A Wind-Tunnel Investigation of the Influence of Separation Distance, Lateral Stagger, and Trailer Configuration on the Drag-Reduction Potential of a Two-Truck Platoon

A wind-tunnel study was undertaken to investigate the drag reduction potential of two-truck platooning, in the context of understanding some of the factors that may influence the potential fuel savings and greenhouse-gas reductions. Testing was undertaken in the National Research Council Canada 2 m × 3 m Wind Tunnel with two 1/15-scale models of modern aerodynamic tractors paired with dry-van trailers configured with and without combinations of side-skirts and boat-tails.

Separation distances of 0.14, 0.28, 0.49, 0.70 and 1.04 vehicle lengths were tested (3 m, 6 m, 10.5 m, 15 m, and 22.5 m full scale). Additionally, within-lane lateral offsets up to 0.31 vehicle widths (0.8 m full scale) were evaluated, along with a full-lane offset of 1.42 vehicle widths (3.7 m full scale). This study has made use of a wind-averaged-drag coefficient as the primary metric for evaluating the effect of vehicle platooning.

The lead-vehicle model experienced improved drag reduction as the separation distance decreased, with no significant influence of vehicle configuration on the results. Of the matched vehicle-model pairs, the case with side-skirts showed the lowest magnitude of drag reduction for the trailing model at most separation distances, while the case with boat-tails showed the largest drag reductions for the trailing model at most separation distances. Of the mismatched pairs, placing the more aerodynamically-efficient vehicle model in the lead position resulted in a greater drag reduction for the trailing vehicle and the full platoon. No significant sensitivity to the range of within-lane lateral offsets tested (up to 0.31 model widths, or 0.8 m full-scale) were observed in the wind-tunnel tests. The trailing model experienced significant reductions of wind speed preceding the front grille, in excess of 70% at close distances, which indicates the potential for significant reductions of cooling flow rates for a full-scale vehicle. Estimates of potential fuel saving and greenhouse-gas reductions are also provided.