Device for reducing oscillations in a wind turbine blade during standstill and method of using same
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 flow-disrupting flexible sleeve ( 15 ) for fitting over a blade tip and extending part-way along its length having a tip end which in use overlies a blade tip with a first edge which in use overlies a blade leading edge; and at the opposite edge a longitudinal slit, with tensioning bands ( 26 ) provided on the sleeve at opposite edges adjacent the slit for tensioning the sleeve in the longitudinal direction.
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 wind turbine blade, the sleeve defining a longitudinal direction and a lateral direction, the sleeve comprising:
a tip end which in use overlies the blade tip,
an open end spaced from the tip end in the longitudinal direction,
a first region extending in the longitudinal direction and which in use overlies a blade leading edge,
a slit opposite the first region and extending in the longitudinal direction, the slit defining a first slit edge and a second slit edge spaced from the first slit edge in the lateral direction to define an opening through the sleeve from an outer surface of the sleeve to an inner surface of the sleeve, wherein in use the first slit edge is on one lateral side of a blade trailing edge, the second slit edge on the other lateral side of the blade trailing edge, and the blade trailing edge projects through the opening defined by the slit in the sleeve, and
tensioning bands on the sleeve adjacent the first and second slit edges of the slit for tensioning the sleeve in the longitudinal direction.
2 . The device according to claim 1 wherein the tensioning bands comprise bands of material secured to a material of the sleeve.
3 . The device according to claim 1 wherein the tensioning bands comprise an elastic material.
4 . The device according to claim 3 wherein the tensioning bands comprise an elastomer.
5 . The device according to claim 1 wherein the tensioning bands comprise a high strength woven material.
6 . The device according to claim 1 wherein one or more additional tensioning bands are provided extending laterally across the sleeve.
7 . The device according to claim 6 wherein the additional tensioning bands comprise an elastomer.
8 . The device according to claim 1 wherein tensioning lines are attached to ends of the tensioning bands at the sleeve open end, by which longitudinal tension is configured to be applied to the sleeve.
9 . The device according to claim 8 further comprising a rigid strip or hoop which in use extends around the blade at a position between the sleeve and a blade root to which the tensioning lines are secured.
10 . The device according to claim 9 further comprising one or more lines in use extending from the strip or hoop to a point on the blade root or a rotor hub.
11 . The device according to claim 1 wherein the flexible sleeve is formed of a material which provides a high surface roughness when fitted on the blade.
12 . The device according to claim 11 wherein the flexible sleeve is formed of a net-like material.
13 . The device according to claim 1 wherein the flexible sleeve is formed of a fabric material with a plurality of flow-disrupting members protruding from and secured to the fabric material and distributed spaced over the sleeve.
14 . The wind turbine blade having a device according to claim 1 fitted thereon.
15 . A method of fitting a device according to claim 1 on a wind turbine blade comprising the steps of: positioning the sleeve of the device over the blade with the tip end fitting over the blade tip and the sleeve extending over and along the blade with the slit arranged at the blade trailing edge, and applying tension to the tensioning bands so that the sleeve is tightly held against a blade surface at a region of the trailing edge.
16 . The method according to claim 15 wherein the sleeve of the device is provided with lateral tensioning bands, the method further comprising the step of, as the sleeve is longitudinally tensioned, allowing the lateral bands to become tensioned, thereby holding the sleeve tightly against the blade surface.