Wind-Tunnel Study of the Traffic-Wake Impacts for Road-Vehicle Aerodynamics

When driving in traffic, the wakes of leading vehicles reduce the wind speed experienced by a following vehicle, lowering its drag relative to isolated driving. These wake effects can persist to large intervehicle distances, on the order of hundreds of meters, while lateral convection due to cross winds can influence vehicles in adjacent lanes. Wind tunnel testing was conducted at 30% scale for light- and heavy-duty-vehicle models in a large wind tunnel with a traffic-wake simulation system, expanding upon a previous study that examined only heavy vehicles. Three variants of the DrivAer model, four variants of the AeroSUV model, and three variants of a zero-emission heavy-duty-truck model were tested with a range of simulated wake conditions that varied the type, forward distance, and lane position of the wake-source vehicle(s), for a range of yaw angles up to 11deg. Results show drag reductions of up to about 10% for the heavy-truck model, and up to about 20% for the passenger-vehicle models. Surface-pressure measurements provide insights about the sources of drag reduction in wake effects, highlighting the balance between strongly-varying forward-surface pressure differences and mild base-pressure increases.