Aerodynamical Resistance in Cycling on a Single Rider and on Two Drafting Riders: CFD Simulations, Validation and Comparison with Wind Tunnel Tests

The present work intends to validate computational fluid dynamics (CFD) simulations to subsonic wind tunnel experiments. The models tested in the wind tunnel at NTNU (a mannequin and real cyclist in static position) were scanned using a 3D scanner consisting 48 single-lens reflex cameras surrounding the object in three heights (low/ground-midi-above). The simulations were obtained using the Unsteady Reynolds Averaged Navier-Stokes solver STARCCM+ from CD-Adapco. A hybrid meshing technique was used in order to discretize both surface and volume. Polyhedral cells were used on the model surface and in the near volume while a structured grid was used in the rest of the domain. An unsteady RANS approach was used and the turbulence was modeled using the Menter implementation of the k-ω model. The boundary layer was fully resolved and no wall functions were used and. The first part of the paper aims to validate the numerical model. In the second part CFD simulations were used to analyse the aerodynamic properties of two drafting cyclists varying the distance between them from 1 to 4 m with 1 m increments. A good overall agreement between the simulations and the experiments was found proving the value of CFD as a complementary tool to conventional wind tunnel testing.