When two vehicle bodies are involved in a passing maneuver, interesting and intricate aerodynamic interactions occur between them. This has been an area of active interest in Motorsports for quite some time. The existing literature shows only few studies in this area, and, as such, very little is known about the complex aerodynamics of racing in proximity. The aim of this thesis is to develop a Computational Fluid Dynamics (CFD) methodology capable of describing the transient effects that occur in this scenario, and to subsequently analyze the flow field. This is achieved by simulating the flow over two tandem simplified vehicle bodies (the Ahmed body) in a virtual wind tunnel where one body is kept stationary while the other was allowed to move in the longitudinal direction with a small velocity. In order to achieve reliable CFD results when one of the solid objects is moving, a new meshing methodology, called the "Overset mesh" model, was implemented in the CFD process. The simulations were run using a commercial finite volume CFD code Star-CCM+ using the unsteady Reynolds Averaged Navier-Stokes (URANS) solver. The collected CFD statistics include all time dependent vehicle aerodynamic performance parameters like drag, lift, side-force, and three moment coefficients, in addition to the full 3D description of the flow field surrounding the two vehicles. Additionally, the CFD results were compared against fully transient and quasi-steady-state experimental results, and encouraging correlations between the CFD and experiments were observed. The veracity of the CFD work presented in this thesis provided significant insight into the complex aerodynamics of a passing maneuver, and lays the foundation for further analysis in this area using more complex vehicle shapes and more complex tandem racing or passing maneuvers at a yaw angle.
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