Reynolds number effect on the response of a rough wall turbulent boundary layer to local wall suction

The combined effect of Reynolds number () and localised wall suction applied through a porous strip on a fully rough wall turbulent boundary layer (TBL) is investigated using hot-wire anemometry. The measurements show that the response of the TBL to suction is modulated by the ratio , where and are the suction and friction velocities, respectively. For example the suction impact on the mean velocity and the turbulence intensity profiles, which is felt across the boundary layer, decreases as decreases. Interestingly, the velocity spectra contour maps reveal that suction reduces the energy at all scales of motion across the boundary layer. Further, measurements of the velocity skewness indicate that the TBL undergoes a structural change when the ratio is relatively important. However, the measurements also reveal that TBL does not show a relaminarisation behaviour as it can be observed in a smooth wall TBL with similar localised wall suction. This lack of relaminarisation is due to the development of a growing internal boundary layer which evolves on a rough surface within the existing TBL.