The Effect of Cross-Flow Vortex Trap Devices on the Aerodynamic Drag of Road Haulage Vehicles

The effect of Cross-Flow Vortex Trap Devices (CVTDs) on the local flow field and vehicle drag at a range of yaw angles has been investigated in wind tunnel experiments. The CVTD is a flow control device proposed by Bauer and Wood that aims to reduce the sensitivity of articulated road haulage vehicles to crosswinds by managing the tractor-trailer gap cross-flow. A 1/10th scale model is used in a low-speed wind tunnel at a Reynolds number of 900,000. The aerodynamic drag force is measured using a load cell connected to a rotating, raised ground plane. This research also uses tuft flow visualization to examine the local flow fields and pressure taps to determine trailer pressure distributions. It is found that a configuration of four 45% length CVTDs reduces the wind-averaged drag coefficient by 12%. The drag mechanisms responsible for the reduced drag include a lower average pressure on the trailer front face, removal of the separation on the leeward side of the trailer due to a reduction in the gap cross-flow, and an increase in pressure on the leeward side of the trailer behind the tractor-trailer gap. Furthermore, it is found that the drag reduction performance increases with CVTD length but does not vary with the number of CVTDs between one and four. These results suggest that using a single CVTD or flexible sheet of material at the centerline of the cab-gap is the most viable solution, as there is no further benefit to using multiple devices. In addition, it allows for the greatest CVTD length without impeding articulation.