WONG H.   Miau J.  

Flow Separation Control with a Truncated Ellipse Airfoil In Cycling Aerodynamics

Reporter: WONG H.

Flow Separation Control with a Truncated Ellipse Airfoil in Cycling Aerodynamics
Department of Aeronautics and Astronautics, National Cheng Kung University, Tainan, Taiwan (R.O.C)
Research Center for Energy Technology and Strategy, National Cheng Kung University Tainan, Taiwan(R.O.C)


Aerodynamic resistance is always an issue in competitive cycling. In order to gain aerodynamic advantages and structural stiffness of the bike, the teardrop shape is widely used by bicycle manufacturers today. It is a combination of a circular cylinder and symmetric NACA airfoil. Although it does provide drag reduction, this design still suffers from early flow separation and vortex generation in the low Reynolds number range (30000-50000). Studying the pressure distribution and flow development on a number of airfoils with Computational Fluid Dynamics (CFD), we were able to obtain a new airfoil design called the Truncated Ellipse (TE). The TE shows a much lower drag coefficient and flow separation delay compared with the teardrop shape. In our flow visualization experiment we compared a TE airfoil and a teardrop shape with the same chord length and width using dye-injection and the Particle Image Velocimetry (PIV) method in a water channel and the oil-film method in a wind tunnel, respectively. The experimental results show that the TE has flow separation occurred at the base of the airfoil at a 0 degree yaw angle and delayed flow separation at low yaw angles (<15 degrees) due to the development of a separation bubble near the leading edge . This indicates that the TE airfoil has much better aerodynamic performance than the teardrop shape. Our research has implications for the future prospects of aerodynamic bicycle design.

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