ROTOR BLADE WITH SERRATIONS

Abstract

A rotor blade for a wind turbine is provided, wherein the rotor blade includes serrations along at least a portion of the trailing edge section of the rotor blade. The serrations include a first tooth and at least a second tooth, and the first tooth is spaced apart from the second tooth. The area between the first tooth and the second tooth is at least partially filled with porous material such that generation of noise in the trailing edge section of the rotor blade is reduced. Furthermore, the embodiments relate to a wind turbine including at least one such a rotor blade.

Claims

1. A rotor blade for a wind turbine, wherein the rotor blade comprises serrations along at least a portion of the trailing edge section of the rotor blade, the serrations comprise a first tooth and at least a second tooth, and the first tooth is spaced apart from the second tooth, wherein the area between the first tooth and the second tooth is at least partially filled with porous material such that generation of noise in the trailing edge section of the rotor blade is reduced.

2. The rotor blade according to claim 1, wherein the open area fraction of the porous material is greater than 10 percent and/or smaller than 90 percent.

3. The rotor blade blade according to claim 1, wherein the porous material is a mesh comprising a plurality of strands which are connected to each other in a regular pattern.

4. The rotor blade blade according to claim 1, wherein the porous material is made of an open-cell foam.

5. The rotor blade blade for a wind turbine, wherein the rotor blade comprises serrations along at least a portion of the trailing edge section of the rotor blade, the serrations comprise a first tooth and at least a second tooth, and the first tooth is spaced apart from the second tooth, characterized in that wherein the area between the first tooth and the second tooth is at least partially filled with a plurality of fibers such that generation of noise in the trailing edge section of the rotor blade is reduced.

6. The rotor blade blade according to claim 5, wherein the fibers are arranged substantially parallel to each other, in particular in substantially chordwise direction of the rotor blade.

7. The rotor blade blade according to claim 5, wherein the fibers are tapered in direction towards the trailing edge of the rotor blade.

8. The rotor blade blade according to claim 5, wherein the plurality of fibers comprises a first portion which is arranged within the chordal plane of the rotor blade, and a second portion which is arranged outside the chordal plane of the rotor blade.

9. The rotor blade blade according to claim 8, wherein the second portion is adjacent to the trailing edge of the rotor blade.

10. The rotor blade blade according to claim 5, wherein the fibers are arranged such that the trailing edge of the rotor blade between the tip of the first tooth and the tip of the second tooth is formed by a substantially straight line.

11. The rotor blade blade according to claim 5, wherein the fibers are arranged such that the trailing edge of the rotor blade between the tip of the first tooth and the tip of the second tooth is formed by a line which is deviating from a straight line in the direction towards the leading edge of the rotor blade.

12. The rotor blade blade according to claim 1, wherein an aerodynamic device for manipulating an airflow which is flowing across the aerodynamic device is mounted upstream of the first tooth and the second tooth.

13. The rotor blade blade according to claim 12, wherein the aerodynamic device is arranged at a pressure side and/or at a suction side of the rotor blade.

14. The rotor blade blade according to claim 12, wherein the aerodynamic device comprises a plurality of fins and/or a plurality of ridges.

15. A wind turbine with at least one rotor blade according to claim 1.

Description

BRIEF DESCRIPTION

[0053] Some of the embodiments will be described in detail, with references to the following figures, wherein like designations denote like members, wherein:

[0054] FIG. 1 shows a wind turbine;

[0055] FIG. 2 shows an inventive rotor blade for a wind turbine;

[0056] FIG. 3 shows a serrated panel with porous material between adjacent teeth;

[0057] FIG. 4 shows serrations with a plurality of fibers in a first embodiment;

[0058] FIG. 5 shows serrations with a plurality of fibers in a second embodiment;

[0059] FIG. 6 shows serrations with a plurality of fibers in a third embodiment;

[0060] FIG. 7 shows serrations with a plurality of fibers in a fourth embodiment;

[0061] FIG. 8 shows serrations with a plurality of fibers in a fifth embodiment;

[0062] FIG. 9 shows serrations with fins on one side and a plurality of fibers;

[0063] FIG. 10 shows serrations with fins on both sides and a plurality of fibers;

[0064] FIG. 11 shows serrations with ridges and a plurality of fibers;

[0065] FIG. 12 shows a first variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0066] FIG. 13 shows a second variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0067] FIG. 14 shows a third variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0068] FIG. 15 shows a fourth variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0069] FIG. 16 shows a fifth variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0070] FIG. 17 shows a sixth variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0071] FIG. 18 shows a seventh variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0072] FIG. 19 shows an eighth variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0073] FIG. 20 shows a ninth variant how to arrange a region of porous material at the trailing edge section of a rotor blade;

[0074] FIG. 21 shows a tenth variant how to arrange a region of porous material at the trailing edge section of a rotor blade; and

[0075] FIG. 22 shows an eleventh variant how to arrange a region of porous material at the trailing edge section of a rotor blade.

DETAILED DESCRIPTION

[0076] The illustration in the drawings is in schematic form. It is noted that in different figures, similar or identical elements may be provided with the same reference signs.

[0077] In FIG. 1, a wind turbine 10 is shown. The wind turbine 10 comprises a nacelle 12 and a tower 11. The nacelle 12 is mounted at the top of the tower 11. The nacelle 12 is mounted rotatable with regard to the tower 11 by means of a yaw bearing. The axis of rotation of the nacelle 12 with regard to the tower 11 is referred to as the yaw axis.

[0078] The wind turbine 10 also comprises a hub 13 with three rotor blades 20 (of which two rotor blades 20 are depicted in FIG. 1).

[0079] The hub 13 is mounted rotatable with regard to the nacelle 12 by a main bearing. The hub 13 is mounted rotatable about a rotor axis of rotation 14.

[0080] The wind turbine 10 furthermore comprises a main shaft, which connects the hub 13 to a rotor of a generator 15. The hub 13 is connected directly to the rotor of the generator 15, thus the wind turbine 10 is referred to as a gearless, direct driven wind turbine. As an alternative, the hub 13 may also be connected to the rotor of the generator 15 via a gearbox. This type of wind turbine is referred to as a geared wind turbine.

[0081] The generator 15 is accommodated within the nacelle 12. It comprises the rotor and a stator. The generator 15 is arranged and prepared for converting the rotational energy from the rotor into electrical energy.

[0082] FIG. 2 shows a rotor blade 20 of a wind turbine. The rotor blade 20 comprises a root section 21 with a root 211 and a tip section 22 with a tip 221. The root 211 and the tip 221 are virtually connected by the span 26 which follows the shape of the rotor blade 20. If the rotor blade were a rectangular shaped object, the span 26 would be a straight line. However, as the rotor blade 20 features a varying thickness, the span 26 is slightly curved, i.e., bent as well. Note that if the rotor blade 20 was bent itself, then the span 26 would be bent, too.

[0083] The rotor blade 20 furthermore comprises a leading edge section 24 with a leading edge 241 and a trailing edge section 23 with a trailing edge 231.

[0084] The trailing edge section 23 surrounds the trailing edge 231. Likewise, the leading edge section 24 surrounds the leading edge 241.

[0085] At each spanwise position, a chord line 27 which connects the leading edge 241 with the trailing edge 231 can be defined. Note that the chord line 27 is perpendicular to the span 26. The shoulder 28 is defined in the region where the chord line comprises a maximum chord length.

[0086] FIG. 2 furthermore discloses serrations 30 which are located in the outboard section of the rotor blade 20. More particularly, the serrations 30 are located at the trailing edge section 23 of the rotor blade 20. The serrations 30 comprise a plurality of adjacent teeth. The chordwise extension of the teeth is decreasing towards the tip 221 of the rotor blade 20. Note that a plurality of fibers is entirely filling the area between adjacent teeth of the serrations 30 (symbolized by the hatched area). The trailing edge 231 in the outboard section of the rotor blade where the serrations 30 are attached is represented by the outermost part of the fibers and the tips of the serrations 30.

[0087] FIG. 3 shows a serrated panel 41 which is arranged and prepared for being attached to a rotor blade for a wind turbine. The serrated panel 41 comprises a porous material between its serrations. Exemplarily, the serrated panel 41 is made of plastic and has been produced by injection molding. The serrated panel 41 comprises an attachment portion 43 which is arranged and prepared for attaching the serrated panel 41 to the remaining part of the rotor blade. The serrated panel 41 furthermore comprises a portion with serrations 30. The serrations comprise a plurality of teeth. In particular a first tooth 31, a second tooth 32, a third tooth 33 and a fourth tooth 34 are illustrated in FIG. 3. All teeth 31-34 shown in FIG. 3 have substantially the same shape, namely a triangular shape as seen in a top view. The triangles comprise rounded tips. Alternatively, the triangle-shaped teeth may also comprise a sharp tip. In the area 35 between the first tooth 31 and the second tooth 32 a mesh is placed. The mesh serves as porous material for modifying the recovery of the pressure gradient from the pressure side to the suction side in a favorable, noise reducing way. Furthermore, the mesh is designed to shift the frequencies of the generated noise to higher values. The mesh is made of a plurality of first strands which are substantially parallel to each other and which cross a plurality of second strands which themselves are substantially parallel to each other as well. Thus, a regular and reproducible porous material is obtained. The mesh fills the whole area 35 between the first tooth 31 and the second tooth 32. It also covers the areas between the further teeth 32, 33, 34 of the serrations 30.

[0088] Note that the rotor blade may also comprise a plurality of serrated panels 41 with one panel being lined up next to each other in spanwise direction. Adjacent panels may advantageously overlap at its sides in order to reduce whistle tones which otherwise might be generated at the border where two adjacent panels meet.

[0089] FIG. 4 shows another serrated panel 41. In this embodiment, the porous material is realized by a set of fibers 42. These fibers 42, which can also be described as bristles or needles, are orientated in substantially chordwise direction of the rotor blade. This has to be understood that the serrated panel 42 is arranged and prepared to be attached to the remaining part of the rotor blade in such a manner that the fibers 42 are orientated in chordwise direction after attaching the serrated panel 41 to the remaining rotor blade. Note that the fibers 42 between the first tooth 31 and the second tooth 32 all end at approximately the same chordwise position. Thus, a straight trailing edge 231 is obtained.

[0090] In contrast to that, the length of the fibers between the second tooth 32 and the third tooth 33 as well as between the third tooth 33 and the fourth tooth 34 are varying. This leads to a trailing edge 231 which is retracted, i.e. shifted towards the leading edge once the serrated panel 41 has been attached to the remaining rotor blade. Such a shape of the fibers 42 has the advantage that more flexibility in the design of the porous material is given and further improvement potential regarding noise reduction is given. In the embodiment of FIG. 4 only a variation in the length of the fibres 42 is realized. This means that still all fibers 42 are arranged within the chordal plane of the rotor blade.

[0091] FIG. 5 shows an embodiment of the invention wherein the fibers 42 are within the chordal plane in a first portion 36, but which are outside of the chordal plane in a second portion 37. Thus, an undulating or wavy shape of the porous material as viewed in a cross-sectional view is obtained. This design also has the potential of further improvement of noise reduction. Note that FIG. 5 illustrates a permanent deflection of the fibers 42 out of the chordal plane in the second portion 37 and not a bending of the fibers 42 under extreme loading. Variations in the orientation of the fibers 42 due to loading of the fibers 42 may additionally occur.

[0092] It may be advantageous that the fibers 42 are tapered towards the trailing edge 231. This may be advantageous in terms of structural considerations.

[0093] Regarding the length variations of the fibers, a sine wave shape may be particularly advantageous.

[0094] Exemplary dimensions of a fiber between adjacent teeth may be two millimeters in diameter and between one and ten centimeters in length.

[0095] FIGS. 6 to 12 disclose exemplary embodiments how the serrations and the plurality of fibers may be concretely configured and arranged.

[0096] FIG. 6 shows a first tooth 31 and a second tooth 32, being separated and spaced apart by an area 35. In this area 35, a plurality of fibers 42 is arranged. The fibers 42 are orientated substantially parallel to each other. Additionally, the fibers 42 are orientated substantially parallel to the chordwise direction of the rotor blade at this radial position, i.e. at this spanwise position.

[0097] In comparison to FIGS. 4 and 5, which illustrate the arrangement of the fibers 42 between the teeth 31, 32, 33, 34 in a more schematic way, FIG. 6 seeks to illustrate an exemplary configuration and arrangement of the fibers 42 in a more detailed manner. For instance, the fibers 42 are depicted as three-dimensional objects, showing that the fibers 42 may in practice advantageously have a certain thickness in order to provide the desired stiffness. As a result, the fibers 42 do not substantially bend during standard operation conditions of the wind turbine, as neither the serrations 31, 32 do.

[0098] FIG. 7 shows an alternative embodiment of the invention. The only difference of this embodiment compared to the embodiment as illustrated in FIG. 6 is the chordwise length of the fibers 42. While in the embodiment of FIG. 6 the lengths of the fibers are chosen such that the result is a straight trailing edge of the rotor blade, in the embodiment of FIG. 7 the fibers in the center portion of the area 35 between adjacent teeth 31, 32 are chosen to have a comparatively shorter length.

[0099] FIG. 8 illustrates another variant of how to configure and arrange the fibers 42. Like in the embodiment of FIG. 6, the lengths of the fibers 42 are chosen such that the result is a straight trailing edge 231 of the rotor blade. As a difference, the thickness of the fibers 42 decreases towards the respective tips of the fibers 42. In other words, the fibers 42 are tapered towards the tip. Optionally, the teeth 31, 32 of the serrations may also feature a decreasing thickness.

[0100] FIGS. 9 to 12 shows various examples how a serrated panels with fibers can be combined with other aerodynamic devices.

[0101] FIG. 9 illustrates the arrangement of fins 44 upstream of the teeth 31, 32 of the serrated panel 41. The fins 44 can be seen as another means to manipulate the airflow across the rotor blade such that eventually the noise, which is generated in the trailing edge section of the rotor blade, is reduced. The fins 44 may be arranged on one side of the serrated panel 41, e.g. at the suction side.

[0102] The fins 44 may alternatively also be arranged on both sides of the serrated panel, i.e. at both the pressure and the suction side. Such an embodiment is illustrated in FIG. 10. The fins which are arranged at the suction side of the rotor blade are referred to as suction side fins 441, the fins which are arranged at the pressure side of the rotor blade are referred to as pressure side fins 442.

[0103] FIG. 11 illustrates an embodiment of a serrated panel 41 with ridges 45. The ridges 45 have the objective to guide the airflow and/or break up spanwise coherence of the airflow. The ridges may be arranged at the pressure side of the rotor blade (as in the example shown in FIG. 11), at the suction side of the rotor blade, or on both sides. The ridges 45 may be arranged upstream of the serrations and may extend the fibers 42.

[0104] FIGS. 12 to 22 show eleven different variants how to arrange a region of porous material at the trailing edge section 23 of a rotor blade.

[0105] As seen in chordwise direction 271 from the leading edge towards the trailing edge of the rotor blade, the trailing edge section 23 starts with a base line f0, which extends substantially perpendicular to the chordwise direction 271. Continuing further towards the trailing edge 231, the trailing edge section 23 comprises a first region 52. The first region 52 is characterized by substantially solid material. The first region 52 is limited at the one side by the base line f0 and at the other side by a first dividing line f1. Continuing further towards the trailing edge 231, the trailing edge section 23 further comprises a second region 53. The second region 53 is characterized by substantially porous material. The second region 53 is limited at the one side by the first dividing line f1 and at the other side by a second dividing line f2. The second dividing line f2 coincides with the trailing edge 231 of the rotor blade.

[0106] The first and second dividing lines f1, f2 may in principle have any shape: They may be periodic or non-periodic, straight or curved, its derivatives may be continuous or discontinuous (in spanwise direction 272), et cetera. Some possible design choices are disclosed in FIGS. 12 to 22.

[0107] In FIG. 12, the first dividing line f1 is serrated and the second dividing line f2 is straight.

[0108] In FIG. 13, both the first dividing line f1 and the second dividing line f2 are serrated. Both dividing lines f1, f2 have the same periodicity.

[0109] The embodiment of FIG. 14 is similar to the one of FIG. 13, but the serrations of the second dividing line f2 are pointing away from the base line f0 instead of towards the base line f0.

[0110] The embodiment of FIG. 15 is also similar to the one of FIG. 13, but the serrations of the second dividing line f2 are smoothenedthey actually resemble more comprising a wave form instead of serrations.

[0111] In FIG. 16, both the first dividing line f1 and the second dividing line f2 comprise a wave form. Both dividing lines f1, f2 have the same periodicity.

[0112] In FIG. 17, the first dividing line f1 is serrated and the second dividing line is chosen such that only a part of the area between adjacent teeth of the first region 52 is filled with porous material, i.e. with the second region 53.

[0113] In FIG. 18, both the first dividing line f1 and the second dividing line f2 resemble a pulse form. Both dividing lines f1, f2 have the same periodicity.

[0114] In FIG. 19, both the first dividing line f1 and the second dividing line f2 comprise a wave form, in particular a sine wave form. The periodicity of the first dividing lines f1 differs from the periodicity of the second dividing line f2.

[0115] In FIG. 20, both the first dividing line f1 and the second dividing line f2 have a random form, resulting in a chaotic pattern.

[0116] The embodiment of FIG. 21 resembles FIG. 19, but both dividing lines f1, f2 having the same periodicity instead of differing periodicities.

[0117] Finally, in FIG. 22, both the first dividing line f1 and the second dividing line f2 are straight.

[0118] Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

[0119] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.