Blade for a wind turbine

Abstract

Wind turbine blade having at least one longitudinal hollow element that defines an aerodynamic outer surface and an inner cavity having an inner surface. The blade also comprises at least one spar (1), disposed in the inner cavity and bonded to the inner surface by at least two bonding surfaces (13) located on bonding surfaces (2) of the spar (1). The spar (1) comprises, on at least one bonding zone (2), at least three fibre fabric layers (3) and at least one central core (4) and at least one lateral core (5) disposed between the at least three fibre fabric layers (3). This makes it possible to increase the resistance to shear stresses in the adhesive bond of the spar (1) to the inner surface of the longitudinal hollow element and decrease the required amount of adhesive.

Claims

1. A wind turbine blade comprising: at least one longitudinal hollow element that defines: an external aerodynamic surface, and an inner cavity having an inner surface in which there are a pressure zone and a suction zone, at least one spar (1), disposed in the inner cavity and bonded to the inner surface in at least two bonding surfaces (13) disposed in bonding zones (2) of the spar (1), and is characterised in that the spar (1) comprises, in at least one bonding zone (2): at least three fibre fabric layers (3), and at least one central core (4) and at least one lateral core (5) disposed between the at least three fibre fabric layers (3).

2. The wind turbine blade, according to claim 1, wherein at least three fibre fabric layers are disposed parallel therebetween and transversely or obliquely with respect to the bonding surface (13). 20

3. The wind turbine blade, according to claim 1, characterised in that the at least three fibre fabric layers (3) extend between the bonding zones (2) of the spar.

4. The wind turbine blade, according to claim 1, characterised in that each fibre fabric layer (3) is disposed over at least one side of the central core (4) or of the lateral core (5).

5. The wind turbine blade, according to claim 1, characterised in that the bond between the bonding surface (13) of the spar (1) and the inner surface is executed by means of an adhesive bond.

6. The wind turbine blade, according to claim 1, characterised in that: the at least one lateral core (5) comprises an adjacent side (14) and at least one divergent side (7) with respect to, at least, one lateral side (6) of the at least one central core (4) according to an angle of divergence (9), the at least one central core (4) comprises at least two fibre fabric layers (3) disposed on at least part of one of the lateral sides (6), wherein one of the fibre fabric layers (3) extends up to the bonding surface (13) directly on said lateral side (6) and another of the fibre fabric layers (3) is disposed on the divergent side (7) of the lateral core (5), such that the at least two fibre fabric layers (3) are separated therebetween from the corresponding lateral side (6) of the central core (4) up to the at least one bonding surface (13).

7. The wind turbine blade, according to claim 6, characterised in that the angle of divergence (9) is less than or equal to 60°.

8. The wind turbine blade, according to claim 6, characterised in that the angle of divergence (9) is less than or equal to 30°.

9. The wind turbine blade, according to claim 6, characterised in that the lateral core (5) also comprises a lateral surface (8) parallel to the lateral side (6) of the central core (4) and adjacent to the divergent side (7).

10. The wind turbine blade, according to claim 9, characterised in that the lateral surface (8) of the lateral core (5) has a constant height throughout the entire spar (1).

11. The wind turbine blade, according to claim 1, characterised in that the spar (1) comprises four fibre fabric layers (3), one central core (4) and, in each spar bonding zone (2), two lateral cores (5) disposed such that in the bonding surface (2) each fibre fabric layer (3) is separated from the adjacent layer by a lateral core (5).

12. The wind turbine blade, according to claim 1, characterised in that the thickness of at least one central core (4) is greater than the thickness of at least one lateral core (5).

13. The wind turbine blade, according to claim 1, characterised in that the thickness of the central core (4) decreases throughout the length of the spar (1) from the blade root zone to the blade tip zone.

14. The wind turbine blade, according to claim 1, characterised in that the thickness of the lateral cores (5) increases throughout the length of the spar (1) from the blade root zone to the blade tip zone.

15. The wind turbine blade, according to claim 14, characterised in that the thickness of the central core (4) decreases throughout the length of the spar (1) from the blade root zone to the blade tip zone and the width of the spar (1), which is the sum of the thicknesses of the central core (4) and of the lateral cores (5), is constant throughout its length.

16. The wind turbine blade, according to claim 1, characterised in that the central core (4) extends between the two bonding surfaces (13) comprises two lateral cores (5), each of which is disposed next to the central core (4) in each bonding zone (2).

17. The wind turbine blade, according to claim 1, characterised in that the central core (4) extends between the two bonding surfaces (13) and comprises four lateral cores, two of which are disposed on the sides of the central core (4) in each bonding zone (2).

18. The wind turbine blade, according to claim 1, characterised in that the central core (4) and lateral cores (5) extend between the two bonding surfaces (13) in at least one blade zone.

Description

DESCRIPTION OF THE DRAWINGS

[0039] In order to complement the description being made and with the aim of helping to better understand the characteristics of the invention, in accordance with a preferred embodiment thereof, said description is accompanied, as an integral part thereof, by a set of drawings where, in an illustrative and non-limiting manner, the following has been represented:

[0040] FIG. 1a shows a view of a spar of the state of the art having a C-shaped configuration;

[0041] FIG. 1a shows a graph representing the distribution of shear stress in the spar of FIG. 1a;

[0042] FIG. 2 shows a view of a spar of the wind turbine blade of the present invention having a C-shaped configuration;

[0043] FIG. 3a shows a view of a spar of the wind turbine blade of the present invention having a double T-shaped configuration;

[0044] FIG. 3b shows a graph representing the distribution of shear stress in the spar of FIG. 3a;

[0045] FIG. 4 shows a view wherein the cores and fibre layers of the spar of the blade of the present invention can be observed;

[0046] FIG. 5 shows a view of the spar in the blade tip zone; and

[0047] FIG. 6 shows a profile view of a blade wherein the different zones of the blade wherein the thickness of the central core differs are indicated.

PREFERRED EMBODIMENT OF THE INVENTION

[0048] Following is a description, with the help of FIGS. 1 to 6, of embodiments of the present invention.

[0049] FIG. 1a shows an example of the spar of the state of the art. In said figure the distribution of shear stress borne by the adhesive bond between the spar and an inner surface of a longitudinal hollow element wherein said spar is disposed has been represented. As described previously, the distribution of stress is such that two maximum stress peaks are generated. Said peaks correspond to the fibre fabric layers.

[0050] The central core (4) of the spar (1) and the two fibre fabric layers (3) comprised by said spar (1) have been represented in said figure. As can be observed in the figure, the fibre fabric layers (3) are disposed covering the two lateral sides of the central core (4) and also compose the bonding zone (2) of the spar (1) that bonds with the inner side of the blade pressure and suction surfaces. As can be observed in the figure, the bonding zones (2) of the spar (1) are formed by a single central core (4) and by the two fibre fabric layers (3). The thickness (E) of the central core (4) and a first width (A), which is the width of the adhesive bond with the inner side of the blade pressure and suction surfaces for a spar (1) of the state of the art, are also indicated. FIG. 1b shows a graph representing the shear stress generated in the adhesive bond. As described previously, two shear stress peaks appear.

[0051] The present invention describes a wind turbine blade having a spar that ensures a more homogeneous distribution of the shear stress in the adhesive bond between the spar and the inner surface of the longitudinal hollow element.

[0052] The blade comprises at least one longitudinal hollow element that defines an outer aerodynamic surface and an inner cavity having an inner surface having a pressure zone and a suction zone; and comprises at least one spar (1). Said spar (1) is disposed in the inner cavity and is joined to the inner surface by at least two bonding surfaces (13) disposed in the spar bonding zones (2).

[0053] The key of the present invention is that the spar (1) comprises at least three fibre fabric layers (3) and at least one central core (4) and at least one lateral core (5) disposed between the at least three fibre fabric layers (3), disposed in at least one bonding zone (2).

[0054] In one embodiment, the at least three fibre fabric layers (3) are disposed parallel therebetween and transversely or obliquely with respect to the bonding surface (13) in the bonding zone near the bonding surface.

[0055] In one embodiment, the at least three fibre fabric layers (3) extend between the spar bonding zones (2).

[0056] In one embodiment, each fibre fabric (3) layer is disposed on at least one side of the central core (4) or lateral core (5).

[0057] FIG. 2 shows an embodiment wherein the spar (1) of a wind turbine blade of the present invention has been represented with a C-shaped configuration. In said figure, a second width (B), which is the width of the bonding surface (13) of the C-shaped spar (1) of the present invention that bonds with the blade pressure and suction surfaces, is indicated. Said second width (B) is smaller than the first width (A) of the spars of the state of the art. This reduction in the width of the bonding surface (13) of the spar (1) makes it possible to save on adhesive and, due to the distribution of the stress, the use of additional bonding elements or reinforcement elements external to the spar itself are not required.

[0058] FIG. 3a shows an embodiment wherein the spar (1) has a double T-shaped configuration. FIG. 3b shows a graph representing the distribution of shear stress on the bonding surface (13) between the spars (1). The graph shows the stress experienced throughout a third width (C) which is the width of the bonding surface (13) of the spar (1) in this embodiment. As can be seen in graph 3b, in comparison with the graph of FIG. 1b, the shear stress is distributed more homogeneously and the value of the maximum shear stress peak has been reduced.

[0059] The at least three layers of fibre fabric (3) are separated by at least two cores (4, 5) in the bonding zone (2) of the spar (1).

[0060] FIG. 4 shows the cores (4, 5) and fibre fabric layers (3) of the present invention. In this case, a zoom image of the bonding zone (2) is shown in order to represent the layout of the elements in this zone, which is the zone wherein the adhesive bond is executed, in detail. In this embodiment, a central core (4) and a lateral core (5) disposed on both sides of the central core (4) in the bonding zone (2) can be observed. The geometry of said lateral cores (5) is such that, in the bonding zone (2), all the fibre fabric layers (3) are substantially parallel. The bonding surface (13), which is the surface of the spar (1) that is bonded to the inner surfaces of the longitudinal hollow element, has also been represented.

[0061] In one example of embodiment, such as that shown in FIG. 4, the lateral core (5) comprises an adjacent side (14), at least one divergent side (7) that diverges from at least one of the lateral sides (6) of the central core (4) according to an angle of divergence (9). In one example of embodiment, said divergence (9) is less than or equal to 60°. Preferably, said angle of divergence (9) is less than or equal to 30°. In one embodiment, said angle of divergence remains constant throughout the spar.

[0062] Likewise, the at least one central core (4) comprises at least two fibre fabric layers (3) disposed on at least part of one of the lateral sides (6). One of the fibre fabric layers (3) extends up to the bonding surface (13) directly on said lateral side (6) and the other fibre fabric layer (3) is also disposed on the divergent side (7) of the lateral core (5) such that at least two fibre fabric layers (3) are separated therebetween from the corresponding lateral side (6) up to the at least one bonding surface (13).

[0063] In one embodiment, the lateral core (5) also comprises a lateral surface (8) parallel to the lateral side (6) of the central core (4) and adjacent to the divergent side (7), which extends between the divergent side (7) and the bonding surface (13). Thus, according to this embodiment, one of the fibre fabric layers (3) extends up to the bonding surface (13) directly on the lateral side (6) of the central core and the other fibre fabric layer (3) is also disposed on the divergent side (7) of the lateral core (5) and on the parallel lateral surface (8), wherein the layer is prolonged up to the bonding surface. In this manner, the layer disposed on the lateral side (6) of the central core (4) and the layer disposed on the parallel lateral surface (8) are disposed parallel therebetween in the bonding zone near said bonding surface (13).

[0064] Preferably, the cores (4) are made of foam, PVC or balsa wood. Also preferably, the bond between the spar (1) and the inner surface is executed by means of an adhesive bond.

[0065] In the example of embodiment shown in FIG. 4, the spar (1) comprises four fibre fabric layers (3), a central core (4) and additionally comprises, in each spar bonding zone (2), two lateral cores (5) disposed in such a manner that in the bonding zone (2), each fibre fabric layer (3) is separated from the adjacent layer by a core (4, 5). This configuration makes it possible for the shear stress and width value of the bonding surface reached in this four-layer configuration to be less than in the configuration of the state of the art: τ′Max<τMax and C<A, respectively, according to FIGS. 1a and 1b and 3a and 3b. This is also the case of the three-layer configuration of FIG. 2, the width of the adhesive bond B is smaller than the width A of FIG. 1 as a consequence of a lower shear value in said bond.

[0066] In one embodiment, at least the lateral surface (8) of the lateral core (5) has a constant height throughout the entire section of the spar (1). In another embodiment, such as that shown in FIG. 5, the lateral cores (5) have a variable height throughout their length and said height varies in the same proportion as the height of the central core (4). This variation, preferably, decreases in height from the blade root zone to the blade tip zone. In one embodiment, the central core (4) and the lateral cores (5) extend between the two bonding surfaces (13) in at least one zone of the blade.

[0067] In one embodiment, the thickness of the central core (4) is greater than the thickness of the lateral cores (5). In another embodiment, the thickness of the central core (4) decreases throughout the length of the spar (1) from the blade root zone to the blade tip zone and/or the thickness of the lateral cores (5) increases throughout the length of the spar (1) from the blade root zone to the blade tip zone.

[0068] Preferably, the width of the spar (1), which is the sum of the thicknesses of the central core (4) and of the lateral cores (5), is constant throughout its length.

[0069] FIG. 6 shows a blade and an embodiment wherein three sections are distinguished (10, 11, 12) wherein the thickness of the central core (4) differs while the width of the spar remains constant throughout its entire length. In this case, the thickness of the central core (4) is smaller the nearer the section to the blade tip zone and, in order to maintain a constant spar width, the thickness of the lateral cores (5) increases throughout the length of the spar (1) from the blade root zone to the blade tip zone. In the figure, a first section (10) has been represented in the zone nearest the blade root, a second section (11) in the intermediate zone of the blade and a third section (12) in the zone of the blade tip.

[0070] In one embodiment, as shown in FIG. 2, the central core (4) extends between the two bonding surfaces (13) and comprises two lateral cores (5), each of which disposed near the central core (4) in each bonding zone (2). In another embodiment, as shown in FIG. 3a, the central core (4) extends between the two bonding surfaces (13) and comprises four lateral cores, two of which are disposed on the sides of the central core (4) in each bonding zone (2).