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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 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.