Experimental Investigation of the Aerodynamic Benefits of Truck Platooning

Lawrence Livermore National Laboratory (LLNL) has conducted a series of scaled wind tunnel tests to investigate the aerodynamic benefits of heavy vehicle platooning and the availability of cooling air for trailing vehicles on two- and three-vehicle platoons. To measure the aerodynamic drag, scale models are mounted onto a LLNL designed splitter plate by means of a low-friction linear bearing and a load cell located within each model trailer. In addition to drag, pressure measurements are made with a pitot probe positioned at the center of each model radiator grill. Particle Image Velocimetry (PIV) and Infrared Thermography (IRT) measurements are used to map the three-dimensional velocity field and flow structures around the vehicles. Three different vehicle platoon configurations have been tested: two aligned vehicles with separation distances of 5′-320′ with and without trailer boattails; three aligned vehicles with 30′, 40′, and 50′ separation distances between first and second vehicles and 5′-220′ separation distances between the second and third vehicles without trailer boattails; two misaligned vehicles with separation distances of 30′, 50′, and 160′ with a misaligned percentage of 0-50% based on the trailer width with and without trailer boattails. Wind tunnel data is acquired for yaw angles ranging from −9° to 9° in 3° increments to account for crosswind effects. The cooling air supply to the trailing vehicle varies with vehicle spacing and becomes quite small and even negative for spacing less than 15′; however, at 120′ and larger separation distances it asymptotically approaches 70% of the lead vehicle air supply. For separation distances of 30′-50′, the aerodynamic benefit for the two-vehicle platoon ranges from 21% to 23% and 10% to 13% for vehicles with and without trailer boattails, respectively. Increasing the number of vehicles in the platoon increases the overall aerodynamic benefit and an additional benefit is achieved by adding boattails to the platoon vehicles.