Study on aerodynamic drag effect of a rear spoiler on a passenger car using CFD

The demand for a high-speed car is increasing in which vehicle stability and fuel economy are a primary concern. The vehicle’s aerodynamics play a crucial role as they influence the overall performance of the vehicles. The study of car aerodynamics involves the study of various forces that are acting on a car while it is moving on the road, i.e., drag force, lift force. The leading cause of aerodynamic drag for automotive vehicles is the flow separation at the rear end of the vehicles. By reducing the drag force, it is possible to improve the fuel economy. To study the delay of flow separation, rear-end spoiler application is tested at the end of a sedan car using a numerical model. This study is conducted by using Computational Fluids Dynamics (CFD) ANSYS software to analyze the flow pattern, drag coefficient Cd, lift coefficient Cₗ, streamline pattern, and pressure contour of a sedan car. The model was tested with seven conditions which are without rear end spoiler attached and with a rear-end spoiler of six different inclination angles (0°, -2°, 2°, 4°, 6° and 8°). The two-equation models utilized in this work are k with the Reynolds-averaged Navier Stokes (RANS) equations for the fluid flow behavior around the sedan automobile. The Reynolds number used is Re = 3.94 x 10⁶. Based on the results, the drag and lift coefficient of all models differs which affect the car fuel efficiency and stability. The velocity streamlines flow and vortex formation pattern differ according to the rear-end spoiler inclination angle.