Abstract:
A wind turbine blade transversely divided in an inboard module ( 13 ) and an outboard module ( 33 ) provided on their end sections with connecting means, comprising, respectively, an inboard spar ( 15 ), an inboard upper shell ( 17 ) and an inboard lower shell ( 19 ); an outboard spar ( 35 ), an outboard upper shell ( 37 ) and an outboard lower shell ( 39 ); and arranged so that the aerodynamic profile of said inboard and outboard modules ( 13, 33 ) is defined by said upper and lower shells ( 17, 19; 37, 39 ), in which the inboard spar ( 15 ) is composed of two cap prefabricated panels ( 21, 23 ) and two web prefabricated panels ( 25, 27 ), and the outboard spar ( 35 ) is composed of first and second prefabricated panels ( 41, 43 ) integrating its caps ( 45, 47 ) and webs ( 49, 51 ). The invention also refers to a method of fabricating said wind turbine blade.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to wind turbine blades and particularly to multi-panel blades for facilitating its manufacture and transportation. 
       BACKGROUND 
       [0002]    Wind turbines include a rotor that supports a number of blades extending radially therefrom for capturing the kinetic energy of the wind and causing a rotational motion of a driving train coupled to an electric generator for producing electrical power. 
         [0003]    The amount of energy produced by wind turbines is dependent on the rotor blade sweeping surface that receives the action from the wind and consequently increasing the length of the blades leads normally to an increase of the power output of the wind turbine. 
         [0004]    However, the size of the blades for land-based wind farms is presently limited to some extent by transportation and infrastructure requirements. In particular, the size of bridges and tunnels limit the size of the blade maximum chord. 
         [0005]    To solve the transportation problems posed particularly by lengthy blades the prior art teaches the division of the blade in two or more longitudinal sections provided with joining means, so that each section may be manufactured individually and all sections may be assembled at the wind turbine site. Examples of this prior art are the following. 
         [0006]    DE 3 109 566 discloses a wind turbine blade subdivided into at least two longitudinal sections which are held together by an expanding bolt. 
         [0007]    U.S. Pat. No. 4,389,182 discloses a wind turbine blade subdivided into several longitudinal sections that are interconnected by tensioning members such as steel cables extending through the blade sections. 
         [0008]    EP 1 244 873 A1 discloses a wind turbine blade subdivided into longitudinal sections that are joined by means of a butt joint comprising a number of clips arranged along the joint, having the respective ends fixed to the sections to be joined, and bolts for fixing said clips. 
         [0009]    WO 2005/100781, WO 2006/103307, WO 2007/051879 in the name of the applicant, disclose wind turbine blades subdivided into longitudinal sections having improved joining means. 
         [0010]    There is also prior art teaching the division of the blade in several transversal sections in addition or independently to the division in longitudinal sections. Examples of this prior are the following. 
         [0011]    EP 1 184 566 A1 discloses a wind turbine blade which is formed by assembling one, two or more longitudinal sections, each of which comprises a core formed by a longitudinal carbon-fibre tube on which a series of carbon fibre or fiberglass cross ribs are mounted and a cover formed by fiberglass or carbon-fibre joined to said ribs. 
         [0012]    WO 01/46582 A2 discloses a wind turbine blade having a plurality of segmented elements attached to a load transmitting box spar and separated by elastic joins which enable the segments to move in relation to one another in order to minimise the tensile stress in the region of the blade in which the segments are located. 
         [0013]    EP 1 965 074 in the name of the applicant discloses a wind turbine blade composed of two cap prefabricated panels and two web prefabricated panels placed side by side in a box shape and at least two shell longitudinal sections forming, respectively, the leading edge and the trailing edge of the corresponding blade section that are placed adjacently to a central spar section, the aerodynamic profile of the blade being defined by said cap panels and said shell panels. 
         [0014]    The current trend in the wind industry to big rotor blades demands new rotor blades designs suitable for complying with the transportation requirements and with the quality manufacturing requirements involved by blades that can reach lengths of 100 m and maximum chords of 8 m. 
         [0015]    The present invention is intended to satisfy said demand. 
       SUMMARY OF THE INVENTION 
       [0016]    An object of the present invention is to provide a wind turbine blade configuration allowing an efficient manufacturing of big wind turbine blades divided in two modules. 
         [0017]    Another object of the present invention is to provide a wind turbine blade configuration allowing an optimized design of big wind turbine blades divided in two modules. 
         [0018]    In one aspect, these and other objects of the present invention are met by providing a wind turbine blade transversely divided in an inboard module and an outboard module provided on their end sections with connecting means, comprising, respectively, an inboard spar, an inboard upper shell and an inboard lower shell; an outboard spar, an outboard upper shell and an outboard lower shell; and arranged so that the aerodynamic profile of said inboard and outboard modules is defined by said upper and lower shells, in which the inboard spar is composed of two cap prefabricated panels and two web prefabricated panels and the outboard spar is composed of first and second prefabricated panels integrating its caps and webs. 
         [0019]    In embodiments of the present invention said two cap prefabricated panels of the inboard spar are composed of main cap parts and root joint parts, the root joint parts being extended until the beginning of the web prefabricated panels and the main cap parts having an initial section coincident with a sector of the root joint parts so that both parts can be joined in said sector. Therefore in the inboard module, where there are significant geometrical and structural differences between the root section and the rest of the spar, the caps are divided in two components in a manner that facilitates its manufacturing without compromising its structural behaviour. 
         [0020]    In embodiments of the present invention, the inboard spar is composed of a first prefabricated panel integrating the upper cap and the webs and of the lower cap as the second prefabricated panel. Therefore the spar of the inboard module is assembled with two panels facilitating its manufacturing. 
         [0021]    In embodiments of the present invention, the outboard spar is composed of a first prefabricated panel integrating the upper cap and the leading edge web and a second prefabricated panel integrating the lower cap and the trailing edge web. Therefore the spar of the outboard module, that is smaller than the spar of the inboard module, is assembled with two panels of similar shape allowing an optimization of its manufacturing. 
         [0022]    In embodiments of the present invention, the prefabricated panels used for assembling the inboard and outboard spars comprise joint flanges that are arranged for conforming joining areas of said prefabricated panels on the outer edges of the inboard and outboard spars. In particular said joint flanges are arranged as parallel flanges by means of, respectively, longitudinal and angular planar extensions of the caps and webs of said prefabricated panels. This joint arrangement facilitates the assembly of the blades. 
         [0023]    In embodiments of the present invention the material of said inboard spar main cap parts comprise glass fibre reinforced plastic or carbon fibre reinforced plastic and balsa wood or PVC foam cores. The laminate may be different along the blade such a solid glass fibre reinforced plastic or carbon fibre reinforced plastic laminate at the joining sector with the root joint parts, then a sandwich structure including skins of glass fibre reinforced plastic or carbon fibre reinforced plastic and a balsa wood or a PVC foam core and finally the core is removed and the metallic inserts that are used to assemble both blade modules are integrated in the laminate. Therefore the laminate is adapted to the cap stability needs. 
         [0024]    In embodiments of the present invention the material of said two root joint prefabricated parts comprise glass fibre reinforced plastic or carbon fibre reinforced plastic. It is a solid laminate and the metallic inserts that are used to assemble the blade to the hub are integrated in it. 
         [0025]    In embodiments of the present invention, the material of said inboard spar web panels comprise glass fibre reinforced plastic and PVC foam cores. The laminate has a sandwich structure including biaxial glass fibre reinforced plastic skins and a PVC foam core that increases the buckling strength. 
         [0026]    In embodiments of the present invention, the material of said outboard spar first and second panels comprise glass fibre reinforced plastic or carbon fibre reinforced plastic and balsa wood or PVC foam cores. The laminate may be different along the blade such a solid glass fibre reinforced plastic or carbon fibre reinforced plastic laminate at the intermediate joint in which are integrated the metallic inserts used to assemble both blade modules, then a sandwich structure including skins of glass fibre reinforced plastic or carbon fibre reinforced plastic and a balsa wood or a PVC foam core and finally a solid glass fibre reinforced plastic or a carbon fibre reinforced plastic laminate at the tip of the spar. Therefore the laminate is adapted to the cap stability needs. 
         [0027]    In another aspect the above-mentioned objects are met by a method of fabricating a wind turbine blade with the above-mentioned features comprising steps of:
       fabricating separately said main cap parts, said root joint parts, said two web prefabricated panels, said first and second prefabricated panels, said inboard upper and lower shells and said outboard upper and lower shells;   assembling said two cap prefabricated panels cocuring said main cap parts and said root joint parts;   assembling said inboard spar bonding the joint flanges of said two cap prefabricated panels and said two web prefabricated panels by means of an adhesive;   assembling said outboard spar bonding the joint flanges of said first and second prefabricated panels by means of an adhesive;   assembling said inboard and outboard modules bonding said shells to said inboard and outboard spars by means of an adhesive;   connecting said inboard and outboard modules.       
 
         [0034]    Other features and advantages of the present invention will be understood from the following detailed description in relation with the enclosed drawings. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0035]      FIG. 1   a  shows in schematic perspective views the main components of the inboard module of a wind turbine blade according to this invention. 
           [0036]      FIG. 1   b  shows in schematic perspective view the main components of the spar of the inboard module of a wind turbine blade according to this invention. 
           [0037]      FIG. 2  shows in schematic perspective view the components of the upper and lower caps of the spar of the inboard module of a wind turbine blade according to this invention. 
           [0038]      FIG. 3   a  shows in schematic perspective views the main components of the outboard module of a wind turbine blade according to an embodiment of this invention. 
           [0039]      FIG. 3   b  shows in schematic perspective view the main components of the spar of the outboard module of a wind turbine blade according to an embodiment of this invention. 
           [0040]      FIG. 4   a  shows in schematic perspective views the main components of the outboard module of a wind turbine blade according to another embodiment of this invention. 
           [0041]      FIG. 4   b  shows in schematic perspective view the main components of the spar of the outboard module of a wind turbine blade according to another embodiment of this invention. 
           [0042]      FIG. 5  is a cross-sectional view of the inboard module of a wind turbine blade according to this invention. 
           [0043]      FIG. 6  is a cross-sectional view of an embodiment of the outboard module of a wind turbine blade according to this invention. 
           [0044]      FIG. 7  is a cross-sectional view of another embodiment of the outboard module of a wind turbine blade according to this invention. 
           [0045]      FIG. 8  is an enlarged view of a joining area of two prefabricated panels belonging to a wind turbine blade according to this invention. 
       
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0046]    This invention provides a multi-panel wind turbine blade structure for optimized quality and transportation. The invention involves splitting the whole blade into an outboard and an inboard modules and each of them in several parts for an assembly on site in order to achieve the following objectives. 
         [0047]    A first objective is to allow the transport of big blades to the field and the assembly on factory to optimize the manufacturing process. 
         [0048]    A second objective is to allow the selection of different materials and/or manufacturing processes and/or structural configurations for the different parts of the blade, particularly for an inboard module and an outboard module. As in any structure, the requirements for the different parts are very different: the inboard module has bigger transversal sections than the outboard module; in both modules the spar is the main load carrying path while the shells are the aerodynamic performance responsible parts but, structurally, less important; within the spars, the caps support higher loads than the webs. A multi-panel blade allows the use of different materials and/or manufacturing processes and/or structural configurations to each part according to its requirements involving an optimization of the blade cost. 
         [0049]    A third objective is to improve the manufacturing process of the blades particularly is aspects such the quality control, the productivity, the logistic and the plants size. 
         [0050]    In single-part blades the quality assurance is strongly conditioned by its size. In multi-panel blades the quality assurance and potential repairs, if needed, are easier and consequently the non-conformity costs can be reduced. Additionally, the statistic quality control is also improved and a better manufacturing process evolution is possible. 
         [0051]    The lead time and tack time of single-part blades manufacturing is high. These times are increasing with the increasing size. Multi-panel blades allow manufacturing the different parts in parallel and the final manufacturing stage of the blade becomes a purely assembly stage. 
         [0052]    Multi-panel blades allow the blade manufacturer to organize the lay-outs according to different criteria and subcontracting the manufacturing of some of these parts, if necessary. 
         [0053]    As illustrated in  FIGS. 1   a,    1   b,    2  and  5  the inboard module  13  of the blade according to this invention is formed by an spar  15  and upper and lower shells  17 ,  19 . 
         [0054]    The spar  15  is formed by an upper cap  21 , a lower cap  23 , a leading edge web  25  and a trailing edge web  27 . The upper and lower caps  21 ,  23  are formed by main cap parts  21 ′,  23 ′ and root joint parts  21 ″,  23 ″. All those spar single components are prefabricated and then assembled using bonding means such as a polyurethane adhesive in specific bonding areas  65  configured by flanges  61 ,  63  of said components with the exception of the assembly of the main cap parts  21 ′,  23 ′ and the root joint parts  21 ″,  23 ″ to form the upper and lower caps  21 ,  23  which is made cocuring said parts for assuring its structural behaviour. 
         [0055]    In this case the main reason for the division of the upper and lower caps  21 ,  23  in said main cap parts  21 ′,  23 ′ and said root joint parts  21 ″,  23 ″ parts is due to, as it can be deduced from  FIG. 2 , the big dimensional differences existing between the root section and the rest of the spar in the inboard module  13 . 
         [0056]    The root joint parts  21 ″,  23 ″ extend from the beginning of the blade to the beginning of the web prefabricated panels  25 ,  27  and the main cap parts  21 ′,  23 ′ are configured with an initial section  22 ′,  24 ′ coincident with a sector of the root joint parts  21 ″,  23 ″ so that both parts  21 ′,  21 ″;  23 ′,  23 ″ can be joined in said coincident sector. Then, the basic non-coincident area between the root joint parts  21 ″,  23 ″ and the main cap parts  21 ′,  23 ′ is the first section of the root joint parts  21 ″,  23 ″ having a full semicircular shape where the metallic inserts that are used to assemble the blade to the hub shall be integrated. 
         [0057]      FIG. 8  shows an enlarged view of the bonding area  65  between the upper cap  21  and the trailing edge web  27  using an adhesive layer  67 . The flange  61  is a longitudinal extension of the upper cap  21  and the flange  63  is an angular extension of the trailing edge web  27  and both flanges  61 ,  63  are configured as parallel planar segments. 
         [0058]    The root joint parts  21 ″,  23 ″ are manufactured in glass fibre reinforced plastic or carbon fibre reinforced plastic over female moulds. The metallic inserts that are used to assemble the blade to the hub are integrated in these parts. 
         [0059]    The upper and lower main cap parts  21 ′,  23 ′ are manufactured in glass fibre reinforced plastic or carbon fibre reinforced plastic and balsa wood or PVC foam cores over female moulds. The metallic inserts that are used to assemble both blade modules are integrated in these parts. 
         [0060]    The leading edge web  25  and the trailing edge web  27  are manufactured in glass fibre reinforced plastic and PVC foam cores over female moulds. 
         [0061]    The shells  17 ,  19  are manufactured in glass fibre reinforced plastic and PVC foam cores over female moulds. 
         [0062]    The shells  17 ,  19  are bonded together at leading and trailing edge and to the spar caps  21 ,  23  by means of a polyurethane adhesive. 
         [0063]    As illustrated in  FIGS. 3   a,    3   b  and  6  the outboard module  33  of the blade according to an embodiment of this invention is formed by an spar  35  and upper and lower shells  37 ,  39 . 
         [0064]    The spar  35  is formed by a first panel  41  integrating the upper cap  45  and the webs  49 ,  51  and by the lower cap  47  as the second panel  43 . These panels are prefabricated and then assembled using bonding means such as a polyurethane adhesive in the specific bonding areas  65  configured by flanges  61 ,  63  of said panels in a similar manner to that described above in reference to  FIG. 8 . 
         [0065]    The first panel  41  is manufactured in carbon fibre reinforced plastic or glass fibre reinforced plastic and balsa wood or foam cores over female moulds. The metallic inserts that are used to assemble both blade modules are integrated in this part. 
         [0066]    The second panel  43  is manufactured in carbon fibre reinforced plastic or glass fibre reinforced plastic and balsa wood or PVC foam cores over female moulds. The metallic inserts that are used to assemble both blade modules are integrated in this part. 
         [0067]    The shells  37 ,  39  are manufactured in glass fibre reinforced plastic and PVC foam cores over female moulds. 
         [0068]    The shells  37 ,  39  are bonded together at leading and trailing edge and to the spar caps  45 ,  47  by means of a polyurethane adhesive. 
         [0069]    In another embodiment of the outboard module  33  shown in  FIGS. 4   a,    4   b  and  7 , the spar  35  is formed by a first panel  41  integrating the upper cap  45  and the leading edge web  49  and by a second panel  43  integrating the lower cap  47  and the trailing edge web  51 . These panels are prefabricated and then assembled using bonding means such as a polyurethane adhesive in specific bonding areas  65  configured by flanges  61 ,  63  of said panels in a similar manner to that described above in reference to  FIG. 8 . 
         [0070]    The first panel  41  is manufactured in carbon fibre reinforced plastic or glass fibre reinforced plastic and balsa wood or PVC foam cores over female moulds. The metallic inserts that are used to assemble both blade modules are integrated in this part. 
         [0071]    The second panel  43  is manufactured in carbon fibre reinforced plastic or glass fibre reinforced plastic and balsa wood or PVC foam cores over female moulds. The metallic inserts that are used to assemble both blade modules are integrated in this part. 
         [0072]    The shells  37 ,  39  are manufactured in glass fibre reinforced plastic and PVC foam cores over female moulds. 
         [0073]    The shells  37 ,  39  are bonded together at leading and trailing edge and to the spar caps  45 ,  47  by means of a polyurethane adhesive. 
         [0074]    An important feature of the present invention is that the materials, structural configuration and manufacturing process of each panel in the inboard and outboard modules of the blade are different, allowing an optimization of the blade design and/or manufacturing. 
         [0075]    Although the present invention has been fully described in connection with preferred embodiments, it is evident that modifications may be introduced within the scope thereof, not considering this as limited by these embodiments, but by the contents of the following claims.