DAMPING SYSTEM FOR WIND TURBINE BLADE EDGE VIBRATION STABILIZATION

Abstract

A wind turbine blade extending in a longitudinal direction between a root end and a tip end and comprising a shell having an outer surface defining a pressure side and a suction side, a leading edge and a trailing edge, a chord having a chord length extending between the leading edge and the trailing edge and a load-bearing structure extending in the longitudinal direction, the wind turbine blade further comprises a dampening system comprising a blade dampening body attached exteriorly to the load-bearing structure or exteriorly to the outer surface of the shell, at least a first dampener located within the blade dampening body and positioned with a component in the chordwise direction of the blade and adapted to absorb vibrational forces the wind turbine blade is subjected to.

Claims

1. A wind turbine blade (10), extending in a longitudinal direction between a root end (17) and a tip end (15) and comprising a shell (48) having an outer surface defining a pressure side and a suction side, a leading edge (18) and a trailing edge (20), a chord having a chord length extending between the leading edge (18) and the trailing edge (20) and a load-bearing structure (46) extending in the longitudinal direction, the wind turbine blade further comprises a dampening system (42) comprising: a blade dampening body (44) attached exteriorly to the load-bearing structure (46) or exteriorly to the outer surface of the shell (48), at least a first dampener (50) located within the blade dampening body (44) and positioned with a component in the chordwise direction of the blade and adapted to absorb vibrational forces the wind turbine blade (10) is subjected to.

2. A wind turbine blade (10) according to claim 1, wherein the dampening system (42) is configured to remain part of the blade or be attached to the blade under design operational conditions for the wind turbine blade.

3. A wind turbine blade (10) according to claim 1, wherein the blade dampening body (44) or dampener (50) protrudes into the shell.

4. A wind turbine blade (10) according to claim 1, wherein the dampener (50) is integrally formed with the blade damper body.

5. A wind turbine blade (10) according to claim 1, wherein the blade dampening body (44) is attached between wind blade sections in a segmented wind turbine blade.

6. A wind turbine blade (10) according to claim 1, wherein the dampener (50) is a liquid dampener or a mass dampener, especially a tuned mass dampener.

7. A wind turbine blade (10) according to claim 1, wherein a plurality of dampening systems or dampeners are attached along the blade.

8. A wind turbine blade (10) according to claim 1, wherein the blade dampening body has the shape of or is located within a fairing (70), dimensioned to create a smooth transition between the dampening body (44) and the shell (48) for reducing drag on wind turbine blade.

9. A wind turbine blade (10) according to claim 1, wherein the dampener comprises an actuator (52), such as a hydraulic, pneumatic or electromechanical actuator, moving a mass (54) along the chordwise direction of the blade.

10. A wind turbine blade (10) according to claim 9, wherein the dampening system further comprises: an acceleration sensor (56), a control valve (58), a hydraulic generator (60) for supplying pressurised hydraulic fluid to the hydraulic actuator by flow through the mass-activated valve, wherein the control valve (58) is configured to change the flow of the pressurised hydraulic fluid to move the actuator (52) in the same direction of the sensed acceleration by the acceleration sensor.

11. A wind turbine blade (10) according to claim 10, wherein the dampening system further comprises: first pressure supply lines (62) connecting the hydraulic generator to the control valve (58) comprising a high-pressure supply line (72) and a low pressure return line (74) and second pressure supply lines (64) connecting the valve to the actuator comprising a first (76) and second supply line (78), the control valve connecting the first pressure supply lines to the second pressure supply lines, the control valve is configurable to obtain: a first configuration, where the high-pressure supply line is connected to the first supply line and the low-pressure supply line is connected to the second supply line, a second configuration, where the high-pressure supply line is connected to the second supply line and the low-pressure supply line is connected to the first supply line, a third configuration, where first pressure supply lines and second pressure supply lines are not connected or equally connected.

12. A wind turbine blade according to claim 10, wherein the control valve is a mass-activated control valve, such as such as a spring-loaded acceleration sensor integrally formed with the valve.

13. A wind turbine blade according to claim 12, wherein the mass-activated control valve comprises an adjustable spring with regard to stiffness and zero-load point and pressure equilibration channels (82) adapted to achieve the first, second and third configuration when the adjustable spring expands and subtracts to allow tuning of the dampening system's frequency response characteristics.

14. A wind turbine blade according to claim 10, wherein the hydraulic generator is housed within a hub joint or a void of the blade.

15. A wind turbine blade according to claim 10, wherein the dampening system further comprises a hydraulic amplifier connected to the hydraulic actuator for active controlling of sensitivity of the dampening system.

16. A wind turbine blade according to claim 1, wherein the dampening body is located within the spanwise outer 30% of the length of wind turbine blade, preferably 15%, most preferably 10%, and in an anti-node of the oscillation shape to be dampened.

17. A wind turbine comprising a number of blades, preferably two or three, according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] 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.

[0054] FIG. 1 is a schematic perspective view of a wind turbine,

[0055] FIG. 2 is a schematic perspective view of a wind turbine blade for a wind turbine as shown in FIG. 1,

[0056] FIG. 3 shows an embodiment of the placement of the dampening system to a wind turbine blade,

[0057] FIG. 4 shows the geometry of internal dampeners,

[0058] FIG. 5 shows an embodiment of the placement of the dampening system on part of the blade,

[0059] FIG. 6 shows an embodiment where a hydraulic actuator is used, and

[0060] FIG. 7 shows a control valve used to passive control the flow of pressurised hydraulic fluid.

DETAILED DESCRIPTION OF THE INVENTION

[0061] In the following figure description, the same reference numbers refer to the same elements and may thus not be described in relation to all figures. The figures show one way of implementing the system and is not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set.

[0062] 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 which may include a tilt angle of a few degrees. 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.

[0063] FIG. 2 shows a schematic view of an exemplary wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end 17 and a tip end 15 and comprises a root section 30 closest to the hub, a profiled section 34 furthest away from the hub and a transition section 32 between the root section 30 and the profiled section 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, and a trailing edge 20 facing the opposite direction of the leading edge 18.

[0064] The profiled section 34 has an ideal or almost ideal blade shape with respect to generating lift, whereas the root section 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 section 30 may be constant along the entire root section 30. The transition section 32 has a transitional profile gradually changing from the circular or elliptical shape of the root section 30 to the airfoil profile of the profiled section 34. The chord length of the transition section 32 typically increases with increasing distance r from the hub. The profiled section 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 r from the hub. The different sections of the blade are commonly referred to as the airfoil of the blade. The profiled section as shown in FIG. 2 may be made up of a number of sections that is assembled. In such cases the wind turbine blade is a segmented blade construction.

[0065] 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 section 32 and the profiled section 34.

[0066] 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.

[0067] Referring to FIG. 3 an embodiment of the invention is shown. Two different embodiments illustrating the placement of the dampening body are shown in FIG. 3. In FIG. 3, a blade extending in a longitudinal direction between a root end 17 and a tip end 15 and comprising a shell 48 having an outer surface defining a pressure side and a suction side, a leading edge 18 and a trailing edge 20, a chord having a chord length extending between the leading edge 18 and the trailing edge 20 and a load-bearing structure 46 extending in the longitudinal direction is shown. In FIG. 3 a), a blade dampening body is attached to the load bearing structure 46 and in FIG. 3 b) the dampening system is attached to the shell 48. In both cases, the dampening system is placed externally onto the blade. However, the dampening system could locally protrude into the shell section.

[0068] As shown in FIGS. 4A) and B), the dampening system may comprise at least a first dampener 50, which is located within the dampening body 44 and positioned such that it has a component in the chordwise direction. This enables the dampener 50 to absorb the vibrations experienced by the wind turbine blade. In FIG. 4, different types of dampeners are shown, namely a liquid mass dampener, shown in FIG. 4A), and a tuned mass dampener, as shown in FIG. 4 B). However, a wide range of different dampeners is envisioned to be used. As shown in FIG. 4, the length of the dampener can be made longer than existing dampener systems, due to it being arranged on the external surface to the wind turbine blade. This has the effect that internal components and structural features of the turbine blade does not affect or limit the shape and length of the dampener.

[0069] The dampener could also be placed with a component in the flapwise direction to alleviate flapwise vibrations. Further, placing a plurality of dampeners at different locations along the blade will allow a range of vibrations to be absorbed. As seen in FIG. 4 a second dampener 68 is present.

[0070] As shown in FIG. 4, the dampening body fully encases the blade structure. However, the dampening body could also partially encase the blade structure or shell as shown in FIG. 5. Further, the dampener may locally protrude into the shell. As shown in FIG. 4 the dampening body or dampener may be dimensioned to follow the contour of the blade. This will create a snug-fit attachment to the wind turbine blade.

[0071] As shown in FIG. 5 the dampening system and dampener does not wrap around the shell but is only attached at the pressure side. In other embodiments, it could be attached to the suction side. The dampening body may comprise a fastener 66 connecting the blade dampening body 44 to the load bearing structure 46 of the blade or to the shell 48. As shown in FIG. 5 the fastener 66 is a bolt/nut connection, but other fasteners are envisioned, such as a screw connection, a glue connection, a clamping connection, an interlocking connection, etc.

[0072] In some embodiments, not shown in the figures, the dampening system is located within a fairing that provides a smooth transition and reduces drag and noise induced by the dampening system.

[0073] In FIG. 6 is shown a dampening system, wherein the dampener is a hydraulic actuator moving a mass along the chordwise direction of the blade. Other actuators are envisioned such as a pneumatic or electromechanical actuator. Moving the mass in a counter phase acceleration will cancel the vibrations of the blade. Changing the direction of the dampener and the actuator will allow different vibrations to be mitigated.

[0074] In FIG. 6 the dampening system comprises an acceleration sensor 56, a control valve 58, a hydraulic generator 60 for supplying pressurised hydraulic fluid to the hydraulic actuator by flow through the control valve. The control valve is configured to change the flow of the pressurised hydraulic fluid flowing in the hydraulic actuator to move the actuator 52 and thereby the mass in the same direction as the sensed acceleration by the acceleration sensor to create a counter-phase reaction force that minimises or cancels the vibrations.

[0075] The hydraulic actuator can in some embodiments be controlled by a passive control valve and in other embodiments an active control valve. As shown in FIG. 6, first pressure supply lines 62 connect the hydraulic generator to the control valve comprising a high-pressure supply line and a low pressure return line and second pressure supply lines 64 connecting the valve to the actuator comprising a first and second supply line. The fluid will be controlled by the control valve connecting the first pressure supply lines to the second pressure supply lines, such that three configurations of the flow of the fluid are obtainable, viz. a first configuration, where the high-pressure supply line is connected to the first supply line and the low-pressure supply line is connected to the second supply line, a second configuration, where the high-pressure supply line is connected to the second supply line and the low-pressure supply line is connected to the first supply line; and a third configuration, where first pressure supply lines and second pressure supply lines are not connected or equally connected creating a zero-flow configuration. Thus, the first and second configurations have opposite flow directions and movement of the mass.

[0076] The control valve can be a passive or an active component. Shown in FIG. 7 is an embodiment, wherein the control valve is a passive component in the form of a mass-activated control valve. The mass-activated control being integral formed with the acceleration sensor. As seen in FIG. 7, the control valve consists of an adjustable spring that can be adjusted with regard to stiffness and zero-load point and pressure equilibration channels 82 that allows tuning of the dampening systems frequency response characteristics. The spring moves the equilibration channels in relation to the supply lines to align or misalign the first and second supply lines with the low- and high-pressure lines changing the flow of the hydraulic fluid. FIGS. 7A), B) and C) correspond to the first, third and second configurations, respectively. The actuator correspondingly moves the mass to create an opposite phase force that minimises or cancels the vibration.

[0077] The mass-activated control valve has the added benefit that no electrical wires or components are needed, making it resistant to lightning strikes.

[0078] The hydraulic generator can be housed within a hub joint or a cavity of the blade. Further, the system could comprise a hydraulic amplifier connected to the hydraulic actuator for active controlling of the sensitivity of the dampening system changing for example the pressure of the hydraulic fluid. The geometry and placement of the equilibration channels can also be used as a controlling parameter.

[0079] In another embodiment, a controller controls the configuration of the mass-activated valve and/or the pressure ratio between the high-pressure line and low-pressure line based on the sensed acceleration by the acceleration sensor, which could be an electronic measurement. The controller further controls the hydraulic amplifier.

[0080] The placement of the dampening system and body could in principle be along the entire length of the wind turbine blade and will be placed based on the specific requirements of the blade, such as located within the spanwise outer 30% of the length of wind turbine blade, preferably 15%, most preferably 10%, and/or in an anti-node of the oscillation shape to be dampened.

LIST OF REFERENCES

[0081] 2 wind turbine [0082] 4 tower [0083] 6 nacelle [0084] 8 hub [0085] 10 blade [0086] 13 shell [0087] 14 blade tip [0088] 15 tip end [0089] 16 blade root [0090] 17 root end [0091] 18 leading edge [0092] 20 trailing edge [0093] 30 root section [0094] 32 transition section [0095] 34 profiled section [0096] 36 tip section [0097] 40 shoulder [0098] 42 dampening system [0099] 44 blade dampening body [0100] 46 load bearing structure [0101] 48 blade shell [0102] 50 first dampeners [0103] 52 actuator [0104] 54 mass [0105] 56 acceleration sensor [0106] 58 control valve [0107] 60 hydraulic generator [0108] 62 first pressure supply lines [0109] 64 second pressure supply lines [0110] 66 fastener [0111] 68 second dampener [0112] 70 fairing [0113] 72 High pressure supply line [0114] 74 Low pressure supply line [0115] 76 first supply line [0116] 78 Second supply line [0117] 80 adjustable spring [0118] 82 pressure equilibration channels