Computational Fluid Dynamics Analysis of Effect of Braking Plate Configurations on the Aerodynamic Behaviors of an Ahmed Car

Abstract

Braking distance, particularly the emergency braking distance at high speed, is essential to ensuring safety. Aerodynamic drag and negative lift can be effectively increased by setting up a plate at the rear of the car, thus improving the grip of the tires and reducing the braking distance. The Ahmed car model was selected for the numerical simulation. The aerodynamic behavior of the car with different configurations of plates at different opening angles was simulated using an improved delayed detached eddy simulation based on the shear stress transfer k-ω turbulence model, and the numerical method used in this study was verified using wind tunnel tests. Results showed that the upstream plate is optimal for increasing the car aerodynamic braking performance and noticeably reduces the fluctuation in aerodynamic forces. The aerodynamic drag is more sensitive to the installation position of the plate than aerodynamic lift. The aerodynamic forces on the car body and plate increase as the opening angle and size increase (except for the aerodynamic lift of a car body with a downstream plate), and the greatest effect is on the car body. Aerodynamic braking distance decreases as the opening angle and size of the plate increase, especially for the upstream plate. The optimal opening angle of the downstream plate is approximately 70°, and the braking effect is not significantly because of the small downstream plate.