Aerodynamic forces acting on Ahmed-type vehicles under fluctuating headwind conditions

Abstract

Aerodynamic forces of Ahmed-type road vehicles subjected to atmospheric fluctuation were studied in an advanced wind tunnel with programmable settings enabling the generation of pulsating wind speeds. The experiments were performed with a time-averaged airflow speed of approximately 13 m/s, with the fluctuating speed ranging from 2.58 to 2.90 m/s, and periods ranging from 1.5 to 5.0 s. The results of the time-dependent drag and lift forces acting on the vehicle were compared with those under steady wind conditions. Further, the influence of the rear slant angle of the Ahmed model on the forces was addressed. The fluctuation in wind speed showed a greater effect on the aerodynamic forces than predicted. The amplitude of the drag force under the pulsating wind became larger in a vehicle having a shape that experienced a large drag force under steady wind conditions. It is concluded that even under fluctuating wind conditions, there exists a critical angle of 30° at which the vehicle experiences either high or low fluid forces.