CFD Study of Semi-Covered Wheels

By Thibaud Muller and Dr. Kenji Takeda,
School of Engineering Sciences, University of Southampton, UK

Many sports cars have wheel covers that can generate additional lift over that of uncovered wheels. This computational fluid dynamics (CFD) study investigated the aerodynamic differences between semi-covered and isolated wheels. It was carried out as part of the MSc in Race Car Aerodynamics in the School of Engineering Sciences at the University of Southampton, a unique course that teaches the fundamentals of experimental and computational aerodynamics for race car design.

The study used Gridgen for mesh generation in order to allow fine tuning of the structured mesh to ensure accuracy around the complex geometry. This was particularly critical to be able to resolve the tire contact patch correctly. The covered wheel surface mesh is shown in Figure 1.

covered wheel surface mesh
Figure 1: Covered wheel surface mesh.

The wheel tread is meshed using an O-type grid, with the wheel rim constructed using an O-H type configuration, which is illustrated in Figure 2. In order to capture the boundary layer behavior a mesh with y+≈1 is used; the boundary layer mesh contains more than half the total number of cells. A total of 120 blocks were used.

covered wheel grid topology
Figure 2: Covered wheel grid topology.

Both steady and unsteady CFD computations were carried out using Fluent on a dedicated cluster running Windows Compute Cluster Server 2003. A grid convergence study using up to 6.7 million cells indicated that a mesh with 5.5 million cells was adequate to capture the key flow characteristics and forces to within experimental accuracy.

The CFD simulations reveal the topology and effect of the wheel cover on the overall flow field as shown in Figure 3. The interaction between the wheel cover-induced trailing vortices and the flow around the wheel cavity has a significant effect. The quantitative results show that 66 percent more wheel lift is generated with the wheel cover than with the isolated wheel case.

T-Rex mesh on a cut through a blood vessel with an aneurysm
Figure 3: Streamlines coloured by magnitude: (left) semi-covered wheel; (right) isolated wheel.

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