Wind-Tunnel Tests of Vehicle Cooling System Performance at High Blockage 2000-01-0351
Wind tunnels provide a convenient, repeatable method of assessing vehicle engine cooling, yet important draw-backs are the lack of a moving ground and rotating wheels, blockage constraints and, in some tunnels, the inability to simulate ambient temperatures.
A series of on-road and wind-tunnel experiments has been conducted to validate a process for evaluating vehicle cooling system performance in a high blockage aerodynamic wind tunnel with a fixed ground simulation. Airflow through the vehicle front air intake was measured via a series of pressure taps and the wind-tunnel velocity was adjusted to match the corresponding pressures found during the road tests. In order to cope with the inability to simulate ambient temperatures, the technique of Specific Dissipation (SD) was used (which has previously been shown to overcome this problem). Comparisons are drawn between the SD measured on the road (for various modifications and speeds) with those measured in a wind tunnel at high (30%) blockage ratio.
Very good agreement was found, indicating the potential for testing modifications on vehicles in a relatively low cost facility. However a drawback is that the yaw angles generated on road by cross winds cannot be reproduced. It is noted that effects of yaw angle are not considered in most comparable cooling tests and prior work has shown that the effects are small. In general, in order to optimise wind-tunnel velocity, it is preferred to calibrate each test vehicle on the road.