Horizontal directivity of sound emitted from wind turbines

Abstract

Field measurements of noise generated from two different wind turbines, one with an upwind rotor and one with a downwind rotor, have been performed. To examine the radiation characteristics of wind turbine noise, some receiving points were set around each wind turbine and the apparent A-weighted sound power levels were calculated from the obtained data at 200 ms intervals under various wind conditions. Wind turbine operational data were collected at 1 s intervals along with corresponding acoustic data. Additionally, a simple empirical formula for the sound directivity was proposed, assuming the directivity pattern of aerodynamic and mechanical sound to be bi-and omnidirectional, respectively. The results showed that the horizontal directivity of the A-weighted sound pressure level at the ground level for the two different wind turbines is almost the same, whereas the frequency dependence of the sound directivity is different for the individual wind turbines. Furthermore, obtaining data of the rotor rotational speed, output power, and nacelle direction is strongly recommended to assess the characteristics of noise emission, such as the changes in the sound power level, sound directivity, and tonal components of wind turbine noise.

Directivity of amplitude modulation sound around a wind turbine under actual meteorological conditions

“…However, it is necessary to theoretically prove the existence of this phenomenon for AM sound around the tower. Additionally, the time-averaged A-weighted sound pressure levels L Aeq,30s in the crosswind direction were almost 5 dB lower than those in the up-or downwind directions, as demonstrated in our previous study [8,9], which is the result based on the time-averaged sound level L Aeq,10s at 10 s intervals (IEC 61400-11:2012 [20]).…”

“…The mean D AM,30s at 15 intervals was calculated using data within AE7:5 relative to each direction. Figure 7 shows the results for the A-weighted sound pressure levels in 1/1-octave bands, which are the dominant middle-frequency components (250 Hz, 500 Hz, 1 kHz) of WTN [9]. As a reference, the directivity of the time-averaged A-weighted sound pressure level L Aeq,30s at a distance of 50 m was calculated using the same data (see Fig.…”

“…Furthermore, to see the directivity patterns of D AM,30s and L Aeq,30s , these values were fitted using a fourth-order polynomial and a simple formula combined with bi-and omnidirectional patterns [8,9], respectively, as follows:…”

“…We performed field measurements around two different wind turbines under various wind conditions in 2010-2013 to examine the noise directional characteristics, tonal components, and rotor rotational speed dependence of WTN in emission areas [7][8][9]. These studies revealed that the A-weighted sound pressure levels L Aeq,10s in the crosswind direction are almost 5 dB lower than those in the up-and downwind directions, and the relationship between WTN and the rotor speed is extremely strong compared with that with the wind speed at the hub height.…”

Comparative study of the noise generated by the moto-compressor and that generated by the turbo-compressor

“…Aerodynamic sound is generated from the blade passing through the air, and mechanical sound is emitted by some equipment in the nacelle [36].…”