ROTOR BLADE WITH A SERRATED TRAILING EDGE

Abstract

A rotor blade for a wind turbine, wherein the rotor blade includes serrations along at least a portion of the trailing edge section of the rotor blade is provided. The serrations include a first tooth and at least a second tooth, wherein the first tooth is spaced apart from the second tooth. Furthermore, the area between the first tooth and the second tooth is at least partially filled with a plurality of comb elements, wherein the comb elements are arranged substantially parallel to each other and in substantially chordwise direction of the rotor blade such that generation of noise in the trailing edge section of the rotor blade is reduced. The rotor blade is further characterized in that it includes a plurality of ridges including a first ridge and at least a second ridge for manipulating an airflow which is flowing along the ridges.

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, wherein 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 a plurality of comb elements comprising a first comb element and at least a second comb element, wherein the comb elements are arranged substantially parallel to each other and in substantially chordwise direction of the rotor blade, such that generation of noise in the trailing edge section of the rotor blade is reduced, wherein the rotor blade further comprises a plurality of ridges comprising a first ridge and at least a second ridge for manipulating an airflow which is flowing along the ridges.

2. The rotor blade according to claim 1, wherein the ridges are arranged substantially parallel to each other and in substantially chordwise direction of the rotor blade.

3. The rotor blade according to claim 1, wherein the first ridge comprises a length which is at least three times greater, in particular at least five times greater, than its height, and/or at least three times greater, in particular at least five times greater, than its width.

4. The rotor blade according to claim 1, wherein the ridges are aligned with the comb elements.

5. The rotor blade according to claim 1, wherein each comb element of the plurality of comb elements is associated with one ridge of the plurality of ridges.

6. The rotor blade according to claim 1, wherein every second comb element of the plurality of comb elements is associated with one ridge of the plurality of ridges.

7. The rotor blade according to claim 1, wherein the first ridge comprises a trailing edge facing the trailing edge of the rotor blade, and a leading edge facing away from the trailing edge of the rotor blade.

8. The rotor blade according to claim 7, wherein the first ridge comprises a trailing edge which extends onto the first tooth of the serrations.

9. The rotor blade according to one of the claims 7, wherein the trailing edge of the first ridge is smoothly fading out towards the trailing edge of the rotor blade.

10. The rotor blade according to one of the claim 7, wherein the trailing edge of the first ridge has a shape of a quarter circle in a sectional view.

11. The rotor blade according to claim 1, wherein the rotor blade comprises a rotor blade body and a serrated plate, the ridges and the comb elements are mounted on the plate, and the plate is attached to either the pressure side or the suction side of the rotor blade body by an attachment section of the plate.

12. The rotor blade according to claim 10, wherein the leading edge of the first ridge extends onto the surface of the rotor blade body, in particular onto the suction side of the rotor blade body.

13. The rotor blade according to claim 1, wherein the maximum height of the first ridge is less than twenty millimeters.

14. A wind turbine for generating electricity with at least one rotor blade according to claim 1.

Description

BRIEF DESCRIPTION

[0048] Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

[0049] FIG. 1 shows a wind turbine;

[0050] FIG. 2 shows a known art rotor blade of a wind turbine with a serrated trailing edge;

[0051] FIG. 3 shows a trailing edge section of a rotor blade according to a first embodiment of the invention;

[0052] FIG. 4 shows a serrated plate of a rotor blade according to a second embodiment of the invention;

[0053] FIG. 5 shows a top view onto the suction side of a part of a serrated plate of a rotor blade according to a third embodiment of the invention;

[0054] FIG. 6 shows an enlarged view of a part of FIG. 5;

[0055] FIG. 7 shows a top view onto the pressure side of a part of the serrated plate of a rotor blade according to the third embodiment of the invention;

[0056] FIG. 8 shows a top view onto the pressure side of a part of the serrated plate of a rotor blade according to a variant of the third embodiment of the invention; and

[0057] FIG. 9 shows a section view of a serrated plate of a rotor blade with a suction side ridge according to a fourth embodiment of the invention.

DETAILED DESCRIPTION

[0058] 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.

[0059] FIG. 1 is a highly schematic drawing of a wind turbine 10. The wind turbine 10 comprises a tower 11 and a nacelle 12. The nacelle 12 is rotatable mounted at the top of the tower 11. This enables a so-called yaw movement of the nacelle 12 with regard to the tower 11. The nacelle 12 accommodates the generator of the wind turbine 10 and several other components of the wind turbine 10.

[0060] The wind turbine 10 further comprises a hub 13 which is mounted rotatable with regard to the nacelle 12. The hub 13 is able to perform a rotational movement about a rotational axis 14. This rotational movement is transformed into electricity by the generator of the wind turbine 10.

[0061] The energy of the wind is captured by the rotor blades 20. Wind turbines typically comprise at least two rotor blades, preferably three. Each rotor blade 20 is mounted in a pivotable manner to the hub 13 at its respective root section 21. The pivotable attachment of the rotor blade 20 allows for a pitch movement of the rotor blade 20, which in turn allows for an optimum efficiency of the wind turbine 10 over a broad range of wind speeds, typically between three and thirty meter/seconds. The pitch movement is carried out about a pitch axis 15 which basically extends from the root section 21 until the tip section 22 of the rotor blade 20.

[0062] FIG. 2 is a perspective view of a known art rotor blade 20 of a wind turbine. The rotor blade 20 comprises a serrated trailing edge in its tip section 22 and further inboard thereof. The point of the rotor blade 20 which is furthest away from the root section 21 is referred to as the tip 221 of the rotor blade 20. The main portion of the rotor blade 20 is represented by the airfoil portion. The airfoil portion is generally characterized by an airfoil shape of the respective cross-sections. The airfoil shape is able to generate lift when impacted by a flow of a fluid, such as air.

[0063] In FIG. 2, one airfoil is exemplarily drawn in. The airfoil comprises a suction side 26 and a pressure side 25. Both sides 25, 26 are separated from each other by the chord line 27. The chord line 27 is a straight line connecting the leading edge section 24 and the trailing edge section 23 of the rotor blade 20. The trailing edge section 23 frequently has the shape of a relatively sharp edge, in particular towards the tip section 22 of the rotor blade 20.

[0064] FIG. 2 illustrates serrations 30 which are provided at the trailing edge section 23 in the outboard part, i.e. the radially outer half of the rotor blade 20. The serrations 30 comprise a plurality of triangular-shaped teeth. The serrations 30, which may be realized by a serrated plate (which is commonly also referred to as a serrated panel), may e.g. be attached to the pressure side 25 of the rotor blade. Alternatively, the plate may also be slid into a gap (or slit) which is provided at the trailing edge after manufacturing of the two half-shells of the rotor blade.

[0065] FIG. 3 shows a schematic sectional view of a trailing edge section 23 of a rotor blade according to a first embodiment of the invention. The rotor blade comprises a rotor blade body 41 and a plate 42 with serrations. The presence of the serrations is not visible in FIG. 3 due to the sectional view character of the drawing.

[0066] The plate 42 comprises a pressure side 421, a suction side 422, an attachment section 423 and an alignment section 424. The attachment section 423 is destined for attaching the plate 42 to remaining parts of the rotor blade, such as a rotor blade body 41. The alignment section 424 is destined for aligning the plate 42 to the remaining rotor blade during attachment of the plate 42. In the example shown in FIG. 3, the plate 42 is attached to the rotor blade body 41 at the pressure side 25 of the rotor blade body 41. The attachment of the plate 42 at the pressure side 25 of the rotor blade body 41 is advantageous in terms of a minimum aerodynamic impact, compared to an attachment of the plate 42 at the suction side 26 of the rotor blade body 41.

[0067] The alignment section 424 is designed as a step-like flange. A first reason for the provision of such a flange is the improved alignment of the plate 42 with the rotor blade body 41 during attachment of the plate 42 at the trailing edge section 23 of the rotor blade 20. A second reason for the presence of such a flange is ease of manufacturing, as it is relatively complex to manufacture a truly sharp trailing edge compared to the manufacturing of a trailing edge comprising a certain thickness.

[0068] The plate 42 as illustrated in FIG. 3 is equipped with a ridge 50 at its suction side 422. Therefore, the ridge 50 is also referred to as a suction side ridge. The ridge 50 comprises a leading edge 52 and a trailing edge 51. The trailing edge 51 represents the portion of the ridge 50 which is facing towards the trailing edge 231 of the rotor blade. Note that generally that part of the rotor blade which is located furthest downstream is referred to as the trailing edge of the rotor blade. Without the plate 42, the region 411 would represent the trailing edge of the rotor blade; with the plate 42 mounted to the rotor blade body 41, the region 231 represents the trailing edge of the rotor blade.

[0069] The leading edge 52 of the ridge 50 is defined as that part of the ridge 50 which is facing away from the trailing edge 231 of the rotor blade. Alternatively, the leading edge 52 of the ridge 50 may also be defined as that part of the ridge 50 which is facing towards the leading edge of the rotor blade.

[0070] In the exemplary first embodiment of the invention, the ridge 50 has a gradually increasing height at its leading edge 52 and an abrupt edge at its trailing edge 51. The design of the edges 51, 52 has a significant impact how the airflow 43 which is flowing along the ridges 50 is manipulated.

[0071] FIG. 4 shows a perspective view of a serrated plate 42 of a rotor blade according to a second embodiment of the invention. FIG. 4 provides a view on the pressure side of the plate 42. Similar to the serrated plate 42 of the first embodiment illustrated in FIG. 3, also the plate 42 according to the second embodiment of the invention comprises a section which is destined for attaching the plate 42 to the pressure side of a rotor blade body. This section is referred to as the attachment section 423. The plate 42 also comprises an alignment section 424, which is characterized by a small step-like flange.

[0072] In contrast to the first embodiment of the invention, the serrated plate 42 of the second embodiment comprises a plurality of ridges at its pressure side. Therefore, these ridges are referred to as pressure side ridges 502. The pressure side ridges gradually rise at the upstream end (as seen in the direction of the airflow) of the attachment section 423 and smoothly fade out at the bases of the teeth.

[0073] The serrated plate 42 also comprises a plurality of comb elements 33. The comb elements 33 are arranged in the areas 32 between adjacent teeth, such as between the first tooth 311 and the second tooth 312. The ridges 502 and the comb elements 33 are aligned with each other. In particular, they are parallel with each other. Furthermore, every second comb element 33 is aligned and associated with one ridge 502. The ridge-to-comb element ratio is therefore 1:2. It may also be said that every ridge 502 is extended, i.e. prolonged by a comb element 33. Mounting a serrated plate 42 to a trailing edge section of a rotor blade body is a promising way to provide a significant noise reduction at the trailing edge section of the rotor blade.

[0074] FIGS. 5-8 illustrate a part of a serrated plate 42 of a rotor blade according to a third embodiment of the invention. FIG. 5 shows a top view onto the suction side of a part of the plate, FIG. 6 shows an enlarged view thereof, FIG. 7 shows a top view onto the pressure side of a part of the serrated plate and FIG. 8 shows a variant of the pressure side design of FIG. 7.

[0075] The plate 42 comprises a plurality of ridges on its suction sidethe ridges are therefore also referred to as suction side ridges 501. The suction side ridges 501 approximately start (as seen in the direction of the airflow) at the alignment section 424 of the plate 42 and extend over the entire surface of the respective teeth, e.g. the first tooth 311 or the second tooth 321. Again, the area 32 between the teeth, such as between the first tooth 311 and the second tooth 312, is filled with a plurality of comb elements 33. The suction side ridges 501 are aligned with the comb elements 33 such that every second comb element 33 builds an extension of a corresponding ridge 501. In the embodiment of FIGS. 5-8, there exist half as much suction side ridges 501 than comb elements 33.

[0076] As can be seen in FIG. 6, which is an enlarged view of a part of FIG. 5, the suction side ridges 501 do not only extend along the complete chordwise extension of the teeth, but even extend slightly further downstream. In other words, the ridges 501 even slightly exceed the flanks, i.e. the sides, of the teeth. Thus, an optimum connection and guidance for the airflow flowing along the ridges and along/across the teeth of the serrations is ensured.

[0077] FIG. 6 also illustrates the relatively small width 55 of an exemplary suction side ridge 501 compared to its length 53 (the length 53 of one of the ridges is exemplarily shown in FIG. 5).

[0078] FIG. 7 shows the bottom side, i.e. the pressure side 421 of the serrated plate 42 according to the third embodiment of the invention. Note that, while the suction side of the plate is relatively flat and planar, the pressure side 421 of the plate 42 features a certain convexity (which is insinuated by the dashed line in FIG. 7). The pressure side 421 of the plate 42 in the embodiment as illustrated in FIG. 7 does not comprise any ridges. Therefore, only the teethed structure of the plate (cf. the first tooth 311 and the second tooth 312) and the presence of the plurality of comb elements 33 between the teeth of the serrations is visible.

[0079] FIG. 8 shows a variant of the pressure side 421 of the plate 42, thus a variant of the third embodiment of the invention. In this case, the plate 42 comprises a plurality of ridges at its pressure side 421, which is also referenced as pressure side ridges 502. These pressure side ridges 502 partly prolong and directly connect to the respective comb elements 33. However, particularly the ridges 502 being arranged in the center part of the teeth smoothly fade out on the surface of the respective teeth and do not directly connect to the associated comb elements 33. The ridge-comb element ratio is 1:2 thus, the same as at the suction side of the plate 42.

[0080] Finally, FIG. 9 illustrates a sectional view of serrated plate 42 with a suction side ridge 501 according to a fourth embodiment of the invention.

[0081] The fourth embodiment differs from e.g. the first embodiment in that it comprises a suction side ridge 501 which prolongs upstream towards the leading edge of the rotor blade and thus create a certain slot 56 between the suction side 422 of the plate 42 and the attachment section 423 of the plate 42. Additionally, a slot 56 is present between the suction side ridge 501 and the attachment section 423 of the plate 42.

[0082] The suction side ridge 501 as shown in FIG. 9 has its maximum height 54 close to its trailing edge 51. The shape of the trailing edge 51 of the suction side ridge 501 resembles a quarter circle. This shape is suggested to efficiently reduce the noise being generated at the trailing edge 51 of the suction side ridge 501.

[0083] The leading edge 52 of the suction side ridge 501 has a slowly increasing height, as seen in the direction of the airflow.

[0084] A design as in FIG. 9 represents a promising option as it allows for extending the suction side ridges 501 further upstream, while still ensuring a stable attachment of the plate 42 to the remaining part of the rotor blade.

[0085] 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.

[0086] 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.