Non-modal transient growth of disturbances in pulsatile and oscillatory pipe flows
Non-modal transient growth of disturbances in pulsatile and oscillatory pipe flows
复制标题
脉动和振荡管流中扰动的非模态瞬态增长
DOI：
10.1017/jfm.2020.940
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发表时间：
2021-01-25
影响因子：
3.7
通讯作者：
Avila, Marc
中科院分区：
文献类型：
--
作者：
Xu, Duo;Song, Baofang;Avila, Marc
在定常、脉动或振荡速率下，层流流过管道时，会经历一个亚临界湍流过渡。我们进行了广泛的线性非模态的稳定性分析，这些流量和表明，足够高的脉动振幅的经典升力机制的流向涡优于螺旋扰动表现出奥尔式的机制。在振荡流中，能量放大仅取决于基于斯托克斯层厚度的雷诺数，并且对于足够高的振荡频率和雷诺数，轴对称扰动占主导地位。在高频极限下，这些轴对称扰动与Biau最近发现的扰动完全相似（J. Fluid Mech.，vol.794，2016，R4）用于平板上的振荡流。在脉动和振荡管流的所有制度中，最佳螺旋和轴对称扰动在减速阶段被触发，并在通常小于一个周期内达到峰值。它们的最大能量增益与振荡流分量的雷诺数成指数关系。我们的数值计算揭示了一个合理的机制，在脉动和振荡管流实验观察到的湍流。
Abstract Laminar flows through pipes driven at steady, pulsatile or oscillatory rates undergo a subcritical transition to turbulence. We carry out an extensive linear non-modal stability analysis of these flows and show that for sufficiently high pulsation amplitudes the stream-wise vortices of the classic lift-up mechanism are outperformed by helical disturbances exhibiting an Orr-like mechanism. In oscillatory flow, the energy amplification depends solely on the Reynolds number based on the Stokes-layer thickness, and for sufficiently high oscillation frequency and Reynolds number, axisymmetric disturbances dominate. In the high-frequency limit, these axisymmetric disturbances are exactly similar to those recently identified by Biau (J. Fluid Mech., vol. 794, 2016, R4) for oscillatory flow over a flat plate. In all regimes of pulsatile and oscillatory pipe flow, the optimal helical and axisymmetric disturbances are triggered in the deceleration phase and reach their peaks in typically less than a period. Their maximum energy gain scales exponentially with Reynolds number of the oscillatory flow component. Our numerical computations unveil a plausible mechanism for the turbulence observed experimentally in pulsatile and oscillatory pipe flow.