Twisted blade root
A rotor blade for a wind turbine having a blade root, a transition piece and an aerodynamic part, wherein the blade root essentially is optimized for fixation of the blade to the hub and the aerodynamic part essentially is optimized to extract energy from the wind and wherein the transition part realizes a beneficial transition between the blade root and the aerodynamic part. The rotor blade can perform better both aerodynamically and structurally compared to a classic design when the blade part located near the axis, approximately the part between 0% L and 50% L is provided with one or more of the following characteristics: more twist than usual, attached flow stimulating measures at the suction side, flow blocking measures at the pressure side, thicker profiles than usual, a triangular shape of the profile back and back twist.
1. A rotor blade assembly of length L larger than 40 meters for a wind turbine which comprises a fixation side at longitudinal position L=0 for the fixation of the blade to the hub and a tip at the opposite side at longitudinal position L and a suction side which comprises in the range between 5% L and 50% L vortex generators wherein said assembly comprises at 20% L profiles with a thickness of more than 45% c.
2. The rotor blade assembly according to claim 1 wherein the profile thickness at 20% L is more than 50% c.
3. The rotor blade assembly according to claim 1 wherein the profile thickness at 20% L is more than 55% c.
4. The rotor blade assembly according to claim 1 wherein the profile thickness at 40% L is more than 31% c.
5. The rotor blade assembly according to claim 1 wherein the profile thickness at 40% L is more than 33% c.
6. The rotor blade assembly according to claim 1 wherein the profile thickness at 40% L is more than 37% c.
7. The rotor blade assembly according to claim 1 wherein the profile thickness at 60% L is more than 28% c.
8. The rotor blade assembly according to claim 1 wherein the profile thickness at 60% L is more than 30% c.
9. The rotor blade assembly according to claim 1 wherein the profile thickness at 60% L is more than 32% c.
10. The rotor blade assembly according to claim 1 which in blade longitudinal direction comprises a continuous range of profiles of minimally 33% c and maximally 70% c thickness wherein the twist difference in said range is more than 5 degrees.
11. The rotor blade assembly according to claim 1 which in blade longitudinal direction comprises a continuous range of profiles of minimally 40% c and maximally 70% c thickness wherein the twist difference in said range is more than 10 degrees.
12. The rotor blade assembly according to claim 1 wherein the fins of said vortex generators have a height above the blade surface of at least 2% c.
13. A rotor blade assembly according to claim 1 which comprises at the pressure side between 5% L and 25% L an addition or flow blocking measures.
14. The rotor blade assembly according to claim 1 wherein the flow blocking measure protrudes from the profile surface over a distance between 0.2% c and 3% c.
15. The rotor blade assembly according to claim 1 wherein the flow blocking measure comprises a radial flow blocking element of which a cross section with a plane parallel to the local blade surface comprises a concavity.
16. The rotor blade assembly according to claim 1 wherein the flow blocking measure comprises an element with a mounting surface and a flow blocking surface wherein at least 10% of the flow blocking surface has an angle with the blade longitudinal direction of more than 30 degrees, e.g. about 45 degrees.
17. The rotor blade assembly according to claim 1 wherein the flow blocking measures comprise artificial roughness in the range between 1% c at the suction side up to, via the leading edge, 50% c at the pressure side.
18. The rotor blade assembly according to claim 1 which comprises at the pressure side between 5% L and 25% L a radial flow blocking element with a concavity at its pressure side.
19. The rotor blade assembly according to claim 1 wherein at the pressure side, e.g. at the trailing edge the flow blocking measure comprises a three dimensional shape such as wavy strip or a zigzag strip or a repetitive series of elements.
20. The rotor blade assembly according to claim 1 wherein the largest chord is less than 6.5% L.
21. The rotor blade assembly according to claim 1 comprising a profile at 15% L wherein the suction side of said profile between 55% c and 98% c has less slope change than 8 degrees.
22. The rotor blade assembly according to claim 1 comprising a profile at 15% L wherein the pressure side of said profile between 45% c and 98% c has less slope change than 12 degrees.
23. A first and second rotor blade assemblies each according to claim 1 and having a similar shape, wherein the first rotor blade assembly further comprises a first pattern of flow manipulators which is optimized for a first turbine in a first situation and the second rotor blade assembly further comprises a second pattern of flow manipulators which is optimized for a second turbine in a second situation.