Flow topology in the wake of a cyclist and its effect on aerodynamic drag

T. N. Crouch, D. Burton, N. A T Brown, M. C. Thompson, J. Sheridan

Research output: Contribution to journalArticle

34 Citations (Scopus)

Abstract

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° 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 identified on the suction surfaces of the mannequin's back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low- and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin's back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.

Original languageEnglish
Pages (from-to)5-35
Number of pages31
JournalJournal of Fluid Mechanics
Volume748
DOIs
Publication statusPublished - Jun 2014
Externally publishedYes

Fingerprint

aerodynamic drag
Aerodynamic drag
wakes
drag
Drag
topology
Topology
Flow structure
pedals
suction
eccentrics
strokes
velocity distribution
cycles
three dimensional flow
skin friction
Skin friction
flow visualization
flow characteristics
Flow visualization

Cite this

Crouch, T. N. ; Burton, D. ; Brown, N. A T ; Thompson, M. C. ; Sheridan, J. / Flow topology in the wake of a cyclist and its effect on aerodynamic drag. In: Journal of Fluid Mechanics. 2014 ; Vol. 748. pp. 5-35.
@article{fe0a54adb4bc4e659f0ad1f9ffcac14b,
title = "Flow topology in the wake of a cyclist and its effect on aerodynamic drag",
abstract = "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° 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 identified on the suction surfaces of the mannequin's back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low- and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin's back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.",
keywords = "aerodynamics, wakes/jets",
author = "Crouch, {T. N.} and D. Burton and Brown, {N. A T} and Thompson, {M. C.} and J. Sheridan",
year = "2014",
month = "6",
doi = "10.1017/jfm.2013.678",
language = "English",
volume = "748",
pages = "5--35",
journal = "Journal of Fluid Mechanics",
issn = "0022-1120",
publisher = "Cambridge University Press",

}

Flow topology in the wake of a cyclist and its effect on aerodynamic drag. / Crouch, T. N.; Burton, D.; Brown, N. A T; Thompson, M. C.; Sheridan, J.

In: Journal of Fluid Mechanics, Vol. 748, 06.2014, p. 5-35.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Flow topology in the wake of a cyclist and its effect on aerodynamic drag

AU - Crouch, T. N.

AU - Burton, D.

AU - Brown, N. A T

AU - Thompson, M. C.

AU - Sheridan, J.

PY - 2014/6

Y1 - 2014/6

N2 - 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° 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 identified on the suction surfaces of the mannequin's back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low- and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin's back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.

AB - 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° 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 identified on the suction surfaces of the mannequin's back and are discussed with velocity field measurements to elucidate the time-average flow topologies, showing the primary flow structures of the low- and high-drag flow regimes. The proposed flow topologies are then related to the measured surface pressures acting on the suction surface of the mannequin's back. These measurements show that most of the variation in drag is due to changes in the pressure distribution acting on the lower back, where the large-scale flow structures having the greatest impact on drag develop.

KW - aerodynamics

KW - wakes/jets

UR - http://www.scopus.com/inward/record.url?scp=84899495961&partnerID=8YFLogxK

UR - http://www.mendeley.com/research/flow-topology-wake-cyclist-effect-aerodynamic-drag-1

U2 - 10.1017/jfm.2013.678

DO - 10.1017/jfm.2013.678

M3 - Article

VL - 748

SP - 5

EP - 35

JO - Journal of Fluid Mechanics

JF - Journal of Fluid Mechanics

SN - 0022-1120

ER -