Anti-oscillation apparatus and technique for securing wind turbine blades against oscillations

Abstract

The invention relates to a wind turbine blade oscillation preventer comprising an aperture and a sleeve and having a peripheral extent and a longitudinal extent, the preventer being configured for removable application over a wind turbine blade and configured to extend longitudinally thereover and peripherally thereabout; the preventer having a non-aerodynamic exterior surface which exhibits a rough surface capable of disrupting smooth or laminar airflow over a substantial portion of the longitudinal and peripheral extent of the sleeve when the preventer is in place on a wind turbine blade. The preventer further comprises a smooth interior surface extending along a substantial portion of the longitudinal extent of the sleeve. The invention also relates to a method of application of a blade oscillation preventer over wind turbine blades which comprise serrations at a trailing edge thereof.

Claims

1. A wind turbine blade oscillation preventer comprising an aperture and a sleeve and having a peripheral extent and a longitudinal extent, said preventer being configured for removable application over a wind turbine blade and configured to extend longitudinally thereover and peripherally thereabout; said preventer having a non-aerodynamic exterior surface which exhibits a rough surface capable of disrupting smooth or laminar airflow over a substantial portion of said longitudinal and peripheral extent of said sleeve when said preventer is in place on the wind turbine blade; and wherein said preventer further comprises a smooth interior surface extending along a substantial portion of said longitudinal extent of said sleeve and wherein said preventer comprises a resilient collar at said aperture portion.

2. The preventer of claim 1, wherein said smooth interior surface is formed from an abrasion resistant, low-friction material.

3. The preventer of claim 1, wherein said smooth interior surface extends from an aperture region of said sleeve and internally within said sleeve.

4. The preventer of claim 1, wherein said non-aerodynamic exterior surface is an external surface of a first, outer layer of said sleeve; said smooth interior surface is an internal surface of a second, inner layer of said sleeve.

5. The preventer of claim 4, wherein respective said first and said second layers extend from an aperture region of said preventer.

6. The preventer of claim 4, wherein said first and said second layers include separate and distinct layered materials.

7. The preventer of claim 1 wherein said smooth interior surface is provided in the form of a liner inside said sleeve and extending from an aperture region thereof.

8. The preventer of claim 7 wherein said liner extends inside substantially the full longitudinal and peripheral extent of said preventer.

9. The preventer of claim 1 wherein said exterior surface extends over substantially the full longitudinal extent of said sleeve and around a majority of said peripheral extent of said sleeve.

10. The preventer of claim 1 wherein said collar is generally circular or elliptical.

11. The preventer of claim 1 further comprising a guide line extending from said aperture region.

12. The preventer of claim 1 further comprising a tripping line extending from a distal portion of said smooth interior surface.

13. A method of operating a wind turbine to inhibit oscillations induced by the air flow across at least one of a plurality of blades of the wind turbine when the wind turbine is in a non-operational mode, said wind turbine comprising a blade rotor including the plurality of blades, the blade rotor being rotatably mounted via a hub thereof to a nacelle positioned atop a tower, said at least one blade exhibiting trailing edge serrations; said method comprising: releasably locking the plurality of wind turbine blades of said rotor in place; applying and releasably securing a preventer according to claim 1 to said at least one wind turbine blade so that said preventer covers a region of the blade surface and provides a non-aerodynamic outer surface capable of inducing turbulence in air flow across said at least one blade; said method including disposing said smooth interior surface of said preventer sleeve over and about said serrated trailing edge of said at least one blade during application of said preventer.

14. The method according to claim 13, further comprising: attaching a first guide line to an attachment point on said preventer adjacent said aperture; pulling said sleeve onto said at least one wind turbine blade using said guide line; tying said guide line to a part of said wind turbine to secure said sleeve in place.

15. The method according to claim 14, further including attaching a second line to a distal end of said preventer, so that pulling on said first and second lines pulls the length of said sleeve taut.

16. The method according to claim 15 further including pulling said second line in order to free said smooth interior surface from said serrations prior to removal of said preventer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described in more detail, and by way of example, with reference to the not-to-scale figurative drawings, in which:

(2) FIG. 1 shows an orthogonal figurative view of an example of an oscillation preventer for a wind turbine blade according to aspects of the invention;

(3) FIG. 2 shows an orthogonal view of an example of an oscillation preventer for a wind turbine blade according to additional aspects of the invention;

(4) FIG. 3 shows an orthogonal view of an example of an oscillation preventer for a wind turbine blade according to alternative aspects of the invention;

(5) FIG. 4 shows an orthogonal view of an example of an oscillation preventer for a wind turbine blade according to yet further aspects of the invention;

(6) FIG. 5 shows an orthogonal view of an example of an oscillation preventer for a wind turbine blade according to still additional aspects of the invention;

(7) FIGS. 6a-c show a figurative and schematic impression of an oscillation preventer according to aspects of the invention illustrating figuratively its application over a blade tip provided with trailing edge serrations;

(8) FIG. 7 shows a schematic illustration of a wind turbine;

(9) FIG. 8 shows a schematic illustration of a technique for attaching the anti-oscillation apparatus according to aspects of the invention to a blade of a wind turbine;

(10) FIG. 9 shows a schematic illustration of a wind turbine including an anti-oscillation apparatus according to aspects of the invention, fitted to the wind turbine blades.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(11) The construction of one example of an oscillation preventer 10 is shown in more detail in FIG. 1. The preventer 10 comprises a non-aerodynamic exterior surface 34 of a substantially net-like or otherwise coarse material having at least one open end 20 for manoeuvring onto the tip of a wind turbine blade 5. In the example shown in FIG. 1, the preventer 10 has a sleeve 30 which has the approximate shape of a stocking or pocket, the distal end 32 of which is closed or closed sufficiently to prevent a wind turbine blade tip from protruding through it. Although, the sleeve 30 can be thought of as substantially tubular, in that its length dimension is larger than its width, it will be appreciated the sleeve 30 tapers towards its end 32 to fit more snugly around the smaller diameter of wind turbine blade tip. Further, it may also have a flattened cross-section to follow the flattened cross-section of the blade away from the root. Such a flattened cross-section may enhance compact stowage. The preventer can be seen to have a longitudinal extent corresponding to the elongate stocking shape and a peripheral extent corresponding to the more or less to a circumferential dimension of the stocking shape of the sleeve 30.

(12) The sleeve 30 can comprise a single layer or more than one layer. In the example of FIG. 1 the sleeve 30 comprises two layers, a first, external layer 38 and a second internal layer 37. In all cases, the exterior surface 34 of the sleeve 30 is such that the preventer 10 as a whole will disrupt laminar or smooth airflow over or around it. And in all cases, the sleeve 30 presents an interior surface 35 which is smooth. The smooth interior surface 35 may extend about the whole interior surface of the sleeve 30 or only a portion of it. In particular, the smooth interior surface 35 may extend over a portion of the peripheral extent of the sleeve 30 or over the full extent of the internal periphery of the sleeve 30. In any case, the smooth interior surface 35 preferably extends over substantially the whole longitudinal extent of the interior of the sleeve 30. This will ensure that the preventer 10 is capable of covering the tip portion of a wind turbine blade 5 without the exterior surface contacting a trailing edge thereof or the tips of any trailing edge serrations 7. The construction of the preventer 10 ensures that its smooth internal surface 35 covers trailing edge serrations of a blade 5 thereby shielding the serrations without them contacting the exterior surface 34. In the case illustrated in FIG. 1, the exterior surface 34 constitutes a first outer layer 38 while the smooth internal surface 35 is comprised of a second inner layer 37 or lining layer. The lining layer 37 shown in FIG. 1 extends about substantially the full longitudinal extent of the sleeve 30 and about a portion of the peripheral extent of the sleeve 30. In particular, the smooth internal surface 35 shown in FIG. 1 has the general shape of a tongue 26 which is long enough and broad enough to cover a line of serrations 7 on a blade trailing edge without the tips of these coming into contact with the rough exterior surface 34. In general, the tongue-shaped smooth surface may have a length and a width, wherein the width extends around a peripheral extent of the sleeve covering an arc of the sleeve amounting to at least one tenth of the sleeve circumference, preferably at least one fifth of the sleeve circumference. The length of said tongue 26 may extend along substantially the full length of the sleeve 30 or at least along two-thirds the length of the sleeve 30.

(13) Also visible in FIG. 1 is a distal end of a first line 16 which may be a guide line and which may serve to retain the preventer 10 when it is in place on a blade 5, for example by fastening a proximal end to a part of the wind turbine 1 such as its hub 6 or rotor 4 or nacelle 3. The first guide line 16 may also be used during application of the preventer to a blade 5 by pulling the aperture 20 over the blade tip. The first guide line 16 may be fixed or releasably fastened to the preventer aperture 20 by any suitable means such as a loop 23 which, in aspects of the invention, may be a releasable shackle such as a snap shackle. A second line 17 may also be attachable in a fixed or releasable manner to the preventer 10, preferably to a distal end 32 thereof. Again, the attachment means may be a loop 24 which may be a snap shackle 24. A release control line (not shown) may also run to the snap shackle. The second line 17 may be of assistance during the attachment of the preventer 10 over a blade tip for example by assisting in keeping the sleeve 30 taut during application thereof and also by assisting with guiding the orientation of the preventer 10 during its application. Controllability of the preventer 10 is greatly enhanced if, during application thereof, the second line 17 is pulled to some extent in a direction opposite to the direction of the first guide line 16. By pulling the second line 17 in a direction lateral to a blade axis, the preventer 10 may be guided as it is pulled on to the blade.

(14) In aspects of the invention, the second line 17 may be a tripping line and may in particular be attached at least partly to the material of the smooth internal surface 35. In alternative embodiments, a second guide line may be provided additional to a tripping line or a tripping line may be provided additional to a second guide line. The tripping line may ensure that if it is pulled somewhat when the preventer 10 is in pace on a blade 5, then there will be a tendency for the internal surface material 35, to which the tripping line is attached or attachable, to become taut, to straighten or flatten, and to release itself from underlying serration tips.

(15) In FIG. 2, there is shown an alternative embodiment according to which the sleeve 30 of the preventer 10 may be formed from a single layer incorporating a non-aerodynamic exterior surface material 34 which may extend over the full longitudinal extent of the preventer 10 and about a majority of its peripheral extent. The sleeve 30 may additionally comprise a smooth interior surface 35 in the form of a tongue-shaped insert 28 which extends about a segment of the peripheral extent of the sleeve 30 and which may extend along substantially the whole longitudinal extent of the preventer sleeve 30, i.e. from its aperture region 20 to its distal end 32.

(16) A second guide line 17 connected to the distal end of the preventer 10 may preferably be attached directly or indirectly to a distal end of the smooth interior surface material 35. This may ensure that the line 17 may have a dual functionality as a guide line and also as a tripping line for the smooth interior surface material 35 for enhanced removal of the preventer 10 from a blade 5. Preferably, the smooth internal surface material 35 and the exterior material 34 both extend from the aperture 20 of the preventer 10 and sleeve 30.

(17) A still further optional embodiment is illustrated at FIG. 3, in which the sleeve comprises a first outer layer 38 and a second inner layer 37 in the form of a lining. The lining layer 37 may in particular define the full interior surface of the sleeve 30, that is to say, the totality of that surface which, in use comes into contact with a blade and any serrations 7 at the blade 5. Also illustrated is a first guide line 16 releasably connected to the aperture 20 of the preventer 10 and a second line 17 releasably connected to a distal end 32 of the preventer. The second guide line 17 may be fixedly or releasably connected to the outer layer 38 or to both the inner layer 37 and the outer layer 38. An advantage of connecting the second line 17 to both the second, inner layer 37 and the first, outer layer 38 arises in that a pulling action on the line 17 may serve both to assist in the controllability of the preventer 10 during application or removal from a blade 5 and it may assist in releasing the smooth inner surface 35 from any engagement with e.g. serrations on a blade 5 after it has been in position perhaps for some time. I.e. the second line 17 may perform the function of a guide line 17 for the distal end of the preventer 10 and also the function of a tripping line.

(18) FIGS. 4 and 5 illustrate embodiments in which a collar 44 is provided at an aperture 20 of a preventer of the present invention. The provision of a collar 44 can add a certain amount of additional resilience to the preventer 10 especially at its aperture 20. It can thereby provide enhanced controllability of the preventer during attachment or removal thereof from a blade 5. The collar 44 illustrated in FIG. 4 or 5 may be made of a foam material such that it is both flexible and reasonably stiff. Alternatively, it may be inflatable. Any collar 44 according to the invention may preferably be ring shaped such as elliptical or generally round. An inflatable collar 44 may provide the added advantage that the preventer 10 is made more readily collapsible for transportation to a wind turbine site. In FIG. 5, there is shown a collar which is made of a solid material. The collar 44 may be funnel shaped or frustoconical, as illustrated in FIG. 5. A connection ring 23 or other element for connecting a line 16 to a preventer may advantageously be connectable or connected to a portion of the collar 44. The guide line 16 connections in FIGS. 1-3 may be connected analogously to a collar 44 positioned at an aperture 20 of the illustrated preventer 10 embodiments.

(19) Although not shown in FIG. 5, a second guide line 17 which may also be a tripping line may be attached thereto, preferably although not exclusively as illustrated in FIG. 3. The embodiment illustrated in FIG. 4 may have a first guide line 16 connected as shown in FIG. 5 and may also optionally comprise a second line 17 attached thereto preferably as shown for example in FIG. 1. In aspects of the invention which are not illustrated, a tripping line connected to the distal end 32 of the smooth interior surface material 35 may be additional to a second guide line 17. In one aspect, a connecting loop similar to a connecting loop 24 shown in FIG. 2 may be attached to an outer layer of a 38 sleeve 30 and may serve as an attachment for a second guide line 17 which may be attached at one end to the loop 25 or fastener or which may be passed through the fastener or loop 24 to return for example to an operator, thereby potentially providing two ends of the second guide line 17 on which to pull for the purpose of guiding a preventer 10 into position.

(20) In aspects of the invention, a collar 44 may take the form of a wire hoop. Such a wire hoop may for example be positioned at the very rim of an aperture 20 of the preventer 10 and may be compatible with embodiments illustrated in FIGS. 1-3.

(21) Advantageously, both a second, lining layer 37 and a first, outer layer 38 may extend in a longitudinal direction of the preventer 10 from the collar 44 towards a distal end 32 thereof. That is to say, the elements of the sleeve 30 comprised of an exterior non-aerodynamic surface material 34 and an interior smooth material 35 may extend from a more or less rigid or resilient collar 44. This arrangement can provide additional stability to the preventer, especially during attachment and removal thereof from a blade 5.

(22) In aspects of the invention, the material making up the outer surface 34 of the sleeve 30 may be any material that can be formed into the stocking shape mentioned above, but that will not be too coarse to damage the surface of the wind turbine blade 5 as the preventer 10 is attached. Fibre materials that are soft and flexible are therefore advantageous, such as but not limited to organic fibres like hemp, sisal, jute, and cotton; synthetic or artificial fibres such as polyamide, polypropylene, polyethylene or any suitable thermoplastic fibrous material; and monofilament materials, such as polyethylene or rubber. In the examples described here, the weave or mesh size of the netting is in the range 1010 mm to 100100 mm in mask. Depending on the application, it could also have a finer or a more open mesh.

(23) An example of a method according to aspects of the invention will now be described in more detail with reference to FIGS. 6a-c and FIGS. 8 and 9 of the drawings.

(24) The example oscillation preventer 10 comprises a sleeve 30 that is fitted over the tip of a wind turbine blade 5 when the blade is in a stationary position. Attachment of the sleeve 10 can be carried out in situ when the wind turbine blades 5 of an operational wind turbine 1 have been locked in position for maintenance or repair. Alternatively, the preventer 10 can be attached to a blade 5 in the factory, prior to installation of a rotor 4 on a wind turbine tower 2, and before the wind turbine 1 is connected to the grid to output electricity. In both cases, therefore, the wind turbine can be thought of as being in a non-operational mode. Once the preventer 10 is in place, the blade can be unlocked and can idle in a feathered position, if desired.

(25) The preventer 10 can be secured over the end of the wind turbine blade 5 during the manufacturing process or attached using ropes or pulleys to the root of the blade 5 when the blade is attached to the hub 6 on a nacelle 3 and tower 2. Alternatively, a key advantage with the preventer 10, described above, is that it can be secured over the end of the wind turbine blades of a rotor 4 by service engineers, when the turbine is put into a non-operational mode and the blades are locked down for repair or maintenance.

(26) The process of securing the oscillation preventer 10 over the blades of a wind turbine is shown in FIG. 8 to which reference should now be made. First, the blades 5 are rotated into a position where one of the blades points towards the groundcorresponding to a so/called Y-position of a rotor- and the wind turbine 1 is stopped. For safety, the wind turbine blades 5 may be locked in this position, at least temporarily, in order, for example, to allow service engineers to carry out work such as maintenance on the wind turbine 1, e.g. at the nacelle 3 with the turbine power systems shut down.

(27) A service engineer in the hub 6 of the rotor 4 may let down a distal end of a pull guide rope 16 from a position in the nacelle 3 or the hub 6 of the wind turbine 1. Optionally the other, proximal, end may be secured to the wind turbine body. A service engineer at the ground may secure the guide rope 16 to the preventer aperture 20 for example at a loop 23 secured thereto or at a loop 23 secured to a collar 44. A second guide line 17 may also be attached to a distal end 32 of the preventer 10, for example, by means of an attachment such as a loop 24. The service engineer in the hub 6 or nacelle 3 may then apply a force to the guide rope 16 by pulling on it, while the service engineer on the ground may hold a distal end of line 17. The service engineer in the hub 6 or the nacelle 3 can then pull further on the pull guide rope 16 to pull the open end of the sleeve 10 towards the tip of the wind turbine blade 5, ensuring that the smooth interior surface 34, be it a full lining such as a sock 39 or a partial lining in the form of a tongue 26, or even in the form of an insert 28, is oriented in such a way that the serrations 7 will be covered by that smooth interior surface 35 of the preventer 10. One advantage of the preventer 10 comprising a smooth interior surface in the form of a sock type full lining is that there is no additional requirement to align the smooth interior surface with the blade serrations 7. As shown in FIG. 8, the resilient collar 44 keeps the proximal end of the preventer 10 open allowing it, with some care and attention, to be threaded over the tip of the blade 5 and over the serrations 7. The ground engineer, having a better view point of the blade tip, which for obvious reasons is preferably directed towards the ground for this procedure, is crucial in using the second guide line 17 to guide the proximal and distal ends 32 of the preventer 10 into place. Once the preventer 10 has been threaded over the blade 5, a service engineer in the nacelle 3 or hub 6 can pull further on the pull guide rope 16 sliding the collar 44 upwards and along the length of the blade 5 until it can slide no further.

(28) Once the preventer 10 is in place, a service engineer in the nacelle 3 or hub 6 may secure the proximal end of the pull guide rope 16 to a suitable location on the wind turbine structure (a dedicated tie-off point can be provided for this purpose if required, though one is not strictly necessary). The hub 6 or blade root may be preferred for the tie-off point however, as it allows the tie-off points to rotate with the wind turbine blades. The service engineer at the ground may then release the ground line 17 from the distal end of the preventer for example by actuating a release means from a loop 24. Alternatively, the line 17 may remain in place to be made off at a location on the turbine where it is secured and from where it may be retrieved for a preventer removal operation. The preventer 10 is then in place. To attach the sleeve 10 to the other blades 5 of the wind turbine, the blades are manoeuvred to face towards the ground, and the process described above is repeated. Once a preventer is attached to each blade, the wind turbine blades 5 can be locked in place.

(29) The preventer can be detached from the wind turbine 1 for example simply by releasing the attached guide line 17 which may be connected as a tripping line, from an attachment position and pulling on it to straighten the sleeve 34 and in particular the smooth interior surface 35 such that it frees itself from the serrations 7. The second guide line 17 may thus also function as a tripping line. In alternatives, there may be provided both a guide line 17 for positioning or controlling the distal end 32 of the preventer and an additional tripping line connected to a distal part of the smooth interior surface 35.

(30) The preventer 10, once in place on wind turbine blade 5, then prevents vortex shedding induced oscillation of the wind turbine blade, by deliberately causing turbulent air flow at the blade surface and preventing the air flow from adhering to the blade. In may readily be appreciated that a preventer 10 as described will cause turbulence and prevent or significantly reduce the magnitude of any vortex shedding that occurs.

(31) For this reason, the material for the non-aerodynamic exterior surface is preferably a net-like material, as this has been found to be effective in causing turbulence at the blade surface and in reducing vortex shedding, by efficiently covering the leading edge of the blade. The open mesh or weave of the net ensures an irregular surface air boundary between the air and the blade, and is advantageously used as the sleeve 10 as it is easy to produce, and therefore not costly. Moreover, a net-like material can be collapsed or folded and stowed compactly when not in use. In addition, the use of a net-like material for an outer layer, which may be a first outer layer 38 of the sleeve 30, may allow easier attachment of a tripping line from outside the preventer to an inside lining layer 37 in the sleeve. In particular, a tripping line or second guide line 17 may pass through an aperture in the net-like material of a first outer layer 38. The mesh or weave of the net can for example leave open spaces in the netting having dimensions of around 25 mm to 100 mm, in at least one dimension or square, with a preferable dimension of 50 mm. If the net is too open of course the disruption to the laminar flow of air around the blade will not be reduced significantly for the net to have the desired effect. Additionally, it has been found desirable if the diameter of the cord from which the net is fashioned be in the range 1 mm to 5 mm, with a typical value in use being 2 mm to 3 mm. The net cording can have greater diameter, but then the weight of the net needs to be carefully assessed.

(32) It is not strictly necessary to use a net-like material however as the outer sleeve material for the oscillation preventer 10, and it will be appreciated from the description that any material could be used that has a coarse external surface, either due to the weave of the material or due to the presence of protrusions, indentations specifically engineered into its surface. The temporary surface section could for example be engineered to resemble plastic or foam packaging sheets or filler material. A height 5 to 10 mm for example in the depth of the protrusions or indentations of any surface shape has been found more than sufficient to cause a severe disruption to the laminar flow. Any material may be used for the non-aerodynamic exterior surface which is effective to induce turbulence in air flowing over it. Suitable non-aerodynamic exterior surfaces may have a bumpy, lumpy or highly textured surface or a surface which exhibits multiple protrusions or raised portions whether regular or irregular. In particular, surface irregularities may extend across substantially all the surface or a significant portion thereof and the effect of the textured surface is the interruption of smooth or laminar airflow across all or a substantial part of it.