An experimental characterisation of the wake of a detailed heavy vehicle in cross-wind

The unsteady wakes associated with detailed heavy vehicles with different levels of passive aerodynamic treatment are investigated in a wind tunnel using a 1/3 scale model. Drag coefficient, base pressure and wake total pressure are measured for detailed vehicles at yaw angles up to 15 degrees for six semi-trailer vehicle configurations. Cabin extenders and side-skirts were shown to be more effective at reducing drag under yawed flow conditions, while certain front-end modifications were found to perform best at psi = 0 degrees when the tractor was more able to shield the trailer from oncoming flow. Base pressure was shown to reduce with yaw angle, with the low pressure signature of the main lower vortex tilting upwards on the leeward side of the vehicle's base. Total pressure grid measurements showed two different types of wake, those where the stream-wise vortex formed by flow separating off the roof of the trailer is separated from the bulk vehicle wake by a region of high total pressure, and those where the two are indistinguishable. Vehicles without a distinct trailing vortex in this region were found to exhibit stronger horizontal asymmetries in their base pressure profiles.