Adjoint shape optimization of Ahmed body to improve aerodynamics

Abstract

Analyses are done on the bluff body of a simple ground vehicle's wake structure. A 4 million Reynolds number depending on model length. Results for various geometric configurations of the Ahmed body's flow visualization were achieved. There was a flexible geometric element called the base slant angle. Drag research found that body drag makes up about 85% of all drag. The body's rear end is where most drag is created or developed. Horseshoe vortices build a three-deck structure in wake flow. The base slant angle affects these vortices' strength, existence, and merging. Examined is the applicability of these phenomena to actual ground vehicles. To reduce drag and enhance aerodynamics, the body's shape was modified using the adjoint approach and the adjoint shape optimization tool in ANSYS Fluent. In this study, we found that by changing the tail-end vortex structure and flow separation at the rear part of the vehicle, the optimized back shape or rear slant design of the body provides better flow separation that results in better pressure recovery and reduces drag by roughly 7 to 10 percent, respectively. The comparison of experimental CD values for the Ahmed body at different rear slant angles, including 12.5o, 25o, and 30o. Since it had less variance from empirical data, the computationally computed CD for a 30° base slant angle was chosen to do adjoint shape optimization. Mesh cells of less than three lakhs were used in the CFD process, and skewness quality was checked. 60 m/s of velocity was the boundary condition for the velocity inlet.