The Unsteady Aerodynamic Response of the DrivAer Fastback to Longitudinal Acceleration and Deceleration

This study examines the aerodynamic response of a DrivAer fastback model subjected to longitudinal acceleration and deceleration using a time-varying inlet-velocity approach. The accelerating, non-accelerating, and decelerating cases are compared at a common reference velocity to isolate the influence of acceleration history from the effect of instantaneous flow speed. The results show that the DrivAer fastback produces different drag, lift, lift-balance, and wake-field behavior depending on whether the flow is accelerating or decelerating. In comparison to the non-accelerating case, drag decreases during deceleration and increases during acceleration, while the lift distribution also shifts between the front and rear of the vehicle. Flow-field comparisons show that the changes in aerodynamic force are linked to altered flow behavior around the rear-glass, decklid, and wake regions. These results suggest that a quasi-steady interpretation based only on instantaneous velocity is not sufficient to describe the aerodynamic response of road-vehicle geometry under longitudinal acceleration and deceleration.