Boundary-Layer Control of Bluff Bodies Through Momentum Injection 902225

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.