Aerodynamic drag in cycling pelotons: New insights by CFD simulation and wind tunnel testing

2017

In the last few years increasing attention in the cycling sport has been placed on coaching and supervision of the cyclist. Considerable progress has been made, particularly in the field of training and nutrition, that the physical performance has nearly reached its optimum. In order to further improve the efficiency of the cycling movement, optimizing the position on the bicycle is an absolute prerequisite (bikefitting, n.d.).

Journal of Sports Sciences, 2008

The aims of this study were to measure the aerodynamic drag in professional cyclists, to obtain aerodynamic drag reference values in static and effort positions, to improve the cyclists' aerodynamic drag by modifying their position and cycle equipment, and to evaluate the advantages and disadvantages of these modifications. The study was performed in a wind tunnel with five professional cyclists. Four positions were assessed with a time-trial bike and one position with a standard racing bike. In all positions, aerodynamic drag and kinematic variables were recorded. The drag area for the timetrial bike was 31% higher in the effort than static position, and lower than for the standard racing bike. Changes in the cyclists' position decreased the aerodynamic drag by 14%. The aero-helmet was not favourable for all cyclists. The reliability of aerodynamic drag measures in the wind tunnel was high (r 4 0.96, coefficient of variation 5 2%). In conclusion, we measured and improved the aerodynamic drag in professional cyclists. Our results were better than those of other researchers who did not assess aerodynamic drag during effort at race pace and who employed different wheels. The efficiency of the aero-helmet, and the validity, reliability, and sensitivity of the wind tunnel and aerodynamic field testing were addressed.

arXiv preprint arXiv:1206.0816, 2012

A peloton may be defined as two or more cyclists riding in sufficiently close proximity to be located either in one of two basic positions: 1) behind cyclists in zones of reduced air pressure, referred to as 'drafting', or 2) in zones of highest air pressure, described here alternately as 'riding at the front', 'in the wind', or in 'non-drafting positions'. Cyclists in drafting zones expend less energy than in front positions. Two broad models of peloton dynamics are explored. The first is an energetic model that describes peloton dynamics that oscillate through observable phase states as they emerge from collision avoidance and riders' coupled energy outputs. These phases exhibit behavioural characteristics such as convection patterns and synchronization, among others. Under the second, economic model, we discuss some basic parameters of the peloton as a system of economic exchange, and identify the resources within a peloton for which riders compete and cooperate. These include the energy savings of drafting, a near-front positional resource, and an information resource.

Proceedings of the 3rd International Congress on Sport Sciences Research and Technology Support, 2015

The present work shows a comparison between computational fluid dynamics (CFD) simulations obtained using the Unsteady Reynolds Averaged Navier-Stokes solver STARCCM+ from CD-Adapco and experiments carried out in the subsonic wind tunnel at NTNU. The models tested in the wind tunnel (a mannequin and real cyclist in static position) were 3D scanned using a 3D scanner, consisting 48 single-lens reflex cameras surrounding the object in three heights (low/ground-midi-above). A hybrid meshing technique was used in order to discretize the surface and the volume. Polyhedral cells were used on the model surface and in the near volume while a structured grid was used in the rest of the domain. An unsdeady RANS approach was used and the turbulence was modelled using the Menter implementation of the k-ω model. No wall functions were used and the boundary layer was fully resolved. The first part of the paper focuses on the mannequin while in the second part the comparison between the experimental results and simulation on the real cyclist are presented. An overall good agreement between the simulations and the experiments was found proving that CFD could be a complementary tool to wind tunnel testing.

International Journal of Environmental Research and Public Health, 2020

The drag crisis phenomenon is the drop of drag coefficient (Cd) with increasing Reynolds number (Re) or speed. The aim of this study was to assess the hypothetical drag crisis phenomenon in a sports setting, assessing it in a bicycle–cyclist system. A male elite-level cyclist was recruited for this research and his competition bicycle, helmet, suit, and shoes were used. A three-dimensional (3D) geometry was obtained with a 3D scan with the subject in a static aero position. A domain with 7 m of length, 2.5 m of width and 2.5 m of height was created around the cyclist. The domain was meshed with 42 million elements. Numerical simulations by computer fluid dynamics (CFD) fluent numerical code were conducted at speeds between 1 m/s and 22 m/s, with increments of 1 m/s. The drag coefficient ranged between 0.60 and 0.95 across different speeds and Re. The highest value was observed at 2 m/s (Cd = 0.95) and Re of 3.21 × 105, whereas the lower Cd was noted at 9 m/s (Cd = 0.60) and 9.63 × 1...

Wind Tunnel, InTech, …, 2011

Journal of Fluid Mechanics, 2014

Three-dimensional flows around a full-scale cyclist mannequin were investigated experimentally to explain the large variations in aerodynamic drag that are measured as the legs are positioned around the $360^\circ $ crank cycle. It is found that the dominant mechanism affecting drag is not the small variation in frontal surface area over the pedal stroke but rather due to large changes in the flow structure over the crank cycle. This is clearly shown by a series of detailed velocity field wake surveys and skin friction flow visualizations. Two characteristic flow regimes are identified, corresponding to symmetrical low-drag and asymmetrical high-drag regimes, in which the primary feature of the wake is shown to be a large trailing streamwise vortex pair, orientated asymmetrically in the centre plane of the mannequin. These primary flow structures in the wake are the dominant mechanism driving the variation in drag throughout the pedal stroke. Topological critical points have been id...

Procedia Engineering, 2010

This paper documents a wind tunnel test program that measured the aerodynamic drag (F d ), lift (F l ) and side force (F s ) of 12 contemporary time trial (TT) helmets at yaw angles of 0 to 15°. F d measurements at yaw were subjected to a novel analysis technique adapted from the automotive fuel efficiency literature to provide a single wind averaged drag ( d F ) at a velocity (v) of 14.75 m sec -1 (53 km/h). Ranked wind averaged F d measurements of TT helmets provide a simple performance index and it is recommended that this analytical procedure be adopted by the bike industry to permit uniform F d comparisons of helmets, wheels, frames and other components that are subjected to yaw angle wind tunnel tests.

International Journal of Sports Medicine, 2013

The purpose of this study was to analyse the validity, reliability and sensitivity of velodrome tests to detect small changes in aerodynamic drag in cycling. 12 professional cyclists were assessed to obtain the drag area (SCx) during wind tunnel and velodrome tests. Incremental and steady-state protocols were performed in the velodrome with a portable power meter, and 6 bicycle positions were analysed and compared that involved lowering the handlebars and advancing the pads between 2-5 cm. A significant relationship (r=0.88, p<0.001) between the SCx in the wind tunnel and velodrome tests was found (0.240 ± 0.007 and 0.237 ± 0.008 m2, respectively). The velodrome tests underestimated the SCx (0.0035 ± 0.0038 m2 and p<0.01), which decreased (p<0.001) when the bicycle speed increased (0.0013 m2 each 1 km · h(-1)). The SCx values showed high reliability during the steady-state (r=0.99, p<0.001) and incremental protocols (r=0.94, p<0.001). Small changes in the aerodynamic position affected the SCx (p<0.001), which decreased by 0.011 ± 0.007 m2 (4.6 ± 2.9%, 95% CI=2.7-6.4%). In conclusion, the validity, reliability and sensitivity of velodrome tests to detect small changes in aerodynamic drag in cycling were demonstrated. Although SCx values were not interchangeable between different studies, the velodrome tests presented advantages with respect to the wind tunnel tests.

Computer Methods in Biomechanics and Biomedical Engineering

Extending earlier computer models of bicycle peloton dynamics, we add a deceleration parameter by which deceleration magnitude varies as a function of cyclist strength. This model is validated by applying speed data from a mass-start race composed of 14 cyclists, and running simulation trials using 14 simulated cyclists that generated positional profiles which compare well with the positional profiles observed in the actual mass-start race data. Keeping constant the speed variation profile from the mass-start race as introduced into the simulation, a set of simulation experiments were run, including: varying the number of cyclists; varying the duration of a single near-threshold output event; and varying the course elevation. The results consistently show sorting of pelotons into smaller groups whose mean fitness corresponds with relative group position, i.e. fitter groups are closer to the front. Sorting of pelotons into fitness-related groups provides insight into the mechanics of similar group divisions within biological collectives in which members present heterogeneous physiological fitness capacities.

Proceedings

(MIUN, Ostersund) was opened in 2015 for sports technology research. It is dedicated to analysis of equipment performance and garment development and suitable for roller skiing, running and cycling. The aim of this work was to develop and apply a full-scale method to investigate the aerodynamic behaviour of a cyclist facing front and cross wind at different yaw angles (from 0° to 30°) and speeds. To reach this goal, a rotating structure supported by a force platform was constructed. It includes a set of rollers on which fully unrestrained cycling is possible. The method was applied to the comparison of three wheelsets (differing in material, height and shape of the rim, number and shape of spokes) in terms of drag and side aerodynamic forces during a cyclist's ride at 30 km/h, while keeping all the other factors constant. Resulting curves allowed estimating differences of 4% and 9% when applied to a recent time trial competition with supposed wind conditions.

International Journal of Sports Physiology and Performance, 2021

Cycling time trials are characterised by riders adopting aerodynamic positions, to lessen the impact of aerodynamic drag on velocity. The optimal performance requirements for time trials likely exists on a continuum of rider aerodynamics versus physiological optimisation, yet there is little empirical evidence to inform riders and coaches. The aim of the present study was to investigate the relationship between aerodynamic optimisation, energy expenditure, heat production and performance. Methods Eleven trained cyclists completed five submaximal exercise tests, followed by a time trial. Trials were completed at hip angles of 12˚ (more horizontal), 16˚, 20˚, 24˚ (more vertical) and their self-selected control position. Results The largest decrease in power output at anaerobic threshold compared to control occurred at 12˚ (-16±20W, P=0.026; ES=0.8). There was a linear relationship between upper body position and heat production (R 2 =0.414, P=0.037) but no change in mean body temperature, suggesting that as upper body position and hip angle increase, convective and evaporative cooling also rise. The highest aerodynamic-physiological economy occurred at 12˚ (384 ± 53 W. CdA. L. min-1, ES = 0.4) and the lowest at 24˚ (338 ± 28 W. CdA. L. min-1 , ES = 0.7), versues control (367 ± 41 W. CdA. L. min-1). Conclusion These data suggest that the physiological cost of reducing hip angle is outweighed by the aerodynamic benefit. |These data suggest that riders should favour aerodynamic optimisation for shorter time trial events. The impact on thermoregulation and performance in the field requires further investigation.

Journal of Wind Engineering and Industrial Aerodynamics

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annual Association for the Advancement of Artificial …, 2010

A peloton is a group of cyclists whose individual and collective energy expenditures are reduced when cyclists ride behind others in zones of reduced air pressure; this effect is known in cycling as 'drafting'. Through drafting cyclists couple their energy expenditures. Coupling of cyclists' energy expenditures when drafting is the basic peloton property from which self-organized collective behaviours emerge. Here we examine peloton hysteresis, applying the definition used in the context of vehicle traffic in which a rapid deceleration to a high density state (jam) is followed by a lag in vehicle acceleration. Applying a flow analysis of volume (number of cyclists) over time, peloton hysteresis is examined in three forms: one is similar to vehicle traffic hysteresis in which rapid decelerations and increased flow (or density) are followed by extended acceleration periods and reduced flow. In cycling this is known as the accordion effect. A second kind of hysteresis results from rapid accelerations followed by periods of decreasing speeds and decreasing flow. This form of hysteresis is essentially inverse to traffic hysteresis and the accordion effect. We show this form of hysteresis using data from a mass-start bicycle points-race. A third kind of peloton hysteresis occurs when the drafting benefit is minimized on hills and weaker cyclists lose positions in the peloton, while flow/density is retained. A computer simulation shows this hysteresis among two sets of cyclist agents, each with different output capacity and models hysteresis as a peloton transitions from flat topography to a steep incline on which drafting is negligible.