Alexey Vdovin

Investigation of Wheel Aerodynamic Resistance of Passenger Cars

There are a number of numerical and experimental studies of the aerodynamic performance of wheels that have been published. They show that wheels and wheel-housing flows are responsible for a substantial part of the total aerodynamic drag on passenger vehicles. Previous investigations have also shown that aerodynamic resistance moment acting on rotating wheels, sometimes referred to as ventilation resistance or ventilation torque is a significant contributor to the total aerodynamic resistance of the vehicle; therefore it should not be neglected when designing the wheel-housing area. This work presents a numerical study of the wheel ventilation resistance moment and factors that affect it, using computational fluid dynamics (CFD). It is demonstrated how pressure and shear forces acting on different rotating parts of the wheel affect the ventilation torque. It is also shown how a simple change of rim design can lead to a significant decrease in power consumption of the vehicle. A way of introducing ventilation torque into the driving resistance equation is discussed. The results show that it is possible to assess ventilation resistance moment using CFD. It is demonstrated that brake discs have almost negligible ventilation torque, while the contribution of rims and tyres may vary depending on the rim design used and the velocity of the vehicle. It is also shown that for the designs investigated the equivalent ventilation force has a second order dependency on the vehicle velocity which allows an introduction of a ventilation resistance coefficient CD(vent) that is independent of velocity.

Investigation of Wheel Ventilation-Drag using a Modular Wheel Design Concept

Passenger car fuel consumption is a constant concern for automotive companies and the contribution to fuel consumption from aerodynamics is well known. Several studies have been published on the aerodynamics of wheels. One area of wheel aerodynamics discussed in some of these earlier works is the so-called ventilation resistance. This study investigates ventilation resistance on a number of 17 inch rims, in the Volvo Cars Aerodynamic Wind Tunnel. The ventilation resistance was measured using a custom–built suspension with a tractive force measurement system installed in the Wheel Drive Units (WDUs). The study aims at identifying wheel design factors that have significant effect on the ventilation resistance for the investigated wheel size. The results show that it was possible to measure similar power requirements to rotate the wheels as was found in previous works. The magnitude of the measured ventilation resistance confirms the conclusion that this effect should be taken into account when designing a wheel. It was found that some of the rim design factors have greater influences on the ventilation resistance than others. It was also shown that one of the investigated rims had lower ventilation resistance than measured for the fully-covered wheel configuration.

On the aerodynamic performance of two Silver Arrows from the thirties

Two typical Silver Arrows from the thirties, one Mercedes-Benz W25 and one Auto Union Type C, were used to illustrate the simplicity and the capabilities of modern commercial CFD (Computational Fluid Dynamics) tools to mimic and compare the flow fields around these cars. In a Bachelor thesis carried out during the spring 2014 at Chalmers University of Technology, Bondesson et.al. (2014), six students with no prior CFD experience performed the computations presented in this paper. Since no CAD (Computer Aided Design) data was available on the full-scale cars, 1:18 scale model-cars from CMC-models were used, see Figure 1. The two models were 3D-scanned and reconstructed in order to obtain a detailed geometry needed for CFD simulations. Of course, the performance of these vintage race-cars is always of great general interest, and if these computations could increase the knowledge on the German Silver Arrows it would be an added bonus of this work.

Investigation of vehicle ride height and wheel position influence on the aerodynamic forces of ground vehicles

To prevent test vehicles from movement during experiments in modernaerodynamic wind tunnels, fastening struts are typically used for a rigid connection between the model and the force balance underneath the wind tunnel floor. A weakness of this experimental set-up is that such struts limit the vertical movement of the vehicle. By analysing experimental data from the Volvo Cars wind tunnel and corresponding CFD simulations the differences in measurements using struts with and without vertical displacement have been analysed and compared. The model used was a Volvo S60.