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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.

The paper presents results of an organized and extensive wind tunnel test-program, complemented by flow visualization and full-scale road tests, aimed at assessing the effectiveness of a boundary-layer control procedure for the drag reduction of a cube-van. Wind tunnel results, obtained using 1/6 scale model, at a subcritical Reynolds number of 105, suggest that tripping of the boundary-layer using fences reduce the pressure drag coefficient. The entirely passive character of the procedure is quite attractive from the economic consideration as well as the ease of implementation. The road tests with a full-size cube-van substantiated the trends indicated by the fence data; although the actual drag reduction observed was lower (yet quite significant, 16.6%) than that predicted by the wind tunnel tests. This may be attribute to a wide variety of factors including the differences in the geometry and test conditions. Fuel consumption results also substantiated the drag reduction trend.