GB2486876A

GB2486876A - Wind turbine blade flap

Info

Publication number: GB2486876A
Application number: GB1021534.1A
Authority: GB
Inventors: Chee Kang Lim; Wuh Ken Loh; Ning Ying; Tian Lim
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2010-12-20
Filing date: 2010-12-20
Publication date: 2012-07-04
Also published as: GB201021534D0

Abstract

A wind turbine blade 7 comprises a blade body 8 and a flap 9 moveable between first and second configurations relative to the blade body. The flap comprises first and second skins 10, 12 joined together at their distal ends, the first skin being connected to the blade body. An actuator 16 is operable to move the flap between its first and second configurations. Constraining means 17 is connected between proximal ends of the first and second skins to constrain relative movement of the flap and the blade body. The constraining means may comprise at least one lamina having a U-shaped cross section. The actuator means may be connected to the second skin. The proximal end of the second skin may slide over a surface of the blade body as the flap changes configuration. One skin may be rigid, and the other flexible. A viscoelastic damping material may be provided to damp vibrations of the flap. The flap may be a trailing edge flap.

Description

I

WIND TURBINE BLADES

The present invention relates to rotor blades for wind turbines, and more particularly to such rotor blades having an aerodynamic surface or shape which can be reconfigured.

A typical wind turbine is illustrated in Figure 1. The wind turbine I comprises a tower 2, a nacelle 3 mounted at top of the tower 2 and a rotor 4 operatively coupled to a generator within the nacelle 3. The wind turbine I converts kinetic energy of the wind into electrical energy. In addition to the generator 5, the nacelle 3 houses the various components required to convert the wind energy into electrical energy and also the various components required to operate and optimize the performance of the wind turbine 1. The tower 2 supports the load presented by the nacelle 3, the rotor 4 and other wind turbine components within the nacelle 3.

The rotor 4 includes a central hub 6 and three elongate rotor blades 7a, 7b, 7c of approximately planar configuration which extend radially outward from the central hub 6.

In operation, the blades 7a, 7b, 7c are configured to interact with the passing air flow to produce lift that causes the central hub 6 to rotate about its longitudinal axis. Wind exceeding a minimum level will activate the rotor 4 and allow it to rotate within a plane substantially perpendicular to the direction of the wind. The rotation is converted to electric power by the generator 5 and is usually supplied to the utility grid.

It is necessary to control the operation of wind turbines so as to optimise performance over a wide range of wind speeds and power demand, including local fluctuations in wind speed, known as wind gusts. It is also desirable to be able to control each blade independently so as to balance the loads.

A known method of controlling the operation of wind turbines is to pitch the blades.

However, with particularly long blades, such as in excess of 60 metres, it is not possible to pitch the blades sufficiently quickly to compensate for wind gusts.

As an alternative to pitching the blades, it is possible simply to change the aerodynamic surface shape over at least a part of the length of the blade. The shape can be changed by the provision of adjustable flaps, such as trailing edge flaps, leading edge flaps, slats or spoilers. An advantage of such an arrangement is a faster response to changing conditions than can be achieved with pitching of the blades mentioned above.

It is therefore desirable that the structure of the adjustable flaps must be suited to providing a fast response. This, in turn requires the flaps to be light-weight, which implies that the materials used for the flap should be relatively thin. However, this can give rise to the problem of instability of the flap in heavy wind.

It would therefore be desirable to provide arrangements which overcome, or at least mitigate the above problem.

In accordance with a first aspect of the present invention there is provided a wind turbine blade comprising: a blade body; a flap which can be moved between first and second configurations relative to the blade body, the flap comprising first and second skins joined together at their distal ends, the first skin being connected to the blade body; actuator means operable to cause the flap to move relative to said blade body so as to reconfigure the flap from its first to its second configuration; and constraining means connected between the proximal ends of the first and second skins of the flap so as to constrain relative movement of the flap and the blade body.

The constraining means serves to ensure that the flap can withstand the wind loads typically encountered by preventing the flap from collapsing. The constraining means also increases the overall stiffness of the flap, so as to reduce the deflection of the flap in conditions of high wind.

The term "flap" is intended to refer to any device which may be used to alter the aerodynamic profile of an airfoil section of the rotor blade. For example, the flap may be a trailing edge flap, a leading edge flap a slat or a spoiler.

The constraining means preferably comprises at least one lamina having a substantially U-shaped cross section. In this case, it is preferred that the loop of the "U" shape extend within the region between the two skins of the flap.

It is preferred that the first and second skins of the flap are of substantially equal thickness and that the thickness of the lam ma is between one third and two thirds of the thickness of the first and second skins, for example substantially one half of the thickness. This enables the lam ma to be both relatively light and flexible.

In the preferred embodiment, the constraining means is in the form of two such laminas arranged such that the two U-shaped cross sections substantially coincide, i.e. when viewed in a direction so as to observe the U-shaped cross section head-on, the front lamina completely obscures the rear lamina. In this case, the actuator means may be attached to the second skin at a position between the two laminas.

The constraining means can be made from any suitable material, but is preferably selected from carbon, steel, glass fibre composite, carbon fibre composite, and a para-aramid synthetic fibre, such as that marketed under the Registered Trade Mark Kevlar.

The actuator means is preferably connected between the blade body and the second skin of the flap and is operable to cause the second skin to move relative to said blade body so as to reconfigure the flap from its first to its second configuration. With such an arrangement, it is possible to reconfigure the flap simply by applying a suitable force on one of the two skins of the flap, resulting in a simple construction.

It is preferred that the proximal end of the second skin is arranged to slide over a surface of the blade body as the flap moves between its first and second configurations. In this way, it is possible to retain a smooth aerodynamic surface of the turbine blade not only in both configurations of the flap but at all intermediate positions.

One of the skins of the flap is preferably substantially rigid, in which case the other skin is flexible. In the preferred embodiment, the first skin is flexible and the second skin is relatively rigid.

The actuator means may comprise one or more of a pneumatic actuator, a hydraulic actuator, a piezoelectric actuator and an electric actuator. Alternatively, or additionally, the actuator means may comprise a fluid muscle actuator, i.e. an actuator which works like a human skeletal muscle in being able to pull, by contraction, but not to push. In this case, the first configuration of the flap is a "relaxed" configuration which occurs when the actuator means is non energised, and the second configuration is achieved by energising the actuator means.

In its first configuration, the flap may be directed at an angle of substantially 10° toward the suction side of the turbine blade relative to the axis of the blade body.

In its second configuration, the flap may be directed at an angle of substantially 100 toward the pressure side of the turbine blade relative to the axis of the blade body.

The wind turbine blade preferably also comprises means for damping vibrations of the flap, such as a suitable damping material attached to and/or inserted in the flap. The damping material may be in the form of a viscoelastic material, i.e. a material exhibiting both viscosity and elasticity on deformation.

In the preferred embodiment, the flap is a trailing edge flap.

The present invention extends to a wind turbine comprising one or more wind turbine blades as described above.

Preferred embodiments of the present invention will now be described with reference to the accompanying drawings, in which: Figure 1 illustrates the main structural components of a wind turbine; Figure 2 is a schematic cross-sectional view of a wind turbine blade in accordance with a preferred embodiment of the present invention; Figures 3(a) and 3(b) are cross-sectional views illustrating the two different configurations of trailing edge flap in the preferred embodiment of the present invention; and Figure 4 is a perspective view illustrating the preferred arrangement of flexible constraints and actuator in the preferred embodiment of the present invention.

Referring to Figure 2, a wind turbine blade 7 comprises a blade body 8 and a trailing edge flap 9. The trailing edge flap 9 is formed from a first, flexible skin 10 on the suction side 11 of the blade 7, and a second, substantially rigid skin 12 on the pressure side 13 of the blade 7. The skins 10, 12 are each made from thin glass fibre-reinforced composite sheets and are designed such that the flap can withstand the required aero-loading. The distal ends of the first and second skins 10, 12 are joined together by means of an adhesive to form a trailing edge. The proximal end of the first skin 10, i.e. the end nearest the leading edge of the blade 7, is attached to the blade body 8 by means of an adhesive. The proximal end of the second skin 12 is arranged in sliding contact with the inner surface of the blade body 8. The trailing edge flap 9 is shown in a first configuration in which it is directed upwards, i.e. towards the suction side of the blade, by 10°. A fluid muscle actuator comprises a body (not shown) located within, and attached to, the blade body 8 and a retractable arm 16 extending into the trailing edge flap 9 and connected to a region of the inner surface of the second skin 12 towards its proximal end.

Upon energising the fluid muscle actuator 14, the arm 16 is caused to retract, thereby pulling the second skin 12 of the trailing edge flap 9 towards the blade body 8, with the proximal end of the second skin 12 sliding over the inner surface of the blade body 8 so as to maintain an aerodynamic seal, i.e. a smooth outer surface of the rotor blade. This, in turn, causes the first skin 10 of the trailing edge flap 9 to flex downwards, thereby changing the angle of the trailing edge flap 9 into a second configuration in which it is directed downwards, i.e. toward the pressure side 13 of the wind turbine blade 7 at an angle of 10°.

A deformable constraint 17 is connected between the two proximal ends of the first and second skins 10, 12 and serves to resist wind load by preventing collapse of the flap structure. The deformable constraint 17 is in the form of a lamina of U-shaped cross section and made from a suitable material such as carbon, steel, glass fibre composite, carbon fibre composite or Kevlar (RTM). The first and second skins 10, 12 of the trailing edge flap 9 are of substantially the same thickness, and the deformable constraint 18 has a thickness of approximately half that of the skins 10, 12. A first edge of the deformable constraint 17 is rigidly attached by means of an adhesive between the blade body 8 and the first skin 10 of the trailing edge flap 9. The second edge of the deformable constraint 18 is attached only to the second skin 12 of the trailing edge flap 9. The second skin 12 is arranged to slide over an inner surface of the blade body 8.

The deformable constraint 17 serves to increase the stiffness of the trailing edge flap 9 and thereby to guide the movement of the flap 9 between the first and second configurations.

Figure 3(a) illustrates the relative positions of the blade body 8, the first skin 10 and the second skin 12 of the trailing edge flap 9 and the retractable arm 16 of the actuator 14 when the flap 9 is in the first configuration, in which the flap 9 is directed at an upward angle of 100 relative to the blade body 8.

Figure 3(b) illustrates the corresponding relative positions of the same elements shown in Figure 4(a) when the flap 9 is in the second configuration, in which the flap 9 is directed at a downward angle of 10 0 relative to the angle of the blade body 8.

Figure 4 illustrates a preferred arrangement of the second embodiment, in which there are provided two U-shaped flexible constraints 17(a), 17(b) within the trailing edge flap 9.

The two constraints 17(a), 17(b) are laterally spaced apart. The retractable arm 16 of the fluid muscle actuator 14 extends into the region between the two flexible constraints 17(a), 17(b) and is attached to the second skin 12 of the trailing edge flap 9 also in this region.

A mass of viscoelastic material 18 is provided within the flap 9 for inhibiting undesirable damping vibrations of the flap 9.

Although preferred embodiments of the present invention have been described above, it will be apparent to the person skilled in the art that many variations may be made to these without departing from the scope of the present invention, which is defined solely by the claims appended hereto.

Claims

CLAIMS1. A wind turbine blade comprising: a blade body; a flap which can be moved between first and second configurations relative to the blade body, the flap comprising first and second skins joined together at their distal ends, the first skin being connected to the blade body; actuator means operable to cause the flap to move relative to said blade body so as to reconfigure the flap from its first to its second configuration; and constraining means connected between the proximal ends of the first and second skins of the flap so as to constrain relative movement of the flap and the blade body.
2. A wind turbine blade as claimed in claim 1, wherein the constraining means comprises at least one lamina having a substantially U-shaped cross section.
3. A wind turbine blade as claimed in claim 2, wherein the first and second skins of the flap are of substantially equal thickness and wherein the thickness of the lamina is between one third and two thirds of the thickness of the first and second skins.
4. A wind turbine blade as claimed in claim 2 or claim 3, wherein the constraining means comprises two such laminas arranged such that the two U-shaped cross sections substantially coincide, and the actuator means is attached to the second skin at a position between the two laminas.
5. A wind turbine blade as claimed in any one of claims 2 to 4, wherein the constraining means is made from one of carbon, steel, glass fibre composite, carbon fibre composite and a para-aramid synthetic fibre.
6. A wind turbine blade as claimed in any preceding claim, wherein the actuator means is connected between the blade body and the second skin of the flap and is operable to cause the second skin to move relative to said blade body so as to reconfigure the flap from its first to its second configuration.
7. A wind turbine blade as claimed in claim 6, wherein the proximal end of the second skin is arranged to slide over a surface of the blade body as the flap moves between its first and second configurations.
8. A wind turbine blade as claimed in any preceding claim, wherein one of the first and second skins of the flap is substantially rigid and the other of the first and second skins is flexible.
9. A wind turbine blade as claimed in any preceding claim, wherein the actuator means comprises one or more of a pneumatic actuator, a hydraulic actuator, a piezoelectric actuator and electric actuator.
10. A wind turbine blade as claimed in any preceding claim, wherein the flap in its first configuration is directed at an angle of substantially 10° toward the suction side of the turbine blade relative to the axis of the blade body.
II. A wind turbine blade as claimed in any preceding claim, wherein the flap in its second configuration is directed at an angle of substantially 10° toward the pressure side of the turbine blade relative to the axis of the blade body.
12. A wind turbine blade as claimed in any preceding claim, further comprising means for damping vibrations of the flap.
13. A wind turbine blade as claimed in claim 12, wherein the damping means comprises a damping material either attached to and/or inserted in the flap.
14. A wind turbine blade as claimed in claim 13, wherein the damping material comprises a viscoelastic material.
15. A wind turbine blade as claimed in any preceding claim, wherein the flap is a trailing edge flap.
16. A wind turbine comprising one or more wind turbine blades as claimed in any preceding claim.
17. A wind turbine blade substantially as hereinbefore described with reference to the accompanying drawings.
18. A wind turbine substantially as hereinbefore described with reference to the accompanying drawings.