Masking tonal noise from a wind turbine
A method of masking tonal noise from a wind turbine. The wind turbine has a noise generator and a rotor-nacelle-assembly (RNA). The RNA comprises a nacelle and a rotor configured to rotate about a rotor axis with a horizontal projection. The method comprises: feeding a drive signal into the noise generator so that the noise generator emits directional masking noise, wherein the directional masking noise at least partially masks tonal noise from the wind turbine and points in a masking direction with a horizontal projection. The horizontal projection of the masking direction points away from the horizontal projection of the rotor axis.
1 . A method of masking tonal noise from a wind turbine, the wind turbine comprising a noise generator and a rotor-nacelle-assembly (RNA), the RNA comprising a nacelle and a rotor configured to rotate about a rotor axis with a horizontal projection, the method comprising:
feeding a drive signal into the noise generator so that the noise generator emits directional masking noise, wherein the directional masking noise at least partially masks tonal noise from the wind turbine and points in a masking direction with a horizontal projection, and wherein the horizontal projection of the masking direction points away from the horizontal projection of the rotor axis.
2 . The method according to claim 1 further comprises rotating the RNA about a yaw axis to change a yaw angle of the RNA, wherein the masking direction does not change as the yaw angle changes.
3 . The method according to claim 1 further comprises rotating the RNA about a yaw axis to change a yaw angle of the RNA, wherein the masking direction changes as the yaw angle changes.
4 . The method according to claim 1 wherein the rotor defines an upwind direction, a downwind direction, an upstroke direction and a downstroke direction; and at least a component of the horizontal projection of the masking direction points in the upwind direction or the upstroke direction.
5 . The method according to claim 1 wherein the horizontal projection of the rotor axis is oriented at an angle relative to the horizontal projection of the masking direction, and the method comprises: changing the angle by rotating the RNA about a yaw axis; and changing the drive signal in accordance with the change of angle, thereby changing a characteristic of the directional masking noise.
6 . The method according to claim 1 wherein the horizontal projection of the masking direction is at an angle relative to the horizontal projection of the rotor axis; and a characteristic of the directional masking noise is set on the basis of the angle.
7 . The method according to claim 5 wherein the characteristic of the directional masking noise is a frequency profile or sound power of the directional masking noise.
8 . The method according to claim 5 wherein changing the drive signal causes a sound power of the directional masking noise to increase; the tonal noise is a directional tonal noise which points in a tonal noise direction with a horizontal projection; and the change of the angle causes the horizontal projection of the masking direction and the horizontal projection of the tonal noise direction to become more closely aligned with each other.
9 . The method according to claim 5 further comprising generating directional natural masking noise, wherein the directional natural masking noise at least partially masks the tonal noise and points in a natural masking noise direction with a horizontal projection, wherein changing the drive signal causes a power of the directional masking noise to decrease; and the change of the angle causes the horizontal projection of the masking direction and the horizontal projection of the natural masking noise direction to become more closely aligned with each other.
10 . The method according to claim 1 further comprising setting the masking noise direction by rotating the noise generator, or by selecting the noise generator from a set of noise generators.
11 . The method according to claim 10 wherein the masking noise direction is set on the basis of a location of a receptor.
12 . The method according to claim 1 wherein the RNA is oriented at a yaw angle, and the drive signal is based on the yaw angle.
13 . The method according to claim 12 wherein the drive signal is enabled or changed on the basis of the yaw angle.
14 . The method according to claim 1 wherein the drive signal is fed into the noise generator only for a specific operational envelope.
15 . The method according to claim 1 wherein the horizontal projection of the masking direction has at least a component in the crosswind direction with respect to the rotor axis.
16 . A wind turbine, comprising:
a noise generator;
a control system; and
a rotor-nacelle-assembly (RNA), wherein the RNA comprises a nacelle and a rotor configured to rotate about a rotor axis with a horizontal projection,
wherein the control system is configured to feed a drive signal into the noise generator so that the noise generator emits directional masking noise which at least partially masks tonal noise from the wind turbine and points in a masking direction with a horizontal projection, and the horizontal projection of the masking direction points away from the horizontal projection of the rotor axis.
17 . The wind turbine according to claim 16 wherein the horizontal projection of the masking direction has at least a component in the crosswind direction with respect to the rotor axis.
18 . The wind turbine according to claim 16 wherein the noise generator is rotatable about a yaw axis relative to the nacelle.