POD of the Autonomous Near-Wall Region in a Minimal Channel Flow

Abstract

We propose to examine the structure and the dynamics of the empirical eigenfunctions of the autonomous near-wall region in a turbulent minimal channel flow. This simplified and artificial situation consists of a severe restriction of the interactions between the outer flow and the structures of the viscous and buffer layers so that it is possible to maintain turbulence in the near-wall region without any input from the outer flow. This is achieved in a DNS of a pressure-gradient driven turbulent channel flow for a minimal flow unit by damping artificially fluctuations in the outer flow while the near-wall region survives indefinitely. The use of empirical eigenfunctions (determined by the Karhuenen-Loève procedure or Proper Orthogonal Decomposition) reveals being an adequate tool for analysing the low-dimensional dynamics of the flow.