Drag and lift reduction of a 3D bluff body using flaps

We present an experimental study on flow control over a classic 3D bluff-body used in automotive aerodynamics (Ahmed 1983). Flow control is achieved through moving flaps fixed on every edge around the two rear flat surfaces of the model. Different pairs of flaps, with variable angle compared to the walls, are tested. Parametric studies show that the most efficient configuration for the flaps is along the side edges of the rear slant, i.e. in the region where longitudinal vortices are created, and also at the junction between the roof and the rear slant, where the flow separates. We also explore the combinations of different flap configurations. We find interesting results showing cumulative effects between some configurations leading to −25% drag reduction and −105% lift reduction. Finally, particle image velocimetry measurements show that one of the key effects is the control of the longitudinal vortices created at the side edges of the rear slant.