A Review of Reynolds Number Effects on the Aerodynamics of Commercial Ground Vehicles

A review of Reynolds number scaling and high Reynolds number simulation for commercial ground vehicles is presented. The supporting data was extracted from published wind tunnel tests, coastdown tests and computational studies for complete vehicles and vehicle components. For complex vehicles the data suggest that the use of forced transition for higher Reynolds number simulation is a viable test technique however various component specific schemes may be required to replicate the aerodynamics of a full-scale vehicle. The Reynolds number sensitivity of; boundary layer transition control, surface curvature effects, bluff base flows, wheel/tire aerodynamics, and complete vehicle aerodynamics is presented. The data show that the width-based transcritical Reynolds number for commercial vehicles is between 1 and 3 million with the averaged values for edge radius, wheels and full vehicle data sets between 1.6 and 1.8 million. A minimum width-based transcritical Reynolds number value of 3 million is recommended for simulating the aerodynamics of full-scale commercial vehicles operating at a width-based Reynolds number greater than 3 million. If the dominant aerodynamic and fluid dynamic features of the vehicle are well established the minimum width-based transcritical Reynolds number value that may be used is 2 million. To ensure an accurate simulation of full-scale vehicles operating below the 3 million transcritical value future studies should be performed at the vehicle full-scale Reynolds number.