Particle image velocimetry studies of a boundary layer perturbed by localized suction

Abstract

Difference experiments were carried out in a low-Reynolds number (490 based on momentum thickness) flat-plate boundary layer. Particle image velocimetry (PIV) was used to measure the two velocity components parallel to the plate in the boundary layer with and without weak localized suction through two holes at suction speeds of less than 1% of the free-stream value under otherwise identical conditions. The results from the preliminary PIV data show that suction does not affect the mean streamwise velocity profile, but decelerates the boundary layer in the vicinity of the suction holes. This deceleration is on average 6% of the mean speed at 13 viscous length scales above the plate and persists for at least 10 hole diameters downstream of the suction holes. Two-dimensional correlations of streamwise velocity fluctuations imply that even these low suction levels reduce the cross-stream and streamwise length scales in the boundary layer.