4. Conclusions
Research indicated that when identifying site׳s total noise, it is expedient to estimate WT generated and background noise levels, the intensities of which are a function of wind speed. Based on the research data, it is estimated that, when wind speed v≈12 m/s and distance to WT tower is bigger than 100 m, WT generated noise level equals to background noise level. In such cases, the influence of WT noise on the environment could be underrated.
The overview and analysis of literature sources reveal that the level of WT generated noise intensity depends on aerodynamic phenomena of construction elements as well as mechanical generation processes of acoustic noise. WT acoustic noise increases due to land surface and acoustic reflection processes of the surrounding constructions, whereas its absorption is influenced by air density, humidity, and by landscape element aerodynamic flow conditions. Using the algorithm of the Fast Fourier transformation for analysis of measured data, it was determined that WT generated noise is broadband; when distance from power plant increases, the sound pressure evenly reduces. Only in the limits of infrasound, low-frequencies and ultrasound frequencies, a small deviation of noise spectrum intensity from the common trend is observed.
It was determined that WT generated sound in the spectrum of pressure pulsations comparing to the greatest changes in the environment noise spectrum occurs in the frequency range 200–5000 Hz. In infrasound, low-frequency (16–200 Hz) and ultrasound frequency ranges, only insignificant changes are observed. Research indicated that at higher wind velocities (v>10 m/s), WT generated noise is concealed by background noise level.
Submitted WT generated noise level calculation model corresponds to experimental measurements under natural conditions, thus it may be applied for acoustic pollution level areas or other chosen sites for the assessment.