论文标题
飞机和平面式流动中湍流条纹的动力和增殖
Dynamics and proliferation of turbulent stripes in plane-Poiseuille and plane-Couette flows
论文作者
论文摘要
平面剪切流中可观察到的第一个长寿命的湍流结构采用局部条纹的形式，相对于平均流动方向。这些条纹的动力学对于过渡至关重要，最近的研究提出了与定向渗透的类比，在这种渗透中，条纹的增殖最终是导致湍流持续的原因。在本研究中，我们关注内部条纹动力学以及最终的条纹扩展，并分别比较压力和剪切驱动的平面流中的基本机制，分别是平面脉和平面 - 平面流动。尽管总体层流扰动模式相似，但两种情况下的条纹增殖过程在根本上是不同的。从单个条纹的生长和维持开始，我们发现在平面流动中，新条纹是在整个条纹中随机创建的，而在平面poiseuille Flow Streak的创建中，创建呈确定性，并且在下游尖端局部发生。由于上游/下游对称性，与Poiseuille条纹相比，Couette条纹具有两个弱和两个强的层状湍流界面。这些对称性以及内部生长的差异产生了两种根本不同的条纹分裂机制。在飞机上的流动流分裂与原始条纹的伸长生长有关，这是由于条纹尾巴的破裂 /脱落而引起的。在平面流动中，分裂的是从原始条纹的扩展和沿条纹的一个划分到两个较小的条纹。
The first long-lived turbulent structures observable in planar shear flows take the form of localized stripes, inclined with respect to the mean flow direction. The dynamics of these stripes are central to transition, and recent studies proposed an analogy to directed percolation where the stripes' proliferation is ultimately responsible for turbulence to become sustained. In the present study we focus on the internal stripe dynamics as well as on the eventual stripe expansion, and we compare the underlying mechanisms in pressure and shear driven planar flows, respectively plane-Poiseuille and plane-Couette flow. Despite the similarities of the overall laminar-turbulence patterns, the stripe proliferation processes in the two cases are fundamentally different. Starting from the growth and sustenance of individual stripes, we find that in plane-Couette flow new streaks are created stochastically throughout the stripe whereas in plane-Poiseuille flow streak creation is deterministic and occurs locally at the downstream tip. Because of the up/downstream symmetry, Couette stripes, in contrast to Poiseuille stripes, have two weak and two strong laminar turbulent interfaces. These differences in symmetry as well as in internal growth give rise to two fundamentally different stripe splitting mechanisms. In plane-Poiseuille flow splitting is connected to the elongational growth of the original stripe, and it results from a break-off / shedding of the stripe's tail. In plane-Couette flow splitting follows from a broadening of the original stripe and a division along the stripe into two slimmer stripes.
