Analysis of aerodynamic sound noise generated by a large-scaled wind turbine and its physiological evaluation

Aerodynamic noise generated from a modern large-scale wind turbine was measured and analyzed from an engineering point of view. The measurement items were the sound, the sound pressure level (including the infrasound with extremely low-frequency band) and the corresponding physiological evaluation. Fifteen test subjects received various sound stimuli, including the recorded aerodynamic noise and a synthetic periodical sound, were examined with an electroencephalogram as a physiological evaluation. It was observed from the mapping patterns of brain waves that alpha (1) rhythm, which indicates a relaxed and concentrated state, after the sound stimulus with the frequency band of 20 Hz, showed the lowest value among the other cases. That is, the test subjects cannot keep relaxed and their concentration after hearing the sound stimulus at the frequency band of 20 Hz. The induced rate of alpha (1) rhythm almost decreased when the test subjects listened to all the sound stimuli, and further decreased with decreased frequency. Meanwhile, beta (1) rhythm, which shows a strain state, after the sound stimulus with the frequency band of 20 Hz, showed the highest value among the other cases. Therefore, the infrasound (e.g., low frequency and inaudible for human hearing) was considered to be an annoyance to the technicians who work in close proximity to a modern large-scale wind turbine.