ABSTRAKT

Direct numerical simulations were performed to analyze the effects of time-periodical blowing through a spanwise slot on a turbulent boundary layer. The blowing velocity was varied in a cyclic manner from 0 to 2A⁺ (A⁺ = 0.25,0.50 and 1.00) at a fixed blowing frequency of f⁺ = 0.017. The effect of steady blowing (SB) was also examined, and the SB results were compared with those for periodic blowing (PB). PB reduced the skin friction near the slot, although to a slightly lesser extent than SB. PB was found to generate a spanwise vortical structure in the downstream of the slot. This vortex generates a reverse flow near the wall, thereby reducing the wall shear stress. The wall-normal and spanwise turbulence intensities under PB are increased as compared to those under SB, whereas the streamwise turbulent intensity under PB is weaker than that under SB. PB enhances more energy redistribution than SB. The periodic response of the streamwise turbulence intensity to PB is propagated to a lesser extent than that of the other components of the turbulence intensities and the Reynolds shear stress.