Multi-piece passive load reducing blades and wind turbines using same
A wind turbine includes a tower and a generator on the tower. The generator includes a rotor with at least one assembled blade. The assembled blade includes at least an inner piece, an outer piece, and a joint configured for assembly and disassembly of the inner piece and said outer piece. The outer piece is configured to provide passive load alleviation.
1. A blade kit for a rotor, said blade kit comprising a blade extending axially from a blade root to a blade tip and extending chordwise from a leading edge to a trailing edge and having an airfoil shape along the entire chordwise span, said blade further comprising at least an inner piece, an outer piece, and a joint defined between said inner piece and said outer piece, said inner piece extends from said blade root to said joint, said blade root for coupling to a hub of the rotor, said outer piece extends from said joint to said blade tip, said outer piece is twistable relative to said inner piece to approximate a target pitch value when a given load condition occurs when said blade is fully assembled and coupled to the hub.
2. A blade kit in accordance with claim 1 wherein said outer piece is aft swept.
3. A blade kit in accordance with claim 1 wherein said inboard region of said assembled blade provides a torsional moment that acts in an opposite direction to a torsional moment at said blade tip when said assembled blade is mounted on the rotor.
4. A blade kit in accordance with claim 1 wherein said inboard region is torsionally rigid.
5. A blade kit in accordance with claim 1 wherein said joint is configured to assemble said inner piece and said outer piece at about 70% of a radius of said assembled blade.
6. A blade kit in accordance with claim 1 wherein said outer piece is aft swept with a linear sweep.
7. A blade kit in accordance with claim 6 wherein an angle of the linear sweep is approximately 25 degrees.
8. A blade kit in accordance with claim 1 wherein said outer piece is constructed from at least one of a lighter weight material and a different structure than said inner piece.
9. A blade kit in accordance with claim 1 wherein said outer piece is aft swept in a continuous curvature.
10. A blade kit in accordance with claim 1 wherein said joint comprises a torque tube having a torsional stiffness selected to allow said outer piece to achieve or approximate the target pitch value.
11. A blade kit in accordance with claim 1 wherein said outer piece is aft swept and said inner piece is forward swept to provide a torsional moment acting in an opposite direction to that of said outer piece, to balance a torsional load of said assembled blade.
12. A blade kit in accordance with claim 1 further comprising a flexible fairing configured to span said joint at said assembled blade.
13. A wind turbine comprising:
a tower; and
a generator on said tower, said generator comprising a rotor with at least one assembled blade extending axially from a blade root to a blade tip and extending chordwise from a leading edge to a trailing edge and having an airfoil shape along the entire chordwise span, said blade comprising an inner piece, an outer piece, and a joint defined between said inner piece and said outer piece, said inner piece extends from said blade root to said joint, said blade root for coupling to a hub of said rotor, said outer piece extends from said joint to said blade tip, said outer piece is twistable relative to said inner piece to approximate a target pitch value when a given load condition occurs when said blade is fully assembled and coupled to said hub.
14. A wind turbine in accordance with claim 13 wherein said outer piece is aft swept.
15. A wind turbine in accordance with claim 13 wherein said inboard region is torsionally rigid.
16. A wind turbine in accordance with claim 13 wherein said joint comprises a torque tube having a torsional stiffness selected to allow said outer piece to achieve or approximate the target pitch value.
17. A wind turbine in accordance with claim 13 wherein said outer piece is aft swept and said inner piece is forward swept to provide a torsional moment acting in an opposite direction to that of said outer piece, to balance a torsional load of said assembled blade.
18. A method for assembling a rotor blade on a rotor of a wind turbine, said method comprising:
transporting at least two unassembled pieces of blade, the pieces including an outer blade part having an aft sweep and an inner blade part;
assembling at least the outer blade part and the inner blade part into a blade at a joint, the inner blade part having a blade root for coupling to a hub of the rotor, the inner blade part extending axially between the blade root and the joint, the outer blade part extending axially from the joint to a blade tip, the inner blade part and the outer blade part extending chordwise between a leading edge and a trailing edge and having an airfoil shape along the entire chordwise span, the outer blade part is twistable relative to the inner blade part to approximate a target pitch value when a given load condition occurs when the blade is fully assembled and coupled to the hub; and
assembling the blade onto the rotor of the wind turbine.
19. A method in accordance with claim 18 wherein said assembling at least the outer blade part and the inner blade part at a joint further comprises joining the outer blade part and the inner blade part using a torque tube exhibiting a torsional stiffness selected to allow the outer blade part to achieve or approximate the target pitch value.
20. A method in accordance with claim 18 wherein the outer blade part is constructed from at least one of a lighter weight material than the inner blade part and a different construction, than the inner blade part.