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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.

Full scale heavy vehicle aerodynamic testing requires a very large wind tunnel test section, with few wind tunnels having this capacity worldwide. Small scale testing often requires a loss of model detail as well as introducing Reynolds Number and compressibility effects. A ¾ open jet wind tunnel set-up has been developed at Monash University Wind Tunnel that enables testing of 1:3 scale truck-trailer models, of full-scale length up to 18 metres to be tested. The measured drag on longer vehicles is more strongly affected by horizontal buoyancy and long models create additional blockage when yawed. In addition the length of the model means that special care must be taken to ensure that shear layers emanating from the nozzle at the start of the test section are sufficiently separated from the shear layers and wake at the base of the truck.