Patent Description:
In modern wind turbines, the provision of serrations along the trailing edge of the rotor blades is a commonly-used technique for reducing noise from the blades. In particular, such serrations act to reduce the noise generated at the turbulent trailing edge boundary layer while minimising any reduction in aerodynamic efficiency of the blades.

It is known to provide a separate part including serrations which is retrofitted to a wind turbine blade. Often, the separate part is attached at the trailing edge of the blade, typically by bonding it to the pressure side of the blade, so that the serrations extend outward from the trailing edge. Despite efforts to minimise the thickness of such separate serrated trailing edge parts, attaching such separate parts in this way can lead to a step at the point where the separate part attaches to the surface of the rotor blade, in particular where the edge of the separate part attaches to the surface of the rotor blade. Such a step can create turbulence and noise.

In order to address these issues, it has been proposed to manufacture a wind turbine blade that includes serrations at the trailing edge, thus obviating the need to retrofit a separate part. In particular, it has been proposed to provide a rotor blade formed of two parts: a main blade part or module that forms the majority of the aerodynamic profile of the blade; and, a separate edge part or module including serrations at the trailing edge.

Joining the main blade and separate edge modules together during the manufacturing process can pose difficulties. For example, moving the main blade and separate edge modules to bring them together can be challenging because of, for example, the scale of the parts, the complex or asymmetric geometry of the parts, and the fact that the parts are formed from delicate materials. Furthermore, the parts need to be joined together in such a way that there is a smooth transition, i.e. no step, at the surface of the rotor blade to avoid the generation of noise or turbulence at this transition point.

US Patent Publication No. <CIT> discloses a bonding fixture assembly for use in bonding structural members to form a hollow, spanwise-reinforced airfoil such as a helicopter rotor blade. In particular, <CIT> discloses an inflatable, pressure-applying mandrel tool that co-acts with a female, pressure-applying fixture.

US Patent Publication No. <CIT> discloses a method for bonding additional parts to a composite-material turbomachine part in a thermostatic oven. The method includes placing the turbomachine part equipped with the additional part on a rigid support that cannot deform at an operating temperature and pressure of the thermostatic oven, the rigid support being configured to espouse the desired final shape of the turbomachine part. The turbomachine and additional parts are covered with a vacuum bag, the edges of which are sealed with respect to the rigid support. A vacuum of determined pressure is applied to the vacuum bag. The determined operating pressure is applied to hold the turbomachine and additional parts firmly against the rigid support, and the whole entity is heated to the operating temperature in the thermostatic oven for a determined time.

Patent Publication Nos <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> each disclose a wind turbine rotor blade that has a separate part attached at a trailing edge of the rotor blade.

According to an aspect of the invention there is provided a method of forming a wind turbine blade. The wind turbine blade comprises a main blade module defining a main body of the blade and including a first mating feature. The wind turbine blade comprises a separate edge module defining at least part of a trailing edge of the blade and including a second mating feature. The first mating feature is a tongue and the second mating feature is a recess complementary to the tongue. The method comprises applying an adhesive to at least one of the first mating feature and the second mating feature. The method also comprises arranging the separate edge module relative to the main blade module such that the first and second mating features are mutually adjacent. Arranging the separate edge module relative to the main blade module includes receiving the tongue into the recess. The method also comprises applying a pressure force to squeeze the adhesive to bond the first and second mating features together. The pressure force is caused by removing air from, or injecting air into, an air sealed region.

The method may comprise locating a pressure distributor against the separate edge module to distribute the pressure force that is applied to the first and second mating features.

The method may comprise providing a consolidator at an interface between the main blade module and the separate edge module at an outer surface of the blade. The consolidator may be arranged to ensure that the separate edge module is flush with the main blade module at the interface when the pressure force is applied.

The separate edge module may comprise at least one vent hole extending between the recess and an outer surface of the separate edge module, and wherein squeezing the adhesive causes the adhesive to flow through the at least one vent hole.

Arranging the separate edge module relative to the main blade module may comprise: positioning the main blade module so that the tongue extends in a generally upwards direction; and, placing the separate edge module on the main blade module, wherein the tongue and the recess are shaped so that the separate edge module self-locates relative to the main blade module when placed thereon. The main blade module may be positioned in a cradle, guide or gauge, which may be shaped to verify the profile of the completed blade.

The air sealed region may encapsulate at least the first and second mating features. The method may comprise forming the air sealed region after the separate edge module has been arranged relative to the main body module, and the method may comprise removing air from the sealed region to create a vacuum and cause the pressure force to be applied. In this way the mating features are compressed, and therefore bonded, together.

The air sealed region may be defined by a deformable vacuum bag.

The method may comprise providing an end of the separate edge module that defines the at least part of the trailing edge with a protective cover prior to forming the air sealed region.

Advantageously, this guards against damage being caused to the trailing edge, or a trailing edge feature such as serrations, when the vacuum is created and the vacuum bag is compressed against the separate edge module.

The air sealed region may be defined by one or more inflatable airbags, also referred to as bonding airbags. The method may comprise injecting air into the one or more inflatable airbags to cause the force to be applied by the inflatable airbags applying pressure to an outer surface of the blade in the vicinity of the first and second mating features.

The pressure force applied to the outer surface may be applied progressively in a chordwise direction of the blade towards the trailing edge of the blade. For example, the pressure force may be applied progressively from an open end of the recess to a closed end of the recess. This may be achieved by the provision of a row or series of bonding airbags adjacent to the blade outer surface that are pressurised sequentially or progressively in a direction towards the closed end of the recess.

The method may comprise injecting the one or more inflatable airbags with air at a temperature greater than ambient temperature.

Arranging the separate edge module relative to the main blade module may comprise positioning the main blade module so that the first mating feature extends in a generally upwards direction. The arranging step may comprise clamping the separate edge module in a clamp. The clamp may comprise inflatable airbag clamps, wherein clamping the separate edge module comprises injecting air into the air sealed inflatable airbag clamps. The arranging step may comprise positioning the clamped separate edge module generally above the main blade module. The arranging step may comprise lowering the separate edge module onto the main blade module and using an alignment device to maintain alignment between the main blade module and the separate edge module when arranging the first and second mating features to be mutually adjacent, the alignment device being coupled to the clamp, for example by a frame.

The alignment device may comprise a plurality of alignment rollers that roll against an outer surface of the main blade module as the separate edge module is lowered to maintain alignment of the separate edge module with the main blade module.

Examples of the invention will now be described by way of example with reference to the accompanying drawings, in which:.

<FIG> shows a wind turbine wind turbine (<NUM>). The wind turbine <NUM> includes a tower <NUM>, a nacelle <NUM> rotatably coupled to the top of the tower <NUM>, a rotor including a rotor hub <NUM> mounted to the nacelle <NUM>, and a plurality of wind turbine rotor blades <NUM> and which are coupled to the rotor hub <NUM>. The rotor <NUM> comprises three blades <NUM>, but in other examples the rotor <NUM> may have any suitable number of blades <NUM>. The nacelle <NUM> and rotor blades <NUM> are turned and directed into the wind direction by a yaw system. The nacelle <NUM> houses generating components (not shown) of the wind turbine <NUM>, including the generator, gearbox, drivetrain and brake assembly, as well as convertor equipment for converting the kinetic energy of the wind into electrical energy for provision to the grid. The wind turbine <NUM> is shown in its fully-installed form suitable for operation; in particular, the rotor <NUM> is mounted on the nacelle <NUM> and each of the blades <NUM> are mounted on the rotor and rotor hub <NUM>.

<FIG> shows part of a prior art wind turbine rotor blade <NUM> having attached thereto a separate part <NUM> including a plurality of serrations <NUM>. In particular, the separate part <NUM> is bonded to the blade <NUM> at a pressure side <NUM> of the trailing edge <NUM> of the blade <NUM>, so that the serrations <NUM> extend outwards, i.e. downstream, from the trailing edge <NUM>. It is noted that a step <NUM> is formed at the transition between the pressure-side surface <NUM> of the blade <NUM> and the separate part <NUM>. This step change in thickness causes noise and/or turbulence.

<FIG> shows a part of one of the rotor blades <NUM> of the wind turbine <NUM>. The blade <NUM> is formed by a plurality of parts or modules that are manufactured separately and then joined together. In particular, the blade <NUM> is formed by one or more main blade modules <NUM> and a plurality of separate edge modules <NUM>. The one or more main blade modules <NUM> form the majority of the aerofoil shape or profile of the blade <NUM> and define a leading edge (not shown) of the blade <NUM>. The edge modules <NUM> are premanufactured modules, i.e. they are made separately from the main blade module <NUM>, and attached to the main blade module <NUM> to form the wind turbine blade <NUM>. Each of the separate edge modules <NUM> define part of a trailing edge <NUM> of the blade <NUM>, and the separate edge modules <NUM> are connected or arranged end-to-end along the main blade module <NUM> to define the trailing edge <NUM>. In particular, the separate edge modules <NUM> may be connected or clicked together prior to joining the main blade module <NUM>. Hence each edge module <NUM> may be referred to as a premanufactured trailing edge (PMTE) module. For example, each of the separate edge modules <NUM> may be approximately <NUM> in length (in a spanwise direction of the blade). The separate edge modules <NUM> may be non-identical to conform to the profile of the blade <NUM>. In the described example, the separate edge modules <NUM> each include a plurality of serrations <NUM> at the trailing edge end.

The main blade module <NUM> is preferably formed from composite materials, for example fibre-reinforced plastic such as glass-fibre reinforced plastic (GFRP). The main blade module <NUM> may be formed using any suitable technique known for forming wind turbine blade shells, e.g. vacuum-assisted resin transfer moulding (VARTM). The edge module <NUM> may also be formed from composite materials, e.g. GFRP or just plastic, and may be a moulded part. This may also be formed by VARTM, injection moulding or other suitable technique. Alternatively, the edge module <NUM> could be made from an elastomeric material, such as rubber.

With continued reference to <FIG>, and additional reference to <FIG> - which shows the edge module <NUM> without the serrations - the main blade and separate edge modules <NUM>, <NUM> include respective complementary mating features <NUM>, <NUM> for joining the modules <NUM>, <NUM> together. In particular, the mating feature of the main blade module <NUM> is in the form of a tongue <NUM>, and the mating feature of the separate edge module <NUM> is in the form of a recess <NUM> (as shown in <FIG>) arranged to receive the tongue <NUM>. The recess <NUM> of the edge module <NUM> is at, and faces, an end of the edge module <NUM> opposite to an end that defines the trailing edge <NUM> of the blade <NUM>.

Methods of bringing together and bonding the main blade and separate edge modules <NUM>, <NUM> will now be described.

<FIG> show schematic perspective and sectional views of an apparatus or arrangement <NUM> for forming the wind turbine blade <NUM> from the main blade and separate edge modules <NUM>, <NUM>. The arrangement <NUM> includes a jig or frame <NUM> with frame bars defining a cuboid frame shape that is open at a lower side <NUM> so as to receive the modules <NUM>, <NUM> therein.

The arrangement <NUM> includes a clamping mechanism or arrangement, or simply a clamp, for gripping and moving the separate edge modules <NUM>. In particular, the clamp includes at least one pair of clamping airbags or bladders <NUM> attached to the frame <NUM> and facing each other, and between which the edge module <NUM> is received. The clamping airbags <NUM> define an air sealed region <NUM> and may be inflated by injecting air into the sealed region <NUM>. This causes the clamping airbags <NUM> to apply a pressure force to both sides of the edge module <NUM> to grip or clamp the edge module in place relative to the frame <NUM>. This allows the edge module <NUM> to be moved via movement of the frame <NUM>. In particular, lifting and moving the separate edge module <NUM> using the inflatable and flexible clamping airbags <NUM> reduces the risk of the separate edge modules <NUM> being crushed or otherwise damaged during this process. The use of airbags also allows the jig <NUM> to lift and move edge modules <NUM> that have different geometries.

The arrangement <NUM> includes an alignment device or arrangement for maintaining the relative positions of the main blade and separate edge modules <NUM>, <NUM> when they are being brought together and/or bonded together. In particular, the alignment device in the described example is in the form of pairs of rollers or wheels 40a, 40b attached to the frame <NUM>, and between which the main blade and separate edge modules <NUM> are received. Specifically, two pairs of the rollers 40a are located and spaced apart to receive the edge module <NUM> therethrough so that the rollers 40a contact the edge module <NUM> when it is received therethrough. Similarly, two more pairs of the rollers 40b are located lower in the frame <NUM> and spaced apart to receive the main blade module <NUM> therethrough so that the rollers 40b contact the main blade module <NUM> when it is received therethrough. The rollers 40a, 40b provide a flexible means for ensuring alignment of the modules <NUM>, <NUM> that also guards against damage being caused to the modules <NUM>, <NUM>.

The apparatus <NUM> also has an angled receptor <NUM> attached to a horizontal bar <NUM> internal to the frame <NUM> which is arranged to receive, and maintain the position of, the end of the edge module <NUM> that defines the trailing edge <NUM> of the blade <NUM>.

The apparatus <NUM> also includes pairs of clips <NUM> along an upper end of the frame <NUM>. These allow the apparatus <NUM> to be connected to a hoist, for example, so as to move the apparatus <NUM> with clamped edge module <NUM> into position relative to the main blade module <NUM>, where the edge module <NUM> may be lowered onto the main blade module <NUM>, as described below.

The apparatus <NUM> also includes at least one pair of bonding airbags or bladders <NUM> attached to the frame <NUM> and facing each other, and located adjacent to the tongue <NUM> and recess <NUM> when the main blade and separate edge modules <NUM>, <NUM> are brought together. The bonding airbags <NUM> define an air sealed region <NUM> and may be inflated by injecting air into the sealed region <NUM>. This causes the bonding airbags <NUM> to apply a pressure force to both sides of the modules <NUM>, <NUM> to bond them together, as described in greater detail below.

With reference to <FIG>, a method of forming the wind turbine blade <NUM> is now described. <FIG> shows in schematic form the main blade module <NUM> arranged or positioned such that the end of the blade having the tongue <NUM> extends in a generally upwards direction. The main blade module <NUM> may be held or supported in a structure for maintaining this orientation.

A layer of adhesive <NUM>, for example an adhesive resin, is applied to a surface of the tongue <NUM>, which will act to bond the tongue <NUM> and recess <NUM> together when the main blade and separate edge modules <NUM>, <NUM> are brought together. In addition, or alternatively, the adhesive may be applied to a surface of the recess <NUM>.

The apparatus <NUM> is used to securely clamp or grab the separate edge module <NUM>. In particular, the edge module <NUM> is received into the apparatus so that the trailing edge <NUM> is received into the angled receptor <NUM> so as to guard against bending of the trailing edge <NUM>. The rollers 40a roll against the surface of the edge module <NUM> as it is received into the apparatus so as to maintain the position and orientation of the edge module <NUM>. When the edge module <NUM> is received into the apparatus <NUM> the clamp airbags <NUM> are in a deflated state. Once the edge module <NUM> is in position it is clamped in place by inflating the clamp airbags <NUM> so that a pressure force is applied by the airbags <NUM> on either side of the edge module <NUM>.

The apparatus <NUM> is then moved, for example by a hoist connected to the clips or hooks <NUM>, to position the edge module <NUM> generally above the main blade module <NUM>, with the recess <NUM> of the edge module <NUM> extending generally downwards towards the tongue <NUM> of the main blade module <NUM>. Of course, the adhesive layer may instead be applied at this point instead of prior to the edge module <NUM> being clamped and moved into position.

The apparatus <NUM> is then lowered from the position generally shown in <FIG> to the position generally shown in <FIG>. In particular, the edge module <NUM> is lowered onto the main blade module <NUM> such that the tongue <NUM> and recess <NUM> fit together and are mutually adjacent. As the apparatus <NUM> is lowered, the rollers 40b contact, and roll relative to, the surface of the main blade module <NUM> to maintain alignment between the main blade module <NUM> and the separate edge module <NUM>.

The main blade and separate edge modules <NUM>, <NUM> are then bonded together by injecting air into the bonding airbags <NUM> which forces the tongue <NUM> and recess <NUM> together and bonds them by means of the adhesive. This is described in greater detail with reference to <FIG>, <FIG> and <FIG>.

<FIG> shows a schematic sectional view of the tongue <NUM> and recess <NUM> when they have been brought together to be mutually adjacent by means of the apparatus <NUM> so that the bonding airbags <NUM> are adjacent thereto. The bonding airbags <NUM> are in a deflated state such that they do not apply a pressure force to the main blade or separate edge modules <NUM>, <NUM>. <FIG> shows that there is a gap <NUM> defined between the tongue <NUM> and recess <NUM> and that the tongue <NUM> has a layer of adhesive <NUM> applied to it.

<FIG> shows the bonding airbags <NUM> in a partially inflated state. In particular, the bonding airbags <NUM> are inflated in a manner such that the airbags <NUM> contact, and apply a pressure force at an open end <NUM> of the recess <NUM> of the edge module <NUM> opposite to a closed end <NUM> of the recess <NUM>, as shown in <FIG>. This forces the open end <NUM> of the recess <NUM> of the edge module <NUM> towards the tongue <NUM> and to squeeze the adhesive <NUM> between them. Specifically, by applying the pressure force at the recess open end <NUM> in the first instance the adhesive <NUM> is squeezed further into the recess <NUM> towards the closed end <NUM>. At this stage, the closed end <NUM> of the recess (also referred to as a glue or adhesive chamber <NUM>) starts to fill up with the adhesive <NUM>. The pressure force is then applied progressively from the open end <NUM> to the closed end of the recess <NUM> by sequential inflation of a series of the airbags <NUM> from the open end <NUM> towards the closed end <NUM> Expressed differently, the pressure force is spread out in a chordwise direction of the blade <NUM> in a direction towards the trailing edge <NUM> of the blade. Advantageously, such progressive application of the pressure force causes the flow of adhesive <NUM> to be in a direction into the recess <NUM> towards its closed end <NUM> and therefore both prevents the adhesive <NUM> flowing out of the open end <NUM> of the recess <NUM> (which can cause a step at the blade surface) and facilitates complete filling of the gap <NUM> between the tongue <NUM> and recess <NUM>, thereby improving the quality of the bond. In addition, application of the force in this sequential or progressive manner may prevent the formation of undesirable air cavities in the bond.

<FIG> shows the bonding airbags <NUM> in a fully inflated state, in which the airbags <NUM> apply a pressure force all the way along the surface of the edge module <NUM> in the vicinity of the recess (not labelled in <FIG>), i.e. all the way from the recess open end <NUM> to the recess closed end <NUM> of the recess <NUM>. This forces the gap (not labelled in <FIG>) between the tongue <NUM> and recess <NUM> to be closed, and the main blade and separate edge modules <NUM>, <NUM> to be bonded all the way along the tongue <NUM> and recess <NUM> from the open end <NUM> to the closed end <NUM>. The adhesive <NUM> is squeezed further into the recess <NUM> until the adhesive chamber <NUM> is completely full. The edge module <NUM> may include one or more vent holes <NUM> that extend from the closed end <NUM> of the recess <NUM> to the outer surface of the edge module <NUM>. Once the closed end <NUM> is filled with the adhesive <NUM>, continued application of the pressure force causes the adhesive <NUM> to flow through the vent holes <NUM>. Once the adhesive <NUM> reaches the surface of the edge module <NUM>, and the adhesive <NUM> has cured to a sufficient degree to maintain a bond between the main blade and separate edge modules <NUM>, <NUM>, the bonding process is complete and inflation of the airbags <NUM> may be stopped, or deflation of the airbags <NUM> may be permitted. The provision of the vent hole(s) <NUM> is a relatively simple way to determine when the adhesive has completely filled a gap between the mating features <NUM>, <NUM>. Any adhesive <NUM> that exits the vent holes <NUM> at the surface of the blade <NUM> may easily be removed to ensure the rotor blade surface remains smooth. This may be achieved by, for example, abrading the cured adhesive <NUM> away from the surface of the blade <NUM>.

The bonding airbags <NUM> may include a number of embedded heating elements (not shown) at or near a surface of the airbags <NUM> that contacts the separate edge module <NUM>. Such heating elements would increase the temperature at which the bonding process between the main blade and separate edge modules <NUM>, <NUM> takes place, which can reduce the time taken for the bond to cure. Alternatively, instead of using embedded heating elements, the bonding airbags <NUM> may be injected with heated air which would also increase the temperature at which the bonding process takes place, thereby reducing the cure time between the main blade and separate edge modules <NUM>, <NUM>.

The bonding airbags <NUM> have a flexible surface and so application of the force by the airbags <NUM> to the surface of the blade <NUM> is less likely to cause damage to the blade <NUM> than application of a force by a solid part. Application of a force using such a method requires relatively little effort and manpower.

<FIG> show perspective views of the wind turbine blade <NUM> being supported in a cradle or guide <NUM>. In this example, the cradle <NUM> supports the main blade module <NUM> when the main blade and separate edge modules <NUM>, <NUM> are being bonded, as will be described below. In particular, instead of applying a pressure force by inflating one or more airbags as in the above-described example, in the example described below a deformable bag encapsulates the tongue <NUM> and recess <NUM> (not shown in <FIG>) to form an air sealed region that includes the tongue and recess. Air is then removed from the sealed region to create a vacuum therein, which causes a pressure force that squeezes the tongue and recess together. Such an approach is a particularly simple and inexpensive way to provide an air pressure force to cause bonding of the mating features, and needs minimum tooling.

In the described example, the cradle <NUM> is formed by separate cradle components spaced apart and arranged and shaped to receive the main blade module <NUM> therein. In particular, the main blade module <NUM> is positioned in the cradle <NUM> so that its tongue <NUM> extends in a generally upwards direction. Specifically, a side of each cradle <NUM> includes a hinge <NUM> that allows the cradle <NUM> to be opened up to receive the main blade module <NUM> therein.

The separate edge modules <NUM> may then be placed on the main blade module <NUM> to complete the aerodynamic profile (as shown in <FIG>). The tongue <NUM> and recess <NUM> (not shown in <FIG>) of the main blade and separate edge modules <NUM>, <NUM>, respectively, are shaped such that the separate edge module <NUM> self-locates on the main blade module <NUM> when placed thereon. The cradle <NUM> is also shaped to support the separate edge module <NUM> in its self-locating position when placed on the main blade module <NUM>. Once the main blade module <NUM> and separate edge module <NUM> are in place, the cradle <NUM> is closed back up to verify the shape of the blade <NUM>.

The cradle <NUM> includes a datum reference, e.g. in the form of a cable, bar or laser projection between each of the separate cradle components, which indicates how far the separate edge module <NUM> is to be lowered when being placed on the main blade module <NUM>.

The separate components of the cradle <NUM> may equally be connected together by further components therebetween. In addition, the cradle <NUM> may include a platform or walkway to allow an operator to access the separate edge modules <NUM> when they are placed on the main blade module <NUM>.

Prior to placing the separate edge module <NUM> on the main blade module <NUM>, and similarly to the above-described example, a layer of adhesive is applied to the surface of the tongue <NUM> and/or the recess <NUM> (not shown in <FIG>), to be used to bond the modules <NUM>, <NUM> together.

With additional reference to <FIG>, a method of bonding the main blade module <NUM> and separate edge module <NUM> together is now described when the modules <NUM>, <NUM> are positioned in the cradle <NUM> such that the tongue <NUM> and recess <NUM> are mutually adjacent. <FIG> shows a schematic sectional view of the main blade module <NUM> positioned in the cradle (not shown) so that the tongue <NUM> extends in a generally upwards direction. The separate edge module <NUM> is placed on the main blade module <NUM> so that the tongue <NUM> is received in the recess <NUM>. <FIG> also shows the presence of the gap <NUM> when the tongue <NUM> and recess <NUM> are mutually adjacent, but prior to them being bonded together by means of the adhesive layer.

In the described example, a consolidator <NUM> may optionally be placed at the interface between the main blade module <NUM> and the separate edge module <NUM> at the outer surface of the blade <NUM>. That is, the consolidator <NUM> is placed in the region of the opening of the gap <NUM> at the blade surface. The consolidator <NUM> is in the form of strips that overlap the interface between the modules <NUM>, <NUM> at the blade surface. In the described example, the consolidator strips <NUM> may be formed from plywood covered with polytetrafluoroethylene (PTFE), e.g. Teflon. The consolidator strips <NUM> aim to ensure that the separate edge module <NUM> is flush with the main blade module <NUM> at the interface when a force is applied to bond the modules <NUM>, <NUM> together. The provision of the consolidator <NUM> helps to guard against the formation of a step or ridge at the interface between the modules <NUM>, <NUM>, the presence of which at the surface of the blade <NUM> would be a source or noise and/or turbulence when the blade <NUM> is in operation. The consolidator <NUM> can also assist in guarding against the adhesive <NUM> flowing out of the interface during the bonding process.

In the described example, a pressure distributor <NUM> may optionally be placed against the outer surface of the separate edge module <NUM>. In particular, the pressure distributor <NUM> is located adjacent the recess <NUM> of the separate edge module <NUM>. In the described example, the pressure distributor <NUM> is in the form of a layer of perforated hardboard, e.g. pegboard, covered by a layer of mesh formed by connected strands of metal, fibres, or any other suitable flexible material. The pressure distributor acts to distribute the force that is applied to join the main blade and separate edge modules <NUM>, <NUM> together, in particular to distribute the force applied to the separate edge module <NUM> adjacent to the recess <NUM>. Advantageously, the provision of such a distributor <NUM> may distribute the applied force across the outer surface of the blade <NUM>, or a particular region thereof, to ensure the force is applied in an even manner and so provide an even bond between the modules <NUM>, <NUM>.

With the consolidator <NUM> and pressure distributor <NUM> in place, a deformable vacuum bag <NUM> is then placed around the arrangement. In particular, the vacuum bag <NUM> encapsulates the separate edge module <NUM> and part of the main blade module <NUM> including the tongue <NUM>. The vacuum bag <NUM> is sealed by attaching it to the surface of the main blade module <NUM> along a sealing line or at sealing points <NUM>. Note that the consolidator <NUM> and pressure distributor <NUM> are therefore also encapsulated by the vacuum bag <NUM>. Although in the described example the vacuum bag <NUM> encapsulates the entire separate edge module <NUM> including the trailing edge <NUM>, in different examples the vacuum bag <NUM> may encapsulate the recess <NUM>, but not the trailing edge <NUM>, of the edge module <NUM>, and have sealing points attached to the surface of the separate edge module <NUM>.

A tube (not shown) or other means for removing air is provided to draw air out from the air sealed region <NUM> defined by the vacuum bag <NUM>. In particular, the tube is used to remove air from the sealed region <NUM> to create a vacuum in the sealed region <NUM>. This results in the pressure in the sealed region being lower than outside of the sealed region, and this difference in pressure causes a pressure force to be applied. The arrows <NUM> in <FIG> indicate schematically the direction of the force caused by the pressure difference. Specifically, the pressure force causes the tongue <NUM> and recess <NUM> to be forced together thereby closing the gap <NUM>. In turn, the adhesive layer on the tongue <NUM> and/or recess <NUM> is therefore squeezed, causing the main blade and separate edge modules <NUM>, <NUM> to be bonded together.

As mentioned above, when the pressure force is applied the consolidator <NUM> acts to ensure that the main blade and separate edge modules <NUM>, <NUM> are bonded in such a manner that the interface between these modules <NUM>, <NUM> at the surface of the blade <NUM> is flush. The consolidator <NUM> also acts to ensure that the adhesive does not spew or flow out at the surface of the blade <NUM> in a manner that would result in a ridge or step at the blade surface.

In order to protect the trailing edge <NUM>, in particular the serrations <NUM> (not shown in <FIG>), from being damaged when the vacuum pressure force is applied, a protective cover or shield (not shown) may be provided to cover the end of the separate edge module <NUM> that defines the trailing edge <NUM> prior to forming the air sealed region <NUM> with the vacuum bag <NUM>. In particular, the protective cover may be in the form of a material which guards against the vacuum bag <NUM> pressing against, damaging and/or crushing the serrations <NUM> when air is removed from the sealed region <NUM> to cause the vacuum.

<FIG> summarises steps of the method <NUM> performed to form the wind turbine blade <NUM> in the above-described example. At step <NUM> an adhesive is applied to either or both of the mating features, i.e. the tongue <NUM> and recess <NUM>, of the main blade and separate edge modules <NUM>, <NUM>. At step <NUM> the main blade and separate edge modules <NUM>, <NUM> are arranged relative to each other so that the mating features <NUM>, <NUM> are mutually adjacent. In the example shown in <FIG>, this step involves clamping the separate edge module <NUM> using the clamping airbags <NUM> and lowering the frame <NUM> and clamped edge module <NUM> onto the upwardly-facing main blade module <NUM>. In the example shown in <FIG>, this step involves positioning the main blade module <NUM> in the cradle <NUM> and placing the self-locating edge module <NUM> on the main blade module <NUM>. At step <NUM> a pressure force is applied to squeeze the adhesive <NUM> to bond the first and second mating features <NUM>, <NUM> together. In the example shown in <FIG>, the pressure force is caused by injecting air into the bonding airbags <NUM> whose surface then presses on the surface of the separate edge module <NUM> to press the mating features <NUM>, <NUM> together. In the example shown in <FIG>, the pressure force is caused by removing air from the sealed region <NUM> to create a vacuum which results in the mating features <NUM>, <NUM> being forced together.

In each of the described examples, a pressure force is applied to squeeze the adhesive to bond mating features together, in particular by removing air from, or injecting air into, an air sealed region. Application of a force that is caused by a change of air pressure is advantageous for the bonding process because it facilitates force being applied to parts having complex geometry, e.g. a curved surface such as that of the aerofoil profile of a rotor blade, and being formed of delicate, lightweight materials. In particular, application of an air pressure force to a localised region may be advantageous compared with application of force caused by, for example, a solid part pressing against the main blade and/or separate edge module in that such a solid part is unlikely to conform to the shape of the surface of the complex-shaped modules, potentially causing uneven application of the force and therefore a sub-optimal bond between the modules. Also, such a solid part is unlikely to provide a flexible application of force, thus increasing the risk of causing damage to the modules during the bonding process.

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

In the above-described example, the separate edge modules include serrations at the trailing edge. In different examples, however, the separate edge modules may additionally or alternatively include different features for controlling or disrupting the flow at the trailing edge, e.g. vortex generators. Indeed, in certain examples the separate edge modules may simply define the trailing edge of the rotor blade without any features such as serrations.

The pressure distributor and consolidator are described above in connection with the example in which the vacuum is used to bond the main blade and separate edge modules together. Note, however, that one or both of the pressure distributor and consolidator may also be used in connection with the other example that uses the bonding airbags to bond the modules together.

Claim 1:
A method (<NUM>) of forming a wind turbine blade (<NUM>),
the wind turbine blade (<NUM>) comprising:
a main blade module (<NUM>) defining a main body of the blade (<NUM>) and including a first mating feature (<NUM>); and,
a separate edge module (<NUM>) defining at least part of a trailing edge (<NUM>) of the blade (<NUM>) and including a second mating feature (<NUM>),
wherein the first mating feature is a tongue (<NUM>) and the second mating feature is a recess (<NUM>) complementary to the tongue (<NUM>),
the method (<NUM>) comprising:
applying (<NUM>) an adhesive (<NUM>) to at least one of the first mating feature (<NUM>) and the second mating feature (<NUM>);
arranging (<NUM>) the separate edge module (<NUM>) relative to the main blade module (<NUM>) such that the first and second mating features (<NUM>, <NUM>) are mutually adjacent, wherein arranging the separate edge module (<NUM>) relative to the main blade module (<NUM>) includes receiving the tongue (<NUM>) into the recess (<NUM>); and,
applying (<NUM>) a pressure force to squeeze the adhesive (<NUM>) to bond the first and second mating features (<NUM>, <NUM>) together,
wherein the pressure force is caused by removing air from, or injecting air into, an air sealed region (<NUM>, <NUM>).