Aerodynamics of Fixed and Rotating Spoked Cycling Wheels

Abstract

The performance of a semiracing spoked wheel is numerically and experimentally studied at full size in a wind tunnel. The numerical investigation is divided into two parts. In the first part, the wheel is considered to be fixed (no rotation) and the numerical results are compared to the experimental measurements. The flow past the wheel is treated as stationary and turbulent. The effects of cross wind and the wheel’s speed on the drag, side force, and yaw moment are investigated. Numerical results are presented via diagrams and plots at various yaw angles. Both the measurements and predictions agree quite well and they show a considerable increase in the yaw moment and side force at medium and high yaw angles. The axial drag force initially increases with yaw angle (up to 7.5 deg) and eventually decreases. Ground effects did not affect the overall loads, except for the vertical force at high yaw angles. In the second part, the effects of rotation have been taken into account. The wheel rotates at constant angular velocities and the flow is modeled as nonstationary and turbulent. The aerodynamic performance of the wheel is strongly affected by the rotational speed. In most of the cases, as the latter parameter increases, the loads nonlinearly increase. The rotation generates asymmetrical loading, since the flow is accelerated in one side and decelerated in the other (the Magnus effect). A vertical force is produced, which is dependent on the ratio of the rotational to the free-stream speed. Moreover, in an attempt to assess the effects of the number of spokes to the aerodynamic performance, two other models with 8 and 32 spokes have been numerically tested and compared to the original one (16 spokes). The results revealed, as expected, an increase in the axial drag and vertical force with the number of spokes.