Hostname: page-component-586b7cd67f-l7hp2 Total loading time: 0 Render date: 2024-11-28T16:50:29.088Z Has data issue: false hasContentIssue false
  • English
  • Français

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

Published online by Cambridge University Press:  28 April 2014

T. N. Crouch ,
D. Burton ,
N. A. T. Brown ,
M. C. Thompson  and
J. Sheridan
T. N. Crouch*
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
D. Burton
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
N. A. T. Brown
Affiliation:
Australian Institute of Sport, Belconnen, Canberra, 2617, Australia
M. C. Thompson
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
J. Sheridan
Affiliation:
Fluids Laboratory for Aeronautical and Industrial Research (FLAIR), Department of Mechanical and Aerospace Engineering, Monash University, Clayton, VIC 3800, Australia
*
†Email address for correspondence: [email protected]
Get access Rights & Permissions [Opens in a new window]

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^\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 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.

JFM classification

Aerodynamics: Aerodynamics Wakes/Jets: Wakes/Jets
Type
Papers
Information
Journal of Fluid Mechanics , Volume 748 , 10 June 2014 , pp. 5 - 35
Copyright
© 2014 Cambridge University Press 

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Brownlie, L., Kyle, C., Carbo, J., Demarest, N., Harber, E., MacDonald, R. & Nordstrom, M. 2009 Streamlining the time trial apparel of cyclists: the Nike Swift Spin project. Sports Technol. 2 (1–2), 53–60.CrossRefGoogle Scholar
Carmer, C. F. V., Konrath, R., Schröder, A. & Monnier, J.-C. 2008 Identification of vortex pairs in aircraft wakes from sectional velocity data. Exp. Fluids 44 (3), 367–380.CrossRefGoogle Scholar
Chabroux, V., Mba, M. N., Sainton, P. & Favier, D. 2010 Wake characteristics of time trial helmets using PIV-3C technique. In 15th Int. Symp. on Applications of Laser Techniques to Fluid Mechanics, Lisbon, Portugal, 5–8 July 2010, Available at: http://ltces.dem.ist.utl.pt/lxlaser/lxlaser2010/upload/1586_lfpkgn_4.1.3.Full_1586.pdf.Google Scholar
Hooper, J. D. & Musgrove, A. R. 1997 Reynolds stress, mean velocity, and dynamic static pressure measurement by a four-hole pressure probe. Exp. Thermal Fluid Sci. 15 (4), 375–383.CrossRefGoogle Scholar
Hornung, H. & Perry, A. E. 1984 Some aspects of three-dimensional separation. I—Streamsurface bifurcations. Z. Flugw. Welt. 8, 77–87.Google Scholar
Hucho, W. & Sovran, G. 1993 Aerodynamics of road vehicles. Annu. Rev. Fluid Mech. 25 (1), 485–537.CrossRefGoogle Scholar
Kyle, C. R. & Burke, E. R. 1984 Improving the racing bicycle. Mech. Engng 106 (9), 34–45.Google Scholar
Langston, L. S. & Boyle, M. T. 1982 A new surface-streamline flow-visualization technique. J. Fluid Mech. 125 (1), 53–57.CrossRefGoogle Scholar
Lukes, R. A., Chin, S. B. & Haake, S. J. 2005 The understanding and development of cycling aerodynamics. Sports Engng 8 (2), 59–74.CrossRefGoogle Scholar
Maltby, R. L.1962 Flow visualization in wind tunnels using indicators. Tech. Rep. DTIC Document.Google Scholar
Martin, J. C., Davidson, C. J. & Pardyjak, E. R. 2007 Understanding sprint-cycling performance: the integration of muscle power, resistance, and modeling. Intl J. Sports Physiol. Perform. 2 (1), 5.CrossRefGoogle ScholarPubMed
Martin, J. C., Milliken, D. L., Cobb, J. E., McFadden, K. L. & Coggan, A. R. 1998 Validation of a mathematical model for road cycling power. J. Appl. Biomech. 14, 276–291.CrossRefGoogle ScholarPubMed
Maskell, E. C.1963 A theory of the blockage effects on bluff bodies and stalled wings in a closed wind tunnel. Tech. Rep. DTIC Document.Google Scholar
Maskell, E. C.1973 Progress Towards a Method for the Measurement of the Components of the Drag of a Wing of Finite Span. Procurement Executive, Ministry of Defence.Google Scholar
Mercker, E. & Wiedemann, J. 1996 On the correction of interference effects in open jet wind tunnels. SAE Trans. J. Engines 105 (6), 795–809.Google Scholar
Peake, D. J. & Tobak, M. 1982 Three-dimensional separation and reattachment. DTIC Document 84221.Google Scholar
Perry, A. E. & Chong, M. S. 1987 A description of eddying motions and flow patterns using critical-point concepts. Annu. Rev. Fluid Mech. 19 (1), 125–155.CrossRefGoogle Scholar
Ramberg, S. E. 1983 The effects of yaw and finite length upon the vortex wakes of stationary and vibrating circular cylinders. J. Fluid Mech. 128 (1), 81–107.CrossRefGoogle Scholar
Shepherd, I. C. 1981 A four hole pressure probe for fluid flow measurements in three dimensions. J. Fluids Engng 103, 590–594.CrossRefGoogle Scholar
Cameron, T., Yarin, A. & Foss, J. F.(Eds) 2007 Springer Handbook of Experimental Fluid Mechanics. vol. 1. Springer.Google Scholar
Zdravkovich, M. M., Ashcroft, M. W., Chisholm, S. J. & Hicks, N. 1996 Effect of cyclists’ posture and vicinity of another cyclists on aerodynamic drag. Engng Sport 1, 21–28.Google Scholar
Zhou, J., Adrian, R. J., Balachandar, S. & Kendall, T. M. 1999 Mechanisms for generating coherent packets of hairpin vortices in channel flow. J. Fluid Mech. 387 (1), 353–396.CrossRefGoogle Scholar

Crouch et al. supplementary movie

Surface pressure coefficient distributions showing the development of surface pressures throughout the crank cycle.

Download Crouch et al. supplementary movie(Video)
Video 2.9 MB

Crouch et al. supplementary movie

Contours of out of plane streamwise vorticity throughout a full pedal stroke.

Download Crouch et al. supplementary movie(Video)
Video 5.3 MB

Crouch et al. supplementary movie

Three dimensional representation of the drag map in the wake of the mannequin, coloured by intensity of total drag. Drag maps represent the integrand of Maskell's equation evaluated at each probe measurement point in the wake normalised between 0-1 by the maximum value of the integrand measured throughout the crank cycle.

Download Crouch et al. supplementary movie(Video)
Video 1.6 MB