荷姆霍茲共振器對小型風機之減噪研究

Abstract

本文主要探討利用荷姆霍茲共振器改善小型風力發電機之噪音，並針對產生噪音的區塊設計減噪裝置，進行特定頻率範圍的減噪工作。首先進行吸音係數量測實驗 (ASTM E1050-98:雙麥克風實驗)，驗證荷姆霍茲共振器其吸音係數是否能顯示出在共振頻率下有消音及降低音量的效果。利用有限元素軟體ANSYS模擬荷姆霍茲共振器之聲場，證明所建立之分析模型合理後，即可經由分析來設計不同結構之荷姆霍茲共振器。將荷姆霍茲共振器與多孔性吸音材搭配以增加消音頻寬，利用雙麥克風實驗量測材料之吸音係數，設計出消音效果最好的組合。 使用有限元素軟體ANSYS模擬風機運用減噪裝置後對聲場之影響，預測在所設計的消音頻率範圍內，荷姆霍茲共振器能否使整體風機的噪音降低，最後由電扇模擬風機所產生之噪音，並進行減噪實驗，結果證明本減噪裝置確實能達到減噪的目的。

The goal of the thesis is to explore the potential use of Helmholtz resonator for tackling the noise problems caused by small wind turbines. The capabilities of different types of Helmholtz resonators are investigated via both theoretical and experimental approaches. The most appropriate type of Helmholtz resonator is used to design a noise reductive device for reducing the noise generated by a wind turbine within a specific frequency range. In the experimental study, a sound absorption measurement instrument (ASTM E1050-98: dual microphones experiment) was fabricated to measure the sound absorption coefficients of different types of Helmholtz resonators and study the characteristics (magnitude of sound absorption coefficient and frequency range) of the Helmholtz resonators. In the theoretical study, the finite element (FE) code ANSYS is used to simulate the sound fields of different Helmholtz resonators. The experimental results are used to verify the suitability of the proposed FE models. It has been shown that among the resonators under consideration, the Helmholtz resonator comprises glass-fabric perforated cover plate and hollow box fabricated with porous material can produce the best sound absorption capability for wind turbine application. The results of ANSYS sound field simulations of a small wind turbine with noise reductive device have shown that the proposed noise reduction device does have the noise reduction effects on the sound field generated by the wind turbine. Finally, a simple noise reduction experiment in which the proposed noise reduction device was used to reduce the noise generated by a small fan was conducted to further demonstrate the capability of the proposed noise reduction device. The results have indicated that this noise reduction device achieves the goal of noise reduction and has the potential to find applications in wind turbines.