GB2600148A

GB2600148A - A wind turbine rotor blade assembly with an erosion shield

Info

Publication number: GB2600148A
Application number: GB2016841.5A
Authority: GB
Inventors: Mukherjee Manish
Original assignee: Blade Dynamics Ltd
Current assignee: LM Wind Power UK Ltd
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2022-04-27
Also published as: GB202016841D0

Abstract

A rotor blade assembly for a wind turbine comprises a rotor blade 10 with an attachment surface 72, eg including part of the blade leading edge 56, for an erosion shield 74. The erosion shield 74 has a plurality of through-holes 76 for alignment with a plurality of holes 80 in the attachment surface 72. A plurality of fasteners 78, eg screw rivets, are inserted into the aligned holes 76 and 80 such that the erosion shield 74 is fastened, eg releasably, to the rotor blade 10. The erosion shield 74 may be located in a recess in the attachment surface 72. The gap between the blade surface and the edge of the erosion shield 74 may be sealed by an injectable sealant (90, fig.6). The erosion shield 74 may comprise a layered polymer and/or a ceramic material and have a U-shaped cross-section with a row of holes (98, 99, fig.7) adjacent each longitudinal edge.

Description

A wind turbine rotor blade assembly with an erosion shield

Field of the invention

The present invention relates to a rotor blade assembly for a wind turbine, to a method of manufacturing a rotor blade assembly according to the present invention, and to the use of the erosion shield and fasteners according to the present invention for replacing 10 a damaged leading edge protection of a wind turbine blade.

Background of the invention

Wind is an increasingly popular clean source of renewable energy with no air or water pollution. When the wind blows, wind turbine rotor blades spin clockwise, capturing energy through a main shaft connected to a gearbox and a generator for producing electricity. Rotor blades of modern wind turbines are carefully designed to maximise efficiency. Modern rotor blades may exceed 80 metres in length and 4 metres in width.

Wind turbine rotor blades are typically made from a fibre-reinforced polymer material, comprising a pressure side shell half and a suction side shell half, also called blade halves. The cross-sectional profile of a typical blade includes an airfoil for creating an air flow leading to a pressure difference between both sides. The resulting lift force generates torque for producing electricity.

As wind turbines increase in size, so do blade lengths, often resulting in faster tip speeds. This increases the risk of eroded leading edges due to the continued impact from wind rain, hail, sand and/or airborne particles. Such erosive processes can limit the maximum rotational speed of the rotor blades, hence potentially reducing the power output of the wind turbine. These effects are exacerbated by the fact that wind turbines are increasingly subjected to harsh environmental conditions, such as remote offshore sites, mountain regions or challenging climates.

Leading edge erosion may therefore result in reduced annual energy production and 35 increased need for maintenance and repairs. For reducing damage caused by erosion, some prior art solutions attempt to protect the leading edge of a wind turbine blade using a special paint coating or a protective layer of thermoplastic film. Such coatings can be applied in-mould or post-mould. However, typically the protection provided by a painted coatings tends to diminish over time. Also, polymer films may be difficult to apply and/or bond to the blade surface.

Another known way of addressing these challenges is the implementation of metallic leading edges such as ceramic or polymer caps. Some of these installations, however, lead to an undesired increase in the mass of the blade tip, thus raising loads on the rest of the blade and on the turbine. In addition, as the size of the rotor blades increases, the size of the protective device must also increase. Such large and thick devices tend to be particularly susceptible to cracking due to mechanical impact and vibrations during the operation of the wind turbine. Thus, existing protection solutions are susceptible to defects and poor adhesion, potentially raising operation and maintenance cost substantially.

Another challenge is posed by the need for replaceability of leading edge protection devices. Known devices are bonded onto the blade surface using a suitable adhesive which typically results in the formation of a permanent structural joint, which is difficult to remove in a repair or replacement operation, often necessitating cutting or sawing operations. Also, it is usually impossible to perform this type of replacement operation up tower as oftentimes glue application, bonding and curing/clamping is required.

The manual application of protective caps or flexible coatings often leaves the protective device vulnerable to minor defects, which can lead to enhanced erosion in the long run. 25 This includes the formation of air pockets and wrinkles, negatively impacting the adhesion of the protective devices.

It is therefore a first object of the present invention to provide a leading edge protection solution that is easily applicable to a wind turbine blade.

It is a further object of the present invention to provide a leading edge protection solution that can be easily replaced and/or repaired.

It is another object of the present invention to provide a leading edge protection solution 35 that results in a cost-effective installation, maintenance and/or replacement thereof.

It is another object of the present invention to provide a method of installing or replacing a leading edge protection device that minimizes the formation of defects such as air pockets and wrinkles.

It is another object of the present invention to provide a leading edge protection which leads to extended the lifetimes of wind turbine blades, and which reduces the frequency of repairs.

Summary of the invention

The present invention addresses one or more of the above-discussed objects by providing a rotor blade assembly for a wind turbine, the rotor blade assembly comprising a rotor blade having a pressure side, a suction side, a leading edge, and a trailing edge extending between a tip and a root, wherein the rotor blade comprises an attachment surface for receiving an erosion shield, wherein a plurality of holes are provided in the attachment surface, an erosion shield configured on the attachment surface of the rotor blade, the erosion shield comprising a plurality of through-holes for alignment with the plurality of holes in the attachment surface of the rotor blade, a plurality of fasteners, wherein a fastener is inserted into each of the aligned through-holes of the erosion shield and holes in the attachment surface of the rotor blade such that the erosion shield is fastened, preferably releasably fastened, to the rotor blade.

It was found that the rotor blade assembly of the present invention enables an efficient erosion shield replacement on site and up-tower, thus providing an elegant process of improving the performance of existing wind turbine blades and improving AEP performance significantly. By using a plurality of fasteners to fasten, preferably releasably fasten, the erosion shield to the rotor blade, it is no longer necessary to use adhesive bonding, which is typically irreversible.

The rotor blade will usually comprise a load carrying structure including one or more spar caps and one or more shear webs, as well as an aerodynamic shell having an outer 35 surface forming at least part of an exterior surface of the wind turbine blade. It is preferred that the attachment surface is formed by a recess at the outer surface of the blade shell for receiving the erosion shield. It is preferred that the attachment surface, preferably formed by the recess, extends from the suction side via the leading edge to the pressure side of the blade.

The plurality of holes provided in the attachment surface are preferably holes that have been formed, such as drilled, into or through the blade shell. In a preferred embodiment, the holes provided in the attachment surface are index holes. In some embodiments, the holes provided in the attachment surface are arranged along at least one straight line extending in a substantially spanwise direction of the blade. The plurality of holes provided in the attachment surface may include at least 2, such as at least 4 or at least 6 holes, more preferably at least 8 holes. It is preferred that the holes provided in the attachment surface are arranged both on the suction side and on the pressure side of the blade. In a particularly preferred embodiment, a first set of holes, such as a first line or row of holes, is provided on the suction side, and a second set of holes, such as a second line or row of holes is provided on the pressure side of the attachment surface.

Likewise, the plurality of through-holes of the erosion shield are preferably pre-drilled. The plurality of through-holes may include at least 2, such as at least 4 or at least 6 through-holes, more preferably at least 8 through-holes. It is preferred that the through-holes in the erosion shield are arranged both on the side of the erosion shield that is attached to the suction side and on the side of the erosion shield that is attached to the pressure side of the blade.

In a particularly preferred embodiment, a first set of through-holes, such as a first line or row of through-holes, is provided on the side of the erosion shield attached to the suction side, and a second set of through holes, such as a second line or row of holes, is provided on the side of the erosion shield attached to the pressure side. Typically, the number and the spatial arrangement of the through-holes of the erosion shield will match the number and the spatial arrangement of the holes in the attachment surface of the blade.

In some embodiments, the erosion shield comprises a first row of through-holes adjacent to, and preferably parallel to, its first longitudinally extending edge, the first row preferably comprising 3-25 through holes, and a second row of through holes adjacent to, and preferably parallel to, its second longitudinally extending edge, the second row preferably comprising 3-25 through holes.

The erosion shield may be rigid or semi-flexible. In some embodiments, the erosion shield comprises a thermoplastic material. In other embodiments, the erosion shield is manufactured from extruded sheets of a thermoplastic. In another embodiment, the erosion shield comprises a polyurethane softshell. According to an alternative embodiment, the erosion shield is a metallic shield, preferably comprising stainless steel, nickel and/or titanium.

The erosion shield is preferably provided along at least a section of the leading edge of the blade. The erosion shield may be manufactured in an extrusion process, for example by co-extrusion of two thermoplastics having different material properties. In some embodiments, the erosion shield comprises a polyurethane material. The erosion shield may also comprise one or more components for the prevention of fouling during operation of the rotor blade.

In other embodiments, the erosion shield may be moulded in a mould comprising a moulding surface configured for forming the outer surface of the erosion shield. The erosion shield may be laid up covering a first part of the moulding surface of the mould. The erosion shield may be oriented such that the first surface of the leading edge protection element faces the moulding surface of the mould. In some embodiments, the erosion shield is formed by first laying a metal film layer onto the moulding surface, followed by one or more additional layers, such as a rubber layer. These layers may be bonded to each other by vulcanization of the rubber layer, which creates strong bonding between the two layers. Before bonding the metal film layer and the rubber layer, the metal film layer may be chemically treated to remove any oxide layers, in order to provide a better film bonding surface for the rubber layer. Alternatively, the metal film layer and the rubber layer may be bonded with an adhesive. In such embodiments, the metal film layer forms the outer surface of the erosion shield and the rubber layer forms the inner surface of the erosion shield.

In one embodiment, the erosion shield comprise a plurality of layers of erosion resistant material, said plurality of layers being arranged in a stack from an outermost layer substantially forming said external surface to an innermost layer arranged to be attached to a leading edge of a wind turbine blade, said plurality of layers bonded to adjacent layers in the stack. In a preferred embodiment, the plurality of layers of erosion resistant material have a cohesive strength or tensile strength greater than the adhesive strength or bond strength between adjacent or subsequent layers, such that at least a section of

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an outermost exposed layer will delaminate or peel from said erosion shield under the action of wind when at least a portion of said section of said outermost exposed layer has been eroded or ruptured, to present a relatively smooth external surface of said erosion shield.

It is preferred that one of the plurality of fasteners is inserted into each of the aligned through-holes of the erosion shield and holes in the attachment surface of the rotor blade such that the erosion shield is fastened, preferably releasably fastened, to the rotor blade. In a preferred embodiment, the fasteners are single-sided fasteners. In a particularly preferred embodiment, the fasteners are rivets, preferably screw rivets. It is particularly preferred that the rotor blade assembly comprises no adhesive for bonding the erosion shield to the rotor blade.

This results in an easy and efficient fastening method, which is safe and cost-effective.

In a preferred embodiment, the one or more fasteners are screw rivets. Screw rivets may be made of a polymer material such as nylon, and may comprise two separate parts which can be assembled. In other embodiments, the one or more fasteners comprise rivet screws, such as rivet screws which can be screwed into the threaded sleeve of a rivet tool, wherein the rivet sleeve can be inserted into a hole. Rivet screws may be used in combination with one or more additional screwed components for releasably fastening the cover panel to the blade shell member. The fasteners may be off-the-shelf self-locking polymer fasteners which can be torqued from the outside and do not require any other nut inside. In one embodiment, the fasteners are self-locking plastic nuts.

In a preferred embodiment, the erosion shield is mounted to the attachment surface of the rotor blade by a snap-fit connection. To this end, the erosion shield may contain one or more snap-fit members, such as one or more rails or bushings, that can snap onto one or more edges or cavities of the rotor blades. In another preferred embodiment, the erosion shield is mounted to the attachment surface of the rotor blade by a clip-on interlocking connection. In a preferred embodiment, the erosion shield is mounted to the attachment surface of the rotor blade in a snap-clip arrangement.

In a preferred embodiment, the attachment surface of the rotor blade includes at least part of the leading edge of the rotor blade. Also, the erosion shield is preferably 35 configured for protecting the outermost part of the blade leading edge next to or including the blade tip, as the blade tip and the outermost part of the wind turbine blade are exposed to particles of higher velocities and thereby have a higher risk of erosion damage. In a particularly preferred embodiment, the attachment surface of the rotor blade and the erosion shield extends along the outermost 5-50% of the length of the leading edge such as the outermost 10-30%.

In a preferred embodiment, the attachment surface of the rotor blade is recessed from the adjacent outer surface of the rotor blade. In some embodiments, the attachment surface of the rotor blade is recessed from the adjacent outer surface of the rotor blade in a stepped configuration, such that a step is provided between the attachment surface and the adjacent outer surface. It is preferred that the step is configured to extend substantially complementary to the edges of the erosion shield. It is also preferred that the step has a height which corresponds substantially to the thickness of the erosion shield. In a preferred embodiment, the attachment surface of the rotor blade is recessed from the adjacent outer surface of the rotor blade in a continuously declining configuration, for example as a straight or curved slope extending from the adjacent outer surface to the attachment surface.

The wind turbine blade may also comprise a channel formed at the leading edge of the blade, the channel being configured for receiving the erosion shield such that the erosion shield is provided flush with the surfaces of the blade adjacent the erosion shield. It is preferred that the dimensions of the attachment surface correspond substantially to the dimensions of the erosion shield. In some embodiments, the recessed attachment surface is longer and wider than the corresponding dimensions of the erosion shield. This ensures that sufficient space is available for mounting the erosion shield on the attachment surface.

In a preferred embodiment, a gap between a rotor blade surface and an edge of the erosion shield is sealed with a sealant, preferably an injectable sealant. Thus, in some embodiments, the rotor blade assembly further comprises a sealant arranged between a rotor blade surface and an edge of the erosion shield. According to a preferred embodiment, a sealant is injected to close off the gap between the blade main body and erosion shield. This ensures that there is no ingress of water and dust into the blade and also that aero smoothness is maintained as per design.

In other embodiments, the thickness of the erosion shield may decrease, e.g. by chamfering, towards any or all of the edges, preferably at least towards its longitudinally

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extending edges, for advantageously providing a smooth transition to the adjacent blade surface.

In a preferred embodiment, each of the fasteners comprises a head portion, wherein 5 each of the through-holes of the erosion shield is surrounded by a recess provided at the outer surface of the erosion shield for receiving the head portion of the fastener within the recess such that the head portion of the fastener is substantially flush with the outer surface of the erosion shield. Thus, advantageously, no aero losses occur at the leading edge of the rotor blade. In a preferred embodiment, a washer or an 0-ring is placed in 10 between the erosion shield and the attachment surface at the location of each aligned hole.

In a preferred embodiment, the erosion shield comprises a substantially U-shaped cross-section. Typically, the erosion shield comprises a first and a second longitudinally extending edge, and an outer and an inner arcuate surface extending between the first and the second longitudinally extending edge. The first and second longitudinally extending edges are preferably substantially straight edges. Preferably, the first longitudinally extending edge is attached to the suction side of the wind turbine blade, whereas the second longitudinally extending edge is attached to the pressure side of the wind turbine blade.

The outer and inner surfaces of the erosion shield are typically arcuate or substantially U-shaped. In a preferred embodiment, the inner surface of the erosion shield is complementary to the attachment surface of the rotor blade. Typically, the erosion shield also comprises opposing lateral edges, which are likewise arcuate or substantially U-shaped. In a preferred embodiment, the outer surface of the erosion shield extends across the leading edge such that the erosion shield covers at least part of both the suction side surface and the pressure side surface of the wind turbine blade.

In a preferred embodiment, the erosion shield comprises a polymer material and/or a ceramic material. In a preferred embodiment, the erosion shield comprises a plurality of layers of erosion resistant material.

In another aspect, the present invention relates to a method of manufacturing a rotor 35 blade assembly according to the present invention, the method comprising the steps of providing a rotor blade having a pressure side, a suction side, a leading edge, and a trailing edge extending between a tip and a root, wherein the rotor blade comprises an attachment surface for receiving an erosion shield, forming a plurality of holes in the attachment surface, providing an erosion shield for fastening to the attachment surface of the rotor blade, forming a plurality of through-holes into the erosion shield, arranging the erosion shield onto the attachment surface of the rotor blade such that the plurality of holes in the attachment surface of the rotor blade are aligned with the plurality of through-holes of the erosion shield, inserting a fastener into each of the aligned through-holes of the erosion shield and holes in the attachment surface of the rotor blade such that the erosion shield is fastened, preferably releasably fastened, to the rotor blade.

In some embodiments, the step of forming a plurality of holes in the attachment surface is performed after arranging the erosion shield onto the attachment surface of the rotor blade, preferably by using the through holes of the erosion shield for marking and/or drilling or otherwise forming the holes in the attachment surface. In such embodiment, the plurality of holes in the attachment surface of the rotor blade are inherently aligned with the plurality of through-holes of the erosion shield. In other embodiments, also the plurality of through-holes in the erosion shield are formed after arranging the erosion shield onto the attachment surface of the rotor blade. In some embodiments, the through-holes of the erosion shield and the holes in the attachment surface can be formed during the same drilling operation.

The rotor blade will typically comprise two shell halves which may be manufactured using blade moulds. Usually, first a blade gel coat or primer is applied to the mould. Subsequently, fibre reinforcement and/or fabrics are placed into the mould followed by resin infusion. A vacuum is typically used to draw epoxy resin material into a mould.

Alternatively, prepreg technology can be used in which a fibre or fabric pre-impregnated with resin forms a homogenous material which can be introduced into the mould. Several other moulding techniques are known for manufacturing wind turbine blades, including compression moulding and resin transfer moulding. The shell halves are assembled by being glued or bolted together substantially along a chord plane of the blade In some embodiments, the attachment surface is formed during the blade moulding process, preferably such that the attachment surface of the rotor blade is recessed from the adjacent outer surface of the rotor blade. In some embodiments the attachment surface of the rotor blade is recessed from the adjacent outer surface of the rotor blade 5 in a stepped configuration, such that a step is provided between the attachment surface and the adjacent outer surface. It is preferred that the step is configured to extend substantially complementary to the edges of the erosion shield. This may be achieved by laying out a core or similar element on the blade surface at the region of the attachment surface prior to the fibre lay-up. In other embodiments, a recessed 10 attachment surface can be formed post-moulding, e.g. using a milling process.

The attachment surface preferably extends over at least part of the suction side, at least part of the leading edge and at least part of the pressure side of the rotor blade. The plurality of holes in the attachment surface are preferably formed by a drilling operation.

In a preferred embodiment, a first row of holes is provided in the suction side part of the attachment surface and a second row of holes is provided in the pressure side part of the attachment surface. In some embodiments the attachment surface comprises 4-40 holes, preferably 8-30 holes.

The erosion shield for fastening to the attachment surface of the rotor blade may be formed as indicated above. It is preferred that the erosion shield extends over at least part of the suction side, at least part of the leading edge and at least part of the pressure side of the rotor blade. The plurality of through-holes into the erosion shield are preferably formed by a drilling operation. In a preferred embodiment, a first row of through-holes is provided in a suction side part of the erosion shield and a second row of through-holes is provided in a pressure side part of the erosion shield. In some embodiments the erosion shield comprises 4-40 through-holes, such as 8-30 through-holes.

The step of arranging the erosion shield onto the attachment surface of the rotor blade such that the plurality of holes in the attachment surface of the rotor blade are aligned with the plurality of through-holes of the erosion shield is preferably done by clipping or snapping the erosion shield onto the attachment surface of the rotor blade.

The step of inserting a fastener into each of the aligned through-holes of the erosion shield and holes in the attachment surface of the rotor blade preferably comprises applying rotation or torque to the fasteners, preferably single-side fasteners, such as screw rivets.

In a preferred embodiment, the step of providing a rotor blade comprises providing a recess in the outer surface of the rotor blade to form the attachment surface. The provision of the recess is preferably done as part of the shell moulding operation. In other embodiments, this step can be performed post-moulding, for example by a milling or grinding operation.

In a preferred embodiment, the method further comprises a step of injecting a sealant between a rotor blade surface and an edge of the erosion shield after the erosion shield is releasably fastened to the rotor blade. Typically, the erosion shield comprises a first and a second longitudinally extending edge, an outer and an inner arcuate surface extending between the first and the second longitudinally extending edge, and opposing lateral edges, which are preferably arcuate or substantially U-shaped. The sealant can be injected into any gaps formed between the rotor blade surface and any of the edges of the erosion shield, for example by using an injections cartridge. In particular in embodiments, in which the recessed attachment surface on the rotor blade is longer and wider than the corresponding dimensions of the erosion shield, the sealant can be used to close any gaps between an edge of the attachment surface and an edge of the erosion shield.

In another aspect, the present invention relates to the use of the erosion shield and fasteners according to the present invention for replacing a damaged leading edge protection of a wind turbine rotor blade or for retrofitting the erosion shield to a wind turbine rotor blade with a damaged or eroded leading edge. The fasteners are preferably fasteners for releasably fastening the erosion shield to the wind turbine rotor blade, as further exemplified above.

In another aspect, the present invention relates to an erosion shield for attachment to the surface of a wind turbine rotor blade and for protecting at least part of a leading edge of the rotor blade from erosion, the erosion shield comprising a plurality of through-holes, each for receiving a fastener therein. The plurality of through-holes may include at least 2, such as at least 4 or at least 6 through-holes, more preferably at least B through-holes.

It is preferred that the through-holes in the erosion shield are arranged both on the side of the erosion shield that is attached to the suction side and on the side of the erosion shield that is attached to the pressure side of the blade. In a particularly preferred embodiment, a first set of through-holes, such as a first line or row of through-holes, is provided on the side of the erosion shield attached to the suction side of the rotor blade, and a second set of through holes, such as a second line or row of holes, is provided on 5 the side of the erosion shield attached to the pressure side of the rotor blade. In some embodiments, the erosion shield comprises a first row of through-holes adjacent to, and preferably parallel to, its first longitudinally extending edge, the first row preferably comprising 3-25 through holes, and a second row of through holes adjacent to, and preferably parallel to, its second longitudinally extending edge, the second row preferably 10 comprising 3-25 through holes.

It will be understood that any of the above-described features or embodiments pertain to each of the different aspects of the present invention, such as the rotor blade assembly, the erosion shield, the method of manufacturing the rotor blade assembly, or the use of the erosion shield and fasteners of the present invention. In particular, features and embodiments described with regard to the rotor blade assembly may also apply to the method of the present invention, and vice versa.

Detailed description of the Invention

The invention is explained in detail below with reference to embodiments shown in the drawings, in which corresponding components are identified by the same reference numerals, wherein Fig. 1 shows a wind turbine, Fig. 2 shows a schematic view of a wind turbine blade, Fig. 3 shows a schematic view of an airfoil profile through section I-I of Fig. 4, Fig. 4 shows a schematic view of the wind turbine blade, seen from above and from the side, Fig. 5 is an exploded perspective view of a rotor blade assembly according to the present invention, Fig. 6 is a partial cross sectional view taken along the line A-A' in Fig. 5 in its assembled state, and Fig 7 is a schematic perspective view of an erosion shield according to the present invention.

Detailed Description

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 furthest from the hub 8.

Fig. 2 shows a schematic view of a first embodiment of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

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 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance rfrom the hub. The airfoil region 34 has an airfoil profile 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.

A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

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

Figs. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade. Fig. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use -i.e. during rotation of the rotor -normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

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

Fig. 4 shows other geometric parameters of the blade. The blade has a total blade length 5 L. As shown in Fig. 3, the root end is located at position r= 0, and the tip end located at r = L. The shoulder 40 of the blade is located at a position r = L., and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz, a minimum outer curvature radius ro and a minimum 10 inner curvature radius r which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Ay, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

Fig. 5 is an exploded perspective view of a rotor blade assembly 70 of the present invention. The rotor blade assembly comprises a rotor blade 10 with an attachment surface 72 for receiving an erosion shield 74. In the illustrated embodiment, the attachment surface 72 of the rotor blade includes part of the leading edge of the blade up to the blade tip 14. A plurality of holes 80 are provided in the attachment surface 72, the holes being arranged along a row or line in the embodiment shown in Fig. 5.

The erosion shield 74, which has a substantially U-shaped cross-section, comprises a first and a second longitudinally extending edge 88, 89, and an outer arcuate surface 75 and an inner arcuate surface 73 extending between the first and the second longitudinally extending edges 88, 89, as also shown in the perspective view of Fig. 7. The first and second longitudinally extending edges 88, 89 are substantially straight edges. Preferably, the first longitudinally extending edge 88 is attached to the suction side 54 of the wind turbine blade, whereas the second longitudinally extending edge 89 is attached to the pressure side of the wind turbine blade. The erosion shield also comprises opposing lateral edges 77, 81, which are likewise arcuate or substantially U-shaped.

The erosion shield 74 comprises a number of through-holes 76, which are likewise arranged along a row or line in the illustrated embodiment. The through-holes 76 can be 35 aligned with the plurality of holes 80 in the attachment surface 72 of the rotor blade. Then, respective fasteners 78, preferably single-sided fasteners, such as screw rivets, are inserted into each of the aligned through-holes 76 of the erosion shield 74 and holes 80 in the attachment surface 72 of the rotor blade such that the erosion shield 74 is releasably fastened to the rotor blade.

As illustrated in Fig. 7, the erosion shield may comprise a first row 98 of through-holes 76 adjacent to, and preferably parallel to, its first longitudinally extending edge 88, the first row 98 comprising 5 through holes in the illustrated embodiment, and a second row 99 of through holes 76 adjacent to, and preferably parallel to, its second longitudinally extending edge 89, the second row 99 also comprising 5 through-holes in the illustrated embodiment.

Fig. 6 is partial cross sectional view taken along the line A-A' in Fig. 5 in the assembled state. As seen in Fig. 6, the attachment surface 72 of the rotor blade is recessed from the adjacent outer surface 84 of the rotor blade. Thus, the erosion shield can be arranged within said recess, such that the outer surface 75 of the erosion shield is substantially flush with the adjacent blade surface 84.

As also seen in Fig. 6, a gap 86 between the rotor blade surface and the longitudinally extending edge 88 of the erosion shield 74 is sealed with a sealant 90, preferably an injectable sealant. This advantageously prevents the ingress of moisture and/or particulate matter in between the blade and the erosion shield. Also, each of the fasteners comprises a head portion 79 which is received in a recess 96 provided at the outer surface 75 of the erosion shield 74 that the head portion of the fastener is substantially flush with the outer surface 75 of the erosion shield. A washer 94 or 0-ring around the aligned holes in between the erosion shield and the attachment surface.

In the embodiment illustrated in Fig. 7, the thickness of the erosion shield decreases by chamfering towards its longitudinally extending edges 88, 89, for advantageously providing a smooth transition to the adjacent blade surface.

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

List of reference numerals 2 wind turbine 4 tower 6 nacelle 8 hub 10 blade 14 blade tip 16 blade root 18 leading edge trailing edge 22 pitch axis root region 32 transition region 34 airfoil region shoulder / position of maximum chord 50 airfoil profile 52 pressure side 54 suction side 56 leading edge 58 trailing edge 60 chord 62 median camber line rotor blade assembly 72 attachment surface 73 inner surface of erosion shield 74 erosion shield outer surface of erosion shield 76 through holes in erosion shield 77 first lateral edge of erosion shield 78 fastener 79 head portion of fastener holes in attachment surface 81 second lateral edge of erosion shield 82 recess in blade surface 84 adjacent surface 86 gap 88 first longitudinally extending edge of the erosion shield 89 second longitudinally extending edge of the erosion shield sealant 92 blade shell 94 washer 96 recess at outer surface of the erosion shield 98 first row of through holes 99 second row of through holes chord length dl position of maximum thickness cl, position of maximum camber position of maximum pressure side camber camber blade length La length of rigid arm r local radius, radial distance from blade root thickness Ay prebend

Claims

Claims 1. A rotor blade assembly (70) for a wind turbine, the rotor blade assembly comprising a rotor blade (10) having a pressure side, a suction side, a leading edge, and a trailing edge extending between a tip and a root, wherein the rotor blade comprises an attachment surface (72) for receiving an erosion shield (74), wherein a plurality of holes (80) are provided in the attachment surface (72), an erosion shield (74) configured on the attachment surface (72) of the rotor blade, the erosion shield (74) comprising a plurality of through-holes (76) for alignment with the plurality of holes (80) in the attachment surface (72) of the rotor blade, a plurality of fasteners (78), wherein a fastener is inserted into each of the aligned through-holes (76) of the erosion shield (74) and holes (80) in the attachment surface (72) of the rotor blade such that the erosion shield (74) is fastened to the rotor blade.
2. A rotor blade assembly (70) according to claim 1, wherein the fasteners (78) are single-sided fasteners.
3. A rotor blade assembly (70) according to claims 1 or 2, wherein the fasteners (78) are rivets, preferably screw rivets.
4. A rotor blade assembly (70) according to any of the preceding claims, wherein the erosion shield (74) is mounted to the attachment surface (72) of the rotor blade by a 25 snap-fit or by a clip-on interlocking connection.
5. A rotor blade assembly (70) according to any of the preceding claims, wherein the attachment surface (72) of the rotor blade includes at least part of the leading edge (56) of the rotor blade.
6. A rotor blade assembly (70) according to any of the preceding claims, wherein the attachment surface (72) of the rotor blade is recessed from the adjacent outer surface (84) of the rotor blade.
7. A rotor blade assembly (70) according to any of the preceding claims, wherein a gap (86) between a rotor blade surface and an edge (88) of the erosion shield (74) is sealed with a sealant (90), preferably an injectable sealant.
8. A rotor blade assembly (70) according to any of the preceding claims, wherein each of the fasteners comprises a head portion (79), and wherein each of the through-holes (76) of the erosion shield (74) is surrounded by a recess (96) provided at the outer surface (75) of the erosion shield (74) for receiving the head portion (79) of the fastener within the recess (96) such that the head portion of the fastener is substantially flush with the outer surface (75) of the erosion shield.
9. A rotor blade assembly (70) according to any of the preceding claims, wherein the erosion shield (74) comprises a substantially U-shaped or arcuate cross-section.
10. A rotor blade assembly (70) according to any of the preceding claims, wherein the erosion shield (74) comprises a polymer material and/or a ceramic material.
11. A rotor blade assembly (70) according to any of the preceding claims, wherein the erosion shield (74) comprises a plurality of layers of erosion resistant material. 20
12. A method of manufacturing a rotor blade assembly (70) according to any of the preceding claims, the method comprising the steps of providing a wind turbine rotor blade having a pressure side, a suction side, a leading edge, and a trailing edge extending between a tip and a root, wherein the rotor blade comprises an attachment surface (72) for receiving an erosion shield (74), forming a plurality of holes in the attachment surface (72), providing an erosion shield (74) for fastening to the attachment surface (72) of the rotor blade, forming a plurality of through-holes into the erosion shield (74), arranging the erosion shield (74) onto the attachment surface (72) of the rotor blade such that the plurality of holes in the attachment surface (72) of the rotor blade are aligned with the plurality of through-holes of the erosion shield (74), inserting a fastener into each of the aligned through-holes of the erosion shield (74) and holes in the attachment surface (72) of the rotor blade such that the erosion shield (74) is fastened to the rotor blade.
13. A method according to claim 12, wherein the step of providing a rotor blade comprises providing a recess (82) in the outer surface of the rotor blade to form the attachment surface (72).
14. A method according to claims 12 or 13, wherein the method further comprises a step of injecting a sealant (90) between a rotor blade surface and an edge (88) of the erosion shield (74) after the erosion shield (74) is releasably fastened to the rotor blade.
15. Use of the erosion shield (74) and fasteners as defined in any of claims 1-11 for replacing a damaged leading edge protection of a wind turbine blade or for retrofitting the erosion shield to a wind turbine rotor blade with a damaged or eroded leading edge.