小型風力發電機之葉片減噪研究

Abstract

大型風力發電機多半安裝於人煙較稀少的郊外或沿海地區，而小型風力發電機則裝於市區內或建物屋頂上，小型風力發電機在運轉所產生的噪音，會影響附近居民的居住品質與生活安寧。本文主要探討如何解決小型風力發電機在運轉時，葉片翼尖所產生之低頻噪音的問題。首先利用儀器量測實際聲場狀況，得知其噪音頻率範圍，吸音結構主要採用荷姆霍茲共振器結構，並透過吸音係數量測實驗(ASTM E1050-98:雙麥克風實驗)測量結構的吸音特性，驗證吸音結構理論的正確性。吸音結構的材料主要為寶特瓶、玻璃纖維、組合木，並安裝於玻璃纖維束製成的桁架上，最後構成環狀減噪裝置，架設在小型風力發電機葉片的翼尖區域處，減少風力發電機在轉動時，葉片翼尖所產生的噪音，同時也可降低葉片結構損壞時，所造成的公安危害。以風機實測到的噪音頻率為500Hz設計吸音結構，考慮實際製作的誤差，吸音結構的實際減噪頻率為425Hz，實驗結果得知裝載425Hz吸音結構的減噪裝置在該頻率可減少22dB，而在其他頻率(100Hz-1200Hz)中，噪音減少的分貝從8dB到34dB不等。

Most of the large wind turbines are builtin sparsely populated areas, along the shores or on the outskirts, while the small wind turbines are built on rooftops or in urban areas, where the noise greatly affects the residents. The purpose of the thesis is to explore the solution to the low frequency noise caused by the blade tips of the small wind turbine during operation. The noise frequency range is acquired by testing in a real acoustic field using the acoustic apparatus. The Helmholtz resonator is used for the main sound absorbing structure, which is tested through the ASTM E1050-98 (dual microphones experiment) to determine the sound absorption properties and prove the accuracy of the theories. The sound absorbing structure is composed of plastic bottles, glass fiber, and wood, and is fixed onto a truss made of glass fiber, forming a ring-shaped sound absorbing device. The device is then set up around the blade tips to reduce the noise when the small turbine is operating, and to prevent the broken pieces of the wind blades from scattering when they are damaged.The sound absorbing structure is designed according to the noise frequency range acquired by testing of the blade in a real acoustic field, which is 100-1000Hz. In particular, the noise at the target frequency of 500Hz is to be reduced. Due to the error in the manufacturing process, the actual target frequency becomes 425Hz. The results show that the sound absorbing device equipped with the Helmholtz resonators tuned at 425Hz reduces the noise by 22dB, and the noise in the range from 100Hz to 1200 Hz by 8dB to 34dB.