The shape of a vehicle’s tyre is a crucial consideration to aerodynamic performance. Wheel drag contributes to up to 30% of the overall drag for open-wheel vehicles and yet tyre deformation is completely overlooked all too often by many engineers still relying on generic circular tyre CAD models.
Tyres makes up the most dynamic part of the vehicle as they change shape significantly due to the range of forces acting upon them. For this reason using revolved tyre CAD models in CFD, which resemble the look of the unloaded tyre, often leads to inaccuracies.
Due to their complicated and unpredictable shape, loaded tyres cannot simply be drawn in CAD. FE models provide a good insight into how they deform, but there is some debate over their accuracy. So, what is the solution?
At TotalSim, our approach is to capture the real tyre geometry using 3D scanning technology; we lower the car in racing spec into boxes under each wheel and, after applying an equivalent downforce loading, pour in a wet plaster mix to create an exact mould of the contact patch.
Once set, we remove the car and scan the casts left by the tyre. This scan is then inverted, merged into a second scan of the overall tyre geometry, and used to construct a CFD model with the rest of the vehicle’s geometry.
The result is a more accurate representation of the real world geometry within the CFD model, eliminating a potential source of error and providing the best possible basis for aerodynamic improvements moving forward.
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