Abstract:
A method and system for assembling large wind turbine blades that includes providing a plurality of wind turbine blade segments. An adhesive distribution arrangement is disposed on a surface of at least one of the plurality of the wind turbine blade segments. The adhesive distribution arrangement includes a bonding grid having a plurality of adhesive distribution openings. The wind turbine blade segments are directed together and sufficient adhesive is provided to the bonding grid to substantially fill an area between the wind turbine segments. The adhesive is then cured to form a bonded joint, the bonding grid being incorporated into the bonded joint. A bonding grid for use with the method and system and a segmented wind turbine blade are also disclosed.

Description:
FIELD OF THE INVENTION 
     The present invention is directed to elongated airfoils for use with wind turbines and methods for fabricating elongated airfoils for wind turbines. In particular, the present invention is directed to segmented wind turbine blades and methods for making large, elongated wind turbine blades. 
     BACKGROUND OF THE INVENTION 
     Recently, wind turbines have received increased attention as environmentally safe and relatively inexpensive alternative energy sources. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient. 
     Generally, a wind turbine includes a rotor having multiple wind turbine blades. The wind turbine blades are elongated airfoils configured to provide rotational forces in response to wind. The rotor is mounted to a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in length). In addition, the wind turbines are typically mounted on towers that are at least 60 meters in height. 
     Wind turbine blades may be very large and may require fabrication in two or more pieces. Segmented components provide ease of transportation but require joining of the segments together by bonding in order to fabricate the full turbine blade. The components may be joined together by adhesive or interlocking structure, but conventional joining techniques fail to provide sufficient bonding strength or sufficient durability between sections during wind turbine operation. In addition, known interlocking systems and/or bonding systems require heavy and/or expensive components that result in undesirable weight in the assembled wind turbine blade. 
     Further, due to the large size of the components and the necessity for a strong bond, good distribution of adhesive is required. Currently there is no method of system that provides sufficiently uniform distribution of adhesive to join wind turbine blade segments. 
     What is needed is an improved method and system for fabricating large segmented wind turbine blades that includes durable and strong bonding joints that do not suffer from the drawbacks of known systems. 
     SUMMARY OF THE INVENTION 
     A first aspect of the present invention includes a method and system for assembling large wind turbine blades that includes providing a plurality of wind turbine blade segments. An adhesive distribution arrangement is disposed on a surface of at least one of the plurality of the wind turbine blade segments. The adhesive distribution arrangement includes a bonding grid having a plurality of adhesive distribution openings. The wind turbine blade segments are directed together and sufficient adhesive is provided to the bonding grid to substantially fill an area between the wind turbine segments. The adhesive is then cured to form a bonded joint, the bonding grid being incorporated into the bonded joint. 
     Another aspect of the present invention includes an adhesive distribution arrangement for assembling large wind turbine blades. The arrangement includes a bonding grid having a port for receiving adhesive and a frame, the bonding grid being configured to deliver adhesive to a plurality of adhesive distribution openings. The distribution openings are configured to distribute adhesive onto one or more surfaces of a wind turbine blade segment. 
     Still another aspect of the present invention includes a segmented wind turbine blade. The segmented wind turbine blade includes a first wind turbine blade segment and a second wind turbine blade segment. The first wind turbine blade segment is joined to the second wind turbine blade segment. A bonding grid is disposed between adjacent surfaces of the first wind turbine blade segment and the second wind turbine blade segment. The bonding grid includes a frame having a plurality of cells disposed therein, where the cells are substantially filled with cured adhesive. The distribution of adhesive is substantially uniform across the adjacent surfaces. 
     One advantage of an embodiment is that the bonding grid provides controlled temperature and distribution of adhesive, and provides a quality control to validate the filling of the cavity. 
     Another advantage is that the bonding grid provides a means of controlling the space between joined components to provide strong and uniform junctions between segments. 
     Still another advantage is that the adhesive is distributed substantially uniformly across the bonding grid allowing for the formation of a strong uniform joint. 
     Still another advantage is that the segmented wind turbine blades may be shipped at a substantially reduced cost and easily assembled on-site. 
     Still another advantage is that the method and system of the disclosure enables bonding in a wide variety of environments. 
     Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a side elevational view of a wind turbine according to an embodiment of the present disclosure. 
         FIG. 2  shows a top perspective view of a wind turbine blade according to an embodiment of the present disclosure. 
         FIG. 3  shows a cross-sectional view of a wind turbine blade taken in direction  3 - 3  of  FIG. 2 . 
         FIG. 4  shows a top perspective view of wind turbine blade segments configured to be joined together according to an embodiment of the present disclosure. 
         FIG. 5  shows a cross-sectional view of two wind turbine blade segments being directed together according to an embodiment of the present disclosure. 
         FIG. 6  shows a top view of a bonding grid according to an embodiment of the present disclosure. 
         FIG. 7  shows a cross-sectional view taken in direction  7 - 7  of  FIG. 6 . 
         FIG. 8  shows a cross-sectional view taken in direction  8 - 8  of  FIG. 6 . 
         FIG. 9  shows a cross-sectional view of two wind turbine blade segments being directed together with a bonding grid according to an embodiment of the present disclosure. 
         FIG. 10  shows a top view of a wind turbine segment having a bonding grid disposed thereon according to an embodiment of the present disclosure. 
         FIG. 11  shows a top perspective view of wind turbine blade segments configured to be joined together with a bonding grid disposed on surfaces of one wind turbine blade segment according to an embodiment of the present disclosure. 
         FIG. 12  shows a top perspective view of wind turbine blade segments configured to be joined together with a bonding grid disposed on surfaces of two wind turbine blade segments according to an embodiment of the present disclosure. 
     
    
    
     Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a wind turbine  100  having a nacelle  102  housing a generator (not shown in  FIG. 1 ). Nacelle  102  is a housing mounted atop a tower  104 , only a portion of which is shown in  FIG. 1 . The height of tower  104  is selected based upon factors and conditions known in the art, and may extend to heights up to 60 meters or more. The wind turbine  100  may be installed on any terrain providing access to areas having desirable wind conditions. The terrain may vary greatly and may include, but is not limited to, mountainous terrain or off-shore locations. Wind turbine  100  also comprises a rotor  106  that includes one or more rotor blades  108  attached to a rotating hub  110 . Although wind turbine  100  illustrated in  FIG. 1  includes three rotor blades  108 , there are no specific limits on the number of rotor blades  108  required by the present disclosure. 
       FIG. 2  illustrates a turbine blade  108  according to an embodiment of the present disclosure having a leading edge  201  and a trailing edge  203 . The turbine blade  108  includes an airfoil portion  205  extending from the tip  207  to the root  209 , which is connectable to the hub  110  of the wind turbine. The blade includes a bonded joint  211  dividing a first segment  213  of the blade  108  from the second segment  215  of the blade  108 . The first segment  213  and the second segment  215  are segments of the blade  108 , which are assembled together to provide a complete blade  108 . By segment, it is meant that the wind turbine blade  108  is divided into a plurality of components that, when assembled together, form a complete blade  108 . Although  FIG. 2  shows a blade  108  having two segments, the disclosure is not limited to two segments. For example, blade  108  may be divided into any number of segments including three or more segments. 
       FIG. 3  illustrates a cross-sectional view taken in direction  3 - 3  of the wind turbine blade  108  of  FIG. 2 .  FIG. 3  is a cross-section of a wind turbine blade taken along line  3 - 3  of  FIG. 2 . The wind turbine blade  108  includes a first shell portion  301  and a second shell portion  302 , which are each adhesively or otherwise bonded to a spar cap  304 . In other embodiments, the first shell portion  301  and the second shell portion  302  may be a unitary component. The spar cap  304  may be adhesively or otherwise bonded to the shear webs  303 . In addition, the spar cap  304  and the second shell portion  302  are adhesively or otherwise bonded. The shear web  303 , the spar cap  304  and the first and second shell portions  301 ,  302  may adhered using an adhesive or other suitable joining structure. An outer skin  305  or coating may be applied to the outer surfaces of the blade  108  to provide additional structural support and to aid in aerodynamic performance. In addition, other structures known in the art for wind turbine blade  108  design, such as stiffeners, fasteners or other hardware or structures may be present in the blade  108 . Other arrangements of shear web  303  and spar cap  304  may be provided including varied geometries of support. For example, the shear web  303  and spar cap  304  may be arranged into a box geometry, and “I” geometry, a “T” geometry or any other suitable geometry that provides internal support between the first shell portion  301  and the second shell portion  302 . Further still, the shear web  303  may be arranged as shown and described in the modular interlocking blade configuration in U.S. Patent Publication US2007/0140858 to Bakhuis et al., which is herein incorporated by reference in its entirety. 
       FIG. 4  shows a top perspective view of wind turbine blade segments configured to be joined together according to an embodiment of the present disclosure. As shown in  FIG. 4 , first segment  213  includes a protrusion  401  extending from of the airfoil portion  205 . Protrusion  401  is an extension from the airfoil portion  205  that has a geometry configured to mate a mating cavity  403  of second segment  215 . When mated, the first mating edge  405  of the first segment  213  contacts or is in close proximity to the second mating edge  407  of the second segment. Protrusion  401  and mating cavity  403  are not limited to the arrangement or geometry shown and may include features such as splines, latches, grooves or other features to assist in alignment or inconnection. In addition, the length of the protrusion  401  and the depth of the mating cavity  403  are not limited any may include any arrangement that permits the joining together of the first segment  213  and the second segment  215  through an adhesive joint. The protrusion  401  and mating cavity  403  may be separate structures from the shear web  303  or may be integrated into the shear web  303 . The construction of the protrusion  401  and mating cavity  403  may be any suitable construction for use with wind turbine blades  108  and may include composite materials or reinforcing materials, such as glass or carbon fiber reinforced composites, polyvinyl chloride (PVC) or balsa core, with epoxy or vinyl ester resin and having hardware such as bolts and alignment pins. The protrusion  401  and the mating cavity  403  preferably include a tapered geometry (see e.g.  FIG. 5 ) wherein the tapered geometry includes an angled geometry. For example, the protrusion  401  preferably includes a decreasing cross-sectional area as the protrusion  401  extends from the airfoil portion  205 . Correspondingly, the mating cavity  403  includes an increasing cross-sectional area from the interior to the second mating edge  407 . 
       FIG. 5  shows a cross-sectional view of two wind turbine blade segments  213 ,  215  being directed together according to an embodiment of the present disclosure. As shown, the protrusion  401  and the mating cavity  403  have corresponding geometries that permit mating. Although  FIG. 5  shows a tapered surface, the mating geometries are not so limited and may include any geometry that permits mating and allows the joining of the first segment  213  to the second segment  215 . Further, the tampered surface shown in  FIG. 5  is merely schematic and not limited to the taper shown. In order to join the first segment  213  to the second segment  215  a bonding grid  601  (see  FIG. 6 ) may be used. 
       FIG. 6  shows a top view of a bonding grid  601  according to an embodiment of the present disclosure. As shown, the bonding grid  601  includes a substantially rectangular frame  603  surrounding a plurality of conduits  605  arranged into a grid geometry. The one or more conduits  605  are arranged to form a plurality of cells  607 . The cells  607  define a space into which adhesive may be distributed. The size and geometry of the cells  607  are not limited to the size and geometry shown and may be selected based upon the type of adhesive used, the size of the segments being joined, or other factors that affect the uniformity of adhesive distribution. The one or more conduits  605  include opening  609  arranged along the edges of the cells  607 . The openings  609  are configured to permit the injection of adhesive into the space defined by cell  607 . As the cell  607  is open, the adhesive is permitted to contact any surfaces in contact with the frame  603  and/or the conduits  605 . For example, when the first segment  213  and second segment  215  are brought together (see e.g.,  FIG. 9 ), surfaces of each of the first segment  213  and the second segment  215  are in contact with adhesive provided to cell  607 . 
     In addition to openings  609 , the cells  607  are arranged with one or more vents  611  that permit the escape of gas or air and allow the substantially complete filling of the cells  607  with adhesive. In addition, in certain embodiments of the invention, the one or more vents  611  may be monitored to determine whether adhesive is present and the cells are substantially filled. In addition, the one or more vents  611  may be provided with vacuum or reduced pressure to assist in the distribution of the adhesive. A port  613  may be provided at any suitable location along the frame  603  in order to allow the injections of adhesive into the bonding grid  601 . The port  613  may be any structure capable of receiving adhesive and may include an extension or protrusion that permits the injection of adhesive when the first segment  213  and second segment are brought together (see e.g.,  FIG. 9 ). Adhesives suitable for use with the bonding grid includes any adhesive compositions known in the art for connecting composite materials. Suitable adhesive compositions include, but are not limited to, epoxy, polyester, methylacrylate, vinylester or other adhesive resin. Bonding grid  601  further includes an optional heating element  615  arranged along conduit  605 . 
       FIG. 7  shows a cross-sectional view of frame  603  taken in direction  7 - 7  of  FIG. 6 . As is visible in  FIG. 7 , frame  603  preferably includes a seal  701  arranged along the edges to permit containment of adhesive within cells  607 . The seal may be a foam, rubber, polymer or other compressible or deformable material suitable for providing sealing of adhesive, while being conformable to a surface of the first segment  213  and/or the second segment  215 . The frame  603  desirably provides a uniform spacing between the first segment  213  and the second segment  215  across the bonding joint  211  by maintaining a frame thickness along the length of the bonding grid  601 . The frame  603  can be made from polyvinyl chloride (PVC), acrylonitrile butadiene styrene (ABS) and/or chlorinated polyvinyl chloride (CPVC). 
       FIG. 8  shows a cross-sectional view taken in direction  8 - 8  of  FIG. 6 . As shown in  FIG. 8 , the conduit  605  includes an opening  609  arranged on edges thereof. The conduit may be a pipe, hose or other suitable structure capable of conveying adhesive. The conduit  605  is preferably a lightweight, inexpensive semi-rigid material capable of maintaining strength when incorporated into the assembled wind turbine blade  108 . For example, the conduit  605  maybe a butyl, nitrile, neoprene and/or polyvinyl chloride piping material. The openings  609  are not limited to mere openings and may be configured in any suitable manner to distribute adhesive. For example, the openings  609  may be configured to a nozzle geometry to permit efficient distribution of the resin. In addition, the conduit  605  may include an optional heating element  615  arranged along one or more edges of the conduit  605 . The heating element  615  may be utilized in low temperature ambient environments to maintain adhesive viscosity during injection or prevent freezing. In addition, heating element  615  may be utilized to assist or facilitate curing of the adhesive. The heating element  615  may be any suitable heating element. In one embodiment, the heating element  615  is an electrically resistive heater that is connectable to an exterior electrical source. The present invention is not limited to the resistive wire/heater and may include fluid heating, chemical heating or any other type of heating that provides temperature control to the adhesive. An alternate approach includes combining the frame  603  with the conduit  605  by means of adding intermittent spacing structures to the conduit. In this embodiment, the conduit  605  is flexible enough to provide the sealing function while spacers ensure a minimum gap. 
       FIG. 9  shows a cross-sectional view of two wind turbine blade segments  213 ,  215  being directed together with a bonding grid  601  according to an embodiment of the present disclosure. The bonding grid  601  is intermediate to the first segment  213  and the second segment  215 . The first segment  213  and the second segment  215  are brought into close proximity wherein the bonding grid  601  is configured to contact both the first segment  213  and second segment  215 . The bonding grid  601  is preferably disposed on a surface of one of the first segment  213  or the second segment  215  prior to bringing the segments together (see e.g.,  FIG. 10 ).  FIG. 10  shows a top view of a wind turbine segment having a bonding grid  601  disposed thereon according to an embodiment of the present disclosure. When mated, the first mating edge  405  of the first segment  213  contacts or is in close proximity to the second mating edge  407  of the second segment, forming a substantially continuous surface on the outer surface of wind turbine blade  108  (see e.g.,  FIG. 2 ). 
     In one embodiment, the first segment  213  and second segment  215  are each in a sealed contact with the bonding grid by contacting and/or compressing the seal  701  of the frame  603  of the bonding grid  601 . Adhesive is provided to the bonding grid  601  via port  613  (see e.g.,  FIG. 6 ). The adhesive is distributed to cells  607 . The adhesive is provided until the cells  607  are substantially full. Once the adhesive is sufficiently distributed, the adhesive may be cured. “Cure”, “cured”, “curing” and grammatical variations thereof as utilized herein mean that the adhesive is permitted to dry and/or cross-link sufficiently to provide an adhesive bond. Curing may be at ambient temperatures or elevated temperatures. In addition curing may be in the presence or absence of a catalyst. The bonding grid  601  is preferably incorporated into the bonding joint and remains in place subsequent to curing. 
       FIGS. 11 and 12  show alternate arrangements of the bonding grid  601  prior to joining the first segment  213  to the second segment  215 .  FIG. 11  shows a top perspective view of wind turbine blade segments  213 ,  215  configured to be joined together with a bonding grid  601  disposed on surfaces of one wind turbine blade segment  213  according to an embodiment of the present disclosure.  FIG. 12  shows a top perspective view of wind turbine blade segments  213 ,  215  configured to be joined together with a bonding grid  601  disposed on surfaces of two wind turbine blade segments according to an embodiment of the present disclosure. The present disclosure is not limited to the arrangement shown in  FIGS. 11 and 12 , but may include disposing the bonding grid on one, two, three or more surfaces of either or both of first segment  213  and/or second segment  215 . Further, the bonding grid may be initially adhered to the surface of first segment  213  and/or second segment  215  prior to joining the first segment  213  to the second segment. 
     While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.