wake and blockage effects. The above findings can provide practical criteria for the drag evaluation of generic bluff objects with this measurement technique.

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

The accuracy of the "PIV wake rake" method to measure the drag of transiting objects is evaluated. Tomographic particle image velocimetry measurements are conducted on a sphere towed at different speeds, within a Reynolds number range where the drag coefficient is constant. In contrast to PIV wake rake application on steady models in wind tunnels, where the upstream conditions can be accurately controlled and known a priori, measurement of the flow field prior to the passage of the model is essential for an accurate estimation of the drag for towed models when control of the undisturbed conditions is more challenging. The drag resolution of the technique is estimated to prospect the use of the technique in large-scale applications. A resolution of approximately 20 drag counts is obtained which is coarser than wind tunnel experiments but comparable to techniques used for field measurements.

The aerodynamic drag of a human-scale wind tunnel model is obtained from large-scale particle tracking velocimetry measurements invoking the conservation of momentum in a control volume surrounding the model. Lagrangian particle tracking is employed to obtain the velocity and static pressure statistics in a thin volume in the wake of a cyclist mannequin at freestream velocities between 12.5 and 15 m/s, corresponding to Reynolds numbers from 5 × 10 5 to 6 × 10 5 based on the torso length. The spatial distributions of the time-average streamwise velocity and pressure coefficient match well with previous works reported in literature. The streamwise velocity fluctuations in the wake of the cyclist's model are presented, clearly demonstrating the unsteady nature of the main wake flow structures. Furthermore, the obtained aerodynamic drag follows the expected quadratic increase with increasing freestream velocity. The accuracy of this drag estimation is evaluated by comparison to force balance data and corresponds to 30 drag counts. The three terms composing the overall drag force, ascribed to the mean and fluctuating streamwise velocity and the mean pressure, are also evaluated separately, demonstrating that the resistive force is dominated by the contribution of the mean streamwise momentum deficit, whereas the contribution of the pressure term is negligible. Graphical abstractThe data presented in the figures in this work is available online (https ://doi.org/10.4121/uuid:7f42e 060-766d-4bf1-86c4-c648c 79431 7c)

Elite level cycling events are performed at speeds in excess of 50 km/h. At these speeds, over 90% of the resistance forces come from aerodynamic resistance (C D A). Recently bicycle-mounted pitot tubes, such as the Notio Konect (NK) have become more commercially available making C D A easier to measure. Its reliability and sensitivity would be useful for riders and coaches to be able to understand what constitutes as a change in C D A. Accordingly, the aim of this study was to establish the intra-and inter-effort reliability and sensitivity of the C D A measures of the NK. Seven elite level track riders were used in this study which was broken into two parts: (1) Reliability and (2) Sensitivity. For both parts of the experiment, riders performed identical efforts, riding at ∼50 km/h for six laps of a 250 m indoor velodrome. For reliability, the riders performed six efforts without any changes in position or resistance. For sensitivity, they performed the efforts with a rod with discs of a known diameters attached at each end to vary the C D A by a known amount. For the reliability assessment, low coefficient of variation of intra -(0.47%) and inter-effort (0.9%) reliability were measured. With regards to sensitivity, the smallest changes in resistance (from 5 -6 cm, i.e. 1.2% or 0.002 m 2 ) was identified by the NK. The data in this experiment suggests that the NK is a highly reliable in measuring C D A can detect changes up to at least 1.2% in an indoor velodrome using elite level track riders. Highlights. The Notio Konect showed high levels of inter-and intra-effort reliability.. The Notio Konect could detect a change as small as 1.2% in aerodynamic drag.. The findings suggest that the Notio Konect is suitable for detecting small changes in aerodynamic drag in a velodrome setting.

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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.