Technical field

The present invention relates generally to wind turbine blades and more specifically to a wind turbine blade having a bulkhead.

Background

Modern wind turbines comprise a plurality of wind turbine blades attached at their respective root ends to a central rotor hub. The wind turbine blades typically comprise aerodynamic shells defining a substantially hollow interior of the blade. It is known for some wind turbine blades to include a work platform arranged near the root end of the blade for maintenance personnel to stand on when working in the hub of the turbine. Such a work platform may be connected to the hub, or may alternatively be connected to the blade shell near the root end of the blade. In some wind turbine blade, a work platform may comprise an access opening to provide maintenance personnel access to the interior of the blade. As the length of wind turbine blades increases to capture more energy from the wind, so too does the root diameter of such blades in order to support the increased weight of the blade. The root diameter of some wind turbine blades may exceed 4 m. As such, a central portion of a work platform may be over 2 m away from the blade shell where the perimeter of the platform is supported. The size of such work platforms can therefore make it difficult to provide a work platform with the requisite stiffness. Whilst the platform could be made thicker, this would increase the cost of the work platform and/or increase the weight of the blade. Manufacturing the platform from stronger materials typically increases the weight and/or cost of the blade. Using stronger materials for the work platform would also significantly increase cost. It is against this background that the present invention has been developed. Summary of Invention

In a first aspect of the invention there is provided a wind turbine blade which extends longitudinally from a root end to a tip end. The blade comprises a shell having an aerodynamic contour and defining a substantially hollow interior of the blade, a bulkhead arranged in the interior of the blade at the root end, and at least one shear web arranged in the interior of the blade. The shear web has longitudinally-extending surfaces connected to inner surfaces of the shell. A root end of the at least one shear web is connected to the bulkhead.

The root end of the at least one shear web is preferably directly connected to the bulkhead such that the shear web and bulkhead are adjacent to one another.

The shell may be a structural shell. The shell may therefore comprise spar caps integrated with laminate layers of the shell or otherwise connected thereto. The spare caps are to be regarded as part of the shell. Preferably the shear web is connected between spar caps of the shell. Connecting the shear web to the inner surfaces of the shell includes connecting includes connecting the shear web to one or more spar caps in examples where the spar caps define part of an inner surface of the shell.

The bulkhead may provide a work platform. The bulkhead may be substantially circular. The or each shear web may extend across a full chord of the bulkhead, dividing the bulkhead into a plurality of sections. The bulkhead may have a sandwich structure comprising core material arranged between first and second skins. The core material may be structural foam. The skins may be formed of fibre-reinforced plastic such as glass-fibre reinforced plastic (GFRP).

A perimeter of the bulkhead may be connected to an inner surface of the outer shell. Preferably the bulkhead is connected to the inner surface of the outer shell via an adhesive bond.

The bulkhead may comprise a flange extending around the perimeter of the bulkhead. The bulkhead flange may be T-shaped in cross section. Alternatively, the bulkhead flange may be L-shaped in cross section. Preferably, the bulkhead is fixed to the outer shell via an adhesive bond between the bulkhead flange and the inner surface of the outer shell. The or each shear web may comprise a mounting flange at the root end of the shear web. The shear web may be connected to the bulkhead via the mounting flange. The mounting flange may be T-shaped in cross section. Alternatively, the mounting flange may be L- shaped in cross section.

The or each shear web may be adhesively bonded to the bulkhead. Preferably the or each shear web is adhesively bonded to the bulkhead via the mounting flange at the root end of the shear web.

The wind turbine blade may comprise at least two shear webs connected to the bulkhead. The at least two shear webs may be mutually spaced apart in a chordwise direction of the blade. The bulkhead may comprise an access hole arranged to provide personnel access to the interior of the blade.

The or each shear web may partition the interior of the blade adjacent the bulkhead into a plurality of cavities.

At least one access hole may be provided in the or each shear web. The at least one access hole may be arranged to provide personnel access between the plurality of cavities. The at least one access hole may be provided near the root end of the shear web, adjacent to the bulkhead.

A plurality of access holes may be provided in the or each shear web. The access holes may be mutually spaced apart. The access holes may provide safe access between the cavities irrespective of blade orientation. The plurality of access holes may be mutually offset in a height direction of the shear web. Additionally or alternatively, the plurality of access holes may be mutually offset in a longitudinal direction of the shear web. The height direction may be referred to as the thickness direction of the blade. The height direction may be substantially perpendicular to longitudinal and chordwise directions of the blade. Accordingly, one access hole may be arranged relatively close to a leeward side of the blade, whilst another access hole may be arranged relatively close to a windward side of the blade. The access holes provide convenient and safe access between cavities irrespective of blade orientation. Further, one access hole may be arranged nearer to the root end of the shear web than the other, maximising material in a height direction of the shear web at each access hole location to increase the strength of the shear web.

In other words, the access holes may be mutually offset in the height direction and/or in the longitudinal direction of the shear web.

In a second aspect of the invention there is provided a process for assembling a wind turbine blade. The process comprises providing first and second half shells, arranging a bulkhead at a root end of the first half shell, and arranging at least one shear web in the first half shell. The process further comprises joining the first and second half shells together and joining the shear web and bulkhead to inner surfaces of the first and second half shells. A root end of the shear web is connected to the bulkhead such that the bulkhead and shear web stabilise each other during the assembly process.

The shear web may be connected to the bulkhead prior to arranging the shear web and the bulkhead in the first half shell.

Brief description of Figures

Embodiments of the present invention will now be described by way of non-limiting example only, with reference to the accompanying figures, in which:

Figure 1 is a schematic perspective view of a wind turbine blade comprising a blade shell and a bulkhead arranged in a root portion of the blade shell;

Figure 2 is a schematic perspective view showing the root portion of the blade shell, the bulkhead and shear webs connected to the bulkhead in more detail;

Figure 3a is a schematic cross-sectional view showing the connection between the shear webs, bulkhead and blade shell;

Figure 3b is a detailed view of the connection between the bulkhead and blade shell; Figure 4 is a schematic perspective view of the root portion in an example wherein the shear webs comprise an access hole; and

Figure 5 is a schematic perspective view of the root portion in an example wherein the shear webs comprise a plurality of offset access holes.

Detailed description

Figure 1 is a schematic perspective view of a wind turbine blade 10 in accordance with an example of the invention. The blade 10 extends from a root end 12 to a tip end 14 in a spanwise (S) direction, and between a leading edge 16 and a trailing edge 18 in a chordwise direction (C). The wind turbine blade 10 comprises a shell 20 which defines an aerodynamic contour configured to capture energy from wind incident on the blade 10. In this example the blade 10 comprises a first half shell 22a and a second half shell 22b which are joined together to form the blade shell 20. In this example, the first half shell 22a defines a leeward side 24a of the blade 10, and the second half shell 22b defines a windward side 24b of the blade 10.

The blade shell 20 is a substantially hollow structure. As such, the blade shell 20 defines a substantially hollow interior 26. A bulkhead 28 and two shear webs 30 are arranged in the hollow interior 26 in this example. The bulkhead 28 is arranged in a spanwise portion of the blade shell 20 near the root end 12 of the blade 10, i.e. in a root portion 32 of the blade 10. The blade shell 20 has a substantially circular contour in the root portion 32 of the blade 10. As such, the bulkhead 28 in this example is substantially circular.

The two shear webs 30 arranged in the blade shell interior 26 extend longitudinally in the spanwise direction (S) of the blade 10 and are configured to take up shear loading experienced by the blade 10 in use. The shear webs 30 are spaced apart in the chordwise direction (C) of the blade 10. Accordingly, a first shear web 30a is closer to the leading edge 16, and a second shear web 30b is closer to the trailing edge 18 in this example. Each shear web 30 comprises longitudinally-extending surfaces 34 (shown in Figure 2) via which the shear web 30 is connected to an inner surface 36 of the blade shell 20. In this example, each shear web 30 is rigidly connected between the windward and leeward half shells 22a, 22b by means of adhesive.

In this example, the blade shell 20 is a structural shell comprising spar caps (not shown) integrated with laminate layers of each half shell 22. In other examples the spar caps may be connected to the shell 20, for example by means of adhesive. To form a load-bearing spar structure, the shear webs 30 are arranged between spar caps associated with the first and second half shells 22a, 22b. As such, connecting the shear webs 30 to the inner surface 36 of the shell 20 in this example comprises connecting the shear webs 30 between mutually opposed spar caps.

A root end 38 of each shear web 30 is connected to the bulkhead 28 as shown most clearly in Figures 2 and 3a. Figure 2 shows the root portion 32 of the blade 10 with the second half shell 22b omitted for clarity. As shown, the root end 38 of each shear web 30 is connected directly to the bulkhead 28. That is to say, the root end 38 of each shear web 30 is arranged immediately adjacent to the bulkhead 28. In this example, the shear webs 30 are rigidly connected to the bulkhead 28, and the bulkhead 28 is rigidly connected to the inner surface 36 of the blade shell 20.

Connecting the shear webs 30 to the bulkhead 28 provides structural support to the bulkhead 28 thereby increasing the rigidity of the bulkhead 28. In particular, the shear webs 30 support a central portion 40 of the bulkhead 28 furthest from a perimeter 42 of the bulkhead 28. As such the required load-bearing capacity of the bulkhead 28 is reduced in comparison to bulkheads not connected to a shear web 30. This allows the bulkhead 28 in this example to be formed of relatively lightweight materials, such as composites. Rigidly connecting the shear webs 30 to the bulkhead 28 therefore facilitates the provision of large bulkheads 28 in large blades 10 without unduly increasing the weight of the blade 10.

As shown by the dashed lines in Figure 2, the shear webs 30 in this example extend across a full chord of the bulkhead 28, effectively dividing the bulkhead 28 into a plurality of sections 44a, 44b, 44c. In this example, a middle section 44b of the bulkhead 28 comprises an access hole 46 arranged to provide personnel access to the interior 26 of the blade 10. The access hole 46 in this example is arranged near the perimeter 42 of the bulkhead 28, i.e. near the blade shell 20, to facilitate safe access to the interior 26 of the blade 10 when the blade 10 is oriented substantially horizontally as shown in Figure 2.

The bulkhead 28 provides a work platform on which maintenance personnel can stand when carrying out work in the blade interior 26. In use, the blade 10 is connected at its root end 12 to a central rotor hub of a wind turbine (not shown), and the bulkhead 28 therefore further provides a work platform to support personnel working in an interior of the rotor hub. The access hole 46 may comprise a cover (not shown) to stop personnel from falling or tripping through the access hole 46 when the blade 10 is in a vertical orientation. Connecting the shear webs 30 to the bulkhead 28 permits the use of larger access holes 46 than would otherwise be possible without compromising the structural performance of the bulkhead 46 because the stiffness of the bulkhead is sufficient by virtue of the connection to the shear webs 30.

Referring now to the cross-sectional view of the root portion 32 shown in Figure 3a, the bulkhead 28 in this example comprises a sandwich structure in which a panel of core material 48 is arranged between first and second skins 50a, 50b. The core material panel 48 in this example comprises a lightweight structural foam, such as closed cell PVC foam. The skins 50a, 50b of the bulkhead 28 preferably comprise multi-axial reinforcing fibres to transfer shear loads from the shear webs 30 to the blade shell 20 most effectively. In another example, the first and second skins 50a, 50b may comprise glass fibre chopped strand mats.

The bulkhead 28 in this example comprises a flange 52 extending around its perimeter 42 via which the bulkhead 28 is connected to the inner surface 36 of the blade shell 20. As shown most clearly in the enlarged view of Figure 3b, the bulkhead flange 52 in this example is substantially T-shaped in cross section. The bulkhead 28 is connected to the blade shell 20 by an adhesive bond 54 between the bulkhead flange 52 and the inner surface 36 of the blade shell 20. The T-shaped bulkhead flange 52 provides a plurality of load paths to transfer load from the bulkhead 28 to the blade shell 20, and provides a wider surface area over which to distribute the loads more evenly. The bulkhead flange 52 therefore minimises stress concentrations at the joint between the bulkhead 28 and the blade shell 20.

The blade shell 20 in the root portion 32 is supported by the bulkhead 28 as a result of the rigid connection between the bulkhead 28 and blade shell 20. As such, the bulkhead 28 helps to stabilize the blade shell 20 in use and prevents ovalization of the blade shell 20 in the root portion 32. As such, the bulkhead 28 ensures that the blade shell 20 stays substantially circular at the root end 12 of the blade 10. Structural loads are therefore evenly distributed around the root end 12 of the blade 10 at which the blade is connected to the rotor hub.

As shown in Figure 3a, the shear webs 30 in this example have a sandwich structure comprising a core material panel 56 laminated between fibrous reinforcing skins 58a, 58b. In this example the fibrous reinforcing skins 58a, 58b comprise multi-axial reinforcing fibres. Preferably the reinforcing fibres are biaxial fibres which take up and transfer the shear loads experienced by the blade 10 in use most effectively. In this example the reinforcing fibres are glass fibres.

As previously mentioned, the shear webs 30 are rigidly connected to the bulkhead 28 at their respective root ends 38. In this example, the root end 38 of each shear web 30 comprises a mounting flange 60. The mounting flange 60 in this example is substantially T-shaped in cross section. The shear webs 30 are connected to the bulkhead 28 via an adhesive bond 62 between the mounting flange 60 and the bulkhead 28. The rigid connection between the shear webs 30 and the bulkhead 28 provides a plurality of load paths via which the shear loads taken up by the web 30 in use can be unloaded. The rigid connection between the shear webs 30 and bulkhead 28 facilitates efficient transfer of loads from the web 30 to the bulkhead 28, and the loads are then distributed over a large area afforded by the bulkhead 28.

Loads transferred to the bulkhead 28 can then be offloaded to the blade shell 20 via the rigid connection between the bulkhead 28 and blade shell 20. The rigid connection between the perimeter 42 of the bulkhead 28 and the blade shell 20 spreads the loads in the bulkhead 28 such that loading transferred to the bulkhead 28 is dissipated around the perimeter 42 and safely transferred to the blade shell 20. As such, the above described shear web and bulkhead scheme provides a stiffer blade 10 with a higher load-bearing capacity than blades having shear webs that are not connected to a bulkhead.

The configuration of the shear webs 30 connected to the bulkhead 28 also provides advantages in the manufacture and assembly of the wind turbine blade 10, as will now be described.

As is generally known in the art, the process of making a wind turbine blade 10 typically comprises forming a first and second half shell 22a, 22b in separate moulds. Adhesive may be provided on the inner surface 36 of one or more of the half shells 22a, 22b. One or more shear webs 30 are arranged in the first half shell 22a and connected to the inner surface 36 of the first half shell 22a. A bulkhead 28 is bonded to the inner surface 36 of the first half shell 22a before the half shells 22a, 22b are joined together to form a complete blade shell 20. The bulkhead 28 and shear webs 30 are connected to an inner surface 36 of the second half shell 22b when the half shells are joined together.

However, the process of making a wind turbine blade 10 in accordance with examples of the present invention further comprises connecting the root end 38 of each shear web 30 to the bulkhead 28. As such, in this process each shear web 30 is rigidly connected to the bulkhead 28 before the first and second half shells 22a, 22b are joined together to form the blade shell 20.

The shear webs 30 are arranged substantially perpendicular to the bulkhead 28 and extend longitudinally in the spanwise direction (S) of the half shell 22a. As such, the bulkhead 28 and shear webs 30 stabilise each other during the assembly process. The bulkhead and shear web configuration therefore facilitates an assembly process that doesn’t require additional tooling such as a jig or frame to support the shear webs 30 during assembly of the blade 10.

In some other examples, each shear web 30 may be connected to the bulkhead 28 prior to arranging the shear web 30 and the bulkhead 28 in the first half shell. As such, the bulkhead 28 and shear webs 30 can be arranged in the half shell 22a as a sub-assembly, reducing the time taken to assemble and connect components in the first half shell 22a. Pre-assembling the shear webs 30 with the bulkhead 28 may be further beneficial in ensuring accurate alignment of the webs 30 with the bulkhead 28 without the constraints of working in the curved half shell 22a.

As shown in Figure 3a, connecting the respective root ends 38 of the shear webs 30 to the bulkhead 28 effectively partitions the interior 26 of the blade 10 adjacent to the bulkhead 28 into a plurality of cavities 64a, 64b, 64c. A central cavity 64b is accessible via the previously described access hole 46 in the bulkhead 28 (shown in Figure 2) in this example. In this example, leading edge and trailing edge cavities 64a, 64c may be accessed from the central cavity 64b via access holes 66 in the shear webs 30 as will now be described with reference to Figures 4 and 5.

Figure 4 is a schematic perspective view of the root portion 32 of the blade shell with the second half shell 22b and bulkhead 28 omitted to more clearly show the root end 38 of each shear web 30. Each of the shear webs 30 in this example comprises an access hole 66 to provide personnel access between the plurality of cavities 64. The access holes 66 are provided near the root end 38 of the shear web 30 to provide convenient access to each of the cavities 64 from the access hole 46 in the bulkhead 28.

Further, the root end 38 of the shear web 30 experiences lower stresses in use than portions of the shear web 30 further along the spanwise length of the blade 10. As such, providing access holes 66 in the shear webs 30 near their respective root ends 38 minimises any impact such holes 66 could have on the structural performance of the shear web 30. The access holes 66 in this example are arranged at a mid-height of the shear web 30, wherein the height direction ( h ) of the shear web 30 is substantially perpendicular to the spanwise (S) and chordwise (C) directions of the blade 10. In other examples the access holes 66 may be arranged nearer to the inner surface 36 of one of the half shells 22, i.e. nearer a top 68 or bottom 70 of the shear web 30 in the orientation of the blade 10 shown in Figure 4.

Providing access holes 66 in the shear webs 30 facilitates personnel access to each of the cavities 64 whilst minimising the number of access holes 46 needed in the bulkhead 28. Access is therefore provided to each of the cavities 64a, 64b, 64c in the blade interior 26 without compromising the strength of the bulkhead 28. Further, a relatively large access hole 46 can be provided in the bulkhead 28 because the structure of the bulkhead is not weakened by numerous access holes provided therein.

Figure 5 is a schematic perspective view of the root portion 32 of the blade 10 in a further example wherein each of the shear webs 30 comprises two access holes 66. The access holes 66 of each shear web 30 in this example are mutually offset in the height direction (h) of the web 30. One access hole 66a in each shear web 30 is therefore arranged closer to the leeward side 24a of the blade 10, and the other access hole 66b is arranged closer to the windward side 24b of the blade 10.

The height direction (h) offset in the arrangement of the access holes 66 ensures that personnel can access each of the cavities 64 safely irrespective of the orientation of the blade 10. In the orientation of the blade 10 shown in Figure 5, personnel may safely access the leading and trailing edge cavities 64a, 64c from the central cavity 64b via the access holes 66a arranged at the bottom 70 of each shear web 30, i.e. nearest the leeward half shell 22a.

In this example the access holes 66 are also offset in a longitudinal direction (L) of the shear web 30. The longitudinal direction (L) of the shear web 30 is substantially parallel to the spanwise direction (S) of the blade 10. One of the access holes 66 in each shear web 30 is therefore arranged nearer to the root end 38 of the shear web 30 than the other. Such an arrangement ensures that the material removed from the shear web 30 to form the access holes 66 is spread over two or more longitudinal portions of the shear web 30. The shear web 30 therefore comprises enough material at each longitudinal position along the length of the shear web 30 to take up and transfer the shear loads experienced by the blade 10 in use. In this example, the access holes 66 in each of the shear webs 30 are also offset from the corresponding access holes 66 in the other shear web. This ensures that there is at least one full height shear web 30 at each longitudinal position along the blade 10.

Providing access holes 66 in a shear web 30 which are offset in both the longitudinal (L) and height ( h ) directions of the shear web 30 therefore facilitates safe and convenient access to each of the cavities 64 of the interior 26 of the blade 10, without adversely affecting the load-bearing capacity of the shear web 30.

Many modifications may be made to the examples described above without departing from the scope of the present invention as defined in the accompanying claims.

Whilst the blade 10 in the examples described herein comprises two shear webs 30 arranged in the blade interior 26, in other examples the blade 10 may comprise any number of shear webs 30. Connecting the or each shear web 30 to the bulkhead 28 results in the same structural advantages as previously described with reference to examples having two shear webs 30. The access hole 46 in the bulkhead 28 in an example where a blade 10 comprises a single shear web 30 may be provided in an off-centre portion of the bulkhead 28 such that access to the blade interior 26 is not blocked by the shear web 30. In some examples the bulkhead 28 may comprise a plurality of access holes 46. The access holes 46 may provide direct access to the various cavities 64 in the blade interior 26 without requiring access through one or more of the shear webs 30. Alternatively or additionally, an access hole 46 may be provided near to each of the windward and leeward sides 24a, 24b of the blade 10 to facilitate safe access to the blade interior 26 in different blade orientations.

Whilst the bulkhead 28 described herein with reference to Figures 1 to 5 is a single composite component, in other examples, the bulkhead 28 may be formed of a plurality of bulkhead sections. Such bulkhead sections may be bonded together in the blade shell 20. In some examples, the or each shear web 30 may be connected to a bulkhead section prior to the bulkhead sections being connected together to form the bulkhead 28.

It will be appreciated that whilst the shear webs 30 are rigidly connected directly to the bulkhead 28 in the examples described above, in some examples the shear webs 30 may be bonded to the bulkhead 28 via a spacer or other component between the shear web and bulkhead. In such an example, a rigid bond between the bulkhead 28, an intermediate component and the shear web 30 serves to rigidly fix the shear web 30 to the bulkhead 28 such that the structural advantages discussed herein apply equally. In some examples, the shear web mounting flange 60 and/or the bulkhead flange 52 may be substantially L-shaped in cross section. Alternatively, the shear web mounting flange 60 and/or the bulkhead flange 52 may comprise two L-shaped flanges arranged to form a substantially T-shaped flange. It will be appreciated that features described in relation to each of the examples above may be readily combined with features described with reference to other examples without departing from the scope of the invention as defined by the following claims.