论文标题
脉动和振荡管流中干扰的非模式瞬态生长
Non-modal transient growth of disturbances in pulsatile and oscillatory pipe flow
论文作者
论文摘要
层流通过稳定，脉动或振荡速率驱动的管道流动，经历了次临界向湍流的过渡。我们对这些流量进行了广泛的线性非模式稳定性分析，并表明，对于足够高的脉动振幅，经典升降机制的河流涡流的表现优于表现出ORR样机制的螺旋干扰。在振荡流中，能量扩增仅取决于雷诺数的数量，基于stokes层厚度以及足够高的振荡频率和雷诺数的数字，轴对称干扰占主导地位。在高频限制中，这些轴对称干扰与Biau（2016）最近确定的振荡流完全相似。在脉动和振荡管流的所有机制中，最佳的螺旋和轴对称干扰在减速阶段都会触发，并在通常小于一个时期内达到峰值。它们的最大能量增益量表呈指数级，振荡流量的雷诺数数量。我们的数值计算揭示了在脉冲和振荡管流中实验观察到的湍流的合理机制。
Laminar flows through pipes driven at steady, pulsatile or oscillatory rates undergo a sub-critical 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 (2016) 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.
