Abstract:
A method of manufacturing a wind turbine blade is described, the blade being formed from at least a pair of blade shells being joined together. For at least a portion of the wind turbine blade, the blade shells are joined by an overlamination applied between the edges of the blade shells, thereby substantially reducing or eliminating the need for a structural adhesive to join the blade shells, particularly in the area of the leading edge of the blade or the root region of the blade trailing edge. The overlamination can be formed from the same material as the blade shells themselves, thereby minimising the possibility of structural faults or cracks due to differences in materials or stiffness levels at the interface between the blade shells.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to a system and method for joining sections of wind turbine blades, in particular for joining wind turbine blade shells to form a wind turbine blade. 
       BACKGROUND OF THE INVENTION 
       [0002]    Wind turbine blades are generally made from composite materials, in particular glass and/or carbon fibre material which is infused with a resin and cured to form a solid structure. 
         [0003]    A known approach to wind turbine blade manufacturing is to form separate blade shell sections. Such shells are formed by the arrangement of layers of fibre material in suitably-shaped moulds which are infused with a resin which is subsequently cured. The solid blade shells can then be adhered together to form a larger wind turbine blade structure. Such shells are traditionally formed as half-portions of a wind turbine blade, e.g. a first shell corresponding to an upwind- or pressure-side of a wind turbine blade and a second shell corresponding to a downwind- or suction-side of a wind turbine blade. 
         [0004]    The shells are joined by an adhesive applied at the interface between the shells, typically along the edges of the shells, which are then brought into contact with each other and allowed to cure. An example of a prior art bonding between blade shells is shown in  FIG. 5 , where an adhesive  100  is located between the edges of upper and lower blade shells  102 ,  104  along the leading edge  106  of the blade. 
         [0005]    In order to improve the bonding between shells along such adhesive lines, additional adhesive flanges  108  may be provided as part of the shells to retain adhesive within the bond area between the blade shells. The adhesive flanges  108  are normally located on the interior of the blade, possibly as part of one of the blade shells  102 ,  104 , such that as the shells are brought together, the adhesive flange  108  is positioned on the internal side of the bond line between the edges of the shells  102 ,  104 , to catch and collect any excess adhesive  110  which may be squeezed between the shell edges into the blade interior. 
         [0006]    Once the shells have adhered to each other along the bond area, additional finishing operations may be required in order to provide a smooth outer surface in the area of the bond line between the blade shells. Such finishing operations may comprise a grinding or polishing of the external surface of the bond line, and/or an overlamination  112  of the bond line to provide for an aerodynamically suitable external surface. 
         [0007]    The adhesives used in such bonding areas add considerable weight and cost to the final blade structure. In addition, the use of such adhesives can result in the formation of structural cracks or faults in the finished blade, due to the differences in material composition and associated stiffness between the fibre composite-based blade shells and the adhesive used in the bond lines. 
         [0008]    It is an object of the invention to provide a system and method for the joining of wind turbine blade sections which addresses the above problems, in particular providing reduced weight and adhesive use for a wind turbine blade, while improving the performance of bonding areas in wind turbine blades. 
       SUMMARY OF THE INVENTION 
       [0009]    Accordingly, there is provided a method of manufacturing at least a portion of a wind turbine blade, wherein the method comprises the steps of:
       providing a first blade shell having a first edge,   providing a second blade shell having a second edge, and   joining said first blade shell to said second blade shell along at least a portion of said first edge and said second edge by providing an overlamination extending between said first edge and said second edge.       
 
         [0013]    The overlamination replaces the use of structural adhesive at the edge between the blade shells. A structural adhesive is understood to be an adhesive that can be used to produce a load-bearing joint. 
         [0014]    Preferably, the overlamination is applied to external surfaces of said first edge and said second edge. Locating the overlamination on external surfaces of the blade allows for ease of application of the overlamination to secure the blade shells together. In addition, the overlamination can be easily inspected after application to ensure that the overlamination has been adequately applied, and acts to join the blade shells together. 
         [0015]    The overlamination will be understood as a matrix of fibre material and a resin. Preferably, the overlamination is formed from the same material as the blade shells. 
         [0016]    It will he understood that the join between said portion of said first edge and said second edge is substantially formed without a structural adhesive. Rather, the join is formed by using resin to secure the overlamination to the blade shells. As substantially no structural adhesive is used between said portion of said first edge and said second edge, accordingly the blade shells are joined using the overlamination. 
         [0017]    Preferably, along said portion of said first edge and said second edge, the blade shells are joined solely using the overlamination, wherein no additional adhesive or glue is used along said portion of said first edge and said second edge. 
         [0018]    Accordingly, the weight and cost of the wind turbine blade may be minimized, due to the reduced need for structural adhesive joints. Additionally, the overlamination may be selected such that the overlamination material has substantially similar material and stiffness properties to the blade shells, thereby reducing the likelihood of structural faults or cracks due to different material or stiffness properties. 
         [0019]    Preferably, said first and second blade shells are arranged wherein a recess is defined at the interface between said first edge and said second edge, and wherein said overlamination is received at least partly within said recess. 
         [0020]    By providing the overlamination within a recess in the blade shells, accordingly the aerodynamic profile of the finished wind turbine blade may be preserved as the overlamination and the associated recess can be dimensioned to comply with the desired airfoil profile. 
         [0021]    There is further provided a method of manufacturing at least a portion of a wind turbine blade, wherein the method comprises the steps of:
       providing a first blade shell having a first tapered section along at least a portion of an edge of said first shell;       
 
         [0023]    providing a second blade shell having a second tapered section along at least a portion of an edge of said second shell;
       bringing together said first and second blade shells such that said first tapered section abuts said second tapered section to form a recess channel located along a boundary between the edges of said first and second blade shells; and   applying a laminate in said recess channel to join said first and second blade shells.       
 
         [0026]    As the recess may be formed from tapered edges of the blade shells, such tapering can be formed during manufacture of the blade shells themselves, e.g. by the selection of suitably-profiled blade moulds. Additionally or alternatively, such tapering may be provided by a cutting or grinding of the edges of the blade shells. By a tapered section, it will be understood that such tapering may comprise an even tapering or a stepped tapering, and such tapering may extend through the entire thickness of the blade shell, or may extend to a certain depth through the blade shell wall. 
         [0027]    Preferably, said laminate is arranged to substantially fill said recess channel. 
         [0028]    In one aspect, the maximum thickness of said laminate is substantially equal to the thickness of said first and second blade shells adjacent said edges. 
         [0029]    By having the laminate as the same depth as the shell thickness, the aerodynamic profile of the airfoil profile of the designed blade is preserved through the use of the laminate at the interface between the shells. 
         [0030]    Preferably, the blade shells are formed from a layup of a plurality of layers of fibre material, e.g. glass fibre, carbon fibre, etc., wherein said tapered section comprises a tapering through the body of the blade shell to a single layer or ply of fibre material. 
         [0031]    Preferably, said laminate is applied such that the exposed surface of the laminate is substantially flush with the exposed surfaces of the first and second blade shells adjacent said recess channel. 
         [0032]    The arrangement of the laminate in this manner provides for a smooth aerodynamic profile for the external surface of the blade in the region of the overlamination. 
         [0033]    In a preferred aspect, said first and second tapered sections are located along the leading edges of respective said first and second blade shells. 
         [0034]    Preferably, said step of applying a laminate comprises arranging said laminate in said recess channel to complete the aerodynamic profile along the leading edge boundary between said first and second blade shell portions. 
         [0035]    In an additional or alternative aspect, said first and second tapered sections are located along the respective trailing edges of said first and second blade shells, preferably the trailing edges adjacent the root and of said first and second blade shells. 
         [0036]    Preferably, the method comprises the step of providing a laminate or overlamination formed from substantially the same material as said first and second blade shells. 
         [0037]    By providing the laminate from the same material as the blade shells, accordingly there is no difference in the stiffness properties between the blade shells and the laminate. Such a selection of material considerably reduces the possibility of structural crack formation due to stiffness variations along bond lines between shells. 
         [0038]    In one aspect, the blade shells are at least partly formed from a matrix of a fibre-composite laminate material and a cured resin. 
         [0039]    Preferably, said step of applying a laminate or providing an overlamination comprises:
       positioning at least one layer of fibre material along at least a portion of said first edge and said second edge of said blade shells, preferably in said recess channel;   infusing said at least one layer of fibre material with a resin; and   curing said resin to bond said first and second blade shells.       
 
         [0043]    The step of infusing may comprise applying resin to surface of fibre material, e.g. roller application, vacuum infusion, etc. Alternatively, the step of applying a laminate may comprise positioning a precast laminate piece in said recess channel, and attaching said laminate piece in said recess channel. It will be understood that the resin may be any resin suitable for use in a composite structure, preferably at least one of, or a combination of, the following: polyester, vinyl ester, polyurethane, epoxy. 
         [0044]    In one aspect, the method further comprises the step of treating the external surface of the laminate, such that the laminate is flush with the adjacent external surface of the first and second blade shells. The step of treating may comprise any surface treatment suitable for producing an aerodynamically smooth surface substantially free from defects, for example a polishing operation. 
         [0045]    In one aspect, said steps of providing first and second blade shells may comprise forming at least one of said first and second blade shells in a blade shell mould, wherein said first and/or second tapered section is defined in said mould. 
         [0046]    In one aspect, a blade shell mould is provided having a tapered section defined in the surface profile of the mould. In an alternative aspect, a tapered section is defined using a mould insert 
         [0047]    In an additional or alternative aspect, said steps of providing first and second blade shells may comprise forming a tapered section along at least a portion of an edge of a blade shell by performing a machining operation on said blade shell. Said machining operation may comprise grinding, cutting, etching, polishing, etc.
       There is further provided a wind turbine blade comprising:   a first blade shell, and   a second blade shell,   wherein for at least a portion of a boundary between said first and second blade shells, said first and second blade shell portions are joined by an overlamination.       
 
         [0052]    The overlamination is applied to external surfaces of said first and second blade shells. 
         [0053]    It will be understood that said at least a portion of a boundary between said first and second blade shells is provided substantially without structural adhesive. 
         [0054]    Preferably, said first and second blade shell portions are joined solely by an overlamination. 
         [0055]    Preferably, there is provided a wind turbine blade comprising:
       a first blade shell having a first tapered section along at least a portion of an edge of said first shell; and   a second blade shell having a second tapered section along at least a portion of an edge of said second shell,   wherein said first and second blade shells are arranged such that said first tapered section abuts said second tapered section to form a recess channel located along a boundary between the edges of said first and second blade shells, and   wherein the wind turbine blade further comprises a laminate located in said recess channel, said laminate joining said first and second blade shells.       
 
         [0060]    Preferably, said laminate is formed from substantially the same material as said first and second blade shells. 
         [0061]    Preferably, said laminate comprises at least one layer of fibre material and a cured resin. 
         [0062]    Preferably, the wind turbine blade comprises a recess channel extending along at least a portion of the leading edge of said wind turbine blade, preferably along substantially all of the leading edge, wherein a laminate is located in the leading edge recess channel and joins said first and second blade shells along said at least a portion of the leading edge of said wind turbine blade. 
         [0063]    Additionally or alternatively, the wind turbine blade comprises a recess channel extending along at least a portion of the trailing edge of the wind turbine blade, wherein a laminate located in the trailing edge recess channel joins and said first and second blade shells along said at least a portion of the trailing edge of said wind turbine blade. 
         [0064]    Preferably, said trailing edge recess channel extends along the trailing edge in the root region of the wind turbine blade, wherein the laminate joins said first and second blade shells along the trailing edge in the root region of the wind turbine blade. 
         [0065]    There is further provided a wind turbine comprising at least one wind turbine blade as described above. 
     
    
     
       DESCRIPTION OF THE INVENTION 
         [0066]    An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: 
           [0067]      FIG. 1  shows a wind turbine; 
           [0068]      FIG. 2  shows a schematic view of a wind turbine blade according to the invention; 
           [0069]      FIG. 3  shows a schematic view of an airfoil profile of the blade of  FIG. 2 ; 
           [0070]      FIG. 4  shows a schematic view of the wind turbine blade of  FIG. 2 , seen from above and from the side; 
           [0071]      FIG. 5  illustrates an enlarged cross-sectional view of a leading edge adhesive bond for a prior art wind turbine blade; and 
           [0072]      FIG. 6  illustrates an enlarged cross-sectional view of a bond for a wind turbine blade according to the invention, along a wind turbine blade leading edge. 
       
    
    
       [0073]    It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings. 
         [0074]      FIG. 1  illustrates a conventional modern upwind wind turbine  2  according to the so-called “Danish concept” with a tower  4 , a nacelle  6  and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub  8  and three blades  10  extending radially from the hub  8 , each having a blade root  16  nearest the hub and a blade tip  14  furthest from the hub  8 . The rotor has a radius denoted R. 
         [0075]      FIG. 2  shows a schematic view of a wind turbine blade  10 . The wind turbine blade  10  has the shape of a conventional wind turbine blade and comprises a root region  30  closest to the hub, a profiled or an airfoil region  34  furthest away from the hub and a transition region  32  between the root region  30  and the airfoil region  34 . The blade  10  comprises a leading edge  18  facing the direction of rotation of the blade  10 , when the blade is mounted on the hub, and a trailing edge  20  facing the opposite direction of the leading edge  18 . 
         [0076]    The airfoil region  34  (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region  30  due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade  10  to the hub. The diameter (or the chord) of the root region  30  is typically constant along the entire root area  30 . The transition region  32  has a transitional profile  42  gradually changing from the circular or elliptical shape  40  of the root region  30  to the airfoil profile  50  of the airfoil region  34 . The chord length of the transition region  32  typically increases substantially linearly with increasing distance r from the hub. 
         [0077]    The airfoil region  34  has an airfoil profile  50  with a chord extending between the leading edge  18  and the trailing edge  20  of the blade  10 . The width of the chord decreases with increasing distance r from the hub. 
         [0078]    It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub. 
         [0079]      FIG. 3  shows a schematic view of an airfoil profile  50  of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile  50  has a pressure side  52  and a suction side  54 , which during use—i.e. during rotation of the rotor—normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil  50  has a chord  60  with a chord length c extending between a leading edge  56  and a trailing edge  58  of the blade. The airfoil  50  has a thickness t, which is defined as the distance between the pressure side  52  and the suction side  54 . The thickness t of the airfoil varies along the chord  60 . The deviation from a symmetrical profile is given by a camber line  62 , which is a median line through the airfoil profile  50 . The median line can be found by drawing inscribed circles from the leading edge  56  to the trailing edge  58 . The median line follows the centres of these inscribed circles and the deviation or distance from the chord  60  is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord  60  and the suction side  54  and pressure side  52 , respectively. 
         [0080]    Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d f  of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line  62 , the position d t  of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d p  of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber. 
         [0081]      FIG. 4  shows some other geometric parameters of the blade. The blade has a total blade length L. As shown in  FIG. 2 , the root end is located at position r=0, and the tip end located at r=L. The shoulder  40  of the blade is located at a position r=L w , and has a shoulder width W, which equals the chord length at the shoulder  40 . The diameter of the root is defined as D. Further, the blade is provided with a prebend, which is defined as Δy, which corresponds to the out of plane deflection from a pitch axis  22  of the blade. 
         [0082]    The wind turbine blade  10  generally comprises a shell made of fibre-reinforced polymer, and is typically made as a pressure side or upwind shell part  24  and a suction side or downwind shell part  26  that are attached together along bond lines  28  extending along the trailing edge  20  and the leading edge  18  of the blade  10 . Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of 30 or 40 metres in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading. 
         [0083]    With reference to bond lines  28 , an enlarged view of a leading edge bond line according to an aspect of the invention is illustrated in  FIG. 6 . In this embodiment, the leading edges of the blade shells  24 , 26  are joined using an overlamination, which eliminates the need for a structural adhesive  100  between the blade shells  24 , 26 . 
         [0084]    In this case, it will be understood that the bond line  28  refers to the general area of an overlamination joining the upwind and downwind shells  24 , 26 . 
         [0085]    In  FIG. 6 , the pressure side or upwind shell part  24  and the suction side or downwind shell part  26  meet at the leading edge  18  of the blade  10 , in the area of a bond line  28 . The shells  24 , 26  comprise layers or fibre material  70  suspended in a cured resin, which may be applied around portions of a core material  72 , e.g. balsa wood, foam, etc. The bodies of the shells  24 , 26  are tapered in thickness towards the leading edge  18  ends of the shells  24 , 26 , at least along a portion of the leading edge  18 . 
         [0086]    The shells  24 , 26  may be integrally formed with such a tapering of the leading edge  18  ends of the shells  24 , 26 , e.g. through the use of suitably-shaped blade shell moulds (not shown) having shell profile surfaces, and/or mould inserts, incorporating a leading edge tapering profile. Additionally or alternatively, the tapering of the leading edge  18  ends of the shells  24 , 26  may be fully or partially formed through a post-moulding process, e.g. a cutting, grinding or polishing of the leading edge  18  ends of the shells  24 , 26  after said shells  24 , 26  have been removed from a blade shell mould (not shown). 
         [0087]    Once the shells  24 , 26  are provided with tapered ends, the shells  24 , 26  are brought together and closed to form a wind turbine blade  10 , such that the leading edge end of the upwind shell  24  abuts the leading edge end of the downwind shell  26 , without the presence of a structural adhesive between the shell ends. Accordingly, the tapered leading edge  18  ends of the shells  24 , 26  come together to form a recess channel  74  along a portion of the leading edge  18  of the blade  10 . 
         [0088]    An overlamination  76  is applied in the recess channel  74 , the overlamination  76  extending between the tapered portions of the upwind and downwind shells  24 , 26  and acting to join the shell leading edges together. In the embodiment of  FIG. 6 , the overlamination  76  is selected such that the overlamination  76  substantially fills the recess channel  74  and is flush with the adjacent surfaces of the wind turbine blade shells  24 , 26 , thereby preserving the aerodynamic profile of the leading edge  18  of the blade  10 . 
         [0089]    The overlamination  76  preferably comprises a plurality of layers of fibre material applied to the leading edge  18  of the blade  10 , the layers of fibre material provided in a resin which bonds the layers of fibre material together, while also bonding to the tapered portions of the upwind and downwind shells  24 , 26 . 
         [0090]    The overlamination  76  may be provided in the form of separate layers which are subsequently infused with a resin, and/or the overlamination  76  may be provided as a bundle or a stack of layers may be applied as a pre-preg, which may be at least partially infused with an uncured resin, where the pre-preg may be infused with additional resin to bond the overlamination  76  to shells  24 , 26 , wherein the resin is subsequently cured. 
         [0091]    Preferably, the overlamination  76  is formed from the same material as the body of the wind turbine blade shells  24 , 26 , e.g. as a glass- and/or carbon-fibre material infused with a suitable resin, e.g. polyester, vinyl ester, epoxy, etc. 
         [0092]    The overlamination  76  allows for the blade shells  24 , 26  to be joined without the use of a relatively heavy and expensive structural adhesive. Furthermore, as the overlamination  76  may be formed from the same material as the body of the blade shells  24 , 26 , accordingly the fault resistance of the leading edge join between the shells  24 , 26  is increased, as the differences in stiffness levels and other material properties between the shells and the joining material are substantially eliminated. 
         [0093]    Preferably, the overlamination  76  can be used in joins between substantially circular-profile portions of the airfoil profile of the wind turbine blade  10 , e.g. along the leading edge  18  of the blade  10 , and/or along the trailing edge  20  near the root and  16  of the blade  10 . It will be understood that the joining method of the invention may be combined with other joining techniques in other areas of the blade, e.g. using structural adhesive between the blade shells. 
         [0094]    The step of infusing the overlamination  76  may comprise applying a resin to the surface of a fibre material applied in the recess channel  74 , e.g. using a roller application, vacuum infusion, etc. Alternatively, the step of applying a laminate may comprise positioning a precast laminate piece in said recess channel  76 , and attaching the laminate piece in said recess channel with a cured resin. 
         [0095]    The embodiment of  FIG. 6  shows the leading edge  18  ends of the blade shells  24 , 26  ending in a tapered section. It will be understood that the tapering of the blade shells  24 , 26  at the leading edge  18  may comprise a full or partial tapering of the thickness of the blade shell body at said ends. In one aspect, the tapering may extend through the body of the blade shells  24 , 26  to a single layer of fibre material. Additionally or alternatively, the leading edge  18  ends of the shells  24 , 26  may comprise a stepped tapering or a partial tapering through the thickness of the shell body. 
         [0096]    Preferably, the tapering is performed to have a substantially constant cross-section along a portion of the longitudinal length of the blade shells  24 , 26 . Additionally or alternatively, the tapering may be performed in a serrated or zig-zag manner along the longitudinal direction of the blade shells  24 , 26 . Additionally or alternatively, the tapering may be performed in a undulating or wave-like manner along the longitudinal direction of the blade shells  24 , 26 . 
         [0097]    The use of a overlamination to join blade shell components allows for the manufacture of a wind turbine blade having reduced use of structural adhesive. 
         [0098]    Additionally, the use of overlaminations formed from substantially the same material as the body of the blade shell components themselves results in reduced risk of structural faults along the bond line between components, due to substantially identical stiffness levels and material properties between the shell components and the joining material. 
         [0099]    The invention is not limited to the embodiment described herein, and may be modified or adapted without departing from the scope of the present invention.