Active Flow Control at the Rear End of a Generic Car Model Using Steady Blowing

Numerous aerodynamic designs of automotive vehicle have been made to reduce aerodynamic drag for lower fuel consumption. Indeed, automotive industry was primarily interested in the passive control based on the shape changes. But, as shape modifications are limited by several factors, this industry is recently more focused on active flow control. In this experimental investigation, the influence of continuous blowing along the sharp edge between the roof and the rear window is addressed. This actuation represents a new configuration based on a steady blowing tangentially to the surface of the rear window of the 25 slanted Ahmed body model. The study was carried out in a wind tunnel at Reynolds numbers based on the model length up to 2:78106. The actuation leads to a maximum drag reduction slightly upper than 10% obtained with a Reynolds number of 1:74106 and a blowing velocity of 0:65V0, where V0 is the freestream velocity. Reductions between 6% and 7% were obtained for the other studied cases. These aerodynamic drag measurements were used to evaluate the actuator efficiency which reveals a maximum efficiency of 9. Visualizations show that tangential steady blowing increase the separated region on the rear window and consequently disrupt the development of the counter-rotating longitudinal vortices appearing on the lateral edges of the rear window. It is also noted that the flow is reattached to the upper half of the rear window. As the actuation occurred directly on the recirculation region at the top of the rear window wall, the flow control was seen very effective.