Numerical Investigation of Aerodynamic Properties of Ahmed Body for Different Rear Slanted Surface Configurations

Abstract

The present study investigates aerodynamic characteristics of the Ahmed Body numerically, in case of that small rectangular flaps are attached to the leading edge of the rear slanted surface with a rear tilt angle of 25° and 35°. Numerical calculations have been conducted for three-dimensional, turbulent, steady, incompressible flow. Three different flap configurations have been considered: single flap, two flaps and three flaps. The commercial computational fluid dynamics solver ANSYS Fluent is used for the computations. To validate the numerical model, numerical solutions have been conducted with different combinations of turbulence model and wall functions, considering the values of drag coefficient obtained in a previous experimental work which studied slanted surface with flaps attached. Accordingly, k-epsilon Realizable turbulence model with Menter-Lechner wall function estimates the drag coefficient with an error of 8.8%. Results of the numerical calculations have shown that the best performance is obtained for the Ahmed model with 25° rear slant angle with three flaps mounted on the leading edge of the rear slanted surface, which provides a reduction in drag coefficient by 2.3%, compared to the model without flaps. Mechanisms for drag reduction are found to rely on generating a suction line along the leading edge of the rear slanted surface, which provides attached flow, although it is reversed. As for the 35° Ahmed model with flaps, on the other hand, no decrease in the drag coefficient is observed.