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

  • T. N. Crouch (a1), D. Burton (a1), N. A. T. Brown (a2), M. C. Thompson (a1) and J. Sheridan (a1)...
Abstract
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.

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Corresponding author
Email address for correspondence: timothy.crouch@monash.edu
References
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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), 5360.
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), 367380.
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.
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), 375383.
Hornung H. & Perry A. E. 1984 Some aspects of three-dimensional separation. I—Streamsurface bifurcations. Z. Flugw. Welt. 8, 7787.
Hucho W. & Sovran G. 1993 Aerodynamics of road vehicles. Annu. Rev. Fluid Mech. 25 (1), 485537.
Kyle C. R. & Burke E. R. 1984 Improving the racing bicycle. Mech. Engng 106 (9), 3445.
Langston L. S. & Boyle M. T. 1982 A new surface-streamline flow-visualization technique. J. Fluid Mech. 125 (1), 5357.
Lukes R. A., Chin S. B. & Haake S. J. 2005 The understanding and development of cycling aerodynamics. Sports Engng 8 (2), 5974.
Maltby R. L.1962 Flow visualization in wind tunnels using indicators. Tech. Rep. DTIC Document.
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.
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, 276291.
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.
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.
Mercker E. & Wiedemann J. 1996 On the correction of interference effects in open jet wind tunnels. SAE Trans. J. Engines 105 (6), 795809.
Peake D. J. & Tobak M. 1982 Three-dimensional separation and reattachment. DTIC Document 84221.
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), 125155.
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), 81107.
Shepherd I. C. 1981 A four hole pressure probe for fluid flow measurements in three dimensions. J. Fluids Engng 103, 590594.
Cameron T., Yarin A. & Foss J. F.(Eds) 2007 Springer Handbook of Experimental Fluid Mechanics. vol. 1. Springer.
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, 2128.
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), 353396.
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Journal of Fluid Mechanics
  • ISSN: 0022-1120
  • EISSN: 1469-7645
  • URL: /core/journals/journal-of-fluid-mechanics
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