Transient Aerodynamic Interactions of Mixed-Size Road Vehicles During Multi-Lane Highway Overtaking

Abstract

Multi-lane overtaking among mixed-size vehicles produces highly transient aerodynamic interactions that challenge vehicle stability. This study investigates the unsteady aerodynamic response of a heavy-duty truck, an SUV, and a passenger sedan during an overtaking maneuver using transient CFD in ANSYS Fluent with dynamic deforming meshes and the SST k-ω turbulence model. The vehicles travel at constant velocities of 25.0, 30.5, and 36.1 m/s, respectively, under two conditions: a zero-crosswind reference case and a combined crosswind case (+5 m/s longitudinal, +10 m/s transversal). The results reveal pronounced variations in drag, lift, side force, and moment coefficients, complemented by center-of-pressure tracking. Under zero-crosswind conditions, localized channelization induces flow acceleration and pressure gradients during maximum vehicle overlap. Under crosswind conditions, the truck generates a leeward wake that initially shields the overtaking vehicles. However, exiting this wake shadow into the ambient crosswind shear layer triggers severe, rapid increases in lateral loads, vertical unloading, and aerodynamic moments. These findings demonstrate that transient wake-boundary transitions represent critical stability risks, providing vital input for future vehicle-dynamics models, intelligent transportation systems (ITS) and predictive advanced driver assistance systems (ADAS) applications.