Wind turbine blade having deployable aerodynamic devices

Abstract

A wind turbine blade is described, as well as a trailing edge plate for a wind turbine blade. A flexible flow modulation device, e.g. an acoustic flap or a plurality of serrations, is arranged at the trailing edge of a wind turbine blade, wherein the flexible device is coupled to at least one aerodynamic device, preferably vortex generators. As the flexible device is bent by action of flow over the wind turbine blade, the at least one aerodynamic device is deployed to provide for attached flow over the bent flexible device.

Claims

1. A wind turbine blade having an airfoil profile with a leading edge and a trailing edge and a chord extending therebetween, the wind turbine blade further comprising: a trailing edge panel comprising a base portion and at least one flexible member projecting from a side of the base portion, wherein the base portion is attached to a surface of the wind turbine blade such that the at least one flexible member projects from the trailing edge of the wind turbine blade, wherein said at least one flexible member is arranged to flex under action of airflow over the wind turbine blade, and wherein the flexing of said at least one flexible member acts to deploy at least one aerodynamic device from the base portion of the trailing edge panel.

2. The wind turbine blade of claim 1, wherein the at least one flexible member comprises: a plurality of flow modulation devices projecting from the trailing edge of the wind turbine blade, wherein said plurality of flow modulation devices are arranged to flex under the action of the airflow over the wind turbine blade, and wherein the flexing of said plurality of flow modulation devices acts to deploy the at least one aerodynamic device from the base portion of the trailing edge panel, wherein the at least one aerodynamic device comprises vortex generators.

3. The wind turbine blade of claim 2, wherein said vortex generators are located adjacent the trailing edge, within 5% of the length of chord from the trailing edge.

4. The wind turbine blade of claim 2, wherein at least a portion of said vortex generators are integrally formed with at least a portion of the said flow modulation devices, wherein movement of said flow modulation devices produces corresponding movement of said vortex generators.

5. The wind turbine blade of claim 2, wherein said plurality of flow modulation devices are at least partly integrated with said base portion.

6. The wind turbine blade of claim 2, wherein the trailing edge panel comprises a plurality of reinforcing elements extending between said flow modulation devices and said vortex generators, said reinforcing elements operable to translate a movement of said flow modulation devices into a movement of said vortex generators.

7. The wind turbine blade of claim 6, wherein said reinforcing elements comprise at least one of the following: a wire or rod at least partly embedded in or connected between a flow modulation device and a vortex generator, and/or a structural rib defined on said trailing edge panel extending between a flow modulation device and a vortex generator.

8. The wind turbine blade of claim 2, wherein said base portion comprises a substantially planar member having a plurality of elements defined on said planar member, said plurality of elements outlining a plurality of planar vortex generator profiles, wherein said plurality of elements are arranged to project above the surface of the wind turbine blade under action of the bending or flexing of the flow modulation devices such that said plurality of planar vortex generator profiles form vortex generators projecting above the plane of the surface of the planar member, to form wake vortices downstream of the projecting vortex generators.

9. The wind turbine blade of claim 8, wherein the planar vortex generator profiles have a V-shaped or serrated tooth profile.

10. The wind turbine blade of claim 8, wherein said planar vortex generator profiles comprise a pair of vortex generator vanes, wherein said vortex generator vanes comprise a planar body, having a first side substantially in line with a direction of flow over said wind turbine blade and a second side arranged at an acute angle to the direction of flow.

11. The wind turbine blade of claim 1, wherein the wind turbine blade comprises a plurality of flow modulation devices projecting from the trailing edge of the blade, wherein said plurality of flow modulation devices comprise serrations.

12. A wind turbine comprising at least one wind turbine blade as claimed in claim 1.

13. A trailing edge panel for attachment to the trailing edge of an airfoil, wherein the panel comprises: a base portion for attachment to a surface of an airfoil; and at least one flexible member projecting from a side of said base portion, said at least one flexible member to be arranged in the wake of the airfoil, wherein the trailing edge panel is substantially formed from a flexible material, and wherein flexing of said trailing edge panel acts to deploy at least one aerodynamic device on said base portion of said panel.

14. The trailing edge panel of claim 13, wherein the panel comprises: a plurality of flow modulation devices, projecting from a side of said base portion, said flow modulation devices to be arranged in the wake of the airfoil.

15. The trailing edge panel of claim 14, wherein the plurality of flow modulation devices comprises a plurality of serrations.

16. The trailing edge panel of claim 13, wherein the airfoil comprises a wind turbine blade.

Description

DESCRIPTION OF THE INVENTION

(1) An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

(2) FIG. 1 shows a wind turbine;

(3) FIG. 2 shows a schematic view of a wind turbine blade according to the invention;

(4) FIG. 3 shows a schematic view of an airfoil profile of the blade of FIG. 2;

(5) FIG. 4 shows a schematic view of the wind turbine blade of FIG. 2, seen from above and from the side;

(6) FIG. 5 illustrates a top plan view of a trailing edge plate according to an aspect of the invention;

(7) FIG. 6 illustrates a perspective view of the trailing edge plate of FIG. 5;

(8) FIG. 7 shows side views of the trailing edge plate of FIG. 5 before and after flexing of the plate;

(9) FIG. 8 illustrates a top plan view of an alternative design of trailing edge plate according to the invention; and

(10) FIG. 9 illustrates alternative constructions of the trailing edge plate of FIG. 5.

(11) It will be understood that elements common to the different embodiments of the invention have been provided with the same reference numerals in the drawings. Furthermore, it will be understood that the drawings shown are representative, and are not to scale or illustrative of relative widths and lengths.

(12) FIG. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called Danish concept with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The rotor has a radius denoted R.

(13) FIG. 2 shows a schematic view of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

(14) The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 is typically constant along the entire root area 30. The transition region 32 has a transitional profile 42 gradually changing from the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increasing distance r from the hub.

(15) The airfoil region 34 has an airfoil profile 50 with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

(16) It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

(17) FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during usei.e. during rotation of the rotornormally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

(18) Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.t of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

(19) FIG. 4 shows some other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 2, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=L.sub.w, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. Further, the blade is provided with a prebend, which is defined as y, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

(20) The wind turbine blade 10 generally comprises a shell made of fibre-reinforced polymer, and is typically made as a pressure side or upwind shell part 24 and a suction side or downwind shell part 26 that are glued together along bond lines 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Wind turbine blades are generally formed from fibre-reinforced plastics material, e.g. glass fibres and/or carbon fibres which are arranged in a mould and cured with a resin to form a solid structure. Modern wind turbine blades can often be in excess of 30 or 40 metres in length, having blade root diameters of several metres. Wind turbine blades are generally designed for relatively long lifetimes and to withstand considerable structural and dynamic loading.

(21) In order to reduce trailing edge operational noise of the wind turbine blades, at least one member, preferably at least one flexible member, is arranged to project from at least a portion of the trailing edge 20 of the blade 10. Such a member may comprise an acoustic flap, and/or a series of serrations, bristles or other projecting flow modulation devices. Such members may be incorporated into and integrally formed with the structure of the wind turbine blade 10, or may be provided as a separate element which can be attached to a wind turbine blade 10 after initial manufacture or can be retrofitted to an existing blade.

(22) With reference to FIGS. 5 and 6, an embodiment of a trailing edge panel or plate according to an embodiment of the invention is indicated at 70. The trailing edge panel 70 comprises a base portion 72 for attachment to the surface of a wind turbine blade 10, and a series of serrations 74 projecting from said base portion 72. The serrations 74 extend from a base end 74a to a tip end 74b, which is to be arranged in the wake of a wind turbine blade 10. Accordingly, the base portion 72 is arranged at the leading edge side 70a of the trailing edge panel 70, and the serrations 74 are arranged at the trailing edge side 70b of the panel 70.

(23) With reference to the side view illustrated in FIG. 7(a), the serrations 74 may project in substantially the same plane as the base portion 72. Alternatively, it will be understood that the serrations 74 are arranged to project at an angle to the plane of the base portion 72, preferably between approximately 0-25 degrees to the plane of the base portion 72. Preferably, the trailing edge panel 70 is formed from a material which is flexible enough to bend under action of flow over the panel 70.

(24) On the base portion 72 of the panel 70, a series of projecting elements 76 are provided. In the embodiment of FIGS. 5 and 6, the projecting elements are formed as partial cut-outs 76 defined by a through-going channel provided in the base portion 72, the channel outlining a partially cut-out shape in the base portion 72. The elements or partial cut-outs 76 are generally arranged to have a base end 76a located towards the trailing edge side 70b of the panel 70, with a tip end 76b located towards the leading edge side 70a of the panel 70. The base end 76a of the partial cut-outs 76 is preferably integral with the base portion 72 of the panel 70, along a bending line 78. In the embodiment shown in FIGS. 5 and 6, the partial cut-outs 76 are in the shape of a V-shaped projection, pointing in the direction of the leading edge side 70a of the panel 70.

(25) The elements 76 defined by the partial cut-outs are arranged to be substantially in line with the projecting serrations 74. In the embodiment shown in FIGS. 5 and 6, the base end 76a of three elements 76 are arranged adjacent the base end 74a of each serration 74 of the trailing edge panel 70, but it will be understood that any number of elements 76 may be arranged to be in line with each serration 74 of the panel 70, e.g. each serration 74 may be arranged in line with a single element 76.

(26) The elements 76 defined by the partial cut-outs are effectively linked with the projecting serrations 74, such that a movement of a serration 74 will result in a corresponding movement of a linked element 76. In a first aspect, a serration and at least one element may be linked through the intrinsic structural properties of the trailing edge panel 70, wherein the bending of the trailing edge panel 70 itself results in a linked levering movement between the serration and the elements. Such a structural linkage may be due to the mechanical properties of the panel itself, e.g. in the case of a panel formed using a fibre-composite material, the fibres in such a panel may be arranged such that the primary fibre direction is substantially transverse to a hinge axis of the serrations. Furthermore, it will be understood that a reinforcing rib or corrugation may extend between a serration and linked elements, to provide for an improved structural link between the serration and the elements.

(27) Additionally or alternatively, a mechanical linkage may be arranged between a serration 74 and one or more elements 76, e.g. the use of a connecting wire or rod embedded in or provided on the panel 70, and connecting the serration and the said elements.

(28) While the elements 76 of FIGS. 5 and 6 are shown having the base end 76a located towards but spaced from the trailing edge side 70b of the base portion 72, it will be understood that the elements 76 may be positioned such that the base end 76a located towards but spaced from the trailing edge side 70b of the base portion 72, for example such that the base end 76a of the elements is coincident with the base end 74a of the serrations 74, substantially defining a hinge or fulcrum between the serrations 74 and the elements 76.

(29) It will be understood that the term cut-out is used to define an element which is partially integrated with the body of the base portion via a base end, and which is defined by a through-going channel arranged in the base portion about the periphery of the remainder of the element, such that the element may be deflected or bent relative to the plane of the base portion 72, along a bend line located at the base end of the element. In this regard, the cut-out may be formed integrally with the base portion as a result of a moulding operation which defines the surrounding channels as part of the moulding operation, and/or the cut-outs can be cut or etched into the base portion 72, e.g. into a blank of a trailing edge panel 70. In addition, while the projecting elements 76 of the embodiment of FIGS. 5 and 6 are defined in the body of the base portion 72, it will be understood that in other embodiments of the invention, the projecting elements 76 may be arranged to project from the leading edge side 70a of the base portion 72 of the panel 70.

(30) FIG. 7 illustrates a side view of the panel 70 of FIGS. 5 and 6, which can be attached to the trailing edge 20 of a wind turbine blade 10 (not shown in FIG. 7). With reference to FIG. 7(a), in an at-rest state, the serrations 74 project from the base portion 72 of the panel 70 in their normal plane. In this state, the elements or partial cut-outs 76 of the base portion 72 are arranged such that the elements 76 are in register with and flush with the adjacent surfaces of the panel 70, and do not significantly influence the aerodynamics of the panel 70.

(31) In FIG. 7(b), the serrations 74 of the panel 70 are deflected from their at-rest position by an angle , for example due to the forces generated from airflow over a wind turbine blade 10. Due to the linkage between the serrations 74 and the elements 76, the elements 76 are correspondingly levered into a deployed position wherein the elements 76 project above the plane of the surface of the base portion 72 of the panel 70. In the embodiment shown in FIG. 7, the elements 76 are levered by an angle corresponding to the deflection angle of the serrations 74, but it will be understood that a 1:1 correspondence between the levered angles is not limiting, and that the elements 76 may be raised by an angle greater than or less than a.

(32) In a further aspect of the invention, it will be understood that a connecting portion (not shown) may be provided between the free edges of the elements 76 and the adjacent surface of the base portion 72. Such a connecting portion may be in the form of a flexible membrane, which acts to form an aerodynamic bridge between the surface of the base portion 72 and the projecting element 76. By utilising a flexible member between the base portion 72 and the elements 76, the transition between the general surface of the wind turbine blade 10 and the projecting elements 76 will be smoothened, and will prevent airflow impacting on the area beneath the projecting elements 76.

(33) Additionally or alternatively, said connecting portion may be arranged to have a limited length, wherein the elements 76 are prevented from being raised above the surface of the base portion 72 beyond said length.

(34) In an alternative embodiment, a covering layer (not shown) may be provided on the trailing edge plate 70, wherein a relatively flexible sheet is applied to cover at least a portion of said base portion 72 and said elements 76. The raising or levering of said elements 76 will subsequently act to deform the covering layer in a manner to define a vortex generator shape at said trailing edge 20.

(35) As the elements 76 defined by the partial cut-outs are raised above the surface of the trailing edge panel 70, they are brought into the airflow over the wind turbine blade 10. The shape of the elements 76 is chosen such that the projecting elements 76 act as vortex generators in the airflow, creating a tip vortex downstream of the tip end 76b of the projecting elements 76. The tip vortex acts to draw airflow having relatively high momentum from outside the relatively slow-moving boundary layer into contact with the surface of the serrations 74, thereby re-energising the boundary layer of airflow along the serrations and delaying flow separation.

(36) As the vortex generators are effectively only deployed when the serrations 74 are deflected to an extent sufficient to lever the projecting element 76 into the oncoming airflow, accordingly the aerodynamic properties of the wind turbine blade as a whole are unaltered for operational conditions wherein the serrations are substantially undeflected from the at-rest state, e.g. for low-velocity wind conditions, where flow separation over trailing edge serrations is not a significant issue. As the velocity of the airflow over the wind turbine blade increases to the extent that the serrations are deflected, the vortex generators are levered above the adjacent surface level and deployed into the airflow. Accordingly, the vortex generators have a dynamic deployment based on the airflow over the wind turbine blade, as the greater the wind velocity, the greater the serration deflection, and consequently the higher that the elements 76 will project above the surface of the blade and into the oncoming airflow.

(37) The trailing edge panel 70 is arranged to be attached to the trailing edge 20 of a wind turbine blade 10, as part of an initial assembly operation or as a retrofit to an existing blade. The panel 70 may be attached using any suitable mechanism, e.g. adhesive bonding, bolting, riveting, welding, overlamination, etc. It will be understood that the trailing edge panel 70 is attached to the blade in such a manner so as to not impede the bending of the serrations and/or the projecting elements. Alternatively, the serrations and/or the projecting elements may be incorporated into the blade structure during manufacture of the blade shells, to provide for vortex generators which are deployable from a surface of the blade, based on a deflection of a trailing edge projection such as serrations.

(38) While the elements or partial cut-outs 76 of FIGS. 5-7 are in the form of an arrowhead or V-shaped projection, it will be understood that any suitable cut-out shape may be used. For example, crenelated or square-shaped elements may be used.

(39) With reference to FIG. 8, an embodiment of the invention is shown, wherein the elements are provided in the form of pairs of vortex generator vanes 80 defined in the body of the base portion 72 of a trailing edge panel 71. The vortex generator vanes 80 comprise a planar body attached to or integral with the base portion 72 of the panel 70 along a base end 78a, with a tip end 78b of the vanes 80 arranged towards the leading edge side 70a of the panel 70. The vanes 80 are arranged having a first side 82a substantially in line with a direction of flow over said wind turbine blade and a second side 82b arranged at an acute angle to the direction of flow.

(40) With reference to FIG. 9, two examples of a trailing edge panel according to embodiments of the invention are shown at 73 and 75. In these embodiments, a reinforcing structural member 84 extends between the elements 76 and the adjacent serrations 74, thereby facilitating the linked movement between the elements 76 and the associated serrations 74. The reinforcing structural member 84 may comprise any suitable connecting member, e.g. a wire, brace, rod, etc. which can be arranged to extend between the elements 76 and the serrations 74, Preferably, the member 84 is relatively flexible and/or is incorporated into the structure of the trailing edge panel 70.

(41) In FIG. 9(a), the panel 73 is configured wherein the members 84 extend from attachment points adjacent the tip ends 76b of the elements 76 in a direction in line with the flow direction over the wind turbine blade 10, to separate attachment points on the body of the serrations 74. As can be seen in FIG. 9(a), such attachment points may be distributed on the body of the serrations 74 at different lengths along the serrations in the direction of the trailing edge side 70b. In FIG. 9(b), the panel 75 is configured wherein the members 84 extend from attachment points adjacent the tip ends 76b of the elements 76 to a common attachment point of the adjacent serration 74, located towards the tip end 74b of the serrations 74.

(42) Accordingly, a flexing of the serrations 74 results in a corresponding raising of the elements 76, to act as vortex generators deployed from the trailing edge panel 70.

(43) While the above embodiments describe systems providing for a passive actuation and deployment of the elements 76 as vortex generators, based on the bending of the trailing edge serrations 74, it will be understood that the invention may further extend to the use of actuators or piezoelectric materials, which are operable to deploy vortex generators at the trailing edge of a wind turbine blade based on a detected deflection of the trailing edge serrations.

(44) While in the above-described embodiments, the trailing edge panel 70 comprises serrations 74, it will be understood that any other trailing edge device may be used without departing from the invention. For example, the trailing edge panel 70 may additionally or alternatively comprise an acoustic flap and/or bristles. Such trailing edge devices may then be coupled to the element or elements 76 of the panel using any of the above-described linkages. Furthermore, while the preferred embodiments describe the use of deployable vortex generators at the trailing edge of a wind turbine blade, the invention may also relate to the use of other aerodynamic devices, such as microtabs, microflaps, etc., which may be deployable at the trailing edge of a wind turbine blade.

(45) The use of such deployable vortex generators at the blade trailing edge results in a relatively simple mechanism for preventing flow separation over trailing edge devices such as serrations, which provides for ease of manufacturability and installation, and which provides for a dynamic adjustment of blade aerodynamics based on wind turbine operating conditions.

(46) The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.