From lab to full scale Active Flow Control drag reduction: How to bridge the gap?

Active Flow Control (AFC) is being investigated as a tool for boundary layer separation delay. Increasing lift by delaying stall has been the most common objective. More recently AFC is also being studied for drag reduction and mitigation of unsteadiness, resulting from massively separated flows. As such, fuel savings of heavy ground vehicles, while challenging, is a worthy task due to the huge economic, environmental and political impact. This paper describes a series of experiments aimed at increasing the base pressure on the trailer-end of a large truck-trailer configuration driving at highway speeds. In parallel to fundamental studies, not reviewed here for brevity, two road test campaigns were completed; a half scale wind tunnel test and smaller scale generic vehicle model wind tunnel experiments are described and analyzed. The method currently uses a 1/4 cylinder shaped rear-end mounted add-on device in which an array of synchronized Suction and Oscillatory blowing (SaOB) actuators is mounted. The passive as well as active effects of the steady suction and unsteady sideways-oscillating blowing are documented and careful experimentation allows the energy budget to be directly calculated from wind tunnel experiments. Good agreement between road tests and scaled tunnel model tests was found on the path to product development.