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

Abstract

The effect of Cross-Flow Vortex Trap Devices (CVTDs) on the local flowfield 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 tractortrailer gap cross-flow. A 1/10 th 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 visualisation to examine the local flowfields, 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 that are responsible for the reduced drag include a lower average pressure on the trailer front face, a removal of the separation on the leeward side of the trailer due to a reduction in 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 centreline 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.

Drag Reduction of a Simplified Truck Model Using Cab Roof Fairings

“…Numerical simulation results show that the CVTD can achieve a drag reduction of about 24%. Story et al [12] tested the effect of CVTD on the aerodynamic drag in a wind tunnel experiment. The test is performed for a scaleddown model at a Reynolds number of 900,000.…”

Comparison of the Effectiveness of Drag Reduction Devices on a Simplified Truck Model through Numerical Simulation

“…One relatively simple drag reduction device used in the gap is called a cross-flow vortex trap device (CVTD) and consists of equally spaced vertical slabs mounted on the front face of the trailer [11]. It was suggested in an experimental study [12] that the drag mechanisms were lower average pressure on the trailer's front face, removal of flow separation on the leeward side of the trailer due to less gap cross flow, and increased pressure on the back of the tractor. The authors of [12] investigated the effect of the size (horizontal length) of CVTDs on drag reduction, and their results showed that larger CVTDs led to greater drag reduction.…”

“…It was suggested in an experimental study [12] that the drag mechanisms were lower average pressure on the trailer's front face, removal of flow separation on the leeward side of the trailer due to less gap cross flow, and increased pressure on the back of the tractor. The authors of [12] investigated the effect of the size (horizontal length) of CVTDs on drag reduction, and their results showed that larger CVTDs led to greater drag reduction. It was also found in the same study [12] that the drag reduction performance did not change with the number of CVTDs when that number was between one and four.…”

“…The authors of [12] investigated the effect of the size (horizontal length) of CVTDs on drag reduction, and their results showed that larger CVTDs led to greater drag reduction. It was also found in the same study [12] that the drag reduction performance did not change with the number of CVTDs when that number was between one and four. However, it was demonstrated in a numerical study [13] that while roughly the same drag reduction was obtained using one and two CVTDs, further drag reduction was achieved when three CVTDs were deployed.…”