Tire Deformation Modeling and Effect on Aerodynamic Performance of a P2 Race Car

Abstract

The development work of a race car revolves around numerous goals such as drag reduction, maximizing downforce and side force, and maintaining balance. Commonly, these goals are to be met at the same time thus increasing the level of difficulty to achieve them. The methods for data acquisitions available to a race team during the season is mostly limited to wind tunnel testing and computational fluid dynamics, both of which are being heavily regulated by sanctioning bodies. While these methods enable data collection on a regular basis with repeat-ability they are still only a simulation, and as such they come with some margin of error due to a number of factors. A significant factor for correlation error is the effect of tires on the flow field around the vehicle. This error is a product of a number of deficiencies in the simulations such as inability to capture loaded radius, contact patch deformation in Y direction, sidewall deformation and overall shifts in tire dimensions. These deficiencies are evident in most WT testing yet can be captured in CFD. It is unknown just how much they do affect the aerodynamics performance of the car. That aside, it is very difficult to correlate those findings as most correlation work is done at WT which has been said to be insufficient with regards to tire effect modeling. Some work had been published on the effect of tire deformation on race car aerodynamics, showing a large contribution to performance as the wake from the front tires moves downstream to interact with body components. Yet the work done so far focuses mostly on open wheel race cars where the tire and wheel assembly is completely exposed in all directions, suggesting a large effect on aerodynamics. This study bridges the gap between understanding the effects of tire deformation on race car aerodynamics on open wheel race cars and closed wheel race cars. The vehicle in question is a hybrid of the two, exhibiting flow features that are common to closed wheel race cars due to each tire being fully enclosed from front and top. At the same time the vehicle is presenting the downstream wake effect similar to the one in open wheel race cars as the rear of the wheelhouse is open. This is done by introducing a deformable tire model using FEA commercial code. A methodology for quick and accurate model generation is presented to properly represent true tire dimensions, contact patch size and shape, and deformed dimension, all while maintaining design flexibility as the model allows for different inflation pressures to be simulated. A file system is offered to produce CFD watertight STL files that can easily be imported to a CFD analysis, while the analysis itself presents the forces and flow structures effected by incorporating tire deformation to the model. An inflation pressure sweep is added to the study in order to evaluate the influence of tire stiffness on deformation and how this results in aerodynamic gain or loss. A comparison between wind tunnel correlation domain to a curved domain is done to describe the sensitivity each domain has with regards to tire deformation, as each of them provides a different approach to simulating a cornering condition. The Study suggests introducing tire deformation has a substantial effect on the flow field increasing both drag and downforce.In addition, flow patterns are revealed that can be capitalized by designing for specific cornering condition tire geometry. A deformed tire model offers more stable results under curved and yawed flow. Moreover, the curved domain presents a completely different side force value for both deformed and rigid tires with some downforce distribution sensitivity due to inflation pressure.