Abstract
In this study, we attempted a novel drag reduction technique for 25° and 35° 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° Ahmed model at specific angles; up to 21% pressure coefficient reduction was achieved for the 25° Ahmed model (flap configurations at slant side edge) and 6% for the 35° 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.
Highlights
Reducing the global consumption of vehicle fuel is a crucial and urgent necessity if we are to respond swiftly and appropriately to climate change
We demonstrated the efficiency of adding specially designed flaps on the four edges of a standard Ahmed model’s slant surface to break down the longitudinal vortices and reduce the aerodynamic drag
The optimal pressure drag coefficient reduction, 21.2%, was obtained with a large flap placed on the side at 80° angle
Summary
Reducing the global consumption of vehicle fuel is a crucial and urgent necessity if we are to respond swiftly and appropriately to climate change. Research on drag reduction, which enhances fuel efficiency, represents a very significant environmental concern. To reduce aerodynamic drag effectively, we surely need a comprehensive understanding of the flow structure around the vehicle. For a basic bluff vehicle type of body (i.e. the Ahmed model), up to 85% of the total drag is pressure drag and the remainder is friction drag.[1] Ahmed et al.[1] found that the rear end contributes as much as 91% to the total pressure drag and is especially predominant at high speeds, as confirmed by Hucho and Sovran[2] in 1993
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