Wind turbine blade

The invention relates to a wind turbine blade, with a gener ally hollow blade body comprising an upper and a lower half shell and first and second elongated webs each extending in the lengthwise direction of the blade and being disposed be tween and connected to the upper and the lower half shell, with the second web being arranged closer to the trailing edge of the blade and extending only along a part of the trailing edge, with each web comprising an upper and a lower flange connecting the respective web to the respective half shell, and with the first and second webs being supported via respective first and second reinforcement structures relative to the respective half shell, which reinforcement structures extend in the lengthwise direction of the blade, wherein each first and second reinforcement structure supporting the first and second web comprises at least one stack composed of sev eral pultruded composite strips comprising carbon fibers with the strips being fixed in a resin matrix.

As commonly known, wind turbine blades are parts of a wind turbine which is used for generating electric power. A wind turbine usually comprises three blades attached to a hub, which is connected to a generator arranged in a nacelle. The blades interact with the passing wind resulting in a rotation of the hub finally driving the generator.

A turbine blade usually comprises a hollow blade body with an upper and a lower half shell, which are usually separately produced and fixed to each other. Within this hollow blade body first and second elongated webs are arranged, which con nect both half shells and support them while also transfer ring the loads acting on the respective shells due to aerody namic reasons and the circular movement of the blade when ro tating. The load comprises pressure and suction loads on the upper and lower half shell and compressive and tensile loads. A wind turbine blade with this common setup is for example disclosed in EP 2791 500 B1.

For supporting the half shells and for transferring the re spective loads each elongated web extends in the lengthwise direction and is connected to the respective half shell via a flange provided at the respective web side, which flange is attached to an inner layer of the upper and lower half shell by an adhesive. For transferring the loads respectively sup porting the respective shells each web is supported via re spective first and second reinforcement structures relative to the respective half shell. Such a reinforcement structure is commonly also named as a spar cap. Like the respective webs and their flanges, also these reinforcement structures or spar caps extend in a lengthwise direction of the blade. These reinforcement structures, as for example also disclosed in EP 2791 500 Bl, are made of stacks comprising separate carbon fiber pultrusion strips, which are arranged above each other and fixed in a resin matrix. During the manufacturing of such a pultruded strip the carbon fibers are pulled through a supply of liquid resin, which resin is then heated and cured finally forming the respective pultruded strip. These pultruded carbon fiber strips show excellent mechanical properties in taking the respective loads and distributing them and also absorb high bending moments which arise during the blade rotation.

In a known wind turbine blade design as for example disclosed in EP 2791 500 Bl the blade comprises two first webs, which extend almost entirely over the length of the blades and which are arranged in the central body area, i.e. in the ar ea, where the upper and lower half shell, seen in the drop like cross section, have a large distance. Also a second web is provided, which second web is arranged close to the trail ing edge of the blade. This second web extends only along a part of the trailing edge, which part often has a specific edge design and is subjected to specific loads, which are taken respectively distributed by this second web. All webs comprise an elongated web body with the flanges ar ranged at the ends of the web body. Each web is supported by two reinforcement structures, i.e. spar caps, so that in to tal six spar caps are arranged in both shells for supporting the three webs. As three webs and six spar caps need to be integrated, the total mass of such a known turbine blade is high, although the mass of the spar caps itself is somehow reduced due to the usage of carbon fiber pultrusion stacks, which on the other hand are expensive.

Thus, there is a need for an improved wind turbine blade de sign allowing a proper load support and having a less complex and heavy design.

For addressing this problem a wind turbine blade as mentioned above is characterised in that each at least one stack com posed of the pultruded composite strips is an integral part of the respective first and second web and builds the respec tive flange, which is attached to the inner layer of the re spective upper and lower shell.

The inventive wind turbine blade is characterised in a spe cific arrangement regarding the first and second reinforce ment structures and has an improved design over known blade designs. The at least one stack forming the respective first and second reinforcement structure is composed of several pultruded composite strips comprising carbon fibers with the strips being fixed in a resin matrix. In this embodiment the respective first and second spar cap are made of carbon fiber pultrusion strips. This respective first and second rein forcement structure is an integral part of the respective first and second web and builds the respective flange, which is attached to the inner layer of the respective shell by means of the adhesive. The second web according to this em bodiment has a H-shape with a central web body and the inte gral reinforcement flanges attached to the web body. As the web body comprises a resin matrix, this matrix also integral- ly extends into the respective flanges respectively carbon strip stacks making the respective flange of the H-shaped webs very stiff and a mechanically well adapted piece. The web body may comprise a core for example made of balsa wood, PET or PVC which is arranged in a glass fiber envelope or casing which is resin infused. When producing the web, all respective parts, i.e. the web body parts and the carbon pul- trusion strips can easily be arranged in a common web mould by simply inserting the respective core and the fiber layers respective fabrics and the pultruded strips and by finally infusing the total web setup.

A specific advantage of this embodiment is that this H-shaped web can be produced external to the respective shells, al ready comprising the respective spar cap. This allows a sim plified production of the spar caps and especially allows for a proper inspection of the web respectively the connection of the reinforcement structures, i.e. the spar caps to the web body. Furthermore, the adhesive connection of the web flang es, i.e. the spar caps, to the inner layer of the upper and the lower shell needs to take less loads, and the respective reinforcement structures respectively the spar caps are an integral part of the web. As no adhesive joint is given be tween the web and the carbon strip reinforcement structures as they are an integral part of each web, the overall robust ness of the blade can be increased.

The inventive reinforcement structure arrangement can be re alised in different blade setups. It is possible that both webs extend over approximately the same length of the blade. Here boteh webs are arranged in the hollow blade at positions where the half shells have a rather far distance to each oth er. In an alternative the second web can be arranged closer to a trailing edge of the blade and extends only along a part of the trailing edge. Here the second web is adjacent to the trailing edge for stiffening this area. The flange integral first and second reinforcement structures respectively the carbon stacks may furthermore comprise biax ial glass and/or carbon fiber layers between each pair of strips which layers are infused with resin. For bonding the strips to each other fiber layers or fiber fabrics are in serted between the respective strips of the stack. The over all stack therefore has a sandwich setup with a pultruded strip is followed by a fiber layer or fabric which is fol lowed by another strip etc. Inventively the biaxial fiber layers are infused with resin, which resin builds the resin matrix into which the whole stack is embedded. A biaxial fi ber layer comprises fibers being arranged at an angle of 0° and other fibers being arranged at an angle of e.g. ±45°.

Such a biaxial layer is advantageous, as it allows to take loads of different directions respectively of different types, e.g. loads due to a flapwise or an edgewise bending of the blade.

As the web with the flanges is produced external to the re spective half shell, the flange design can be adjusted to the respective needs simply by using a respective web mould de signed also for arranging and infusing the pultrusion strip stack together with the biaxial layers. The prefabricated webs are then attached to the separately moulded shells, to which they are attached by an adhesive.

In another embodiment of the invention each of the first and second flange integral reinforcement structures comprises more than one stack arranged in parallel, preferably three stacks which are arranged adjacent to each other. This allows for shaping the overall shape of the respective flange, i.e. the spar caps, along the slightly bended shape of the respec tive upper and lower inner layer, so that the respective spar caps closely follow the inner layer shape.

As the reinforcement structures, i.e. the spar caps are in integral part of the webs and build their flanges, the design of the respective shell in the area to which the web flanges are attached can be adjusted. Preferably the inner layer is arranged closer to the outer layer in an area where the re spective flange of the respective web is attached to the in ner layer. The cross section respectively the thickness of the shell in the attachment area is reduced, as no spar cap needs to be integrated in the respective half shell, which have less weight but are still mechanically stiff.

It is possible, that the inner layer is attached directly to the outer layer. Here the inner layer, which is distanced to the outer layer in areas adjacent to the flange attachment areas due to the usual integration of core elements, is guid ed towards the outer layer and is directly attached to it, so that the thickness in this zone is very small. In an alterna tive an additional stiffening means is arranged between the inner and the outer layer of the respective half shell, which stiffening element is preferably quite thin so that the over all thickness of this area is still smaller compared to adja cent areas. Such a stiffening means may comprise several glass fiber layers which are embedded in the overall resin matrix of the shell. The fiber fabrics are very thin, so that even when several layers are stacked the overall thickness is not significantly higher. In an alternative a core element embedded in the overall shell resin matrix may be provided. This high density core element further stiffens or reinforces this area, but it's thickness is small so that again the overall thickness of this area is kept small. Whichever stiffening means is integrated, it provides a better support and load transfer via the first and second web.

For adjusting the mechanical properties of the blade in areas next to the respective flange attachment areas several fur ther core elements may be provided between the outer and the inner layer of the respective upper and lower half shell. These core elements, just like the ones which ma be sand wiched in the thinned flange attachment area of the respec tive shell may be made of a material with a sufficient high density like foam, wood, polymer or a composite material com- prising fiber layer or fabrics being infused with a resin for example, while this enumeration is not final.

The core elements, no matter what material is used, is an in tegral part of the respective shell and is sandwiched between the outer and inner layer. If a wooden or polymer core ele ment is used, this element is produced as a preform and is then inserted into the respective shell mould, when the re spective layers or elements for setting up the respective half shell are inserted into the shell mould. It is fixed to the shell by the resin. In case core elements being made of composite material like glass fiber layers are used, the re spective layer stack may be provided directly in the shell mould and may then be co-infused with the resin when the overall shell infusion is performed.

The invention also refers to a wind turbine comprising sever al wind turbine blades as described, preferably three turbine blades.

Other objects and features of the present invention will be come apparent from the following detailed description consid ered in conjunction with the accompanying drawings. The draw ings, however, are only principle sketches designed solely for the purpose of illustration and do not limit the inven tion. The drawings show:

Fig. 1 a principal sketch of a wind turbine,

Fig. 2 a view of an inventive wind turbine blade of a first embodiment comprising a first web and a sec ond web,

Fig. 3 a view of an inventive wind turbine blade of a sec ond embodiment comprising a first web and a second web, Fig. 4 a cross section through the blade of fig. 2 along the line IV - IV,

Fig. 5 an enlarged view of the section V of fig. 3 of a first embodiment, and

Fig. 6 an enlarged view of the section V of fig. 3 of a second embodiment.

Fig. 1 shows a principal sketch of a wind turbine 1 compris ing a tower 2, a nacelle 3 mounted on top of the tower 2 and a rotor 4 comprising three wind turbine blades 5 attached to a hub 6, which is operatively coupled to a generator arranged in the nacelle 3, which generator is driven by the rotational energy of the rotor 4 for producing electric power as common ly known.

The invention relates to the setup of the wind turbine blades

5.

Fig. 2 shows a principle drawing of a turbine blade 5 of a first embodiment with a root 7 for attaching the blade 5 to the hub and with a tip 8 at the other blade end. It further more comprises a leading edge 9 and a trailing edge 10.

Fig. 3 shows a principle drawing of a turbine blade 5 of a second embodiment with a root 7 for attaching the blade 5 to the hub and with a tip 8 at the other blade end. It further more comprises a leading edge 9 and a trailing edge 10.

The blade 5 comprises, see fig. 4, a hollow blade body 11, which is made of an upper half shell 12 and a lower half shell 13, which are fixed to each other with an adhesive 14 and which encase a hollow space 15. In this space 15 a first web 16 and a second web 17 are arranged. The first web 16 is arranged at a position where the upper half 12 and the lower half 13 almost have the greatest distance respectively the blade has nearly its maximum profile thickness. As fig. 2 shows, the web 16 extends almost over the whole length of the blade 5 starting adjacent to the root 7 and ending adjacent to the tip 8.

The second web 17 is arranged closer to the trailing edge 10. It may be arranged in different way. As fig. 2 shows the sec ond web 17 may, just like the first web 16, extend almost over the whole length of the blade 5 starting adjacent to the root 7 and ending adjacent to the tip 8. Both webs may extend preferably parallel, but this is not compulsory. As fig. 3 shows, it is also possible that the web 17 extends only over a part of the blade length close to the trailing edge 10.

Both first and second webs 16, 17 are used for supporting the blade shells 12, 13 and for taking and distributing the re spective loads resting on the blade and resulting from aero dynamic reasons due to the rotation of the rotor 4 and me chanical reasons due to the weight of the blade 5 itself.

While in the following in reference to figs. 5 and 6 the set up of the first web 16 is described in detail, it is to ben noted that the same description is valid also for the setup of the second web 17.

The first web 16 comprises a web body 18 which, see for exam ple fig. 5 showing the enlarged section V of fig. 4, compris es a core 19, for example made of balsa wood, a stable foam or a composite material etc. showing the needed mechanical properties for stiffening the whole web 16. The core 19 is encased in one or more glass fiber layers 20 which are resin infused, i.e. embedded in a cured resin 21.

The web 16 further comprises two flanges 22 which are an in tegral part of the web 16 and which are integrally attached to the ends of the web body 18. Fig. 5 shows only one flange, the setup of the other flange is the same. Each flange 22 al so comprises an integrated reinforcement structure 23 com prising a stack 24 made of several pultrusion strips 25 com- prising carbon fibers embedded in a resin. Although fig. 5 shows only three strips 25, only two or more than three strips may be provided. Between each pair of adjacent strips 25 one or more layers 26 of biaxial glass fiber fabric, which are infused with resin for fixing the strips 25, are inter posed. A biaxial fiber layer or fabric comprises fibers being arranged in an angle of 0° with other fibers being arranged at an angle of e.g. ± 45°. The whole arrangement of the strips 25 and the fiber layers 26 is completely embedded in the overall resin 21 embedding all components of the web 16. Thus the reinforcement structure 23, i.e. the carbon pultru- sion strips 25 with the interleaved fiber layers 26 is an in tegral part of the web 16, which can therefor be produced as a single complete piece external to the respective half shell 12, 13 itself and can be attached to them when the blade 5 is finally finished.

Due to the separate manufacturing of both webs 16, 17, which, as mentioned, are identical in their setup, the half shells 12, 13 are also manufactured separately in their respective moulds. As the reinforcement structures 23 are an integral parts of the respective webs 16, 17 respectively build the respective flanges of each web 16, 17, no specific reinforce ment structures need to be integrated into the respective half shell 12, 13. It is therefore possible, see figures 5 and 6, to have a specific design in the areas of the shells 12, 13, to which the webs 16, 17 are attached by their re spective flanges 22.

Fig. 5 shows a first embodiment of such a shell design, while in fig. 5 only the design of the respective attachment area for the flange 22 of the web 16 of the shell 12 is shown, but the same description is also valid for the design of the re spective attachment zone for the flange 22 of the web 17 as well as for the attachment zones of the shell 13.

Each shell 12, 13 comprises an outer layer 27 comprising one or more glass fiber layers 28, and an inner layer 29 also comprising one or more glass fiber layers 30. Between the outer and the inner layers 28, 29 respective core elements 31 are sandwiched. These core elements 31 may be made of balsa wood, high density foam or any other especially light weight stiffening material.

As fig. 5 clearly shows, in the attachment area, where the web flange is attached, the inner layer 29 is guided closer to the outer layer 27 respectively, see fig. 5, in direct contact, as shown by the respective glass fiber layers 28,

30. Therefore the shell area is very thin. As shown it is possible to arrange additional stiffening means 32, here in form of additional glass fiber layers 33 in this area, either adjacent to the glass fiber layer(s) 30 of the inner layer 29, or sandwiched between the glass fiber layers 28 and 30. While in fig. 5 only one glass fiber layer 28, 30 and 33 is shown, it is possible that more of each of these layers may be provided.

Preferably several glass fiber layers 33 are provided. They may be uniaxial layers or biaxial layers, while also both typs may be integrated in a random order, e.g. a uniaxial layer is followed by a biaxial layer which is followed by a uniaxial layer etc, or any other order. A biaxial fiber layer or fabric comprises fibers being arranged in an angle of 0° with other fibers being arranged at an angle of e.g. ± 45°. Such a biaxial layer is advantageous, as it allows to take loads of different directions respectively of different types, e.g. loads from a flapwise or an edgewise bending of the blade. A uniaxial layer is preferably adapted to stiffen against a flapwise bending.

As a whole the respective attachment area is a way thinner than the blade sections adjacent to the attachment section.

For attaching the respective flange 22 of each web 16, 17 to the half shell 12, 13, an adhesive 34 is used, by which the flange 22 is firmly attached to the respective shell 12, 13. For manufacturing the inventive blade 5, as already men tioned, both the webs 16, 17 and the shells 12, 13 are manu factured separately in respective moulds. The respective com ponents of the webs 16, 17 and the shells 12, 13 are arranged in the specific mould, whereupon the mould respectively the component setup is infused with resin for firmly embedding all components. The web components are embedded in the resin 21, while the shell components are embedded in the resin 35.

Thereafter both half shells 12, 13 are arranged above each other, with the webs 16, 17 being arranged between them and fixed to the respective shells 12, 13 by the adhesive 34. Al so the adhesive 14 is provided, so that the whole blade 5 is firmly fixed.

Fig. 6 shows another embodiment of a blade design in the at tachment region for the respective web flange 22. Again the inner layer(s) 29 respectively their glass fiber layers 30 are guided to the outer shell surface closer to the outer layer 27 respectively the outer glass fiber layer(s) 30, but not in direct contact. As shown, at least one core element 36 is sandwiched or interpost between the outer and the inner layer 27, 29 respectively the outer and inner glass fiber layers 28, 30. This core element 36 may also be made of a light weight stiffening material, which is adapted to act as a stiffening means 32, like balsa wood, high density foam or the like.

Even if such a core element 31 is integrated, again the over all thickness of the shell 12, 13 in this attachment area is clearly smaller than the thickness of the shell 12, 13 in the adjacent parts, in which the core elements 31 are sandwiched. Therefore it is possible, as shown in figures 5 and 6, to in tegrate the respective flanges 22 of the web 16 and the flanges of the web 17 into respective recesses provided in the surface of the inner layer 29 of the respective shell 12, 13 by means of the adhesive 34. This allows to sink the re- spective flange 22 into the inner layer 29 or surface, it may be almost flush with the surface. A very compact design and setup can be realised, which reduces the overall mass of the blade and with advantage provides only one adhesive joint be tween the web integral reinforcement structure 23 and the shell 12, 13. As no adhesive joint between the respective re inforcement structure 23, i.e. their respective spar cap com prising the stack 24 of the pultrusion carbon strips 25, and the web body 18 is given, the robustness of the blade design can be increased.

Another advantage is that the joint itself, realised by the adhesive 34, can be repaired, if need be, as it is possible to drill into this joint area from the outside of the blade 5, as only glass fiber layers in a matrix resin 35, may be also a core element 36, are arranged in this area, which can easily be drilled.

Another advantage resulting from the separate manufacturing of the H-shaped webs 16, 17 is that the web quality can be inspected thoroughly, so that a perfect web quality can be secured and, in case of need, any repair may be done directly at the web manufacturing side without effecting the shell mould leadtime.

Again, the basic setup of all webs arranged in the blade is the same. Each web comprises a respective web body with a core and resin in view outer glass fiber layer, and an inte grated flange comprising an integrated reinforcement struc ture composed of at least one stack of pultruded strips com prising carbon fibers, no matter if the respective web ex tends almost over the whole blade length or only over a part of it. Each of these web flange integrated reinforcement structure may also comprise two or more parallel carbon pul trusion stacks allowing to shape the geometry of the respec tive flange according to the geometry of the attachment area, if necessary. Independent of the final web setup, they all have in common that the respective reinforcement structure respectively the spar cap is completely integrated into the web.

Although the present invention has been described in detail with reference to the preferred embodiment, the present in vention is not limited by the disclosed examples from which the skilled person is able to derive other variations without departing from the scope of the invention.