Transient ground effect aerodynamics

The aerodynamic development of vehicles in wind tunnels is currently performed via a series of static measurements. However, vehicles exploiting ground effect tend to be highly dynamic undergoing rapid changes in speed and attitude. Clearly therefore there is scope for an improvement in the fidelity of testing. At present the considerable diffculty of measuring body forces whilst simultaneously making variations to a model attitude prohibits transient investigations. Satisfying the demand for a dynamic testing capability formed the initial stages of the research. Having established the present performance of the hardware and software in use at the R.J. Mitchell wind tunnel an advanced data acquisition and motion control system was developed.Experimental system identification methods were employed to determine the dynamic response of the force balance and pressure transducers. This knowledge was integrated into a data processing algorithm that effectively isolated the aerodynamic effects during the transient investigation.As automotive vehicle models can be considered as bluff bodies their movement during dynamic testing has the potential to alter the test section wind speed due to varying blockage effects. To overcome this a controller was developed to maintain a constant wind speed. Tests were performed to allow the fan drive system and wind circuit to be characterised. The system was found to be non-linear a gain scheduling controller was therefore developed that improved the control of wind speed control without employing a complex non-linear controller.Results from the dynamic test programme clearly demonstrated the transient aerodynamic effects upon a wing in ground effect. These results were dependent upon motion amplitude, frequency and mean ground clearance. Comparisons were made with static results and dynamic testing results out of ground effect