S0506-2-6 Experimental study on the vortex structure of turbulence over permeable walls

Abstract

In order to understand the turbulent vortex production mechanism over porous walls, using the PIV experimental data, quadrant analyses and quadrant-hole analyses of the Reynolds shear stress are performed. The investigated flow fields are turbulent channel flows whose bottom walls are made of porous media. Three kinds of the porous media which have almost the same porosity but different permeability are used. From those analyses, it is found that the contribution of near-wall sweeps becomes the most dominant near the permeable wall while ejections tend to be weakened due to the wall permeability. As a result, longitudinal vortices hardly survive and transverse vortices, which used correspond to the vortex heads of hairpin or hook like vortices, develop over permeable walls.