Patent Publication Number: US-2012027618-A1

Title: Angled blade root

Description:
FIELD OF THE INVENTION 
     The present subject matter relates generally to wind turbines and, more particularly, to an angled blade root for a wind turbine rotor blade. 
     BACKGROUND OF THE INVENTION 
     Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, generator, gearbox, nacelle, and one or more rotor blades. The rotor blades capture kinetic energy from the wind using known airfoil principles and transmit the kinetic energy through rotational energy to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid. 
     To ensure that wind power remains a viable energy source, efforts have been made to increase energy outputs by modifying the size and capacity of wind turbines. One such modification has been to increase the length and surface area of the rotor blades. However, the magnitude of deflection forces and loading of a rotor blade is generally a function of blade length, along with wind speed, turbine operating states, blade stiffness, and other variables. This increased loading not only produces fatigue on the rotor blades and other wind turbine components but may also increase the risk of a sudden catastrophic failure of the rotor blades, for example, when excess loading causes deflection of a blade resulting in a tower strike. 
     Accordingly, a rotor blade configuration that allows for the use of longer rotor blades without increasing the likelihood of a tower strike would be welcomed in the technology. 
     BRIEF DESCRIPTION OF THE INVENTION 
     Aspects and advantages of the invention will be set forth in part in the following description, or may be obvious from the description, or may be learned through practice of the invention. 
     In one aspect, the present subject matter discloses a rotor blade for a wind turbine. The rotor blade may generally include a blade root defining a planar surface, a blade tip and a body extending between the blade root and the blade tip. The body may define a longitudinal axis and may include a pressure side and a suction side extending between a leading edge and a trailing edge. Additionally, an angle may be defined between the planar surface and a reference plane extending perpendicular to the longitudinal axis. The angle may be greater than 0 degrees and less than about 10 degrees. 
     In another aspect, the present subject matter discloses a wind turbine. The wind turbine may include a plurality of rotor blades. Each rotor blade may include a blade root defining a planar surface, a blade tip and a body extending between the blade root and the blade tip. The body may define a longitudinal axis and may include a pressure side and a suction side extending between a leading edge and a trailing edge. Additionally, an angle may be defined between the planar surface and a reference plane extending perpendicular to the longitudinal axis. The angle may be greater than 0 degrees and less than about 10 degrees. 
     In another aspect, the present subject matter discloses a blade root for a wind turbine rotor blade. The blade root may generally comprise a substantially cylindrically shaped member extending lengthwise along a longitudinal axis and defining a planar end surface. Additionally, an angle may be defined between the planar end surface and a reference plane extending perpendicular to the longitudinal axis. The angle may be greater than 0 degrees and less than about 10 degrees. 
     These and other features, aspects and advantages of the present invention will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which: 
         FIG. 1  illustrates a perspective view of one embodiment of a wind turbine; 
         FIG. 2  illustrates a perspective view of one embodiment a rotor blade in accordance with aspects of the present subject matter; 
         FIG. 3  illustrates a side view of an outboard portion of the rotor blade shown  FIG. 2 , particularly illustrating a blade root of the rotor blade; 
         FIG. 4  illustrates a top view of the blade root shown in  FIG. 3 ; and, 
         FIG. 5  illustrates a partial side view of a wind turbine having the rotor blade shown in  FIGS. 2-4  installed thereon. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents. 
     In general, the present subject matter is directed to a rotor blade for a wind turbine having an angled blade root. In particular, the blade root of the rotor blade may define a planar end surface oriented at an angle relative to the longitudinal axis of the rotor blade. Accordingly, when the rotor blade is installed onto a wind turbine hub, an increase in the amount of tower clearance defined between the rotor blade and the wind turbine tower may be achieved. Such increased tower clearance may allow for longer and/or lighter rotor blades to be utilized on a wind turbine, thereby increasing the efficiency and/or output of the wind turbine and/or decreasing the costs required to manufacture each rotor blade. 
     Referring now to the drawings,  FIG. 1  illustrates perspective view of one embodiment of a wind turbine  10 . As shown, the wind turbine  10  includes a tower  12  extending from a support surface  14 , a nacelle  16  mounted on the tower  12 , and a rotor  18  coupled to the nacelle  16 . The rotor  18  includes a rotatable hub  20  and at least one rotor blade  22  coupled to and extending outwardly from the hub  20 . For example, in the illustrated embodiment, the rotor  18  includes three rotor blades  22 . However, in an alternative embodiment, the rotor  18  may include more or less than three rotor blades  22 . Each rotor blade  22  may be spaced about the hub  20  to facilitate rotating the rotor  18  to enable kinetic energy to be transferred from the wind into usable mechanical energy, and subsequently, electrical energy. For instance, the hub  20  may be rotatably coupled to an electric generator (not shown) positioned within the nacelle  16  to permit electrical energy to be produced. 
     Referring now to  FIGS. 2-4 , one embodiment of a rotor blade  100  having an angled blade root  102  is illustrated in accordance with aspects of the present subject matter. In particular,  FIG. 2  illustrates a perspective view of the rotor blade  100 .  FIG. 3  illustrates a side view of an inboard portion of the rotor blade  100  shown in  FIG. 2 , particularly illustrating the blade root  102  of the rotor blade  100 . Additionally,  FIG. 4  illustrates a top view of the blade root  102  shown in  FIG. 3 . 
     As shown, the rotor blade  100  generally includes a blade root  102  and a blade tip  104  disposed opposite the blade root  102 . A body  106  of the rotor blade  100  extends lengthwise along a longitudinal axis  108  between the blade root  102  and the blade tip  104  and generally serves as the outer shell of the rotor blade  100 . As is generally understood, the body  106  may define an aerodynamic profile to enable the rotor blade  100  to capture kinetic energy from the wind using known aerodynamic principles. Thus, the body  106  may generally include a pressure side  110  and a suction side  112  extending between a leading edge  114  and a trailing edge  116 . Additionally, the rotor blade  100  may have a span  118  defining the total length of the blade  100  between the blade root  102  and the blade tip  104  and a chord  120  defining the total length of the body  106  between the leading edge  114  and the trailing edge  116 . As is generally understood, the chord  120  may vary in length with respect to the span  118  as the rotor blade  100  extends from the blade root  102  to the blade tip  104 . It should be readily appreciated that the longitudinal axis  108  of the rotor blade  100  may extend parallel to the span  118 . 
     As indicated above, the body  106  of the rotor blade  100  may generally define an aerodynamic profile or shape. For example, in several embodiments, the body  106  may define an airfoil shaped cross-section, such as by defining a symmetrical or cambered airfoil-shaped cross-section. In addition, the rotor blade  100  may also be aeroelastically tailored. Aeroelastic tailoring of the rotor blade  100  may entail bending of the blade  100  in a generally chordwise direction and/or in a generally spanwise direction. The chordwise direction generally corresponds to a direction parallel to the chord  120  of the rotor blade  100 . The spanwise direction generally corresponds to a direction parallel to the span  118  or longitudinal axis  108  of the rotor blade  100 . Aeroelastic tailoring may further entail twisting of the rotor blade  100 , such as twisting the blade  100  in a generally chordwise and/or spanwise direction. 
     Referring particularly to  FIGS. 3 and 4 , the blade root  102  of the rotor blade  100  may generally comprise a substantially cylindrically shaped member extending outwardly from the aerodynamically shaped body  106  of the rotor blade  100 . For example, as shown in  FIG. 3 , the blade root  102  may extend from the body  106  along a longitudinal axis  122  oriented parallel to and/or coaxial with the longitudinal axis  108  of the rotor blade  100 . In general, the blade root  102  may be configured to be mounted or otherwise attached to the hub  20  of a wind turbine  10 . For example, as shown in  FIG. 4 , a plurality of stud or bolt holes  124  may be defined through a planar end surface  126  of the blade root  102  for receiving a corresponding number of studs or bolts (not shown). As is generally understood, the studs or bolts may be used to attach the blade root  102  to a pitch bearing  128  ( FIG. 5 ) disposed within and/or coupled to the hub  20 . For instance, the blade root  102  may be configured to be rigidly attached to the pitch bearing  128  such that the end surface  126  contacts against and extends parallel to a corresponding surface of the pitch bearing  128 . However, it should be appreciated by those of ordinary skill in the art that the blade root  102  may be attached to the hub  20  using any other suitable means and/or attachment method known in the art. 
     It should be appreciated that, several embodiments, the blade root  102  may be formed integrally with the body  106  of the rotor blade  100 . Alternatively, the blade root  102  may comprise a separate component configured to be separately attached to the body  106 . 
     As particularly shown in  FIG. 3 , in accordance with several embodiments of the present subject matter, the end surface  126  of the blade root  102  may be oriented at an at an angle  130  relative to the rotor blade  100 . Specifically, the end surface  126  may be configured such that an angle  130  is defined between the end surface  126  and a reference plane  132  extending perpendicular to the longitudinal axis  108  of the rotor blade  100  and/or the longitudinal axis  122  of the blade root  102 . As such, when the blade root  102  is attached to the hub  20  of a wind turbine  10 , the longitudinal axis  108 ,  122  of the rotor blade  100  and/or the blade root  102  may be oriented at a non-perpendicular angle relative to the interface defined between the end surface  126  and the pitch bearing  128 . It should be appreciated that, as used herein, the term “reference plane” corresponds to an imaginary plane defined perpendicular to the longitudinal axis  108 ,  122  of the rotor blade  100  and/or the blade root  102  and extending parallel to the chord  120  of the rotor blade  100 . 
     In general, the angle  130  defined between the end surface  126  of the blade root  102  and the reference plane  132  may comprise any suitable angle greater than 0 degrees. However, in several embodiments, the angle  130  may range from greater than 0 degrees to less than about 10 degrees, such as from about 0.5 degrees to about 5 degrees or from about 0.5 degrees to about 3 degrees or from about 0.5 degrees to about 2 degrees or from about 1 degree to about 2 degrees and all other subranges therebetween. 
     In several embodiments, the planer end surface  126  may be defined in the blade root  102  such that the end surface  126  is angled towards the pressure side  110  of the rotor blade  100 . For example, as shown in  FIG. 3 , the plane defined by the end surface  126  may be angled inwardly between a first edge  134  defined on the suction side  112  of the rotor blade  100  and a second edge  136  defined on the pressure side  110  of the rotor blade  100 , with the first edge  134  generally corresponding to the point on the end surface  126  disposed furthest away from the blade tip  104  of the rotor blade  100  and the second edge  136  generally corresponding to the point on the end surface  126  disposed closest to the blade tip  104 . As such, when the rotor blade  100  is installed on a wind turbine hub  20 , the rotor blade  100  may be angled away from the tower  12 . Moreover, in one embodiment, the end surface  126  may be defined in the blade root  102  such a centerline  138  defined halfway between the first and second edges  134 ,  136  is generally aligned with and extends parallel to the chord  120  of the rotor blade  100 . Accordingly, the tower clearance defined between the rotor blade  100  and the tower  12  may be maximized when the blade  100  is pitched to its power position during operation (i.e., a position at which the pressure side  110  of the rotor blade  100  faces directly into the wind). 
     It should be appreciated that the end surface  126  of the blade root  102  may be formed using any suitable manufacturing method and/or means known in the art. For instance, in several embodiments, the blade root  102  may be initially formed having an end surface oriented substantially perpendicularly to the longitudinal axis  108 ,  122  of the rotor blade  100  and/or the blade root  102  (i.e., substantially parallel to the reference plane  132 ). In such embodiment, the angled end surface  126  may be formed by cutting, grinding or otherwise removing portions of the blade root  102  using any suitable cutting, grinding and/or machining equipment. Alternatively, the blade root  102  may be initially formed having the angled end surface  126 . 
     Referring now to  FIG. 5 , there is illustrated one embodiment of the rotor blade  100  shown in  FIGS. 2-4  installed on a wind turbine hub  20 . Specifically,  FIG. 5  illustrates the difference in tower clearance  144 ,  146  achieved through the use of the disclosed rotor blade  100  as compared to a conventional rotor blade  22  (indicated by dashed lines). As shown, when the blade root  102  of the disclosed rotor blade  100  is secured to the hub  20  (e.g., by securing the end surface  126  to a portion of the pitch bearing  128 ), the interface defined between the end surface  126  and the hub  20  is oriented at a non-perpendicular angle relative to the longitudinal axis  108  of the rotor blade  100 . Thus, due to the angled interface, the rotor blade  100  may be configured to extend outwardly away from the tower  12 . In contrast, when the blade root  140  of a conventional rotor blade  22  is secured to the hub  20 , the interface defined between the rotor blade  22  and the hub  20  is oriented perpendicular to the longitudinal axis  142  of the blade  22  and, thus, the rotor blade  22  extends generally parallel to the tower  12 . Accordingly, the tower clearance  144  defined between the disclosed rotor blade  100  and the tower  12  may be significantly higher than the tower clearance  146  defined between the conventional blade  22  and the tower  12 . 
     This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.