Radiation characteristics of noise generated from a wind turbine

Abstract

In Japan, the development of large-scale wind power generation facilities has been promoted since about 2000. Nationwide investigations of the acoustic characteristics of wind turbine noise have been conducted at various wind farms. In this study, to examine the horizontal and vertical radiation characteristics of noise generated from wind turbines, field measurements of noise from a single wind turbine with a rated power of 1.5 MW have been performed. Some receiving points were set circularly around the wind turbine and mounted on a nearby lightning tower. Meteorological and associated wind turbine operational data were collected at 1 s intervals along with corresponding acoustic data. In addition, the sound pressure level distributions at distances of 50 m to 200 m from the wind turbine were investigated. Results revealed distinguishable horizontal directivity of wind turbine noise. The A-weighted sound pressure levels in the crosswind direction are almost 5 dB lower than those in the up-and downwind directions. Furthermore, it has been found that the sound directivity around the wind turbine could be expressed by a simple empirical formula, assuming the wind turbine to be a point source with combined bi-and omnidirectional patterns.

Horizontal directivity of sound emitted from wind turbines

“…3(a). However, the correlation between L WA and the wind speed at hub height is only moderate, because the change in the wind speed is rapid as well as irregular under actual meteorological conditions, as mentioned in a previous study [9]. On the other hand, the correlation between L WA and the output power or rotor speed is extremely strong compared with that with the wind speed at hub height, as presented in Figs.…”

“…Figure 1 shows the arrangement of the receiving points around the upwind and downwind turbines [9]. The upwind turbine (hereinafter referred to as WT.A) has been operated since 2003 and its rated output power, rotor rotational speed, and wind speed are 1.5 MW, 20 rpm, and 12 m/s, respectively.…”

“…These mean values synchronized with the acoustic data were calculated over 10 s periods. Figure 2 shows the operational conditions of the wind turbines during the measurements [9]. The solid line in the figure represents the power curve for each wind turbine.…”

“…To simplify the modeling of the directivity pattern of wind turbine noise at the ground level, we have focused on the difference between the sound pressure levels in the up-or downwind direction and those in the other directions, which was obtained through field measurements [9]. A simple regression formula was applied, assuming the directivity pattern of aerodynamic and mechanical sound to be bi-and omnidirectional, respectively.…”

“…We have also examined the radiation characteristics of wind turbine noise under various wind conditions [8,9]. Field measurements of noise around a wind turbine with an upwind rotor have been performed to investigate the horizontal directivity of the A-weighted sound pressure level in 1/1-octave bands.…”