Wind turbine rotor blade add-on

Abstract

Wind turbine rotor blade add-on The invention describes a rotor blade add-on (1) comprising a mounting portion (10) adapted for adhesive mounting to a surface (20S) of a wind turbine rotor blade (2); characterized by a plurality of spacers (1S) protruding from an inner surface (10S) of the mounting portion (10), wherein the height (H1S) of each spacer (1S) corresponds to the intended thickness (H4L) of an adhesive layer (4L) to be formed between the rotor blade surface (20S) and the inner surface (10S) of the mounting portion (10), and is less than the initial thickness (H40) of a soft adhesive layer (4). The invention further describes a method of mounting the claimed rotor blade add-on (1) to a wind turbine rotor blade (20).

Description

[0001] 2024PF00549

[0002] Wind turbine rotor blade add-on

[0003] Background

[0004] A wind turbine rotor blade generally comprises an airfoil portion over most of its length. The airfoil portion has a pressure side and suction side extending between a leading edge and a trailing edge. The aerodynamic behaviour of a wind turbine rotor blade can be altered as desired by attaching various types of component, commonly refereed to as "rotor blade extensions" or "rotor blade add-ons".

[0005] An add-on is usually designed for use at a specific region of the rotor blade, for example on either the suction side or the pressure side; near the tip end of the rotor blade or near the root end; near the leading edge or near the trailing edge, etc. An add-on can be designed to achieve a specific purpose, for example a vortex generator add-on placed near the leading edge can increase annual electrical production (AEP) by increasing the induced stall margin. Another type of rotor blade extension is a serrated trailing-edge add-on, attached along the trailing edge over an outer portion of the airfoil. Such a serrated trailing edge add-on is effective at reducing aerodynamic noise.

[0006] An add-on may be mounted to a wind turbine rotor blade in various ways, for example it is known to fasten an add-on to a rotor blade using threaded fasteners, rivets, etc. However, fasteners can lead to damage to the laminate of the rotor blade as a result of unfavourable shear forces between the add-on and the rotor blade. Fasteners can also lead to problems arising from lightning strikes, for example in a flashover event, when high electrical currents may flow between a fastener and an electrical conductor in the interior of a rotor blade. The use of fasteners to attach add-ons can therefore result in damage to the rotor blade, with expensive repair procedures and loss of earnings during shutdown . 2024PF00549

[0007] For these reasons, it may be preferable to attach an add-on using a suitable adhesive, for example a two-component adhesive paste which will cure to form a robust bond between rotor blade and add-on.

[0008] However, in order for the add-on to remain attached over its intended lifetime, the adhesive bond must fulfil several criteria. The thickness of the adhesive bond at any region between the surface of the rotor blade and the add-on should be the recommended thickness for that region, however the recommended thickness may be lower along outer edges of the add-on and thicker towards the centre. Furthermore, the adhesive layer should be uninterrupted by voids. A void is an unintended cavity or gap in the adhesive layer, and can occur for various reasons. For example, it is usual to apply the adhesive along the rotor blade surface, in a width to match or slightly exceed the width of the add-on. If care is not taken to apply a uniform layer of adhesive, some regions may be patchily applied and these can result in voids when the add-on is later placed on the adhesive layer. A void may allow water to creep between the add-on and rotor blade, and may freeze during cold conditions, ultimately causing the add-on to detach from the rotor blade.

[0009] The adhesive paste can be applied in the spanwise direction using a combed spatula to form uniformly thick rows of adhesive with "empty rows" in between. Using this approach, the add-on is placed over the adhesive and pressure is then applied in order to spread the adhesive to close the spanwise gaps. However, if this procedure is not performed correctly, quite long spanwise voids may remain.

[0010] In another approach, adhesive is applied generously to the rotor blade surface (i.e. to a thickness that is greater than the desired layer thickness) , the add-on is placed over the adhesive, and pressure is applied to the add-on with the intention of forcing excess adhesive out from under the addon. If this is done correctly, the resulting adhesive layer has the desired thickness. However, it is difficult to apply 2024PF00549 pressure uniformly to the add-on. This may be because the add-on can bend or deform slightly when too much pressure is applied. If this occurs, too much of the soft (i.e. not yet cured) adhesive is pushed out from under the add-on. After removing the pressure, the add-on resumes its original shape, and a void ensues at any location from which too much adhesive was pushed out.

[0011] Equally, insufficient pressure can result in a void. If the technician does not apply enough pressure to the add-on, a void can remain, for example in a region where the inner surface of the add-on was not brought into contact with the adhesive layer. Another type of defect (a "kissing bond") can arise when the thickness of the initial adhesive layer and the applied pressure were insufficient to achieve the required physical contact between the adhesive and the inner surface of the add-on.

[0012] A void in the cured adhesive will generally go undetected until the add-on partially or completely detaches from the rotor blade during the service life of the wind turbine. This type of fault results in an expensive and hazardous repair procedure, particularly in the case of an offshore wind turbine, and significant loss of earnings while the wind turbine is unable to operate.

[0013] It is therefore an object of the invention to overcome the problems outlined above.

[0014] This object is achieved by the claimed rotor blade add-on, the claimed wind turbine rotor blade, and the claimed method of mounting an add-on to a wind turbine rotor blade.

[0015] Description

[0016] According to the invention, the rotor blade add-on comprises a mounting portion adapted for adhesive mounting to a surface of a wind turbine rotor blade in a procedure in which excess adhesive is expelled from underneath the mounting portion. Unlike the known types of rotor blade add-on, the inventive 2024PF00549 add-on comprises a plurality of spacers protruding from an inner surface of the mounting portion. The height of the spacers corresponds to the intended thickness of the adhesive layer (i.e. the adhesive bond) that will be formed between the rotor blade surface and the inner surface of the mounting portion. The spacer height is also is less than the initial thickness of a soft adhesive layer which will be applied for example to the rotor blade surface. In other words, the height of each spacer is less than the thickness of the soft (i.e. not yet cured) adhesive, and exceeds the cured layer thickness. When that add-on is mounted to a rotor blade, excess adhesive will be forced out from underneath the add-on so that the thickness of the soft adhesive layer will be reduced to the desired layer thickness as defined by the spacer height.

[0017] An advantage of the inventive rotor blade add-on is that it can be mounted to the rotor blade without risk of voids in the adhesive layer. Furthermore, when mounting the add-on to a wind turbine rotor blade, a technician can - intentionally or not - apply more pressure than would be recommended for an equivalent prior art add-on, without any risk of creating any of the types of void described above. This is because the spacers essentially form a "bridge" between the add-on and the rotor blade surface and effectively prevent unintended distortion or buckling of the add-on as a result of excessive pressure .

[0018] A wind turbine rotor blade can be augmented by one or more of the inventive rotor blade add-ons . A wind turbine with such rotor blades benefits from the very low likelihood of an addon becoming detached owing to a void in its adhesive layer. Since the service life of an inventive add-on is favourably long, costs associated with repair of rotor blade add-ons can be minimized.

[0019] According to the invention, the method of mounting an add-on to a wind turbine rotor blade comprises steps of providing an add-on with a mounting portion which comprises a plurality of 2024PF00549 spacers protruding from an inner surface of the mounting portion and wherein the height of the spacers corresponds to the intended thickness of the adhesive layer that will be formed between the rotor blade surface and the inner surface of the mounting portion. The spacer height is also is less than the thickness of an initial adhesive layer. The method comprises further steps of forming the initial adhesive layer on the rotor blade surface and / or on the inner surface of the mounting portion of the rotor blade add-on; arranging the rotor blade add-on in place relative to the rotor blade; and applying pressure to the rotor blade add-on to bring the spacers into contact with the rotor blade surface by forcing excess adhesive from underneath the add-on.

[0020] An advantage of the inventive method is that, even if more pressure than necessary is applied to the add-on when pressing it onto the adhesive, the spacers ensure that the applied pressure does not distort or bend the spacer out of shape, and effectively prevent too much adhesive being forced out from underneath the add-on. A technician can therefore apply pressure generously over the outer surface of the addon, achieving the required uniform adhesive layer thickness.

[0021] Particularly advantageous embodiments and features of the invention are given by the dependent claims, as revealed in the following description. Features of different claim categories may be combined as appropriate to give further embodiments not described herein.

[0022] In the following, it may be assumed that a wind turbine comprises the usual configuration of three rotor blades mounted to a hub, and each rotor blade can be assumed to comprise a root end and an airfoil portion with a pressure side and a suction side. The length of a rotor blade can be in the order of 40 - 100 m, or even more, in the case of an offshore wind turbine. Particularly in the case of such long rotor blades, add-ons may be used to prevent rotor stall at low rotational speeds, and to reduce aerodynamic noise when the rotor turns at higher speeds . 2024PF00549

[0023] In the following, without restricting the invention in any way, it may be assumed that the rotor blade add-on can be a composite, i.e. a fibre-reinforced polymer, an injection- moulded thermoplastic polymer, etc. The terms "add-on" and "extension" may be used interchangeably.

[0024] To this end, the add-on may be formed to comprise an arrangement of functional elements extending from the mounting portion. For example, a vortex generator add-on can comprise fin-like elements extending outward from its outer surface and arranged in a pair-wise fashion to encourage the formation of vortices. When mounted near the leading edge of a wind turbine rotor blade, such an add-on serves to maintain an attached boundary layer in the airflow passing over the rotor blade. Similarly, an add-on can be a spoiler mounted in an inboard region of the rotor blade. In a further example, a serrated add-on for attaching to the rotor blade trailing edge (in an outboard portion of the rotor blade) can comprise triangular elements or "serrations" arranged to extend into the airflow beyond the trailing edge. When mounted to a wind turbine rotor blade, such an add-on serves to reduce the aerodynamic noise created by the rotor blades during operation of the wind turbine. In a further example, an addon can be a fairing, for example a fairing shaped to form a smooth transition between segments of a segmented rotor blade, or a fairing shaped to cover a hatch or access opening to the interior of a rotor blade. A fairing may generally have a smooth outer surface, i.e. without any functional elements extending from its mounting portion.

[0025] The spacers of an add-on can have any suitable form or geometry. For example, spacers may be formed as elongate ribs extending in an essentially spanwise direction along the underside of the add-on. Such a "rib-like spacer" can follow a straight path, an angular path, a sinusoidal path, etc.

[0026] In a preferred embodiment of the invention, a spacer has the form of a pin or stud, extending inward from the mounting surface of the add-on. Such a stud-like spacer can have any 2024PF00549 suitable cross-sectional shape, for example the cross- sectional shape of a stud can have the form of a cross, a triangle, etc. In a preferred embodiment of the invention, the cross-sectional shape of a stud or spacer is essentially circular .

[0027] The cross-sectional shape of a spacer can be uniform over its entire length. Equally, the cross-sectional shape of a spacer can segue from one shape (e.g. a disc) to another (e.g. a cross) from one end of the spacer to the other. Alternatively or in addition, the circumference of a spacer can decrease with increasing distance from the add-on, i.e. a spacer can have a tapered or rounded shape. Depending on its shape, the width or diameter of a spacer can be in the order of 3 mm - 20 mm. Of course, the plurality of spacers formed on the underside of an add-on need not all be the same, and various combinations of the different types of spacer can be used as appropriate .

[0028] Regardless of their lateral dimensions, the spacer heights are formed so the outer ends of the spacers will meet the surface to which the add-on will be mounted. For example, and add-on may be intended for use near the leading edge of a rotor blade, which has a curved shape. The thickness of the adhesive layer may reduce gradually towards the outer edges of the add-on, for example from 10 mm at its thickest part, reducing towards a few millimetres or less at its thinnest part. To allow for the desired thickness profile of the adhesive layer, spacers formed in the inner regions of the add-on's mounting surface may be longer than spacers formed in the outer regions .

[0029] Preferably, the shapes of the spacers and their arrangement on the inside surface are determined during the design phase of a rotor blade extension, and the spacers are formed in one piece with the mounting surface (for example by injection moulding) . Alternatively or in addition, a spacer can be manufactured separately and attached, for example by gluing, to the mounting surface of the add-on. 2024PF00549

[0030] The distance between any two spacers can be selected according to various factors. For example, the width of the add-on, the (local) thickness of the adhesive layer and the viscosity of the adhesive can all influence the choice of spacer distance. In a preferred embodiment of the invention, the distance between adjacent spacers can be in the order of 10 mm to 50 mm.

[0031] The spacers of an add-on can be arranged in any suitable configuration. For example, if the add-on has an essentially elongate shape, it can be advantageous to arrange the spacers in rows parallel to the main direction of the add-on. For example, the underside of the mounting portion of a trailing- edge serration can comprise two or more parallel rows of spacers. The rows can be a suitable distance apart, and the spacers of adjacent rows can be offset relative to each other to form a "zig-zag" pattern.

[0032] The adhesive used to bond the add-on to the rotor blade can be any suitable type of adhesive, preferably a two-component adhesive is used. A two-component adhesive may be supplied in a cartridge with a mixing nozzle, allowing the correct mixture to be applied directly to the mounting surface of the rotor blade extensions and / or to the rotor blade surface.

[0033] The initial adhesive layer can be formed on the rotor blade surface and / or on the inner surface of the mounting portion of the rotor blade add-on, for example using a combed spatula or other suitable tool. The desired thickness of the adhesive layer at its thickest part can be in the order of 10 mm, as indicated above. Since the spacer height determines the thickness of the cured adhesive layer, the height of a spacer formed at the corresponding region of the add-on is also in the order of 10 mm. If the method of mounting the add-on includes a step of forcing excess adhesive out from underneath, the initial adhesive layer thickness can be in the order of 20 mm - 30 mm, and this is reduced to the desired layer thickness by applying pressure against the outer surface of the add-on. 2024PF00549

[0034] A technician preferably uses a tool such as a pressure roller over the outer surface of the add-on, in order to achieve satisfactory distribution of the adhesive between the rotor blade and the add-on.

[0035] Other objects and features of the present invention will become apparent from the following detailed descriptions considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for the purposes of illustration and not as a definition of the limits of the invention.

[0036] Figure 1 shows a wind turbine;

[0037] Figure 2 shows a cut-away view of a prior art add-on mounted to a rotor blade of a wind turbine of Figure 1;

[0038] Figures 3 - 5 illustrate problems associated with mounting the prior art add-on of Figure 2;

[0039] Figure 6 shows an embodiment of the inventive add-on;

[0040] Figures 7 - 8 illustrate the inventive method;

[0041] Figure 9 - 11 show various forms of spacer provided on embodiments of the inventive rotor blade extension.

[0042] In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

[0043] Figure 1 shows a wind turbine 2 with the usual configuration of three rotor blades 20 mounted to a hub 21. The rotor blades 20 have been augmented by add-ons 1,3 in this case vortex generators with small elements 10F, 30F placed to protrude into the boundary layer and arranged to improve the performance of the aerodynamic rotor 20, 21 at low wind speeds, and trailing-edge serrations with long triangular elements 10F, 30F placed to reduce aerodynamic rotor noise. 2024PF00549

[0044] Figure 2 shows a cut-away view of a prior art add-on 3 and the adhesive layer 4L that bonds the add-on 3 to the suction surface 20S of the rotor blade 20. The diagram shows several types of void 5 in the adhesive layer 4L. Generally, voids in the adhesive layer 4L can be the result of unintentional errors in the add-on mounting procedure as explained in the introduction.

[0045] This is illustrated in Figure 3 and Figure 4, which show (in partial cross-section) how excess pressure might be inadvertently applied to the prior art rotor blade extension 3 when this is placed on the soft adhesive layer 4. For clarity, functional elements of the add-on 3 are not shown. Using a suitable tool 6 such as a pressure roller as shown here (being rolled in the direction indication) , a technician applies pressure to the add-on 3. However, when too much force is applied as indicated in Figure 3, the mounting portion 30 of the add-on 3 can be distorted from its actual shape (indicated by the broken line) and pushed too close to the rotor blade surface 20S. This action forces too much adhesive 4E to be expelled from under the mounting portion 30. After removing the tool 6, the mounting portion 30 of the add-on 3 can return to its original shape. This is shown in Figure 4, which illustrates a final stage after removal of the excess adhesive 4E and curing the adhesive layer 4L. The insufficient quantity of adhesive at any location where excessive pressure was applied will result in a cavity or void 5 in the cured adhesive layer 4L. Figure 5 shows how pressure should be applied to the mounting portion 30 of the prior art add-on 3. Here, just enough pressure is being applied to push out the excess adhesive 4E, leaving an adhesive layer 4L with the correct thickness H4L over the width of the mounting portion 30. However, much skill is required to perform this step correctly. When mounting such an add-on 3 in the field (i.e. to an already installed rotor blade) , the procedure can be challenging even for a skilled technician . 2024PF00549

[0046] Figures 6 - 11 illustrate the invention and explain how the inventive add-on 1 avoids the problems described above. Figure 6 shows an embodiment of the inventive add-on 1, in this case a trailing-edge serration, looking towards the inside surface IOS of its mounting portion 10. Spacers IS protrude from the inside surface 10S at various points. In this exemplary embodiment, the spacers IS are arranged in two parallel rows as indicated by the ghost lines, offset relative to each other to form a zig-zag pattern of spacers IS along the inside surface 10S of the mounting portion 10.

[0047] The distance or pitch DIS between spacers IS is chosen in consideration of the deformability or "bendability" of the add-on 1, and are spaced sufficiently close to prevent deformation of the add-on 1 when pressure is applied during the mounting procedure. The spacers IS allow pressure to be applied generously to the add-on without risking deformation of the add-on 1, as illustrated in Figure 7 and Figure 8. The height H40 of the initial adhesive layer 4 can be higher than the intended layer thickness H4L as shown in Figure 7. After applying the adhesive to the surface 20S of the rotor blade 20 as shown here, the rotor blade extension 1 is placed over the soft adhesive 4. The diagram shows that the spacers IS on the underside 10S of the mounting portion 10 may at first not make contact with the rotor blade surface 20S on account of the initial layer thickness H40. In a next step as shown in Figure 8, pressure is being applied using a suitable tool 6 to push out excess adhesive 4E. As soon as the spacers IS come into contact with the rotor blade surface 20S, the addon 1 cannot be pressed any closer to the rotor blade surface 20S. This prevents too much adhesive from being forced out from under the add-on 1. As a result, applying pressure generously over the outer surface of the add-on 1 achieves the desired thickness H4L over the entire extent of the adhesive bond 4L as indicated in Figure 8.

[0048] Figures 9 - 11 show the underside 10S of the mounting portion 2024PF00549

[0049] 12

[0050] In Figure 9, the spacers IS are in the shape of a cross. In Figures 10 and 11, the spacers IS are shown as circular protrusions with rounded outer ends. The diameter or width W1S of a spacer IS can be in the order of 5 mm. In each case, the height HIS of each spacer IS corresponds to the desired thickness H4L of the adhesive layer 4L that will bond the add-on 1 to a rotor blade 20.

[0051] Although the present invention has been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of the invention.

[0052] 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. Any pronoun denoting a specific gender shall be understood to apply equally to any gender identity.

Claims

2024PF00549Claims1. A rotor blade add-on (1) comprising a mounting portion (10) adapted for adhesive mounting to a surface (20S) of a wind turbine rotor blade (2) ; characterized by a plurality of spacers (IS) protruding from an inner surface (10S) of the mounting portion (10) , wherein the height (HIS) of each spacer (IS) corresponds to the intended thickness (H4L) of an adhesive layer (4L) to be formed between the rotor blade surface (20S) and the inner surface (10S) of the mounting portion (10) , and is less than the initial thickness (H40) of a soft adhesive layer ( 4 ) .

2. A rotor blade add-on according to the preceding claim, wherein the width (W1S) of a spacer (IS) is in the order of 3 mm to 20 mm.

3. A rotor blade add-on according to any of the preceding claims, wherein the distance (DIS) between adjacent spacers (IS) is in the order of 10 mm to 50 mm.

4. A rotor blade add-on according to any of the preceding claims, wherein the cross-sectional shape of a spacer (IS) is essentially circular.

5. A rotor blade add-on according to any of the preceding claims, wherein a spacer (IS) is formed in one piece with the mounting portion (10) and / or a spacer (IS) is attached to the inner surface (10S) of the mounting portion (10) .

6. A rotor blade add-on according to any of the preceding claims, wherein the rotor blade add-on (1) comprises an arrangement of functional elements (10F) extending from the mounting portion (10) .

7. A rotor blade add-on according to any of the preceding claims, wherein the rotor blade add-on (1) is any of: a2024PF0054914 vortex generator, a serrated trailing-edge extension, a fairing, a spoiler.

8. A rotor blade add-on according to any of the preceding claims, wherein the rotor blade add-on (1) is manufactured as a fibre-reinforced polymer and / or an injection-moulded thermoplastic polymer.

9. A wind turbine rotor blade (20) comprising a number of rotor blade add-ons (1) according to any of claims 1 to 8.

10. A wind turbine rotor blade according to the preceding claim, wherein a rotor blade add-on (1) is a vortex generator mounted in the vicinity of the leading edge (20LE) of the rotor blade (20) .

11. A wind turbine rotor blade according to claim 9 or claim 10, wherein a rotor blade add-on (1) is a serrated trailing- edge extension mounted at the trailing edge (20TE) of the rotor blade (20) .

12. A wind turbine rotor blade according to any of claims 9 to 11, wherein a rotor blade add-on (1) is a fairing mounted over a junction of a segmented rotor blade (20) .

13. A method of mounting a rotor blade add-on (1) according to any of claims 1 to 8 to a wind turbine rotor blade (20) , which method comprises forming an initial adhesive layer (4) on the rotor blade surface (20S) and / or on the inner surface (10S) of the mounting portion (10) of the rotor blade add-on (1) , wherein the thickness (H40) of the initial adhesive layer (4) exceeds the intended adhesive layer thickness (H4L) ; arranging the mounting portion (10) of the rotor blade add-on (1) relative to the rotor blade (20) ; and applying pressure to the rotor blade add-on (1) to push out excess adhesive (4E) and to bring the spacers (IS) into contact with the rotor blade surface (20S) .2024PF005491514. A method according to the preceding method claim, wherein the desired thickness (H4L) of the adhesive layer at its thickest part is in the order of 10 mm, and the initial adhesive layer thickness (H40) is in the order of 20 - 30 mm.

15. A method according to any of the preceding method claims, comprising a step of using a pressure roller (6) to apply pressure over the mounting portion (10) of the rotor blade add-on ( 1 ) .

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