The results of this study indicate that a rear adjustable spoiler significantly improves the aerodynamic performance of a fastback vehicle. Computational fluid dynamics simulations were conducted in ANSYS Fluent to optimize the spoiler’s height and angle for enhanced stability and aerodynamic efficiency. The NACA 4412 airfoil was selected due to its superior lift-to-drag ratio compared to other airfoils. Simulations were performed at three Reynolds numbers (4.87×106, 9.75×106, and 14.61×106), with spoiler heights ranging from 5 to 15 cm. The findings revealed that a 10 cm height provides an optimal balance between drag reduction and increased downforce. At this height, a 0° angle resulted in the lowest drag under normal driving conditions, improving aerodynamic efficiency without significantly affecting downforce. However, in sudden braking conditions, increasing the spoiler angle to 45°–60° significantly enhanced downforce, thereby improving tire grip and braking performance. The results confirm that an adjustable rear spoiler can effectively reduce lift, thereby increasing road adhesion at high speeds and enhancing braking performance without compromising aerodynamic efficiency. However, higher spoiler angles also increase drag, which may impact fuel consumption. These findings provide valuable insights into optimizing high-performance and energy-efficient vehicle designs, offering a foundation for future advancements in vehicle aerodynamics.

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