WO2011068405A1

WO2011068405A1 - Wind turbine blade with variable surface area and wind turbine equipped therewith

Info

Publication number: WO2011068405A1
Application number: PCT/NL2010/050811
Authority: WO
Inventors: Albertus Van Den Brink
Original assignee: Ewt Ip B.V.
Priority date: 2009-12-02
Filing date: 2010-12-02
Publication date: 2011-06-09
Also published as: WO2011068405A9; NL2003896C2

Abstract

The invention relates to a blade for a wind turbine, comprising a blade root for connecting to a hub of the wind turbine, a leading edge extending in span direction from the blade root to a tip, and a trailing edge extending in span direction from the blade root to the tip. The leading and trailing edge, the tip and the blade root together define a blade surface area. The blade further includes means for varying the effective blade surface area, these surface area-varying means comprising at least one movable flap, which is pivotable about a shaft extending substantially transversely of the span direction. The invention further relates to a wind turbine, comprising a mast, a hub mounted rotatably thereon and a number of blades as defined above mounted on the hub.

Description

Wind turbine blade with variable surface area and wind turbine equipped therewith

The invention relates to a blade for a wind turbine, comprising a blade root for connecting to a hub of the wind turbine, a leading edge extending in span direction from the blade root to a tip and a trailing edge extending in span direction from the blade root to the tip, wherein the leading and trailing edge, the tip and the blade root together define a blade surface, and means for varying the effective blade surface area, these surface area-varying means comprising at least one movable flap. Such a wind turbine blade is known, for instance from WO 02/051730.

The design of a blade for a wind turbine is always a compromise between a number of - often contradictory - requirements. Ά blade must thus be light, but also strong and stiff, and moreover aerodynamically efficient. The blade must furthermore meet this latter requirement within a range of wind velocities varying between practically windless and stormy. The blade must further be designed such that at very high wind velocities the loads on both the static construction and the rotating part of the wind turbine remain within determined limits .

The result of these requirements is that the design of existing turbine blades is such that wind turbines produce a low power at low wind velocities. This is because these blades are designed particularly to limit the loads at high wind velocities, this having an adverse effect on the aerodynamic efficiency at low wind velocities. In combination with a trend toward increasingly greater powers, this results in new designs for wind turbine blades having to be disproportionally larger and heavier to be able to withstand the maximum forces. Modern wind turbines thus have blades with a length of 45 metres and a weight of about 7 to 9 tons. The hub of a modern wind turbine can weigh 12 to 18 tons and the housing for the generator up to 70 tons. The weight of the mast varies with the length, from 150 tons for a mast of 80 metres to more than 300 tons for a mast of 120 metres.

Wind turbines are moreover placed mainly in areas where higher average wind velocities occur in order to thus maximize the power generated. These are often thinly populated and usually poorly accessible areas, so that placing of wind turbines in these areas often requires great effort and high investment. The transport of the large and heavy components of wind turbines to these types of area is furthermore a complex logistical undertaking entailing high cost.

Already described in said earlier document WO 02/051730 is a wind turbine with blades which are provided on their trailing edge with movable or deformable flaps. In the embodiments with movable flaps these flaps are pivotable in each case about a shaft running in span direction of the relevant blade, in the same way as wing flaps in an aircraft. In this text span direction" is otherwise understood to mean the direction from the blade root to the tip of the blade. By moving or deforming the trailing edge flaps the effective surface area of the blades can be varied and adjusted to the prevailing wind strength. Because this creates the option of reducing the effective surface area of the blades at high wind velocities and increasing it at low wind velocities, a higher efficiency is realized over the whole operating range of the wind turbine than is possible with integral blades.

This known wind turbine has the drawback however that the variation in surface area which can be achieved in this manner is relatively small. When larger flaps are used the construction of the blades is hereby seriously weakened, which must be compensated by a heavier construction. The operation of the flaps is moreover slow, which can cause heavy loads in the case of sudden gusts of wind.

WO 03/025389 describes another type of wind turbine, with blades whose effective surface area can be varied. Use is made here of slidable panels which, as desired, wholly cover or leave partially clear openings in the blades of the wind turbine. These openings also result in a considerable weakening of the blades, which must be structurally compensated by reinforcing parts of the blades. The operating mechanism and the guiding of the movement of the panels is here also relatively complex and heavy.

Finally, American patent 7,396,207 describes a wind turbine, each blade of which is formed by a combination of a mast and a boom, between which is tensioned a reefable sail. The surface area of the blade is varied by reefing the sail, more or less in the manner in which the operation of the sails in traditional Dutch windmills was adjusted by arranging sailcloth thereon or, conversely, removing it.

The invention now has for its object to further develop a blade for a wind turbine of the above described type such that the effective surface area thereof can be adjusted to prevailing wind velocities in rapid, simple and efficient manner. According to the invention this is achieved in such a wind turbine blade in that the at least one flap is pivotable about a shaft extending substantially transversely of the span direction. With this arrangement of the flap, in fact tangentially relative to the rotating movement of the blade, a compact and robust embodiment of the surface area-varying means is achieved which enables rapid and simple variation of the effective surface area of the blade. The load on the wind turbine can hereby be limited at high wind velocities without this adversely affecting the efficiency at lower wind velocities; this is because a greater total blade surface area can be selected than would be allowable without the surface area-varying means. Because the wind turbine will be exposed to lower loads, it can also be given a lighter and simpler construction than conventional wind turbines. Transport of the parts hereby also becomes easier.

An optimal adjustment of the blade to the prevailing conditions can be achieved when the surface area-varying means comprise a number of flaps which are substantially parallel to each other and which are pivotable about shafts substantially parallel to each other. The surface area can thus be greatly varied .

When the flaps are situated within the blade surface area, the aerodynamic design of the blade is not influenced by the presence of -the flaps,, or hardly so, and in any case less than in the case of flaps protruding from the trailing edge of the blade as in WO 02/051730.

The at least one flap is preferably movable between a collapsed position, in which it defines a substantially continuous plane with surrounding parts of the blade, and an extended position in which the flap encloses an angle with a main plane of the blade and leaves clear an opening therein. Not only is the effective surface area of the blade thus changed when the flap(s) is/are extended, but also the flow around the blade and thereby the aerodynamic efficiency.

In its extended position the at least one flap preferably encloses substantially a right angle with the main plane of the blade. In this position the air can thus flow almost undisturbed through the opening(s) in the blade left clear by the flap(s), whereby the turbine generates almost no power and so does not produce any load. This position of the flap(s) corresponds functionally with a vane position of a blade in a wind turbine with blades having an adjustable angle of incidence. The movable flaps according to the invention in fact make a system for adjusting the variable pitch unnecessary. Because such an adjusting system for wind turbine blades is normally relatively large and heavy, the construction is hereby further made lighter and simpler.

The at least one flap can preferably be fixed in at least one position lying between its collapsed and extended positions. The option of placing the flap(s) in a number of intermediate positions enables the power of the wind turbine to be optimally controlled.

In a preferred embodiment of the blade each blade has two side edges which enclose a non-right angle with the main plane of the blade. The flaps can thus pivot alongside one another without making contact with each other.

A structurally simple embodiment of the blade is obtained when the leading edge forms part of a beam extending in span direction from the blade root and the flap(s) is/are pivotally mounted in the beam.

In order to enable realization of an aerodynamically optimal form of the blade it is then recommended that the flap(s) is/are profiled and mounted cantilevered in the beam. As a result of the profile of the flaps the ends thereof will follow a path during a pivoting movement which is not easy to accommodate in a bearing.

When at least some of the flaps can be jointly operated, control of the power of the wind turbine is simplified.

For this purpose the blade can advantageously be provided with at least one operating member connected to the flaps and extending in span direction.

In order to enable simple reciprocal movement of the flaps between their collapsed and extended position the wind turbine blade can advantageously be provided with at least two operating members, which are connected to each of the flaps on either side of the respective pivot shaft. An operating mechanism similar to that usual in Venetian blinds is thus formed.

It is also possible in addition or instead for the at least one operating member to extend through the beam. The operating member is thus well integrated in the blade both structurally and aerodynamically.

In order to enable rapid and simple movement of the flaps between their different positions the at least one operating member is preferably connected to a drive arranged in the blade root .

In order to prevent the blade being exposed to excessively high loads in the unlikely event the drive were to become jammed, it is preferably provided with a slip coupling arranged between the drive and the at least one operating member-. The invention also relates to a wind turbine comprising a mast and a hub mounted rotatably thereon and to a number of blades as described above mounted on the hub.

In such a wind turbine the flaps of the different blades can preferably be moved synchronously in order to ensure a smooth running of the turbine and a uniform loading of the hub.

A structurally simple embodiment of the wind turbine is obtained when the blades are mounted non-movably on the hub. This is possible in that the pivotable flaps obviate the necessity of an adjusting mechanism for the variable pitch.

The invention will now be elucidated on the basis of three embodiments, wherein reference is made to the accompanying drawing in which corresponding components are designated with reference numerals increased in each case by 100, and in which:

Fig. 1 is a front view of a wind turbine blade according to a first embodiment of the invention, wherein the flaps are shown in their collapsed position,

Fig. 2 is a view corresponding to fig. 1 of the blade with the flaps in their extended position,

Fig. 3 shows a cross-section along line III-III in fig. 1,

Fig. 4 shows a cross-section along line IV-IV in fig. 2,

Fig. 5 shows a cross-section corresponding to fig. 3 and 4 of the flaps in an intermediate position,

Fig. 6 shows a cross-section along line VI-VI in fig. 1 and 2,

Fig 7 is a top view of a hub of a wind turbine with a blade according to the invention mounted thereon,

Fig. 8 is a perspective view of a wind turbine with three blades according to an alternative embodiment of the invention, wherein the flaps are shown in their collapsed position,

Fig. 9 is a perspective view of the upper part of the wind turbine of fig. 8, wherein the flaps are shown in an intermediate position, Fig. 10 and 11 are views corresponding to fig. 9 with the flaps in respectively the wholly extended and wholly collapsed position,

Fig. 12 is a perspective view of the upper part of the wind turbine from a different angle, wherein details of the blade root and hub are shown,

Fig. 13 and 14 are perspective views of a blade according to yet another embodiment of the invention with respectively extended and collapsed flaps,

Fig. 15 is a cut-away front view of a part of the blade of fig. 13 and 14 close to the blade root, with collapsed flaps,

Fig. 16 is a cut-away view as according to arrow XVI in fig. 15, and

Fig. 17 is a view corresponding to fig. 16 with the flaps in wholly extended position.

According to the invention a blade 1 for a wind turbine 2 comprises a blade root 3 connected to a hub 4 of wind turbine 2. A leading edge 5 and a trailing edge 6 extend from blade root 3 to a tip 7 of blade 1. The direction from blade root 3 to tip 7 of blade 1 is designated here as the "span direction". The terms "leading" and trailing" relate to the flow direction of the air over blade 1, this in turn being determined by the rotation direction of blade 1. Leading edge 5, trailing edge 6, blade tip 7 and blade root 3 together define a blade surface area S.

Wind turbine blade 1 is further provided with means for varying the effective blade surface area, these surface area-varying means here comprising a number of movable flaps 8. According to the invention these flaps 8 extend transversely of the span direction and are each pivotable about a shaft A. This shaft A is parallel to the longitudinal axis of the associated flap 8 and so also lies transversely of the span direction of blade 1. In the shown embodiment flaps 8 are substantially rectangular and their pivot shafts A are mutually parallel.

In the shown embodiment the leading edge 5 forms part of a beam 9 extending in the span direction from blade root 3. Flaps 8 are bearing-mounted at their leading edges 10 in this beam 9 by means of pivot bearings 11. Because blade 1 is aerodynamically profiled, this is also the case for flaps 8. They are therefore mounted in cantilevered manner here so that their trailing edges 12 are freely movable.

Flaps 8 are each movable between a collapsed position (fig.

1, fig. 3 and full lines in fig. 6) and an extended position (fig.

2, fig. 4 and broken lines in fig. 6) . In the collapsed position flaps 8 define a continuous plane with each other and with surrounding parts of blade 1, while in their extended position flaps 8 enclose an angle with a main plane of blade 1 and form openings 13 in blade surface S. As can be seen in fig. 4, the angle between the flaps and the plane of blade 1 is roughly a right angle in the extended position. In this position of flaps 8, which is particularly intended for very high wind velocities, the aerodynamic load on blade 1 is almost zero in both axial direction and the rotation direction. Blade 1 will therefore also exert practically no load on wind turbine 2, whereby the fixed parts of wind turbine 2 and the generator applied therein can be given a lighter construction than is possible in conventional wind turbines.

In the shown embodiment flaps 8 of blade 1 can be jointly operated. Present for this purpose are two operating members 14 which extend in span direction between a part 15 situated close to root 3 and a part 16 of blade 1 close to tip 7. Flaps 8 are enclosed here between these two blade parts 15, 16 and the leading edge beam 9, so within surface S of blade 1. Each operating member 14 is formed here by a continuous cable which has an outward cable segment 17 and a return cable segment 18, wherein cable segments 17, 18 extend on either side of flaps 8. Each cable segment 17, 18 is connected to each of the flaps 8, wherein connections 19, 20 are situated on either side of pivot shaft A. At the position of blade parts 15, 16 the operating cables are guided over cable pulleys 21, 22. The cable pulleys 21 in blade part 15 close to root 3 are connected in the shown embodiment to an electrical drive or winch 23, whereby one of the two cable segments 17, 18 can be hauled in as desired. This is in fact an operating mechanism as known from Venetian blinds.

By hauling in or pulling in cable segments 17 of the two operating members 14 from the collapsed position shown in fig.

1 and 3, flaps 8 are moved to the extended position shown in fig.

2 and 4. Winch 23 can otherwise be braked or blocked in one or more intermediate positions, whereby flaps 8 are only partially extended, as can be seen in fig. 5. The aerodynamic efficiency of blade 1 can thus be varied within broad limits so as to arrive at an optimal compromise at any wind velocity between the power generated by wind turbine 2 and the loads exerted thereon. It will otherwise be apparent that the operation of flaps 8 of each blade 1 must be synchronized with the operation of flaps 8 of the other blades 1 in order to avoid uneven loads.

In an alternative embodiment of the invention blade 101 no longer has a fixed tip part. Flaps 108 thus extend here, from a strongly curved {fig. 12) blade part 115 situated at blade root 103, over the whole span width of blade 101 up to tip 107. The "Venetian blind operation" cannot be applied in this embodiment, and operating member 114 is received instead in leading edge beam 109. Operating member 114 can now also be embodied as a continuous cable which can be connected at the position of each flap 108 to a lever or cable pulley, which is connected in turn to the pivot shaft of flap 108. It is also possible to envisage other transmissions, such as chains and chain wheels, gear racks and toothed wheels or rotating shafts and right-angled

transmissions .

It can otherwise be clearly seen in this embodiment that the different components of wind turbine 102, such as raast 124, hub 104 and housing 125 for the generator, have a considerably smaller and lighter form than in conventional wind turbines.

In yet another embodiment blade 201 is longer and has a higher aspect ratio, and has a larger number of flaps 208 than in the foregoing embodiments (fig. 13, 14). In this embodiment the leading edge beam 209 is embodied as a box construction closed on the rear side by a girder 226 in which flaps 208 are bearing-mounted by means of pivot bearings 211 (fig. 15). The profile of flaps 208 is indicated schematically here by profile lines 233. Incorporated into leading edge beam 209 in this embodiment is an operating member 214 which again takes the form of a continuous cable with an outward segment 217 and a return segment 218 (fig. 16) . Both cable segments 217, 218 are once again connected to each of the flaps 208, and connections 219, 220 are situated on either side of pivot shafts A.

Both cable segments 217, 218 are further each connected to a drive 227, 228, here in the form of motors with screw spindles. A slip coupling 229 is arranged between each cable segment 217, 218 and the associated drive 227, 228, whereby flaps 208 can still be moved to their extended (neutral) position in the case of high load in the event one of the drives 227, 228 were to fail. Further arranged between each pair of flaps 208 in cable segments 217, 218 are cable tensioners 230 with which cable segments 217, 218 can be adjusted such that all flaps 208 move synchronously.

Further shown clearly in this embodiment is that each flap

208 has two side edges 231 which enclose a non-right angle with the main plane of blade 201. This is shown by the fact that the side edges in fig. 16 enclose an angle with ribs 232, which in principle lie transversely of the main plane of blade 201. The mutually connecting oblique side edges 231 ensure on the one hand that the blade surface remains aerodynamically closed, while flaps 208 can still pivot to their extended position (fig. 17) without making contact with each other.

Although the invention is described above on the basis of three embodiments, it will be apparent that it is not limited thereto but can on the contrary be varied in many ways. The form and dimensions of the flap(s) and the operation thereof could take a different form. The flaps could thus extend over a smaller part of the span of the blade than shown and described here, for instance from a position halfway along the blade, to the tip. The surface area of that part of the blade subjected to the greatest loads can thus be varied. It is also possible to envisage the blade having a central beam with flaps in both the leading edge and the trailing edge. In particular conditions this can result in a more efficient construction.

The scope of the invention is therefore defined solely by the following claims.

Claims

1. Blade for a wind turbine, comprising:

- a blade root for connecting to a hub of the wind turbine, - a leading edge extending in span direction from the blade root to a tip, and

- a trailing edge extending in span direction from the blade root to the tip,

wherein the leading and trailing edge, the tip and the blade root together define a blade surface area, and

- means for varying the effective blade surface area, these surface area-varying means comprising at least one movable flap, characterized in that the at least one flap is pivotable about a shaft extending substantially transversely of the span direction.

2. Blade as claimed in claim 1, characterized in that the surface area-varying means comprise a number of flaps which are substantially parallel to each other and which are pivotable about shafts substantially parallel to each other.

3. Blade as claimed in claim 2, characterized in that the flaps are situated within the blade surface area.

4. Blade as claimed in any of the foregoing claims, characterized in that the at least one flap is movable between a collapsed position, in which it defines a substantially continuous plane with surrounding parts of the blade, and an extended position in which the flap encloses an angle with a main plane of the blade and leaves clear an opening therein.

5. Blade as claimed in claim 4, characterized in that in its extended position the at least one flap encloses

substantially a right angle with the main plane of the blade.

6. Blade as claimed in claim A or 5, characterized in that the at least one flap can be fixed in at least one position lying between its collapsed and extended positions.

7. Blade as claimed in any of the claims 2-6, characterized in that each blade has two side edges which enclose a non-right angle with the main plane of the blade.

8. Blade as claimed in any of the foregoing claims, characterized in that the leading edge forms part of a beam extending in span direction from the blade root and the flap(s) is/are pivotally mounted in the beam.

9. Blade as claimed in claim 8, characterized in that the flap(s) is/are profiled and mounted cantilevered in the beam.

10. Blade as claimed in any of the claims 2-9, characterized in that at least some of the flaps can be jointly operated.

11. Blade as claimed in claim 10, characterized by at least one operating member connected to the flaps and extending in span direction .

12. Blade as claimed in claim 11, characterized by at least two operating members, which are connected to each of the flaps on either side of the respective pivot shaft.

13. Blade as claimed in claim 8 or 9 and 11 or 12, characterized in that the at least one operating member extends through the beam.

14. Blade as claimed in any of the claims 11-13, characterized in that the at least one operating member is connected to a drive arranged in the blade root.

15. Blade as claimed in claim 14, characterized by a slip coupling arranged between the drive and the at least one operating member.

16. Wind turbine, comprising a mast, a hub mounted rotatably thereon and a number of blades as claimed in any of the foregoing claims mounted on the hub.

17. Wind turbine as claimed in claim 16, characterized in that the flaps of the different blades can be moved

synchronously .

18. Wind turbine as claimed in claim 16 or 17, characterized in that the blades are mounted non-movably on the hub.