The application of laser diagnostics to cycling aerodynamics

To improve the aerodynamic performance of cyclists, detailed information of the flow field is required around these highly three-dimensional bluff-body geometries. Using traditional measurement techniques with cyclists in a wind tunnel, it is often difficult or impractical to acquire detailed flow field surveys. In this paper two examples are discussed where highresolution Particle Image Velocimetry has been undertaken in a water channel to investigate the wake dynamics of a single pedalling cyclist and the flow between multiple cyclists. These areas have previously been difficult to measure experimentally using intrusive measurement techniques. The first example provides a comparison of the phase-averaged wake of a 1:4.5 scale pedalling cyclist/bicycle combination in the water channel and that of a full-scale cyclist mannequin of similar geometry and position in a wind tunnel. The second example shows an application of PIV to measure the flow field between two drafting cyclists. Good agreement is observed between the large-scale wake of the scale model and full-scale mannequin despite an order-of-magnitude difference in Reynolds number. The drafting model shows that for spacings greater than a bike length, the trailing rider has negligible effect on the wake of the upstream rider