Influence of Tire Deformation on the Vehicle Aerodynamics

As an irreversible driving resistance, aerodynamic drag has a significant influence on the efficiency and range of vehicles. Up to 25% of the vehicle aerodynamic drag is caused by the wheels and wheel arches. The most important tools for the aerodynamic optimization of vehicles are measurements in the wind tunnel and computational fluid dynamics (CFD). During wind tunnel measurements, tires can deform in the same way as in open road driving. However, due to their complex geometry and deformability in combination with wheel rotation, integrating deformed tire geometries in CFD is a challenge. In a project funded by the Research Association for Automotive Technology (FAT), the University of Stuttgart and the University of Darmstadt are jointly characterizing the flow around the wheel, taking real tire deformation into account. Measurement campaigns in the wind tunnel have shown that tire deformation has a significant influence on aerodynamics. Furthermore, a tire deformation test rig was developed that makes it possible to measure the shape of the rotating tire while rolling on a flat belt and to vary parameters such as wheel load, camber, toe and tire pressure as required. A process was developed which makes it possible to generate tire geometries with real tire deformation for aerodynamic CFD analysis.