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13:30   Aerodynamics of cycling; wake analysis Chair: Andrea Sciacchitano 13:30 20 mins AN ANALYSIS OF THE WAKE OF PEDALLING CYCLISTS IN A TANDEM FORMATION Nathan Barry, David Burton, John Sheridan, Nick Brown, Mark Thompson Abstract: Aerodynamics has been shown to be a critical factor in the performance of cyclists with drag being the dominant resistive force at racing speeds. Many cycling events involve athletes riding in close proximity. Previous studies have shown that flow interactions result in significant drag reductions for tandem cyclists; inline parallel to the flow (Barry et al. 2014). However, the flow mechanisms associated with these changes have not been well characterised to date. This paper seeks to address the questions of how the tandem wake differs from the single rider case, and whether these changes are responsible for the reduction in drag. Wake surveys were taken behind cyclists in the Monash University three-quarter open jet wind tunnel with a blockage ratio of 7%. Measurements were taken using a multi-hole pressure probe (TFI Cobra) which resolves three components of velocity and pressure from the incoming flow. Velocity data was then phase-averaged over segments of the crank cycle to capture the time varying behaviour of the pedalling cyclist wake. Wake profiles of streamwise velocity and vorticity show significant changes to the flow field with the position of the legs around the crank cycle. These changes are consistent between the single and tandem cases. The magnitude and distribution of vorticity in the tandem wake is equivalent to the single rider case. However, the magnitude of streamwise velocity fluctuations in the tandem wake are smaller. These results show that the wake of a trailing cyclist does not differ greatly from the single rider case. Changes in flow conditions caused by the motion of the cyclist’s legs are persistent in the tandem wake despite upstream flow changes. This indicates that the geometry of a cyclist has such a dominant influence on the formation of hip vortices and the flow field that wake behaviour is largely independent of inflow conditions. The similarity in the wakes of the two cases suggests that the large drag reduction evident for a trailing rider is not attributable to energy recovery or disruption to dominant vortex structures in the wake. 13:50 20 mins A COMPARISON OF THE WAKE STRUCTURES OF SCALE AND FULL-SCALE PEDALLING CYCLING MODELS Timothy Crouch, David Burton, Mark Thompson, John Sheridan, Nicholas Brown, James Venning Abstract: This paper presents a novel approach to better understand the unsteady aerodynamics associated with a dynamically pedalling cyclist. Using high resolution Particle Image Velocimetry in a water channel, the large-scale wake structure is analysed for various phases of the crank cycle of a 1:4.5 scale-model cyclist/bicycle under both static and pedalling conditions. Both quasi-static and dynamic pedalling leg results are compared with detailed velocity field surveys made in the wake of a full-scale pedalling cyclist mannequin of similar geometry and position in a wind tunnel. A time-averaged and phase-averaged analysis of the various flow regimes that occur throughout the pedal stroke shows good agreement between scale-model and full-scale mannequin investigations. This is highlighted in figure 1 which for dynamic pedalling conditions compares phased averaged streamwise vorticity fields in a plane downstream of the full scale wind tunnel model and the scale water channel model. For this phase of the crank cycle, where a pair of strong counter rotating streamwise voritces are formed, excellent agreements is observed between scale-model and full-scale results despite the Reynolds number differing by an order of magnitude between both sets of results (Re# full scale ≈700,000, Re# 1:4.5 scale ≈70,000). This highlights the robustness of the formation of the primary wake flow structures when subjected to varying Reynolds number, bicycle/rider geometry and quasi-steady/dynamic pedalling conditions. 14:10 20 mins DRAFTING EFFECT IN CYCLING: INVESTIGATION BY WIND TUNNEL TESTS Marco Belloli, Stefano Giappino, Fabio Robustelli, Claudio Somaschini Abstract: Cyclists travelling in groups experience a significant reduction in the wind resistance and those behind consume less energy due to the shielding effect of the front cyclist. We investigated drafting effects by wind tunnel tests realizing a test set-up with two cyclists pedalling at different longitudinal distance. Drag reduction effects on both the leading and the trailing cyclist are confirmed. The presence of lateral wind is also investigated showing a significant reduction of the drafting effect also for light winds.