| Summary: | 博士 === 國立成功大學 === 航空太空工程學系 === 87 === The phenomenon of flow separation on airfoils and its control have been investigated for decades. The leading-edge flap excitation, which is one of the active control concepts, has been proved to be an effective approach to improve the aerodynamic performance of the stalled airfoil. In this dissertation, experiments are conducted on a NACA 633-018 model airfoil in both wind tunnel and towing water tank to investigate the aerodynamic effect and induced flow structure of leading-edge flap excitation at stalled angles of attack. In addition to the elementary parameters of excitation frequency, amplitude and flap neutral position, six mode shapes of flap motion are applied in the experiments. Pressure distributions are measured and the aerodynamic coefficients are obtained from the surface pressure measurement and their integration. The phase-averaging technique for the pressure measurement data along with the flow visualization is applied to account for the vortex evolution and the relationship with the flap motion. The mode shape is shown to be a critical parameter in the current study. A sinusoidal mode shape is the least effective, and the optimal mode shape can increase 40%-extra lift increment compared to the sinusoidal mode. With the optimal excitation, the lift stall is postponed to a higher AOA than 28 degrees. The results show that the mode shape with a quick ramp-up, hold and then quick ramp-down motion produces the best aerodynamic improvement. The excitation effective-ness is closely related to the timing of the downstroke motion; while only at a low stalled angle of 20 degree, the ramp-up motion shows its effect on aerodynamic performance. The effect of upstroke motion at low angles of attack is then explained by different vortices developing time-scale at various angles of attack.
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