WO2019209317A1

WO2019209317A1 - A passively activated stall strip on a wind turbine, method of installing, and method of operation

Info

Publication number: WO2019209317A1
Application number: PCT/US2018/029835
Authority: WO
Inventors: Drew Eisenberg
Original assignee: Siemens Gamesa Renewable Energy A/S; Siemens Gamesa Renewable Energy, Inc.
Priority date: 2018-04-27
Filing date: 2018-04-27
Publication date: 2019-10-31

Abstract

A wind turbine blade and methods are provided. Wherein a passively activated stall strip is arranged on the wind turbine blade and is passively activated. A first edge of the passively activated stall strip is secured to the wind turbine blade. The passively activated stall strip is activated or deactivated by a change of the location of the stagnation point.

Description

A PASSIVELY ACTIVATED STALL STRIP ON A WIND TURBINE, METHOD OF INSTALLING, AND METHOD OF OPERATION

TECHNICAL FIELD

[0001] The present disclosure is directed, in general, to the wind power industry, and more particularly to the aerodynamics of a wind turbine blade.

BACKGROUND

[0002] Wind turbine blades are aerodynamically shaped to efficiently extract energy from the wind. Referring to FIG. 1, a transverse sectional profile of a wind turbine blade 10 is illustrated. The airfoil 10 includes a leading edge LE, trailing edge TE, pressure side PS and suction side SS. Chord line CL joins the leading edge LE and the trailing edge TE. The airfoil 10, a cross section of the blade, may be turned toward or away from the wind to control the production of power.

[0003] The angle a is referred to as the angle of attack of the airfoil 10. The angle of attack illustrated in FIG. 1 is a positive angle of attack. When air hits the wind turbine blade, the air flow is bifurcated in opposite direction from a stagnation point. The stagnation point is defined as a point that the fluid flow is brought to zero velocity. The stagnation point varies based on the angle of attack.

[0004] A stall strip arranged on the airfoil may be used to separate the airflow from the blade to create early onset of stall. When the stall strip is always engaged, for example the stall strip is a rigid protrusion on the airfoil, the increased drag on the airfoil occurs at all angles of attack and reduces overall power production. It is desirable to have a stall strip which does not increase drag at all angles of attack.

SUMMARY

[0005] Variously disclosed embodiments include systems and methods that may be used to facilitate a passively activating stall strip on a wind turbine, method of installing, and method of activating.

[0006] In one example, a wind turbine blade is provided. The wind turbine includes a pressure side between a leading edge and a trailing edge, and a passively activated stall strip arranged on the blade. The first edge of the passively activated stall strip is secured to the blade and a second edge is loose. The passively activated stall strip is activated or deactivated by a change of the location of a stagnation point.

[0007] In another example, a method of operation is provided. A wind turbine includes a blade, the blade includes a pressure side between a leading edge and a trailing edge. The method includes pitching the blade to regulate the rate of power. The angle of attack is changed via the pitching. A passively activated stall strip is activated or deactivated by a change of the location of the stagnation point due to the change of the angle of attack. A first edge of the passively activated stall strip is secured to the blade and a second edge is loose.

[0008] In another example, an installation method is provided. The method includes adhering a first edge of a passively activated stall strip to the pressure side of a wind turbine blade, and ensuring the second edge of the passively activated stall strip is loose from the wind turbine blade. The passively activated stall strip is movable between a position essentially flush against the blade and a position with a gap between the second edge and the blade, and the passively activated stall strip is activated or deactivated by a change of the location of the stagnation point.

[0009] The foregoing has outlined rather broadly the technical features of the present disclosure so that those skilled in the art may better understand the detailed description that follows. Additional features and advantages of the disclosure will be described hereinafter that form the subject of the claims. Those skilled in the art will appreciate that they may readily use the conception and the specific embodiments disclosed as a basis for modifying or designing other structures for carrying out the same purposes of the present disclosure. Those skilled in the art will also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure in its broadest form.

[0010] Also, before undertaking the Detailed Description below, it should be understood that various definitions for certain words and phrases are provided throughout this patent document, and those of ordinary skill in the art will understand that such definitions apply in many, if not most, instances to prior as well as future uses of such defined words and phrases. While some terms may include a wide variety of embodiments, the appended claims may expressly limit these terms to specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] FIG. 1 illustrates a transverse sectional profile of a prior art wind turbine blade.

[0012] FIG. 2 and FIG. 3 illustrates partial transverse section profiles of wind turbine blade airfoil with a passively activated stall strip according to embodiments of the invention.

[0013] FIG. 4 and FIG. 5 illustrates a perspective view of a partial passively active stall strip according to various embodiments.

[0014] FIG. 6 and FIG. 7 illustrates an airfoil according to embodiments of the invention.

[0015] FIG. 8 illustrates lift response curves according to embodiments.

DETAIFED DESCRIPTION

[0016] Various technologies that pertain to systems and methods that facilitate a passively activated stall strip, a method of installing a passively activated stall strip, and a method of activating a passively activated stall strip will now be described with reference to the drawings, where like reference numerals represent like elements throughout. The drawings discussed below, and the various embodiments used to describe the principles of the present disclosure in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the disclosure. Those skilled in the art will understand that the principles of the present disclosure may be implemented in any suitably arranged apparatus. It is to be understood that functionality that is described as being carried out by certain system elements may be performed by multiple elements. Similarly, for instance, an element may be configured to perform functionality that is described as being carried out by multiple elements. The numerous innovative teachings of the present application will be described with reference to exemplary non-limiting embodiments.

[0017] FIG. 2 illustrates a partial wind turbine airfoil according to embodiments of the invention. FIG. 2 includes a passively activated stall strip 21 arranged on the pressure side PS of the airfoil 20. A first edge 22 of the passively activated stall strip 21 is downstream from the leading edge FE. A second edge 24 of the passively activated stall strip 21 is upstream from the first edge 22. The location of the second edge 24 being closer to the leading edge FE than the first edge 22. [0018] The first edge 22 of the passively activated stall strip 21 is secured to the pressure side PS and a second edge 24 is loose. Being loose allows the second edge 24 to separate from the pressure side PS. The separation is performed passively.

[0019] FIG. 2 illustrates an embodiment of the passively activated stall strip 21 in a deactivated position. In a deactivated position, the passively activated stall strip 21 lies against the pressure side PS. The passively activated stall strip 21 may be flush or essentially flush against the pressure side PS. According to an embodiment, in the deactivated position, the effect of the passively activated stall strip 21 on the flow is negligible or non-existent. As such, an early stall is not induced when the passively activated stall strip 21 is in the deactivated position.

[0020] FIG. 3 illustrates an embodiment of the passively activated stall strip 21 in an activated position. In the activated position, the passively activated stall strip 21 is not flush on the pressure side PS. At the loose second edge 24, the passively activated stall strip 21 becomes detached at second edge 24. A gap G is formed between the pressure side PS and the passively activated stall strip 21. In an embodiment, the second edge 24, remains upstream from the first edge 22 while in the activated position. In another embodiment, the second edge 24, moves downstream from the first edge 22 while in the activated position.

[0021] FIG. 4 and FIG. 5 illustrate perspective views embodiments of the passively activated stall strip 21 according to different embodiments. Various properties of the passively activated stall strip 21 may facilitate the detachment. For example, thickness and/or stiffness of a material used in the passively activated stall strip 21.

[0022] Any thickness allowing the passively activated stall strip 21 to move between deactivated position and the activated position may be used. According to an embodiment of FIG. 4, the thickness TH is constant between the first edge 22 and second edge 24 of the passively activated stall strip 21. A constant thickness is easily manufactured. The passively activated stall strip 21 may be planar with a constant thickness.

[0023] In the embodiment as illustrated by FIG. 5, the thicknesses TH at first and second edges 22, 24 is less than a thickness TH2 of an interior section 36 between edges 22, 24. For example, the passively activated stall strip 21 is tapered, at least along one side, from section 36 to each edge 22, 24. The smaller thickness TH at the edges and the tapering enables a laminar flow from the passively activated stall strip onto the airfoil while the passively activated stall strip is in the deactivated position. The thicknesses at the first edge 22 and the second edge 24 may be the same or they may be different.

[0024] In an embodiment, the thickness of the first and second edges 22, 24 is between 0.05 mm thick and 0.2 mm thick. In another embodiment, the thickness of the first and second edges 22, 24 is between 0.01 mm thick and 0.5 mm thick. In an embodiment, the thickness TH2 of the interior section 36 is between 0.01 and 4mm. In another embodiment, the thickness TH2 of the interior section 36 is between 0.1 and 4mm.

[0025] In an embodiment, at least a portion of the material used in the passively activated stall strip 21 is flexible. The flexibility may enable detachment from the pressure side PS. For example, to allow the passively activated stall strip 21 to bend near the attached first edge 22 to form gap G. The stiffness of the passively activated stall strip 21 material may be selected based on the thickness of the passively activated stall strip 21. For example, at a thickness of 0.1 mm, the stiffness of the material may be l0-20GPa.

[0026] The placement of the passively activated stall strip 21 on pressure side PS may be based on the aerodynamics of the specific blade and considers at what stagnation point the passively active stall strip is to be activated. An activation occurs when the passively activated stall strip 21 moves from a deactivated position to an activated position. A deactivation occurs when the passively activated stall strip 21 moves from an activated position to a deactivated position. The activation and deactivation are discussed below with the aid of the embodiments of FIG. 6 and FIG. 7.

[0027] Referring to FIG. 6, a first stagnation point SP1, a second stagnation point SP2, a direction of movement Dl , and the passively activated stall strip 21 in the deactivated position, are illustrated. First stagnation point SP1 is located between the leading edge LE of the airfoil and the second edge 24 of the passively activated stall strip 21. Second stagnation SP2 is located between the second edge 24 of the passively activated stall strip 21 and the trailing edge TE. [0028] When the stagnation point is between the second edge 24 and the trailing edge TE there is a high normal pressure force on the passively activated stall strip 24. This pressure forces the passively activated stall strip 21 to be flush against the blade as shown in FIG. 6. When the angle of attack is decreased, the location of the stagnation point moves in a forward direction Dl . A forward direction defined in the direction from a pressure side PS to a suction side SS by way of the leading edge.

[0029] The change in the angle of attack changes the flow direction across the second edge 24. As the location of the stagnation point moves forward across the second edge 24, the flow pushes the passively activated stall strip 21 away at the second edge 24 as shown in FIG. 7. For example, when location of the stagnation point moves forward, for example from a second stagnation point SP2 to a first stagnation point SP1 , the flow changes directions across the second edge 24 and causes the passively activated stall strip 21 to detach at the second edge 24 as shown in FIG. 7. During the detachment, the passively activated stall strip 21 may change shape. In the illustrated embodiment, the second edge 24 bends away from the blade and from the passively activated stall strip 21 , changing the shape of the passively activated stall strip 21. The detachment is a passive activation of the passively activated stall strip 24. The activation changes the aerodynamic forces on the blade.

[0030] Referring to FIG. 7, the first stagnation point SP1, the second stagnation point SP2, a direction of movement D2, and the passively activated stall strip 21 in the activated position, are illustrated. When the passively activated stall strip 21 is activated and the angle of attack is increased, the location of the stagnation point moves in a backward direction D2, which is in the opposite direction than the forward direction. The backward direction D2 may be defined by a movement in the direction from the suction side SS to the pressure side PS by way of the leading edge. As mentioned above, the change in the angle of attack changes the flow direction across the second edge 24. The angle of attack in which the deactivation occurs may not be the same as the angle of attack in which the activation occurred.

[0031] FIG. 8 illustrates an embodiment of a first lift curve FC1 of a blade with a deactivated passively activated stall strip and a second lift curve in FC2 of a blade with an activated passively activated stall strip. The illustration is merely to show how the curves have different responses and not meant to be limiting. Actual curves would be based on factors such as the aerodynamics of the blade, position of the passively activated stall strip, and or characteristics of the passively activated stall strip.

[0032] In operation, the pitch of the wind turbine blade may be changed to regulate the power. When the pitch reduces the angle of attack, such that a preselected location of a stagnation point is reached, the passively activated stall strip is activated A. When the pitch increases the angle of attack, such that a further location is reached, the passively activated stall strip is deactivated D. The lift response of first lift curve LC1 is different than the second lift curve LC2. Similarly, the drag responses are different when the passively activated stall strip is deactivated versus activated.

[0033] While in the above embodiments, the passively activated stall strip 21 is arranged on the pressure side PS, this is merely for illustrative purposes only. One skilled in the art would understand that at least one of the first or second edges 22, 24 of the passively active stall strip 21 may be located on the pressure side PS, the leading edge LE, or the suction side SS. For example, the second edge 24 may be located on the blade 20 at a location of the stagnation point occurring from angles of attack from -20° to 20°. It would be understood that the relative descriptions described above, for example the location of the second edge 24 being upstream from the first edge 22 or that the second edge 24 being closer to that the leading edge LE than the first edge 22 are according to the illustrated embodiments. It would be understood that these relative locations would differ as the location of the second edge 24 is moved forward along the blade. For example, if the second edge 24 were on the suction side, the first edge 22 may be closer to the leading edge LE than the second edge 24.

[0034] In the above embodiments, the passively activated stall strip 21 is smooth in the spanwise direction, which is between the blade root and blade tip. One skilled in the art would understand that passively activated stall strip 21 may be irregular, for example serrated, in the spanwise direction.

[0035] Also, it should be understood that the words or phrases used herein should be construed broadly, unless expressly limited in some examples. For example, the terms“include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The singular forms “a”,“an” and“the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. Further, the term“and/or” as used herein refers to and encompasses any and all possible combinations of one or more of the associated listed items. The term“or” is inclusive, meaning and/or, unless the context clearly indicates otherwise. The phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like.

[0036] Also, although the terms "first", "second", "third" and so forth may be used herein to refer to various elements, information, functions, or acts, these elements, information, functions, or acts should not be limited by these terms. Rather these numeral adjectives are used to distinguish different elements, information, functions or acts from each other. For example, a first element, information, function, or act could be termed a second element, information, function, or act, and, similarly, a second element, information, function, or act could be termed a first element, information, function, or act, without departing from the scope of the present disclosure.

[0037] In addition, the term "adjacent to" may mean: that an element is relatively near to but not in contact with a further element; or that the element is in contact with the further portion, unless the context clearly indicates otherwise. Further, the phrase“based on” is intended to mean “based, at least in part, on” unless explicitly stated otherwise.

[0038] Although an exemplary embodiment of the present disclosure has been described in detail, those skilled in the art will understand that various changes, substitutions, variations, and improvements disclosed herein may be made without departing from the spirit and scope of the disclosure in its broadest form.

[0039] None of the description in the present application should be read as implying that any particular element, step, act, or function is an essential element, which must be included in the claim scope: the scope of patented subject matter is defined only by the allowed claims. Moreover, none of these claims are intended to invoke a means plus function claim construction unless the exact words "means for" are followed by a participle.

Claims

CLAIMS What is claimed is:

1. A wind turbine blade comprising:

a pressure side between a leading edge and a trailing edge; and

a passively activated stall strip arranged on blade,

wherein a first edge of the passively activated stall strip is secured to the blade and a second edge is loose, and

wherein the passively activated stall strip is activated or deactivated by a change of the location of a stagnation point.

2. The wind turbine blade according to claim 1,

wherein the second edge is separated from the blade and a gap is formed between the stall strip and the blade in an activated position.

3. The wind turbine blade according to any of the claims 1-2,

wherein the effect of the passively activated stall strip on the flow is negligible or non existent in the deactivated position.

4. The wind turbine blade according to any of the claims 1-3,

wherein the second edge is located on the pressure side in a deactivated position.

5. The wind turbine blade according to claim 4,

wherein the second edge is located closer to the trailing edge in the activated position than when the passively activated stall strip is in a deactivated position.

6. The wind turbine blade according to any of the claims 1-3,

wherein the second edge is located on the suction side in a deactivated position.

7. The wind turbine blade according to claim 6,

wherein the second edge is located closer to the leading edge in the activated position than when the passively activated stall strip is in a deactivated position.

8. The wind turbine blade according to any of the claims 1-3,

wherein the second edge is located on the leading edge area in a deactivated position.

9. The wind turbine blade according to any of the claims above,

wherein the passively activated stall strip changes shape in the activated position.

10. The wind turbine blade according to any of the claims above,

wherein an activation occurs when the stagnation point moves in a forward direction.

11. The wind turbine blade according to any of the claims above,

wherein an activation occurs when the stagnation point moves to a preselected location.

12. The wind turbine blade according to any of the claims 1-11,

wherein a thickness of the passively activated stall strip is constant.

13. The wind turbine blade according to any of the claims 1-11,

wherein a thickness of the first edge and second edge is less than a thickness in an interior section of the passively activated stall strip.

14. The wind turbine blade according to any of the claims above,

wherein the thickness of the stall strip is greater than 0.01 and less than 4 mm thick.

15. The wind turbine blade according to any of the claims above,

wherein the stall strip is bendable.

16. The wind turbine blade according to any of the claims above,

wherein a spanwise edge of the stall strip is smooth.

17. The wind turbine blade according to any of the claims above,

wherein a spanwise edge of the stall strip is serrated.

18. A method of operation, a wind turbine comprising a blade, the blade comprising a leading edge and a trailing edge, the method comprising

pitching the blade to regulate the power; and

changing the angle of attack via the pitching;

wherein a passively activated stall strip is activated or deactivated by a change of the location of the stagnation point, and

wherein a first edge of the passively activated stall strip is secured to the blade and a second edge is loose.

19. The method according to claim 18, comprising:

reducing the angle of attack via the pitching

in response to reducing the angle of attack, the location of stagnation point of the blade moves forward, and a gap is formed between the blade and the second edge.

20. The method according to any of the claims 18-19,

21. A method according to claim 18-20,

wherein the second edge of the passively activated stall strip is located on the blade at an angle of attack from -20° to 20° after the adhering.

22. The method according to any of the claims 18-21 ,

23. The method according to any of the claims 18-21 ,

24. The method according to any of the claims 18-21 ,

wherein the second edge is located on the leading edge in a deactivated position.

25. The method according to any of the claims 18-24,

26. The method according to any of the claims 18-25,

wherein an activation occurs in response to the location of the stagnation point moving to a preselected location.

27. The method according to any of the claims 18-26,

wherein a thickness of the passively activated stall strip is constant.

28. The method according to any of the claims 18-26,

29. The method according to any of the claims 18-28,

wherein the stall strip is bendable.

30. A method, comprising:

adhering a first edge of a passively activated stall strip to a wind turbine blade; and ensuring a second edge of the passively activated stall strip is loose from the wind turbine blade,

wherein the passively activated stall strip is movable between a position essentially flush against the blade and a position with a gap between the second edge and the blade, and

wherein the passively activated stall strip is activated or deactivated by a change of the location of the stagnation point

31. A method according to claim 30