Trailing edge add-on

Abstract

The present invention relates to the trailing edge (20) of the rotor blade (20 TE The present invention describes a wind turbine rotor blade add-on (1) having a plurality of serrated teeth (10) arranged to extend outward from the ) the serrated teeth (10) having an elongated shape defined by a base (10B) and two at least partially curved side edges (10S) converging at the tip (10T), the length of the serrated teeth (10) from the base (10B) to the tip (10T) being at least 6 times the width of the serrated teeth (10) at the base (10B), the side edges (10S) of the serrated teeth (10) including a convex curved portion, and the closest distance (1G) between adjacent serrated teeth (10) being at most 1 mm. TE Further details will be given regarding wind turbine rotor blades (20) equipped with several such add-ons (1) attached to the ).

Description

[Technical Field]

[0001] Background technology Acoustic noise emission is a crucial parameter for obtaining permission to install wind turbines in various countries. Today's wind turbines can have very large aerodynamic rotors (with diameters of around 160m or more), and long rotor blades are a significant contributor to the acoustic noise emission of wind turbines. Acoustic noise from wind turbines is primarily caused by their rotor blades, occurring when air moving along the positive and negative pressure sides of the rotor blades recombines beyond the trailing edge.

[0002] The inherently linear trailing edge of a rotor blade efficiently scatters acoustic waves to observers near the wind turbine, who perceive the scattered acoustic waves as "trailing edge noise." This trailing edge noise occurs when turbulent boundary layer flow scatters across the linear trailing edge, generating sound pressure fluctuations that can be carried over large distances, which can make it difficult to meet noise regulations at the inmission point.

[0003] Trailing edge noise can be mitigated to some extent by attaching a serrated “sawtooth” add-on to the trailing edge along a portion of the outer region of the rotor blade. Established trailing edge add-on designs include rows of triangular “teeth” that function to reduce the radiation efficiency of noise generated at points along the blade span. The shape of the serrated teeth of such conventional add-ons is triangular, defined by a base and two linear sides that converge at the tip or apex of the triangle. This type of serrated trailing edge reduces radiative emission through several mechanisms. At low frequencies, the size of the corresponding turbulent vortices is large, and the serrations appear as an intermediate between the solid surface and the wake of the airfoil, mixing the acoustic impedance of the airfoil edge (the ratio of sound pressure to the corresponding volume velocity through a solid surface with very high impedance and a fluid such as air with very low impedance), thus reducing scattering intensity. At higher frequencies, the serrations create an incidence angle between the convective turbulence and the airfoil edge, which has the effect of reducing the radiation efficiency of scattered acoustic waves. In a further embodiment, the serrations induce a canceling interference effect between the noise scattered at the base of each serration and the noise scattered along its linear side. Such a “sawtooth” add-on scatters first from the base of each triangular tooth, then along the linear edge of each triangular tooth, and finally at the vertex or tip of each triangle. The time delay from base to tip induces some canceling interference in the acoustic field. However, the known noise reduction effect of serrated trailing edges is limited. Therefore, if further noise reduction is required to obtain permission to install a wind turbine, the wind turbine operator may need to reduce the maximum aerodynamic rotor speed of the wind turbine. However, this comes at the expense of a reduction in the wind turbine's annual power output (AEP), and is therefore an inadequate solution.

[0004] Therefore, an object of the present invention is to provide a wind turbine rotor blade add-on with improved noise reduction performance.

[0005] This objective is achieved by the claimed wind turbine rotor blade add-on and the claimed wind turbine rotor blade.

[0006] explanation According to the present invention, the rotor blade add-on comprises a plurality of serrated teeth arranged to extend outward, i.e., downstream, from the trailing edge of the rotor blade. The serrated teeth have an elongated shape defined by a base and two lateral edges that converge at the tip.

[0007] The features of the add-on of the present invention are that the length of the serrated teeth from the base to the tip is at least six times greater than the width of the serrated teeth, the lateral edges of each serrated tooth exhibit a convex marginal curvature, and the distance from the base of one serrated tooth to the base of an adjacent serrated tooth is a maximum of 1 mm.

[0008] The geometric shape of a serrated tooth can be defined by three points: two outer points of its base and the point where its lateral edges converge. These three points also define a smaller “foundation” triangle, i.e., a triangle with a smaller surface area essentially contained within the serrated tooth. In the context of this invention, the convex edge of the add-on serrated tooth lies outside the linear edge of the foundation triangle, as is evident from the drawings.

[0009] The performance of the add-on shall be understood as its performance in the context of acoustic noise emission, i.e., the effect of the add-on's shape and form on trailing edge noise. As described above, trailing edge noise is acoustic noise caused by turbulent behavior at and beyond the trailing edge of the rotor blade. The rotor blade add-on of the present invention has been shown to provide a remarkably significant reduction of such trailing edge acoustic noise. The performance of the wind turbine rotor blade add-on of the present invention has been shown (e.g., in wind tunnel tests) to exceed the performance of equivalent add-ons having “triangular” or sawtooth serrations as known from the prior art.

[0010] Maintaining a high aspect ratio of at least 6:1 for the add-on for any given length of serration tooth in any given flow direction (measured from the midpoint of the base of the serration to its tip) effectively reduces the spanwise width of any serration tooth (measured across its base) and improves the possibility of canceling interference of noise radiated along the edges of the serration teeth. The high aspect ratio of each serration tooth of the add-on of the present invention ensures that even relatively small turbulences are affected by the acoustic impedance mixing of the add-on, making the serrations effective even at higher frequencies. The favorable shape of the serration teeth of the add-on of the present invention reduces the angle of incidence of turbulence convection beyond the tooth edges and ensures that the turbulence correlates significantly across the width of the serration teeth.

[0011] The convex curvature of the serrated teeth and the very small gaps between the outer corners of adjacent serrated teeth optimize noise reduction. Appropriate selection of the geometric parameters of the serrated teeth ensures that turbulence scatters acoustic energy as inefficiently as possible, thus mitigating the noise observed at the relevant inmission point. The curvature of the serrated edges allows for a balanced combination of the noise reduction mechanisms enumerated above: namely, the mixing of acoustic impedances, the angle of incidence of turbulence across the edge, and the canceling interference of adjacent source locations. This combination of geometric features results in acoustic noise reduction at critical frequencies, such as between 500 Hz and 1500 Hz.

[0012] The wind turbine rotor blade of the present invention has a root portion and an airfoil portion and can have a length exceeding 80 m. The rotor blade further comprises at least one example of the add-on of the present invention, which is attached to the trailing edge of the airfoil portion of the rotor blade. A wind turbine generally has three rotor blades, each of which may have an add-on in essentially the same arrangement along a portion of its trailing edge.

[0013] Particularly advantageous embodiments and features of the present invention are given by dependent claims, as will be revealed in the following description. Features from different claim categories may be combined as necessary to give further embodiments not described herein.

[0014] Without limiting the present invention, it may be assumed that the add-on comprises a mounting band or strip to facilitate the step of attaching the add-on to the trailing edge of a wind turbine rotor blade. A row of serrated teeth extends downstream from this mounting band. The lower edge of the serrated teeth is assumed to be along a continuous line referred to herein as the baseline. The mounting band may serve to attach the add-on directly to the trailing edge of the wind turbine rotor blade. Alternatively, the mounting band may serve to attach the add-on to further mounting means that can be attached to the trailing edge of the rotor blade.

[0015] The add-on of the present invention may be manufactured as a single unit, comprising a row of serrated teeth and a mounting band. For example, the add-on may be manufactured using additive manufacturing techniques such as injection molding, laser cutting, vacuum forming, and 3D printing, subtractive manufacturing techniques such as milling, and stamping. The add-on may be made from suitable materials, such as rigid and durable plastics (thermoplastics), reinforced composites, wood, vulcanized materials, metals or metal alloys, or combinations thereof, and may optionally be made with a surface coating.

[0016] The advantageous performance of the add-on of the present invention is, to some extent, a result of the specific shape of the serrated teeth. The lateral edges of the serrated teeth exhibit a convex curve over at least a portion of their length between the base and tip of the serrated teeth; that is, the serrated teeth are essentially "iron-shaped" and have a shape similar to that of an ironing plate on a clothes iron.

[0017] The lateral edges of a serrated tooth may include curved and straight portions, for example, a straight portion that begins at the base and transitions into a curved portion, with the curved portion terminating at the tip. The point where the curved portion transitions into the straight portion is preferably selected such that the serrated tooth has a convex curve over most of its length. The serration may also include, for example, a concave portion, with an inflection point in the curvature of the edge between the convex or straight portion and the concave portion.

[0018] Alternatively, the lateral edges of the serrated teeth are curved along their entire length. In such embodiments, the lateral edges of the serrated teeth preferably have the form of a conical arc or an ogive. The conical arc may have the form of a tangential ogive, i.e., a line starting at the baseline and tangent to the lateral edge is perpendicular to the baseline (the lateral edge intersects the baseline at a 90° angle).

[0019] Similarly, a conical arc may have the shape of a secant ogive, that is, a line starting at the baseline and tangent to the lateral edge at an angle with respect to the normal.

number

[0020] The angle at which the lateral edge of an ogive-shaped serrated tooth intersects the baseline can be expressed with respect to the base triangle enclosed by the serrated tooth, that is, the triangle formed between the three outer points of the serrated tooth. For example, the angle δ determined between the major axis of the base triangle and the hypotenuse (straight lateral edge) of the base triangle can be expressed as follows:

number

[0021] The general shape of the serration teeth of the add-on of the present invention can be defined in terms of its aspect ratio. The serration teeth of the add-on of the present invention have a relatively high aspect ratio, that is, their length is significantly longer than their width. The minimum aspect ratio for the serration teeth of the add-on of the present invention is 6:1 and can be on the order of 12:1. The aspect ratio of the serration teeth of the add-on of the present invention can be expressed as follows. [Number]

[0022] In other words, in a preferred embodiment of the present invention, the length of the serration tooth is at least 6 times and at most 12 times the width of the serration tooth. Experiments and simulations were performed to identify suitable dimensions for the serration teeth of the add-on of the present invention. For example, it has been established that the length of the serration tooth from the base to the tip should preferably not be less than 30 mm and not exceed 200 mm. Similarly, it has been established that the width of the serration tooth at its base should preferably not be less than 3 mm and not exceed 33 mm.

[0023] The improvement in the performance of the add-on of the present invention, that is, the reduction of the acoustic noise caused by the rotor blade, is a result of the suitable shape (high aspect ratio and convex curvature along the side edge) described above and the narrow spacing between adjacent serration teeth of the add-on. Any two adjacent serration teeth are separated by a gap of at most 1 mm. This is the distance between the outer corner of one serration tooth and the outer corner of its adjacent serration tooth. This distance is preferably at most 0.5 mm.

[0024] The serrations can be essentially flat, i.e., the thickness of the serration teeth can be essentially constant over the entire area. In a preferred embodiment of the present invention, in order to increase the aerodynamic efficiency of the add-on and improve its structural strength, the thickness of the serration teeth can decrease towards the edge, i.e., the thickest part of the serration teeth is towards the center. In a preferred embodiment of the present invention, the thickness of the serration teeth is up to 80% of its width. For example, a serration tooth having a width of 50 mm can have a thickness of 40 mm or less.

[0025] The serration teeth can be symmetric about its longitudinal axis. For example, this axis is at a right angle and intersects the baseline at the midpoint of the base. However, alternative shapes of the serration teeth are possible. For example, the longitudinal axis of the serration teeth may intersect the baseline at an angle with respect to the normal, and / or the longitudinal axis of the serration teeth may intersect the baseline at a point other than the midpoint.

[0026] The add-on of the present invention can be attached to the rotor blade so as not to affect the lift of the airfoil at its operating angle of attack. Since the add-on essentially does not affect the lift of the airfoil at this position, it can be called the "liftless" position of the add-on. Alternatively, in a further preferred embodiment of the present invention, the add-on can be attached to the rotor blade at an angle with respect to the liftless position towards the positive pressure side of the airfoil, and as a result, the add-on also increases the lift on the airfoil.

[0027] The add-on of the present invention can be attached to the rotor blade along any suitable portion of its length. Since it has been observed that acoustic noise mainly occurs downstream of the external rotor blade part, one or more add-ons can preferably be attached to the trailing edge within the outermost 30% of the length of the rotor blade in the span direction. The add-ons in such an arrangement can be arranged adjacent to each other or spaced apart as required.

[0028] Other objects and features of the present invention will become apparent from the following detailed description, which will be considered in conjunction with the accompanying drawings. However, it should be understood that the drawings are provided for illustrative purposes only and not as a definition of the limitations of the present invention. [Brief explanation of the drawing]

[0029] [Figure 1] This figure shows an exemplary embodiment of the add-on of the present invention, positioned along the trailing edge of a wind turbine rotor blade. [Figure 2] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 3] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 4] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 5] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 6] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 7] This figure shows an exemplary implementation of the add-on of the present invention. [Figure 8] This is a cross-sectional view through an exemplary serrated tooth of the add-on of the present invention. [Figure 9] This figure shows a possible embodiment of how the add-on of the present invention can be attached to a wind turbine rotor blade. [Figure 10] This figure shows a possible embodiment of how the add-on of the present invention can be attached to a wind turbine rotor blade. [Figure 11] This figure shows a wind turbine with several rotor blades, as shown in Figure 1. [Figure 12] This figure shows a wind turbine rotor blade with an add-on to conventional technology.

[0030] In the diagram, the same number refers to the same object throughout. The objects in the diagram are not necessarily drawn to scale.

[0031] Figure 1 shows the trailing edge 20 of the wind turbine rotor blade 20 TE An exemplary embodiment of the Add-on 1 of the present invention is shown, positioned along the trailing edge 20 of the rotor blade 20. TE It is mounted along the . Each add-on 1 comprises a plurality of serrated teeth 10 extending outward from an elongated strip 11 (used to attach the add-on 1 to the rotor blade). Unlike the sawtooth shape of conventional add-ons, the serrated teeth 10 of the add-on 1 of the present invention have a shape that can be described as a “flat iron” shape, having a form similar to the bottom plate of a clothes iron, with a high aspect ratio of at least 6:1. The enlarged portion of the figure shows that adjacent serrated teeth 10 are separated by a small gap 1G of 1 mm or less, preferably 0.5 mm or less. The combined effect of the high aspect ratio, the convex curvature along the side edges, and the narrow gap 1G between adjacent serrated teeth 10 significantly reduces trailing edge noise of the wind turbine. Experiments have shown a reduction of more than 3 dB in perceived wind turbine noise at the inmission point at the relevant frequencies.

[0032] Figures 2 to 7 show possible geometric shapes for a serrated tooth 10 of an example of add-on 1 of the present invention. Each serrated tooth 10 is defined by two lateral portions 10S that extend from its lower edge 10B or an outer point of its base and converge at its tip 10T. The base or "root" of the serrated tooth can have any form, for example, a straight line extending essentially parallel to the trailing edge of an airfoil. Similarly, the base of the serrated tooth can be curved or angular.

[0033] The serrated teeth 10 extend outward from the elongated band 11 or mounting band, and the lower edge 10B of the row of serrated teeth 10 aligns with a common baseline 11B. The baseline 11B essentially defines one of the longer edges of the mounting band 11.

[0034] In Figure 2, the serrated tooth 10 has a length L of 100 mm and a width W of 10 mm, and therefore the aspect ratio of the serrated tooth 10 of this add-on 1 is 10:1. In Figure 3, the serrated tooth 10 has a length of 140 mm and a width of 20 mm, and therefore the aspect ratio of the serrated tooth 10 of this add-on 1 is 7:1. Each figure also shows a smaller underlying isosceles triangle T (dashed line) contained within the serrated tooth 10 and defined by the same three vertices. The convex lateral edge 10S of the serrated tooth lies outside the linear lateral edge of triangle T.

[0035] In Figure 4, the serrated teeth 10 have a conical arch shape, in this case a secant ogive shape. In such embodiments, the side edges 10S of the serrated teeth 10 intersect the baseline 11B at a non-zero angle with respect to the normal 11N, so that this angle θ is at most 4.76°. In the embodiments shown here, the angle θ is approximately 1°.

[0036] As described above, the angle at which the lateral edge of the ogive-shaped serrated tooth 10 intersects the baseline 11B can be expressed with respect to the geometric shape of the base triangle T enclosed by the serrated tooth, i.e., the triangle T formed between the three outer points of the serrated tooth 10. The angle δ determined between the major axis of the serrated tooth 10 and the hypotenuse (linear lateral edge) of the base triangle T is given by equation (1) above, and the angle θ at which the lateral edge of the ogive-shaped serrated tooth intersects the baseline is preferably less than 2 / 3δ, more preferably less than 1 / 3δ.

[0037] In Figure 5, the serrated teeth 10 have a conical arch shape, in this case a tangential ogive shape. In such an embodiment, the lateral edge 10S of the serrated teeth 10 intersects the baseline 11B at a right angle, i.e., the tangent of the lateral edge 10S occurring at the baseline 11B coincides with the normal 11N. Another way to describe this shape is that the angle θ determined between the lateral edge 10S and the normal is reduced to 0° at the intersection of the lateral edge and the baseline 11B.

[0038] In the diagram above, the serrated teeth 10 of add-on 1 are essentially symmetrical around their major axis 10L, that is, the major axis 10L is aligned with its midpoint 10B. mid It intersects with the base 10B at this point. In Figures 1 to 5, the long axis 10L of the serrated tooth 10 is perpendicular to the baseline 10B. In the alternative embodiment shown in Figure 6, the long axis 10L of the serrated tooth 10 is perpendicular to the midpoint 10B mid If the serrated tooth intersects the base 10B at a point offset from the normal (shown by a dashed line), it may be asymmetrical. In a further alternative embodiment shown in Figure 7, the serrated tooth 10 may be asymmetrical if its major axis 10L intersects the baseline 11B at an angle β offset from the normal (shown by a dashed line). The outward convex shape of the side edge of the serrated tooth 10 is adjusted accordingly.

[0039] In alternative embodiments, the adjacent serrated teeth 10 of the add-on 1 of the present invention may differ with respect to parameters θ, L, W, and β within the limits described above.

[0040] In any of the embodiments shown in Figures 2 to 7, it can be assumed that the gap between adjacent serrated teeth 10 of add-on 1 is a maximum of 1 mm.

[0041] Figure 8 shows a cross-section through the serrated tooth 10 of an embodiment of add-on 1 of the present invention. Here, the thickness of the serrated tooth 10 decreases from the maximum thickness in the center to the minimum thickness along the side edge 10S. The figure shows the thickness h at a point along the length of the serrated tooth 10. x and width w x This illustrates the following: For example, a serrated tooth 10 having a width of 10 mm at its base may have a maximum thickness of 3 mm at its center, tapering to 0.2 mm at its outer edge 10S. Height h x width w xThis ratio may be essentially constant along the length of the serration teeth 10. The cross-sectional shape of the serration teeth 10 may be essentially elliptical as shown here (the serration teeth essentially have a continuous curved surface). Alternatively, the cross-sectional shape may be essentially polygonal (the serration teeth have several planes intersecting at various edges).

[0042] Figures 9 and 10 show alternative ways of attaching the add-on 1 to the airfoil 20A of a wind turbine rotor blade. In Figure 9, the add-on 1 is attached so as to be disposed in an essentially "lift-free" position 20Z. When attached in this way, the add-on does not contribute to the lift force on the airfoil 20A. Alternatively, as shown in Figure 10, the add-on 1 can be attached to the rotor blade at an angle inclined towards the positive pressure side of the airfoil 20A. Here, the add-on 1 is inclined at an angle of approximately 3° with respect to the lift-free position 20Z so that it can contribute to the lift force on the airfoil 20A.

[0043] Figure 11 shows a wind turbine 2 having an aerodynamic rotor with three rotor blades 20. Each rotor blade 20 has an arrangement of one or more examples of the add-on 1 of the present invention along its trailing edge 20 TE The add-on 1 is disposed in the outer region of the rotor blade 20 as shown here.

[0044] Figure 12 shows a wind turbine rotor blade having a prior art add-on 3. Here, the shape of each serration tooth 30 is triangular, that is, each serration tooth 30 has the shape of an isosceles triangle. Adjacent serration teeth intersect directly at the baseline, that is, there is no gap between adjacent teeth. The aspect ratio of the length of the serration teeth 30 of the prior art add-on 3 to the width is generally 4:1 or less. In these design aspects, the prior art add-on functions as described in the introduction section.

[0045] While the present invention is disclosed in preferred embodiments and variations thereof, it will be understood that numerous additional modifications and variations can be made without departing from the scope of the invention. For example, one or more add-ons can be incorporated during the manufacture of the rotor blade. Of course, any existing wind turbine rotor blade can be upgraded by replacing the existing “serrated” trailing edge add-ons with a suitable number of add-ons of the present invention. Furthermore, while a rotor blade may have several identical add-ons, each having the same serration teeth, it is equally possible to equip the rotor blade with add-ons having different serration tooth geometric shapes while conveniently maintaining a high aspect ratio, for example, the serration teeth of the add-ons may vary in length or width while each having the same high aspect ratio. It should also be noted that a wind turbine rotor blade may also have one or more add-ons, each containing one or more serration teeth having shapes different from those described above.

[0046] For clarity, please understand that throughout this application, the use of "one (a)" or "one (an)" does not exclude multiple items, and "comprising" does not exclude other steps or elements.

Claims

1. The trailing edge (20) of the rotor blade (20 ＴＥ A wind turbine rotor blade add-on (1) comprising a plurality of serrated teeth (10) arranged to extend outward from the ) wherein the serrated teeth (10) have an elongated shape defined by a base (10B) and two at least partially curved side edges (10S) converging at the tip (10T), - The length of the serrated teeth (10) from the base (10B) to the tip (10T) is at least six times greater than the width of the serrated teeth (10) at the base (10B). - The lateral edge (10S) of the serrated tooth (10) includes a convex curved portion, - A wind turbine rotor blade add-on (1) in which the closest distance (1G) between adjacent serrated teeth (10) is a maximum of 1 mm.

2. The add-on according to claim 1, wherein the length (L) of the serrated teeth (10) is up to 12 times the width (W) of the serrated teeth (10) at its base (10B).

3. The add-on according to claim 1 or 2, wherein the nearest distance (1G) between adjacent serrated teeth (10) is at most 1.0 mm, more preferably at most 0.5 mm.

4. The add-on according to any one of claims 1 to 3, wherein the side edge (10S) of the serrated tooth (10) intersects its base (10B) at an angle of up to 4.76° with respect to the normal, more preferably at an angle of up to 2° with respect to the normal.

5. The add-on according to any one of claims 1 to 4, wherein at least a portion of the lateral edge (10S) of the serrated tooth (10) has a conical arc shape.

6. The add-on according to claim 5, wherein the conical arc is a secant ogive.

7. The add-on according to claim 5, wherein the conical arc is a tangent ogive.

8. Width of serrated tooth (10) (w ｘ ) thickness (h ｘ The add-on according to any one of claims 1 to 7, wherein the ratio of ) is at most 0.

8.

9. The add-on according to any one of claims 1 to 8, wherein the serrated teeth (10) are symmetrical with respect to the longitudinal axis (10L).

10. An add-on according to any one of claims 1 to 9, comprising an elongated band (11) for facilitating attachment to a wind turbine rotor blade (20), wherein the serrated teeth (10) extend outward from the elongated band (11).

11. An add-on according to any one of claims 1 to 10, manufactured as an injection-molded part from a thermoplastic material.

12. A wind turbine rotor blade (20) comprising a root portion and an airfoil portion, wherein the trailing edge (20) of the airfoil portion of the rotor blade (20) ＴＥ A wind turbine rotor blade (20) further comprising several add-ons (1) according to any one of claims 1 to 11, attached to a wind turbine rotor blade (20).

13. The add-on (1) is within the outermost 30% of the rotor blade span, and the trailing edge (20 ＴＥ A wind turbine rotor blade according to claim 12, which is mounted on a )

14. The wind turbine rotor blade according to claim 12 or 13, wherein the add-on (1) is inclined toward the positive pressure side of the airfoil (20A) at an angle (α) of at least 0° with respect to the airfoil no-lift position (20Z).

15. A wind turbine (2) comprising several rotor blades (20) according to any one of claims 12 to 14.

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