Improvements relating to modular wind turbine blades

Abstract

According to the invention, a method of assembling a modular wind turbine blade is provided, the modular wind turbine blade comprising a first blade module and a second blade module, the first blade module and the second blade module being connectable together at an interface to form at least a portion of the modular wind turbine blade. The method includes the steps of providing a first blade module and a second blade module. Each blade module includes a housing defining an outer surface of the blade module, a connection region of the housing defining an interface end of the blade module, and a longitudinally extending spar cap embedded in the housing. The spar cap has a tapered end in the connection region in which a thickness of the spar cap decreases toward the interface end of the blade module, thereby defining a tapered recess in the outer surface of the blade module. The method also includes arranging the first blade module and the second blade module end-to-end with the tapered recesses aligned to define a bridge recess. The tapered recess of the first blade module defines a first end of the bridge recess, and the tapered recess of the second blade module defines a second end of the bridge recess. The method further includes arranging a layer stack in the bridge recess and across the interface between the first blade module and the second blade module. The layer stack includes a plurality of pre-cured layers interleaved with a prepreg intermediate layer. The prepreg intermediate layer includes a fibrous material pre-impregnated with an uncured resin. The method further includes the step of applying heat to the stack of layers in the bridge recess such that the resin in the prepreg intermediate layer moves in the bridge recess. The method further includes the step of curing the resin to integrate the pre-cured layers with one another to form a spar bridge across the interface, the spar bridge for connecting the spar caps of the first and second blade modules.

Description

Technical Field

[0001] The present invention relates generally to modular wind turbine blades and, more particularly, to a method of assembling a modular wind turbine blade. Background Art

[0002] There is a continuing desire to generate higher levels of electricity from both onshore and offshore wind farms. One way to achieve this is to provide modern wind turbines with larger wind turbine blades to increase the swept area of ​​the rotor so that the wind turbine captures more energy from the wind. Wind turbine blades can be designed as modular assemblies formed from two or more blade modules to facilitate transportation of the components. The blade modules can then be connected together at the wind farm site to form the blade.

[0003] Modern wind turbine blades typically include a reinforced spar structure that provides structural support for the outer shell of the blade. The spar structure typically includes longitudinally extending spar caps that absorb the bending loads experienced by the blade in use. The spar caps of adjacent blade modules can be connected to transfer loads across the interface between the blade modules. In some examples, a modular wind turbine blade may include a connecting element (such as a spar bridge) to connect the spar cap of one blade module to the corresponding spar cap of an adjacent blade module.

[0004] The spar bridge may be a separate spar component that is configured to be connected between corresponding spar caps of adjacent blade modules. However, connecting the spar caps using the spar bridge may present a number of challenges. For example, it may be difficult to achieve a consistent bond gap thickness between the abutting surfaces of the spar caps and the spar bridge due to manufacturing tolerances of these components. In addition, because modular wind turbine blades are typically assembled at or near the wind turbine site, field assembly constraints may also complicate the alignment of the spar caps and the spar bridge. An inaccurate or inconsistent connection between the spar caps and the spar bridge may result in stress concentrations when the modular wind turbine blades are loaded in service.

[0005] It is in this context that the present invention has been developed. Summary of the invention

[0006] According to the present invention, there is provided a method of assembling a modular wind turbine blade, the modular wind turbine blade comprising a first blade module and a second blade module, the first blade module and the second blade module being connectable together at an interface to form at least a portion of the modular wind turbine blade. The method comprises the following steps: providing a first blade module and a second blade module. Each blade module comprises a shell defining an outer surface of the blade module, a connection region of the shell defining an interface end of the blade module, and a longitudinally extending spar cap embedded in the shell. The spar cap has a tapered end in the connection region, in which the thickness of the spar cap decreases toward the interface end of the blade module, thereby defining a tapered recess in the outer surface of the blade module. The method further comprises the following steps: arranging the first blade module and the second blade module end-to-end with the tapered recesses aligned to define a bridge recess. The tapered recess of the first blade module defines a first end of the bridge recess, and the tapered recess of the second blade module defines a second end of the bridge recess. The method further comprises the steps of arranging a layer stack in the bridge recess and across the interface between the first blade module and the second blade module. The layer stack comprises a plurality of precured layers interlaced with prepreg interlayers. The prepreg interlayers comprise fiber materials pre-impregnated with uncured resin. The method further comprises the steps of applying heat to the layer stack in the bridge recess so that the resin in the prepreg interlayers moves in the bridge recess. The method further comprises the steps of curing the resin to integrate the precured layers with each other, thereby forming a spar bridge across the interface, the spar bridge being used to connect the spar caps of the first blade module and the second blade module.

[0007] The pre-cured layer preferably comprises reinforcing fibers fixed in a cured polymer resin matrix. For example, the pre-cured layer may comprise a carbon fiber reinforced polymer (CFRP). In a preferred example, the pre-cured layer is a pultrusion, such as a CFRP pultrusion. The use of pultrusion is advantageous because the pultrusion process enables precise control of the fiber orientation in the pre-cured layer. Thus, the pultrusion may comprise highly uniformly arranged longitudinally extending reinforcing fibers, which increases the strength of the spar bridge.

[0008] The prepreg intermediate layer includes a fiber material pre-impregnated with an uncured resin before being arranged between the precured layers. In some examples, the prepreg intermediate layer may include fibers in the form of woven fibers, unidirectional fibers, biaxial fibers, multiaxial fibers, or chopped strands. The uncured resin includes various individual polymer chains that are not bonded together, i.e., not cross-linked. Therefore, the step of curing the resin to integrate the precured layers with each other includes the following steps: cross-linking the polymer chains in the resin. Cross-linking the polymer chains can occur at ambient temperature, or in some examples, heat can be applied to the layer stack in the bridge recess to promote cross-linking of the polymer chains, thereby curing the resin.

[0009] The stack of layers arranged in the bridge recess preferably includes prepreg interlayers interleaved between each pair of adjacent precured layers. This helps to ensure that resin is provided between each pair of adjacent layers, i.e. resin in the prepreg interlayers. This in turn helps to ensure that all precured layers in the stack are fully bonded together, minimizing voids and / or dry spots between precured layers, thereby minimizing stress concentrations in the spar bridge when it transfers loads between the spar caps of the first blade module and the second blade module in use.

[0010] Providing the spar bridge as a stack of precured layers interleaved with prepreg interlayers means that the layer stack has a certain flexibility in the bridge recess before the resin in the prepreg interlayer is cured. In other words, the precured layers, or at least the ends of the precured layers, can move relative to each other in the bridge recess. The initial flexibility of the uncured spar bridge in the bridge recess means that the layers in the stack can conform to the contours of the recesses of the first blade module and the second blade module. This flexibility of the uncured spar bridge and the relative movement facility between the ends of the precured layers means that the geometry of the spar bridge adapts to the tapered ends of the spar caps and mitigates any misalignment or inaccuracies in the connection between the spar caps and the spar bridge.

[0011] In some examples, the step of applying heat to the layer stack in the bridge recess may include the step of heating the layer stack to at least 60° C., preferably at least 70° C., and more preferably at least 80° C. Heating the layer stack to at least 60° C. initially reduces the viscosity of the resin in the prepreg intermediate layer, allowing the resin to fully penetrate the entire bridge recess. In addition, heating the layer stack to the above temperature can promote cross-linking of polymer chains in the resin to accelerate the curing process, thereby reducing the overall time required to assemble the modular wind turbine blade on site.

[0012] In some examples, the step of applying heat to the layer stack in the bridge recess may comprise the step of arranging a heating device, such as a heating blanket, in the connection area. Thus, the layer stack may be heated from the outside of the modular blade. Using a heating device may facilitate targeted application of heat to the bridge recess. Thus, when forming a spar bridge, using a heating device may help avoid overheating of adjacent parts of the skin.

[0013] In some examples, prior to the step of curing the resin, the method may further include the step of arranging a vacuum film on the layer stack in the bridge recess to define a sealing area containing the layer stack. The method may further include the step of evacuating the sealing area under vacuum pressure to consolidate the layer stack in the bridge recess so that the layer stack conforms to the contours of the recesses of the first blade module and the second blade module. Consolidating the layer stack in the bridge recess under vacuum pressure applies additional force to the layer stack, pressing the stacked layers into the bridge recess to further ensure that the pre-cured layers are accurately aligned in the bridge recess.

[0014] The tapered end of each spar cap preferably defines a mitered surface, which is configured to connect to the spar bridge. Evacuating the sealing area under vacuum pressure to consolidate the layer stack in the bridge recess preferably causes the layer stack to conform to the mitered surface of the spar cap. Therefore, consolidating the layer stack in the bridge recess can help ensure that the pre-cured layers in the layer stack are in contact with the mitered surfaces of the spar caps, i.e., directly or indirectly. In particular, consolidating the layer stack in the bridge recess helps to minimize the gaps or voids between the pre-cured layers in the stack and the spar caps of the first blade module and the second blade module. This helps to provide a continuous load path between the spar caps of the first blade module and the second blade module so that loads are transferred between the spar caps via the spar bridge in use.

[0015] Each pre-cured layer preferably comprises a single pre-cured component, such as a single pre-cured pultrusion. Thus, each pre-cured layer in the stack preferably comprises a single component extending between the spar caps of the first blade module and the second blade module. This configuration further helps to provide a continuous load path for transferring loads between the spar caps of the first blade module and the second blade module in use.

[0016] In some examples, the step of arranging the layer stack may include the steps of: continuously arranging longer pre-cured layers in the bridge recess to form a spar bridge, the spar bridge having a first end with a tapered thickness and a second end with a tapered thickness. For example, the method may include the steps of: continuously arranging longer pultrusions in the bridge recess. The tapered end of the spar bridge preferably defines a mitered surface that is configured to connect to the mitered surfaces of the spar caps of the first blade module and the second blade module. For example, the taper of the first end of the layer stack preferably matches the taper of the tapered end of the spar cap of the first blade module, and the taper of the second end of the layer stack preferably matches the taper of the tapered end of the spar cap of the second blade module. This configuration helps minimize the variation in the bond gap thickness between the mitered surfaces of the spar caps and the corresponding mitered surfaces of the spar bridge.

[0017] In preferred examples, at least some of the prepreg interlayers may extend longitudinally beyond the ends of their adjacent precured layers. Arranging the prepreg interlayers to extend beyond the ends of their adjacent precured layers helps to ensure that the prepreg interlayer material, particularly the resin in the prepreg, is provided between the ends of the adjacent precured layers to ensure that these ends are fully bonded together when the resin cures. Furthermore, in some examples, the prepreg interlayer extending beyond the ends of its adjacent precured layers may help to bond the precured layers to the corresponding tapered ends of the spar caps.

[0018] The spar caps of the first blade module and the second blade module may comprise an electrically conductive material. In these examples, the prepreg interlayer preferably comprises an electrically conductive material. The layer stack is preferably arranged in the bridge recess and the prepreg interlayer is in electrical contact with at least one of the spar caps. Thus, for example, in the event of a lightning strike on the blade, the electrically conductive prepreg interlayer may help conduct current between the spar caps of the first blade module and the second blade module, i.e. across the interface between the blade modules. Thus, the electrically conductive prepreg interlayer may reduce the risk of arcing or flashover between the electrically conductive spar caps by providing a safe path for conducting the current. The "electrical contact" may be achieved via direct contact or indirect electrical contact between the prepreg interlayer and the spar cap, i.e. the prepreg interlayer may be in electrical contact with the spar cap via another electrically conductive material.

[0019] In some examples, the pre-cured layers may also include an electrically conductive material. In such examples, arranging an electrically conductive prepreg interlayer as described above may also help to minimize the risk of arcing or flashover between the spar caps and the pre-cured layers.

[0020] In a preferred example, at least some of the prepreg intermediate layers have a width greater than the width of their adjacent precured layers. This configuration helps to ensure that the resin is provided across the entire width of the precured layers to ensure that the precured layers are fully bonded to their respective adjacent precured layers when the resin cures. Therefore, the risk of dry spots or gaps between adjacent precured layers is minimized.

[0021] The prepreg interlayer preferably includes excess resin. Thus, the prepreg interlayer preferably includes more resin than is required to integrate the precured layers to one another to form the spar bridge. Firstly, the excess resin helps to ensure that sufficient resin is provided to integrate the precured layers to one another. However, more particularly, the excess resin may help to fill any empty spaces throughout the bridge recess. For example, when heat is applied to the layer stack, causing the resin in the prepreg interlayer to migrate in the bridge recess, the excess resin may permeate throughout the bridge recess, including locations where no prepreg material is arranged. Thus, the excess resin may help to provide a continuous load path through the spar bridge by minimizing voids in the spar bridge, thereby minimizing the risk of stress concentrations forming in the spar bridge during use.

[0022] In a preferred example, the prepreg intermediate layer may comprise a fiber volume fraction (FVF) of 30% to 70%, preferably 45% to 55%, for example 50%. FVF is the volume ratio of fiber to resin in a material.

[0023] In some examples, curing the resin may integrate the precured layers with the tapered ends of the spar caps. In other words, the resin in the prepreg interlayer may bond the precured layers of the spar bridge to the tapered ends of the spar caps of the first blade module and the second blade module. In these examples, providing the prepreg interlayer including excess resin may be particularly advantageous because the excess resin may be used to integrate the precured layers with the tapered ends of the spar caps. Thus, this configuration may advantageously reduce the number of process steps involved in assembling a modular wind turbine blade.

[0024] In some examples, the method may include the step of arranging prepreg fiber material in the recesses of the first and second blade modules prior to arranging the layer stack in the bridge recesses. In these examples, the precured layers forming the spar bridge may be integrated, i.e. bonded, with the tapered ends of the spar caps by the resin in the prepreg fiber material arranged in the recesses. Thus, the step of curing the resin may involve curing both the resin in the prepreg intermediate layer and the resin in the prepreg fiber material.

[0025] Prepreg fiber material is fiber material pre-impregnated with uncured resin before being arranged in the recesses of the first and second blade modules. In some examples, the prepreg fiber material may include woven fibers, unidirectional fibers, biaxial fibers, multiaxial fibers, or fibers in the form of chopped strand mats.

[0026] Arranging the prepreg fiber material in the recesses of the first blade module and the second blade module, i.e., between the mitered surface of the spar cap and the corresponding surface of the spar bridge, is particularly advantageous for forming a strong connection between the spar bridge and the spar cap. For example, when the precured layers of the spar bridge are arranged in a stack in the bridge recess, manufacturing and assembly tolerances may cause slight misalignment between the mitered surface of the spar cap and the precured layers of the spar bridge. Therefore, the thickness of the bonding gap defined between the corresponding ends of the spar cap and the spar bridge can vary. Arranging the prepreg fiber material between the spar cap and the spar bridge advantageously mitigates the potential risks associated with varying bonding gap thickness. For example, when the spar bridge is connected to the spar cap, the prepreg fiber material advantageously provides a cushioning effect. The prepreg fiber material includes a fiber material and an uncured resin, and is therefore configured to conform to the contour of the surface between which the prepreg fiber material is arranged. The prepreg fiber material mitigates the variation of the surface, i.e., smoothing misalignment and slight surface defects, by filling any recesses or discontinuities in the surface.

[0027] Furthermore, providing the prepreg fiber material between the spar cap and the spar bridge may ensure that the resin is provided throughout the bond gap so that there are no dry spots or gaps between the spar cap and the spar bridge. Heating the layer stack in the bridge recess may further involve heating the prepreg fiber material arranged in the recesses of the first blade module and the second blade module. When heated, the viscosity of the resin in the prepreg fiber material may initially decrease, causing the resin to move throughout the bond gap to fill any variations or discontinuities on the abutting surfaces of the spar cap and the spar bridge.

[0028] In the example where the prepreg fiber material is arranged in the recesses of the first blade module and the second blade module, such prepreg fiber material preferably comprises an electrically conductive material. For example, the prepreg fiber material may comprise carbon fibers. Thus, the prepreg fiber material arranged between the spar cap and the spar bridge may facilitate electrical conduction between the spar cap and the spar bridge. In the event of a lightning strike, the electrically conductive fiber material in the recesses advantageously ensures continuous electrical conduction between the spar cap and the spar bridge, thereby avoiding arcs or "flashovers" that may damage the outer shell of the blade module.

[0029] In the example where the prepreg fiber material is arranged in the recesses of the first and second blade modules, i.e. between the spar caps and the spar bridges, the prepreg intermediate layers and / or precured layers of the spar bridges may be in indirect electrical contact with the spar caps via the prepreg fiber material in the recesses.

[0030] In a preferred example, the method may include the following steps: before arranging the layer stack in the bridge recess, arranging the layer stack of prepreg fiber material in the recess of the first blade module and the second blade module. In some examples, each prepreg fiber material layer arranged in the recess, that is, the prepreg fiber material layer arranged on the miter surface defined by the tapered end of the spar cap may include a woven fiber layer, a unidirectional fiber layer, a biaxial fiber layer, a multiaxial fiber layer or a fiber layer in the form of chopped strands. In some examples, the prepreg fiber material may include a plurality of different prepreg fiber material layers, that is, in some examples, these prepreg fiber material layers may include different fiber materials. Multiple prepreg fiber material layers can more closely conform to the contour of the butt surface (i.e., the miter surface) of the spar cap and the spar bridge, thereby providing a better cushioning effect.

[0031] The prepreg fiber material includes a fiber material pre-impregnated with a resin. The fiber material may be pre-impregnated with a toughening resin, such as Gurit's SE75. The use of a toughening resin (compared to a non-toughening resin) may increase the bonding strength of the prepreg fiber material to the precured layers of the spar caps and spar bridges, thereby providing a stronger bond between the spar caps and spar bridges.

[0032] In some examples, the method may include the step of arranging a plurality of side-by-side layer stacks in the bridge recess to form the spar bridge. For example, the method may include the step of arranging two or three side-by-side layer stacks in the bridge recess to form the spar bridge. Forming the spar bridge with a plurality of side-by-side layer stacks may increase the flexibility of the spar bridge, and may therefore allow the spar bridge, i.e., the precured layers and prepreg intermediate layers, to better conform to the recesses of the first blade module and the second blade module.

[0033] In some examples, the step of arranging the first blade module and the second blade module end-to-end may include the following steps: spacing the first blade module and the second blade module in the longitudinal direction. As the first blade module and the second blade module are spaced apart in the longitudinal direction, the length of the spar bridge may increase. A longer spar bridge may include longer pre-cured layers that are softer and therefore easier to twist and bend when arranged in the recesses of the first blade module and the second blade module. Therefore, spacing the blade modules apart in the longitudinal direction may promote greater tolerance for misalignment or geometric deviations between the recesses of the first blade module and the second blade module.

[0034] In an example where the first blade module and the second blade module are spaced apart in the longitudinal direction, the method may further comprise the steps of providing an open-ended U-shaped channel and aligning the U-shaped channel with the recesses of the first blade module and the second blade module. In such an example, the bridge recess may thus be defined by the recesses of the first blade module and the second blade module and the U-shaped channel. Thus, the U-shaped channel preferably spans the interface between the first blade module and the second blade module, and the step of arranging the layer stack in the bridge recess preferably comprises the steps of arranging the layer stack in the U-shaped channel.

[0035] The U-shaped channel can be configured to enhance the connection between the first blade module and the second blade module. In some examples, the U-shaped channel can provide an additional load path for transferring loads between blade modules during use. For example, the U-shaped channel can be formed by a composite material such as a fiber reinforced polymer. The U-shaped channel can include one or more layers of multiaxial fiber reinforced materials, such as biaxial or triaxial fiber reinforced materials. The U-shaped channel can include one or more layers of fiber reinforced materials, and the fiber reinforced materials include unidirectional reinforced fibers. The unidirectional reinforced fibers preferably extend in the longitudinal direction. The U-shaped channel can include glass fiber reinforced plastic (GFRP). The U-shaped channel can include carbon reinforced fibers.

[0036] In some examples, the method may further include the step of sealing the U-shaped channel to the first blade module and the second blade module, i.e., to the spar caps and / or shells of the first blade module and the second blade module. The method may further include the step of sealing the vacuum membrane to the U-shaped channel such that the sealing area is defined between the vacuum membrane, the recesses of the first blade module and the second blade module, and the U-shaped channel. In examples where the first blade module and the second blade module are spaced apart in the longitudinal direction, this configuration may advantageously facilitate consolidation of the layer stack in the bridge recess under vacuum pressure.

[0037] In some examples, the layer stack may be preassembled prior to arranging the layer stack in the bridge recess. Preassembling the layer stack "offline" (i.e., separately from the first blade module and the second blade module) may facilitate faster on-site assembly of a modular wind turbine blade. For example, when assembling a modular wind turbine blade, the preassembled layer stack may be arranged in the bridge recess in a single assembly step. Preassembling the layer stack may also enable greater control and precision in the assembly of the layer stack without on-site assembly constraints.

[0038] The step of pre-assembling the layer stack may include the following steps: providing a plurality of pre-cured layers and at least one pre-preg interlayer, and assembling the pre-cured layers and the pre-preg interlayer into a stack of the pre-cured layers and the pre-preg interlayers interlaced. In such an example, the method may also include the following steps: heating the stack to a certain temperature to increase the viscosity of the resin in the pre-preg interlayer, thereby temporarily bonding the pre-cured layers together in the stack.

[0039] The tack of a prepreg interlayer refers to the intrinsic tack of the prepreg interlayer and can be viewed as a measure of the mechanical force required to separate the interlayer from an adjacent precured layer, and vice versa. Heating the stack to a low temperature can reduce the viscosity of the resin in the prepreg interlayer, causing at least some of the resin to migrate between the precured layers. Thus, heating the stack can increase the wettability of the precured layers adjacent to the respective prepreg interlayers. This in turn can increase the adhesion of the interlayer to the precured layers to temporarily bond these layers together in the stack.

[0040] In these examples, the preassembled stack is preferably heated to a low temperature, such as 20°C to 30°C, so that at least some of the resin in the prepreg interlayer migrates between the precured layers. It is worth noting that heating the layer stack to a low temperature preferably causes some of the resin to migrate between the precured layers, but does not cause the polymer chains in the resin in the prepreg interlayer to crosslink, thereby keeping the resin in an uncured viscous state. Therefore, the step of heating the layer stack when preassembling the layer stack includes the following steps: heating the layer stack to a temperature below the curing temperature of the resin in the prepreg interlayer.

[0041] In a preferred example, the prepreg interlayer may be precooled before being arranged between the precured layers in the stack. For example, when the layer stack is preassembled, the prepreg interlayer may be provided as a precooled prepreg interlayer. Therefore, the initial temperature of the prepreg interlayer in the stack may be lower than the precured layer. Precooling the prepreg interlayer helps to ensure that the resin in the prepreg interlayer has a high viscosity and therefore does not move or flow relative to the fiber material in the prepreg interlayer before being arranged in the stack. Precooling the prepreg interlayer reduces the viscosity of the prepreg interlayer, thereby improving the handling of the interlayer. The step of applying heat to the layer stack when the layer stack is preassembled may include the following steps: heating the precooled prepreg interlayer from below ambient temperature to ambient temperature. For example, the prepreg interlayer may be precooled to a temperature between -10°C and 10°C, and applying heat to the layer stack may involve heating the layer stack to ambient temperature, such as between 20°C and 30°C.

[0042] In some other examples, the step of preassembling the layer stack may include the following steps: assembling precured layers interleaved with prepreg interlayers into a stack, and fixing the adjacent precured layers together by providing an adhesive between adjacent precured layers and curing the adhesive. The adhesive provided between adjacent precured layers is preferably an ambient curing adhesive and / or an adhesive having a lower curing temperature than the resin in the prepreg interlayer and / or an adhesive having a shorter curing time than the resin in the prepreg interlayer. Therefore, the adhesive provided between the precured layers is preferably cured to fix the adjacent precured layers together, while the resin in the prepreg interlayer remains uncured until after the preassembled stack is arranged in the bridge recess.

[0043] In examples where adhesive is provided between adjacent precured layers when preassembling the layer stack, such adhesive is preferably provided in a central region of the stack. Thus, the adhesive preferably secures the central portions of adjacent precured layers together. In preferred examples, the ends of adjacent precured layers are not secured together with adhesive and may simply be constrained by the viscosity of the prepreg interlayer. Thus, the ends of the precured layers may move relative to each other, providing a degree of flexibility to the stack such that the ends of the stack may still conform to the recesses of the first blade module and the second blade module when arranged in the bridge recess.

[0044] In some other examples, the step of preassembling the layer stack may include the steps of assembling the precured layers interleaved with the prepreg interlayer into a stack, and tying the layers in the stack together. For example, one or more fiber materials (such as prepreg fiber materials) may be used to tie the layers together.

[0045] In some examples, the step of preassembling the layer stack may include the following steps: arranging a vacuum film on the stacked layers to form a sealing area. The sealing area can be evacuated under vacuum pressure to consolidate the layers in the stack. The vacuum pressure can compress the layer stack in the sealing area. Compressing the uncured prepreg interlayer between the precured layers may cause the interlayer to temporarily bond the precured layers together. In some examples, the layer stack in the sealed volume can be heated while the layer stack is consolidated under vacuum pressure. As previously described, heating the layer stack can increase the viscosity of the resin in the prepreg interlayer, thereby temporarily bonding the precured layers together in the stack. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Examples of the present invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which:

[0047] Figure 1is a schematic exploded view of a modular wind turbine blade having a first blade module and a second blade module connected together at an interface via a spar bridge;

[0048] Figure 2 is a schematic cross-sectional view of a spar bridge connecting spar caps of a first blade module and a second blade module;

[0049] Figure 3 is a schematic cross-sectional view of a spar bridge connecting spar caps of a first blade module and a second blade module, wherein the blade comprises a prepreg fiber material arranged between the spar caps and the spar bridge;

[0050] Figure 4 is a schematic diagram of a stage in a method of pre-assembling a stack of layers forming a spar bridge; and

[0051] Figure 5 is a schematic diagram of stages in another method of preassembling a stack of layers that form a spar bridge. DETAILED DESCRIPTION

[0052] As described above by way of background, assembling a wind turbine blade from a plurality of blade modules may facilitate providing larger wind turbine blades while still being able to transport the large blade components to the wind turbine site. Figure 1 The schematic exploded view of shows an example of a modular wind turbine blade 10 , which comprises a first blade module 12 a and a second blade module 12 b which can be connected together at an interface 14 to form at least a portion of the modular wind turbine blade 10 .

[0053] The first blade module 12a and the second blade module 12b each include an outer shell 16a, 16b that defines an outer surface 18a, 18b of the blade modules 12a, 12b. The blade modules 12a, 12b each include a longitudinally extending spar cap 20a, 20b embedded in their respective outer shells 16a, 16b. The spar caps 20a, 20b may be part of a reinforced spar structure that provides structural support for the outer shells 16a, 16b of each blade module 12a, 12b. For ease of reference, the spar caps 20a of the first blade module 12a may be referred to as first spar caps, and the spar caps 20b of the second blade module 12b may be referred to as second spar caps.

[0054] The outer shell 16a, 16b of each blade module 12a, 12b comprises a connection area 22a, 22b, which defines an interface end 24a, 24b of the blade module. In the connection area 22a of the first blade module 12a, the first spar cap 20a has a tapered end 26a, in which the thickness of the first spar cap 20a decreases towards the interface end 24a of the first blade module 12a. Therefore, the tapered end 26a of the first spar cap 20a defines a tapered recess 28a in the outer surface 18a of the first blade module. For ease of reference, the tapered recess 28a of the first blade module 12a is referred to herein as the first tapered recess.

[0055] Furthermore, in the connection region 22b of the second blade module 12b, the second spar cap 20b has a tapered end 26b. The thickness of the second spar cap 20b decreases towards the interface end 24b of the second blade module 12b, and the tapered end 26b of the second spar cap 20b defines a tapered recess 28b in the outer surface 18b of the second blade module 12b. For ease of reference, the tapered recess 28b of the second blade module 12b is referred to herein as a second tapered recess.

[0056] Still refer to Figure 1 To assemble the modular wind turbine blade 10, the first blade module 12a and the second blade module 12b are arranged end to end with the tapered recesses 28a, 28b aligned. Thus, the aligned first tapered recesses 28a and second tapered recesses 28b define a bridge recess 30 spanning the interface 14 between the blade modules. The first tapered recess 28a defines a first end 32a of the bridge recess 30, and the second tapered recess 28b defines a second end 32b of the bridge recess 30.

[0057] like Figure 1 As shown, in some examples, when the first blade module 12a and the second blade module 12b are arranged so that their respective tapered recesses 28a, 28b are aligned, they can be spaced apart in the longitudinal direction L. In such an example, the U-shaped channel 34 can be arranged to be aligned with the first tapered recess 28a and the second tapered recess 28b. Therefore, the bridge recess can be defined by the tapered recesses 28a, 28b of the first blade module 12a and the second blade module 12b and the U-shaped channel 34.

[0058] In order to connect the first blade module 12a and the second blade module 12b, more specifically, to connect the spar caps 20a, 20b of the first blade module 12a and the second blade module 12b, a layer stack 36 is arranged in the bridge recess 30, spanning the interface 14 between the blade modules 12a, 12b. As will be described in more detail later, the layer stack 36 in the bridge recess 30 forms a spar bridge connecting the spar caps 20a, 20b of the first blade module 12a and the second blade module 12b. Figure 1 The blade modules 12a, 12b shown in FIG. 1 include two spar caps 20a, 20b, respectively, and it should be understood that, according to the description provided herein, each spar cap 20a is connected to the opposing spar cap 20b. Figure 1 For clarity in FIG. 1 , only the first layer stack 36 for connecting the first pair of spar caps 20a, 20b is shown.

[0059] Additional references Figure 2 , which shows a cross-sectional view of a spar bridge 38 in a bridge recess 30, a layer stack 36 includes a plurality of precured layers 40 interlaced with prepreg interlayers 42. The precured layers 40 are cured before being arranged in the layer stack 36, for example, the precured layers 140 may include pultrusion. The prepreg interlayers 42 include a fiber material pre-impregnated with an uncured resin, that is, the fiber material is pre-impregnated with the resin before being arranged in the layer stack 36. Therefore, by arranging the prepreg interlayers 42 between the precured layers 40 in the layer stack 36, resin is provided between the precured layers 40. In a preferred example, the prepreg interlayers 42 include excess resin, for example 50% by weight of resin.

[0060] In some examples, a continuously longer pre-cured layer 40 may be arranged in the bridge recess 30. Figure 2 As shown, in such an example, the continuously longer pre-cured layers 40 can form a spar bridge 38 having a first end 44a and a second end 44b, each of which has a tapered thickness. In use, the tapered ends 44a, 44b of the spar bridge 38 advantageously gradually transfer loads between the spar bridge 38 and the first and second spar caps 20a, 20b. The tapered ends 26a, 26b of the spar caps 20a, 20b can each define a miter surface 46a, 46b, and the tapered ends 44a, 44b of the spar bridge 38 can also define a miter surface 48a, 48b. Therefore, the spar bridge 38 can be connected to each spar cap 20a, 20b via a miter joint formed between the miter surfaces 46a, 48a and 46b, 48b.

[0061] In some examples, the ply stack 36 may be arranged such that the first end 44a of the spar bridge 38 tapers at substantially the same rate as the tapered end 26a of the first spar cap 20a. Additionally, the second end 44b of the spar bridge 38 preferably tapers at substantially the same rate as the tapered end 26b of the second spar cap 20b. This helps reduce thickness variations in the bond gap defined between the tapered end 26 of each spar cap 20 and the spar bridge 38, i.e., between the scarfed surfaces 46, 48 of the spar cap 20 and the spar bridge 38.

[0062] After arranging the layer stack 36 in the bridge recess 30, in some examples, the layers 40, 42 may be consolidated to conform to the contours of the tapered recesses 28a, 28b of the first and second blade modules 12a, 12b (at Figure 1 ). For example, the vacuum membrane 52 may be disposed over the layer stack 36 to define a sealing area containing the layer stack 36, and the sealing area may then be evacuated under vacuum pressure. In examples where the bridge recess 30 is additionally defined by the U-shaped channel 34, the U-shaped channel 34 may also define a portion of the sealing area when the vacuum membrane 52 is disposed over the layer stack 36. Evacuating the sealing area under vacuum pressure compresses the layer stack 36 in the bridge recess 30 to conform to the contour of the tapered recesses 28a, 28b defining the bridge recess 30. Thus, consolidating the layer stack 36 also helps reduce variations in the bond gap thickness between the miter surfaces 46, 48 of the spar cap 20 and the spar bridge 38.

[0063] After the layer stack 36 is arranged in the bridge recess 30, heat may be applied to the layer stack 36. Applying heat to the layer stack 36 means that the resin in the prepreg intermediate layer 42 is heated, which advantageously reduces the viscosity of the resin, allowing the resin to move in the bridge recess 30, i.e., penetrate the entire bridge recess 30. Applying heat to the layer stack 36 preferably includes heating the layer stack 36 to at least 60°C. This helps ensure that the viscosity of the resin is initially reduced to penetrate the entire bridge recess 30. In addition, heating to at least 60°C can accelerate the cross-linking of polymer chains in the resin, thereby reducing the time required to cure the resin.

[0064] After moving in the bridge recess 30, the resin from the prepreg interlayer 42 is cured to integrate the prepreg layers 40 with each other. Curing the resin to integrate the prepreg layers 40 forms a spar bridge 38 across the interface 14 between the first blade module 12a and the second blade module 12b, as shown in FIG. Figure 2 The spar bridge 38 is used to connect the spar caps 20a, 20b of the first blade module 12a and the second blade module 12b to transfer loads between the spar caps in use.

[0065] In some examples, the spar bridge 38 can also be used to electrically connect the first spar cap 20a and the second spar cap 20b. For example, the spar caps 20a, 20b of the first blade module 12a and the second blade module 12b can include a conductive material, such as carbon fiber. Therefore, in the event that the modular wind turbine blade 10 is struck by lightning during use, the spar caps 20a, 20b can conduct electricity from the lightning strike. Advantageously, the spar bridge 38 can be configured to safely conduct electricity between the first spar cap 20a and the second spar cap 20b and avoid flashover, i.e., arcing, between the conductive spar caps.

[0066] For example, the prepreg interlayer 42 may include an electrically conductive material, such as carbon fiber, and the prepreg interlayer 42 may be arranged in the layer stack 36 in electrical contact with at least one of the spar caps 20a, 20b. Electrical contact refers to direct contact between two conductive components, such as the spar cap 20 and the prepreg interlayer 42, as well as indirect electrical contact between the two conductive components via one or more other conductive components arranged therebetween.

[0067] like Figure 2 As shown, at least some of the prepreg interlayers 42 preferably extend longitudinally beyond the ends of their adjacent precured layers 40. This arrangement can promote the above-mentioned electrical contact between the prepreg interlayers 42 and the spar caps 20a, 20b. In addition, this configuration helps ensure that sufficient resin is provided between the ends of the precured layers 40 to fully bond the adjacent precured layers 42 together.

[0068] Figure 3 1 shows a schematic cross-sectional view of a spar bridge 38 in another example of a modular wind turbine blade 10. For example, Figure 3 As shown, in some examples, assembling the modular wind turbine blade 10 may also include placing a prepreg fiber material 54 in the tapered recesses 28a, 28b of the first blade module 12a and the second blade module 12b before placing the layer stack 36 in the bridge recess 30. The prepreg fiber material 54 may provide a cushioning effect between each end 44a, 44b of the spar bridge 38 and the tapered end 26a, 26b of the spar cap 20a, 20b. Therefore, the prepreg fiber material 54 arranged in the tapered recesses 28a, 28b and between the scarfed surfaces 46, 48 of the spar cap 20a, 20b and the spar bridge 38 may help mitigate inconsistencies or variations in bond gap thickness. For example, the prepreg fiber material 54 may be configured to conform to the contours of the tapered recesses 28 a, 28 b and the spar bridge 38 to absorb variations in the scarfed surfaces 46 , 48 and fill any gaps or voids between the spar caps 20 a, 20 b and the spar bridge 38 .

[0069] In a preferred example, the prepreg fiber material 54 arranged in the tapered recesses 28a, 28b may be electrically conductive. In such an example, the prepreg intermediate layer 42 may be arranged to be in indirect electrical contact with the first spar cap 20a and the second spar cap 20b via the prepreg fiber material 54 in the tapered recesses 28a, 28b. Therefore, in such an example, the prepreg intermediate layer 42 is preferably arranged in the layer stack 36 so as to be in contact with the prepreg fiber material 54 in the tapered recesses 28a, 28b.

[0070] like Figure 4 and Figure 5As shown, in some examples, the layer stack 36 may be preassembled before arranging the layer stack 36 in the bridge recess 30. Preassembling the layer stack 36 (i.e., arranging the layer stack "offline") may facilitate faster on-site assembly of the modular wind turbine blade 10 because multiple layers in the layer stack 36 may be arranged in the bridge recess 30 in a single process step. Preassembling the layer stack 36 involves securing adjacent precured layers 40 together in the layer stack 36. An "adjacent precured layer 40" is a precured layer 40 that is closest to another precured layer 40. Therefore, it will be understood that two precured layers 40 interleaved with a prepreg interlayer 42 between the two precured layers 40 may be referred to herein as "adjacent precured layers 40."

[0071] First reference Figure 4 , the layers 40 in the layer stack 36 can be temporarily bonded together by the resin in the prepreg interlayer 42. For example, the precured layers 40 and the prepreg interlayer 42 can be assembled into the layer stack 36, wherein the precured layers 40 are interleaved with the prepreg interlayer 42. Thereafter, the layer stack 36 can be heated to increase the viscosity of the resin in the prepreg interlayer 42. The prepreg interlayer 42 is arranged between the precured layers 40, and thus, the increased viscosity or adhesion of the resin is used to temporarily bond the precured layers 40 together in the layer stack 36.

[0072] In some examples, such as Figure 4 As shown, heating the layer stack 36 may involve localized heating. Thus, localized resin regions in the prepreg interlayer 42 may move between adjacent precured layers 40 to temporarily bond the precured layers 40 together at specific locations.

[0073] Figure 5 Another example of a method for preassembling the layer stack 36 is shown. As shown, in some examples, adjacent precured layers 40 in the layer stack 36 can be fixed together by providing an adhesive 56 between adjacent precured layers 40 and then curing the adhesive 56. If the prepreg intermediate layer 42 extends along the entire length of the layer stack 36, the prepreg intermediate layer 42 is preferably configured to allow the adhesive 56 disposed between the precured layers 40 to penetrate through the prepreg intermediate layer 42. In other examples, the prepreg intermediate layer 42 may be interrupted in the location where the adhesive 56 is disposed.

[0074] Figure 5A preferred example is shown in which an adhesive 56 is disposed in a central region of the layer stack 36 to secure together central portions 58 of adjacent precured layers 40. Securely securing the central portions 58 of the precured layers 40 together advantageously secures the precured layers 40 together while maintaining the flexibility of the layer stack 36 at the first end 44a and the second end 44b. Thus, during assembly of the blade 10, when the layer stack 36 is arranged in the bridge recess 30, the first end 44a and the second end 44b are still able to conform to the contours of the tapered recesses 28a, 28b in the first blade module 12a and the second blade module 12b.

[0075] Although Figure 4 or Figure 5 , but both preassembly methods described may also include: arranging a vacuum film on the preassembled layer stack 36, and evacuating the sealing area defined by the vacuum film to consolidate the preassembled layer stack 36. The vacuum pressure may help compress the layers 40, 42 together. In particular, this may compress the prepreg interlayer 42 between adjacent precured layers 40, which may increase the adhesion of the prepreg interlayer 42 to its adjacent precured layers 40.

[0076] In some examples, the method of assembling the modular wind turbine blade 10 may include arranging a plurality of layer stacks 36 side by side in the bridge recess 30. For example, each layer stack 36 may be as previously described with reference to Figure 4 and Figure 5 In some examples, the layer stack 36 can be arranged side by side and consolidated into a single pre-assembled component, thereby reducing the process steps required to arrange the layer stack 36 in the bridge recess 30 on site.

[0077] It should be understood that the above description is used to illustrate multiple possible examples of the invention. Features associated with any of the examples above can be easily combined with any other features described with reference to a different example without departing from the scope of the invention as defined in the appended claims.

Claims

1. A method of assembling a modular wind turbine blade (10), the modular wind turbine blade (10) comprising a first blade module (12a) and a second blade module (12b), the first blade module (12a) and the second blade module (12b) being connectable together at an interface (14) to form at least a portion of the modular wind turbine blade, the method comprising the following steps: A first blade module (12a) and a second blade module (12b) are provided, each blade module comprising: a shell (16a, 16b) defining an outer surface (18a, 18b) of the blade module; a connection region (22a, 22b) of the shell defining an interface end (24a, 24b) of the blade module; and a longitudinally extending spar cap (20a, 20b) embedded in the shell, the spar cap having a tapered end (26a, 26b) in the connection region, wherein the thickness of the spar cap decreases towards the interface end of the blade module, thereby defining a tapered recess (28a, 28b) in the outer surface of the blade module; Arranging the first blade module (12a) and the second blade module (12b) end-to-end with the tapered recesses (28a, 28b) aligned to define a bridge recess (30), the tapered recess of the first blade module defining a first end (32a) of the bridge recess, and the tapered recess of the second blade module defining a second end (32b) of the bridge recess; Arranging a layer stack (36) in the bridge recess (30) and across the interface (14) between the first blade module (12a) and the second blade module (12b), the layer stack comprising a plurality of pre-cured layers (40) interleaved with pre-preg interlayers (42), wherein the pre-preg interlayers comprise a fiber material pre-impregnated with an uncured resin; applying heat to the layer stack (36) in the bridge recess (30) to cause the resin in the prepreg intermediate layer to move in the bridge recess; and The resin is cured to integrate the pre-cured layers (40) with each other to form a spar bridge (38) across the interface (14), the spar bridge being used to connect the spar cap (20a) of the first blade module (12a) and the spar cap (20b) of the second blade module (12b).

2. The method according to claim 1, wherein: The step of applying heat to the layer stack (36) in the bridge recess (30) comprises the step of heating the layer stack to at least 60°C, preferably at least 70°C, more preferably at least 80°C.

3. The method according to claim 1 or 2, wherein: Prior to curing the resin, the method further comprises the steps of: arranging a vacuum film (52) on the layer stack (36) in the bridge recess to define a sealing area containing the layer stack; and The sealing area is evacuated under vacuum pressure to consolidate the layer stack in the bridge recess so that the layer stack conforms to the contour of the tapered recess (28a) of the first blade module (12a) and the tapered recess (28b) of the second blade module (12b).

4. A method according to any preceding claim, wherein: The step of arranging the layer stack (36) includes the steps of: successively arranging longer pre-cured layers in the bridge recess (30) to form a spar bridge (38) having a first end (44a) with a tapered thickness and a second end (44b) with a tapered thickness.

5. A method according to any preceding claim, wherein: At least some of the prepreg intermediate layers (42) extend longitudinally beyond the ends of their adjacent precured layers (40).

6. A method according to any preceding claim, wherein: The spar caps (20a) of the first blade module and the spar caps (20b) of the second blade module comprise an electrically conductive material, wherein the prepreg intermediate layer (42) comprises an electrically conductive material, and wherein the layer stack (36) is arranged in the bridge recess such that the prepreg intermediate layer is in electrical contact with at least one of the spar caps.

7. A method according to any preceding claim, wherein: At least some of the prepreg interlayers (42) have a width greater than that of their adjacent precured layers (40).

8. A method according to any preceding claim, wherein: The prepreg intermediate layer (42) comprises a fiber volume fraction (FVF) of 30% to 70%, preferably 45% to 55%, for example 50%.

9. The method according to any preceding claim, further comprising the steps of: A prepreg fibre material (54), preferably a ply stack of prepreg fibre material, is arranged in the tapered recess (28a) of the first blade module and the tapered recess (28b) of the second blade module before arranging the ply stack in the bridge recess.

10. The method according to any preceding claim, further comprising the steps of: A plurality of side-by-side layer stacks (36) are arranged in the bridge recess (30) to form the spar bridge.

11. A method according to any preceding claim, wherein: The step of arranging the first blade module (12a) and the second blade module (12b) end to end comprises the step of spacing the first blade module and the second blade module in a longitudinal direction, and wherein the method further comprises the step of: A U-shaped channel (34) with an open end is provided and aligned with the tapered recess (28a) of the first blade module and the tapered recess (28b) of the second blade module so that the bridge recess (30) is defined by the tapered recess of the first blade module, the tapered recess of the second blade module and the U-shaped channel.

12. A method according to any preceding claim, wherein: The layer stack (36) is preassembled before being arranged in the bridge recess.

13. The method according to claim 12, wherein: The step of pre-assembling the layer stack (36) comprises the following steps: Providing a plurality of precured layers (40) and at least one prepreg intermediate layer (42); Assembling the precured layers and the prepreg interlayers into a stack of the precured layers and the prepreg interlayers interleaved with each other; and The stack is heated to a temperature to increase the viscosity of the resin in the prepreg intermediate layer, thereby temporarily bonding the precured layers together in the stack.

14. The method according to claim 12, wherein: The step of pre-assembling the layer stack (36) comprises the following steps: assembling a stack of precured layers (40) interleaved with prepreg interlayers (42); and The adjacent pre-cured layers are secured together by providing an adhesive (56) between the adjacent pre-cured layers and curing the adhesive.

15. The method according to claim 14, wherein: The adhesive (56) is disposed in a central region of the layer stack (36) to secure central portions of adjacent pre-cured layers (40) together.

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