On-site investigation of running aerodynamics

Abstract We present an on-site aerodynamic investigation of runners through the Ring of Fire (RoF) methodology. The Lagrangian Particle Tracking (LPT) technique is used with helium filled soap bubbles as tracer particles and LED illumination; the acquired time-resolved data are processed through the Shake-the-Box (STB) algorithm. The RoF measurements are performed with six athletes running at an average speed of 8 m/s, resulting in a Reynolds number of 2 × 10 5 , based on the shoulder width. While existing studies largely focus on numerical simulations and experimental measurements performed on static human models, the present analysis investigates the wake flow topology of moving runners, thus addressing a significant gap in the literature. Specifically, the ensemble-averaged streamwise velocity and vorticity fields, along with the pressure coefficient distribution in the wake, are investigated. The results reveal that, close to the athlete, the wake shape closely resembles the runner’s body outline, with the torso area exerting the greatest influence. Moreover, in the near wake, a downwash effect from the head and an upwash effect from the hips are identified. This flow behaviour is further supported by the streamwise vorticity distribution analysis, which confirms the consistent formation of vortical structures across different athlete passages. Additionally, the aerodynamic drag is evaluated by applying the momentum conservation within a control volume containing the athlete. The results, presented in terms of the drag area, reveal that the overall drag area is largely independent of the control volume length, while the individual drag area contributions vary along the wake, with the greatest variations detected close to the athlete. The computed drag areas are 30–40% lower than most of the values reported in previous experimental and numerical studies, a difference attributed to the higher realism of the experimental measurements performed in this study, which capture the fully unsteady nature of the running motion. Moreover, a linear increase in the drag area with the athlete’s height squared is found.