Patent Publication Number: US-2012027588-A1

Title: Root flap for rotor blade in wind turbine

Description:
FIELD OF THE INVENTION 
     The present disclosure relates in general to wind turbine rotor blades, and more particularly to flaps mounted on the rotor blades. 
     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 of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as 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. 
     Rotor blades in general are increasing in size, in order to become capable of capturing increased kinetic energy. However, the shape of a typical wind turbine rotor blade results in a relatively large separation region, due to the contour of the rotor blade. Specifically, the contour of the inner portion of the rotor blade adjacent to and including the root may cause such separation. In some cases, this inner portion may include 40%, 50% or more of the rotor blade. The separation region causes relatively significant energy losses by creating drag. Further, these losses are amplified as rotor blade sizes are increased. 
     Thus, an improved rotor blade assembly would be advantageous. For example, a rotor blade assembly that reduces or eliminates the separation region adjacent to the root of the rotor blade would be desired. 
     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 embodiment, a rotor blade assembly for a wind turbine is disclosed. The rotor blade assembly includes a rotor blade having exterior surfaces defining a pressure side, a suction side, a leading edge, and a trailing edge extending in a generally span-wise direction between a tip and a root. The rotor blade assembly further includes a flap extending in the generally span-wise direction from the root towards the tip. The flap includes an inner surface and an outer surface, the inner surface conformingly mounted to at least one of the pressure side, the suction side, or the trailing edge, the outer surface and at least one of the pressure side or the suction side defining a generally continuous aerodynamic surface. 
     In another embodiment, a method for reducing the separation region of a rotor blade for a wind turbine is disclosed. The method includes mounting a flap to a rotor blade, and rotating the rotor blade on the wind turbine. The rotor blade has exterior surfaces defining a pressure side, a suction side, a leading edge, and a trailing edge extending in a generally span-wise direction between a tip and a root. The flap extends in the generally span-wise direction from the root towards the tip. The flap includes an inner surface and an outer surface, the inner surface conformingly mounted to at least one of the pressure side, the suction side, or the trailing edge, the outer surface and at least one of the pressure side or the suction side defining a generally continuous aerodynamic surface. 
     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  is a side view of a wind turbine according to one embodiment of the present disclosure; 
         FIG. 2  is a top perspective view of a rotor blade assembly according to one embodiment of the present disclosure; 
         FIG. 3  is a bottom perspective view of the rotor blade assembly of  FIG. 2 ; 
         FIG. 4  is a top perspective view of a rotor blade assembly according to another embodiment of the present disclosure; 
         FIG. 5  is a bottom perspective view of the rotor blade assembly of  FIG. 4 ; 
         FIG. 6  is a cross-sectional view of a rotor blade assembly according to one embodiment of the present disclosure; 
         FIG. 7  is a cross-sectional view of a rotor blade assembly according to another embodiment of the present disclosure; 
         FIG. 8  is a cross-sectional view of a rotor blade assembly according to another embodiment of the present disclosure; 
         FIG. 9  is a cross-sectional view of a rotor blade assembly according to another embodiment of the present disclosure; 
         FIG. 10  is a cross-sectional view of a rotor blade assembly according to another embodiment of the present disclosure; and, 
         FIG. 11  is a cross-sectional view of a rotor blade assembly according to another embodiment of the present disclosure. 
     
    
    
     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. 
       FIG. 1  illustrates a wind turbine  10  of conventional construction. The wind turbine  10  includes a tower  12  with a nacelle  14  mounted thereon. A plurality of rotor blades  16  are mounted to a rotor hub  18 , which is in turn connected to a main flange that turns a main rotor shaft. The wind turbine power generation and control components are housed within the nacelle  14 . The view of  FIG. 1  is provided for illustrative purposes only to place the present invention in an exemplary field of use. It should be appreciated that the invention is not limited to any particular type of wind turbine configuration. 
     Referring to  FIGS. 2 through 11 , a rotor blade  16  according to the present disclosure may include exterior surfaces defining a pressure side  22  and a suction side  24  extending between a leading edge  26  and a trailing edge  28 , and may extend from a blade tip  32  to a blade root  34 . The exterior surfaces may be generally aerodynamic surfaces having generally aerodynamic contours, as is generally known in the art. 
     In some embodiments, the rotor blade  16  may include a plurality of individual blade segments aligned in an end-to-end order from the blade tip  32  to the blade root  34 . Each of the individual blade segments may be uniquely configured so that the plurality of blade segments define a complete rotor blade  16  having a designed aerodynamic profile, length, and other desired characteristics. For example, each of the blade segments may have an aerodynamic profile that corresponds to the aerodynamic profile of adjacent blade segments. Thus, the aerodynamic profiles of the blade segments may form a continuous aerodynamic profile of the rotor blade  16 . Alternatively, the rotor blade  16  may be formed as a singular, unitary blade having the designed aerodynamic profile, length, and other desired characteristics. 
     The rotor blade  16  may, in exemplary embodiments, be curved. Curving of the rotor blade  16  may entail bending the rotor blade  16  in a generally flapwise direction and/or in a generally edgewise direction. The flapwise direction may generally be construed as the direction (or the opposite direction) in which the aerodynamic lift acts on the rotor blade  16 . The edgewise direction is generally perpendicular to the flapwise direction. Flapwise curvature of the rotor blade  16  is also known as pre-bend, while edgewise curvature is also known as sweep. Thus, a curved rotor blade  16  may be pre-bent and/or swept. Curving may enable the rotor blade  16  to better withstand flapwise and edgewise loads during operation of the wind turbine  10 , and may further provide clearance for the rotor blade  16  from the tower  12  during operation of the wind turbine  10 . 
     The rotor blade  16  may further define a chord  42  and a span  44  extending in chord-wise and span-wise directions, respectively. As shown in  FIGS. 2 through 5 , the chord  42  may vary throughout the span  44  of the rotor blade  16 . Thus, as discussed below, a local chord  46  may be defined for the rotor blade  16  at any point on the rotor blade  16  along the span  44 . Further, the rotor blade  16  may define a maximum chord  48 , as shown. 
     Additionally, the rotor blade  16  may define an inner board area  52  and an outer board area  54 . The inner board area  52  may be a span-wise portion of the rotor blade  16  extending from the root  34 . For example, the inner board area  52  may, in some embodiments, include approximately 33%, 40%, 50%, 60%, 67%, or any percentage or range of percentages therebetween, or any other suitable percentage or range of percentages, of the span  44  from the root  34 . The outer board area  54  may be a span-wise portion of the rotor blade  16  extending from the tip  32 , and may in some embodiments include the remaining portion of the rotor blade  16  between the inner board area  52  and the tip  32 . Additionally or alternatively, the outer board area  54  may, in some embodiments, include approximately 33%, 40%, 50%, 60%, 67%, or any percentage or range of percentages therebetween, or any other suitable percentage or range of percentages, of the span  44  from the tip  32 . 
     As illustrated in  FIGS. 2 through 11 , the present disclosure may further be directed to a rotor blade assembly  100 . The rotor blade assembly  100  may include a flap  110  and the rotor blade  16 . The flap  110  is a generally static flap mounted to the rotor blade  16  in the inner board area  52  of the rotor blade  100 . The flap  110  extends in the generally span-wise direction from the root  34  towards the tip  32 . Thus, one end of the flap  110  is positioned at the root  34 , while the other end is positioned between the root  34  and the tip  32  in the inner board area  52 . As discussed below, the flap alters the contour of a portion of the rotor blade  16  adjacent to the root  34 . This alteration reduces or eliminates any separation region in this portion of the rotor blade  16 , and further reduces the drag associated with the rotor blade  16  and increases the performance rotor blade  16 . 
     The flap  110  includes an inner surface  112  and an outer surface  114 , as shown in  FIGS. 2 through 11 . The inner surface  112  is conformingly mounted to at least one of the pressure side  22 , the suction side  24 , or the trailing edge  28 . Thus, the aerodynamic contour of the inner surface  112  conforms to at least one of the pressure side  22 , the suction side  24 , or the trailing edge  28 , such that when the flap  110  is mounted to the rotor blade  16 , relatively little or no air may pass between the inner surface  112  and the pressure side  22 , the suction side  24 , and/or the trailing edge  28 . 
     For example,  FIGS. 2 through 7  and  9  illustrate various embodiments of an inner surface  112  conformingly mounted to a pressure side  22 , suction side  24 , and trailing edge  28  of a rotor blade  16 .  FIG. 6  illustrates one embodiment of an inner surface  112  mounted to a relatively minimal portion of the pressure side  22  and the suction side  24 .  FIG. 7  illustrates one embodiment of an inner surface  112  mounted to a relatively substantial portion of the suction side  24  and a relatively minimal portion of the pressure side  22 .  FIG. 9  illustrates another embodiment of an inner surface  112  mounted to a relatively minimal portion of the pressure side  22  and the suction side  24 . 
     Further,  FIG. 8  illustrates one embodiment of an inner surface  112  conformingly mounted to a pressure side  22  and trailing edge  28 , wherein the inner surface  112  is mounted to a relatively substantial portion of the pressure side  22 .  FIGS. 10 and 11  illustrate various embodiment of an inner surface  112  conformingly mounted to a pressure side  22 , wherein the inner surface  112  is mounted to a relatively substantial portion of the pressure side  22 . 
     As mentioned above, in some embodiments, the inner surface  112  may be mounted to a relatively substantial portion of the pressure side  22  and/or suction side  24 . This portion may be defined relative to the local chord  46 . For example, the inner surface may be mounted to between approximately 20% and approximately 60%, such as between approximately 20% and approximately 50%, such as between approximately 20% and approximately 40%, such as between approximately 20% and approximately 30%, of the local chord  46  on the pressure side  22  and/or suction side  24 . In other embodiments, the inner surface  112  may be mounted to a relatively minimal portion of the pressure side  22  and/or the suction side  24 . This portion may also be defined relative to the local chord  46 . For example, the inner surface may be mounted to between approximately 0% and approximately 20%, such as between approximately 0% and approximately 15%, such as between approximately 0% and approximately 10%, such as between approximately 0% and approximately 5%, of the local chord  46  on the pressure side  22  and/or suction side  24 . 
     It should be understood that the inner surface  112  may be conformingly mounted to any one or more of the pressure side  22 , the suction side  24 , or the trailing edge  28 , and further that the inner surface  112  may be mounted to a relatively substantial portion or a relatively minimal portion of any one or more of the pressure side  22 , the suction side  24 , or the trailing edge  28 . Further, it should be understood that the relatively substantial portion and relatively minimal portion discussed above are not limited to the above disclosed ranges, and rather that any suitable range or percentage is within the scope and spirit of the present disclosure. 
     As shown in  FIGS. 2 through 11 , the outer surface  114  of the flap  110  defines a generally continuous aerodynamic surface with one or more of the exterior surfaces of the rotor blade  16 . For example, the outer surface  114  and at least one of the pressure side  22  or the suction side  24  define a generally continuous aerodynamic surface. A generally continuous aerodynamic surface is a surface that has a generally continuous aerodynamic contour. Thus, when two surfaces define a generally continuous aerodynamic surface, there is relatively little interruption in the aerodynamic contour at the intersection of the two surfaces. As shown in  FIGS. 2 through 7  and  9 , for example, the outer surface  114  and the suction side  24  define a generally continuous aerodynamic surface. Further, in  FIGS. 2 through 11 , the outer surface  114  and the pressure side  22  define a generally continuous aerodynamic surface. 
     The outer surface  114  of the flap  110  may include a pressure side portion  122  and/or a suction side portion  124 . The pressure side portion  122  may define a generally aerodynamic surface with the pressure side  22  of the rotor blade  16 , as discussed above, while the suction side portion  124  may define a generally aerodynamic surface with the suction side  24 , as discussed above. In some embodiments, the outer surface  114  of the flap  110  may include only the pressure side portion  122  and suction side portion  124 , which may meet at both generally chord-wise ends of the flap  110 , as shown in  FIG. 11 . 
     In other embodiments, however, the outer surface  114  may further include additional surfaces. For example, in some embodiments, as shown in  FIGS. 2  through  10 , the outer surface  114  may further include a planer portion  126 . The planer portion  126  may extend between the pressure side portion  122  and the suction side portion  124 , or between one of the pressure side portion  122  or suction side portion  124  and the inner surface  112 . 
     The planer portion  126  in exemplary embodiments extends in the generally span-wise direction. Thus, in some embodiments the planer portion  126  may extend generally parallel to the span  44  of the rotor blade  16 . Alternatively, however, the planer portion  126  may extend at any suitable angle to the span  44 , as desired or required. In further alternative embodiments, the planer portion  126  may extend in any suitable angle relative to the rotor blade  16 . 
     Further, as shown, the planer portion  126  in some embodiments is generally perpendicular to the local chord  46  of the rotor blade  16 . Thus, as the planer portion  126  extends, such as in the generally span-wise direction, the planer portion  126  at any location may be generally perpendicular to the local chord  46  at that location. Alternatively, however, the planer portion  126  may be positioned at any suitable angle to perpendicular, or have any other suitable angle relative to the rotor blade  16 . 
     In some embodiments, as shown in  FIGS. 2 through 10 , the flap  110  may extend in the generally chord-wise direction no further than the maximum chord  48  of the rotor blade  16 . In these embodiments, at no location along the flap  110  in the generally span-wise direction does the flap  110  extend further than the maximum chord  48  of the rotor blade  16 . In embodiments wherein the flap  110  includes a planer portion  126 , the planer portion  126  may extend no further than the maximum chord  48  of the rotor blade  16 . In embodiments wherein the flap  11  only includes a pressure side portion  122  and a suction side portion  124 , neither the pressure side portion  122  nor the suction side portion  124  extends any further than the maximum chord  48  of the rotor blade  16 . In other embodiments, as shown in  FIG. 11 , however, the flap  110  may extend in the generally chord-wise direction further than the maximum chord  48  of the rotor blade  16 , as desired or required. In these embodiments, at any location along the flap  110  in the generally span-wise direction, the flap  110  may extend further than the maximum chord  48  of the rotor blade  16 . 
     In some embodiments, as shown in  FIGS. 2 through 5 , the flap  110  may have a generally decreasing cross-sectional area in the span-wise direction towards the tip  32 . Alternatively, however, the flap  110  may have a generally increasing cross-sectional area in the span-wise direction towards the tip  32 , or may have a generally constant cross-sectional area. 
     The present disclosure may further be directed to a method for reducing the separation region of a rotor blade  16  for a wind turbine  10 . The method includes the step of mounting a flap  110  to a rotor blade  16 , as discussed above. The method further includes rotating the rotor blade  16  on the wind turbine  10 . 
     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.