Abstract:
There is provided a wind power installation rotor blade comprising a suction side, a pressure side, a region near the root, a rotor blade tip a rotor blade leading edge and a rotor blade trailing edge. The rotor blade further has a plurality of stagnation points along the length of the rotor blade, which together can form a stagnation point line. A plurality of vortex generators is provided in the region of the stagnation point line. The stagnation point line is disposed on the underside (generally referred to as the pressure side) of the rotor blade.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    The present invention concerns a wind power installation rotor blade. 
         [0003]    2. Description of the Related Art 
         [0004]    A rotor blade of a wind power installation has a rotor blade root region, a rotor blade tip, a rotor blade leading edge, a rotor blade trailing edge, a suction side and a pressure side. Typically the rotor blade is connected at its rotor blade root region to a hub of a wind power installation. In that way the rotor blades are connected to a rotor of the wind power installation and cause the rotor to rotate if there is sufficient wind. That rotation can be converted into electric power by an electric generator. 
         [0005]    The rotor blade is moved by the principle of aerodynamic lift. When wind is incident on a rotor blade air is guided along the blade both above it and also below it. The blade is typically curved in such a way that the air above the blade involves a longer path around the profile and therefore has to flow more quickly than the air along the underside. Therefore a reduced pressure is generated above the blade (suction side) and an increased pressure is generated below the blade (pressure side). 
         [0006]    EP 1 944 505 A1 shows a wind power installation rotor blade having a plurality of vortex generators on the suction side of the rotor blade. 
         [0007]    EP 2 484 898 A1 describes a wind power installation rotor blade having a plurality of vortex generators. The vortex generators are provided in the region near the rotor blade root. 
         [0008]    WO 2013/014080 A2 shows a wind power installation rotor blade having a plurality of vortex generators. In addition that specification describes how a rotor blade can be retro-fitted with the vortex generators. In that case the vortex generators are provided at the suction side of the rotor blade and in the region near the rotor blade root. 
         [0009]    WO 2007/140771 A1 shows a rotor blade of a wind power installation having a plurality of vortex generators on the suction side of the rotor blade. 
         [0010]    WO 2008/113350 A2 also shows a wind power installation rotor blade having a plurality of vortex generators. The vortex generators are provided on the suction side of the rotor blade. 
         [0011]    WO 2006/122547 A1 shows a rotor blade of a wind power installation having a plurality of vortex generators on the suction side of the rotor blade. 
         [0012]    WO 2012/082324 A1 shows a wind power installation rotor blade having a plurality of vortex generators, the vortex generators being provided in the region near the rotor blade root. 
       BRIEF SUMMARY 
       [0013]    Operation of the wind power installation involves sound emission which is to be reduced as much as possible to improve acceptance of wind power installations among the population. 
         [0014]    There is provided a wind power installation rotor blade having a suction side, a pressure side, a region near the root, a rotor blade tip, a rotor blade leading edge and a rotor blade trailing edge. The rotor blade further has a plurality of stagnation points along the length of the rotor blade, which together can form a stagnation point line. A plurality of vortex generators is provided in the region of the stagnation point line. The stagnation point line is disposed on the underside (generally referred to as the pressure side) of the rotor blade. 
         [0015]    The stagnation point is that point at the surface of the rotor blade, at which the speed of the flow disappears so that kinetic energy can be completely converted into a pressure energy. The position of the stagnation point can be changed by changing the pitch angle. The stagnation point is that point at which the flow divides up, and a part of the flow flows over the suction side of the rotor blade and the other part flows over the pressure side. 
         [0016]    According to an aspect of the invention the vortex generators are provided in the longitudinal direction at more than 50%, in particular more than 60% of the length of the rotor blade (that is to say the last 50% to 40% of the rotor blade in the direction of the rotor blade tip are provided with vortex generators in the region of the stagnation point line). 
         [0017]    The shape of the vortex generators can be for example a semicircle, oval or arrow-shaped in plan view. The diameter of the vortex generators is less than 100 mm. The spacing between adjacent vortex generators is at least one times the diameter and is at a maximum ten times the diameter of the vortex generators. 
         [0018]    The height of the vortex generators is at a maximum one-quarter of the diameter. The 3D shape of the vortex generators can represent a disk of constant thickness or a portion of a sphere of a round basic shape. 
         [0019]    Further configurations of the invention are subject-matter of the appendant claims. 
     
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         [0020]    Advantages and embodiments by way of example of the invention are described in greater detail hereinafter with reference to the drawing. 
           [0021]      FIG. 1  shows a diagrammatic view of a wind power installation according to the invention, 
           [0022]      FIG. 2  shows a diagrammatic view of a rotor blade according to a first embodiment, 
           [0023]      FIG. 3  shows a diagrammatic sectional view of a rotor blade according to a first embodiment, 
           [0024]      FIG. 4  shows a perspective view of a portion of a wind power installation rotor blade according to a second embodiment, and 
           [0025]      FIG. 5  shows a polar diagram to illustrate a variation in the lift coefficient in relation to the effective angle of incidence for a wind power installation rotor blade. 
       
    
    
     DETAILED DESCRIPTION 
       [0026]      FIG. 1  shows a diagrammatic view of the wind power installation according to one embodiment of the invention. The wind power installation  100  has a pylon  102  and a pod  104 . Provided on the pod  104  is a rotor  106  having three rotor blades  200  and a spinner  110 . In operation the rotor blade  106  is caused to rotate by the wind and then thereby causes rotation of an electric generator in the pod, which generates electric power from the rotation. The pitch of the rotor blades or the angle of incidence of the rotor blades  200  can be altered by pitch motors at the rotor blade roots of the respective rotor blades  200 . 
         [0027]      FIG. 2  shows a diagrammatic view of a wind power installation rotor blade according to a first embodiment. The rotor blade  200  has a rotor blade leading edge  211 , a rotor blade trailing edge  212 , a rotor blade tip  213  and a rotor blade root region  214 . The rotor blade further has a longitudinal direction L which extends from the rotor blade root region  214  to the rotor blade tip  213 . The rotor blade further has a stagnation point line  215  which extends on the pressure side of the rotor blade. As the cross-section of the rotor blade change in the longitudinal direction L the stagnation point also changes for each portion of the rotor blade. Thus a stagnation point line  215  can be formed from the plurality of stagnation points. A plurality of vortex generators  300  is provided in the region of the stagnation point line  215 . The rotor blade  200  is releasably fixed to the rotor  106  of the wind power installation by the rotor blade root region  214 . The end of the rotor blade root region  214  which is fixed to the rotor  106 , for example to the rotor hub, is of a round configuration and can be releasably fixed to the hub of the rotor  106  by way of a plurality of screw connections. 
         [0028]    The vortex generators  300  are provided in the region of the stagnation point line  215  at a predetermined angle of incidence, for example the nominal angle of incidence. 
         [0029]    Optionally the vortex generators  300  can be provided as from a length of 50% to 100% of the rotor blade, as from the rotor blade root region  214 . In particular the vortex generators  300  can be provided at between 60% and 100% of the length of the rotor blade, as from the rotor blade root region  214 . 
         [0030]    Due to the provision of the vortex generators in the region of the stagnation points of the rotor blade it is possible to positively influence detachment of the flow at the rotor blade trailing edge. 
         [0031]    The vortex generators  300  can be circular, oval or arrow-shaped in plan view. The diameter of the vortex generators is less than 100 mm (for example 20 mm). The spacing between adjacent vortex generators  300  is at least one times the diameter of the vortex generators and at a maximum ten times the diameter of the vortex generators. The height of the vortex generators is at a maximum one-quarter of the diameter of the vortex generators. The three-dimensional shape can correspond to a disk of constant thickness or a portion of a sphere with a round basic shape. An arrow-shaped plan-view outline can represent a pyramid shape. While the orientation in the flow direction is unimportant in the case of a round basic shape the pyramid is oriented with its tip in the flow direction. 
         [0032]      FIG. 3  shows a diagrammatic sectional view of a wind power installation rotor blade according to the first embodiment. The rotor blade  200  has a rotor blade leading edge  210 , a rotor blade trailing edge  212 , a suction side  216  and pressure side  217 . The vortex generators  300  are provided in the region of the pressure side  217  and in the region of the stagnation point or the stagnation point line  215 . 
         [0033]      FIG. 4  shows a perspective view of a portion of a rotor blade according to a second embodiment. In this portion the rotor blade  200  has two vortex generators  300  which are provided in the region of the stagnation point line  215 . Optionally the vortex generators  300  can be so provided in the region of the stagnation point line  215  that in nominal operation they are disposed in the region of the stagnation point line. If the effective angle of incidence increases globally or locally due to a changing wind condition (for example with a gusty wind or in operation in shear wind conditions) the stagnation point moves behind the vortex generators and vortex filaments  400  occur at the vortex generators, which stabilize larger detachment regions on the suction side and which thus still provide for a flow in contact and for maintenance of lift, even under disadvantageous afflux flow conditions.  FIG. 4  shows the central line  215   b  between the suction and pressure sides, the stagnation point line  215   a  with an effective angle of incidence α eff  at nominal speed (nominal range) and the stagnation point line  215   c  at the effective angle of incidence α eff  in the stall region. 
         [0034]      FIG. 5  shows a polar diagram to illustrate the variation in the lift coefficient in relation to the effective angle of incidence or pitch angle at a Reynolds number of 6 million. This shows the variation in the lift coefficient C L  in relation to the effective flow angle α eff  for a rotor blade without vortex generators  600  and for a rotor blade having vortex generators  500 . It can thus be seen from  FIG. 5  that the use of the vortex or eddy generators according to the invention leads to a delay in the beginning of detachment of the air flow. The lift coefficient C L  is increased, that is to say the rotor blade with the vortex generators according to the invention can achieve a higher lift coefficient and can attain a higher effective angle of incidence α eff . The maximum lift coefficient C L  is thus pushed out to higher angles of incidence of the rotor blade. For the wind power installation, in on-going operation, that signifies an improvement in the steady-state detachment characteristics of the profile with at the same time minimization of the negative increase in resistance. That explains the reduction in noise in respect of rotor blades in steady-state afflux flow conditions so that the wind power installation according to the invention provides reduced sound emission.