Superstructures and exact coherent states in the asymptotic suction boundary layer

本项目的目的是研究渐近吸力边界层情况下的精确相干结构与湍流超结构之间的关系。这种流动是在平行剪切流和空间发展的边界层之间传递的一族流动的一部分，因此为几个剪切流中的上部结构提供了一个灵活的模型。精确相干结构的范围已经从覆盖整个领域的大尺度结构扩展到包括一系列更小的结构，这些结构一直延伸到科尔莫戈罗夫尺度。将这些结构叠加在一起，就支持了汤森附加的涡流假说。演示渐近吸力边界层的这一图景是本提议的一个目标。在分析方面，我们已经证明了准线性近似在描述孤立的和堆叠在一起的精确相干结构方面的力量：准线性近似允许状态的自洽叠加。为了与致力于流动的拉格朗日方面的研究小组共同感兴趣，我们专注于将均匀动量带描述为切变流中一个显著的大尺度结构。这应该使我们能够捕捉到从靠近墙的结构到通向自由流区的上层建筑的全部范围。网络中的合作将使我们能够将渐近吸力边界层的结果与其他剪切流的结果进行比较。

The aim of this project is to study the relation between exact coherent structures and turbulent superstruc- tures for the case of the asymptotic suction boundary layer (ASBL). This flow is part of a family of flows that mediates between parallel shear flows and spatially developing boundary layers, and thus provides a flexible model for superstructures in several shear flows. The range of exact coherent structures has been extended from that of large scale ones that reach across the entire domain to also include a cascade of smaller structures that reach all the way down to the Kolmogorov scale. Stacking such structures together gives support for Townsend’s attached eddy hypothesis. Demonstrating this picture for the asymptotic suction boundary layer is one goal of the present proposal. On the analytical side, we have demonstrated the power of the quasi-linear approximation in describing exact coherent structures in isolation and when stacked together: the quasilinear approximation allows for a self-consistent superposition of states. In a joint interest with the groups working on Lagrangian aspects of flows, we focus on the characterization of uniform momentum zones as a prominent large scale structure in shear flows. This should allow us to capture the full range of structures from the ones close to the wall to superstructures towards the free stream region. The collaborations in the network will enable us to compare the results for the asymptotic suction boundary layer with other shear flows.