A Wind Tunnel Simulation Facility for On-Road Transients

Abstract

This paper outlines the creation of a facility for simulating on-road transients in a model scale, ¾ open jet, wind tunnel. Aerodynamic transients experienced on-road can be important in relation to a number of attributes including vehicle handling and aeroacoustics. The objective is to develop vehicles which are robust to the range of conditions that they will experience. In general it is cross wind transients that are of greatest significance for road vehicles. On-road transients include a range of length scales but the most important scales are in the in the 2-20 vehicle length range where there are significant levels of unsteadiness experienced, the admittance is likely to be high, and the reduced frequencies are in a band where a dynamic test is required to correctly determine vehicle response. Based on measurements of on-road conditions, the aim was for the turbulence generation system to achieve yaw angles up to 6-8°, equating to a lateral turbulence intensity of 8-10% with a frequency range extending up to 10 Hz. In a wind tunnel, the generation of scales larger than the scale of the vehicle is impractical with passive grids and so an active turbulence generation system is required. The system includes a pair of vertical airfoils at the upstream end of the test section. The yawing of the wind tunnel jet requires correct handling at the downstream end of the test section and hence additional outlets were incorporated with cascading shutters to control collector width and effective location. Similarly, additional, shuttered, inlets were incorporated at the upstream end of the test section. The maximum steady state yaw angle range achieved was ±8° steady state, extending to ±11° in dynamic operation. The turbulence generation system can be programmed to reproduce specific events as measured on-road, with time appropriately scaled for model testing. Tests with a vehicle model validated that the turbulence generation system operating in a steady state mode results in the same steady forces as achieved yawing the model on a turntable. The system's ability to model specific on-road conditions was also demonstrated.