The Effect of a Moving Floor on Wind-Tunnel Simulation of Road Vehicles

The importance of using a moving floor to simulate the flow around a passenger car in a wind tunnel is considered. Measurements on a typical l/3^rd scale car at normal ground clearance show that floor movement reduces drag by about 8% and reduces lift by nearly 30%. The effect on lift is more pronounced when the vehicle is yawed to the flow. Experiments on an idealised car shape show that there is a marked effect of floor movement if the underbody has rear upsweep. However in the near wake of a flat-based version of that model, with a straight underbody throughout, detailed velocity surveys show surprisingly little effect of floor movement. On the other hand, measurements of the structure of the wakes of a fixed wheel on a stationary floor and a rotating wheel on a moving floor show a large effect of floor movement.