EFFECT OF SURFACE-ROUGHNESS ON A TURBULENT WALL-ATTACHING OFFSET JET

Abstract

The flow characteristics of a two-dimensional offset jet discharged parallel to a rough wall is experimentally investigated by using a split film probe. The distributions of the mean velocity and turbulent stresses in the flow field are obtained and compared with those of the wall attaching offset jet on a smooth wall. It is found that the wall-attaching region on the rough wall is longer than on the smooth wall for the same offset height and the jet speed. The normal distance of the maximum velocity point is farther away from the wall than that for the smooth wall case because of the thick wall boundary layer established by the surface roughness. It is also found that the roughness of the wall accelerates the relaxation process towards redeveloped plane wall jet and that it exhibits a quite different turbulent diffusion behavior especially near the wall from that in the wall jet over a smooth surface.