Study of the effects of windshield angle on the drag force of cars

Vehicle aerodynamic drag significantly affects fuel efficiency at highway speeds. The windshield angle influences drag, but its quantitative effect on sport utility vehicles (SUVs) remains underexplored. This study investigates the relationship between windshield inclination and drag coefficient using computational fluid dynamics. To this end, a simplified 3D model of a 2013 BMW X5 was constructed in SolidWorks. Steady-state CFD simulations were performed in ANSYS Fluent using the pressure-based solver and RNG k-ε turbulence model with standard wall functions. The windshield angle varied from 30° to 90° in 5° increments. A mesh independence study, near-wall y+ verification, and explicit convergence criteria based on drag stabilization were implemented to ensure methodological robustness. The results show that the drag coefficient increases nearly linearly with windshield angle, from 0.346 at 30° to 0.415 at 90°. Pressure contour analysis shows surface pressure on the windshield rises from 14.2 Pa at 30° to 26.3 Pa at 90°. Velocity fields reveal enlarged low-velocity zones at the windshield base as angle steepens. Overall, the increased drag is predominantly attributable to higher pressure drag on forward-facing surfaces rather than to substantial modifications in the base wake structure. The results offer quantitative guidance for optimizing windshield design to balance aerodynamics and ergonomics in SUVs.