Aerodynamics Study of Automobile Car Ahmed Body using CFD Simulation to Predict the Drag Coefficient and Down Forces

The Ahmed body is a simplified car used in automotive industry to investigate the influence of the flow structure on the drag. The external aerodynamics of the car determines many relevant aspects of an automobile such as stability, comfort and fuel consumption at high cruising speeds. The flow around the vehicles is characterized by high turbulent and three dimensional flow separations and there is a growing need for more insight into the physical features of these dynamical flows. The CFD (Computational Fluid Dynamics) analysis is used to find the parameter in the automobile industry. The air flow over ground vehicle is analyzed and coefficient of drag is calculated using CFD (Ansys Fluent). For this calculation, Ahmed body (simplified car body) as ground vehicle is considered which is commonly used as test case in industry. The Ahmed body is made up of a round front part, a movable slant plane placed in the rear of the body to study the separation phenomena at 25º and 35º angles. Aerodynamic drag is one of the main obstacles to accelerate a solid body when it moves in the air. About 50 to 60% of total fuel energy is lost only to overcome this adverse aerodynamic force. To win a race, which may be decided by fraction of second, the racing cars need a faster acceleration, which is possible by reducing the drag force by optimizing its shape to ensure stream-lining or reducing the separation. By adding vortex generators on the roof and extending the rear body of the car aerodynamically which could reduce the drag of the vehicle by 25% which further improves the fuel efficiency of the vehicle. The amount of grip available in the tires along with aerodynamic drag and engine power set the theoretical limits for the vehicle's velocity around the track, especially in cornering and it is thus of particular interest when designing a vehicle to increase this grip while keeping drag to a minimum. By adding a pair of flaps to a spoiler its aerodynamic downforce can be improved and additional downforce can be generated while cornering and braking by an actuating mechanism which closes the gap between the flaps. Also leading edge slats are also added to delay the separation of the slack side of the spoiler which reduces the aerodynamic drag at high angle of attack.