Contribution of Add-On Components to the Aerodynamic Drag of a Cab-Over Truck-Trailer Combination Vehicle

Results from a wind tunnel testing program of a cab-over truck-trailer combination vehicle are presented. The model is scaled at 1:3, and represents an accurate replica of currently available trucks and trailers in Australia. Cooling intakes have not been modelled. Reynolds number independence is established to the maximum obtainable in the wind tunnel test configuration adopted equating to a full-scale forward speed of 57 km/h. The wind tunnel is a ¾ open jet facility with a nozzle area of 10.9m². The vehicle is mounted on a turntable to a 6 component force balance. A range of vehicle add-on devices are investigated, including boat-tails, side skirts, cab extenders, air-dams and roof fairings. Drag measurements are presented over a yaw angle range of 10 degrees. The results are compared to previous experiments in the literature and demonstrate that significant aerodynamic drag and fuel efficiency improvements remain easily obtainable by the industry by applying basic aerodynamic principles. The mechanisms by which base pressure is influenced by the various add on devices is discussed.