Simulation of road vehicle natural environment in a climatic wind tunnel

This paper describes the development of natural climatic conditions in a closed loop full-scale automotive wind tunnel. The tunnel simulates wind, different rainfalls, a range of air temperature as well as several road conditions. It generates, under controlled heat loading, wind speeds of up to 50 km h with different approach boundary conditions, rainfalls from drizzle to cloudburst, controlled air temperature over the range of 30–20°C below zero and road inclines up to 15° in any direction. The design and optimization process of the tunnel functions is outlined and examples of its use in vehicle development are given. The need to comply with the standardised recommended practice requirements and a compact design are important features of the tunnel. The tunnel provides an important test bed for close scrutiny of the relationship between rainwater ingress, vehicle speed, road condition, heat loading and vehicle geometry. The tunnel can also be used to study vehicle thermal management, vehicle thermal comfort, engine cold starting, and wipers efficiency in severe cold weather. Computational fluid dynamic (CFD) simulation is used to optimize and assess the performance of a number of key tunnel components. To validate the CFD developed model, the resulting flow field around a bluff body placed on the tunnel is closely scrutinized and verified against well-established and published data. Moreover, the numerical prediction is experimentally validated using laser sheet visualisation (LSV). The resulting tunnel is approximately 9.5 m long, 9.5 m high and 3 m wide.