Advanced Techniques for Flow Simulation in Automotive Climatic Wind Tunnels

Two techniques for advanced flow-simulation in automotive, climatic wind-tunnels have been presented. These are the Slotted-Wall Extension * for improved flow simulation over the test vehicle, and methods for improved thermal boundary-layer simulation. The Slotted-Wall Extension gives a reference q-correction that is relatively independent of vehicle configuration and blockage, prevents the formation of shear layers in the nozzle exit flow, suppresses mean-flow pulsations in the test chamber, and reduces vehicle pressure-simulation errors, with resultant improvement in critical cooling airflows.

Measurements over a heated, flat surface show that the open road thermal boundary-layer exhibits a turbulent temperature profile, and can be split into a thin sublayer region in which most of the temperature change occurs, and an outer layer in which a shallow, linear temperature gradient exists. From a practical viewpoint, adequate outer layer simulation can be easily obtained by heating the lower 0.5 m to 1 m of the wind tunnel flow to a temperature that is up to 5 deg C above ambient. Future trends towards lower automobile underbody clearances would necessitate the simulation of the thermal sublayer region. This can be achieved by the tangential injection of hot air along the wind tunnel floor.