The Ring of Fire (RoF) measurement concept, introduced by Terra et al. (Exp Fluids 58:83.

The Ring of Fire (RoF) measurement concept to perform on-site experiments of aerodynamic drag for transiting objects is investigated with a study that identifies the main sources of uncertainty.The main contributors to the uncertainty of the drag measurement are examined for the case of a cyclist riding through the measurement domain. A sensitivity analysis is conducted that assesses how the estimated drag is affected by the choice of PIV image processing parameters. The size of the crosssection considered in the control volume formulation is also investigated. It is found that the accuracy of the estimated drag depends on the procedure used to detect the edge of the momentum deficit region in the wake. Moreover imposing mass conservation yields the most accurate drag measurements. The drag estimation has little dependence upon the spatial resolution of the measurement as long as the interrogation window size stays within 5% to 25% of the equivalent diameter of the object cross section. Experiments are conducted in a sport-hall, where the aerodynamic drag estimates from the RoF are compared to a conventional torque power meter installed on the bicycle, and different rider's postures as well as equipment variations are considered.Although the discrepancy in the absolute value of drag can be as high as 20%, power metering and RoF agree within 4% on relative drag variations.

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 3.2 × 10 5 . The measurements upstream and in the wake of the athlete are conducted at a rate of 2 kHz within a measurement plane of approximately 1000 × 1700 mm 2 . The non-dimensional, ensemble-averaged streamwise velocity fields compare well to literature and the ensemble-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 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, however, matches literature well.

No abstract

No abstract