| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 88 === This thesis is intended to study the basic turbine cascade flow and apply acoustic excitation into the flow field. Acoustic excitation is employed to improve the aerodynamic performance of the turbine blade by moving backward the laminar separation point and moving forward the turbulent separation point. It especially modifies the pressure distribution on the suction surface of the blade, resulting in moving the aerodynamic load forward.
The 3D-turbine blade with rotating turbine axis is simulated by 2D-turbine cascade. The variations of parameters of turbine cascade (such as flow angle stagger angle , which directly affect the configuration of the wind tunnel and its flow field, were considered when designing the wind tunnel. In this study, the wind tunnel is designed to match 9 groups of the configuration parameters of turbine cascade.
The pressure and velocity measurements are conducted to calculate the averaged pressure coefficients on the suction and pressure surfaces and to investigate the wake properties behind the turbine cascade. The required parameters in the experiments include averaged flow velocity and its fluctuation intensity(U+u′), pressure coefficients(Cp) on blade surface, energy spectrum in the wake, and inflow Reynolds number(Re).
Acoustic excitation technique is performed with external excitation and internal excitation. According to the experimental results, effective excitation frequencies fall in the range between 100 and 400 Hz. Internal excitation significantly modifies the pressure distribution on the suction surface of the blade more than the external excitation. The lock-in phenomenon occurs in the wake when acoustic excitation is applied. Concerning the mode shape of the acoustic inputs, the square waves of acoustics contribute more in the variation of pressure distribution on the suction surface than the sinusoidal acoustics, when operates in the low Reynolds number (Re<36000).
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