System and method for passive load attenuation in a wind turbine
In accordance with certain embodiments, a wind turbine blade includes an outer skin and an internal support structure. The skin has a closed airfoil shape and includes an outer surface, an inner surface, and opposite sides along a length of the blade. The internal support structure is disposed within the closed airfoil shape. The internal support structure includes at least one shear load bearing member disposed across the opposite sides and oriented lengthwise along the length of the blade. The internal support structure further includes a plurality of bending load bearing members disposed along the inner surface in a lengthwise direction along the length of the blade. The internal support structure is configured to position a shear center and a center of aerodynamic pressure loading of the blade at different locations relative to one another.
1. A wind turbine blade, comprising:
a skin comprising a closed airfoil shape, an outer surface, an inner surface, and opposite sides along a length of the blade; and
an internal support structure disposed within the closed airfoil shape, comprising:
at least one shear load bearing member that is disposed across the opposite sides and that is oriented lengthwise along the length of the blade; and
a plurality of bending load bearing members disposed along the inner surface in a lengthwise direction along the length of the blade, wherein the internal support structure is configured to position a shear center and a center of aerodynamic pressure loading at different locations relative to one another.
2. The wind turbine blade of claim 1 , wherein the at least one shear load bearing member comprises a beam and the plurality of bending load bearing members comprise a pair of side structures disposed on opposite sides of the beam, wherein the side structures are off center relative to the opposite sides of the beam.
3. The wind turbine blade of claim 2 , wherein the pair of side structures comprise different materials from one another.
4. The wind turbine blade of claim 1 , wherein the internal support structure has a C-shaped cross-section defined by the at least one shear load bearing member and a pair of bending load bearing members.
5. The wind turbine blade of claim 1 , wherein the internal support structure has a Z-shaped cross-section defined by the at least one shear load bearing member and a pair of bending load bearing members.
6. The wind turbine blade of claim 1 , wherein the at least one shear load bearing member comprises a pair of beams and the plurality of bending load bearing members comprise a pair of side structures disposed on opposite sides of each beam, wherein the side structures comprise different materials relative to one another.
7. The wind turbine blade of claim 1 , wherein the at least one shear load bearing member comprises a pair of beams and the plurality of bending load bearing members comprise a pair of side structures disposed on opposite sides of each beam, wherein the beams and side structures are arranged in a box-shaped configuration.
8. The wind turbine blade of claim 1 , wherein the plurality of bending load bearing members comprise different materials configured to produce a structural eccentricity in the internal support structure in a direction of increasing material thickness.
9. The wind turbine blade of claim 1 , wherein the internal support structure comprises a material including carbon, or glass, or any combinations thereof.
10. The wind turbine blade of claim 1 , wherein the internal support structure is configured for passively attenuating a wind load applied to the wind turbine blade by feathering the closed airfoil shape.
11. A wind turbine blade, comprising:
a skin having a closed airfoil shape;
a beam disposed across the closed airfoil shape and oriented in a lengthwise direction along the length of the wind turbine blade, wherein the beam is configured to bear a shear load; and
first and second side structures disposed on opposite sides of the beam, wherein the beam and the first and second side structures are oriented unsymmetrical relative to one another to provide twisting of the closed airfoil shape in response to bending of the wind turbine blade.
12. The wind turbine blade of claim 11 , wherein the beam and the first and second side structures are configured to provide eccentricity between a shear center and a center of aerodynamic pressure loading.
13. The wind turbine blade of claim 11 , wherein off-center portions of the first and second side structures are coupled to the beam.
14. The wind turbine blade of claim 1 , wherein the first and second side structures comprise different materials configured to produce a structural eccentricity in the wind turbine blade in a direction of increasing material thickness.
15. A wind turbine, comprising:
a rotor comprising a plurality of blades mounted atop a tower, each of the plurality of blades further comprising:
a skin having a closed airfoil shape, an outer surface, an inner surface, and opposite sides along the length of the blade ; and
an internal support structure disposed within the closed airfoil shape, comprising:
at least one shear load bearing member that is disposed across the opposite sides and that is oriented lengthwise along the length of the blade; and
a plurality of bending load bearing members disposed along the inner surface in a lengthwise direction along the length of the blade, wherein the internal support structure is configured to position a shear center and a center of aerodynamic pressure loading at different locations to one another.
16. A method of manufacturing a wind turbine blade, comprising:
providing a skin having a closed airfoil shape, an outer surface, an inner surface, and opposite sides along a length of the blade; and
providing an unsymmetrical internal support structure within the closed airfoil shape to position a shear center and a center of aerodynamic pressure loading at different locations relative to one another.
17. The method of claim 16 , wherein providing an unsymmetrical internal support structure further comprises:
disposing at least one shear load bearing member across the opposite sides and that is oriented lengthwise along the length of the blade; and
disposing a plurality of bending load bearing members along the inner surface in a lengthwise direction along the length of the blade.
18. The method of claim 17 , wherein disposing the at least one shear load bearing member comprises disposing a beam and disposing the plurality of bending load bearing members comprises disposing a pair of side structures opposite sides of the beam, wherein the side structures are off center relative to the opposite sides of the beam.
19. The method of claim 17 , wherein disposing the at least one shear load bearing member comprises disposing a pair of beams and disposing the plurality of bending load bearing members comprises disposing a pair of side structures on opposite sides of each beam, arranging the beams and side structures in a box-shaped configuration, wherein the side structures comprise different materials relative to one another.
20. The method of claim 18 , wherein providing the skin and providing the unsymmetrical internal support structure comprises providing fibers inclined at an angle relative to an axis of the blade.
21. A method for operating a wind turbine, comprising: rotating a wind turbine blade; and attenuating a wind load on the wind turbine blade by passively twisting the wind turbine blade to a feathered position in response to bending of the wind turbine blade due to the wind load via an eccentricity between centers of shear loading and aerodynamic pressure loading.