Superstructures and exact coherent states in the asymptotic suction boundary layer

点击翻译按钮获取中文摘要

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.