Quadrant analyses of separating and reattaching turbulence over rib-mounted porous walls

Abstract

In order to understand the effect of the wall permeability on the turbulent vortex structure in a recirculating flow near a porous wall, based on the PIV experimental data of rib-mounted porous wall flows, quadrant and quadrant-hole analyses of the Reynolds shear stress are performed. The investigated flow fields are turbulent flows in rib-mounted channels whose bottom walls are made of porous media. Three kinds of porous media are used. They have almost the same porosity but different permeability. From the discussions through the analyses, as the wall permeability increases each quadrant event of the Reynolds shear stress tends to be damped in the region behind the rib and the vortex motions having stronger vertical fluctuating energy appear. It is considered that this vertical fluctuation comes from a perturbation mode which is similar to that induces the Kármán vortex.