Wheel Drive Unit Lift Corrections in Automotive Wind Tunnels

Paper in proceeding, 2024

Correct simulations of rotating wheels are essential for accurate aerodynamic investigations of passenger vehicles. Therefore, modern automotive wind tunnels are equipped with five-belt moving ground systems with wheel drive units (WDUs) connected to the underfloor balance. The pressure distribution on the exposed areas of the WDU belts results in undesired lift forces being measured which must be considered to obtain accurate lift values for the vehicle. This work investigates the parasitic WDU lift for various configurations of a crossover SUV using numerical simulations that have been correlated to wind tunnel data. Several parameters were considered in the investigation, such as WDU size, WDU placement, tyre variants and vehicle configurations.

The results show that the parasitic lift is more sensitive to the width than the length of the WDU. However, the belt length is also important to consider, especially if the wheel cannot be placed centred. Varying the tyre pattern changes the parasitic lift and the effect is coupled to the rim design. The lift correction reduces for wider tyres, as there is less exposed belt area. Modifying the tyre shoulder and sidewall geometry or considering different vehicle configurations only results in minor differences. Finally, fitting the same wheels to a different vehicle, causes deviations only at the rear wheels due to differences in the shielding from the front wheel wake.

Generally, the largest differences in parasitic lift occur when there is a shift in the balance between the inner and outer low-pressure zones at the upstream tyre shoulders. In this work, such changes are observed when there is a considerable alteration of the separation point on the tyre shoulder or the amount of outwash from the wheel wake.