Abstract:
A wind turbine blade ( 10 ) including: a spar cap ( 18 ) having first fibers ( 38 ) oriented parallel to a longitudinal axis ( 40 ) of the blade ( 10 ); and a fiber member ( 50, 52, 54, 56, 58 ) joined to the spar cap at a joint ( 30, 32, 34 ) and having second fibers ( 80 ). The second fibers are oriented at a first angle (α, β) relative to the longitudinal axis along portions remote ( 100, 130 ) from the joint and are curved toward the longitudinal axis in a harmonizing region ( 102, 122, 132 ) proximate the joint.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to wind turbine blade blades. In particular, the invention relates to an improved arrangement for reinforcing fibers within fiber reinforced blades. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional wind turbine blades are built of a fiber reinforced composite material. The fiber material of the fiber-reinforced composite part may include in particular mineral fibers and polymer fibers. The fiber material may thus include fiber glass, metallic fibers or carbon fibers. Moreover, the fiber material may include all kind of polymer fibers, such as aromatic polyamides, polyethylene, polyurethane or aramide fibers. The fiber material may include different types of fiber materials and may form a composite material. The blades may be formed by covering core components and spar caps with a fiber reinforced matrix composite skin.  FIG. 1  shows one type of blade  10  prior to an application of a fiber reinforced matrix. The blade  10  includes a fore section core  12  including a fore section core leading edge  14  and fore section core trailing edges  16 ; spar caps  18  including a spar cap leading edge  20  and a spar cap trailing edge  21 ; a web core  22  disposed between and separating the spar caps  18  and an aft section core  24  including an aft section core leading edge  26  and an aft section core trailing edge  28 . The fore section core trailing edges  16  abut the spar cap leading edge  20  to form fore section/spar cap joints  30 . The aft section core leading edge  26  and the spar cap trailing edge  22  form an aft section/spar cap joints  32 . The web core  22  forms web core/spar cap joints  34 . 
         [0003]    The core components may be made of wood, or foam derived from polyvinylchloride (PVC), polyethylene terephthalate (PET), polyeurethane (PU), or other suitable materials known to those of ordinary skill in the art. The spar caps may be made of fiber reinforced matrix composite material. Visible at the spar cap end  36  are spar cap fibers  38 . The spar cap fibers  38  run parallel to a long axis  40  of the spar cap  18  and are oriented this way to be in tension when the blade is flexed in directions  42  normal to a spar cap major surface  44 . The web core  22  keeps the spar caps  18  properly positioned during blade flex and the spar caps  18  and associated web skin (not shown) are also expected to transfer force from one spar cap to another during blade flex. Each blade also includes a pressure side  46  and a suction side  48 . 
         [0004]    Blade skins may be applied in various ways.  FIG. 2  shows a fore section outer airfoil skin  50 , a fore section inner airfoil skin  52 , web skins  54 , an aft section outer airfoil skin  56 , and an aft section inner airfoil skin  58 . Each skin may include one layer or more than one layer of preformed fiber mats. It can be seen in  FIG. 2  that instead of being continuous, the outer, inner, and web skins are discrete. In instances where the skins are discrete the skin may overlap underlying joints to provide sufficient structural stability. For example, the fore section outer airfoil skin  50  and core section inner airfoil skin  52  may overlap the fore section/spar cap joints  30 . An amount of overlap may be, for example, three inches or more. Similarly, the aft section outer airfoil skin  56 , and the aft section inner airfoil skin  58  may overlap the aft section/spar cap joint  32 . In the instance of the web core  22  and the spar caps  18 , where the intersecting components are not parallel, when spanning the web core/spar cap joints  34  a transitioning portion  60  of the web skins  54  may transition from an orientation of the web core  22  to an orientation of the respective spar cap  18 . For example, a first portion  62  of the web skin  54  may be at a non zero angle with respect to the spar cap  18 , while the transitioning portion  60  may transition from the non zero angle to parallel to the spar cap  18 . 
         [0005]    As shown in  FIG. 3 , in an alternate configuration the fore section outer airfoil skin  50  and the aft section outer airfoil skin  56  may form a continuous outer airfoil skin  70 . Similarly, the fore section inner airfoil skin  52  and a fore web skin  72  may form a continuous combined fore section inner skin  74 . Likewise, the aft section inner airfoil skin  58  and a web aft skin  76  may form a continuous combined aft inner skin  78 . In such instances it is evident that every joint will be adequately spanned by a covering skin. 
         [0006]      FIG. 4  is a view of either the pressure side  46  or a suction side  48  of a blade  10  having discrete airfoil skin sections as disclosed in  FIG. 2 . The fore section outer airfoil skin  50  and aft section inner airfoil skin  58  typically include outer airfoil skin fibers  80  arranged in a prior art biax pattern, such as a criss cross pattern. The fore section outer airfoil skin  50  and aft section inner airfoil skin  58  may overlap the spar cap  18  to form outer skin/spar cap overlaps  82 . These overlaps may be in the range of at least 2-3″ long. It can be seen that the spar cap fibers  38  that run parallel to the spar cap long axis  40  form angles α and β with the spar cap fibers  38 .  FIG. 5  is a view of either the pressure side  46  or a suction side  48  of a blade  10  having a prior art continuous airfoil skin sections as disclosed in  FIG. 3 . The continuous outer airfoil skin  70  and the associated outer airfoil skin fibers  80  completely cover the spar cap  18 , yet still form angles α and β with the spar cap fibers  38 . 
         [0007]      FIG. 6  is a view of a web core  22  and spar cap  18 , where the web skins  54  are discrete, as disclosed in  FIG. 2 . A fillet  90  can be seen where the web core  22  meets the spar cap  18 . The web skin  54  includes a first portion  92  that forms an angle with the spar cap  18 , and a prior art transitioning portion  94  that transitions the web skin  54  from the first portion  92 , across the fillet  90 , to being parallel to the spar cap  18 . The transitioning portion  94  overlaps the spar cap by a web/spar cap overlap  96 . These overlaps may also be in the range of at least 2-3″ long. Also visible within the web skin  54  are web fibers  98 . It can be seen that within the web/spar cap overlap  96  the web fibers  98  again form angles α and β with the spar cap fibers  38 . 
         [0008]    In instances where the web skins  54  are part of a continuous fore section inner airfoil skin  74 , the continuous inner skins  74 ,  78  would overlap the fore section/spar cap joints  30  and the aft section/spar cap joints  32  in a manner similar to that shown in  FIG. 5  where the continuous outer airfoil skin  70  completely cover the spar cap  18 . 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The invention is explained in the following description in view of the drawings that show: 
           [0010]      FIG. 1  is a view of a prior art core section of a turbine blade. 
           [0011]      FIG. 2  is a side view of a prior art turbine blade using the core section of  FIG. 1 , showing inner, outer, and web skins. 
           [0012]      FIG. 3  is a side view of a prior art turbine blade using the core section of  FIG. 1 , showing different inner, outer, and web skins. 
           [0013]      FIG. 4  is a side view of a prior art turbine blade using the core section of  FIG. 1 , showing how discrete prior art skins meet a spar cap. 
           [0014]      FIG. 5  is a side view of a prior art turbine using the using the core section of  FIG. 1 , showing how a continuous prior art airfoil skin spans a spar cap. 
           [0015]      FIG. 6  is a perspective view of the turbine blade of  FIG. 1 , showing a discrete prior art web skin. 
           [0016]      FIG. 7  is a side view of the turbine blade and an exemplary embodiment of the fiber geometry disclosed herein when used with discrete skins. 
           [0017]      FIG. 8  is a side view of the turbine blade and another exemplary embodiment of the fiber geometry disclosed herein when used with discrete skins. 
           [0018]      FIG. 9  is a side view of the turbine blade and another exemplary embodiment of the fiber geometry disclosed herein when used with discrete skins. 
           [0019]      FIG. 10  is a side view of the turbine blade and another exemplary embodiment of the fiber geometry disclosed herein when used with a continuous skin. 
           [0020]      FIG. 11  is a side view of the turbine blade and another exemplary embodiment of the fiber geometry disclosed herein when used with a continuous skin. 
           [0021]      FIG. 12  is a perspective view of the turbine blade and an exemplary embodiment of the fiber geometry disclosed herein when used with a discrete web skin. 
           [0022]      FIG. 13  is a side view of a turbine blade and another exemplary embodiment of the fiber geometry disclosed herein. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    The reinforcing fibers present within components of wind turbine blades provide reinforcement when in tension to resist blade deflection. The spar caps  18 , which are separated by the web core  22  resist blade flex, particularly in directions  42  normal to the pressure side  46  and suction side  48 . During this flex the web skins  54  provide structural reinforcement for the web core  22 . In addition, the web fibers  98  transfer stress from one spar cap  18  to another during blade flex. However, in web/spar cap overlaps  96 , where the spar cap fibers  38  and web fibers  98  are proximate each other they also form angles α and β with each other. 
         [0024]    The present inventor has recognized that the angles α and β prevent smooth transition of the force from, for example, the spar cap fibers  38  directly to the web fibers  98 . When angles α and β are present the forces transfer from the spar cap fibers  38  and into the matrix material proximate the spar cap fibers  38 . The matrix material begins to transfer the force to the web fibers  98  by yielding somewhat, but because the web fibers  98  are at an angle (α and β) to the spar cap fibers  38 , and because the web fibers  98  can only offer resistance when in tension, (i.e. fibers only resist force along an axis of the fiber), the web fibers  98  initially only take a portion of the force present in the matrix material. As the resin yields more and the web fibers  98  physically take a relative orientation closer to parallel to the force in the resin, they take more of the force present in the resin. However, while the matrix material is effective to yield a certain amount to transfer force, yielding too much may cause the matrix material to fail. In addition, the matrix material is significantly weaker in tension than the fibers. This force transfer phenomenon occurs proximate where the inner and outer skins overlap the spar caps  18 . To accommodate this phenomenon conventional blade design includes thicker joints (a.k.a. interfaces) between abutting fiber reinforced matrix composite components of the blade, which equates to areas adjacent the spar caps  18 . This ensures that there exists enough matrix material and fiber to handle the forces. Therefore, conventional blades proximate the spar caps  18 , where outer skins, inner skins, and web skins join/interface with the spar caps  18 , are relatively heavy and thick. 
         [0025]    The present inventor has devised a novel geometry for fibers in components made of fiber reinforced matrix composite materials that provides for improved transfer of force at joints of adjacent and structurally interdependent components. Specifically, the novel geometry calls for the fibers within a first component and proximate a joint to approach being parallel to fibers in the adjacent component that are also proximate the joint. Approaching parallel means fiber ends in a harmonizing region approach an orientation that is more parallel to fibers in the adjacent component proximate the joint. Such a geometry reduces angles (α and β), and thereby increases a transfer of force to the adjacent fibers. 
         [0026]      FIG. 7  is a view of either the pressure side  46  or a suction side  48  of a blade  10  having discrete outer airfoil skin sections as disclosed in  FIG. 2 , but incorporating the novel fiber geometry disclosed herein. However, these teachings also apply to the inner skins where they meet the spar caps  18 . For sake of clarity only one side is illustrated. It can be seen that in a non harmonizing region  100  the airfoil skin fibers  80  form a first pattern, for example a biax pattern. A skin may include one or more layers of fibers, and if each layer forms a biax pattern, then a skin may include one or more layers of biax fibers. In a harmonizing region  102 , which is separated from the non harmonizing region  100  by a harmonizing line  104 , the airfoil skin fibers  80  change from their first pattern to an orientation where the ends of the airfoil skin fibers  80  within the harmonizing region curve toward being more parallel to the spar cap fibers  38 . The harmonizing region  102  may span the relevant joint, but it need not. Shown is one geometry illustrating a gradual curving of the airfoil skin fibers  80 , but other curve rates may be utilized. For example, the harmonizing region  102  may be smaller, which would necessitate a less gradual curve. Likewise, the harmonizing region  102  may be larger and thus a more gradual curve could be employed. An edge  106  of the harmonizing region  102  may be considered an asymptote for the curve of the ends of the airfoil skin fibers  80 . 
         [0027]    In one exemplary embodiment in order to effect the transition from the non harmonizing region  100  to a harmonizing region  102  a layer of fibers  80  may be formed by a single mat  101  that spans both regions  100 ,  102  as shown on the left side of  FIG. 7 . In this instance, within the single mat the fibers  80  may have differing orientations. In another exemplary embodiment in order to effect the transition from the non harmonizing region  100  to a harmonizing region  102 , two or more separate mats may be used to complete a single layer. For example, a first mat  103  may be associated primarily with the non harmonizing region  100  and a second mat  105  may be associated primarily with the harmonizing region  102 . As shown in the lower right of  FIG. 7 , the first mat  103  and the second mat  105  may abut each other at a mat abutting line  107 . In this case the edges of the first mat  103  and the second mat  105  abut, and so individual fibers  80  abut. As indicated by the arrows associated with the mat abutting line  107 , the mat abutting line  107  may be to the right or left of, or centered on the harmonizing line  104 . When to the left of the harmonizing line  104 , the first mat  103  would have fibers  80  having patterns of both regions  100 ,  102 , while the second mat  105  would have fibers  80  having the pattern of the harmonizing region  102 . When to the right of the harmonizing line  104 , the second mat would have fibers  80  having patterns of both regions  100 ,  102 , while the first mat would have fibers  80  having the pattern of the non harmonizing region  100 . In an exemplary embodiment where the mat abutting line  107  is centered on the harmonizing line  104  the first mat  103  would have fibers  80  of the non harmonizing region pattern, while the second mat  105  would have fibers  80  of the harmonizing pattern as disclosed above. The first mat  103  and the second mat  105  can be any size necessary. In an exemplary embodiment the second mat  105  may be anywhere from approximately five inches long to twelve inches long. 
         [0028]    Alternatively, as shown in the upper right of  FIG. 7 , the ends of the first mat  103  and the second mat  105  may overlap to form a mat overlap  108 . This configuration may show improved force transfer from one mat to another due to the overlapping fibers  80 . Similar to the mat abutting line  107 , the mat overlap  108  may be to the right or left of, or cover the harmonizing line  104 , as indicated by the arrows associate with the mat overlap  108 . When to the left of the harmonizing line  104 , the first mat  103  would have fibers  80  having patterns of both regions  100 ,  102 , while the second mat  105  would have fibers  80  having the pattern of the harmonizing region  102 . When to the right of the harmonizing line  104 , the second mat  105  would have fibers  80  having patterns of both regions  100 ,  102 , while the first mat  103  would have fibers  80  having the pattern of the non harmonizing region  100 . In the exemplary embodiment where the harmonizing line  104  is within the mat overlap  108  each mat  103 ,  105  would have fibers of both regions  100 ,  102 . 
         [0029]    In a hybrid of exemplary embodiments with discrete skins, the two non harmonizing regions  100  of  FIG. 7  could be spanned by a single mat. In this case the above described end configurations are possible for each end of the single mat. Within a span of the single mat the fibers  80  could be configured to have as many curves and asymptotes as desired. Such an exemplary embodiment would simplify manufacturing by reducing from two to one the number of mats needed for one spar cap  18 . 
         [0030]    The airfoil skin fibers  80  in the harmonizing region  102  of  FIG. 7  each curve toward the edge  106  of the harmonizing region  102 . However, individual airfoil skin fibers  80  may have differing paths within the harmonizing region  102 . Varying patterns within the harmonizing region  102  may be used as necessary to provide optimized local force transfer characteristics. For example,  FIG. 8  shows a variation of the harmonizing region  102  of  FIG. 7 , where various airfoil skin fibers  80  curve toward differing asymptotes. For clarity only one axis of the biax layer is shown, though in practice both axes would be present, such that the fibers with one axis help hold the fibers of the other axis in place. Airfoil skin fibers  80  of group  1  may use the edge  106  of the harmonizing region  102  as their asymptote  110 . Airfoil skin fibers  80  of group  2  may approach a second asymptote  112 . Airfoil skin fibers  80  of group  3  may approach a third asymptote  114 , and airfoil skin fibers  80  of group  4  may approach a fourth asymptote  116 . Four asymptotes have been used for illustration here, but any number of asymptotes is possible. It can be seen that the groups  1 ,  2 ,  3 ,  4 , may be patterned in any way. As shown in  FIG. 8 , there is a repeating pattern of  1 ,  2 ,  3 ,  4 ,  1 ,  2 ,  3 ,  4 , etc. A variation could be  1 ,  1 ,  2 ,  2 ,  3 ,  3 ,  4 ,  4 ,  1 ,  1 ,  2 ,  2 ,  3 ,  3 ,  4 ,  4 , etc, or any number of each group. 
         [0031]    It can be seen in this pattern that ends (within the harmonizing region  102 ) of fibers of group  4  are shorter than are ends of fibers of group  1 . Further, the ends of fibers of group  4  may not curve to the same degree or length as the ends of fibers of group  1 . Consequently, the group  1  fibers may be more efficient at transferring load from the spar caps  18  to the skin. For this reason the pattern may be varied such that groups with shorter ends in the harmonizing region  102  are present with greater number within the pattern. An example of this is illustrated in  FIG. 9 , where the pattern includes  4 ,  4 ,  4 ,  4 ,  3 ,  3 ,  3 ,  2 ,  2 ,  1 , which may repeat. Thus, the ends of group  4 , which may be less efficient than the ends of group  1 , make up for any inefficiency by larger numbers. 
         [0032]    Any number of asymptotes, any number of groups, and any pattern of groupings may be envisioned to optimize force transfer. 
         [0033]      FIG. 10  is a view of either the pressure side  46  or a suction side  48  of a blade  10  having a continuous outer airfoil skin as disclosed in  FIG. 3 , but incorporating the novel fiber geometry disclosed herein. For sake of clarity only a portion of the airfoil skin fibers  80  are illustrated. In this exemplary embodiment, since the airfoil skin fibers  80  span the spar cap  18 , there may not be an asymptote. In such case on one side of the spar cap, such as proximate the leading edge  20  of the spar cap  18 , the airfoil skin fibers  80  may curve as in  FIGS. 7-9  but instead of reaching an end point the airfoil skin fibers  80  may continue and blend with airfoil skin fibers  80  proximate the trailing edge  21  of the spar cap  18 . This may form a harmonizing region  122 . The harmonization region  122  may be wider than and encompass the spar cap  18 , but it need not. A line of symmetry  120  may coincide with the longitudinal axis  40  of the spar caps  18 . However, as with the patterns of  FIGS. 7-9 , the line of symmetry  120  may vary within the spar cap  18 . For example, the line of symmetry for a first group of fibers may be at a different location with respect to the longitudinal axis  40  than a line of symmetry for a second group of fibers. As with  FIGS. 7-9 , there may be many different lines of symmetry for many different fiber groups, and the fiber groups and lines of symmetry may be patterned as desired to improve localized force transfer between the components. It is also possible for hybrid exemplary embodiments to combine layers of discrete outer airfoil skin sections with layers with a continuous outer airfoil skin in any manner consistent with the novel geometry disclosed herein. 
         [0034]      FIG. 11  is a variation of the configuration of  FIG. 10 , where there exist several lines of symmetry  120  such that groups  201 ,  202 , and  203  of airfoil skin fibers  80  may form symmetric patterns about respective lines of symmetry  120 , and where the lines of symmetry  120  may be disposed at various locations. As with the teachings of  FIGS. 8 and 9 , this will afford greater control over local force transfer characteristics. 
         [0035]    The teachings of  FIGS. 7-9  also apply to the inner skins where they meet the spar caps  18  or any joint where, at the joints, the components are essentially parallel and the skins is discrete. The teachings of  FIGS. 10-11  also apply to any components where components are essentially parallel, and one component can span the other component. 
         [0036]      FIG. 12  shows a web core  22  where it meets with a spar cap  18  at a web core/spar cap joint  34 , where a discrete web skin  54  spans from the web core  22  to the spar cap  18  across the fillet  90 . For sake of clarity only one axis of a biax pattern is shown. The web skin  54  includes a first portion  92  that forms an angle with the spar cap  18 , and a transitioning portion  94  that transitions the web skin  54  from the first portion  92 , across the fillet  90 , to being parallel to the spar cap  18 , to form an overlap  96 . The novel geometry for the web fibers  98  includes a non harmonizing region  130  and a harmonizing region  132 . It can be seen that in a non harmonizing region  130  the web fibers  98  form a first pattern, for example a biax pattern. In a harmonizing region  132 , which is separated from the non harmonizing region  130  by a harmonizing line  136 , the web fibers  98  change from their first pattern to an orientation where the ends of the web fibers  98  within the harmonizing region curve toward being more parallel to the spar cap fibers  38 . The harmonizing region  132  may span the relevant joint, but it need not. The harmonizing line  136  may extend into the first portion  92  by any desired amount. Shown is one geometry showing a gradual curving of the web fibers  98 , but other curve rates may be utilized. For example, the harmonizing region  132  may be smaller, which would necessitate a less gradual curve. Likewise, the harmonizing region  132  may be larger and thus a more gradual curve could be employed. An edge  138  of the harmonizing region  102  may be considered an asymptote for the curve of the ends of the web fibers  98 . Further, web fibers  98  within the overlap  96  may take any pattern such as, but not limited to those described in  FIGS. 7-9 . Similar to the exemplary embodiment shown in  FIG. 7 , in order to effect the transition from the non harmonizing region  130  to a harmonizing region  132  a layer of fibers  80  may be formed by a single mat that spans both regions  130 ,  132 . In this instance, within the single mat the fibers  80  may have differing orientations. In another exemplary embodiment in order to effect the transition from the non harmonizing region  130  to a harmonizing region  132 , two or more separate mats may be used to complete a single layer. A first mat  135  and a second mat  137  may abut each other at a mat abutting line. Alternatively, the ends of the first mat  135  and the second mat  137  may overlap to form a mat overlap  139 . The above described web fiber geometry for the web core/spar cap joint  34  applies to embodiments with discrete inner skins and continuous inner skins since both cover the web core/spar cap joint  34 . 
         [0037]    As shown in  FIG. 13 , the novel geometry may also be applied to a leading edge  140  and/or trailing edge  142  of the blade  10  itself. For example, the airfoil skin fibers  80  may form a leading edge harmonizing region  144  in which the ends of the airfoil skin fibers  80  approach being parallel to a respective portion of the leading edge  140  proximate the respective airfoil skin fiber ends. Likewise, the airfoil skin fibers  80  may form a trailing edge harmonizing region  146  in which ends of the airfoil skin fibers  80  approach being parallel to a respective potion of the trailing edge  144  proximate the respective airfoil skin fiber ends. Such a configuration would improve strength near the edges of the blade where the blade halves are joined because all airfoil skin fibers  80  proximate a seam between the blade halves would be nearly parallel to each other. 
         [0038]    The novel geometry for reinforcing fibers within reinforced composite materials being joined provides increased strength, and therefore blades may be designed using less material to accommodate a same load. Decreased material yields a decrease in manufacturing costs, and decreased weight yields more efficient operation. Consequently, the disclosure herein represents an improvement in the art. 
         [0039]    While various embodiments of the present invention have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions may be made without departing from the invention herein. Accordingly, it is intended that the invention be limited only by the spirit and scope of the appended claims.