Acoustic Environment of Low Power Wind Turbines

Abstract

Small wind energy production (wing and rotor modular low-power wind turbines) in country side territories has steadily developed in order to diversify energy resources to meet various economic needs. With respect to environment impact the issue of sound pollution by such machinery is emphasized as well as its scale - boundaries of acoustic pollution. The boundaries can be estimated if knowing noise characteristics of the source (sound power, amplitude frequency characteristics of spread sounds), acoustic emission (directivity factor of sound emission) and conditions of terrain affecting it. Applying mathematical analogue methods of study of source-generated sound fields in the present research a mathematical model of a point source sound field has been applied to define acoustic emission of a source of a more complex geometrical form and size. Mathematical relationships between a noise source sound power and acoustic emission levels (Lp or LpA, ) have been identified. Basing on patterns of geometrical acoustics the format of acoustic emission intensity has been defined at r distance from the sound source. The format is expressed by the pattern 10lg(1+(h/r)²)/r², dBA. Higher-intensity sound zones of a wind turbine have been identified, i.e., when directivity factor of sound emission is ŋ>5 dBA. Using received analytical expressions of alteration of acoustic emission it is possible to calculate boundaries of areas of noise pollution generated by low-power wing wind turbines.