CFD simulations of an isolated cycling spoked wheel: Impact of the ground and wheel/ground contact modeling

Abstract

Spoked wheels are the most frequently used wheel type in road cycling competitions and their aerodynamic optimization is crucial for cyclist performance. The aerodynamic performance of wheels is generally analyzed by wind tunnel tests or CFD simulations for isolated wheels. There is a large number of options to model the wheel/ground contact in CFD simulations, including different clearances between tire and ground and different heights of solid contact patches (step). However, it is unclear to what extent these modeling options influence the CFD results. The present paper systematically analyzes the impact of these options on the computed forces and moments of an isolated cycling spoked wheel and elucidates the flow behavior around this wheel for zero yaw conditions. The wheel drag coefficient for the cases where the ground is included in the simulations using a clearance or a step is 1.0% and about 1.8% lower compared to the case without ground, respectively, whereas the rotational moment is about 2.0% lower for all the wheel/ground contact modeling approaches compared to the case without ground. The gap clearance (≤20 mm) and step height (≤10 mm) should be kept minimal to avoid a significant influence on the forces and moments. In addition, the presence of the ground influences the flow behavior in the lower section of the wheel including the pressure distribution on the exterior of the wheel. This study is intended to help researchers and manufacturers to perform accurate CFD simulations of cycling spoked wheels and to optimize their aerodynamics.