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（ASBL）情况下精确相干结构与湍流超结构之间的关系。这种流动是平行剪切流和空间发展边界层之间的一系列流动的一部分，从而为几种剪切流中的上层结构提供了灵活的模型。精确相干结构的范围已经从跨越整个域的大尺度结构扩展到还包括一系列小结构，这些小结构一直延伸到柯尔莫哥洛夫尺度。将这些结构叠加在一起，支持了汤森的附着涡流假说。证明渐近吸力边界层的这幅图是本建议的目标之一。在分析方面，我们已经证明了准线性近似在描述孤立和堆叠在一起时的精确相干结构的能力：准线性近似允许状态的自洽叠加。在一个共同的兴趣与工作组的拉格朗日方面的流动，我们专注于表征的均匀动量区作为一个突出的大尺度结构的剪切流。这将使我们能够捕捉到从靠近壁面的结构到朝向自由流区域的上层结构的全部范围。网络中的合作将使我们能够比较渐近吸力边界层与其他剪切流的结果。

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.