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CFD investigation on wheel modelling and car aerodynamics

Anandh Ramesh Babu
Göteborg : Chalmers tekniska högskola, 2019. Master's thesis - Department of Mechanics and Maritime Sciences; 2019:58, 2019.
[Examensarbete på avancerad nivå]

It has been estimated that approximately 25% of the drag of a passenger vehicle is due to the wheels and wheel housings. So studying the flow patterns around them have been of great importance for several years. Traditionally, wind tunnel experiments have been used to study the aerodynamic performance of vehicles but with growing computational resources, CFD investigations have proven to be vital, especially in the initial stages of development. With growing regulations on vehicle performances, it is of paramount importance to be able to accurately simulate the flow around wheels. The work included two studies: simulations of a rotating cylinder to represent a simplified wheel geometry and simulations of a full scale car. In the first study, the Rotating Wall(RW) and Sliding Mesh(SM) methods were investigated on a cylinder and it was found that the case was extremely mesh and timestep dependent. To obtain comparable results, very fine mesh and timestep had to be employed which were computationally expensive. A parametric study was performed on the SM case to understand the mesh, geometry and timestep dependency. Investigations were done to see if pseudo-parallelization of mesh updating in SM method could speed up the simulations. About 35% reduction in total time and 68% reduction in mesh updating time was noted. In the second study, aerodynamic analysis was performed on the car and wheels. Moving Reference Frame(MRF) and SM wheel modelling approaches were investigated and their differences were analyzed. Investigations on how blanking of rims affect the aerodynamic performance of a car was performed. It was noted that blanking reduced the drag by about 29 CdA counts and increased downforce by 21 ClA counts. An investigation on whether performing simulations with a timestep of 2.5e-4s on the mesh was done by comparing the results to a finer timestep of 1e-4s. It was found that the 2.5e-4s yields acceptable results. Finally, pseudo-parallelization of the interface updating was tested on the car by splitting the wheel interface into three interfaces. About 21% reduction in updating time and 5% reduction in total time was observed using this method. It was inferred that the method can be used for speeding up SM simulation and it can be further improved by creating more interfaces and evenly distributing the number of cells on each interface.

Nyckelord: Car aerodynamics, CFD, wheel modelling, SM optimizing, wheel blanking, pseudo-parallelization of SM.

Publikationen registrerades 2019-06-13. Den ändrades senast 2019-06-13

CPL ID: 256813

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