Abstract:
A rotor blade element and a method for improving the efficiency of a wind turbine rotor blade are provided. The wind turbine rotor blade element is adapted for mounting on the wind turbine rotor blade. The wind turbine rotor blade has a trailing edge, a suction side and a pressure side. The blade element has a trailing edge, a first surface and a second surface. The first surface forms a pressure side surface portion. The second surface has a suction side surface portion and a contact surface.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is the US National Stage of International Application No. PCT/EP2010/065646 filed Oct. 18, 2010 and claims the benefit thereof. The International Application claims the benefits of European application No. 10172377.3 filed Aug. 10, 2010, both of the applications are incorporated by reference herein in their entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to rotor blade element, especially a wind turbine rotor blade element, a wind turbine rotor blade, a wind turbine and a method for improving the efficiency of a wind turbine rotor blade. 
     BACKGROUND OF THE INVENTION 
     Blade elements provided for improving the efficiency and for changing the aerodynamic profile of a wind turbine rotor blade and such elements mounted to a trailing edge of a blade are well known from patent literature. Example hereof are EP 1 314 885 B, EP 2 195 525 A, WO 2009/026929 A1, EP 2 031 242 A1, US 2010/143151 A, EP 1 775 464 A and U.S. Pat. No. 5,328,329 A. The elementary features like normal elastic trailing edge or serrated edge are also much known from the cited literature. 
     In US 2010/0143151 A1 a wind turbine blade is disclosed, which includes a permeable flap extending from a trailing edge of the blade. The flap can be retrofit to existing blades and may flush with the outer surface of the blade. 
     In U.S. Pat. No. 5,328,329 a width extender is provided, which is used to modify existing fan blades in order to enable them to rotate at slower speed thereby reducing the noise associated with them while at the same time maintaining proper work efficiency. The width extender is fixably connected along the trailing edge of an existing fan blade by, for example, adhesive bonding. 
     In EP 2 195 525 A, WO 2009/026929 A1 and EP 2 031 242 A1 a blade element for mounting on a wind turbine blade is provided. The blade element has a shape so that, by mounting in a first longitudinal part of the wind turbine blade, it changes the profile of the first longitudinal part from the first airfoil profile with an essentially pointed trailing edge and a first chord length to a changed airfoil profile with a blunt trailing edge. The changed airfoil profile is a truncated profile of an imaginary airfoil profile with an essentially pointed trailing edge and a second chord length which is larger than the first chord length. 
     In EP 1 775 464 A2 a wind turbine with a blade rotor which reduces noise by the inclusion of a set of flexible bristles is disclosed. The set of flexible bristles is aligned in at least one row on the trailing edge of the aerodynamic profile of the blade and protrudes over it. 
     In EP 1 314 885 B1 a method and an apparatus for improving the efficiency of a wind turbine rotor are disclosed. The wind turbine rotor comprises a serrated panel connected to each wind turbine rotor blade, an upper and a lower surface on each panel, a plurality of span-wise, periodic indentations on each panel, means for connecting the serrated panel to a trailing edge on each of the wind turbine rotor blades of the wind turbine rotor such that the serrated panel extends from the trailing edge into airflow behind the trailing edge. The serrations on each wind turbine rotor blade have an angle different from 0° relative to a mounting surface on each of the wind turbine rotor blades. The serrations on each of the serrated panels have a given stiffness allowing for an angle of the serrations to change passively in response to speed and angle of the airflow at the trailing edge of each of the wind turbine rotor blades due to flexing of the serrations and the serrated panel. 
     SUMMARY OF THE INVENTION 
     It is a first objective of the present invention to provide a rotor blade element which improves the efficiency of a wind turbine rotor blade and reduces noise during operation of a wind turbine rotor blade. It is a second objective of the present invention to provide a wind turbine rotor blade with an improved efficiency and reduced noise during operation. A third objective is to provide a wind turbine with improved efficiency and reduced noise during operation. It is a forth objective of the present invention to provide a method for improving the efficiency of a wind turbine rotor blade. 
     The objectives are solved by the independent claims. The depending claims define further developments of the invention. All described features are advantageous individually or in any combination with each other. 
     The inventive rotor blade element is adapted for mounting it on a wind turbine rotor blade. The wind turbine rotor blade comprises a trailing edge, a suction side and a pressure side. The blade element comprises a trailing edge, a first surface and a second surface. The first surface forms a pressure side surface portion. The second surface comprises a suction side surface portion and a contact surface. Preferably, the contact surface is adapted for connecting the rotor blade element to the pressure side of the rotor blade. 
     The inventive rotor blade element has the advantage that it is easy to fit to a rotor blade. Furthermore, it may preferably have a form that makes it a natural prolongation of a trailing surface or trailing edge of the rotor blade. The rotor blade may comprise a chord length which is defined as a length from the trailing edge to the leading edge of the blade. The inventive rotor blade element may prolong the chord length of the rotor blade by connecting an inventive rotor blade element to the trailing edge of the blade. 
     Furthermore, the inventive rotor blade element improves the efficiency of the rotor blade and reduces aerodynamic noise generated by a trailing edge of the rotor blade. Moreover, the inventive rotor blade element can be retro-fit to existing rotor blades. As the blade element may be made of a light weight material and/or may be limited in size, a high level of safety can be ensured if, for example, a blade element comes off from a height or falls down from a rotor blade. 
     Preferably, the inventive rotor blade element may comprise a trailing edge flange which is adapted for attaching the rotor blade element to the trailing edge of a wind turbine rotor blade. Preferably, the trailing edge flange is located between the contact surface and the suction side surface portion of the inventive rotor blade element. For example, the trailing edge flange may have the shape of an edge. 
     The trailing edge flange has the advantage that the suction side surface portion of the rotor blade element may flush with the suction side of the wind turbine rotor blade which is equipped with the inventive rotor blade element. Due to the trailing edge flange the suction side surface portion of the rotor blade element may form an even suction side surface with the suction side of the wind turbine rotor blade. 
     The first surface may comprise a curvature, preferably a concave curvature. The curvature can be adapted for prolonging the pressure side of a wind turbine rotor blade. The suction side surface portion of the inventive rotor blade element may also comprise a curvature, preferably a convex curvature. The curvature of the suction side surface portion may correspond to the curvature of the suction side of the wind turbine rotor blade. The curvature can be adapted for prolonging the suction side surface of the rotor blade. Furthermore, the contact surface of the inventive rotor blade element may comprise a curvature, preferably, a convex curvature. The curvature of the contact surface may correspond to the curvature of the pressure side of the blade. Advantageously, the contact surface can be adapted for being attached to part of the pressure side of the wind turbine rotor blade. 
     Moreover, the rotor blade element may comprise elastic material. For example, the rotor blade element may comprise plastic material and/or thermoplastic material and/or a composite structure, for example comprising glass fibre. Preferably, the inventive rotor blade element may be made of plastic material and/or thermoplastic material and/or a composite structure like, for example, glass fibre. 
     The inventive rotor blade element may elastically bend or deform along the trailing edge of the blade so as to follow the dynamic curvature of the blade to which it is attached during operation. The blade element may further elastically bend or deform in relation to the aero-dynamical influences, like for example wind speed or wind resistance, during operation of the rotor blade. 
     Making the blade element of light weight material and limiting the size of the blade element, a high level of safety is ensured, for example, if a blade element is dropped from a height or falls down from a rotor blade. Generally, the inventive rotor blade element can be produced by injecting moulding. 
     Moreover, the rotor blade element may have a length, for instance at its trailing edge, of between 0.4 m and 1.0 m. Generally, the inventive rotor blade element can be one long stripe or can be segmented, for example in approximately 0.4 to 1.0 m long segments when attached to a rotor blade. This makes the blade elements easier to handle. Furthermore, the rotor blade element can be extended along substantially the whole length of the trailing edge of the rotor blade or along only the most distal part such as the most distal 8 m, for instance measured from the tip of the blade. 
     The inventive rotor blade element may comprise a double-sided adhesive tape for fixing the rotor blade element to the rotor blade. Advantageously, the double-sided adhesive tape can be located at the contact surface. The inventive rotor blade element can be prepared for, and be mounted on the rotor blade by, for example, double-sided adhesive tape. Alternatively, it can be prepared for and be mounted on the rotor blade by glue or a combination of glue and double-sided adhesive tape. The rotor blade element can be mounted, for example glued or taped, on a rotor blade from factory or can be retro-fit. 
     The rotor blade element may have a serrated or straight trailing edge. 
     Furthermore for various embodiments of the invention, the blade element may be designed to comprise a winglet which may ensure to reduce the fall-speed through open air for a blade element which is falls down from a height. This in turn increases safety for personnel in the vicinity of a turbine which is equipped with the inventive rotor blade element. Therefore, the inventive rotor blade element may advantageously comprise a winglet. 
     The inventive rotor blade comprises at least one rotor blade element as previously described. For example, one rotor blade element can be attached to the trailing edge of the rotor blade. Alternatively, a number of rotor blade elements, for example formed as segments, may be attached to the trailing edge of the rotor blade. 
     Furthermore, the rotor blade may comprise a tip. The rotor blade element may extend along the whole length of the trailing edge of the rotor blade. Alternatively, the rotor blade element may extend along the length of the trailing edge of the rotor blade of at least 8 m measured from the tip. 
     The rotor blade element can be fixed to the rotor blade by glue and/or by tape, for instance by a double-sided adhesive tape. 
     The inventive wind turbine comprises at least one rotor blade, preferably three rotor blades, as previously described. Generally, the inventive rotor blade and the inventive wind turbine have the same advantages as previously mentioned in the context with the inventive rotor blade element. 
     The inventive method for improving the efficiency of a wind turbine rotor blade is related to a rotor blade which comprises a trailing edge. At least one inventive rotor blade element as previously described is mounted to the trailing edge of the wind turbine rotor blade. Preferably, the at least one rotor blade element is fixed to the rotor blade by glue and/or by tape, for instance by a double-sided adhesive tape. Furthermore, the at least one rotor blade element may be mounted to the trailing edge of a newly manufactured rotor blade or it may be retro-fitted to the trailing edge of an already used or previously manufactured rotor blade. 
     The inventive method has the same advantages as the previously described inventive rotor blade element. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Further features, properties and advantages of the present invention will become clear from the following description of an embodiment in conjunction with the accompanying drawings. All mentioned features are advantageous separate or in any combination with each other. 
         FIG. 1  schematically shows a wind turbine. 
         FIG. 2  schematically shows a rotor blade in a plan view on the plane defined by the blade&#39;s span and the blade&#39;s chord. 
         FIG. 3  schematically shows a chord wise section through the airfoil portion of the blade shown in  FIG. 2 . 
         FIG. 4  schematically shows a rotor blade which is equipped with a number of inventive rotor blade elements. 
         FIG. 5  schematically shows an inventive rotor blade element in a perspective view. 
         FIG. 6  schematically shows part of a wind turbine rotor blade with an inventive rotor blade element in a perspective and sectional view. 
         FIG. 7  schematically shows a further variant of part of an inventive wind turbine rotor blade element in a perspective view. 
         FIG. 8  schematically shows the rotor blade element of  FIG. 7  equipped with a double-sided adhesive tape in a perspective view. 
         FIG. 9  schematically shows another variant of an inventive rotor blade element with a winglet. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  schematically shows a wind turbine  1 . The wind turbine  1  comprises a tower  2 , a nacelle  3  and a hub  4 . The nacelle  3  is located on top of the tower  2 . The hub  4  comprises a number of wind turbine blades  5 . The hub  4  is mounted to the nacelle  3 . Moreover, the hub  4  is pivot-mounted such that it is able to rotate about a rotation axis  9 . A generator  6  is located inside the nacelle  3 . The wind turbine  1  is a direct drive wind turbine. 
       FIG. 2  shows a wind turbine blade  5  as it is usually used in a three-blade rotor. However, the present invention shall not be limited to blades for three-blade rotors. In fact, it may as well be implemented in other rotors, e.g. one-blade rotors or two-blade rotors. 
     The rotor blade  5  shown in  FIG. 2  comprises a root portion  23  with a cylindrical profile and a tip  22 . The tip  22  forms the outermost part of the blade. The cylindrical profile of the root portion  23  serves to fix the blade to a bearing of a rotor hub  4 . The rotor blade  5  further comprises a so-called shoulder  24  which is defined as the location of its maximum profile depth, i.e. the maximum chord length of the blade. Between the shoulder  24  and the tip  22  an airfoil portion  25  extends which has an aerodynamically shaped profile. Between the shoulder  24  and the cylindrical root portion  23 , a transition portion  27  extends in which a transition takes place from the aerodynamic profile of the airfoil portion  25  to the cylindrical profile of the root portion  23 . The span of the blade  5  is designated by reference numeral  28 . 
     A chord-wise cross section through the rotor blade&#39;s airfoil section  25  is shown in  FIG. 3 . The aerodynamic profile shown in  FIG. 3  comprises a convex suction side  33  and a less convex pressure side  35 . The dash-dotted line extending from the blade&#39;s leading edge  29  to its trailing edge  21  shows the chord  38  of the profile. Although the pressure side  35  comprises a convex section  37  and a concave section  39  in  FIG. 3 , it may also be implemented without a concave section at all as long as the suction side  33  is more convex than the pressure side  35 . 
     The suction side  33  and the pressure side  35  in the airfoil portion  25  will also be referred to as the suction side and the pressure side of the rotor blade  5 , respectively, although, strictly spoken, the cylindrical portion  23  of the blade  5  does not show a pressure or a suction side. 
       FIG. 4  schematically shows a wind turbine rotor blade  5 . A number of inventive rotor blade elements  40  are attached and fixed to the trailing edge  21  of the turbine blade  5 . The rotor blade elements  40  are connected to the trailing edge  21  close to the tip  22 . Preferably, the inventive rotor blade elements  40  cover or extend along at least 8 m of the trailing edge  21  measured from the tip  22 . 
       FIG. 5  schematically shows an inventive rotor blade element  40  in a perspective view. The rotor blade element  40  comprises a trailing edge  46 , a first surface  41  and a second surface  42 . The first surface  41  forms a pressure side surface portion, which can be adapted to flush with the pressure side  35  of the rotor blade  5 . The second surface  42  comprises a suction side surface portion  43 , which can be adapted to flush with the suction side  33  of the rotor blade  5 , and a contact surface  44  for connecting the rotor blade element  40  to the pressure side  35  of the rotor blade  5 . 
     The inventive rotor blade element  40  further comprises a trailing edge flange  45 , which preferably has the shape of an edge which fits to the trailing edge  21  of the rotor blade  5 . 
     The first surface  41  has a concave curvature corresponding to the curvature of part of the pressure side  35  of the rotor blade  5  to prolong the rotor blade  5  in its chord length  38 . The suction side surface portion  43  has a convex curvature corresponding to the convex curvature of the suction side  33  of the rotor blade  5  to flush with the suction side  33  and to prolong the suction side  33  in chord direction  38 . The contact surface  44  has a convex curvature corresponding to the curvature of the concave section  39  of the pressure side  35  to which the contact surface  44  is adapted to be attached to. 
       FIG. 6  shows part of an inventive rotor blade  5  to which an inventive rotor blade element  40  is mounted. The inventive rotor blade element  40  is glued or taped with its contact surface  44  to the concave portion  39  of the pressure side  35  of the rotor blade  5  at the trailing edge  21 . The trailing edge  21  is attached to the trailing edge flange  45 . 
     The suction side  33  and the suction side portion  42  of the rotor blade element  40  form an even surface, especially with the same convex curvature. Ideally, there is a smooth change from the suction side  33  of the rotor blade  5  to the suction side portion  42  of the rotor blade element  40 . The first surface  41  provides a smooth change to the pressure side  35  of the rotor blade  5  and prolongs the pressure side  45  at the trailing edge  21  of the rotor blade  5 . 
       FIGS. 7 and 8  show a further variant of an inventive rotor blade element  50  with a serrated trailing edge  56 . In  FIG. 7  part of the rotor blade element  50  is shown in a sectional and perspective view. In  FIG. 8  the rotor blade element  50  is shown in a perspective view onto its second surface  42 . In the  FIGS. 7 and 8  the trailing edge  56  of the rotor blade element  50  has a serrated shape. Furthermore, in  FIG. 8  the contact surface  44  comprise a double-sided adhesive tape  57 , for example, for connecting the rotor blade element  50  to the pressure side  35  of the rotor blade  5 , as shown in  FIG. 6 . 
       FIG. 9 , schematically shows another variant of an inventive rotor blade element  60 . The blade element  60  comprises a winglet  49  which will ensure to reduce the fall-speed through open air for the blade element  60  in case that it falls down from a height, for example. This increases the safety for personnel in the vicinity of the turbine.