Devices and methods for mitigating vibrations in wind turbines
The present disclosure relates to devices ( 300 ) for wind turbine blades ( 22 ) and methods ( 400 ) for reducing vibrations in wind turbines ( 10 ). More particularly, the present disclosure relates to devices ( 300 ) for mitigating vortex induced vibrations and stall induced vibrations, wind turbine blades ( 22 ) comprising such devices ( 300 ), and methods ( 400 ) for reducing wind turbine vibrations when the wind turbine ( 10 ) is parked, especially during wind turbine installation and/or maintenance. A device ( 300 ) is configured to be arranged around a wind turbine blade ( 22 ) and comprises three or more air flow modifying elements ( 305 ) comprising a concave outer surface ( 323 ) configured to face away from a wind turbine blade ( 22 ). The device further comprises a supporting structure ( 310 ) configured to support the plurality of air flow modifying elements ( 305 ). An angular distance ( 307 ) between adjacent air flow modifying elements ( 305 ) in cross-section is substantially constant.
1. A device for mitigating vibrations of a parked wind turbine, the device configured to be arranged around a blade of the wind turbine, comprising:
a length along a longitudinal direction and a cross-section perpendicular to the longitudinal direction, the cross-section including a radial direction and a tangential direction;
three or more air flow modifying elements comprising a concave outer surface configured to face away from the blade;
a supporting structure configured to support the air flow modifying elements; and
a constant angular distance in cross-section between adjacent air flow modifying elements.
2. The device of claim 1 , wherein an inner surface of the air flow modifying elements is convex.
3. The device of claim 1 , wherein the air flow modifying elements, in cross-section, comprise a same shape and size.
4. The device of claim 1 , wherein each of the air flow modifying elements contact an adjacent one of the air flow modifying elements.
5. The device of claim 4 , wherein an outer end of a first air flow modifying element and an outer end of a second adjacent air flow modifying element are separated by a tangential air gap.
6. The device of claim 1 , wherein each of the air flow modifying elements is completely separated from adjacent ones of the air flow modifying elements by a tangential air space.
7. The device of claim 1 , wherein a first air flow modifying element is configured to be arranged in front of a leading edge of the blade and a second air flow modifying element is configured to be arranged behind a trailing edge of the blade.
8. The device of claim 1 , wherein a radial axis of symmetry of at least one of the air flow modifying elements in cross-section lies in a different direction than a corresponding local radial direction.
9. The device of claim 1 , wherein the device is configured to provide a radial gap between the air flow modifying elements and a local surface of the blade when the device is mounted to the blade.
10. The device of claim 1 , wherein the supporting structure comprises a tip support and a root support, the tip support configured to be closer to a blade tip of the blade than the root support.
11. A wind turbine blade comprising the device for mitigating vibrations of a parked wind turbine according to claim 1 .
12. A method for mitigating vibrations in a parked wind turbine, the method comprising:
moving a vibration mitigating device around a blade of the wind turbine and towards a root of the blade, wherein the device includes three or more air flow modifying elements each having a concave outer surface configured to face away from the blade, and wherein an angular distance between adjacent ones of the air flow modifying elements in cross-section is constant; and
securing the device to the blade.
13. The method of claim 12 , wherein the moving comprises pulling one or more ropes attached to a supporting structure of the device.
14. The method of claim 12 , wherein the blade is pointing downwards.
15. The method of claim 12 , further comprising removing the device from the wind turbine blade before starting or resuming operation.
16. A device for mitigating vibrations of a parked wind turbine, the device configured to be arranged around a blade of the wind turbine, comprising:
three or more air flow modifying elements, each of the air flow modifying elements comprising a C-shaped or U-shaped cross-section;
wherein an opening of the C-shaped or U-shaped cross section faces away from the blade; and
a supporting structure configured to keep a same distance between adjacent ones of the air flow modifying elements.
17. The device of claim 16 , wherein the supporting structure is further configured to maintain a substantially constant distance between the air flow modifying elements and a geometric center of the device in cross-section.
18. The device of claim 16 , adjacent ones of the air flow modifying elements are separated by a tangential air space.
19. The device of claim 16 , wherein a first air flow modifying element is configured to be positioned in front of a leading edge of the blade and a second air flow modifying element is configured to be positioned behind a trailing edge of the blade.
20. The device of claim 16 , wherein the supporting structure comprises a tip support and a root support to which the air flow modifying elements are attached.