EFFECTS OF RIBLETS ON VORTEX DEVELOPMENT IN THE WAKE BEHIND A SINGLE ROUGHNESS ELEMENT IN THE LAMINAR BOUNDARY-LAYER ON A FLAT-PLATE

The experimental results of the effect of riblets on vortex developmen t in the wake behind a single roughness element (a small cylinder) in the laminar boundary layer on a flat plate are presented in this paper . The investigation showed that riblets could substantially affect the way vortices develop in the wake behind a single roughness element (s o called ''vortex street''). A triangular riblet located length wise i n the flow approximately halved the height and span of the vortex stre et by comparison with the height and span of the vortex street on a sm ooth surface of the hat plate. Furthermore, the riblet steadied the fl ow inside the vortex street, resulting in delay of the turbulence. Acc ording to hot-wire measurements, this large influence of riblets on th e vortex street behavior was related to changes in the inner vortex st ructure.