Noise reducer for a wind turbine rotor blade

Abstract

The present invention relates to a wind turbine rotor blade assembly comprising a rotor blade and a noise reducer (70) configured on the rotor blade. The noise reducer (70) comprises a plurality of aligned spine members (72), each spine member having a length and comprising a first section (74) extending along a first part of the length of the spine member, and a second section (76) extending along a second part of the length of the spine member, wherein the first section (74) has a higher stiffness than the second section (76).

Claims

1. A wind turbine rotor blade assembly comprising: a rotor blade having exterior surfaces defining a pressure side, a suction side, a leading edge and a trailing edge, each of the pressure side, the suction side, the leading edge and the trailing edge extending between a tip end and a root end, the rotor blade defining a span and a chord; a noise reducer (70) configured on the rotor blade, the noise reducer (70) comprising a plurality of aligned spine members (72), each spine member having a length and comprising: a first section (74) extending along a first part of the length of the spine member, and a second section (76) extending along a second part of the length of the spine member, wherein the first section (74) has a higher stiffness than the second section (76), wherein the first section (74) is adjacent to the second section (76) such that an interface (82) is formed between the first section (74) and the second section (76), and wherein a chordwise location of the interface (82) varies between different ones of the spine members (72) of the noise reducer (70).

2. The wind turbine rotor blade assembly according to claim 1, wherein each spine member comprises a proximal end (78) and a distal end (80), wherein the second section (76) includes the distal end (80).

3. The wind turbine rotor blade assembly according to claim 1, wherein the second section (76) of the spine member is formed from a material having a modulus of elasticity of 1 GPa or less.

4. The wind turbine rotor blade assembly according to claim 3, wherein the material has a modulus of elasticity of 0.1 GPa or less.

5. The wind turbine rotor blade assembly according to claim 1, wherein the second section (76) is substantially cone-shaped.

6. The wind turbine rotor blade assembly according to claim 1, wherein the interfaces (82) of the plurality of spine members (72) are arranged along an undulated, spanwise extending path across the noise reducer (70).

7. The wind turbine rotor blade assembly according to claim 1, wherein the spine members (72) of the noise reducer are arranged to form a serrated structure (90a, 90h, 90c).

8. The wind turbine rotor blade assembly according to claim 1, wherein the spine members (72) have a circular or elliptical cross section at least along part of their length.

9. The wind turbine rotor blade assembly according to claim 1, wherein a diameter or thickness of the spine members (72) decreases from the first section (74) to the second section (76).

10. The wind turbine rotor blade assembly according to claim 1, wherein a diameter or thickness of the first section (74) is higher than a diameter or thickness of the second section (76).

11. The wind turbine rotor blade assembly according to claim 1, wherein adjacent spine members (72) are connected along at least part of their respective first sections (74).

12. The wind turbine rotor blade assembly according to claim 1, wherein each of the spine members further comprises a third section (84) extending along a third part of the length of the respective spine member and including the proximal end (78) of the respective spine member, wherein the respective third sections (84) of the aligned spine members (72) form a mounting plate for mounting of the noise reducer (70) to the rotor blade.

13. A wind turbine comprising a wind turbine rotor blade assembly according to claim 1.

14. A panel for a wind turbine rotor blade, wherein the panel is configured for attachment to the wind turbine rotor blade, the panel comprising: a plurality of aligned spine members (72), each spine member having a length and comprising: a first section (74) extending along a first part of the length of the spine member, and a second section (76) extending along a second part of the length of the spine member, wherein the first section (74) has a higher stiffness than the second section (76), wherein the first section (74) is adjacent to the second section (76) such that an interface (82) is formed between the first section (74) and the second section (76), and wherein a chordwise location of the interface (82) varies between different ones of the spine members (72) of the noise reducer (70).

15. The panel for a wind turbine rotor blade according to claim 14, wherein the panel is configured for attachment to a trailing edge of the wind turbine rotor blade.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a wind turbine;

(3) FIG. 2 shows a schematic view of a wind turbine blade according to the invention;

(4) FIG. 3 shows a schematic view of an airfoil profile of the blade of FIG. 2;

(5) FIG. 4 shows a schematic view of the wind turbine blade of FIG. 2, seen from above and from the side;

(6) FIG. 5 illustrates a set of trailing edge serrations;

(7) FIG. 6 is a partial perspective view of a noise reducer according to one embodiment of the present invention;

(8) FIG. 7 shows a top view of a noise reducer according to the present invention;

(9) FIG. 8 is a partial perspective view of a noise reducer according to one embodiment of the present invention;

(10) FIG. 9 is a partial perspective view of a noise reducer according to one embodiment of the present invention; and

(11) FIG. 10 is a partial perspective view of a noise reducer according to another embodiment of the present invention.

(12) It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings.

(13) FIG. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8, the blade extending in a spanwise direction between the root 16 and the tip 14. The rotor has a radius denoted R.

(14) FIG. 2 shows a schematic view of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18. A noise reducer 70 in the form of an array of trailing edge serrations 21 is provided along a portion of the trailing edge 20 of the blade. In general, flow of air over the wind turbine blade 10 extends from the leading edge 18 to the trailing edge 20 in a generally transverse or chordwise direction. While the noise reducer 70 in FIG. 2 is depicted as being arranged along a middle portion of the blade, it is recognised that the noise reducer may be arranged for instance closer to the tip of the blade 10, or that it may be arranged along for instance the entire airfoil region 34 of the blade 10.

(15) The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 is typically constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increasing distance r from the hub.

(16) The airfoil region 34 has an airfoil profile 50 with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

(17) It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

(18) FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use—i.e. during rotation of the rotor—normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58, The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

(19) Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

(20) FIG. 4 shows sonic other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 2, the root end is located at position r=0, and the tip end located at r=L. The shoulder 41 of the blade is located at a position r=L.sub.w, and has a shoulder width W, which equals the chord length at the shoulder 41. The diameter of the root is defined as D. Further, the blade is provided with a pre-bend, which is defined as Δy, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

(21) The wind turbine blade 10 generally comprises a shell made of fibre-reinforced polymer, and is typically made as a pressure side or upwind shell part 24 and a suction side or downwind shell part 26 that are glued together along bond lines 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of 30 or 40 metres in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading.

(22) With reference to FIG. 5, an enlarged view of a plurality of prior art serrations 100 of the serrated trailing edge 21 are shown. The serrations 100 comprise a base end 102 which is arranged at the trailing edge 20 of the wind turbine blade 10, and a tip end 104 which extends downwind of the blade trailing edge 20. A notional line extending from a midpoint of the base 102 to the apex or tip end 104 defines a height H of the serration. The illustrated serrations are substantially planar, but it will be understood that the serrations may vary in depth or thickness, in particular having tapered or chamfered edges. The serrations 100 are shown as having a profile substantially corresponding to an isosceles triangle, but it will be understood that other serration shape profiles may be used, e.g. curved, wave-shaped profiles, or crenulated edges.

(23) FIG. 6 is a partial perspective view of a noise reducer 70 according to one embodiment of the present invention. The noise reducer 70 comprises a plurality of aligned spine members 72a, 72b, each spine member having a length Ls, as illustrated for spine member 72a. Each spine member comprises a first section 74a, 74b extending along a first part of the length of the spine member 72a, 72b, and a second section 76a, 76b extending along a second part of the length of the spine member, wherein the first section 74a, 74b has a higher stiffness than the second section.

(24) As also seen in FIG. 6, each spine member comprises a proximal end 78 and a distal end 80, as illustrated for spine member 72b, wherein the second section 76 includes the distal end 80. As also seen FIGS. 9 and 10, the second section 76 is substantially cone-shaped. An interface 82 exists between the first section 74 and the adjacent second section 76. Preferably, each spine member 72 may further comprise a third section 84a, 84b, extending along a third part of the length of the spine member 72 and including the proximal end 78 of the spine member 72, wherein the respective third sections 84a, 84b of the aligned spine members 72a, 72b form a mounting plate 86 for mounting of the noise reducer 70 to the rotor blade. As illustrated in FIGS. 8 and 9, the third section 84 may have a substantially semi-circular or semi-elliptical cross section.

(25) As best seen in FIGS. 9 and 10, the chordwise location of the interfaces 82a, 82b each vary between different spine members of the noise reducer. The spine members will usually be substantially aligned along the chordwise direction of the blade, as seen FIG. 2.

(26) FIG. 7 is a top view of a noise reducer 70 according to the present invention, comprising 54 spine members substantially aligned in a chordwise direction. When arranged on the rotor blade, air flows over the noise reducer 70 in a generally transverse or chordwise direction as indicated by arrow Fc. As indicated by the dashed curve in FIG. 7, the interfaces 82 of the plurality of spine members are arranged along an undulated, spanwise extending path across the noise reducer 70. The spanwise direction is indicated at Sp. Also, collectively the plurality of spine members 72 forms a serrated structure with serrations 90a, 90b, 90c.

(27) As best seen in FIG. 8, the spine members 72 may have a circular or elliptical cross section at least along part of their length, in particular along their first section 74 and their second section 76. The diameter of the spine members 72 may decrease from the first section 74 to the second section 76. Thus, a diameter or thickness of the first section 74 is higher than a diameter or thickness of the second section 76.

(28) As illustrated in FIGS. 9 and 10, adjacent spine members 72a, 72b are connected along at least part of their respective first sections 74a, 74b, preferably along their entire respective first sections 74a, 74b. By contrast, the respective second sections 76a, 76b of adjacent spine members are not connected to each other and can thus swing or resonate individually. The spine members 72 may provide a substantially ribbed or undulated surface 88 of the noise reducer 70.

(29) The invention is not limited to the embodiments described herein and may be modified or adapted without departing from the scope of the present invention.