In cycling aerodynamics, the NACA airfoil and teardrop shape have been widely used on bicycles recently. However, both of their aerodynamic performances are still being questioned in low Reynolds number range (30 000-80 000) due to early flow separation and vortex generation.
The aim of this project was to find a new geometric design providing better aerodynamic performance compared with the traditional symmetric NACA airfoil and teardrop shape at a certain Reynolds number range using 2D Computational Fluid Dynamics (CFD). By studying the flow separation point, aerodynamic coefficients and flow development on many different foils having the same chord length and thickness, we defined all the important geometric parameters influencing the performance. Our final CFD results gave us a new geometry called TE (Truncated Ellipse) which follows most of the Kammtail principles. The TE shows a much lower drag coefficient along the chord direction of the foil compared with the symmetric NACA airfoil and the teardrop shape. At low yaw angles (≤ 10 degrees), the performance is better the TE foil is acting as a bluff body and thus the flow separation is delayed. At higher yaw angles (>10 degrees), the aerodynamic drag coefficient combined with an extremely high aerodynamic lift coefficient give a much lower drag coefficient along the chord direction. This high aerodynamic lift is given by the separation bubble found on the TE at a high yaw angle. This research has implications on the future prospects of aerodynamic bicycle design.

Keywords: Cycling aerodynamics, CFD, Flow separation, Aerodynamic coefficients, Streamlining.

ABBOTT, I. H., VON DOENHOFF, A. E. (1959). Theory of Wing Sections. Dover Publishing, New York.
ALAM, F., SUBIC, A. and AKBARZADEH, A. (2008). Aerodynamics of bicycle helmets, in M. Estivalet & P. Brisson (eds), The Engineering of Sport 7, vol. 1, Springer, Paris, pp. 337–344.
ANSYS FLUENT user guide, p.333-334.
BURKE, E. (2003). High-Tech Cycling. Second Ed.
CHABROUX, V., BARELLE, C., and FAVIER, D. (2008). Aerodynamics of time trial bicycle helmets, in M. Estivalet & P. Brisson (eds), The Engineering of Sport 7, vol. 2, Springer, Paris, pp. 401–410.
CROUCH T. N., BURTON D., BROWN N. A. T., THOMPSON M. C., and SHERIDAN J. (2014). Flow topology in the wake of a cyclist and its effect on aerodynamic drag. J. Fluid Mech 748, 5–35.
DEFRAEYE, T., BLOCKEN, B., KONINCKX, E., HESPEL, P., CARMELIET, J. (2011). CFD analysis of drag and convective heat transfer of individual body segments for different cyclist positions, Department of Civil Engineering, Katholieke Universiteit Leuven, Heverlee, Belgium.
ELINI, D. C., ATHANASIOS, T. I., and DIONISSIOS, M. P. (2012). Evaluation of the turbulence models for the simulation of the flow over a National Advisory Committee for Aeronautics (NACA) 0012 airfoil, Department of Mechanical Engineering and Aeronautics, Fluid Mechanics Laboratory (FML), University of Patras, 26500 Patras, Greece.
GIBERTINI, G., GRASSI, D. (2008). Sports Aerodynamics, Helge Norstrud Editor, pp.23-48.
GIBERTINI, G., GRASSI, D., MACCHI, M. and DE BORTOLI, G. (2010). Cycling shoe aerodynamics, Sports Engineering 12(3): 155–161.
GIBERTINI G., CAMPANARDI G., GRASSI D., and GUERCILENA L. (2011). The Study of Details Effects in Cycling Aerodynamics: Comparison between Two Different Experimental Approaches, Politecnico di Milano - Dipartimento di Ingegneria Aerospaziale, Italy.
GODO, M. N., CORSON, D., and LEGENSKY, S. M. (2010). A comparative aerodynamic study of commercial bicycle wheels using CFD, Intelligent Light, Acussim Software.
HARDER, P., CUSACK, D., MATSON, C., LAVERY, M. (2010). Airfoil Development for the Trek Speed Concept Triathlon Bicycle.
HOFFMAN, J. (2006). Simulation of turbulent flow past bluff bodies on coarse meshes using General Galerkin methods: drag crisis and turbulent Euler solutions, Comp. Mech. 38 pp.390-402.
HOFFMAN, J. and JANSSON, N. (2009). A computational study of turbulent flow separation for a circular cylinder using skin friction boundary conditions, in proceedings for Quality and Reliability of Large-Eddy Simulations II, Pisa, Italy.
HOFFMAN, J., JOHNSON, C. (2011). Analysis of Separation in Turbulent Incompressible Flow, Computational technology laboratory, School of computer science and communication, Royal Institute of technology.
HOSOI, A. E. (2014). Drag kings: characterizing large-scale flows in cycling aerodynamics, Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA.
HU, H., YANG, Z. (2008). An Experimental study of the laminar flow separation on a low-Reynolds-number airfoil, Journal of fluid engineering, vol. 130.
KYLE, C.R. & BURKE, E.R. (1984). Improving the racing bicycle. Mechanical Engineering, 106 (9), 34–35.
KYLE, C. R. (1989). The aerodynamics of handlebars & helmets, Cycling Science 1(1): 22–25.
KYLE, C. R. (1990). Windtunnel tests of bicycle wheels & helmets, Cycling Science 2(1): 27–30.
LINDSEY W. F. (1937). Report No.619, Drag Of Cylinders Of Simple Shape, Langley Memorial Aeronautical Laboratory, National Advisory Committee For Aeronautics, Langley Field, VA.
LUKES, R. A., CHIN, S. B. & HAAKE, S. J. (2005). The understanding and development of cycling aerodynamics. Sports Engng 8 (2), 59–74.
MARZOUK, O., NAYFEH, A. H., ARAFAT, H. N., AKHTAR, I. (2006). Modeling Steady-State and Transient Forces on a Cylinder, Virginia Tech, Blacksburg, VA 24061.
NAYFEH, A. H., OWIS, F., HAJJ, M. R. (2003). A model for the coupled lift and drag on a circular cylinder, Proceedings of DETC03, ASME 2003 Design Engineering Technical Conferences and Computers and Information in Engineering Conference.
NONWEILER, T. (1956). The air resistance of racing cyclists. Cranfield College of Aeronautics, Cranfield.
PRAMPERO DI, P.E., CORTILI, G., MOGNONI, P. & SAIBENE, F. (1979). Equation of motion of a cyclist. Journal of Applied Physiology, 47 (1), 201–206.
SAYER, A. & STANLEY, P. (1994). Drag force on rotating racing cycle wheels, Journal of Wind Engineering and Industrial Aerodynamics 53(3): 431–440.
SHELDAHL, R. E., KLIMES, P. C. (1981). Aerodynamic Characteristics of seven symmetrical airfoil sections through 180-degree angle of attack for use in aerodynamic analysis of vertical axis wind turbines
TEW, G. & SAYER, A. (1999). Aerodynamics of yawed racing cycle wheels, Journal of Wind Engineering and Industrial Aerodynamics 82(1): 209–222.
UCI cycling regulations, General organization of cycling as a sport.
VERSTEEG H. K., MALALASEKERA W. (2007). An Introduction to Computational Fluid Dynamics – The Finite Volume Method, 2nd edition, Pearson, Prentice Hall.
WHITE, F. M. (2006). Viscous Fluid Flow, McGraw-Hill International edition, 3rd edition.
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.