Aerodynamic characteristics and liquid film movement morphology of the DrivAer model in rainfall environments

Variations in the aerodynamic characteristics of passenger vehicles in rainy environments are considered a critical hazard to driving safety. This research comprehensively compares the characteristics of wind–rain flow and the distribution of the liquid film on the vehicle's body under different rainfall intensities and incoming flow velocities. A rational rainfall environment is constructed based on computational fluid dynamics simulations, which employ the two-way coupled Eulerian–Lagrangian method and the Euler–liquid film model. The results indicate that the drag coefficient increases with rainfall intensity and exhibits a nearly linear relationship. Momentum coupling between raindrops and airflow over the roof of the vehicle results in lift reduction in rainfall environment. The liquid film on the car body surface becomes thicker as the rain intensity increases, and its distribution causes an increment in the ratio of viscous drag to total aerodynamic drag. Furthermore, velocity exerts a considerable influence on the aerodynamic forces and the morphology of liquid films in rainfall conditions. Increases in velocity mitigate the tendency of vehicles to experience amplified drag in the presence of rain. As the incoming flow velocity increases, the morphology of the liquid film evolves from point-like to rivulet-like, and the uniform distribution of the liquid film on the body surface is disrupted. As a consequence of the reduction in the number of raindrops captured in the wake, the wake structure remains largely unchanged.