POD analysis of low Reynolds turbulent porous channel flow

Snapshot proper orthogonal decomposition (POD) is utilized to understand the turbulent channel flow physics over permeable porous surfaces. Our aim is to study how the flow structures vary in different wall permeabilities. The data needed for POD algorithm are provided by large eddy simulation (LES). Utilizing Volume-Averaged Navier-Stokes (VANS) equations inside the permeable wall, eliminates the need for detailed knowledge of the pore microstructure and porous medium can be easily specified with global properties like porosity and permeability. The bulk mean Reynolds number is 5500 and simulations are carried out in three different porosities, 0, 0.8 and 0.95. The reasons why the quasi-streamwise vortices become shorter and absent above a permeable wall are discussed. POD analysis has revealed that permeability of wall amends the size and even shape of the large scale, energetic dominant structures of the flow and these alterations are more vivid in highly permeable walls in which large spanwise vortical structures that stem from the Kelvin-Helmholtz instability are dominant structures of the flow.