Aerodynamic development of an executive-class electric sedan: A case study of the Stelato S9

Aerodynamic drag reduction has become increasingly important for battery-electric vehicles (EVs), particularly in the low drag coefficient ( C _d ) regime, where further aerodynamic improvement progressively depends on production-oriented refinement under realistic engineering constraints. This study investigates the aerodynamic development process of the production executive-class electric sedan Stelato S9 under progressively constrained styling, engineering, and manufacturing conditions, with emphasis on the evolving role of steady-state CFD simulations during different development stages. During the early-stage pre-clay development phase, extensive steady-state CFD simulations were conducted under relatively high geometric freedom to establish a low-drag vehicle architecture. Representative aerodynamic optimization measures associated with front-end pressure redistribution, wheel-region flow organization, and rear-body wake regulation collectively achieved a drag reduction of approximately 26 counts (Δ C _d  ≈ −0.026). As aerodynamic development progressed, subsequent refinement increasingly relied on localized production-oriented optimization measures under constrained geometric conditions. Three rounds of clay-model aerodynamic refinement and wind-tunnel validation were subsequently conducted, yielding measured drag coefficients of C _d  = 0.214, 0.216, and 0.211, with corresponding CFD predictions of C _d  = 0.213, 0.220, and 0.218, respectively. The results indicate that steady-state CFD simulations generally provided reliable aerodynamic trend prediction for optimization measures dominated by attached or geometry-constrained flow structures, whereas significantly larger discrepancies were observed for optimization measures involving strongly separated rear-body wake flows. Across the investigated clay-model configurations, the baseline drag-coefficient prediction error of the CFD simulations remained within approximately 4% compared with the wind-tunnel measurements. The final production vehicle achieved a drag coefficient of C _d  = 0.196 at 120 km/h through the combined effects of exterior aerodynamic refinement, underbody aerodynamic optimization, and electronic rearview mirrors. Overall, the present study provides production-oriented engineering insight into aerodynamic development characteristics and CFD applicability in the sub-0.20 C _d regime under realistic engineering constraints.