Mean Velocity Profiles and Drag Measurements in Turbulent Boundary Layer Flows over Permeable Substrates

The impact of permeable substrates on skin-friction drag was evaluated experimentally under turbulent flow conditions using a modified flat plate boundary layer setup. Several 3D-printed geometric patterns were examined, taking into account the effective interfacial 'slip-lengths' emerging for each geometry. For a flat plate case with no pressure gradient, these slip lengths are related to the wall-normal shift in the mean streamwise velocity profile for the turbulent boundary layer. Direct force measurements were conducted and compared against a smooth wall test case. Particle image velocimetry (PIV) was used to measure the shift in the mean streamwise velocity profile and estimate changes in turbulence statistics. To obtain a finer representation of the mean velocity profiles, the PIV images were analyzed using a technique that yields single-pixel resolution in the wall-normal direction. These measurements were used to characterize near-wall changes in flow over the permeable substrates relative to smooth wall conditions.