Numerical Investigation of the Influence of Tire Deformation and Vehicle Ride Height on the Aerodynamics of Passenger Cars

Francesco Fabio Semeraro,Paolo Schito

doi:10.3390/fluids7020047

Abstract

Wheels and wheel houses contribute up to 25% of the total aerodynamic drag of passenger cars and interact in a complex way with their surroundings. Rims and tires induce complex flow separation mechanisms in a highly unsteady regime and the proximity to the ground enhances these phenomena. To have a clearer understanding of the flow mechanisms that develop around wheels and inside wheel houses, the effect of tire deformation and vehicle ride height on the aerodynamics of passenger cars has been investigated with unsteady CFD simulations. Tire deformation is modelled with an empirical formulation that provides close-to-real deformed shapes, while vehicle ride height changes are made by applying vertical translations the vehicle body. Slick tire geometries and closed rims have been analysed and their rotation has been modelled with a tangential velocity component applied to their surface. The investigation has been conducted in three steps: different car heights and tire deformation levels have been investigated separately and then combined, classifying the results on the basis of the drag of the vehicle. Results show that even small tire deformation levels can significantly affect the aerodynamic drag, thus deformation should be included in simulations and treated with caution.

Highlights

Aerodynamic efficiency for passenger cars is a topical point of interest in recent years.Car manufacturers are forced to rapidly improve their designs by more and more stringent homologation procedures such as WLTP [1], which has been applied since September 2017 in Europe
The results are compared for configurations that belong to the same group because the variation applied to ride height when this parameter is treated alone is more than the ride height change when tire deformation is considered
The investigation described in this work aims at explaining how changes in vehicle ride height and tire deformation contribute to the overall drag of a passenger car

Summary

Introduction

Aerodynamic efficiency for passenger cars is a topical point of interest in recent years.Car manufacturers are forced to rapidly improve their designs by more and more stringent homologation procedures such as WLTP [1], which has been applied since September 2017 in Europe. Compared to previous regulations (i.e., NEDC), WLTP cycles better represent realistic driving scenarios, requiring a high level of optimisation for most of vehicle components. Due to the differences between NEDC and WLTP test cycles, vehicle parameters such as car weight, tire rolling resistance and aerodynamic drag have different relative weights. For WLTP, vehicle weight and aerodynamics are the most influencing parameters due to longer and stronger acceleration phases and a higher average velocity [2]. This is why aerodynamics offers a significant room for improvement and it currently is one of the most investigated car properties

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Conclusion