Turbulent diffusion behind vehicles: Experimentally determined influence of vortex pair in vehicle wake

The wake of a moving vehicle was simulated using a wind tunnel with a moving floor. The vehicle models, both block-shaped and ‘true’ scale models of actual automobiles, were held in a fixed position while the floor moved at the upstream air speed. This simulates an automobile travelling on a straight highway in still ambient air.Vertical and lateral profiles of mean and fluctuating velocities and mean tracer concentration were obtained. Profiles were taken at distances of 15–60 model heights downstream. Two exhaust source positions were used: at the center of the rear of the vehicle and on the side just behind the rear wheel. It was found that the models of true vehicles induce a pair of vortices in the wake that modify the velocity and concentration patterns in a minor way from that of the block-shaped vehicle.