It is a well-known fact that the tyre shape changes with increasing velocity. This investigation has shown that the tyre shape also depends on the type of struts used for connecting the vehicle body to the force balance. Tyre deformations depending on the vehicle velocity for the cases of fixed and floating struts were measured. The floating struts allow displacement in the vertical direction, which leads to higher wheel centre positions, and most importantly to substantial body lift, especially for the rear part of the vehicle. The lift of the wheel centres and vehicle body were measured using laser displacement transducers and presented. In comparison to the difference in wheel centre lifts, the differences in radial expansion and axial compression of the tyres were insignificant. Experimental and numerical tests have shown that there were substantial differences in aerodynamic drag and lift forces acting on the vehicle for the two sets of struts that were investigated. Firstly, it has been shown that as a result of geometrical changes in tyres and suspension, and independently of the struts used, the drag coefficient decreased with speed. The drop was more significant for the case of fixed struts, resulting in 13 drag counts reduction between tests for 80 km/h and 240 km/h. For the floating struts a drop of 8 drag counts was measured. Secondly, an important observation was made that aerodynamic drag coefficient was always higher if floating struts were used. The difference increases with speed and can be as high as 8 drag counts. Numerical simulations confirmed both trends discussed, though it should be noted that the magnitude of differences estimated by CFD was smaller. A number of reasons for this have been suggested and have to be further investigated. Comparing total aerodynamic lift coefficients, the values for the case of floating struts were always somewhat higher, with the maximum difference observed at 80 km/h where the difference measured was as high as 8 lift counts. It has also been shown that in the case of floating struts there is a slight shift of lift forces towards the rear of the vehicle, meaning a reduction for front lift coefficient and corresponding increase for the rear one. To conclude, it should be stated that even though traditionally aerodynamic coefficients for passenger vehicles are considered to be Reynolds independent, this assumption should be treated with caution. The geometrical changes in terms of tyre deformations and vehicle body lift, as shown in this investigation, may result in significant alteration of aerodynamic forces.
Investigation of vehicle ride height and wheel position influence on the aerodynamic forces of ground vehicles
2014
10 Seiten, Bilder, 10 Quellen
Aufsatz (Konferenz)
Englisch
On the Influence of Ride Height Changes on the Aerodynamic Performance of Wheel Designs
British Library Conference Proceedings | 2014
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