CFD Investigation of Wheel-Region Aerodynamics and Front-Wheel Air-Deflector Performance Under Varying Inflow Speeds, Crosswind, and Two-Vehicle Platooning

Wheel-region flow has a substantial influence on the aerodynamic drag of passenger cars; however, wheel-specific aerodynamic responses under varying inflow speeds, crosswind, and steady-state platooning conditions have not yet been sufficiently characterized. In this study, a previously validated numerical framework based on a 1:2.5-scale DrivAer fastback model was employed to perform three-dimensional, steady-state, incompressible Reynolds-averaged Navier–Stokes simulations using the realizable k-ε turbulence model. The parametric analysis considered inflow speeds of 10–40 m/s, spoke-closure ratios of 0–100%, yaw angles of 0–20°, bilateral front-wheel air deflectors with full-scale heights of 10–60 mm, and steady two-vehicle platooning with an inter-vehicle spacing of 0.5L. Variations in inflow speed and spoke closure had only limited effects on the total-vehicle drag coefficient, whereas the drag coefficients of individual wheels exhibited non-monotonic behavior. Under crosswind conditions, the lateral redistribution of underbody flow and shielding effects between the wheels produced pronounced left–right asymmetry in wheel drag. As the air-deflector height increased, the total-vehicle drag coefficient decreased monotonically from 0.2447 for the baseline configuration to 0.2213 for the 60 mm configuration, with the drag-reduction effect approaching saturation between 50 and 60 mm. The 60 mm air deflector reduced the total-vehicle and front-left-wheel drag coefficients by 9.6% and 70.8%, respectively, while increasing the rear-left-wheel drag coefficient by 34.2%. Under the combined condition of a 60 mm air deflector and a yaw angle of 5∘, the total-vehicle and front-left-wheel drag coefficients further decreased to 0.2186 and 0.002045, respectively, whereas the rear-left-wheel drag coefficient increased to 0.007489, demonstrating that the combined effect varied with wheel position. In steady-state platooning with a spacing of 0.5L, the front-left- and rear-left-wheel drag coefficients of the following vehicle decreased by 66.0% and 31.6%, respectively, relative to the isolated-vehicle condition. Furthermore, installing the 60 mm air deflector on the leading vehicle produced additional reductions of 35.5% and 19.3% in the front-left- and rear-left-wheel drag coefficients of the following vehicle, respectively, compared with the platooning condition without the air deflector. These results demonstrate that direct control of wheel-arch inflow is more effective than spoke closure for reducing total-vehicle and front-wheel drag, and that the aerodynamic effects of the air deflector vary among individual wheels depending on its height, crosswind conditions, and inter-vehicle aerodynamic interactions.