Effects of uniform blowing or suction from a spanwise slot on a turbulent boundary layer flow

Effects of uniform blowing or suction from a spanwise slot on a turbulent boundary layer flow are investigated using the direct numerical simulation technique. The magnitudes of blowing or suction are less than 10% of the free-stream velocity. The skin friction and near-wall turbulence intensities are significantly changed by blowing and suction. In the case of uniform blowing, the skin friction on the slot rapidly decreases. The streamwise vortices above the wall are lifted up by blowing, and thus the interaction of the vortices with the wall becomes weaker. Accordingly, the lifted vortices become stronger in the downstream due to less viscous diffusion (above the slot) and more tilting and stretching (downstream of the slot), resulting in the increase of the turbulence intensities as well as the skin friction downstream of the slot. The opposite is observed in the case of uniform suction. The velocity fluctuations and Reynolds shear stress react quickly to blowing but recover slowly in the downstream, as compared to the case of suction. For both cases of blowing and suction, the streamwise turbulence intensity recovers quickly from blowing or suction, while other components of the turbulence intensities and Reynolds shear stress recover in a longer downstream distance.