Search Results

The paper studies effectiveness of two fundamentally different concepts of boundary-layer control for reduction of drag of bluff bodies: Moving Surface Boundary-layer Control (MSBC) involving momentum injection delaying separation; and tripping of the boundary-layer, using judiciously located fences, to interrupt pressure recovery. Wind tunnel tests, with two-dimensional models of rectangular prisms and 1/12 scale model of a typical tractor-trailer truck configuration, show both the approaches to be quite effective promising a significant reduction in the aerodynamic resistance. A flow visualization study, conducted in a closed circuit water tunnel using slit lighting and polyvinylchloride tracer particles, complements the wind tunnel tests. It shows, rather dramatically, effectiveness of the boundary-layer control procedures.

The concept of moving surface boundary-layer control has proved quite successful in increasing lift and delaying stall of slender bodies like airfoil sections. This paper assesses effectiveness of the concept in reducing drag of bluff bodies such as a two dimensional flat plate at large angles of attack, rectangular prisms and three dimensional models of trucks through an extensive wind tunnel test-program. Results suggest that injection of momentum through moving surfaces, achieved here by introduction of bearing mounted, motor driven, hollow cylinders, can significantly delay separation of the boundary-layer and reduce the pressure drag. A flow visualization study, conducted in a closed-circuit water tunnel using slit lighting and polyvinylchloride tracer particles, complements the wind tunnel tests. It shows, rather dramatically, effectiveness of the moving surface boundary-layer control.