Wind-tunnel characterisation of road-vehicles in crosswind conditions

Assessing the aerodynamic response of road vehicles under crosswind conditions is essential for understanding vehicle stability and safety. Such assessments require reliable aerodynamic data; however, much of the existing literature is based on experiments performed under disparate conditions or limited yaw-angle ranges. As a result, consistent and comparable reference datasets spanning multiple road-vehicle classes remain scarce. The present paper provides a consistent set of aerodynamic coefficients for the six load components (longitudinal, lateral and vertical forces; roll, pitch and yaw moments) for four vehicle classes: a saloon car (DrivAer geometry), a small lorry, a double-decker coach and an articulated lorry. The experimental campaign was conducted on reduced geometric scale models in the low-turbulence test section of the Politecnico di Milano wind tunnel under uniform flat-ground conditions, covering wind-yaw angles from 0°to 180°. The results show a strong dependence of crosswind aerodynamics on vehicle geometry, with pronounced differences between low-profile and high-sided vehicles. High-sided vehicles develop substantially larger lateral-force and rolling-moment coefficients, reaching up to approximately thirty times the saloon-car values when the double-decker coach or the trailer unit of the articulated lorry is considered. For the saloon car, a dependence of the aerodynamic loads on wind speed is observed. Abrupt changes in side-force and rolling-moment trends occur at specific yaw angles for smoother geometries, whereas sharp-edged configurations (small lorry and articulated trailer) exhibit smoother and more continuous behaviour. Overall, the results provide a coherent dataset for benchmarking, CFD validation and crosswind-stability studies across diverse road-vehicle classes.