Optimizing Fastback Passenger Car Aerodynamics Using Adjustable Rear Spoiler and CFD Structural Evaluation

Abstract

Aerodynamic efficiency plays a crucial role in passenger car performance, influencing stability, fuel consumption, and overall driving safety. Fastback-type vehicles are susceptible to high drag and lift forces due to their sloping rear geometry, which increases wake turbulence and reduces fuel economy. This study aims to optimize the aerodynamic performance of a fastback passenger car by employing an adjustable rear spoiler and validating the results through both computational fluid dynamics (CFD) simulations and experimental wind tunnel testing. The methodology involved testing spoiler configurations at multiple angles (0°, 10°, 15°, 20°, 22°, 25°, 30°, and 35°). Aerodynamic parameters such as drag coefficient (CD), downforce, surface pressure distribution, wake velocity, turbulence kinetic energy, and lift-to-drag ratio were analyzed. Additionally, structural evaluation using Von Mises stress distribution ensured durability, while fuel consumption analysis quantified efficiency gains across speeds from 60 to 180 km/h. The results demonstrated that the 20–22° spoiler angle provided the optimal configuration, achieving a minimum drag coefficient of 0.258, substantial downforce growth with increasing speed, and up to 8.5% fuel savings at 180 km/h compared to the stock setup. Structural analysis confirmed that over 70% of the spoiler surface experienced low stress (0–50 MPa), with less than 5% subjected to stresses above 150 MPa, ensuring safety under aerodynamic loading. The novelty of this research lies in its integrated approach, combining aerodynamic, structural, and fuel consumption evaluations to deliver a comprehensive framework for spoiler optimization.