Modal and non-modal stability of boundary layers forced by spanwise wall oscillations
Modal and non-modal stability of boundary layers forced by spanwise wall oscillations
复制标题
翼展壁振动迫使边界层的模态和非模态稳定性
DOI：
10.1017/jfm.2015.387
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发表时间：
2015
影响因子：
3.7
通讯作者：
T. Zaki
中科院分区：
文献类型：
--
作者：
M. Hack;T. Zaki
考察了受时谐跨向壁面运动影响的边界层中的模态和非模态扰动增长。沿流的Blasius流和沿展向的Stokes层的叠加会导致基流周期间隔内的强模态放大。基态冻结相的线性稳定性分析表明，这种增长是由于无粘不稳定性，这与展向斯托克斯层的拐点有关。在以相位为函数跟踪最不稳定模式时，壁处新拐点的产生及其向自由流的传播导致模式交叉。Floquet分析中计算的基模比瞬时特征函数的增长率低得多。此外，在瞬态生长分析中，还研究了导致kklebanoff条纹形成的代数抬升机制。壁面作用力显著减弱了与抬升相关的壁面法向速度扰动。这种效应归因于压力场的形成，压力场将能量从壁法向向展向的速度扰动重新分配。线性理论的结果解释了Hack & Zaki （J.流体力学）在相同流型中从击穿到湍流的直接数值模拟的观察结果。， vol. 760, 2014a, pp. 63-94)。当旁路机制占主导地位时，由于较弱的非模态增长，流动稳定。然而，在高振幅壁面振荡时，由于模态不稳定性的快速增长，促进了过渡。
Modal and non-modal perturbation growth in boundary layers subjected to time-harmonic spanwise wall motion are examined. The superposition of the streamwise Blasius flow and the spanwise Stokes layer can lead to strong modal amplification during intervals of the base-flow period. Linear stability analysis of frozen phases of the base state demonstrates that this growth is due to an inviscid instability, which is related to the inflection points of the spanwise Stokes layer. The generation of new inflection points at the wall and their propagation towards the free stream leads to mode crossing when tracing the most unstable mode as a function of phase. The fundamental mode computed in Floquet analysis has a considerably lower growth rate than the instantaneous eigenfunctions. Furthermore, the algebraic lift-up mechanism that causes the formation of Klebanoff streaks is examined in transient growth analyses. The wall forcing significantly weakens the wall-normal velocity perturbations associated with lift-up. This effect is attributed to the formation of a pressure field which redistributes energy from the wall-normal to the spanwise velocity perturbations. The results from linear theory explain observations from direct numerical simulations of breakdown to turbulence in the same flow configuration by Hack & Zaki (J. Fluid Mech., vol. 760, 2014a, pp. 63–94). When bypass mechanisms are dominant, the flow is stabilized due to the weaker non-modal growth. However, at high amplitudes of wall oscillation, transition is promoted due to fast growth of the modal instability.
影响因子：
4.6
作者：
Hack M
通讯作者：
Hack M
通过壁振动减阻的湍流线性分析进行模式预测
影响因子：
3.7
作者：
Blesbois O
通讯作者：
Blesbois O