Numerical Investigations on Crosswind Aerodynamics and its Effect on the Stability of a Passenger Car

In crosswind, or while passing another vehicle in still air, the flow around an automobile becomes asymmetric, thus altering the yawing moment, drag and lift. This paper discusses the details of crosswind aerodynamics of a typical sedan. The investigations, limited to numerical analysis, were carried out to predict the drag and lift coefficients, and the yaw moments on the selected car using a commercially available CFD software, FLUENT. The analysis was carried out for three car speeds, six crosswind angles and five crosswind velocities in various combinations. The results have shown that the drag coefficient initially decreases at 15° crosswind angle and then increases as the crosswind angle is increased. Further, the drag coefficient, lift coefficient and the yaw moment increase as the crosswind velocity increases. It is observed that the flow field around the car, especially at the rear, changes substantially with a change in the crosswind angle. The results clearly bring out the change in the vortex structure behind the car with the change in crosswind angle and velocity and confirm that the vehicle stability becomes poor at lower vehicle speeds and higher crosswind angles.