Streak instability in near-wall turbulence revisited
Streak instability in near-wall turbulence revisited
复制标题
重新审视近壁湍流中的条纹不稳定性
DOI：
10.1080/14685248.2017.1294757
复制
发表时间：
2017
影响因子：
1.9
通讯作者：
Cassinelli A
中科院分区：
文献类型：
--
作者：
Cassinelli A
条纹和流向涡的再生循环在近壁湍流的维持中起着核心作用。特别是再生循环中的条纹破裂阶段是流向涡形成的核心过程，但目前对它的理解特别是在真实的湍流环境中是有限的。本研究的目的是获得基本的洞察条纹崩溃的基础物理机制中存在的背景湍流波动。我们进行了一个基于直接数值模拟的数值实验，其中条纹是由以前的线性理论计算的体强迫人工产生的。当强迫振幅增加时，人工驱动条纹会在相当大的振幅范围内产生壁面法向速度和展向速度的强烈波动。这种横向速度波动在λ+x <$200 − 300（λ+ x是内标度的流向波长）处显示出最大值，但它只出现在λ+x <$3000 − 4000处。进一步检查与动态模式分解表明，相关的流场是由驱动条纹和交替的横向速度结构的蜿蜒曲折的运动，清楚地让人想起在以前的研究中发现的弯曲模式条纹不稳定性。最后，它示出，这些结构是合理地沿沿着的二次不稳定的临界层对齐，表明周围的湍流不显着修改的无粘曲折的条纹击穿机制，通过条纹不稳定性和/或条纹瞬态增长。
The regeneration cycle of streaks and streamwise vortices plays a central role in the sustainment of near-wall turbulence. In particular, the streak breakdown phase in the regeneration cycle is the core process in the formation of the streamwise vortices, but its current understanding is limited particularly in a real turbulent environment. This study is aimed at gaining fundamental insight into the underlying physical mechanism of the streak breakdown in the presence of background turbulent fluctuation. We perform a numerical experiment based on direct numerical simulation, in which streaks are artificially generated by a body forcing computed from previous linear theory. Upon increasing the forcing amplitude, the artificially driven streaks are found to generate an intense fluctuation of the wall-normal and spanwise velocities in a fairly large range of amplitudes. This cross-streamwise velocity fluctuation shows its maximum at λ+x≈ 200 − 300 (λ+xis the inner-scaled streamwise wavelength), but it only appears for λ+x≲ 3000 − 4000. Further examination with dynamic mode decomposition reveals that the related flow field is composed of sinuous meandering motion of the driven streaks and alternating cross-streamwise velocity structures, clearly reminiscent of sinuous-mode streak instability found in previous studies. Finally, it is shown that these structures are reasonably well aligned along the critical layer of the secondary instability, indicating that the surrounding turbulence does not significantly modify the inviscid inflectional mechanism of the streak breakdown via streak instability and/or streak transient growth.
DOI：
--
发表时间：
2015
期刊：
影响因子：
--
作者：
F. Alizard
通讯作者：
F. Alizard
影响因子：
3.7
作者：
Jiménez, J;Pinelli, A
通讯作者：
Pinelli, A
影响因子：
3.7
作者：
de Giovanetti, Matteo;Hwang, Yongyun;Choi, Haecheon
通讯作者：
Choi, Haecheon