Patent Publication Number: US-2023160363-A1

Title: Rotor blade for a wind turbine and wind turbine

Description:
The present invention relates to a rotor blade for a wind turbine according to claim  1  and to a wind turbine according to claim  13 . 
     Rotor blades of wind turbines and wind turbines with rotor blades are generally known and disclosed, for example, in the documents EP 3 330 530 A1, EP 3 147 499 A1, EP 2 840 255 A2, EP 1 019 631 B1, WO 2019/030205 A1, WO 2018/046067 A1, WO 2010/046000 A2 and NL 1030111. 
     In particular, the present invention relates to rotor blades of a wind turbine and to wind turbines having such rotor blades, which have a rotor diameter of 1.5 m to 8 m and a length of the rotor blade of about 0.75 m to about 4 m, respectively. 
     It is the object of the present invention to present a rotor blade of a wind turbine and a wind turbine with such rotor blades, which have a good starting behavior with low noise emissions. 
     This object is solved with a rotor blade according to claim  1  and a wind turbine according to claim  13 . 
     In a known manner, a rotor blade of a wind turbine has a rotor blade root for fastening the rotor blade to a rotor shaft or to a hub. The rotor blade root defines a reference plane. The hub is typically attached to the rotor shaft. In operation, the rotor shaft or its axis of rotation is at least approximately aligned in the direction of the incoming wind. 
     A profile region of the rotor blade adjoins the rotor blade root and extends into a rotor blade tip region facing away from the rotor blade root. Preferably, the profile region extends to the rotor blade tip, i.e. to the free end of the rotor blade; however, it is also conceivable that the profile region ends at a distance from the rotor blade tip, in the rotor blade tip region, and the rotor blade has a rotor blade element of different shape following the profile region to the rotor blade tip. 
     A rotor blade nose and a rotor blade rear edge extend along the entire length of the profile region. A blade profile of the rotor blade, which extends over the entire profile region from the rotor blade nose to the rotor blade rear edge, has an upper side forming a suction side and a lower side forming a pressure side. 
     The upper side is on the leeward side and the lower side on the windward side. 
     A chord of the blade profile extends through the rotor blade nose and the rotor blade rear edge. The chord and the reference plane enclose a chord angle, wherein the lower side of the blade profile faces the reference plane and the upper side of the blade profile faces away from the reference plane. 
     The distance between the reference plane and the chord is increasing in the direction towards the rotor blade nose. 
     The reference plane BE encloses, in the assembled state of the rotor blade  10 , with the rotor shaft  18  and thus its axis of rotation  20  an angle of attack β of preferably maximum 70° and minimum 50°. This angle of attack β is the smallest measurable angle between the axis of rotation  20  and the reference plane BE. 
     The lower side of the blade profile is designed to be impelled by the wind. 
     According to the invention, the chord angle increases over the profile region, from the rotor blade root towards the rotor blade tip region. 
     Experiments and computer simulations have shown that such a rotor blade and wind turbines with such rotor blades already show a good cp value at low wind speeds of, for example, 4.5 m to 5 m per second with low noise emissions and thus exhibit good start-up characteristics. 
     In a preferred manner, the chord angle increases continuously, especially preferably at least approximately linearly, resulting in a rotor blade with high efficiency and simple construction. This increase in chord angle occurs preferentially up to the rotor blade tip. However, the chord angle can also increase linearly from the rotor blade root to the rotor blade tip region and more strongly in the rotor blade tip region, which supports a good starting behavior at low wind speeds. 
     Preferably, the chord angle is between 0° and 4° in an initial section immediately adjacent to the rotor blade root and between 20° and 26° in the rotor blade tip region. This leads to good results for rotor blade lengths of approx. 0.75 m to approx. 4 m and thus rotor diameters of approx. 1.5 m to approx. 8 m. 
     Preferably, the chord angle at the rotor blade root-side end of the profile region is 0°. 
     Preferably, the rotor blade rear edge is at least approximately straight. This leads to a particularly simple design of the rotor blade. 
     The particularly simple structure and the good efficiency are supported if the rotor blade rear edge, as is preferred, runs at least approximately in the reference plane. 
     Preferably, the profile depth decreases over the entire profile region, from the rotor root towards the rotor blade tip region. This allows the mechanical stress on the rotor blade to be kept low. 
     Preferably, the profile depth decreases continuously, especially preferably linearly. This also leads to a particularly simple and efficient rotor blade. 
     Preferably, the profile depth, starting at the rotor blade root and extending into the rotor blade tip region, decreases to half to one quarter, preferably at least approximately to one third. This results in a rotor blade that is simple, stable and efficient in design. 
     Preferably, the profile thickness also decreases over the entire profile region, from the rotor blade root towards the rotor blade tip region. This is preferably continuous, in particular at least approximately linear. This allows the blade profile to have at least approximately the same shape throughout the profile region (it is similar), resulting in a particularly simple structure. 
     It has been shown that a preferably at least approximately constant ratio of profile thickness to profile depth over the entire profile region leads to an efficient rotor blade that is simple in structure. Preferably, this ratio is at least approximately 0.07. 
     Preferably, the ratio of the profile depth, measured at the rotor blade root-side end of the profile region, to the length of the profile region (measured in the longitudinal direction of the rotor blade) is at least approximately 0.2. 
     The rotor blade is designed to rotate about the axis of rotation of the wind turbine, the axis of rotation being oriented at least approximately in the direction of the incoming wind during operation, and the rotor blade, as preferred, being on the windward side. It can then be impelled by the wind undisturbed. 
     The blade profile is preferably a normal profile with a convex curved upper side and an S-shaped curved lower side, whereby on the lower side the transition from the convex to the concave shape is located close to the profile nose, preferably within the first 15% of the profile depth. This results in a slender blade profile. 
     A wind turbine equipped with such rotor blades has a rotor shaft defining an axis of rotation with a hub fixed thereon, to which the rotor blades are attached. During operation of the wind turbine, the axis of rotation is aligned at least approximately in the direction of the incoming wind and the rotor blades are located on the windward side for undisturbed inflow. 
     The wind turbine preferably has two to five, especially preferably three rotor blades. On the one hand, this ensures a symmetrical design and, on the other hand, smooth running. 
     Preferably, the wind turbine is designed in the form of a shrouded wind turbine to achieve a particularly good efficiency. 
     Preferably, the rotor blade is designed to extend with its longitudinal direction at least approximately in radial direction to the axis of rotation. The same applies to wind turbines with two or more rotor blades, whereby these are evenly distributed in the circumferential direction. 
     The rotor blade nose preferably extends at least approximately in a plane perpendicular to the reference plane. 
     It is also possible to arrange the rotor blade root on the hub or on the rotor shaft to be pivotable about a pivot axis running in the longitudinal direction of the rotor blade, this in particular in order to pivot the rotor blade into a neutral position when no driving force is to be generated, or to optimize the incident flow. 
     For the sake of completeness, it should be mentioned that in operation the rotor blade nose, in the direction of rotation of the rotor blade, is leading and the rotor blade rear edge is trailing. Preferably, the rotor blade root is provided with two fastening lugs for fastening to the hub or rotor shaft, respectively, the passage of which is at least approximately perpendicular to the reference plane. 
    
    
     
       The invention is described in more detail with reference to the figures. They show, purely schematically: 
         FIG.  1    in view of a rotor blade according to the invention; 
         FIG.  2    a section through the rotor blade according to  FIG.  1    along the line of intersection B-B; 
         FIG.  3    a section through the rotor blade according to  FIG.  1    along the section line C-C; 
         FIG.  4    a section through the rotor blade according to  FIG.  1    along the section line D-D; 
         FIG.  5    a section through the rotor blade according to  FIG.  1    along the section line E-E; 
         FIG.  6    a section through the rotor blade according to  FIG.  1    along the section line F-F; 
         FIG.  7    a side view of the rotor blade according to  FIGS.  1  to  6    in the direction of arrow VII of  FIG.  1   ; 
         FIG.  8    the rotor blade according to  FIGS.  1  to  7    in side view in the direction of arrow VIII of  FIG.  1   ; 
         FIG.  9    a section through the rotor blade along section line A-A of  FIG.  1   ; 
         FIG.  10    a view from below of the rotor blade shown in  FIGS.  1  to  9   ; 
         FIG.  11    a top view of the rotor blade shown in  FIGS.  1  to  10   ; 
         FIG.  12    a longitudinal section through the rotor blade along the section line G-G of  FIG.  1   , which runs at right angles to an axis of rotation; 
         FIG.  13    a perspective view of a wind turbine with three rotor blades according to  FIGS.  1  to  12   ; and 
         FIG.  14    in perspective view of a wind turbine designed in the manner of a shrouded wind turbine with three rotor blades according to  FIGS.  1  to  12   . 
     
    
    
     The rotor blade  10  shown in  FIGS.  1  to  12    has a rotor blade root  12  and a profile region  16  directly adjoining the rotor blade root  12  and extending into a rotor blade tip region  13  remote from the rotor blade root  12 . The rotor blade  10  is designed to be fastened with the rotor blade root  12  to a hub or to be fastened to the hub. This hub is seated in a known manner in a rotationally fixed manner on a rotor shaft  18 , which defines an axis of rotation  20  for the rotor blade  10 . In this connection, further reference is made to  FIGS.  13  and  14    and the relevant description below. 
     A leading rotor blade nose  22  in the direction of rotation D of the rotor blade  10  and a trailing rotor blade rear edge  24  extend over the entire profile region  16 . 
     In the embodiment shown, the profile region  16  extends to the rotor blade tip  26 , that is, to the free end of the rotor blade  10 . However, it is conceivable that the profile region  16  extends only into the rotor blade tip region  14  and that the rotor blade  10  then has a rotor blade element of a different shape following the profile region  16  to the rotor blade tip  26 . 
     In the profile region  16 , the rotor blade  18  has a blade profile  28  which, in a known manner, forms a suction side with its upper side  30  and a pressure side with its lower side  32 . The blade profile  28  extends from the rotor blade nose  22  to the rotor blade rear edge  24 . 
     In  FIG.  2   , an arrow W indicates the direction of the wind flowing against the rotor blade during operation. Thus, the lower side  32  is on the windward side and the upper side  30  is on the leeward side. 
     The blade profile  28  has a chord  34  that passes through the rotor blade nose  22  and the rotor blade rear edge  24  and defines a chord angle α. This chord angle α is defined by the (smallest) angle between the chord  34  and a reference plane BE. 
     In the embodiment example, the reference plane BE is defined by the planar surface of the rotor blade root  12 . The reference plane E further extends in the longitudinal direction L of the rotor blade  10  extending radially with respect to the axis of rotation  20 . 
     As can be seen from  FIG.  2   , the reference plane BE defines an angle of attack β of minimum of 50° and maximum of 70° with the axis of rotation  20 . 
     As can be seen in particular from  FIGS.  2  to  6   , the chord angle α increases continuously over the entire profile region  16 , from the rotor blade root  20  in the direction of the rotor blade tip  26  up to the latter. 
     Usually, the rotor blade  10  attached to the rotor shaft  18  or a hub seated thereon is covered by a shaft hood  68  up to the beginning of the profile region  16  on this side, i.e. the rotor blade root  12 , as shown in connection with  FIGS.  13  and  14   . 
     Immediately adjacent to the rotor blade root  12 , the chord angle α is 0° in the embodiment example shown. However, it is also possible for this to be a few degrees of angle, up to 4° for example. 
     In the embodiment example shown, the chord angle at the rotor blade tip is about 26°. However, it can also be selected smaller or larger. In the rotor blade tip region  14 , the chord angle α is preferably between 20° and 28°. 
     As can be seen in particular from  FIGS.  2  to  6    in conjunction with  FIG.  1   , the chord angle α increases linearly from the rotor blade root  12  in the direction of the rotor blade tip  26 . 
     In the view according to  FIG.  1   , the rotor blade nose  22  and the rotor blade rear edge  24  are straight. As a result of the change of the chord angle a, the rotor blade nose  22 , as can be seen in particular from  FIGS.  7  to  12   , runs slightly curved while the rotor blade rear edge  24  (compare  FIG.  10   ) is located approximately in the reference plane BE over its entire length. 
     The profile depth  38 , i.e. the distance between the rotor blade nose  22  and rotor blade rear edge  24 , decreases continuously over the entire profile region  16 , from the rotor blade root  12  in the direction of the rotor blade tip  26 , linearly in the embodiment example shown. 
     At the rotor blade tip  26 , in the embodiment example shown, the profile depth  38  is one third of the profile depth  38  at the rotor blade root  12  side end of the profile region  16 . 
     The ratio of the profile depth  36  at the rotor blade root side end of the profile region  16  to the length of the profile region  36  — i.e. the distance between the rotor blade root  12  and the rotor blade tip  26  — is 0.2. 
     The profile thickness  40  also decreases continuously over the entire profile region  16  from the rotor blade root  12  to the rotor blade tip  26 , linearly in the embodiment example shown. 
     The ratio of the profile thickness  40  to the profile depth  38  is approximately 0.07 over the entire profile region  16 . Consequently, this is a very slender blade profile  28 . 
     As can be seen in particular from  FIGS.  2  to  6   , the blade profile  28  shown is a normal profile with a convexly curved upper side  30  and an S-shaped curved lower side  32 , where on the lower side  32  the transition from the convex to the concave region is close to the rotor blade nose  22 ; the distance from the rotor blade nose  22  is about 10% of the profile depth  38 . 
     As this particularly can also be seen from  FIGS.  13  and  14   , the rotor blade  10  is designed to rotate about the axis of rotation  20  of the wind turbine, the axis of rotation being at least approximately in the direction of the incoming wind W and the rotor blade  10  being located upwind of the wind turbine. 
     The two wind turbines shown in  FIGS.  13  and  14    are each equipped with three rotor blades  10  according to  FIGS.  1  to  12    and as described above. 
     These rotor blades  10  are fastened to the hub  42  by means of two bolts which are not shown and which, as shown in particular in  FIG.  9   , each engage through a fastening lug  44  of the rotor blade root  12 . The longitudinal direction of these fastening lugs  44  and thus of the bolts runs at right angles to the reference plane BE. 
     In the embodiment of the wind turbine shown in  FIG.  13   , a streamlined generator housing  48 , in which a generator  50  for generating electrical energy is arranged, is seated on a vertical support  46 . Attached to the hub  46 , which sits on the rotor shaft  18  driving the generator  50 , are the three rotor blades  10  evenly distributed in the circumferential direction. A tail assembly  52  is located at the leeward end of the generator housing  48  to align the generator housing  48  about the vertical axis of the vertical support  46  such that the axis of rotation  20  is aligned against the incoming wind  36 . The rotor blade roots  12  are covered by the shaft hood  68 . 
     The embodiment of the wind turbine shown in  FIG.  14    is designed as a shrouded wind turbine as disclosed in document WO 2019/076514 A1, but the three rotor blades  10  are designed according to  FIGS.  1  to  12   . 
     Sitting on the vertical support  36 , rotatable about the vertical axis, is a shroud  54  which is formed rotationally symmetrical to the axis of rotation  22  and has a wing-shaped cross-section. The inner upper surface  56  of the shroud delimits a flow channel  58  for the wind. A guiding element  60  is annular and formed rotationally symmetrical to the axis of rotation  20 . The outer diameter of the guiding element  60  is smaller than the smallest clear width of the flow channel  58 . 
     The guiding element profile nose  62  is located upstream with respect to the shroud profile nose  64  and the guiding element profile rear edge  66  is located downstream with respect to the shroud profile nose  64 , but upstream with respect to the smallest clear width of the flow channel  58 . 
     The propeller with the three rotor blades  10  for driving the electrical generator  50  is located at least approximately at the guiding element profile rear edge  66 . 
     To align the shroud  54 , and thus the axis of rotation  20 , against the incoming wind  36 , the shroud  54  is motor rotatable about the axis of the vertical support  46 . 
     The present subject invention may also be defined as follows:
     A rotor blade of a wind turbine having a rotor blade root  12  for attaching the rotor blade  10  to a hub, a profile region  16  adjoining the rotor blade root  12  and extending into a rotor blade tip region  14  remote from the rotor blade root  12 , a rotor blade nose  22  and a rotor blade rear edge  24  extending over the entire profile region  16 , an upper side  30  forming a suction side and a lower side  32  forming a pressure side of a blade profile  28  extending over the entire profile region  16  from the rotor blade nose  22  to the rotor blade rear edge  24 , as well as a chord  34  of the blade profile  28  extending through the rotor blade nose  22  and the rotor blade rear edge  24 ,   wherein a chord angle α between a reference plane BE and the chord  34  increases over the profile region  16 , from the rotor blade root  12  towards the rotor blade tip region  14 .   

     The reference plane BE extends in the longitudinal direction L of the rotor blade  10 , and the chord  34  at the rotor blade root-side end of the profile region  16  extends at least approximately in it. 
     The upper side  30  of the blade profile  28  faces away from the reference plane BE and is located on the leeward side; correspondingly, the lower side  32  is located on the windward side. 
     The reference plane E encloses an angle of attack β between preferably 50° and 70° with the axis of rotation  20  and thus the incoming wind.