SAE International Further Investigations on the Flow Around a Rotating, Isolated Wheel with Detailed Tread Pattern 2015-01-1554

Efforts in aerodynamic optimization of road vehicles have been steadily increasing in recent years, mainly focusing on the reduction of aerodynamic drag. Of a car's total drag, wheels and wheel houses account for approx. 25 percent. Consequently, the flow around automotive wheels has lately been investigated intensively. Previously, the authors studied a treaded, deformable, isolated full-scale tire rotating in contact with the ground in the wind tunnel and using the Lattice-Boltzmann solver Exa PowerFLOW. It was shown that applying a common numerical setup, with velocity boundary condition prescribed on the tread, significant errors were introduced in the simulation. The contact patch separation was exaggerated and the flow field from wind tunnel measurements could not be reproduced. This investigation carries on the work by examining sensitivities and new approaches in the setup. A new validation case, which has the wheel rotating with small ground clearance, is tested both numerically and experimentally. Thus, the effect of tread rotation can be investigated separately from the effect of a deformed contact patch. In the simulation this is achieved by including the whole wheel in a sliding mesh region. For the wind tunnel a new motor-driven support sting was built to enable wheel rotation without ground contact. In order to validate the test case, flow field measurements are captured in the wind tunnel using a twelve-hole probe. Moreover, the treaded tire is compared to a smooth tire of the same outer contour in order to evaluate the tread's influence on the flow field.