Wind turbine with hinged blades having a hinge position between inner and outer tip end of the blades

Abstract

A wind turbine (1) comprising a tower (2), a nacelle (3) and a hub (7) is disclosed. The hub (7) comprises a blade carrying structure (4) with one or more wind turbine blades (5) connected to thereto. Each of the wind turbine blades (5) defines an aerodynamic profile having a thickness which varies along a length of the wind turbine blade (5). Each of the wind turbine blades (5) is connected to the blade carrying structure (4) via a hinge (6) at a hinge position of the wind turbine blade (5), each wind turbine blade (5) thereby being arranged to perform pivot movements relative to the blade carrying structure (4) between a minimum pivot angle and a maximum pivot angle. The hinge position is arranged at a distance from the inner tip end (5a) and at a distance from the outer tip end (5b), and the thickness, or the thickness-to chord ratio, at the hinge position is larger than the thickness, or the thickness-to-chord ratio, at the inner tip end (5a) and larger than the thickness, or the thickness-to-chord ratio, at the outer tip end (5b).

Claims

1. A wind turbine comprising a tower, a nacelle mounted on the tower via a yaw system, a hub mounted rotatably on the nacelle, the hub comprising a blade carrying structure, and one or more wind turbine blades connected to the blade carrying structure, wherein each of the wind turbine blades extends along a longitudinal direction between an inner tip end and an outer tip end, and defines an aerodynamic profile with a suction side and a pressure side, each extending between a leading edge and a trailing edge, the leading edge and the trailing edge each extending between the inner tip end and the outer tip end, the aerodynamic profile further having a thickness which varies along the longitudinal direction of the wind turbine blade between the inner tip end and the outer tip end, and wherein each of the wind turbine blades is connected to the blade carrying structure via a hinge at a hinge position of the wind turbine blade, each wind turbine blade thereby being arranged to perform pivot movements relative to the blade carrying structure about a pivot axis arranged substantially perpendicular to the longitudinal direction of the wind turbine blade, between a minimum pivot angle and a maximum pivot angle, the hinge position being arranged at a distance from the inner tip end and at a distance from the outer tip end, and wherein the thickness at the hinge position is larger than the thickness at the inner tip end and larger than the thickness at the outer tip end.

2. The wind turbine according to claim 1, wherein the hinge position of each of the wind turbine blades is at a position defining a maximum thickness.

3. The wind turbine according to claim 1, wherein the thickness of the aerodynamic profile of each of the wind turbine blades decreases from the hinge position towards the inner tip end and from the hinge position towards the outer tip end.

4. The wind turbine according to claim 1, wherein each of the wind turbine blades has a centre of mass for the wind turbine blade at rest, the centre of mass being positioned between the hinge position and the inner tip end of the wind turbine blade.

5. The wind turbine according to claim 1, further comprising a balancing mass arranged on the nacelle at a position opposite to an attachment position of the hub.

6. The wind turbine according to claim 1, wherein the wind turbine is a downwind wind turbine.

7. The wind turbine according to claim 1, further comprising biasing means biasing the wind turbine blades towards a position providing a maximum rotor diameter of the wind turbine.

8. The wind turbine according to claim 1, further comprising end stop mechanisms arranged to slow pivot movements of the wind turbine blades in a region near the minimum pivot angle and/or in a region near the maximum pivot angle.

9. The wind turbine according to claim 8, wherein the end stop mechanism comprises a spring and/or a damper.

10. The wind turbine according to claim 1, further comprising a stop mechanism arranged to move the wind turbine blades to a safe pivot angle in the case of an emergency.

11. The wind turbine according to claim 10, wherein the safe pivot angle arranges the wind turbine blades in such a manner that each wind turbine blade extends along a direction which is substantially parallel to a rotational axis of the hub.

12. The wind turbine according to claim 10, wherein the stop mechanism comprises a release mechanism and at least one spring biased wire interconnecting the release mechanism and each of the wind turbine blades.

13. The wind turbine according to claim 1, wherein the blade carrying structure comprises one or more arms, and wherein each of the wind turbine blades is mounted on one of the arms of the blade carrying structure.

14. The wind turbine according to claim 1, wherein each of the wind turbine blades comprises an inner portion including the inner tip end and an outer portion including the outer tip end, and wherein the inner portion and the outer portion are joined to each other.

15. The wind turbine according to claim 14, wherein each of the wind turbine blades further comprises a hinge portion including the hinge position, and wherein the hinge portion interconnects the inner portion and the outer portion.

16. The wind turbine according to claim 1, wherein the hinge of each of the wind turbine blades is embedded in the wind turbine blade.

17. The wind turbine according to claim 1, wherein each of the wind turbine blades is provided with at least one winglet.

18. The wind turbine according to claim 1, further comprising at least one deployable airbrake.

19. The wind turbine according to claim 1, wherein the hinge position of each of the wind turbine blades is at a position defining a maximum chord of the wind turbine blade.

20. A wind turbine comprising a tower, a nacelle mounted on the tower via a yaw system, a hub mounted rotatably on the nacelle, the hub comprising a blade carrying structure, and one or more wind turbine blades connected to the blade carrying structure, wherein each of the wind turbine blades extends along a longitudinal direction between an inner tip end and an outer tip end, and defines an aerodynamic profile with a suction side and a pressure side, each extending between a leading edge and a trailing edge, the leading edge and the trailing edge each extending between the inner tip end and the outer tip end, the aerodynamic profile further having a thickness which varies along the longitudinal direction of the wind turbine blade between the inner tip end and the outer tip end, and wherein each of the wind turbine blades is connected to the blade carrying structure via a hinge at a hinge position of the wind turbine blade, each wind turbine blade thereby being arranged to perform pivot movements relative to the blade carrying structure about a pivot axis arranged substantially perpendicular to the longitudinal direction of the wind turbine blade, between a minimum pivot angle and a maximum pivot angle, the hinge position being arranged at a distance from the inner tip end and at a distance from the outer tip end, and wherein a thickness-to-chord ratio at the hinge position is larger than a thickness-to-chord ratio at the inner tip end and larger than a thickness-to-chord ratio at the outer tip end.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in further detail with reference to the accompanying drawings in which

(2) FIG. 1 is a view from behind of a wind turbine according to an embodiment of the invention,

(3) FIG. 2 is a side view of the wind turbine of FIG. 1 with the wind turbine blades in a first position,

(4) FIG. 3 is a side view of the wind turbine of FIGS. 1 and 2 with the wind turbine blades in a second position,

(5) FIG. 4 is a cross sectional view of the nacelle of the wind turbine of FIGS. 1-3,

(6) FIG. 5 illustrates a wind turbine according to an embodiment of the invention with the wind turbine blades in three different positions,

(7) FIG. 6 shows a wind turbine blade for a wind turbine according to an embodiment of the invention,

(8) FIG. 7 shows the wind turbine blade of FIG. 6 in three different positions,

(9) FIG. 8 shows a detail of the wind turbine blade of FIGS. 6 and 7,

(10) FIG. 9 shows a blade carrying structure comprising a deployable airbrake,

(11) FIGS. 10 and 11 illustrate a hinge for a wind turbine blade of a wind turbine according to a first embodiment of the invention,

(12) FIGS. 12 and 13 illustrate a hinge for a wind turbine blade of a wind turbine according to a second embodiment of the invention, and

(13) FIGS. 14-16 are side views of wind turbines according to three embodiments of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

(14) FIG. 1 shows a wind turbine 1 according to an embodiment of the invention. The wind turbine 1 comprises a tower 2 and a nacelle 3 mounted on the tower 2. A hub (not visible) is mounted rotatably on the nacelle 3, the hub comprising a blade carrying structure 4 with three arms. A wind turbine blade 5 is connected to each of the arms of the blade carrying structure 4 via a hinge 6. Thus, the wind turbine blades 5 rotate along with the hub, relative to the nacelle 3, and the wind turbine blades 5 can perform pivoting movements relative to the blade carrying structure 4, via the hinges 6.

(15) Each wind turbine blade 5 defines an aerodynamic profile having a thickness which varies along the length of the wind turbine blade 5 between an inner tip end 5a and an outer tip end 5b. The hinge 6 is arranged at a hinge position of the wind turbine blade 5, the hinge position 6 being at a distance from the inner tip end 5a as well as at a distance from the outer tip end 5b, and the thickness of the wind turbine blade 5 is larger at the hinge position than at the inner tip end 5a as well as at the outer tip end 5b.

(16) FIG. 2 is a side view of the wind turbine 1 of FIG. 1. In FIG. 2 the hub 7 can be seen. The wind turbine blades 5 are in a position in which they define a maximum rotor diameter of the wind turbine 1. The wind turbine blades 5 are biased towards this position by each of the wind turbine blades 5 being connected to a weight 8 arranged inside the tower 2, via a wire 9. The weight 8 pulls the wire 9, and thereby pulls the wind turbine blades 5 towards the position shown in FIG. 2. Accordingly, when no other forces act on the wind turbine blades 5, the wind turbine blades 5 will be in the position shown in FIG. 2, and a maximum rotor diameter will be defined. This is the case when the wind speed is low, and the hub 7 therefore rotates at a low rotational speed.

(17) FIG. 3 is a side view of the wind turbine 1 of FIGS. 1 and 2. In FIG. 3 the wind speed is higher than in the situation illustrated in FIG. 2. Thereby a centrifugal force acts on the wind turbine blades 5, due to higher rotational speed of the hub 7. The centre of mass of each wind turbine blade 5 is positioned at a position between the hinge 6 and the inner tip end 5a. Therefore the centrifugal force acting on the wind turbine blades 5 seeks to pivot the wind turbine blades 5 towards the position illustrated in FIG. 3. Additionally, the aerodynamic forces acting on the wind turbine blades 5 seek to pivot the wind turbine blades 5 towards the position illustrated in FIG. 3. In the situation illustrated in FIG. 3, the centrifugal force in combination with the aerodynamic forces acting on the wind turbine blades 5 balance the total force vector in the same direction acting on the wind turbine blades 5, originating from the weight 8 and the wire 9. In general the pivot angle of the wind turbine blades 5 is changed with increased rotational speed and wind speed until a new state of equilibrium is found between all forces on the wind turbine blades 5. Obviously all other secondary forces and moments on the wind turbine blades 5, such as bearing friction at the hinge 6, are included as well.

(18) The pivoting of the wind turbine blades 5 between the position shown in FIG. 2 and the position shown in FIG. 3 takes place gradually, and the exact position of the wind turbine blades 5 is a result of a balance between the force originating from the weight 8 and the centrifugal force.

(19) In the situation illustrated in FIG. 3 the rotor diameter is significantly smaller than in the situation illustrated in FIG. 2. Accordingly, an increased wind speed automatically results in a smaller rotor diameter, and a decreased wind speed automatically results in a larger rotor diameter. Thus, the rotor diameter is automatically adapted to the prevailing wind conditions.

(20) FIG. 4 is a cross sectional view of the nacelle 3 of the wind turbine of FIGS. 1-3. It can be seen how the wire 9 is guided through the nacelle 3 and into the tower 2.

(21) FIG. 5 illustrates a wind turbine 1 according to an embodiment of the invention at three different wind speeds. The wind turbine 1 could, e.g., be the wind turbine of FIGS. 1-3.

(22) The left most drawing shows the wind turbine 1 at a low wind speed. In this case the rotational speed of the hub 7 is low, and therefore the centrifugal force acting on the wind turbine blades 5 is small. Accordingly, the rotor diameter is maximum.

(23) The middle drawing shows the wind turbine 1 at a wind speed which is higher than the wind speed of the left most drawing. Accordingly, the rotational speed of the hub 7 is higher, and the centrifugal force acting on the wind turbine blades 5 is larger. Additionally, the aerodynamic forces acting on the wind turbine blades 5 are also larger. As a consequence, the wind turbine blades 5 have been pivoted towards a position defining a smaller rotor diameter.

(24) The right most drawing shows the wind turbine 1 at a high wind speed. In this case the rotational speed of the hub 7 is very high, and therefore the centrifugal force acting on the wind turbine blades 5 is large. In addition, the aerodynamic forces at the high wind speed push the wind turbine blades 5 into the shown position. This has the consequence that the wind turbine blades 5 have been pivoted to a position defining a minimum rotor diameter. It can be seen that the wind turbine blades 5 are arranged substantially parallel to a rotational axis of the hub 7. This position is sometimes referred to as ‘barrel mode’.

(25) FIG. 6 shows a wind turbine blade 5 for a wind turbine according to an embodiment of the invention. The wind turbine blade 5 is connected to a blade carrying structure 4 forming part of a hub 7, via a hinge 6. Thereby the wind turbine blade 5 is able to perform pivot movements relative to the blade carrying structure 4. The position of the wind turbine blade 5 relative to the blade carrying structure 4 defines a pivot angle 10. In FIG. 6 the wind turbine blade 5 is arranged with its longitudinal direction substantially parallel to a rotational axis of the hub 7. This position defines a maximum pivot angle 10. Furthermore, this position defines a minimum rotor diameter, as described above.

(26) An end stop mechanism 11 in the form of a resilient pad is mounted on the blade carrying structure 4. When the wind turbine blade 5 is pivoted to a position defining a minimum pivot angle 10, the wind turbine blade 5 abuts the end stop mechanism 11, resulting in a soft stop for the pivot movement. Thereby collisions between the wind turbine blade 5 and the blade carrying structure 4 are avoided.

(27) FIG. 7 shows the wind turbine blade 5 of FIG. 6 in three different positions, i.e. at three different pivot angles. It can be seen that the different pivot angles result in different distances between the wind turbine blade 5 and the rotational axis 12 of the hub 7, and thereby in different rotor diameters.

(28) FIG. 8 shows a detail of the wind turbine blade 5 of FIGS. 6 and 7. It can be seen that the hinge 6 is embedded in the wind turbine blade 5. As an alternative, the hinge 6 could be mounted on an outer surface of the wind turbine blade 5.

(29) FIG. 9 shows a blade carrying structure 4 carrying a wind turbine blade 5 and having a deployable airbrake 13 mounted thereon.

(30) In the left part of FIG. 9 the deployable airbrake 13 is in a retracted position, where it is almost flush with an outer surface of the blade carrying structure 4. When the deployable airbrake 13 is in this position, it performs no braking action, i.e. the deployable airbrake 13 does not restrict the rotational movement of the blade carrying structure 4, and thereby of the hub 7.

(31) In the right part of FIG. 9 the deployable airbrake 13 is in a deployed position, where it protrudes from the outer surface of the blade carrying structure 4. When the deployable airbrake 13 is in this position, it restricts the rotational movements of the blade carrying structure 4, and thereby of the hub 7, due to wind resistance. Thereby the deployable airbrake 13 performs a braking action.

(32) During normal operation, the deployable airbrake 13 may be in the retracted position illustrated in the left part of FIG. 9. When braking of the wind turbine is required, the deployable airbrake 13 may be moved to the deployed position illustrated in the right part of FIG. 9 in order to provide the braking action.

(33) FIGS. 10 and 11 show a wind turbine blade 5 for a wind turbine according to a first embodiment of the invention from two different angles. The wind turbine blade 5 is connected to a blade carrying structure 4 via a hinge 6. The hinge 6 is connected to the wind turbine blade 5 via two brackets 14 attached to an outer surface of the wind turbine blade 5.

(34) FIGS. 12 and 13 show a wind turbine blade 5 for a wind turbine according to a second embodiment of the invention. FIG. 12 shows the entire wind turbine blade 5, while FIG. 13 shows a detail of the wind turbine blade 5. The wind turbine blade 5 is connected to a blade carrying structure 4 via a hinge 6. The hinge 6 has a portion which is embedded in the wind turbine blade 5, and thereby the actual hinge 6 does not protrude from the outer surface of the wind turbine blade 5.

(35) The part of the blade carrying structure 4 which is shown in FIGS. 12 and 13 comprises a cylinder 15 being directly connected to the hinge 6. A rod 16 is received in the cylinder 15. The rod 16 is mounted pivotally on a protruding portion 17 of the wind turbine blade 5. By moving the rod 16 inwards or outwards with a controlled force, the wind turbine blade 5 will pivot around the hinge 6 between a minimum pivot angle and a maximum pivot angle.

(36) FIG. 14 is a side view of a wind turbine 1 according to an embodiment of the invention. The wind turbine 1 of FIG. 14 is very similar to the wind turbine 1 of FIGS. 1-3, and it will therefore not be described in detail here.

(37) In the wind turbine 1 of FIG. 14, each of the wind turbine blades 5 is provided with a winglet 18 at the inner tip end 5a. The winglets 18 extend away from the blade carrying structure 4 and towards the pressure side of the wind turbine blades 5. The winglets 18 allow for a design of the wind turbine blades 5 in which specific aerodynamic properties are obtained with shorter wind turbine blades 5. In particular, providing the winglets 18 at the inner tip ends 5a as illustrated in FIG. 14 shortens the part of the wind turbine blade 5 arranged between the hinge 6 and the inner tip end 5a, thereby allowing a reduced overhang, i.e. the required distance between the tower 2 and the hub 7.

(38) It should be noted that the winglets 18 could, alternatively, extend towards the blade carrying structure 4 and towards the suction side of the wind turbine blades 5. As another alternative, the wind turbine blades 5 could be provided with winglets 18 at the inner tip end 5a extending towards the pressure side as well as towards the suction side of the wind turbine blades 5.

(39) FIG. 15 is a side view of a wind turbine 1 according to an alternative embodiment of the invention. The wind turbine 1 of FIG. 15 is very similar to the wind turbine 1 of FIG. 14, and it will therefore not be described in detail here.

(40) In the wind turbine 1 of FIG. 15, the inner tip ends 5a of the wind turbine blades 5 are not provided with winglets. Instead, each of the wind turbine blades 5 is provided with a winglet 19 at the outer tip end 5b. The winglets 19 extend towards the suction side of the wind turbine blades 5. Similarly to the embodiment of FIG. 14, the winglets 19 illustrated in FIG. 15 allow for a design of the wind turbine blades 5 in which specific aerodynamic properties are obtained with shorter wind turbine blades 5. In particular, providing the winglets 19 at the outer tip ends 5b as illustrated in FIG. 15 allows the length of the part of the wind turbine blade 5 arranged between the hinge 6 and the outer tip end 5b to be reduced, thereby resulting in less complicated blade transport.

(41) It should be noted that the winglets 19 could, alternatively, extend towards the pressure side of the wind turbine blades 5. As another alternative, the wind turbine blades 5 could be provided with winglets 19 at the outer tip end 5b extending towards the pressure side as well as towards the suction side of the wind turbine blade 5.

(42) FIG. 16 is a side view of a wind turbine 1 according to another alternative embodiment of the invention. The wind turbine 1 of FIG. 16 is very similar to the wind turbines 1 of FIGS. 14 and 15, and it will therefore not be described in detail here.

(43) In the wind turbine 1 of FIG. 16, each of the wind turbine blades 5 is provided with a winglet 18 at the inner tip end 5a, as described above with reference to FIG. 14, as well as a winglet 19 at the outer tip end 5b, as described above with reference to FIG. 15.

(44) It should be noted that, even though the winglets 18, 19 illustrated in FIG. 16 are such that the winglets 18 at the inner tip end 5a extend towards the pressure side of the wind turbine blades 5 and the winglets 19 at the outer tip end 5b extend towards the suction side of the wind turbine blades 5, it could also be envisaged that both winglets 18, 19 extend towards the pressure side of the wind turbine blade 5, that both winglets 18, 19 extend towards the suction side of the wind turbine blade 5, or that the winglets 18 at the inner tip end 5a extend towards the suction side of the wind turbine blade 5, while the winglets 19 at the outer tip end 5b extend towards the pressure side of the wind turbine blade 5. As another alternative, the wind turbine blades 5 could be provided with winglets at the inner tip end 5a and/or at the outer tip end 5b which extend towards the pressure side as well as towards the suction side of the wind turbine blades 5.

(45) It should further be noted that the winglets 18, 19 illustrated in FIGS. 14-16 could attain various geometric forms and inclination angles, i.e. the angle between the winglet 18, 19 and the main wind turbine blade 5. The winglets 18, 19 shown in FIGS. 14-16 are illustrations on two possible variants, where winglet 18 has a sharp winglet end, and winglet 19 has a rounded winglet end. The inclination angle is in both cases about 60°. In other preferred embodiments the inclination angle may be about 90°.