Aerodynamic drag reduction and flow control of Ahmed body with flaps

In this study, we attempted a novel drag reduction technique for 25 degrees and 35 degrees Ahmed models by experimenting with two types of flap structures, respectively, added to the slant edges of the two models. Different pairs of flaps were added at various angles compared to the slant for the sake of comparison. The study comprehensively analyzed the effects of the big-type and small-type flaps on the aerodynamic drag and near wake of an Ahmed model in a greater range of flap mounting angles. Parametric analysis results confirmed that large and small flaps are most efficient when configured on the 25 degrees Ahmed model at specific angles; up to 21% pressure coefficient reduction was achieved for the 25 degrees Ahmed model (flap configurations at slant side edge) and 6% for the 35 degrees Ahmed model (flap configurations at both slant side and top edges). The velocity and pressure contours indicated that the key to drag reduction is to weaken (if not eliminate) the longitudinal vortex created at the side edges of the rear slant.