Twisted blade root

Abstract

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.

Claims

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.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1: Horizontal axis wind turbine,

(2) FIG. 2: Cross section of rotor blade according to line I-I in FIG. 1,

(3) FIG. 3: Cross section of rotor blade,

(4) FIG. 4: Cross section of rotor blade,

(5) FIG. 5: Cross section of rotor blade,

(6) FIG. 6: Cross section of rotor blade,

(7) FIG. 7: Cross section of rotor blade,

(8) FIG. 8: Cross section of rotor blade with zigzag profile at pressure side,

(9) FIG. 9: Rotor blade,

(10) FIG. 10: Rotor blade,

(11) FIG. 11: Rotor blade,

(12) FIG. 12: Close up of part 62 in FIG. 10,

(13) FIG. 13: Twist and chord distribution,

(14) FIG. 14: Twist rate and thickness distribution.

DETAILED DESCRIPTION

(15) Detailed description of the invention with examples according to figures:

(16) FIG. 1 shows a horizontal axis turbine 1 with a tower 2, a nacelle 3 and a hub 4 with thereto attached rotor blade 6 with blade root 7 and tip 8. Also another rotor blade is shown with leading edge 9 and trailing edge 10, which blade comprises 2 parts: the part attached to the hub and the part 12 which e.g. can adjust the blade pitch angle. The parts come together at position 11. The direction of rotation is 5. Cross section I-I is shown in FIG. 2.

(17) In FIG. 2 the chord c and the thickness t are indicated and also chord line 33 which at chord wise position 0% c coincides with the leading edge 21 and oat chord wise position 100% c with the trailing edge 22. The cross section shows the main girders 27 and 28 at respectively the suction side 24 and the pressure side 28, with in between the front shearweb 25 and the back shearweb 26. An example of a design inflow 29 is shown which has an angle of attack 30 with the chord line 33. The flow manipulators 31 and 32 show respectively vortex generators and a flow blocking element which optionally is comprised with a concavity 39 at the pressure side. The triangle defined by sides 34, 35 and 36 is inside the profile back side. Side 35 coincides with the back shearweb, and sides 34 and 36 have maximum distances 37 and 38 to the outer contour of the profile.

(18) FIG. 3 shows the same cross section, although this time with a diverging trailing edge realized by addition 40. Note that the chord definition which is applied for the twist definition in this application intersects at the back side the middle of the flat trailing edge. The definitions of the chord and thickness in this application which are relevant for the relative thickness should be determined without extensions or additions 40, 50, 51, 53.

(19) FIG. 4 shows a cross section with a flow blocking element 50 which is located closer to the leading edge than in FIG. 3.

(20) FIG. 5 shows addition 51 which extends over both the pressure side and the suction side.

(21) FIG. 6 shows flow blocking element 54 in the form of Gurney flap. The chord line again intersects the flat trailing edge half way.

(22) FIG. 7 shows artificial roughness 55, which provides an effective flow blockage, can be attached easily, which reduces the roughness sensitivity of the blade and which opposes high negative pressure gradients. Between position 80 at the pressure side at approximately 45% c and position 82 at approximately 98% c the tangents 81 and 82 show the difference in slope 84 of the profile contour.

(23) FIG. 8 shows a 3D view of flow lines 56 and radial flow blocking element 57. FIGS. 9, 10, 11 and 12 show a view at the pressure side of (a part of) a rotor blade.

(24) FIG. 9 shows radial flow blocking element 60 with a zigzag pattern and multiple concavities 65 at the pressure side thereof of which one is indicated.

(25) FIG. 10 shows radial flow blocking element 61 with wavy pattern and close up 62 which is shown in FIG. 12. Element 61 comprises at its pressure side concavities 66 of which one is indicated.

(26) FIG. 11 shows radial flow blocking elements 63 with a concave inflow side 67 (just one concavity indicated). On a single element 63 is ay position 69 the plane 70 through door the flow blocking plane drawn which has an angle 71 with the blade longitudinal axis 68. The normal to plane 70 is not perpendicular to the curve which connects elements 63. Element 63 can, due to its small dimensions, over maximally its full length be joint to the blade or has 2 or more non-continuous joints 71 with the blade. A shown embodiment of element 63 comprises 2 joints 71 which connect element 63 to the blade, e.g. by double sided adhesive tape. According to a beneficial embodiment the flow blocking surface of element 63 does not touch the blade surface, but instead allows air to flow between the element 63 and the blade surface over a height of e.g. 0.01% c to 2% c or in particular between 0.1% c and 0.5% c. By inclining the flow blocking surface by an angle with said curve as shown in FIGS. 8-12 a more effective blockage of the flow is realized, which can be understood since rotational effects will drive stagnant flow outwardly (centrifugal forces) what is not obstructed in the case of longitudinal embodiments as in U.S. Pat. No. 6,910,867 B2 (Corten) and EP2343450A1 (LM), but (partly) is blocked by the embodiments according to the invention. FIG. 12 shows a close up of part 62 in FIG. 10.

(27) FIG. 12 shows again the radial flow blocking element 61 with the wavy pattern and also the joint surfaces 64 which are in the direction wherein the element extends in not continuous. At position 73 the plane 74 through the radial flow blocking surface is drawn and has an angle 75 with the blade longitudinal axis 68.

(28) FIG. 13 shows the distribution of the twist and the chord according to an embodiment according to the invention and also a classical twist distribution. In the figure the twist difference according to this embodiment of the invention between 15% R and 20% R 5 and is the back twist between 5% R and 10% R also 5 or even 7.

(29) FIG. 14 shows the distribution of the twist rate and the relative thickness according to an embodiment of the invention.

(30) For clarification the flow manipulators like the vortex generators are drawn larger than in reality in several figures. The zigzag pattern of waves in the ribs and the artificial roughness are drawn with a well visible amplitude, while the amplitude of a beneficial embodiment can be larger of smaller.

(31) Although the invention is described inter alia by several examples and figures, one should understand that the invention is not limited hereto. Several changes can be made by the person skilled in the art without getting out of the scope of the claims. An example is the application of the invention on a wind turbine with 2 rotor blades which have a common center part which intersects with the rotational axis. In such a case one should understand that the position L=0 coincides with the position R=0 and that the tip is located at position L=R.

(32) Another example is that of a blade which consists of multiple part in longitudinal direction, then L is related to the assembly of parts which is located between the hub and the blade tip. Also in chord wise direction the blade can consist of more than one part in which case the chord of the from the multiple parts assembled blade should be used.

(33) The person skilled in the art will understand that the invention is applicable to multiple wind turbines, such as wind turbine of both the horizontal axis type and the vertical axis type, onshore and offshore wind turbines, wind turbines with pre-bent blades, wind turbines with a tilt angle and in particular when this tilt angle is between 2 and 7, wind turbines with a cone angle and in particular when this cone angle is between 2 and 7, stall regulated and pitch regulated turbines, variable speed and constant speed turbines, turbines in farms, turbines which are retro fitted and get a new rotor, wind turbines for wind classes 1, 2, 3, 4 of 5, and turbulence classes a, b, c, wind turbines with active flaps or active vortex generators or which use aero-elastic tailoring and wind turbines with rotors which have their maximum power coefficient at a design between 2 and 15 and in particular between 4 and 14 and more in particular between 7 and 13, wind turbines with rotors which contain glass fibers of carbon fibers, optionally in combination with a thermo harder of thermo plastic. In addition hereto the person skilled in the art will immediately combine the invention with technology described in the references and will consider this as non-inventive embodiments according to the invention.

(34) One should that the term comprises does not exclude other elements or steps, that the term a does not exclude plurality and that the denotation comprises x should be explained as comprises at least x, wherein x e.g. is the number of degrees twist. The references to figures in the claims serve illustration purposes and should not be considered as limiting.

(35) The discussion of the referenced patent texts in this document considers the inventors opinion and has no legal status. Finally the physical explanation in this document is added for illustrative reasons and does not have a relation to the validity of the attached claims.