Numerical simulation of the combined effects of the rear spoiler and the curvature of the lateral surfaces on the lift and drag forces on the sedan type vehicle

In recent years, Aerodynamic analysis of automobiles became one of the most important parameters which affect the power of the companies to be present in world markets. Therefore, they can be considered as one of the most important factors in aerodynamic design of vehicles. The formation of the vortex and consequently the pressure drop in the rear of the vehicle can increase the aerodynamic forces.
This paper investigates the methods for reduction of the vortices volume in the rear part of a sedan type vehicle by changing in geometry of the vehicles
. For this purpose, firstly in order to choosing the appropriate turbulence model and 3D simulation of incompressible flow around the Ahmed model (which its experimental results are available) was simulated using computational fluid dynamics. Then, the values of aerodynamic coefficients of a car model were studied by adding spoiler and creating curvature at its lateral surfaces. The results of this study indicated that the vortex volume formed at the rear of the vehicle can be simulated more precisely by using the Boundary-layer mesh around the model and analyzing the flow using the DES-SSTK-ω turbulence model Relative to the model K-ω-SST. Additionally, simultaneously use of the spoiler and the curvature of the lateral surfaces reduce fuel consumption and increase the stability of the vehicle due to a 26.3 % reduction in rear drag coefficient and a 5.2 % reduction in the lift coefficient, with respect to the simple car model.