Wind turbine blade

The invention refers to a wind turbine blade, comprising an elongated blade body extending from a root to a tip with a trailing edge, whereby at least one beam-like reinforcement means is integrated in the blade body adjacent to the trail ing edge for reinforcing the region of the trailing edge, with the reinforcement means extending partly over the length of the blade body.

Modern wind turbines comprise several, usually three wind turbine blades attached to a rotor. The blades are interact ing with the wind making the rotor rotate, as is commonly known.

Each wind turbine blade comprises an elongated blade body having a root for attaching the blade to the rotor hub. The blade body extends from the root to a tip. The elongated body varies its cross sectional shape widely over its length. The cylindrical root section changes to a flattened air-foil cross section, which gets smaller and smaller towards the tip. The flat blade has a leading edge and a trailing edge at the opposite body side as well known. Especially the cross section of the blade body in the region of the trailing edge varies significantly over the body length.

It is necessary to provide reinforcement means at or within the blade body for providing the respective needed stiffness in view of the loads resting on the blade. A high stiffness in the edge region is required, also in the region of the trailing edge, which, as mentioned, varies its shape and thickness significantly. For stiffening the trailing edge re gion one or more beam-like reinforcement means in form of glass fiber beams, each beam comprising many separate glass fiber web layers embedded in a matrix like a resin, are ar ranged in respectively integrated in the blade body. The de- sign of these glass fiber reinforcement beam(s) in view of the required mechanical properties respectively stiffness is challenging, as the beam thickness is constrained by the lim ited space near the trailing edge. So the integration of the beam-like glass fiber reinforcement means is difficult.

Another aspect is that a thick trailing edge glass reinforce ment beam design leads to an irregular trailing edge core shape, it becomes long and slender, which increases the trailing edge core manufacturing difficulties. The trailing edge cores are arranged adjacent to the glass beam, and as the shape of the glass beam is quite complex and varying over its length, the trailing edge cores are also difficult in manufacturing and shaping.

Finally the relatively thick glass beam reinforcement signif icantly increases the blade mass and the mass moment, which in turn has an influence on other structural components like the setup of the shell and the root and a high impact on the blade bearing capacity and the design of the hub.

It is an object of the invention to provide an improved wind turbine blade.

For solving the problem an inventive wind turbine blade is characterised in that the reinforcement means is a pre-casted carbon beam comprising carbon fibers.

In the inventive wind turbine the beam-like reinforcement means is realised by a pre-casted carbon beam comprising car bon fibers. This carbon beam is pre-casted respectively pre fabricated and can therefore be easily arranged in the mould, in which the blade is manufactured respectively setup and in fused. This carbon beam replaces the glass fiber beam rein forcement, which is used in the prior art, and which is built layer by layer in the mould and finally infused. So the in ventive blade therefore no longer shows the disadvantages re- suiting from the in-mould integration of the glass fiber lay er beam.

The carbon beam comprises carbon fibers, which are embedded in a casting agent, preferably a resin respectively a resin matrix. As the beam is pre-casted, it can be exactly shaped to the needs respectively in view of the available space in the trailing edge region. So it can be exactly adjusted to the given geometry respectively can be designed to the needs especially also in view of the needed mechanical properties.

Furthermore the carbon beam shows enhanced mechanical proper ties over a comparable glass beam, so that the carbon beam comprising the carbon fibers is smaller in its design while providing better mechanical properties in view of stiffening or reinforcing the trailing edge region.

With the smaller design also a reduction of weight goes along, resulting in a reduced weight or mass of the blade, which finally results in the possibility to adapt the overall blade design especially regarding the root region etc.

Regarding the final setup of the carbon beam several embodi ments are provided. According to a first embodiment the car bon beam is made of a single pultruded carbon fiber profile or of one or more stacks of two or more pultruded carbon fi ber profiles casted in a matrix material. According to this embodiment the carbon beam is built by one or more pultruded carbon fiber profiles, preferably by stacking two or more pultruded carbon fiber profiles above each other. The beam may comprise only one such stack, while it may also comprise two or more stacks arranged side by side. A biaxial material, preferably a carbon biaxial material, may be inserted between each two adjacent stacked pultruded carbon fiber stacks to enhance the transverse propertires of the carbon beam. Each pultruded carbon fiber profile comprises carbon fibers, which are embedded in a matrix material like a resin. Finally the whole stack or the several stacks are embedded in the matrix material like the resin for fixing the stacked profile and to finally build the beam. The matrix material can be different from the resin for fixing the stacked profile.

As the beam is made of separate stacked pultruded carbon fi ber profiles, it is possible to vary the overall cross sec tional shape of the final carbon beam. So the hight and/or width of the stack respectively the carbon beam varies over the carbon beam length. The final carbon beam for example may become thicker and wider, seen from the root to the tip, which can be realised by varying the number of stacked pro files and by using profiles with different width etc. This allows for a simple design variation of the carbon beam and for adapting it to the given space.

Preferably the carbon beam has a rectangular cross section. The invention is not restricted to such a rectangular cross section, as also a trapezoidal, a polygonal or a partially rounded cross section or the like may be advantageous, de pending on the given space and the integration of the carbon beam in the overall blade body shell.

For integrating the carbon beam, preferably the carbon beam having a rectangular cross section or at least one rectangu lar edge region etc., it is preferable that an elongated core element having a wedge-like cross section is arranged at least at one side of the carbon beam and extends at least partially over the length of the carbon beam. If a rectangu lar carbon beam is used, preferably on both sides respective wedge-like core elements are arranged. They preferably extend over at least a part of the carbon beam length, preferably over the whole beam length and allow for a softer transition of the carbon beam to the adjacent shell regions, to which it is mechanically connected by means of fiber webs and respec tive infused matrix material, from which the shell is built.

Preferably the carbon beam is arranged at one side next to an outer layer or surface of the blade body. In this embodiment the carbon beam is quite small in thickness, although provid ing excellent mechanical properties. So it is possible to ar range the beam at the side of the blade body, preferably at the suction side, while it is certainly also possible to pro vide two carbon beams at both sides, i.e. the pressure side and the suction side. The one or both carbon beams are ar ranged close to the trailing edge, but need not necessarily extend directly into the very end edge region. As the carbon beam is, as mentioned, quite slim or thin, it is easily pos sible to integrate him into the shell setup. This can be done by respective fiber webs covering the carbon beam, which fi ber webs are infused in a resin matrix etc.

As it is possible to arrange a carbon beam only at one blade side close to the outer blade surface, a respective rein forcement beam preferably needs to be placed at the other side. Here it is possible to integrate a reinforcement glass beam comprising glass fibers, which glass beam is arranged opposite to the carbon beam at the opposite side next to an outer layer or surface of the blade body. The carbon beam is connected to the reinforcement glass beam by means of a con nection web which is embedded in a respective resin matrix, so that both beams arranged at the opposite blade body sides are firmly connected to the respective shell region and are firmly connected to each other, so that the trailing edge re gion is well stiffened. In an alternative it is also possible to integrate a second carbon beam at the opposite side next to the outer layer, which second carbon beam being set up like the first carbon beam, while both carbon beam being con nected by means of a connection web embedded in the resin ma trix. Here a carbon beam to carbon beam connection is given.

For filling the remaining space in the trailing edge region extending directly to the edge it is preferably that a foam core element, which extends, seen in the cross section, to wards the trailing edge, is sandwiched at least partially be tween an upper and a lower shell of the blade body, and espe cially the carbon beam and the glass beam. As mentioned, only one carbon beam may be integrated at the upper or lower shell, or two carbon beams may be integrated in the upper and lower shell, or one carbon beam and one glass beam may be in tegrated in the upper and lower shell. However the final beam setup is, the remaining space in the trailing edge region is filled with the foam core element, which extends along the trailing edge region to the tip and which extends into the trailing edge. So this foam core element is sandwiched be tween the outer and inner shell, which shells may be provided with the respective beams.

Finally it is preferable that a further core element is con nected to a wedge-like core element and/or to the glass beam next to the respective outer layer. Each upper and lower shell is built with further respective core elements, which are preferably connected to the integrated beam, either the carbon beam or the glass beam. If a wedge-like core element is arranged next to the carbon beam, the further core element is connected to this wedge-like core element. The connection is also realised by means of fiber web layers covering the connection region and by infusing it in a respective resin matrix.

The carbon beam described previously in the first embodiment is made of several pultruded carbon fiber profiles. In an al ternative it is possible that the carbon beam is made of sev eral pultruded carbon fiber rods or carbon fiber rovings casted in a matrix material. According to this embodiment, no separate carbon fiber profiles, preferably of rectangular shape, are used, but pultruded carbon fiber rods having e.g. a circular or oval shape are used, which are arranged side by side and above each other, according to the needs respective ly the space available. The pultruded carbon fiber rods are also somehow adjustable or variable in their shape, when ar ranging them to the multi rod arrangement, so that they can be deformed to a certain extent and the resulting carbon beam can be overall shaped, when it is finally embedded in the pre-cast matrix material. So this arrangement allows for an alternative setup of the carbon beam, and especially allows to shape the carbon beam with a cross section corresponding to the space defined by the outer layers and the trailing edge respectively the shells, as will be mentioned later.

In an alternative to using carbon fiber rods also carbon fi ber rovings may be used, which are pre-casted in a matrix ma terial. These rovings maybe used in form of strands or in form of webs which can be stacked above each other for build ing a web stack, which can also be adjusted in its shape due to the given space. The rovings will finally be infused with a matrix material.

The carbon beam of this second embodiment shows the same pos itive aspects and features as the carbon beam according to the first embodiment. It can also be shaped as a thin, plate like carbon beam, like in the first embodiment, or it can be, as it is somehow formable in its shape, be adjusted to the given space in the trailing edge region for filling it, as will be mentioned in detail below.

The carbon beam made of fiber rovings casted in a matrix ma terial may solely comprise carbon fiber rovings. Alternative ly it is also possible that the carbon beam comprises hybrid carbon/glass fiber rovings. If the rovings are used in form of webs a stack can be built which stack is a hybrid stack comprising carbon fibers as well as glass fibers, when the overall stack is finally infused in the resin material.

Preferably the carbon beam extends towards the trailing edge and is arranged next to at least one outer layer respectively surface of the blade body. Other than the first alternative, here the carbon beam, no matter how it is built in the second embodiment, directly extends into the trailing edge respec tively ends close to it. It is arranged adjacent or attached to at least one blade body side respectively shell or outer layer, but it can preferably also extend to the opposite side of the blade body having a cross section corresponding to the space defined by the outer layers respectively the upper and lower shell and the trailing edge. According to this embodi ment, the cross section of this carbon beam, either made of the pultruded carbon fiber rods or the rovings or fiber web layers infused in the respective matrix material, corresponds to the given space in the trailing edge region respectively directly at the trailing edge. This allows for filling this space with the carbon beam having the enhanced mechanical properties, so the trailing edge itself can directly be rein forced. A remaining small space, especially between the car bon beam and the final edge, may be filled with glass fiber webs and matrix material, while only little web and resin amount is used for filling that space, as most of it is filled by the inventive carbon beam.

Furthermore a foam core element may be arranged adjacent to the carbon beam extending further into the blade body and ex tending between the outer layers respectively both shells. This foamed core element fills further space in the trailing edge region and stiffens it. The foam core element connects to further shell core elements, which are arranged in both outer layers respectively the upper and lower shell stiffen ing the same.

Apart from the wind turbine blade, the invention also refers to a wind turbine, with a rotor comprising several wind tur bine blades as described above.

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 shows a principle sketch of an inventive wind tur bine comprising three inventive turbine blades, Fig. 2 shows a partial cross section view of a wind tur bine blade in the trailing edge region of a first embodiment of the wind turbine blade,

Fig. 3 shows a partial cross section view of a wind tur bine blade in the trailing edge region of a second embodiment of the wind turbine blade, and

Fig. 4 a cross sectional view of another embodiment of a carbon beam.

Fig. 1 shows a principle sketch of an inventive wind turbine 1, comprising a tower 2 with a nacelle 3 attached to the tow er top and a rotor 4 having a hub 5, to which three wind tur bine blades 6 are attached. Each wind turbine blade comprises a longitudinal blade body 7 with a root 8, by which it is at tached to the hub, and a tip 9 at the blade body end. In view of the rotation direction each blade 6 further has a leading edge 10 and a trailing edge 11 on the other side. The respec tive trailing edge region of each blade 6 is specifically de signed according to the invention, which will be described in more detail in the following.

Fig. 2 shows a first embodiment of an inventive wind turbine blade 6 as a partial cross section view of the trailing edge region 12, which runs into the trailing edge 11. The blade body 7 comprises a first or upper shell 13 and a second or lower shell 14. The first or upper shell 13 comprises an out er layer 15 or layer stack, while the second or lower shell 17 comprises an outer layer 16 or layer stack, which are built of one or preferably several fiber webs which are fi nally infused in a resin matrix.

Resulting from this shell construction, the inner 17 of the blade body 7 is hollow resulting in the necessity of rein forcing the shell structure. Problems specifically arise in the trailing edge region 12, which significantly varies its cross section seen from the root to the tip. According to the invention at least one reinforcement means 18 in form of a pre-casted respectively pre-fabricated carbon beam 19 comprising carbon fibers is integrated in the shell structure, here in the second or lower shell 14. In this em bodiment the carbon beam 19 is made of a stack of three sepa rate pultruded carbon fiber profiles 20, which are stacked above each other with carbon biaxial layers (not shown) be tween the profiles and which are pre-casted in a matrix mate rial, usually a resin, which matrix material is used for fix ing the separate profiles to a single carbon beam. The matrix material 30 is shown as an encapsulating material, but it al so infuses the stack between the respective profiles, which may be distanced by some sandwiched glass fiber webs allowing an infusion of the sandwich area.

As fig, 2 shows, the carbon beam has a rectangular cross sec tion, as all pultruded carbon fiber profiles 20 have a rec tangular cross section. It is obvious that by varying the width of the separate carbon fiber profiles 20 it is possible to vary the overall width of the stack respectively the car bon beam 19. It is furthermore possible to vary the cross sectional shape from a rectangular shape for example to a trapezoidal shape or the like simply by using pultruded car bon fiber profiles 20 having different width. Finally it is obvious that by varying the number of stacked carbon fiber profiles 20 the hight of the stack and finally the carbon beam 19 can also be varied.

The carbon beam 19 is arranged at the second or lower shell 14 next to the outer layer stack or layer 16. On both sides of the carbon beam 19 elongated core elements 21 having a wedge-like cross section are arranged for providing a smooth transition to the outer layer 16. These wedge-like core ele ments 21 may be made of wood like balsawood or a foam materi al or the like. Adjacent to the right wedge-like core element 21 a further core element 22 is arranged, which has also a wedge-like edge section so that it smoothly fits with the core element 21. This core element 22 is also integrated into the shell 14 and stiffens the same.

On the opposite side respectively at the first or upper shell 13 another reinforcement means 23 in the form of a reinforce ment glass beam 24 is integrated in the shell 13 respectively next to the outer layer 15. This glass beam 24 comprises a stack of separate glass fiber web layers which are embedded in the shell resin matrix and which glass beam stiffens the first or upper shell 13.

The carbon beam 19 and the glass beam 23 are connected by a connection web 25, which as a side web closes the trailing edge region 12 to the hollow inner 17 of the blade body 7.

The connection web 25 is also embedded in the resin matrix material and therefore firmly attached to the respective in ner fiber webs 26 covering the core elements 20, 21 and the carbon beam 19 respectively a core element 27 arranged in the upper shell 13 and connected to the glass beam 24.

As fig. 2 furthermore shows, the remaining space between the upper and the lower shell 13, 14 and the connection web 25 is filled with a foam element 28 which extends, seen in the cross section, towards the trailing edge 11 and is directly connected to the resin infused shells 13, 14 and sandwiched in part between the carbon beam 19 and the wedge-like core element 21 on the one side and the glass beam 24 on the other side. This foam element 28 completely fills the remaining space and stiffens the direct edge area.

The carbon beam 19 provides extraordinary mechanical proper ties and allows for a very good stiffening and reinforcement of the trailing edge region 12. It allows to replace a large mass of glass fiber web and resin embedding the fibers, which are usually used to fill the trailing edge region and rein- force it by building a glass fiber beam extending along the trailing edge respectively the trailing region. Therefore by integrating the comparably small carbon beam 19 the mass of the blade can significantly be reduced. The carbon beam 19 is easy to handle during manufacturing of the blade, as the car bon beam 19 itself can directly be placed into the shell mould, in which the shell is manufactured. Furthermore it is possible to use a light-weight foam element 28 for filling the mature part of the space in the trailing edge region 12, which also contributes to the mass reduction.

The carbon beam 19 extends at least partially over the length of the trailing edge 11, but it runs almost entirely into the tip 9. Over its length it may change its width and/or hight according to the given space respectively the needed rein forcement or mechanical stability and properties.

Fig. 3 shows another embodiment of an inventive wind turbine blade 6, again comprising a blade body 7 with the trailing edge 11 and the trailing edge region 12. It also comprises a first or upper shell 13 with an outer layer 15 and a second or lower shell 14 with an outer layer 16.

In this embodiment also a reinforcement means 18 in form of a carbon beam 19 is integrated in the trailing edge region 12, but, compared to fig. 3, the carbon beam 19 is here arranged very close to the trailing edge 11 and has a cross section which corresponds at least partially to the given cross sec tion of the space between the upper and the lower shell 13,

14.

Here the carbon beam 19 comprises a plurality of pultruded carbon fiber rods 29, which are embedded in a matrix material 30, again preferably a resin. The carbon fibers e.g. extend longitudinal towards the tip 9 and are embedded in the matrix material. The carbon fiber rods 29 are somehow soft and may therefore be arranged in a form where they can somehow be de formed in order to shape the overall cross section of the carbon beam 19, as fig. 3 shows. In this final form or mould the rods 29 are then infused or embedded in the matrix mate rial 30 which afterwards cures, so that a stable but specifi cally designed carbon beam 19 can be built.

The remaining space between the carbon beam 19 and the trail ing edge 11 is filled with fiber webs 31 embedded in the res in matrix 32, which also embeds the respective web layers building the upper and lower shell 13, 14.

Adjacent to the carbon beam 19 a foam element 28 is arranged, which also extends between both shells 13, 14 and which fills the remaining space in the trailing edge region 12 between both shells 13, 14 and a connection web 25, which here con nects the core elements 22 and 27 arranged in the shells 13 and 14 and is covered by respective webs 26, while the whole setup in the trailing edge region 12 is finally infused with the shell matrix material.

Also in this embodiment the carbon beam 19 comprising the pultruded rods 29 extends partially over the trailing edge length, but runs almost entirely to the tip 9. Also here it may certainly vary its width and hight, as it is designed to fill the space as far as possible, which space varies signif icantly along the its length to the tip 9.

While fig. 3 shows a carbon beam 19 made of a plurality of separate pultruded carbon fiber rods 29, which comprise re spective carbon fibers, it is also possible to build a compa rable shape-designed carbon beam 19 by using carbon fiber rovings and embed the in a matrix. Such a carbon beam 19 built of carbon fiber rovings 33, which are embedded in a ma trix material 30, is shown in a cross sectional view in fig. 4. Only carbon fiber rovings may be used, or carbon and glass fiber for building a hybrid beam. The rovings extend along the longitudinal axis of the carbon beam 19 and therefore ex tend along the trailing edge 11 to the tip. Finally also car bon fiber webs may be used. Several fiber webs are stacked for building a web stack, which is then embedded in the ma trix material. This web stack may comprise only carbon fiber webs or layers, but it may also be hybrid stack comprising several sandwiched glass fiber webs or layers, which glass fiber webs or layers allow a better infusion of the whole stack also in its volume.

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.