Investigating cycling aerodynamic can play an important role in addressing the issue of drag reduction while each cyclist want to archive higher speed within less resistance to be winner in the bicycle tour. Up to now, many methods are applied to optimize that value such as decreasing frontal area, using aero-shape for helmet, bike frame. However, before solving those problems, the first important understanding is to describe clearly flow fields behind cyclist that has long been a question of great interest in a wide range of flow behaviors.
This study aimed at to explore flow structures near the cyclist body by using Computational Fluid Dynamics (CFD). Hence, the most significant purpose is to show how flow is generated from the body, then, to explain why wakes has largest contribution to aerodynamic drag from numerical simulation perspective. A 1:5 scaled cyclist model of hood position, which is reproduced by 3D printing technology, is used to describe in detail all surface of the cyclist body. Accordingly, CFD results can provide a state of the art dominant flow structure nearest real case. In addition, other members in our team will do other necessary works such as: drag measurement, hot-wire experiment, flow visualization. The results are obtained from them will verify simulation methodology. This is a key aspect of this thesis is to compare and try to adjust CFD method with experiments.
The main challenge faced by many previous simulating aerodynamic characteristics of sport athletes is to identify large-scale flow structure, because this model is complicate and the phenomena happened as flow past a bluff body. Recently, investigators have observed that they used Large Eddy Simulation (LES) method to solve that problem and obtained a good agreement with experiment. This research shows that a comprehensive understanding of the LES theory and applying compatibly into experiment in water channel and wind tunnel.
As a result, the simulation is classified by two cases. The first case is carried out at Re=11000 with working fluid is water. We can explore unsteady flow developed near the body by doing dye injection, ink dot experiment while using laser sheet. Besides, In CFD results, LES Smagorinsky’s method will analyze near wake flow region from skin-friction line. In particular, some critical points will explain how flow move out the body surface such as: separation line, attachment line, foci, saddle point. In the second case, LES Wall Adapting Local Eddy (WALE) model was employed to simulate flow at higher Reynolds number (65000) that corresponds to hot-wire experiment, which was performed in a wind tunnel. This case focus on time mean and instantaneous results to evaluate effect of wake on aerodynamic drag. Furthermore, some analysis relate to far wake region will provide an understanding of turbulence to develop a quantitative picture. It considers characteristic of coherent structure, wake development and dissipation to explain the results of flow near wake region. In addition, drag coefficient has a small error with results of force balance, which is designed by our teammate. The error of this coefficient is 5.9%. After doing two cases, we can know better flow structure that is helpful in our future purposes is to reduce drag.
For this reason, an experiment of roughness on teardrop is aimed at wind tunnel to measure drag coefficient by using different tapes and sandpaper. It likes a referenced example for cyclist experiment. Therefore, we know some kinds of tape, roughness height can use for drag reduction, which means its roughness height will effect to boundary layer and change the flow behaviors. From that knowledge, in the future, the same method can be applied into full-scale cyclist model to study more about effect of roughness on drag reduction.

ANDERSSON, B. 2012. Computational fluid dynamics for engineers, Cambridge, Cambridge University Press.
BARRY, N., BURTON, D., SHERIDAN, J., THOMPSON, M. & BROWN, N. A. T. 2016. An Analysis of the Wake of Pedalling Cyclists in a Tandem Formation. Procedia Engineering, 147, 7-12.
BEASHEL, P., TAYLOR, J. & ALDERSON, J. 1996. Advanced studies in physical education and sport, Walton-on-Thames, Nelson.
BIXLER, G. D. & BHUSHAN, B. 2013. Fluid Drag Reduction with Shark-Skin Riblet Inspired Microstructured Surfaces. Advanced Functional Materials, 23, 4507-4528.
BLOCKEN, B., DEFRAEYE, T., KONINCKX, E., CARMELIET, J. & HESPEL, P. 2013. CFD simulations of the aerodynamic drag of two drafting cyclists. Computers & Fluids, 71, 435-445.
BRADSHAW, P. 1976. Turbulence, Berlin ; New York, Springer-Verlag.
BURKE, E. 1986. Science of cycling, Champaign, Ill. ; Leeds, Human Kinetics.
CECCIO, S. L. 2010. Friction Drag Reduction of External Flows with Bubble and Gas Injection. Annual Review of Fluid Mechanics, 42, 183-203.
COOPER, K. R. 2008. 5th International Colloquium on Bluff Body Aerodynamics and Applications - July 11 to 15, 2004 Ottawa, Canada - Foreword. Journal of Wind Engineering and Industrial Aerodynamics, 96, Vii-Vii.
CROUCH, T. 2014. Flow topology & large-scale wake structures around elite cyclists. PhD, Monash University.
CROUCH, T. N., BURTON, D., BROWN, N. A. T., THOMPSON, M. C. & SHERIDAN, J. 2014. Flow topology in the wake of a cyclist and its effect on aerodynamic drag. Journal of Fluid Mechanics, 748, 5-35.
CROUCH, T. N., BURTON, D., THOMPSON, M. C., BROWN, N. A. T. & SHERIDAN, J. 2016a. Dynamic leg-motion and its effect on the aerodynamic performance of cyclists. Journal of Fluids and Structures, 65, 121-137.
CROUCH, T. N., BURTON, D., VENNING, J. A., THOMPSON, M. C., BROWN, N. A. T. & SHERIDAN, J. 2016b. A Comparison of the Wake Structures of Scale and Full-scale Pedalling Cycling Models. Procedia Engineering, 147, 13-19.
CUCITORE, R., QUADRIO, M. & BARON, A. 1999. On the effectiveness and limitations of local criteria for the identification of a vortex. European Journal of Mechanics - B/Fluids, 18, 261-282.
DAS, P., TSUBOKURA, M., MATSUUKI, T., OSHIMA, N. & KITOH, K. 2013. Large Eddy Simulation of the Flow-Field around a Full-Scale Heavy-Duty Truck. Procedia Engineering, 56, 521-530.
DEARDORFF, J. 1970. A numerical study of three-dimensional turbulent channel flow at large Reynolds numbers. Journal of Fluid Mechanics, 41(2), 453-480.
DEBRAUX, P., GRAPPE, F., MANOLOVA, A. V. & BERTUCCI, W. 2011. Aerodynamic drag in cycling: methods of assessment. Sports Biomech, 10, 197-218.
DEFRAEYE, T., BLOCKEN, B., KONINCKX, E., HESPEL, P. & CARMELIET, J. 2010. Computational fluid dynamics analysis of cyclist aerodynamics: Performance of different turbulence-modelling and boundary-layer modelling approaches. Journal of Biomechanics, 43, 2281-2287.
DEFRAEYE, T., BLOCKEN, B., KONINCKX, E., HESPEL, P., VERBOVEN, P., NICOLAI, B. & CARMELIET, J. 2014. Cyclist Drag in Team Pursuit: Influence of Cyclist Sequence, Stature, and Arm Spacing. Journal of Biomechanical Engineering-Transactions of the Asme, 136.
DÉLERY, J. 2013. Three-dimensional separated flow topology : critical points, separation lines and vortical structures, ISTE.
DOWLING, A. P. 1989. The Effect of Large-Eddy Breakup Devices on Flow Noise. Journal of Fluid Mechanics, 208, 193-223.
DUCROS, F., NICOUD, F. & POINSOT, T. 1998. Wall-adapting local eddy-viscosity models for simulations in complex geometries. Oxford University Computing Laboratory, Oxford, UK.
FINTELMAN, D. M., HEMIDA, H., STERLING, M. & LI, F. X. 2015. CFD simulations of the flow around a cyclist subjected to crosswinds. Journal of Wind Engineering and Industrial Aerodynamics, 144, 31-41.
FU, S., LI, Q. B. & WANG, M. H. 2003. Depicting vortex stretching and vortex relaxing mechanisms. Chinese Physics Letters, 20, 2195-2198.
GARCIA-LOPEZ, J., RODRIGUEZ-MARROYO, J. A., JUNEAU, C. E., PELETEIRO, J., MARTINEZ, A. C. & VILLA, J. G. 2008. Reference values and improvement of aerodynamic drag in professional cyclists. J Sports Sci, 26, 277-86.
GEORGIADIS, N. J., RIZZETTA, D. P. & FUREBY, C. 2010. Large-Eddy Simulation: Current Capabilities, Recommended Practices, and Future Research. Aiaa Journal, 48, 1772-1784.
GIBBON, J. D. & HOLM, D. D. 2013. Stretching and Folding Processes in the 3D Euler and Navier-Stokes Equations. Procedia IUTAM, 9, 25-31.
GIBERTINI, G. & GRASSI, D. 2008. Cycling Aerodynamics. In: NØRSTRUD, H. (ed.) Sport Aerodynamics. Vienna: Springer Vienna.
GODO, M., CORSON, D. & LEGENSKY, S. 2010. A Comparative Aerodynamic Study of Commercial Bicycle Wheels Using CFD. 48th AIAA Aerospace Sciences Meeting Including the New Horizons Forum and Aerospace Exposition. American Institute of Aeronautics and Astronautics.
GRAPPE, F., CANDAU, R., BELLI, A. & ROUILLON, J. D. 1997. Aerodynamic drag in field cycling with special reference to the Obree's position. Ergonomics, 40, 1299-1311.
GREEN, S. I. 1995. Fluid vortices, Dordrecht ; London, Kluwer Academic Publishers.
GRIFFITH, M. D., CROUCH, T., THOMPSON, M. C., BURTON, D., SHERIDAN, J. & BROWN, N. A. T. 2014. Computational Fluid Dynamics Study of the Effect of Leg Position on Cyclist Aerodynamic Drag. Journal of Fluids Engineering-Transactions of the Asme, 136.
GUVEN, O., FARELL, C. & PATEL, V. C. 1980. Surface-Roughness Effects on the Mean Flow Past Circular-Cylinders. Journal of Fluid Mechanics, 98, 673-701.
HOERNER, S. F. 1965. Fluid dynamic drag : practical information on aerodynamic drag and hydrodynamic resistance, Midland Park, N.J., The Author.
HOUGHTON, E. L. 2013. Aerodynamics for engineering students, Amsterdam ; London
HUNT J.C.R., W. A. A., MOIN P. 1988. Eddies, stream and convergence zones in turbulent flows, . Center for Turbulence Research Report CTR-S88.
JIE-ZHI WU, H.-Y. M., M.-D. ZHOU 2005. Vorticity and Vortex Dynamics, Springer.
JUMARS, P. A., TROWBRIDGE, J. H., BOSS, E. & KARP-BOSS, L. 2009. Turbulence-plankton interactions: a new cartoon. Marine Ecology-an Evolutionary Perspective, 30, 133-150.
KIM, J. H., YOO, J. Y. & KANG, S. H. 2002. Dilatation and vortex stretching effects on turbulence in one-dimensional/axisymmetric flows. Aiaa Journal, 40, 2476-2482.
KYLE, C. R. 1979. Reduction of Wind Resistance and Power Output of Racing Cyclists and Runners Travelling in Groups. Ergonomics, 22, 387-397.
KYLE, C. R. & BURKE, E. 1984. Improving the Racing Bicycle. Mechanical Engineering, 106, 34-45.
LEONARD, A. 1975. Energy Cascade in Large-Eddy Simulations of Turbulent Fluid Flows. Advances in Geophysics, 18, 237-248.
LUKES, R. A., CHIN, S. B. & HAAKE, S. J. 2005. The understanding and development of cycling aerodynamics. Sports Engineering, 8, 59-74.
MA, J., WANG, F. & TANG, X. 2009. Comparison of Several Subgrid-Scale Models for Large-Eddy Simulation of Turbulent Flows in Water Turbine. Berlin, Heidelberg: Springer Berlin Heidelberg.
MCMILLAN, O. J. 1979. Direct Testing of Subgrid-Scale Models. Aiaa Journal, 17, 1340-1346.
MILLET, G. P. & CANDAU, R. 2002. Facteurs mécaniques du coût énergétique dans trois locomotions humaines. Science & Sports, 17, 166-176.
MOLLENDORF, J. C., TERMIN, A. C., 2ND, OPPENHEIM, E. & PENDERGAST, D. R. 2004. Effect of swim suit design on passive drag. Med Sci Sports Exerc, 36, 1029-35.
MOORE, J. K. 2008. AERODYNAMICS OF HIGH PERFORMANCE BICYCLE WHEELS. Master of Engineering, University of Canterbury.
NICOUD, F. & DUCROS, F. 1999. Subgrid-scale stress modelling based on the square of the velocity gradient tensor. Flow, turbulence and Combustion, 62, 183-200.
OGGIANO, L. 2010. Drag reduction and aerodynamic performances in Olympic sports. Philosophiae Doctor, Norwegian University of Science and Technology.
OLDS, T. & OLIVE, S. 1999. Methodological considerations in the determination of projected frontal area in cyclists. J Sports Sci, 17, 335-45.
POPE, S. B. 2000. Turbulent flows, Cambridge, Cambridge University Press.
PUGH, L. G. 1974. The relation of oxygen intake and speed in competition cycling and comparative observations on the bicycle ergometer. J Physiol, 241, 795-808.
QUADRIO, M. 2011. Drag reduction in turbulent boundary layers by in-plane wall motion. Philosophical Transactions of the Royal Society a-Mathematical Physical and Engineering Sciences, 369, 1428-1442.
SARAVI, S. S. 2014. An Investigation on Design and Analysis of Micro-Structured Surfaces with Application to Friction Reduction. Doctor of Philosophy, Brunel University.
SCHETZ, J. A. 1993. Boundary layer analysis, Prentice Hall.
SHANG-RU LI , M., J. J, PHUNG, M. V., TSAI, Z. X. AND LIN, S. Y 2017. Investigation on Wake Structure of a Cyclist Model at the Hoods Position. The 14th Asian Symposium on Visualization. Beijing, China.
TENNEKES, H. & LUMLEY, J. L. 1972. A first course in turbulence.
TIMOTHY CROUCH, J. S., DAVID BURTON, MARK THOMPSON, NICHOLAS A.T. BROWN 2012. A quasi-static investigation of the effect of leg position on cyclist aerodynamic drag. Procedia Engineering 34, 3–8.
TOMIYAMA, N. & FUKAGATA, K. 2013. Direct numerical simulation of drag reduction in a turbulent channel flow using spanwise traveling wave-like wall deformation. Physics of Fluids, 25.
WHITE, C. M. & MUNGAL, M. G. 2008. Mechanics and prediction of turbulent drag reduction with polymer additives. Annual Review of Fluid Mechanics, 40, 235-256.
WILCOX, D. C. 2006. Turbulence modeling for CFD.
YOON, H. S., EL-SAMNI, O. A. & CHUN, H. H. 2006. Drag reduction in turbulent channel flow with periodically arrayed heating and cooling strips. Physics of Fluids, 18.