Aerodynamic characterisation of isolated cycling wheels

Abstract

This study evaluated the aerodynamic performance of isolated cycling wheels, including a 5-spoke wheel and a disc wheel, considering the effects of freestream velocity, wheel type, wheel rotation, and crosswinds. For the first time, the rotational torque of cycling wheels was characterised using a shaft-mounted torque transducer. Force and wake velocity measurements were conducted in a wind tunnel between $10\text{m/s}$ and $22\text{m/s}$, where aerodynamics plays a dominant role in deciding overall resistance. The experimental results show that the wheel rotation has an opposite influence on the axial force of different wheels. A wake analysis effectively captured the influence of freestream velocity, wheel type, and wheel rotation on axial force. Results reveal that multiple vortical regions are formed in the lower wake of the rotating wheels, whereas the vortices in the upper wake are suppressed due to wheel rotation. When crosswinds are present, the disc wheel exhibits thirty times larger steering torque and generates much stronger vortical structures. This study offers valuable insights into the wake behaviour and drag generation around cycling wheels.