Wind Turbine Blade Provided with Surface Mounted Device

Abstract

A wind turbine blade having a surface mounted device attached thereto via at least a first attachment part, which is connected to a part of the device. The first attachment part comprises an outer attachment part providing a first bonding connection between the device and the surface of the blade, wherein the first bonding connection is an elastic bond, and an inner attachment part providing a second bonding connection between the device and the surface of the blade, wherein the second bonding connection has a structural bond. The structural bond prevents the surface mounted device from creeping and the elastic bond region relieves stresses on the bond line, such as peel stresses, whereby the surface mounted device is less likely to be ripped off the surface of the blade due to forces affecting the device or the blade.

Claims

1. A wind turbine blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, said rotor comprising a hub, from which the wind turbine blade extends substantially in a radial direction when mounted to the hub, the wind turbine blade having a longitudinal direction with a tip end and a root end and a transverse direction, the wind turbine blade further comprising: a profiled contour including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift, wherein a surface mounted device is attached to a surface of the wind turbine blade, wherein the surface mounted device is attached to the surface of the wind turbine blade via at least a first attachment part, which is connected to a part of the surface mounted device, characterised in that the first attachment part comprises: an outer attachment part providing a first bonding connection between the surface mounted device and the surface of the wind turbine blade, wherein the first bonding connection is an elastic bond, and an inner attachment part providing a second bonding connection between the surface mounted device and the surface of the wind turbine blade, wherein the second bonding connection has a structural bond.

2. A wind turbine blade according to claim 1, and wherein the first bonding connection has a first elastic modulus and the second bonding connection has a second elastic modulus, and wherein second elastic modulus is higher than the first elastic modulus.

3. A wind turbine blade according to claim 2, wherein the second elastic modulus is at least 100% higher than the first elastic modulus.

4. A wind turbine blade according to claim 1, wherein the first bonding connection is provided via a material having a first hardness, and the second bonding connection is provided via a material having a second hardness, wherein the second hardness is larger than the first hardness

5. A wind turbine blade according to claim 4, wherein the first hardness is less than 90 Shore-A.

6. A wind turbine blade according to claim 4, wherein the second hardness is between 30 and 80 on the Shore-D scale.

7. A wind turbine blade according to claim 1, wherein the outer attachment part surrounds the inner attachment part.

8. A wind turbine blade according to claim 1, wherein the outer attachment part has a width in an interval of 0.2-2.0 cm, advantageously between 0.3 and 1.5 cm, and more advantageously between 0.5 and 1.3 cm, e.g. around 0.8-0.9 CM.

9. A wind turbine blade according to claim 1, wherein the outer attachment part is made of a double-sided tape.

10. A wind turbine blade according to claim 9, wherein the double-sided tape forms a circumferential part between the surface of the wind turbine blade and the surface mounted device, and which forms a cavity between the double-sided tape, the surface of the wind turbine blade and a part of the surface mounted device.

11. A wind turbine blade according to claim 9, wherein the double-sided tape comprises a layer of compressible material.

12. A wind turbine blade according to claim 11, wherein the compressible material is a layer of foam cells, such as acrylic foam.

13. A wind turbine blade according to claim 1, wherein the outer attachment part has a thickness of at least 0.5 mm, and preferably at least 1 mm.

14. A wind turbine blade according to claim 1, wherein the outer attachment part has a thickness of maximum 10 mm, or maximum 7 mm, or maximum 5 mm.

15. A wind turbine blade according to claim 1, wherein the inner attachment part is formed by an adhesive.

16. A wind turbine blade according to claim 15, wherein the adhesive is PU-based, epoxy-based, MMA or a hybrid between the various materials, such as a polymerisable PU mixed in a MMA.

17. A wind turbine blade according to claim 1, wherein the surface mounted device is a chord extender, such as a serrated trailing edge plate.

18. A flow guiding device, which is adapted to be attached to the surface of a wind turbine blade, via at least a first attachment part, characterised in that the attachment part comprises an outer attachment part for providing a first bonding connection between the surface mounted device and the surface of the wind turbine blade, and wherein the outer attachment part is adapted to form a cavity between at least the housing and the surface of the wind turbine blade, the cavity being adapted to be filled with an adhesive that provides a structural bonding to the surface of the wind turbine blade.

19. A method of attaching a surface mounted device to a surface of a wind turbine blade, wherein the wind turbine blade has a longitudinal direction with a tip end and a root end and a transverse direction, wherein the wind turbine blade further comprises a profiled contour including a pressure side and a suction side, as well as a leading edge and a trailing edge with a chord having a chord length extending there between, the profiled contour, when being impacted by an incident airflow, generating a lift, wherein the method comprises the steps of attaching the surface mounted device to the surface of the blade via an outer attachment part providing an elastic bond between the surface mounted device and the surface of the wind turbine blade, and providing an inner attachment part providing a structural bond between the surface mounted device and the surface of the wind turbine blade.

20. A method according to claim 19, which comprises the steps of: a) providing the wind turbine blade, b) arranging the outer attachment part, e.g. a double-sided tape, on the surface of the wind turbine blade so as to form a circumferential part of an attachment part, c) arranging a device for mounting on the surface of the blade on outer attachment part so that a cavity of an attachment part is formed between at least by the outer attachment part, the surface of the wind turbine blade, and a part of the device, d) injecting an adhesive or resin into the cavity, and e) curing or hardening the adhesive or resin so that the device is attached to the surface of the wind turbine blade via an adhesive bonding.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0159] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0160] FIG. 1 shows a wind turbine,

[0161] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade provided with flow guiding device parts according to the invention, seen in perspective,

[0162] FIG. 3 shows a schematic view of an airfoil profile,

[0163] FIG. 4 shows a top view of a wind turbine blade according to the invention,

[0164] FIG. 5 shows various views of a flow guiding device according to the invention and provided with attachment parts according to the invention,

[0165] FIG. 6 shows two embodiments of a proximal part of a flow guiding device according to the invention with an attachment part according to the invention,

[0166] FIG. 7 shows cross-sectional views of two embodiments of attachment parts according to the invention,

[0167] FIG. 8 illustrates an adhesive injection step of a method according to the invention,

[0168] FIG. 9 shows a group of flow guiding devices,

[0169] FIG. 10 shows a first embodiment of top parts of a group of flow guiding devices,

[0170] FIG. 11 shows a second embodiment of top parts of a group of flow guiding devices,

[0171] FIG. 12 shows a third embodiment of top parts of a group of flow guiding devices,

[0172] FIG. 13 shows a fourth embodiment of top parts of a group of flow guiding devices,

[0173] FIG. 14 shows a fifth embodiment of top parts of a group of flow guiding devices,

[0174] FIG. 15 shows a top view of a wind turbine blade provided with serrated trailing edge panels,

[0175] FIG. 16 shows a top view of a serrated trailing edge panel provided with an attachment part according to the invention,

[0176] FIG. 17 shows a top view of a serrated trailing edge panel provided with three attachment parts according to the invention,

[0177] FIG. 18 shows a top view of a first embodiment of a serrated trailing edge panel, where the attachment part is made partly from double-adhesive tape,

[0178] FIG. 19 shows a top view of a second embodiment of a serrated trailing edge panel, where the attachment part is made partly from double-adhesive tape,

[0179] FIG. 20 shows a top view of a third embodiment of a serrated trailing edge panel, where the attachment part is made from partly double-adhesive tape.

[0180] FIG. 21 shows a cross-section of a trailing edge of a blade with a surface mounted device attached to the surface of the blade, and

[0181] FIG. 22 shows a longitudinal cross-section of a surface mounted device attached to the surface of a wind turbine blade.

DETAILED DESCRIPTION OF THE INVENTION

[0182] FIG. 1 illustrates a conventional modern upwind wind turbine 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 farthest from the hub 8.

[0183] 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 side and the leeward 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 and lower camber, which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0184] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. 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 farthest 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.

[0185] 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 42 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 width of the transition region 32 typically increases substantially linearly with increasing distance r from the hub.

[0186] 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.

[0187] 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.

[0188] The wind turbine blade 10 according to the invention is provided with a number of surface mounted devices in form of flow guiding device parts 70, which are grouped together and protrude from the pressure side of the blade in at least the transition region 32 of the blade so as to form a flow guiding device group 95 as shown in top view in FIG. 4. However, advantageously the flow guiding device parts 70 may also extend into the airfoil region 34 and/or the root region 30 of the blade.

[0189] FIGS. 5a-e show a flow guiding device part 70 according to the invention, which is adapted to function as a spoiler and attached to the surface of a wind turbine blade, e.g. as shown in FIGS. 2 and 4. FIG. 5a shows a bottom view, FIG. 5b shows a side view, FIG. 5c shows a rear view, FIG. 5d shows a perspective view showing the rear, and FIG. 5e shows another perspective view showing the front of the flow guiding device part 70.

[0190] It is seen that the flow guiding device part 70 comprises a plate-shaped element 71 that protrudes from the surface of the blade, when the flow guiding device part 70 is mounted to the surface of the blade, and which provides an obstruction to the incoming flow. The plate-shaped element 71 comprises a front surface 72, which faces towards the leading edge 18 of the blade 10 and thus towards the incoming flow, and a rear surface 73, which faces towards the trailing edge 20 of the blade 10 and thus away from the incoming flow.

[0191] The plate-shaped element 71 comprises a proximal part 74 or lower part, which—when the flow guiding device part 70 is mounted to the surface of the blade—is located nearest the blade surface, and a distal part 75 or upper part, which is located farthest from the blade surface. The plate-shaped element 71 is curved in the lengthwise or longitudinal direction and has a first curvature of radius at the proximal part 74 of the plate-shaped element 71 and a second curvature of radius at the distal part 75 of the plate-shaped element.

[0192] In the shown embodiment, the plate-shaped element 70 forms part of the outer surface of a frusto-conical element and thus the second radius of curvature is smaller than the first curvature of radius. However, in an alternative embodiment, the second curvature of radius is larger than the first curvature of radius, which may provide a stiffer structure to the distal part 75 of the plate-shaped element 71. The second radius of curvature may for instance approach infinity, in which case the distal part 75 of the plate-shaped element 71 is straight. In yet another embodiment, the radius of curvature may be constant from the proximal part 74 to the distal part 75 of the plate-shaped element.

[0193] The plate-shaped element 71 is further angled forwards towards the leading edge of the blade so as to provide a pocket between the plate-shaped element 71 and the surface of the blade, said pocket facing towards the leading edge of the blade. Since the plate-shaped element 71 is curved towards the leading edge of the blade (i.e. being concave as seen from the leading edge of the blade), this also attributes to forming the pocket between the surface mounted device and the surface of the blade. With a flexible plate-shaped element 71, this design also allows the surface mounted design to be collapsed or pressed against the surface of the blade, which may be advantageous for transport purposes.

[0194] The flow guiding device part 70 comprises three attachment parts 77, which are utilised to attach the flow guiding device part 70 to the surface of the blade. Each of the attachment parts 77 are tapered from a proximal part to a distal part of the attachment part 77 such that the proximal part has a greater surface area than the distal part. The attachment part may for instance be substantially bell-shaped, conical or frusto-conical shaped. This minimises notch effects at the surface of the blades and provides a gradual transition of loads transferred from the blade 10 and onto the flow guiding device part 70, when the blade bends or the blade shell ovalises. As seen in FIG. 5c, the attachment part 77 is preferably also tapered in the side-view so that the height of the attachment part 77 approaches zero at a circumference, thus minimising the notch effect.

[0195] The attachment part 77 further includes a flexible housing 80, which forms a cavity between at least the flexible housing 80 and the surface of the wind turbine blade. A part of the attachment part 77 may be moulded as a first piece together with the plate-shaped element 71, and the flexible housing 80 may be moulded onto this first piece. Alternatively, the flexible housing may be glued onto and/or mechanically connected to the first piece.

[0196] The flow guiding device part 70 may be attached to three discrete areas on the surface of the blade, wherein the three discrete areas when seen in a top view are arranged in a triangle as for instance seen in FIG. 5a. This provides a particularly simple way of attaching add-ons to the surface of a wind turbine blade, since the three-point attachment will always be able to contact the surface of the blade despite having a complex curvature. The triangle may have an acute angle being at least 5 degrees, or at least 10 degrees.

[0197] The plate-shaped element 71 may, as seen in FIGS. 5a and 5e, further be reinforced with a grid or rib structure 76. The ribs may for instance be arranged along the two end parts of the plate-shaped element 71, and with a rib extending along a distal part of the plate-shaped element. Further or alternatively, the plate-shaped element may be provided with cross-ribs extending from near a distal part and end part and to a proximal and intermediate part of the plate-shaped element 71. This provides a strong triangular rib structure that adds strength to plate-shaped element 71. The rib or grid design may readily be moulded together with the plate-shaped element 71. The grid or rib structure may for instance be provided as surface protrusions.

[0198] The flow guiding device part 70 may further be provided with a grip or the like, e.g. provided on the attachment part 77 as shown in FIG. 5e. This grip 78 may facilitate easier handling for a worker attaching the flow guiding device part 70, which can use the grip to better press the flexible housing against the surface of the blade. This is particularly advantageous, if the flow guiding device parts 70 are mounted on site.

[0199] The thickness t.sub.s of the plate-shaped element 71 is advantageously 0.5-10 mm, e.g. around 1.5-3 mm. The thickness t.sub.r of the rib or grid structure 76 is advantageously 5-50 mm. The longitudinal length l of the surface mounted device is advantageously 20-150 cm, or 25-120 cm. The height h of the surface mounted device is advantageously 3-50 cm. The plate-shaped element 71 is preferably connected to the attachment part 77 such that a spacing s between the proximal part 74 of the plate-shaped element 71 and the surface of the wind turbine blade is in the interval 1-20 mm, e.g. around 10 mm.

[0200] The flow guiding device 70 and the attachment part 77 may be made of polyurethane (PUR) material or a thermoplastic polymer, optionally reinforced with reinforcement fibres, and the attachment part is also made of a polyurethane (PUR) or thermoplastic material. The hardness of the flexible housing 80 is advantageously 20-75 on the Shore A scale, e.g. around 55 on the shore A scale. The hardness of the plate-shaped element 71 is advantageously 45-100 on the shore D scale, e.g. around 75 on the shore D scale.

[0201] FIGS. 6a and 6b show detailed cross-sectional views of a first embodiment and a second embodiment of a flow guiding device part according to the invention and provided with attachment parts according to the invention.

[0202] FIG. 6a shows a first embodiment of the flow guiding device part 70 and the attachment part 77. It is seen that a tapered section of the attachment part 77 and the plate-shaped element are integrally formed, e.g. as a moulded element. The flexible housing 80 is connected to a recess 83 of the tapered section of the attachment part 77. The flexible housing may be glued onto or moulded onto the tapered section. The flexible housing 80 comprises a circumferential lip 82, which is sealed against the surface of the wind turbine blade. This provides a glue cavity 81, which is formed between the surface of the blade, the flexible housing 80 and a lower part of the tapered section of the flow guiding device part 70. A bore or hole 79 is provided through the attachment part 77 and which can communicate with the glue cavity 81 such that an adhesive may be filled into the cavity 81 via the bore 79. The flexible housing further comprises a ventilation hole 88, whereby gas or air is able to escape from the cavity 81 during a step of injecting an adhesive into the cavity. The ventilation hole 88 may also provide a visual confirmation of the filling process, e.g. when liquid adhesive starts pouring out from the hole, the injection of the adhesive may be stopped.

[0203] FIG. 6b shows a second embodiment of a flow guiding device part 70′ and an attachment part 77′, where like numerals refer to like parts of the first embodiment. Therefore, only the difference between the two embodiments is described. The second embodiment differs from the first embodiment in that the flexible housing encases a lower part of the tapered section 77′ or the plate-shaped element 70′, such that the glue cavity 81′ is formed between the flexible housing 80 and the surface of the blade only.

[0204] The lip 82 of the attachment device 77 advantageously has a maximum external dimension, such as an outer diameter, of 1-15 cm, or 2-10 cm. Thus, the proximal part of the attachment device 77 may have this maximum external dimension.

[0205] According to one embodiment shown in FIG. 7a, the circumferential lip 82 may comprise a substantially flat attachment surface 84 for mounting to the blade. The attachment surface may be provided with a pressure-sensitive double adhesive tape 85 for providing a preliminary attachment to the blade surface. The tape 85 may be provided with a liner 86, which is removed prior to fitting the flexible housing 80 to the surface of the blade. The liner 86 is advantageously provided with a tap so that the liner 86 can be pulled out from the lip 82. Thus, the lip 82 of the flexible housing 80 may be pressed against the surface of the blade. Once the device 70 and attachment part 77 is located in the correct position, the liner 86 is removed, whereby the lip 82 is preliminary sealed to the surface of the wind turbine blade and provides the glue cavity 81, and after which injection of adhesive into the cavity 81 may be carried out.

[0206] According to another embodiment shown in FIG. 7b, a circumferential lip 182 of the flexible housing has an inclined attachment surface 184. Similar to the embodiment shown in FIG. 7a, the attachment surface may be provided with a pressure-sensitive double adhesive tape 185 for providing a preliminary attachment to the blade surface, which in turn is provided with a liner 186. The incline of the attachment surface 184 accommodates to the surface of the wind turbine blade, when it is pressed against said surface of the wind turbine blade, which is illustrated with the arrows shown in FIG. 7b.

[0207] FIG. 8 illustrates a step in a method of attaching a surface mounted device to the surface of a wind turbine blade according to the invention. The method comprises a first step of providing the wind turbine blade and a second step of providing the surface mounted device with an attachment part according to the invention, e.g. one of the two embodiments shown in FIG. 6. In a third step, the attachment part of the surface mounted device is positioned on a first discrete area of the surface of the blade so that a cavity is formed between at least the housing and the surface of the wind turbine blade. In a fourth step, illustrated in FIG. 8, an adhesive or resin 91 is filled into the glue cavity. Once the glue cavity 81 has been filled with the adhesive, injection is stopped after which the adhesive 91 in a fifth step is cured or hardened so that the surface mounted device 70 is attached to the surface of the wind turbine blade via an adhesive bonding.

[0208] The adhesive 91 is injected into the glue cavity 81 via the bore 79, e.g. via a syringe or a static mixer. The ventilation hole 88 is preferably located at a proximal part of the flexible housing, such that adhesive 91 filled into the cavity 81 reaches said ventilation hole 88 last. Thereby, the ventilation hole 88 may also be used for visual inspection to check if the cavity has been filled. Alternatively or additionally, the flexible housing may be made in an at least partially transparent material, such that the filling process can be monitored.

[0209] The cavity 81 may remain connected to an adhesive reservoir 90 or chamber during the curing or hardening in the fifth step. Thus, if the adhesive 91 shrinks during the hardening, additional liquid adhesive will be drawn into the cavity and filling the voids. The adhesive 91 of the reservoir 90 should of course harden at a later stage than the adhesive in the cavity such that liquid adhesive is not drawn in the wrong direction.

[0210] The adhesive 90 may for instance be PU-based, epoxy-based or MMA.

[0211] In another embodiment, a micro-environment treatment is carried out in the cavity prior to the fourth step. The micro-environment treatment may for instance be chosen from the group of evacuating the cavity, heating the cavity, or a degasification, e.g. via filling the cavity with nitrogen. Thereby, the cavity may be dried before the injection step, which may improve the adhesive bond even further, since moist is removed prior to the injection. This may be carried out via attaching the appropriate tool to the bore 79 or the ventilation hole 88.

[0212] As shown in FIGS. 2 and 4, the surface mounted devices are advantageously flow guiding devices e.g. in form of spoiler devices, which are grouped together to form a flow guiding device group. The modular construction of this group makes the construction more flexible and reduces peel forces at the ends of the flow guiding device parts. The individual flow guiding device parts are preferably arranged such that the lengthwise directions of the parts are oriented substantially in the longitudinal direction of the blade.

[0213] FIG. 9 shows a back view of a first embodiment of a flow guiding device group. As can be seen, the group comprises a number of individual flow guiding device parts 170, which mutually are separated by gaps 181. The gaps 181 between adjacent flow guiding device parts 170 may for instance be between 5 mm and 30 mm. According to another embodiment (not shown), the flow guiding device parts abut each other.

[0214] FIG. 10 shows the flow guiding device parts 170 seen from the top, here depicted as a proximal part of a plate-shaped element. In the shown embodiment, the gaps 181 between adjacent flow guiding device parts 170 are closed by intermediate elements 196 made of a flexible material, such as rubber. In this particular embodiment, the intermediate elements 179 are attached to a front surface of the plate-shaped elements 170. This may provide a continuous front surface for the flow guiding device group. However, according to a preferred embodiment, the design does not comprise any intermediate elements (corresponding to the embodiment shown in FIG. 9).

[0215] FIG. 11 shows a second embodiment of flow guiding device parts 270 according to the invention. In this embodiment the gaps are also closed by intermediate elements 296 made of a flexible material, such as rubber. In this embodiment, the intermediate parts fill the entire gap between the flow guiding device parts 270 and are attached to both a front surface and back surface of the flow guiding device parts 270.

[0216] FIG. 12 shows a schematic view of a third embodiment of flow guiding device parts 370 according to the invention, seen from the top. In this embodiment, the flow guiding device parts are alternately arranged in front of and behind other flow guiding device parts, such that the flow guiding device parts form a nearly continuous front surface.

[0217] FIG. 13 shows a schematic view of a fourth embodiment of flow guiding device parts 470 according to the invention, seen from the top. It can be seen the flow guiding device parts 470 are staggered in the longitudinal direction. The back surface of one flow guiding device part may abut the front surface of a second flow guiding device part, or there may be a small gap in the transverse direction of the blade.

[0218] FIG. 14 shows a schematic view of a fifth embodiment of flow guiding device parts 570 according to the invention, seen from the top, which is similar to the third embodiment with the exception that the flow guiding device parts 570 are alternately convex and concave in the longitudinal direction. In the shown embodiment, two flow guiding device parts are arranged behind the others. However, they may also advantageously be arranged in front of the other flow guiding device parts, thereby obtaining a slightly different overall design. If the flow guiding device parts are angled forwards to form a pocket between the plate-shaped element and the blade surface, it is clear that two different types of flow guiding device parts are needed.

[0219] The invention has so far been described in relation to surface mounted devices in form of spoiler devices. However, the attachment parts and method according to the method may also be used for attaching other types of flow guiding devices to the surface of a wind turbine blade, e.g. serrated trailing edge panels or Gurney flaps.

[0220] FIG. 15 shows such an embodiment of a wind turbine blade 610, which is provided with a plurality of serrated trailing edge panels 670, which are arranged at the trailing edge of the blade near the blade tip. As seen in FIG. 16, the serrated trailing edge panel 670 may be provided with an attachment part, which comprises a flexible housing 681, which forms a glue cavity 681 between the panel 670 and the blade surface. The panel 670 is adhesively attached to the blade by filling the glue cavity with an adhesive and letting the adhesive cure or harden.

[0221] FIG. 17 shows an alternative embodiment of a serrated trailing edge panel 770, which is provided with three attachment parts, each comprising a flexible housing 780 and forming a glue cavity 681 between the panel 770 and the blade surface. The three attachment parts may, seen in a top view, be arranged in a triangle.

[0222] In the above embodiments, the flexible housing is described as a pre-manufactured element. However, the attachment part or the flexible housing is made from a double-adhesive tape or the like. In the following, such embodiments are exemplified for the attachment of a serrated trailing edge panel. However, the flexible housing made of double-adhesive tape may be used for any surface mounted device, such as spoiler devices or the like.

[0223] FIG. 18 shows a top view of a first embodiment of a serrated trailing edge panel 870, where the flexible housing 880 of an attachment part is made from double-adhesive tape. The double-adhesive tape may be applied to the surface of the wind turbine blade (not shown) as separate parts 880a, 880b, 880c, 880d, which are arranged so that they form a circumferential part. Once the serrated trailing edge panel 870 is arranged on top of the double-adhesive tape, a cavity 881 is formed between the surface of the wind turbine blade, the double-adhesive tape and the serrated trailing edge panel 870. Liquid adhesive may then be injected into the cavity 881, e.g. via a bore 879 in the serrated trailing edge panel 879, and the adhesive propagates (illustrated with contour lines 893) through the cavity 881.

[0224] The double-adhesive tape parts 880a, 880b, 880c, 880d may be arranged so that a small opening 888 is provided in the circumferential part, such that a visual confirmation of the filling process may be provided, e.g. when liquid adhesive starts pouring out from the hole, the injection of the adhesive may be stopped.

[0225] FIG. 19 shows a top view of a second embodiment of a serrated trailing edge panel, where the attachment part is made from double-adhesive tape. The double-adhesive tape may be applied to the surface of the wind turbine blade (not shown) as separate parts 980a, 980b, 980c, 980d, which are arranged so that they form a circumferential part. Once the serrated trailing edge panel 970 is arranged on top of the double-adhesive tape, a cavity 981 is formed between the surface of the wind turbine blade, the double-adhesive tape and the serrated trailing edge panel 970. The double-adhesive tape parts 980a, 980b, 980c, 980d are arranged so that an opening 979 is provided in the circumferential part. Liquid adhesive may then be injected through said opening 979 illustrated with contour lines 993.

[0226] The double-adhesive tape parts 980a, 980b, 980c, 980d may additionally be arranged so that a second small opening 988 is provided in an opposite side of the circumferential part, such that a visual confirmation of the filling process may be provided, e.g. when liquid adhesive starts pouring out from the hole, the injection of the adhesive may be stopped.

[0227] FIG. 20 shows a top view of a third embodiment of a serrated trailing edge panel, where the attachment part is made from double-adhesive tape. The double-adhesive tape may be applied to the surface of the wind turbine blade (not shown) as separate parts 1080a, 1080b, 1080c, 1080d, 1080e, which are arranged so that they form a circumferential part. In the shown embodiment, the parts are arranged to form two cavities.

[0228] Once the serrated trailing edge panel 1070 is arranged on top of the double-adhesive tape, cavities 1081 are formed between the surface of the wind turbine blade, the double-adhesive tape and the serrated trailing edge panel 1070. The serrated trailing edge panel 1070 is further provided with a number of ventilation holes 1088.

[0229] Liquid adhesive may then be injected into the cavities 1081, e.g. via bores 1079 in the serrated trailing edge panel 1079, and the adhesive propagates (illustrated with contour lines 1093) through the cavities 1081. The ventilation holes 1088 may provide a visual confirmation of the filling process may be provided, e.g. when liquid adhesive starts pouring out from the hole, the injection of the adhesive may be stopped.

[0230] In one advantageous embodiment, the double-adhesive tape comprises a layer of compressible material. This provides a viscoelastic housing. The compressible material may for instance be a layer of foam cells, such as acrylic foam. The double-adhesive tape may have a thickness of at least 0.5 mm, and preferably at least 1 mm. Accordingly, a cavity having a height of e.g. 1 mm to 5 mm may be provided. The width of the double-adhesive tape may for instance be 0.8-0.9 cm.

[0231] Thus, the double-adhesive tape provides an outer attachment part in form of an elastic bond between the surface mounted device and the surface of the wind turbine blade, whereas the cured adhesive provides an inner attachment part in form of structural bond equivalent to a firm or rigid connection between the surface mounted device and the surface of the wind turbine blade. The structural bond prevents the surface mounted part from creeping and the elastic bond region relieves stresses on the bond line, such as peel stresses, whereby the surface mounted device is less likely to be ripped off the surface of the blade due to forces affecting the device or the blade. This is illustrated in FIGS. 21 and 22.

[0232] FIG. 21 shows a cross-section of a trailing edge 1020 of a blade 1010 with the serrated trailing edge panel 1070 attached to the surface of the blade 1010. The serrated trailing edge panel 1070 may flex due to pressure fluctuations. This will introduce peel stresses to the attachment part. However, the flexible bond provided by the outer attachment part 1080 relieves these stresses.

[0233] FIG. 22 shows a longitudinal cross-section of the serrated trailing edge panel 1070 attached to the surface of the wind turbine blade 1010. When the blade bends, stresses will be introduced to the attachment part. However, the flexible bond provided by the outer attachment part 1080 in this case functions as an energy release barrier.

[0234] The invention has been described with reference to a preferred embodiment. However, the scope of the invention is not limited to the illustrated embodiment, and alterations and modifications can be carried out without deviating from the scope of the invention.

LIST OF REFERENCE NUMERALS

[0235]

TABLE-US-00001 2 wind turbine 4 tower 6 nacelle 8 hub 10, 610, 1010 blade 14 blade tip 16 blade root 18 leading edge 20, 1020 trailing edge 22 pitch axis 30 root region 32 transition region 34 airfoil region 36 pressure side shell 38 suction side shell 40, 42, 50 Profiled contour 52 Pressure side 54 Suction side 56 Leading edge 58 Trailing edge 60 Chord 62 Camber line/median line 70, 70′, 170, 270, 370, Surface mounted device/flow 470, 570, 670, 770, 870, guiding device 970, 1070 71, 71′ Plate-shaped element 72 Front surface 73 Rear surface 74 Proximal/lower part of surface mounted device 75 Distal/upper part of surface mounted device 76 Grid/rib structure 77, 77′ Attachment part 78 Grip 79, 79′, 879, 979 Bore/hole/opening 80, 80′, Flexible housing 680, 780, 880, 980, 1080 Flexible bond/outer attachment part 81, 81′, 681, 781, 881, Glue cavity 981, 1081 82, 82′, 182 Circumferential lip 83, 83′ Recess 84, 184 Attachment surface 85, 185 Double adhesive tape 86, 186 Liner 88, 1088 Ventilation bore/hole 91 Reservoir 893, 993 Propagation front 92 Adhesive 95 Flow guiding device group 196, 296 Intermediate elements c Chord length d.sub.t position of maximum thickness d.sub.f position of maximum camber d.sub.p position of maximum pressure side camber f camber r local radius, radial distance from blade root t thickness