COMPARISON OF ROAD AND WIND-TUNNEL DRAG REDUCTIONS FOR COMMERCIAL VEHICLES

Drag coefficient reductions arising from streamlining devices to comme rcial vehicles are discussed. Road and wind-tunnel tests are briefly d escribed, including road tests to measure on-road turbulence character istics. Comparison of drag coefficient reductions at high yaw angles s hows road results that are considerably lower than tunnel results, whe reas at low yaw angles the road drag reductions can be higher than tho se measured in the tunnel. It is shown that the effects of atmospheric turbulence (which are always present during road tests when high yaw angles are measured due to the strong crosswinds) are significant. Tun nel data obtained in grid-generated turbulence are closer to results o btained on the road under high yaw angles.