PIV measurements of turbulent flows over porous media with structural surface roughness

Abstract

PIV measurements are performed for turbulent channel flows over porous media with transverse roughness to discuss the effects of structural surface roughness of the porous media. It is found that when the roughness elements have permeability, the streamwise mean velocity becomes larger but turbulence becomes weaker near the wall compared to those in the case with impermeable elements. By the quadrant analysis, it is observed that in the impermeable roughness case, the contribution of Q2 overtakes that of Q4 very near the porous wall while it is not observed in the permeable roughness case. This is because flows through the roughness elements tend to relax the recirculation behind the roughness elements.