Aerodynamic Drag of a Vehicle and Trailer Combination in Yaw

Typical production vehicle development includes road testing of a vehicle towing a trailer to evaluate powertrain thermal performance. In order to correlate tests with simulations, the aerodynamic effects of pulling a trailer behind a vehicle must be estimated. During real world operation a vehicle often encounters cross winds. Therefore, the effects of cross winds on the drag of a vehicle–trailer combination should be taken into account. Improving the accuracy of aerodynamic load prediction for a vehicle-trailer combination should in turn lead to improved simulations and better thermal performance. In order to best simulate conditions for real world trailer towing, a study was performed using reduced scale models of a Sport Utility Vehicle (SUV) and a Pickup Truck (PT) towing a medium size cargo trailer.

The scale model vehicle and trailer combinations were tested in a full scale wind tunnel. Utilizing a full scale wind tunnel allowed for very low blockage conditions and testing at large yaw angles by placing both the vehicle and the trailer entirely on the wind tunnel turntable and balance. This unique setup allowed for the measurement of all aerodynamic forces and moments on the vehicle, which could be used to improve vehicle dynamics modeling of a vehicle-trailer combination. The results of this paper show that the forces and moments on a vehicle-trailer combination change significantly at large yaw angles, and that zero yaw testing may be insufficient to predict the real world aerodynamic performance.