Abstract
An extendable wind turbine blade for being extended in length during operation thereof, the wind turbine blade having an exterior surface with a root region and an airfoil region and comprising a first blade segment including a first portion of the exterior surface, a second blade segment including a second portion of the exterior surface, and a connection mechanism connecting the blade segments, and being configured to bring the wind turbine blade to a retracted state, in which the portions of the exterior surface are flush and adjoining, when the wind turbine blade operates above a threshold rotational speed and to bring the wind turbine blade to an extended state, in which the portions of the exterior surface are disconnected and the blade length is at least 101% of the blade length in the retracted state, when the wind turbine blade operates below the threshold rotational speed.
Claims
1-15: (canceled)
16. An extendable wind turbine blade, comprising: a root end and a tip end, the wind turbine blade extendable along a longitudinal axis running between the root end and the tip end; an exterior surface with a root region and an airfoil region; a leading edge and a trailing edge, and a chord line extending between the leading edge and trailing edge; a first blade segment including a first portion of the exterior surface and a first end; a second blade segment including a second portion of the exterior surface, a second end facing the first end, the second blade segment being separate from the first blade segment; a connection mechanism connecting the first blade segment with the second blade segment in a retracted state when the wind turbine blade operates above a threshold; and the connection mechanism connecting the first blade segment with the second blade segment in an extended state when the wind turbine blade operates below the threshold; wherein, in the retracted state, the wind turbine blade has a first length from the root end to tip end and the first portion of the exterior surface is arranged substantially flush with and adjoining the second portion of the exterior surface, and wherein, in the extended state, the wind turbine blade has a second length from the root end to tip end and the second blade segment is arranged with a gap to the first blade segment so that the first portion of the exterior surface and the second portion of the exterior surface are; and wherein the second length is at least 101% of the first length.
17. The wind turbine blade according to claim 16, wherein the threshold is based on one or more of: a rotational speed threshold, a power threshold, a wind speed threshold, a load threshold, a noise threshold, and a force or acceleration threshold.
18. The wind turbine blade according to claim 16, wherein the connection mechanism is configured to allow a centripetal force when the wind turbine blade operates at a cut-in speed to urge the second blade segment away from the first blade segment thereby bringing the wind turbine blade towards the extended state.
19. The wind turbine blade according to claim 16, wherein the connection mechanism comprise a biasing element configured to apply a biasing force that urges the second blade segment away from the first blade segment so that the wind turbine blade is biased towards the extended state.
20. A wind turbine blade according to claim 19, wherein the biasing element is configured so that the biasing force of the biasing element overcomes a retracting gravitational force urging the second blade segment towards the first section during a top part of a revolution of the wind turbine blade during operation.
21. The wind turbine blade according to claim 16, wherein the connection mechanism comprises an actuator configured to apply an actuation force in a default state and a release state, wherein in the default state the actuator apples an actuation force that urges the second blade segment towards the first blade segment to bring the wind turbine blade to the retracted state.
22. The wind turbine blade according to claim 21, wherein in the release state, the actuator is configured to reduce the actuation force so that a centripetal force or a biasing force from a biasing element overcomes the actuation force to bring the wind turbine blade to the extended state.
23. The wind turbine blade according to claim 21, wherein the actuator is arranged adjacent to the root end of the wind turbine blade.
24. The wind turbine blade according to claim 16, wherein, in the retracted state, the first end is positioned in contact with the second end, and in the extended state, the distance between the first end and the second end is at least 1% of the first length.
25. The wind turbine blade according to claim 16, wherein the connection mechanism comprises a deployable skin layer that, in the retracted state, is collapsed, and, in the extended state, bridges the gap between the first end of the first segment and the second end of the second segment so that the deployable skin layer is arranged substantially flush with the first and second portion of the exterior surface.
26. The wind turbine blade according to claim 16, wherein the connection mechanism comprises: a female section; a male section slidably received by the female section; wherein the female section is attached to either the first or second blade segment and the male section is attached to the other one of the first or second blade segment.
27. The wind turbine blade according to claim 16, wherein the connection mechanism is configured to rotate the second blade segment relative to the first blade segment when bringing the wind turbine blade between the retracted and extended states so that, in the retracted state, the second blade segment is oriented at a first pitch angle and, in the extended state, the second blade segment is oriented at a second pitch angle, wherein a difference between the first and second pitch angles is in the range of 1° to 45°.
28. The wind turbine blade according to claim 27, wherein the connection mechanism comprises: a female section; a male section slidably received by the female section, wherein the female section is attached to either the first or second blade segment and the male section is attached to the other one of the first or second blade segment; and the male section slidably engaging the female section via a threading with a pitch configured to orient the second blade segment at the first pitch angle in the retracted state and to orient the second blade segment at the second pitch angle in the extended state.
29. A wind turbine comprising one or more wind turbine blades according to claim 16, the wind turbine configured to operate at a cut-in speed and at a rated speed, wherein the one or more wind turbine blades are configured so that each wind turbine blade is in the extended state when the wind turbine operates at a speed between the cut-in speed and the rated speed.
30. The wind turbine according to claim 29, wherein the one or more wind turbine blades are configured so that each wind turbine blade is in the retracted state when the wind turbine operates at a speed above the rated speed.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0036] Embodiments of this disclosure will be described in more detail in the following with regard to the accompanying figures. The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.
[0037] FIG. 1 is a schematic perspective view of a wind turbine.
[0038] FIG. 2 is a schematic perspective view of a segmented wind turbine blade for a wind turbine as shown in FIG. 1.
[0039] FIG. 3a is a schematic side view of the segmented wind turbine blade.
[0040] FIG. 3b is a schematic side view of a tip segment of the segmented wind turbine blade.
[0041] FIG. 3c is a schematic side view of a root segment of the segmented wind turbine blade.
[0042] FIG. 4a is a schematic perspective view of a male section of a connection mechanism in the segmented wind turbine blade.
[0043] FIG. 4b is a schematic perspective view of a female section for the connection mechanism.
[0044] FIG. 4c is a schematic perspective view of the female section mated with the male section of the connection mechanism.
[0045] FIG. 5a is a schematic side view of the segmented wind turbine blade in a retracted state.
[0046] FIG. 5b is a schematic side view of the segmented wind turbine blade in an extended state.
[0047] FIG. 6a is a schematic side view of another embodiment of a connection mechanism.
[0048] FIG. 6b is a schematic end view as seen from the tip of a segmented wind turbine blade comprising the connection mechanism of FIG. 6a.
[0049] FIG. 7a shows an example illustrating operational parameters.
[0050] FIG. 7b illustrates how annual energy production can be increased by using the segmented wind turbine blade.
DETAILED DESCRIPTION OF THE INVENTION
[0051] 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 8 and a blade tip 14 farthest from the hub 8.
[0052] 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 an exterior surface 42 having a root region 30 closest to the hub, a profiled or an airfoil region 34 with a tip region 36 farthest 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 8 of FIG. 1, and a trailing edge 20 facing the opposite direction of the leading edge 18. The outermost radial point of the blade 10 from the hub 8 is the tip end 15.
[0053] 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 may be constant along the entire root area. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance from the hub. The airfoil region 34 has an airfoil profile 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 from the hub 8.
[0054] A shoulder 40 of the blade 10 is defined as the position where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34. The outermost third of the airfoil region 34 is typically referred to as the tip region 36. FIG. 2 also illustrates the longitudinal axis L along which the length of the blade is measured.
[0055] FIG. 3a schematically illustrates a segmented wind turbine blade 10. It is made up of at least a root segment 50 and a tip segment 60 divided along a partition line P. To allow joining of the root segment 50 with the tip segment 60, the two segments 50, 60 comprise a connection mechanism 70 including a female receiving section 52 and a mating male section 62 inserted into and engaging with the female receiving section 52. The female receiving section 52 and the male section 62 are slidably engaged and locked in connection via the connection mechanism 70. The connection mechanism 70 is shown in greater detail in FIG. 4c. The connection mechanism 70 connects the root blade segment 50 with the tip blade segment 60 in a retracted state and in an extended state. FIG. 3a shows the blade 10 in the retracted state. The retracted and extended states are described in greater detail in connection with FIGS. 5a-5b. It is clear that the male part can alternatively be part of the root segment 50, and the female part can be part of the tip segment 60.
[0056] FIG. 3b illustrates the tip segment 60 of the segmented blade 10 shown in the previous figures. Aside from the shell with a first portion 44 of the exterior surface 42 that forms the aerodynamic profile of the blade 10, the tip segment 60 further comprises the male section 62 as described above. The male section 62 of the tip segment 60 protrudes beyond (outside) the tip segment shell at a second end 61 opposite the tip end 15 to allow the male section to engage with a corresponding female receiving section 52 arranged in the root segment 50. The male section 62 is shown in greater detail in FIG. 4a.
[0057] FIG. 3c illustrates the root segment 50 of the segmented blade 10. As described above, the root segment 50 comprises a first end 51 opposite of the root end 17 and further a female receiving section 52 at the first end 51. The female section 52 is configured for receiving the male section 62 of the tip segment 60 to allow the root segment 50 and the tip segment 60 to be securely joined. The final blade 10 is obtained by mating the male section 62 with the female receiving section 52 and locking the connection of the two via the connection mechanism 70. The female section 52 is shown in greater detail in FIG. 4b.
[0058] FIG. 4a is a schematic illustration of the male section 62 for the connection mechanism 70 of the segmented wind turbine blade 10. The male section has an insertion end 63 for insertion into the female section 62 shown in FIG. 4b and a fixed end 64 for being fixed to the second end 61 of the tip segment 60.
[0059] FIG. 4b is a schematic illustration of the female receiving section 52 for engaging with the male section 62 shown in FIG. 4a. The female receiving section 52 defines an inner cavity and has a longitudinal closed end 54 and an opposite longitudinal open end 53 at the first end 51 of the root blade segment 50. A biasing device 72 in the form of a biased hydraulic piston of the connection mechanism 70 is positioned at the closed end 54. In the shown embodiment, the hydraulic piston is arranged close to the tip.
[0060] However, in a preferred embodiment, the hydraulic piston may be arranged close to the root end of the blade, e.g., in combination with a wire used to retract the tip blade segment 60, when the hydraulic pressure is applied. By releasing pressure at the cylinder, the blade tip segment may be pushed out.
[0061] FIG. 4c shows the female receiving section 52 and male section 62 slidably engaged with the insertion end 63 of the male section 62 inserted through the longitudinal open end 53 of and into the cavity of the female receiving section 52 to be received therein. The connection mechanism 70 locks the connection between the female section 52 and male section 62 via a stop (not shown) to prevent separation. The biased hydraulic piston 72 engages the male section 62 and comprises a biasing element in the form of a spring (not shown) applying a biasing force on the male section 62 urging it out of the female section 52 thereby urging biasing the blade 10 towards the extended state as shown in FIG. 5b. The connection mechanism 70 further comprises a hydraulic line 73 in fluid communication with the hydraulic piston 72 and a hydraulic actuator 71 (shown in FIGS. 5a-5b). The hydraulics of the connection mechanism 70 are described in greater details in connection with FIGS. 5a-5b.
[0062] FIG. 5a is a schematic illustration of the blade 10 in the retracted state. In this state, the wind turbine blade 10 has a first length L.sub.1 from the root end 17 to tip end 15. Further the first portion 44 of the exterior surface 42 of the root segment 50 is arranged substantially flush with and adjoining the second portion 46 of the exterior surface 42 of the tip segment 60 at the partition line P between the blade segments 50, 60. The actuator 71 is set in a default state applying a fluid pressure on the biased hydraulic piston 72 via the hydraulic line 73 causing the piston 72 to retract and apply an actuation force on the male section 62 and thus the tip segment 60. The connection mechanism 70 is configured so that the actuation force overcomes any forces, e.g. centripetal or gravitational forces, along the longitudinal axis L experienced by the tip segment 60 thereby moving towards and retaining the blade 10 in the retracted state as shown. As shown in FIGS. 5a and 5b, the actuator 71 may be arranged at the root end 17 of the blade and the hydraulic line may extend to the piston 72. However, as mentioned earlier, it is also possible to have all the hydraulics at the root end of the blade. In such an embodiment, a wire can be used to retract the blade tip segment, e.g. when hydraulic pressure is applied, and to release and push the blade tip segment out to the extended state, when the hydraulic pressure is released.
[0063] FIG. 5b is a schematic illustration of the blade 10 in the extended state. When desiring to switch the blade from the retracted state to the extended state, the connection mechanism 70 sets the actuator 71 to a release state in which the hydraulic actuator 71 releases the hydraulic pressure acting on the biased piston 72 via the hydraulic line 73 thereby reducing the actuation force so that the biasing force of the biasing element overcomes the actuation force and forces the male section 62 outward from the female section 52 to bring the blade 10 in the extended state as shown. In the extended state, the first portion 44 of the exterior surface 42 of the root segment 50 and the second portion 46 of the exterior surface 42 of the tip segment 60 are substantially disconnected by a gap G so that the wind turbine blade is extended and has a second length L.sub.2 from the root end 17 to tip end 15 along the longitudinal axis L. The second length L.sub.2 is at least 101% of the first length L.sub.1. The connection mechanism 70 further comprises a deployable skin layer 79 bridging the gap G between the first end 51 of the root segment 50 and the second end 61 of the tip segment 60 so that the deployable skin layer 79 is arranged substantially flush with the first 44 and second portion 46 of the exterior surface 42 and thereby provides an airfoil extension surface between the root and tip segments 50, 60 to increase power capture.
[0064] In the previously shown embodiment, the male and female sections 52, 62 of the connection mechanism 70 each has a mating rectangular cross-sectional shape. In another embodiment as shown in FIG. 6a-6b, the male and female sections 52, 62 of the connection mechanism 70 each has a mating a circular cross-section. Thus, the male section 62, e.g. a shaft such as a carbon shaft or carbon worm shaft, and female section 52 both have a circular cross-sectional shape and slidably engage via a threading 75 with a pitch providing a pre-defined path of the male section 62 relative to the female section 52 between the retracted and extended state. The connection mechanism 70 is thus configured to rotate the tip blade segment 60 relative to the root blade segment 50 when bringing the wind turbine blade 10 between the retracted and extended states so that, in the retracted state, the tip blade segment 60 is oriented at a first pitch angle α.sub.1 about the longitudinal axis L and so that, in the extended state, the tip blade segment 60 is oriented at a second pitch angle α.sub.2 corresponding to feathering of the tip segment relative to the incoming airflow. The angular difference between the first and second pitch angles is in the range of 1° to 45° as shown in FIG. 6b and is chosen according to e.g. the airfoil shape of the wind turbine blade, the chord and twist distribution, and/or the desired load level of the wind turbine blade 10. Further, a biasing device 72 of the connection mechanism 70 in the form of a spring applies a biasing force urging the tip blade segment 60 towards from the root blade segment 50 so that the wind turbine blade 10 is biased towards the retracted state. The connection mechanism 70 further comprises an actuator (not shown), e.g. a hydraulic actuator as previously shown and described, configured for switching between the retracted and extended state. It should be mentioned that the figures are schematic only and that the airfoils typically will have a different camber than the airfoils shown in FIG. 6b.
[0065] FIG. 7a illustrates an example of the operating parameters of a conventional pitch regulated wind turbine as a function of the wind speed. It is seen that the wind turbine starts to generate power, when the wind speed meets a cut-in speed. At the lower wind speeds, the wind turbine blades are operated at given pitch angle until the rotor speed of the wind turbine meets a design rotor speed. At higher wind speeds, the pitch angle starts to be varied and is continued to be varied at wind speeds, where the nominal (or rated) power of the wind turbine is met.
[0066] FIG. 7b illustrates the benefits of using the described segmented blades. Curve 80 illustrates a relationship between the output power from the wind turbine as a function of the wind speed, when the wind turbine blades are in a retracted state, whereas curve 81 illustrates the relationship between the output power from the wind turbine as a function of the wind speed, when the wind turbine blades are in the extended state. It is seen that the coefficient is larger, when the wind turbine blades are in an extended state, which means that additional power can be generated, when the wind speeds are in a region between the cut-in speed and the wind speed, where the nominal or rated power of the wind turbine is met. Thus, the annual energy production (AEP) can be increased by operating the wind turbine blades in the extended state, e.g., when an operational parameter is below a predetermined threshold. As mentioned earlier, the threshold can be based on a number of parameters, such as generated power, rotor speed, wind speed, loads, noise or the like. Curve 82 illustrates an example of a threshold level, where the operational conditions of the wind turbine blades change from the extended state to the retracted state. As also mentioned, the threshold can have an inherent hysteresis to ensure that the wind turbine blades do not inadvertently toggle between the two states at conditions close to the threshold.
TABLE-US-00001 List of References 2 wind turbine 4 tower 6 nacelle 8 hub 10 blade 13 shell 14 blade tip 15 tip end 16 blade root 17 root end 18 leading edge 20 trailing edge 30 root region 32 transition region 34 airfoil region 36 tip region 40 shoulder 42 exterior surface 44 first portion 46 second portion 50 root blade segment 51 first end 52 female section 53 receiving open end 54 closed end 60 tip blade segment 61 second end 62 male section 63 insertion end 64 fixed end 70 connection mechanism 71 hydraulic actuator 72 biasing device 73 hydraulic line 75 threading 79 skin layer 80 P-v curve at retracted state 81 P-v curve at extended state 82 change from extended to retracted state L longitudinal axis L.sub.1 first length L.sub.2 second length P partition line G gap α pitch angle
