In 2001 the FKFS (Research Institute of Automotive Engineering and Vehicle Engines, Stuttgart) took into operation state-of-the-art 5-belt systems for road simulation in the 22.45m2-IVK automotive wind tunnel and in the 1.65m2-IVK model wind tunnel. In these systems, a narrow belt running between the vehicles' wheels is fitted with 4 balance-mounted wheel rotation drives and a vehicle restraint system. The FKFS opted for MTS steel belt technology due to its small size, low power requirements and excellent tracking stability.
Due to air bearings below the belt, the flat-belt wheel rotation units in the full-scale wind tunnel permit aerodynamic force measurements at full wheel load (8 kN) up to 70 m/s. In combination with the hydrostatic suspension of the units, integrated longitudinal force transducers permit realistic measurements of the wheels' rolling resistance. In the model wind tunnel FKFS wheel rotation units with Poly-V belts are used with small wheel loads up to 80 m/s. The models' mounting on the balance is carried out automatically for the first time ever by a manipulator designed by WBI.
Investigations of the boundary layer, as well as minimization of the boundary layer thickness surrounding the vehicle by suction and blowing, combined with the block profile of the boundary layer above the belt yielded a good approximation of the situation above a wide 1-belt system. In combination with boundary layer control, the introduction of road simulation entails increases in aerodynamic drag and marked decreases of lift, particularly with small ground clearances. In production cars, added interference of the wheel rotation generally yields reductions of the drag coefficient up to 0.020. Retroactions from static floor pressures acting on belt surfaces of the wheel rotation units exposed to the test-section floor result in excessively high lift values requiring correction, as opposed to minimum pads with the size of the tire contact area. First approaches are promising.