Numerical analysis of aerodynamic forces acting on a couple of cyclists in cross wind conditions

Cross-wind can strongly influence the results of a cycling stage. Indeed, in stages characterized by cross-wind, echelons formations are assumed by the cyclists. The reason is that the presence of the cross-wind can modify the forces acting on the cyclists both in term of magnitude and direction. Echelons are able to reduce the negative effects of the generated side force and still allow to benefit of drafting, thus reducing wind resistance. Previous investigations on the impact of cross-wind on cycling aerodynamics have been performed considering isolated wheels and single cyclists and more recently with a couple of cyclists without bike. However, to the best of our knowledge, the impact of cross wind on a couple of cyclists including bike has not yet been investigated. In this paper, therefore, Computational Fluid Dynamics (CFD) is used to investigate the impact of cross wind on the aerodynamic resistance of a couple of cyclists. Two different configurations are considered: (i) in-line; when the trailing cyclist is placed in line with the leading cyclist and (ii) echelon; when the trailing cyclist is staggered from the leading cyclist. For each configuration, the impact of different spacing and yaw angles are also assessed. The evaluation is based on validation with wind-tunnel measurements of drag force performed at several yaw angles. For the CFD simulations, the cyclist geometry has been obtained by means of 3D laser scanning of an elite cyclist while the bike geometry has been created using 3D CAD modelling. The 3D steady Reynolds-Averaged Navier-Stokes equations (RANS) are solved in combination with the standard k-e turbulence model and with low-Reynolds number modelling. The results show that the leading cyclist is only slightly affected by the position of the trailing cyclist. Drag and side forces reduction occur to the trailing cyclist when he is located in the wake of the leading cyclist, i.e. moving from an in-line to a staggered position when cross wind is present. Further results and discussions on the interaction of the two cyclists under influence of cross-wind will be presented in the full paper.