稳定性，该振荡基流控制近壁条纹结构的生成。振荡影响条纹模式的最佳能量增长，其特征与直接数值模拟中的特征相当一致。在较长的振荡周期下，较厚的斯托克斯层增强了倾斜条纹模式的最佳生长，而原始条纹模式的最佳生长则减弱。振荡下最佳扰动的转变表明，展向斯托克斯层剪切对修正的贡献比展向速度大得多。提出了一种新的减阻性能估计模型，该模型使用基于振荡下条纹形成修正的展向速度切变加速度，通过振荡引起的倾斜延迟抑制能量传递到流向涡流。这个简单的模型即使在长振荡周期下也能很好地工作，并且在理论上与 Yakeno 等人的模型一致。基于低雷诺数下流向涡流引起的雷诺剪切应力的变化。
The drag-reduction mechanism of spanwise wall oscillation in a turbulent channel was investigated as an extension of the work of Yakeno et al. [“Modification of quasi-streamwise vortical structure in a drag-reduced turbulent channel flow with spanwise wall oscillation,” Phys. Fluids 26, 085109 (2014)] at a low Reynolds number. Flow instability was evaluated by computing the transient energy growth under an oscillating base flow which governed the generation of a near-wall streak structure. Oscillation affected the optimal energy growth of the streak mode, whose characteristics were reasonably consistent with those in a direct numerical simulation. The optimal growth of the tilted-streak mode was enhanced with a thicker Stokes layer under longer oscillation periods, while that of the original streak mode was weakened. The transition of the optimal perturbation under oscillation showed that the spanwise Stokes layer shear contributed considerably more to modification than the spanwise velocity did. A new drag-reduction performance estimation model was suggested using the acceleration of the spanwise velocity shear based on streak formation modification under oscillation, which restrains energy transfer to streamwise vortices via a tilting delay due to oscillation. This simple model worked well even under long oscillation periods and was theoretically consistent with that of Yakeno et al. based on the change in the Reynolds shear stress due to a streamwise vortex at a low Reynolds number.