Aeroacoustic Analysis of a Vertical Axis Wind Turbine

Abstract

Noise pollution and environmental effects have given rise to the dire need of noise reduction of sustainable energy producing equipment. Vertical Axis Wind Turbines (VAWT) are a source of renewable energy and are used for both industrial and domestic purposes. VAWT have gained importance for domestic use since they are easily driven from any direction of wind as compared to HAWT’s. The study of noise characteristics of a VAWT is critical as the VAWT’s are deployed mostly in built up areas and in order to design a low noise VAWT, their noise characteristics must be studied first. This study focuses on the development of a linear microphone array and characterizing acoustic signals on a 5-bladed VAWT in an anechoic chamber at three different TSR (Tip Speed Ratio) values. The TSR values were achieved by using axial fan and motor control. The anechoic chamber is a 15x15x11 ft cell with anechoic wedges to suppress any sound reflections for better acoustic study. The LabVIEW algorithm for logarithmic measure of effective pressure provided a range of SPL spectrums to study the effect of radial distance and TSR on noise propagation. In this experiment, similar acoustic analysis was carried out by 128 MEMS acoustic camera. The results of developed microphone array and acoustic camera depicted good qualitative agreement. The SPL spectrum of VAWT shows that tonal noises such as blade passing frequencies are dominating at lower frequencies whereas broadband noise corresponds to all audible ranges of frequencies. This study shows that the major portion of noise from the source is dominated by aerodynamic noises generated due to vortex generation and trailing edge separations. Moreover, the LabVIEW algorithm for directivity of arrival of noise predicts that maximum SPL values are directed from the trailing edge end of the blade. These observations serve as a basis for futuristic noise reduction and blade optimization techniques.