WO2016189092A1

WO2016189092A1 - A wind turbine blade and method of assembling a wind turbine blade

Info

Publication number: WO2016189092A1
Application number: PCT/EP2016/061920
Authority: WO
Inventors: Paul Trevor Hayden; Peter Anthony Broome
Original assignee: Blade Dynamics Limited
Priority date: 2015-05-28
Filing date: 2016-05-26
Publication date: 2016-12-01
Also published as: GB201509155D0

Abstract

The present invention relates to a wind turbine blade comprising first and second sections (1,2) arranged along the length of the blade. Each section (1,2) comprises an aerodynamic fairing (4) with inner and outer surfaces. The fairing (4) extends across the windward and leeward sides of the blade, and a spar extends between the windward and leeward sides. The spar comprises a shear web (6) with a spar cap (7) at either end positioned between the shear web 6 and the inner surface of the fairing (4). The first and second sections (1,2) meet one another at a joint region, wherein, in the vicinity of the joint region, each section has two recesses in the outer surface of the aerodynamic fairing (4). A first recess is above and a second one below the spar such that in the vicinity of each recess the depth of the spar caps (7) is reduced. The first recesses in the respective segments (1,2) is arranged to align with one another and the second recesses in the respective segments are arranged to align with one another when the first and second sections (1,2) are aligned. A first spar cap bridge (22) is moulded onto the outer surface of the fairing (4) in the first pair of aligned recesses and a second spar cap bridge (22) is moulded onto the outer surface of the fairing (4) in the second pair of aligned recesses.

Description

A WIND TURBINE BLADE AND METHOD OF ASSEMBLING

A WIND TURBINE BLADE

The present invention relates to a wind turbine blade and method of assembling a wind turbine blade. In particular, the invention is concerned with a way of joining together adjacent blade sections in such a blade.

In recent years the demand for longer wind turbine blades has increased significantly. This is because the power available from a wind turbine blade increases with the square of the radius of the blade. Thus, increasing the radius of the blade produces an increase in power output which is disproportionate to the cost of turbine itself and can contribute to a lower cost of energy.

One problem with increasing blade length is the difficulty in transporting the blades to the turbine sites which are often in remote and inaccessible locations.

One way of addressing this is to make the blades in a number of sections and join them together at or close to the site of the finished turbine.

There are a number of considerations which must be met by the joint between the sections. The joining process must be designed to be easy to carry out so that joints can be reliably made in the remote location. Particularly towards the tip of a longer blade, any parasitic mass in the blade creates undue loads on the remainder of the blade. Therefore, any joint should avoid having features such as flanges and fasteners which increase the parasitic mass.

The joint must ensure a good finish for the aerodynamic surface. Particularly when the joint is towards the tip of a larger blade, it will move at very high velocities. Any disturbance to the surface caused by any misalignment of any components in the joint will result in an unnecessary increase in drag and can, in the worst case, result in blade failure. If the joint is to be made up in the field, this good surface must be achievable without requiring a large amount of work to achieve the desired surface finish.

US 2006/0127222 discloses an arrangement in which, in adjacent segments, recesses are formed in the aerodynamic fairing. A connecting element having a complex shape which extends across the full width of the blade is then glued into place in the complimentary recess. This connecting element and the corresponding recess have a complex shape with a large perimeter. The two blade components and the connecting piece must therefore be made to a very high tolerance in order to avoid misalignment between the components. This is very difficult to achieve in practice particularly if the joint is made local to the wind turbine site and is unlikely to result in a high quality joint. Further, the fairing in the vicinity of the joint is required to be far thicker than it otherwise needs to be in order to accommodate the connecting element. This will also significantly increase the parasitic mass of the joint.

WO 2014/165321 discloses a method of joining blade segments. This provides two scarf portions, one in the lower part of the blade and one in the upper part of the blade. When the two blade segments are brought together, a large window is provided in the fairing to allow the scarf portion for the lower part of the blade to be fixed in place in the inner surface of the lower spar cap. Once this is in place, the window is covered over with various components in order to complete the fairing. This is an awkward process as access to the lower scarf portion is via the window in the fairing and is therefore not straightforward. Further, a large number of components are required to be fitted in place in order to fill the window once the lower scarf portion is in place.

Our own earlier disclosure WO 2012/004571 discloses a double scarf joint between the spar caps of adjacent blade segments. In this disclosure, the connection piece can either be a prefabricated component which is adhered in place in the gap between the spar caps and the fairing, or it can be created in situ from a resin impregnated laminated stack which is cured in situ. The final example in this document discloses a method of creating a spar in a factory environment. This has a jig having a U-shaped cross section in which the two ends of the spar are placed before the spar cap is made up in the jig.

The present invention aims to improve on this design by providing a joint between adjacent blade sections which retains the advantages of WO 2012/004571, but which can readily be created in situ.

According to the present invention there is provided a wind turbine blade according to claim 1.

The present invention has recesses in the aerodynamic fairing above and below the spar which reduce the depth of the spar caps in this area. These effectively provide a mould cavity defined by the fairing into which the spar cap bridge is moulded. This provides a number of advantages. Because a significant portion of the mould cavity is defined by the fairing components themselves, these effectively replace the jig disclosed in WO 2012/004571 meaning that the components can be moulded in situ in the aligned recesses. Because the spar caps are moulded into the outer surface of the fairing, any dimensional tolerances will be readily accommodated by the fluidity of the spar cap in the moulding process. This contrasts with US 2006/0127222 where three pre-formed components are bonded together.

Because the recesses which receive the spar cap bridges are formed in the outer surfaces of the fairing, access to the aligned recesses is straightforward. Further, the window which is essential to WO 2014/165321 is not required in the present invention as the recesses are formed on the outer surfaces of the fairing and access to the inside of the blade is not required.

The parasitic mass of the joint is minimal. The recesses can be created without any increase in the wall thickness of the fairing (although the fairing may have an increased wall thickness if this is required for some other purpose) such that there is no need for the large parasitic mass in US 2006/0127222. In view of the recesses producing a corresponding reduction in the depth of the spar cap which is then filled with the spar cap bridge, there is very little additional mass required beyond that which would be present in the remainder of the blade away from the joint region. The recesses may have a uniform depth. However, preferably, the recesses have a tapering depth which increases towards the joint region.

If the spar cap bridge is built up from a stack of laminates, the tapering surfaces mean that the ends of the laminates in the stack will terminate at different regions along the length of the blade thereby removing any stress concentrations from one particular location which would otherwise be the case if all the laminates were to terminate at the same position. Alternatively, the spar cap bridge could have a machined tapered surface. The component that is machined may also be built up from a stack of laminates or another composite manufacturing method such as pultrusions. According to the second aspect of the present invention, there is provided a method of manufacturing a wind turbine blade according to claim 1 , and the method comprising bringing the first and second sections together at the joint region; and moulding the spar cap bridge into the outer surface of the fairing in the respective pairs of aligned recesses. This is a simple method of providing a reliable joint which can be created in situ as set out above.

The spar cap can be allowed to cure in the absence of any pressure. However, preferably, the method further comprises applying a membrane to the top of the spar cap in the aligned recesses during the moulding process and applying pressure to the spar cap during the moulding process. The membrane may be a vacuum bag. However, preferably, the membrane is a pressure bag as this can readily be attached to the fairing above the aligned recesses thereby simply completing a very reliable mould. The surfaces of the recesses can define all but the upper surface of the mould while this is defined by the pressure bag. Alternatively at least part of the sides of the mould may be defined by a tool that attaches the pressure bag. The pressure bag itself is easy to attach and provides a well distributed force across the top of the spar cap bridge. Further, the shear webs in the two sections support the underside of the spar cap bridge during the moulding process. The present invention requires, in the broadest sense, first and second sections to be joined together using this method. In use, however, a blade may well be divided into more sections with the above described joint being created between more than two such sections. Given that the joint is particularly effective in reducing parasitic mass, it is particularly applicable if one of the sections is a tip section as it is towards the radially outermost extremity of the blade where the effect of parasitic mass is the most significant.

Further, the first and second sections may have more than one spar. For example, the sections may have a main spar and a trailing edge spar. Under these circumstances, only one of the spars (ideally the main spar) may be joined using the above described technique. However, preferably, each of the spars is joined in this way.

Because of the nature of the joint, the fairing can extend all the way to the interface between the sections for the entire circumference of the blade. This can provide a particular advantage in the tip section if the tip section fairing is moulded as a seamless single piece as contemplated in our copending application, agent's ref: P135579GB00. The fact that the fairing can extend all the way to the interface with the adjacent section for the entire circumference of the fairing means that the portion of the tip region without a seam extends even further than it would with the joint of the prior art. The tool for moulding the spar cap bridge forms a third aspect of the present invention as defined in claim 9. Preferably the pressurisable portion is a bladder and the tool is provided with an integral heater. This provides an extremely convenient way of making the joint which is suitable for use in the field as the tool can simply be bolted into place without requiring any further alignment and conveniently used with minimal additional peripheral equipment before being removed and reused for another joint.

The cavity in the tool may define some or all of the side wall of the mould cavity for the spar cap bridge. Alternatively the side walls may be defined wholly or partially by the wind turbine fairing. An example of the present invention will now be described with reference to the accompanying drawings, in which:

Fig. 1 is a perspective view of one blade section;

Fig. 2 is an end view of the section; Fig. 3 is an exploded perspective view showing the joint between adjacent shear webs;

Fig. 4 is a perspective view showing the two sections together prior to insertion of the spar cap bridge;

Fig. 5 is a section through line V-V in Fig. 6 but shown during the moulding process; Fig. 6 is a cross section in a plane parallel to the shear webs showing the finished joint between two sections;

Figs. 7A-D are schematic cross-sections showing the moulding process in greater detail with Fig. 7A showing the shell fairing before the joining process; Fig. 7B showing the completed joint; and Figs. 7C and 7D showing two different types of moulding assembly;

Figs. 8A and 8B are views similar to Figs. 7A and 7C showing an alternative assembly arrangement; and

Figs. 9A and 9B are views to similar to Figs. 8A and 8B showing a further alternative arrangement. The blade in most senses has the conventional structure comprising a hollow fairing and a central spar extending along the length of the blade to provide the structural rigidity.

The blade is divided into two or more segments 1, 2. In the present example, the outboard component 1 is a blade tip component while the adjacent component 2 is an inboard component. There may be one or more additional components connected inboard of the second segment 2. The joints for these additional components will be as described below.

The tip component 1 may be a single seamless moulding which may be formed as described in our co-pending application, (agent's ref: P135579GB00). Alternatively, it may be made up of two or more panels. These may be either leading edge or trailing edge panels, or may be windward and leeward panels. However, in the latter case, these windward and leeward panels should be joined to one another in a region spaced from the leading and trailing edges. The blade sections may be made according to the principles disclosed in our earlier WO 2009/034291. The improved joint forming the subject of the present invention will now be described.

As shown in Fig. 1, the fairings 4 in the windward and leeward sides of the section are formed, in the vicinity of the joint region 3 with a respective recess 5. This is positioned immediately adjacent to the shear web 6 which supports the recesses 4. As shown in Fig. 6, the spar is completed by a spar cap 7 on either side of the shear web 6. The spar cap tapers off towards the joint region 3 as the depth of the recess 5 increases. As best shown in Fig. 1, the recesses taper very gradually for a distance of several meters until, in the vicinity of the joint region, they replace the full depth of the spar cap 7. The recesses are formed in the wall of the fairing 4. As will be appreciated from Fig. 1, the only potential for parasitic mass is the side walls 8 and even these need not provide parasitic mass if the external diameter width of these walls is no greater than the width of the shear webs away from the joint region.

In order to connect the two sections, an H connector 10 is positioned between the webs 6 as shown in Fig. 3. This connector will be bonded to one of the webs. The adhesive is then applied either to the other web or to the surface of the H connector 10 which faces this web before the two sections are brought together to the position shown in Fig. 4. This H connector not only provides robust support for the sections during the remainder of the connection process, but it also ensures that the end faces of the webs support one another via the H connector, effectively providing a lap connection to transmit the shear loads between the webs.

The spar cap bridge 11 has a shape which matches the shape of the aligned recesses 4 such that it has a flat upper surface 12 and tapers off towards either end. The spar cap bridge may be a single uncured component. Alternatively, it can be built up within the recess as a series of laminations.

Once the spar cap bridge has been placed in the aligned recesses 4 or built up in the aligned recesses, a pressure bag assembly is brought into place as shown in Fig. 5. This comprises a lid 20 and a plurality of bolts 21 which are screwed into the fairing in the region surrounding the aligned recesses 4. A pressure bag 22 is positioned above the upper surface 12 of the spar cap bridge 11. Pressure is applied to this bag which will then pressurise the spar cap bridge during the moulding process. At this time, the web 6 provides support from beneath the aligned recesses 4.

Once the spar cap bridge is cured, the bag is depressurised and the mould is unbolted. It can then be used for further joints of the same blade or another blade. The holes left by the bolts are then filled and, if necessary, the surface of the joint in the vicinity of the upper face 12 of the spar bridge component 11 can then be made good and coated.

As can be seen from the finished joint in Fig. 6, not only do the shear webs 6 support one another as mentioned above, but also the junction between the spar caps is achieved in a manner which retains the spar cap material and the spar cap bridge components in alignment such that, in terms of their load transmitting capabilities, the joint is as good as the region in the spar caps away from the joint. This is all done with little or no parasitic mass as the joint is kept within or very close to the envelope defined by the spar caps away from the joint region. The spar caps generally consist of uniaxial material oriented along the length of the spar, and this material is replicated in the spar bridge segment 11 such that the load bearing requirements of the spar caps are preserved across the joint region. Because the recesses 4 are tapered as described, each layer of uniaxial material forming the spar cap 11 terminates at a different location along the length of the blade thereby eliminating points of weakness which would otherwise be generated if the layers terminated at a single axial location or a relatively narrowly distributed axial location.

A more detailed arrangement of forming a moulded joint is shown in Figs. 7A to 7D. In this case, the aerodynamic fairing 1 has a shallow region 20 which is much wider than the recess 4 of the previous example. In the centre of the shallow region 20 is a recess 21 corresponding to the recess 4 of the previous example in which the spar cap bridge 22 is formed. On either side of the recess 21 are a pair of shallow connection regions 23 which are provided with a plurality of bolt holes 24 as described below.

On either side of the shear web 6 there is provided an insulation material 25 which may be included to insulate the adjacent parts during the bonding process thereby retaining the heat in the curing components. It should be remembered that these only need to be present in the immediate vicinity of the spar cap and can be made of lightweight material such that the parasitic mass introduced by these components is very small. In particular, because of the thin nature of the fairing 1 in the connection region 23, the insulation material 25 can be made proportionally thinner thereby further decreasing the parasitic mass.

Once the components of the spar cap bridge 22 have been placed in the recess 21 as described above, the moulding tool 26 is then bolted in place as shown in Fig. 7C. The moulding tool comprises a housing 27 with a downwardly depending lip 28 which matches the shape of the underlying fairing 1 and has a plurality of bolt holes which correspond to the bolt holes 24 in the fairing 1. A plurality of bolts 29 are then screwed into lightweight, non-metallic nuts 29A to secure the moulding tool 26 to the fairing 1. Within the moulding tool is a bladder 30 which is connected to a pneumatic fluid (not shown). The housing 27 has vent holes 31 to allow the bladder 30 to expand. The clearance between the bladder 30 and the housing 27 is made as small as possible to reduce the overall size of the tool. It will be appreciated that, while a vacuum bag can be used, a pressure bag is preferred as there is no need to provide a sealed cavity to contain the vacuum. The curing process may be assisted by the presence of a heater 32 in the housing 27 as shown in Fig. 7D. Alternatively, there may be an external heat source, but it is convenient to build all of the equipment necessary to make the joint into a single tool.

As before, once the joint has been made, the bolts 29 are removed and the tool can be reused. The insulation material 25 and nuts 29A can be removed but, as they are lightweight components they are preferably left in place. After the tool has been removed, the joint may be covered by an aerodynamic skin panel 33 which is bonded into shallow recesses 34 on either side of the shallow region 20.

Figs. 8A and 8B showing arrangements similar to that shown in Figs. 7A and 7B and the same reference numerals used for the same components.

Although not shown, the insulation of Figs. 7B to 7D may be present in this example. In this case, the insulation material 25 may not be required as the bolts 29 can be screwed into nuts 35. In this case, the shear web 6 is attached to the fairing 1 by a pair of L-Shaped composite sheets 36. While Figs. 7A to D show a shallow recess in the fairing to receive the spar cap bridge at 22, in Figs. 8 A and B, no such recess is provided and the side walls of the mould cavity are formed entirely by the housing 27.

Figs. 9A and 9B show a similar arrangement to that of Figs. 8A and 8B. The same reference numerals that have been used to designate the same components. This time, however, the housing 27 has only a shallow recess deep enough to accommodate just the bladder 30 which the side walls for the spar cap bridge 22 are defined entirely by the recess 37 in the fairing 1. Taking this further, it is possible to provide an ever deeper recess in the fairing and for housing 27 to be entirely flat such that the bladder 30 is accommodated in the recess in the fairing rather than in the housing 27.

Claims

CLAIMS:

1. A wind turbine blade comprising first and second sections arranged along the length of the blade, each section comprising an aerodynamic fairing with inner and outer surfaces, the fairing extending across the windward and leeward sides of the blade, and a spar extending between the windward and leeward sides, the spar comprising a shear web with a spar cap at either end positioned between the shear web and the inner surface of the fairing; the first and second sections meeting one another at a joint region, wherein, in the vicinity of the joint region, each section has two recesses in the outer surface of the aerodynamic fairing; a first one above and a second one below the spar such that in the vicinity of each recess the depth of the spar caps is reduced, the first recesses in the respective segments being arranged to align with one another and the second recesses in the respective segments being arranged to align with one another when the first and second sections are aligned; and a first spar cap bridge being moulded onto the outer surface of the fairing in the first pair of aligned recesses; and a second spar cap bridge being moulded onto the outer surface of the fairing in the second pair of aligned recesses.

2. A blade according to claim 1, wherein the recesses have a tapering depth which increases towards the joint region.

3. A method of manufacturing a wind turbine blade according to claim 1, the method comprising: bringing the first and second sections together at the joint region; and moulding the spar cap bridge into the outer surface of the fairing in the respective pairs of aligned recesses.

4. A method according to claim 3, further comprising applying a membrane to the top of the spar cap in the aligned recesses during the moulding process and applying pressure to the spar cap bridge during the moulding process.

5. A method according to claim 4, wherein the membrane is a pressure bag.

6. A method according to any one of claims 3 to 5, wherein the shear web supports the spar cap bridges during the moulding process.

7. A method according to any one of claims 3 to 5, wherein the blade comprises more than two sections.

8. A method according to any one of claims 3 to 6, wherein one of the sections is a tip section.

9. A tool for moulding a spar cap bridge, in situ, into a recess in a wind turbine fairing, the tool comprising: a cover having a central moulding portion having a size corresponding to the spar cap bridge; a connecting portion surrounding the central moulding portion, the connecting portion having a lower face profiled to match the surface of the part of the wind turbine fairing surrounding the spar cap bridge, and a plurality of bolt holes for attachment to the wind turbine fairing, the cover having a pressurisable member capable of applying pressure to the spar cap bridge during the curing process.

10. A tool at claim 9, wherein the connecting portion is a downwardly depending skirt which defines a cavity to receive the pressurisable member.

11. A tool according to claim 9 or 10, wherein the pressurisable member is a bladder.

12. A tool according to any of claims 9 to 11, including an integral heater.