Non-equilibrium effects in a turbulent boundary layer due to the destruction of large eddies

Results are presented for a wind tunnel experiment in which a screen element stretched spanwise across the floor of the test section is used. The screen element acts as a passive device introduced into the turbulent boundary layer in order to destroy its large-scale structure. Measurements are made for two streamwise locations of the screen element, for which the ratio of the screen height to the undisturbed boundary-layer thickness is 1.09 and 0.81, respectively. A marked increase in Clauser shape factor and decrease in skin friction are established. Relaxation characteristics as the perturbed boundary layer returns to equilibrium are discussed. The results point to the possibility of using the elimination of the large-scale coherent structure as a drag-reducing technique