An Experimental Study on the Structure of Turbulence over Permeable Porous Walls(Fluids Engineering)

PIV measurements are carried out for turbulent flows in a channel with a porous bottom wall. In the highest permeable wall case among the measured, it is observed that the flow is not laminar and tends to be turbulent even at the bulk Reynolds number of Re_b=1300. It is also found that the flows become more turbulent in the cases of higher permeability. To confirm the effects of the wall roughness and the wall permeability, detailed discussions are made assuming the effective wall roughness of the porous media. The results clearly indicate that the turbulence is induced by not only the wall roughness but the wall permeability. The experimental correlation of the mean velocity with the permeability Reynolds number is then proposed. The measurements have also revealed that as Re_b and or the wall permeability increase, the wall normal fluctuating velocity is less damped near the porous wall due to the effects of the wall permeability. This leads to the increase of the turbulent shear stress resulting in the higher friction factor of turbulent porous wall flows.