Effect of atmospheric stability and low level jets on wind turbine noise

Abstract

Numerous studies from the literature have shown that strong wind shear occurs frequently in stable atmospheres, typically at night. This phenomenon can be associated to low level jets, characterized by a wind speed profile with a maximum at a few hundred meters above the ground. This study investigates the effect of such wind speed profiles on wind turbine noise using a physically-based model. The predictions are obtained by coupling an aeroacoustic source model based on Amiet’s theory and a parabolic equation code for acoustic propagation in an inhomogeneous atmosphere. Two important broadband noise generation mechanisms are considered, namely trailing edge noise and turbulence inflow noise, and the coupling method takes into account the fact that wind turbine blades are moving and extended sources. In order to obtain realistic wind speeds for the simulations, a simple model of nocturnal low-level jet is used, with input parameters based on measurements acquired in Cabauw observatory in the Netherlands. Predictions of the overall sound pressure levels and of the third octave band noise spectra will be presented up to a distance of 1km to show the noise variations due to the wind shear effect.