Wind turbine blade and a method of operating such a wind turbine blade

Abstract

This invention relates to an airfoil modifying device, a wind turbine blade and a method of modifying an airfoil profile of the wind turbine blade. The airfoil modifying device comprises a deformable element connected to a filler element, both configured to deform between a retracted position and an extended position. The airfoil modifying device is passively deformed by the local air pressure acting on the blade surface and thus the airfoil modifying device.

Claims

1. An airfoil profile modifying device (19) for a wind turbine blade (5), the wind turbine blade (5) comprising a blade shell (11) having an original airfoil profile which defines a pressure side (12) and a suction side (13), wherein the airfoil profile modifying device (19) is configured to be arranged on the pressure side (12) or suction side (13) of said wind turbine blade (5) and to modify said original airfoil profile to produce a modified airfoil profile, the airfoil profile modifying device (19) comprising: a deformable element (30) comprising a semipermeable membrane, wherein air is able to pass through said semipermeable membrane; and means for attaching the deformable element (30) to the wind turbine blade (5), whereby the deformable element (30) is adapted for attachment to the wind turbine blade (5) such that the deformable element (30) extends along said pressure side or said suction side (12, 13) from a first edge (21) to a second edge (22), and further from a first end (24) to a second end (25) when attached, wherein said deformable element (30) is configured to deform between a retracted position and an extended position, and wherein the deformable element (30) is passively deformed, when attached, by means of a local external air pressure acting on an outer surface of said airfoil modifying device (19) and equalization of pressure between an interior and an exterior of the deformable element (30) by the air passing through the semipermeable membrane due to a pressure difference between the interior and the exterior of the deformable element (30), the modified airfoil profile produced by the airfoil profile modifying device (19) having smooth and continuous pressure side and suction side surface profiles.

2. The airfoil profile modifying device according to claim 1, wherein the airfoil modifying device (19) further comprises a filler element (29) connected to said deformable element (30), wherein said filler element (29) is further configured to deform between said retracted position and said extended position.

3. The airfoil profile modifying device according to claim 2, wherein said filler element (29) comprises an open cell structure.

4. The airfoil profile modifying device according to claim 1, wherein said deformable element (30) comprises means (33) for passively guiding air into and out of a local chamber, when attached, formed by said deformable element (30) and an original blade surface of the wind turbine blade (5).

5. A wind turbine blade (5) extending from a blade root (7) to a tip end (8) in a longitudinal direction and further from a leading edge (9) to a trailing edge (10) in a chordwise direction, the wind turbine blade (5) comprising a blade shell (11) having an original airfoil profile which defines a pressure side (12) and a suction side (13), wherein at least one airfoil profile modifying device (19) is arranged on one of said pressure and suction sides (12, 13) and attached to said wind turbine blade (5), the at least one airfoil profile modifying device (19) comprising a deformable element (30) which comprises a semipermeable membrane, wherein air is able to pass through said semipermeable membrane, whereby the deformable element (30) is adapted for attachment to the wind turbine blade (5) such that the deformable element (30) extends along said pressure side or said suction side (12, 13) from a first edge (21) to a second edge (22), and further from a first end (24) to a second end (25), wherein said deformable element (19) is configured to deform between a retracted position and an extended position, wherein the deformable element (30) is passively deformed by means of a local external air pressure acting on an outer surface of said pressure side or said suction side (12, 13) and equalization of pressure between an interior and an exterior of the deformable element (30) by the air passing through the semipermeable membrane due to a pressure difference between the interior and the exterior of the deformable element (30), the original airfoil profile being modified by deformation of the at least one airfoil modifying device (19) relative to an original blade surface in a local flapwise direction to produce a modified airfoil profile having smooth and continuous pressure side and suction side surface profiles.

6. The wind turbine blade according to claim 5, wherein the deformable element (30) of said at least one airfoil profile modifying device (19) and the original blade surface form a local chamber, wherein a volume of said chamber is changed as function of said local air pressure.

7. The wind turbine blade according to claim 6, wherein a filler element (29) of said at least one airfoil profile modifying device (19) substantially is arranged within said local chamber, wherein said filler element (29), when extended, forms a predetermined outer profile of the deformable element (30).

8. The wind turbine blade according to claim 5, wherein said at least one airfoil profile modifying device (19) comprises integrated flanges (28) attached to the blade shell (11), or comprises first coupling elements (26) engaging second coupling elements (27) arranged on the wind turbine blade (5).

9. The wind turbine blade according to claim 5, wherein said at least one airfoil profile modifying device (19) comprises a first airfoil modifying device and at least a second airfoil modifying device, wherein said at least second airfoil modifying device is arranged relative to the first airfoil modifying device along the original blade surface.

10. A method of modifying an airfoil profile of a wind turbine blade, the wind turbine blade (5) extending from a blade root (7) to a tip end (8) in a longitudinal direction and further from a leading edge (9) to a trailing edge (10) in a chordwise direction, the wind turbine blade (5) comprising a blade shell (11) having an original airfoil profile defining a pressure side (12) and a suction side (13), wherein the wind turbine blade (5) is configured according to claim 6, wherein said method comprises the steps of: operating said wind turbine blade (5) according to an angle of attack; and passively modifying said original airfoil profile at predetermined angles of attack by deforming the at least one airfoil modifying device (19) in a local flapwise direction by means of a local air pressure acting on said one of said pressure and suction sides (12, 13) to produce the modified airfoil profile having the smooth and continuous pressure side and suction side surface profiles.

11. The method according to claim 10, wherein said predetermined angles of attack are negative angles of attack.

12. The method according to claim 11, wherein said predetermined angles of attack are very low negative angles of attack.

13. An airfoil profile modifying device (19) for a wind turbine blade (5), the wind turbine blade (5) comprising a blade shell (11) having an original airfoil profile which defines a pressure side (12) and a suction side (13), wherein the airfoil profile modifying device (19) is configured to be arranged on the pressure side (12) or suction side (13) of said wind turbine blade (5) and to modify said original airfoil profile to produce a modified airfoil profile, the airfoil profile modifying device (19) comprising: a deformable element (30) comprising a semipermeable membrane, wherein air is able to pass through said semipermeable membrane; and means for attaching the deformable element (30) to the wind turbine blade (5), whereby the deformable element (30) is adapted for attachment to the wind turbine blade (5) such that the deformable element (30) extends along said pressure side or said suction side (12, 13) from a first edge (21) to a second edge (22), and further from a first end (24) to a second end (25) when attached, wherein said deformable element (30) is configured to deform between a retracted position and an extended position, and wherein the deformable element (30) is passively deformed, when attached, by means of a local external air pressure acting on said airfoil modifying device (19) and equalization of pressure between an interior and an exterior of the deformable element (30) by the air passing through the semipermeable membrane due to a pressure difference between the interior and the exterior of the deformable element (30), the modified airfoil profile produced by the airfoil profile modifying device (19) having smooth and continuous pressure side and suction side surface profiles.

Description

DESCRIPTION OF DRAWINGS

(1) The invention is explained in detail below with reference to embodiments shown in the drawings, in which

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows an exemplary embodiment of the wind turbine blade,

(4) FIG. 3 shows the wind turbine blade with a airfoil modifying device in a retracted position,

(5) FIG. 4 shows the wind turbine blade with the airfoil modifying device in an extended position,

(6) FIG. 5a-b show two alternative placements of the airfoil modifying device,

(7) FIG. 6 shows a third alternative placement of the airfoil modifying device,

(8) FIG. 7a-b show two alternative attachments of the airfoil modifying device,

(9) FIG. 8 shows a second embodiment of the airfoil modifying device, and

(10) FIG. 9a-b show a third embodiment of the airfoil modifying device in the retracted position and the extended position.

LIST OF REFERENCES

(11) 1. Wind turbine

(12) 2. Wind turbine tower

(13) 3. Nacelle

(14) 4. Hub

(15) 5. Wind turbine blades

(16) 6. Pitch bearing

(17) 7. Blade root

(18) 8. Tip end

(19) 9. Leading edge

(20) 10. Trailing edge

(21) 11. Blade shell

(22) 12. Pressure side

(23) 13. Suction side

(24) 14. Blade root portion

(25) 15. Aerodynamic blade portion

(26) 16. Transition portion

(27) 17. Length of wind turbine blade

(28) 18. Chord length of wind turbine blade

(29) 19. Airfoil modifying device

(30) 20. Chord line

(31) 21. First edge

(32) 22. Second edge

(33) 23. Camber line

(34) 24. First end

(35) 25. Second end

(36) 26. First coupling elements

(37) 27. Second coupling elements

(38) 28. Flanges

(39) 29. Filler element

(40) 30. Deformable element

(41) 31. Local chamber

(42) 32. Original blade surface

(43) 32a. Inner element

(44) 33. Means for guiding air into and out of local chamber

(45) α Angle of attack

(46) W Wind direction

(47) The listed reference numbers are shown in abovementioned drawings where no all reference numbers are shown on the same figure for illustrative purposes. The same part or position seen in the drawings will be numbered with the same reference number in different figures.

DETAILED DESCRIPTION OF THE DRAWINGS

(48) FIG. 1 shows a modern wind turbine 1 comprising a wind turbine tower 2, a nacelle 3 arranged on top of the wind turbine tower 2, and a rotor defining a rotor plane. The nacelle 3 is connected to the wind turbine tower 2, e.g. via a yaw bearing unit. The rotor comprises a hub 4 and a number of wind turbine blades 5. Here three wind turbine blades are shown, but the rotor may comprise more or fewer wind turbine blades 5. The hub 4 is connected to a drive train, e.g. a generator, located in the wind turbine 1 via a rotation shaft.

(49) The hub 4 comprises a mounting interface for each wind turbine blade 5. A pitch bearing unit 6 is optionally connected to this mounting interface and further to a blade root of the wind turbine blade 5.

(50) FIG. 2 shows a schematic view of the wind turbine blade 5 which extends in a longitudinal direction from a blade root 7 to a tip end 8. The wind turbine blade 5 further extends in a chordwise direction from a leading edge 9 to a trailing edge 10. The wind turbine blade 5 comprises a blade shell 11 having two opposite facing side surfaces defining a pressure side 12 and a suction side 13 respectively. The blade shell 11 further defines a blade root portion 14, an aerodynamic blade portion 15, and a transition portion 16 between the blade root portion 14 and the aerodynamic blade portion 15.

(51) The blade root portion 14 has a substantially circular or elliptical cross-section (indicated by dashed lines). The blade root portion 14 together with a load carrying structure, e.g. a main laminate combined with a shear web or a box beam, are configured to add structural strength to the wind turbine blade 5 and transfer the dynamic loads to the hub 4. The load carrying structure extends between the pressure side 12 and the suction side 13 and further in the longitudinal direction.

(52) The blade aerodynamic blade portion 15 has an aerodynamically shaped cross-section (indicated by dashed lines) designed to generate lift. The cross-sectional profile of the blade shell 11 gradually transforms from the circular or elliptical profile into the aerodynamic profile in the transition portion 16.

(53) The wind turbine blade 5 has a longitudinal length 17 of at least 35 metres, preferably at least 50 metres. The wind turbine blade 5 further has a chord length 18 as function of the length 17, wherein the maximum chord length is found between the blade aerodynamic blade portion 15 and the transition portion 16. The wind turbine blade 5 further has a blade thickness 19 as function of the chord length 18, wherein the blade thickness 19 is measured between the pressure side 12 and the suction side 13.

(54) FIG. 3 shows an exemplary cross-sectional profile of the wind turbine blade 5 with a airfoil modifying device 19 arranged on the pressure side 12. The airfoil modifying device 19 is formed as a flexible device configured to passively deform relative to the blade surface of the pressure side 12 when influenced by the local air pressure. Here, the airfoil modifying device 19 is partly or fully made of an elastic material or composite. The wind turbine blade 5 is operated according to an angle of attack, α, of the wind, W, acting on the wind turbine blade 5.

(55) The airfoil modifying device 19 has local width C.sub.1 measured along the chord line 20 from a first edge 21 facing the leading edge 9 to a second edge 22 facing the trailing edge 10. Here, the airfoil modifying device 19 is arranged adjacent to the trailing edge 10 and extend partly along the pressure side 12. The first edge is positioned at a predetermined distance from the leading edge 9, as illustrated in FIGS. 3-4.

(56) The wind turbine blade 5 has an original airfoil profile formed by the blade shell 11 and thus the original blade surfaces. The profile of the airfoil modifying device 19 is passively deformed by means of the local air pressure acting on its outer surface. Here, the airfoil modifying device 19 is placed in a retracted position in which it substantially follows the original airfoil profile of the wind turbine blade 5, as illustrated in FIG. 3. In this position, the local air flow substantially follows the original airfoil profile along the pressure side 12.

(57) FIG. 4 shows the wind turbine blade 5 with the airfoil modifying device 19 placed in an extended position, wherein the airfoil modifying device 19 is deformed (indicated by arrow) relative to the original blade surface due to the local air pressure. Thereby, modifying the original blade surface and, in turn, also modifying the original airfoil profile of the wind turbine blade 5. In this position, the local air flow substantially follows this modified airfoil profile along the modified pressure side 12′.

(58) The wind turbine blade 5 has an original camber line 23 extending from the leading edge 9 to the trailing edge 10. The camber line 23 is defined by the original airfoil profile of the wind turbine blade 5. When activated, the modified airfoil profile formed by the airfoil modifying device 19 further forms a modified camber line 23′. Thereby, reducing the cambered profile of the wind turbine blade 5 at negative A.sub.OA.sub.S.

(59) In this configuration, the airfoil modifying device comprises a deformable element (see FIG. 8) configured to move freely between the first and second edges 21, 22. The deformable element is configured to function as a semipermeable membrane. Thereby, enabling it to adapt to the local air flow acting on the pressure side 12, 12′. When extending, air is guided into a local chamber formed between the original blade surface (see FIG. 8) and the deformable element via the semipermeable membrane. When retracting, air is guided out of the local chamber via the semipermeable membrane.

(60) FIG. 5a shows a first placement of the airfoil modifying device 19 and FIG. 5b shows a second placement of the airfoil modifying device 19. The airfoil modifying device 19 has local length L.sub.1 measured between a first end 24 facing the blade root 7 to a second end 25 facing the tip end 8.

(61) In FIG. 5a, the airfoil modifying device 19 is arranged fully on the aerodynamic blade portion 15 of the wind turbine blade 5. In FIG. 5b, the airfoil modifying device 19 is arranged partly on the aerodynamic blade portion 15 and partly on the transition portion 16 of the wind turbine blade 5.

(62) As indicated in FIG. 5a, a plurality (indicated by dashed lines) of airfoil modifying devices 19 may be arranged on the pressure side 12. The individual airfoil modifying devices 19 are all passively deformed by means of the local air pressure at the pressure side.

(63) FIG. 6 shows a third placement of the airfoil modifying device 19 where the airfoil modifying device 19 is arranged between the leading and trailing edges 9, 10 of the wind turbine blade 5. Here, the first edge 21 is positioned at a predetermined distance from the leading edge 9. Further, the second edge 22 is positioned at a predetermined distance from the trailing edge 10.

(64) As illustrated in FIGS. 5a, 5b and 6, the local width C.sub.1 of the airfoil modifying device 19 varies along the length of the wind turbine blade 5. The second edge 22 is thereby adapted to follow the trailing edge 10 profile of the wind turbine blade 5.

(65) FIG. 7a-b show two alternative attachments of the airfoil modifying device 19. the airfoil modifying device 19 is connected to the wind turbine blade 5, e.g. to the pressure side 12, at attachment points along the first and second edges 21, 22.

(66) In FIG. 7a, the airfoil modifying device 19 comprises first coupling elements 26 configured to engage second coupling elements 27 arranged on the wind turbine blade 5. Here, the first coupling elements 26 are shaped as hooks or J-shaped edges. The second coupling elements 27 are shaped as matching holes or eyes formed in the blade shell 11. The attachment points are optionally sealed off using a sealant or a deformable sealing element, e.g. a deformable bushing or sleeve.

(67) In FIG. 7b, the airfoil modifying device 19 comprises integrated flanges 28 projecting from the first and second edges 21, 22 respectively. The flanges 28 are configured to be attached to the blade shell 11 using adhesive or suitable fasteners, such as bolts.

(68) In both FIGS. 7a-b, the airfoil modifying device 19 is connected to the wind turbine blade 5, e.g. to the pressure side 12, at further attachment points along the first and second ends 24, 25. These attachment points are configured similarly to those shown in FIGS. 7a-b.

(69) FIG. 8 shows a second embodiment of the airfoil modifying device 19′. In this configuration, the airfoil modifying device 19 further comprises a filler element 29 arranged in the local chamber 31 formed between the deformable element 30 and the original blade surface 32. The filler element 29 is made of a flexible material or composite.

(70) The filler element 29 is configured to add support to the deformable element 30 and to guide it into a desired extended profile. Thereby, allowing the wind turbine blade 5 to transform into a desired modified airfoil profile when the airfoil modifying device 19′ is deformed by the local air pressure.

(71) Here, the filler element 29 has a honeycomb shaped structure forming a plurality of open cells. This honeycomb shaped structure acts as a thin and flexible structure capable of deforming together with the deformable element 30.

(72) An optional inner element 32a extends along the inner surface of the filler element 29. The inner element 32a is connected to the filler element 29 and further to the deformable element 30.

(73) FIG. 9a-b show a third embodiment of the airfoil modifying device 19″ placed in a retracted position and in an extended position. Here, the filler element 29′ has an alternative thin and flexible structure.

(74) The filler element 29′ has a different open celled structure configured to deform, e.g. retract, into a compact state, so that the profile of the airfoil modifying device 19′ substantially follows the original airfoil profile, as illustrated in FIG. 9b. When placed in the compact state, the deformable element 30 will substantially adapt to the shape of the original airfoil profile.

(75) This open celled structure is further configured to deform, e.g. extend, into a deployed state, wherein the filler element 29′ forms a predetermined outer profile. The deformable element 30 will follow this outer profile and thus form a desired outer profile, as illustrated in FIG. 9a. Thereby, forming a modified blade surface of the wind turbine blade 5.

(76) The deformable element 30 is formed as a semipermeable membrane, as indicated in FIG. 4, enabling air to be passively guided into or out of the local chamber 31 and thus the open celled structure formed by the filler element 29, 29′. Alternatively, the deformable element 30 may comprise means 33, e.g. integrated vent holes, configured to passively guide air into and out of the local chamber and, optionally, the open celled structure (indicated by dotted arrows).

(77) The abovementioned embodiments may be combined in any combinations without deviating from the present invention.