The development of modern CFD simulation codes has had a significant impact on reducing costs for testing and modeling. In addition, the use of software allows unlimited and relatively short time changes to any component or part of a vehicle model to meet the requirements and constraints imposed by the manufacturer and the needs of buyers. During this thesis we will focus on the modeling and optimization of the geometry of the air curtain system on Alfa Romeo Tonale 965 using the modeling software Ansa Beta Cae and the fluid dynamics simulation code Star-CCM+. The air curtain is an innovative technology used in several modern cars to ensure improved aerodynamic efficiency: this channeling system is a technology mainly adopted on sports class cars with the aim of reducing aerodynamic drag, but it is also adopted on cars sold to the public, achieving significant benefits in terms of consumption and emissions.