Aerodynamics of isolated cycling wheels using wind tunnel tests and computational fluid dynamics

In this work, the aerodynamic characteristics of isolated bicycle wheels, including a disc wheel and a five-spoke wheel, were investigated using an advanced test rig in a wind tunnel and high-fidelity numerical simulations. The effects of velocity, wheel rotation and yaw angle were systematically investigated. The wheel rotating speed and the freestream velocity reached as high as 20 m/s, and the yaw angle ranged from 0° to 45°. The aerodynamic forces measured by the wind tunnel experiments and numerical simulations were cross-validated, showing close agreement. Moreover, the topology of the wake flow obtained from simulations were compared with those obtained by high-quality Particle Image Velocimetry. When the flow was aligned with the wheel disc plane, the rotational drag decreased with the inflow speed. Moreover, the axial and rotational drag of the five-spoke wheel were higher than that of the disc wheel, making the overall drag higher. As for the effect of the yaw angle, it increased the side force until aerodynamic stall happened around 20 degrees. Meanwhile, the increase of yaw angle also increased the steering moment, especially for the disc wheel. This study provides a deeper understanding of fluid distribution and force generation in cycling wheels.