Cyclist Reynolds number effects and drag crisis distribution

Terra, Wouter; Sciacchitano, Andrea; Scarano, Fulvio

doi:10.1016/j.jweia.2020.104143

Cited by 18 publications

(8 citation statements)

References 37 publications

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“…As far as the authors’ understanding goes, only two papers have assessed the drag crisis in cycling, notably on a cyclist’s leg [ 20 ] and the wake length influence on Re [ 23 ]. However, no study has reported the C d variations across different speeds on an elite road cyclist.…”

Section: Introductionmentioning

confidence: 99%

The Drag Crisis Phenomenon on an Elite Road Cyclist—A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds

Forte

Morais

Neiva

et al. 2020

IJERPH

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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 × 105. A drag crisis was noted between 3 m/s and 9 m/s. Pressure Cd ranged from 0.35 to 0.52 and the lowest value was observed at 3 m/s and the highest at 2 m/s. The viscous drag coefficient ranged between 0.15 and 0.43 and presented a trend decreasing from 4 m/s to 22 m/s. Coaches, cyclists, researchers, and support staff must consider that Cd varies with speed and Re, and the bicycle–cyclist dimensions, shape, or form may affect drag and performance estimations. As a conclusion, this preliminary work noted a drag crisis between 3 m/s and 9 m/s in a cyclist in the aero position.

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Section: Introductionmentioning

confidence: 99%

The Drag Crisis Phenomenon on an Elite Road Cyclist—A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds

Forte

Morais

Neiva

et al. 2020

IJERPH

View full text Add to dashboard Cite

show abstract

“…The increasing turbulence observed when behind a group of riders, even when they are 125 m ahead of a cyclist, is an important result as the majority of cycling aerodynamic research is conducted using low-turbulence wind tunnels or computational fluid dynamics models 12 , 15 , 16 , 20 . Turbulence properties can change the characteristics of the flow around a rider, particularly the initiation of laminar-to-turbulent transition in the boundary layer, which dictates the occurrence of the drag crisis 32 – 34 . It has been previously shown for speed skating, which operates in a very similar Reynolds number range to track cycling, that replicating on-track turbulence in a wind tunnel can induce the drag crisis at a lower wind speed compared to low-turbulence results 19 .…”

Section: Discussionmentioning

confidence: 99%

Measurements of roll, steering, and the far-field wake in track cycling

Fitzgerald

Kelso

Grimshaw

et al. 2022

Sci Rep

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A series of measurements taken with two instrumented track bicycles in a velodrome are presented. The bicycle wheel speed, cadence, roll angle, steering angle, power, and airspeed are recorded. The experimentally-measured values are compared to existing theoretical models of roll and steering angles. The accuracy of the roll angle calculations is dependent on the fidelity of the modelled cyclist path and decreases for higher riding speeds. Experimental measurements of the steering angle show a reasonable agreement to theoretical calculations, albeit with reduced steering angles on the bends at higher speeds. There is also seen an increasing steering angle oscillation within each pedal cycle with increasing bicycle velocity which may influence a cyclist’s rolling resistance and the aerodynamic flow around the bicycle’s front end. Observations are made of changes in the flow field ahead of the bicycle due to the presence of other riders on the track, showing an effective tailwind of up to 0.7 m/s. The measured power shows a decrease at the bend entry due to the changing roll angle. Data presented in this paper provides new insights and can help to provide a validation of values used in existing track cycling analytic models.

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“…Despite the large difference in Reynolds number, they observed a good agreement between the flow fields of both configurations. Among the studies highlighting the effects of the Reynolds number on the cyclist aerodynamics we mention Terra et al [24] that experimentally investigated the Reynolds number influence on the wakes of the arms and legs of a model cyclist varying the velocity in the range 5-25 m/s ( Re = 2.3 × 10 5 -1.2 × 10 6 ) by means of PIV measurements in wind tunnel. They estimated the drag coefficient in terms of the change in wake width and they observed a reduction of C x induced by the body limbs increasing Re, namely in the mid arm region and in the lower leg region.…”

Section: Single Rider Aerodynamicsmentioning

confidence: 99%

Preliminary study on crosswind aerodynamics for a group of road race cyclists

et al. 2021

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Under crosswind conditions, road cyclists experience an extra drag force and a destabilising lateral force. In these conditions a group of cyclists manages to reorganise its spatial formation to minimise these forces forming an echelon, i.e a diagonal single pace line of riders staggered across the road, a configuration which is markedly different from those adopted in wind-free conditions. To study the effect of the crosswind on drag and lateral forces on the riders we performed wind-tunnel experiments using a scale model cyclist and measuring the forces by means of a load cell. Several configurations with one, two, and four cyclists have been investigated varying yaw angles. Results show that, in a basic 4 rider configuration at a 50 $$^{\circ }$$ ∘ yaw angle, a sheltered rider within the echelon experiences less than 30% of the drag of the guttered rider behind the echelon, struggling against the crosswind. Furthermore, we show that an echelon is worth being adopted under crosswind conditions only beyond a 30 $$^{\circ }$$ ∘ yaw angle. At this critical 30 $$^{\circ }$$ ∘ yaw angle the drag on the guttered rider doubles when the gap to the front group increases from 10 cm to 1 m (in real scale). These results can be of interest in defining road cycling race strategies and they allow some significant configurations to be identified and further investigated in more complex experiments.

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Cyclist Reynolds number effects and drag crisis distribution

Cited by 18 publications

References 37 publications

The Drag Crisis Phenomenon on an Elite Road Cyclist—A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds

The Drag Crisis Phenomenon on an Elite Road Cyclist—A Preliminary Numerical Simulations Analysis in the Aero Position at Different Speeds

Measurements of roll, steering, and the far-field wake in track cycling

Preliminary study on crosswind aerodynamics for a group of road race cyclists

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