Aerodynamics of transiting objects via large-scale PIV - the Ring of Fire Concept

Abstract

A novel measurement system, the Ring of Fire, is deployed which enables the aerodynamic drag estimation of transiting cyclists. The system relies upon the use of large-scale stereoscopic PIV and the conservation of momentum within a control volume in a frame of reference moving with the athlete. The rider cycles at a velocity of approximately 8 m/s, corresponding to a torso based Reynolds number of 3.17 × 10^5. The measurements upstream and approximately 1000 × 1700 m^2. The non-dimensional, phase-locked, time-averaged streamwise velocity fields compare well to literature and the time-averaged drag area shows a rather constant value along the wake with an uncertainty of 5%. A comparison with wind tunnel force balance measurements shows significant discrepancies, which may be partly attributed to the bike supports and stationary floor in the wind tunnel measurements. The 25 % drag difference measured between a rider in upright and time-trial position, instead, matches literature well.