Anti-oscillation tool for wind turbine blades
A tool ( 14 ) for reducing vibrations in wind turbine blades at scheduled standstill for example during turbine installation or service, the tool comprising an elongate flexible sock-like sleeve ( 16 ) for fitting over the blades ( 10 ) having an airflow-disrupting function and a guard ( 24 ) of semi-rigid material provided at an edge of the sleeve which overlies the blade trailing edge into which are received aerodynamic enhancing features such as serrations ( 20 ).
1 . A device for fitting to a wind turbine blade during turbine standstill to reduce risk of blade oscillation comprising:
an elongate flow-disrupting flexible sleeve for fitting over a blade tip and extending part-way along a length of the blade, the sleeve having a tip end which in use overlies the blade tip, and an open end, and a first edge region which in use overlies a blade trailing edge, and
an elongate guard provided on the sleeve at the first edge region of the sleeve configured to overlie or receive the blade trailing edge,
wherein the elongate guard is of generally U-shaped section having a pair of sides with an opening therebetween into which a part of the blade trailing edge is to be received, wherein the pair of sides have lower edges which receive the blade trailing edge, and wherein the lower edges are formed with inwardly protruding regions.
2 . The device according to claim 1 wherein the guard is formed of a semi-rigid material.
3 . The device according to claim 1 wherein the material of the sleeve is secured to an interior surface of the guard, whereby a space is created within the first edge region of the sleeve.
4 . The device according to claim 1 wherein a material of the sleeve at the trailing edge defines an opening to an interior of the guard, with opposed edges of the sleeve at the opening joined to opposite sides of the guard.
5 . The device according to claim 4 wherein the opposed edges of the sleeve at the opening therein at the trailing edge are joined to the guard at outer faces of the sides of the guard.
6 . The device according to claim 1 wherein the guard is located inside the sleeve at the trailing edge region thereof.
7 . The device according to claim 1 wherein the lower edges of the guard which receives the blade trailing edge are formed with a widened opening which tapers inwardly towards an interior of the guard.
8 . The device according to claim 7 wherein tapered regions are formed in the inwardly protruding regions.
9 . The device according to claim 1 wherein the material of the sleeve and guard are joined by one or more of adhesive, staples, tape, welding, or stitching.
10 . The device according to claim 1 wherein the guard is formed of a plastics foam material.
11 . The device according to claim 1 wherein the guard is formed of a plurality sections.
12 . The device according to claim 1 wherein the guard is provided with an insert of a material that is relatively stiffer than the guard.
13 . The device according to claim 12 wherein the insert has a generally U-shaped form conforming to an interior of the guard which is located within the guard.
14 . The device according to claim 3 wherein an insert is provided of generally U-shaped form conforming to the interior of the guard and located therein, wherein the trailing edge of the sleeve is held between the guard and the insert.
15 . The device according to claim 1 wherein the flexible sleeve is formed of a material which provides a high surface roughness when fitted on a blade.
16 . The device according to claim 15 wherein the flexible sleeve is formed of a net-like material.
17 . The device according to claim 1 wherein the flexible sleeve is formed of a bag of fabric material or thin flexible sheet with a plurality of flow-disrupting members protruding from and secured to the bag, distributed spaced over the bag.
18 . The device according to claim 17 wherein the flow-disrupting members are of elongate form and are arranged randomly over one or both surfaces of the bag.
19 . The device according to claim 17 wherein a majority of the flow-disrupting members are arranged so that the lengths of the members are arranged at less than 45 degrees to the length of the bag.
20 . The device according to claim 17 wherein the flow-disrupting members extend from the bag surface by between 2 and 10 cm.
21 . The device according to claim 17 wherein the flow-disrupting members are hollow members or comprise foam blocks.
22 . The device according to claim 17 wherein the flow-disrupting members are contained in pockets joined to sleeve.
23 . The according to claim 1 wherein the sleeve is provided with an elongate cap which in use fits over a leading edge of the blade.
24 . The device according to claim 23 wherein the cap is formed of a U-shaped profile.
25 . The device according to claim 23 wherein the cap is formed of a semi-rigid material.
26 . The device according to claim 23 wherein the guard and/or cap are provided with additional flow disrupting features upstanding from the cap and/or guard.
27 . The device according to claim 1 wherein one or more tensioning lines are attached to the sleeve adjacent the open end of the sleeve to secure the sleeve on a blade.
28 . The device according to claim 1 wherein one or more guide lines are attached to the sleeve to guide its lowering from a blade.
29 . A wind turbine blade having a device according to claim 1 fitted thereon.
30 . A wind turbine having one or more wind turbine blades, at least one blade having fitted thereon the device according to claim 1 .
31 . A method of operating a wind turbine to inhibit oscillations induced by the air flow across the blades when the wind turbine is a non-operational state using the device of claim 1 , the method comprising: releasably locking the wind turbine rotor; for each rotor blade pulling a device over the blade so that the guard of the device overlies the blade trailing edge, securing the device and retaining it in position whilst the turbine is in a non-operational state, so that the device covers a region of the blade surface and provides a non-aerodynamic outer surface for inducing turbulence in the air flow across the blade.
32 . The method according to claim 31 wherein the device has a guard of generally U-shaped section with opposed sides, the method further comprising arranging the device so that blade serrations at the blade trailing edge are received between opposite sides of the guard.