Surface Excrescence Transition Study Delivery Order 0053

Abstract : An examination of the effects of surface excrescences on boundary layer transition has been performed, using a unique experimental facility. The experimental study focused on stagnation-line starting condition boundary layers in incompressible flow without sweep effects. The study was performed at flight-representative Reynolds numbers? equivalent to chord Reynolds numbers of 4 to 8 million?and included the effects of favorable pressure gradients. The results for both forward and aft-facing steps indicate a substantial stabilizing effect of favorable pressure gradient on excrescence-induced boundary layer transition. These findings suggest that manufacturing tolerances for laminar flow aircraft could be loosened in areas where even mild favorable pressure gradients exist.