| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 103 === In cycling aerodynamics, many kinds of foils have been used on bicycles during the History (cylinder, tear drop or NACA). The aerodynamic performances in low Reynolds number are studied because of the early flow separation and vortex generation.
From a scientific paper presenting a new foil which has remarkable aerodynamic performances, the project has been launched. The aim is to find a new geometric design providing better aerodynamic performances like the TE (Truncated Ellipse) and the TEM (Truncated Ellipse Modified) in low Reynolds number for 2D and 3D simulations.
Different geometric parameters influence the performances as the thickness and the chord length.
The final CFD results give us the TEM which follows the Kammtail principles. This design shows a lower drag coefficient than TE or NACA. At low yaw angles (≤ 10 degrees), the TEM has better performances and 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 gives a much lower drag coefficient along the chord direction. This high aerodynamic lift is given by the separation bubble found on the TEM at a higher yaw angle.
About 3D simulations, at low yaw angle, the cycling drag coefficient is close to the 2D simulations. But at higher yaw angle, the performances are damaged due to the lift-induced drag. And these results are confirmed by experiences (dye injection, PIV).
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