Vortex-shedding-arrangement The invention relates to a Vortex-shedding-arrangement , which is prepared to be arranged on a tower of a wind turbine. The invention even relates to a tower, which is equipped with the Vortex-shedding-arrangement and to a method to equip the tow ^¬ er with the Vortex-shedding-arrangement.

A wind turbine comprises rotor blades, which are driven by the wind. The rotor-blades are connected via a turning hub with a nacelle. The turning rotor-blades drive an electrical generator via a so called main shaft. Generator and shaft are arranged in the housing of the nacelle. The nacelle is ar ^¬ ranged on top of a tower of the wind turbine.

For the installation of the wind turbine at the respective wind turbine site several production steps might be done as described below as an example:

The nacelle of the wind turbine is equipped at a production site with all components necessary, i.e. with a housing, a main-shaft, a generator, a cooling-system, with power elec- tronics and with control equipment and with other devices, etc .

The ready-made nacelle is transported to the wind turbine site, together with the rotor blades and with the hub. Even the tower is transported to the wind turbine site. The tower may be segmented, due to its overall length and due to transport limitations.

At the wind turbine site the bottom end of the tower is con- nected with a tower-foundation. If the tower is segmented the respective segments of the tower are piled vertically on the bottom end until the whole tower is erected and completed. The nacelle is lifted on top of the tower and is connected there. Hub and rotor blades are lifted and connected to the nacelle .

The tower or its segments are often manufactured at a produc- tion site, which is different to the wind turbine site. The tower or its segments might be transported standing in an up ^¬ right position (thus the tower or its segment is oriented vertically in view to the respective length-axis) from the production site to the wind turbine site. This is done, for example, if the wind turbine is installed offshore: all parts of the wind turbine (i.e. tower (or its segments), nacelle, hub, blades, other equipment, etc.) are transported by spe ^¬ cial ships to the offshore installation site, while the tower is stored on the ship in an upright position as given above.

During the transportation wind is acting on the tower. The respective wind forces are even acting via the tower, which can be seen as a lever, into the tower-connection and transportation means being part of the ship. The wind induces vi- brations into the tower, which are commonly called and known as "vortex induced vibrations, VIV" . The vortex induced vi ^¬ brations might be strong enough to damage the tower and its structural strength. The vortex induced vibrations may even create damages at the transport equipment of the tower, being an integrated part of the ship. The vortex induced vibrations may even create trouble during the installation of the tower as the tower might start to swing and vibrate creating severe danger for the mounting personal. The vortex induced vibrations result from alternating vortex shedding originated by critical wind conditions in view to the circumference of the tower. Vortex shedding is resulting from alternating pressure differences along the surface of the tower and in relation to its cross section.

Several measures are known to dampen vortex induced vibra ^¬ tions . Document EP 3 029 313 Al describes a Vortex-shedding- arrangement, which is called "strake", for a wind turbine tower. The strake is mounted to a wind turbine tower and can be detached after the installation of the wind turbine and its tower. The strake is shaped in a way that vortex induced vibrations during transportation and installation of the wind turbine is reduced. A mounting bracket, which is attached to the wind turbine tower, a leg and operation means are used to attach the strake to the tower. One end of the strake is at- tached via the leg to the operation means. The means and the leg are rotatable in respect to the mounting bracket in a way that the strake, which is connected to the leg, is wrapped around the tower if the leg is rotated in respect to the mounting bracket. The strake is installed at the tower of the wind turbine before the tower is shipped to the installation site. After the installation is completed the strake is de ^¬ tached from the wind turbine tower.

This idea shows a number of disadvantages: The strake is mounted by using a rope, which is located and arranged into the strake. As the strake is only placed on a top third of the tower the rope is still present all the way down from the top of the tower down to its base. The rope is tied there at an anchor point. The rope must be secured and controlled dur- ing the transportation, while the whole mount- and dismount- proceeding of the strake is complicated and time-consuming as well. During erection of the wind turbine tower at site, the strakes also have a tendency to fall off which is not desir ^¬ able and may cause the tower to start vibrate. These vibra- tions complicate to a great extend mounting of the nacelle on top the tower.

It is the aim of the invention to provide an improved Vortex- shedding-arrangement , which can be mounted and dismounted quite easily and which does not need extensive control during the transportation. This aim is solved by the features of claim 1, 6 and 12. Pre ^¬ ferred configurations are addressed by the respective depend ^¬ ent claims. Throughout the description of the invention the phrase "tow ^¬ er" refers to a tower segment as well as to a completed tow ^¬ er, which might in turn comprise a number of tower segments connected to one another. Due to the length of tower segments in modern wind turbines the segments might be influenced by VIV accordingly.

The invention relates to a Vortex-shedding-arrangement , which is prepared to be arranged on a tower of a wind turbine. The invention even relates to a tower, which is equipped with the Vortex-shedding-arrangement and to a method to equip the tow ^¬ er with the Vortex-shedding-arrangement.

The Vortex-shedding-arrangement according to the invention is arranged and prepared to be connected to a surface of a tow- er. The Vortex-shedding-arrangement is prepared to reduce

Vortex-induced-vibrations (VIV) , acting on the tower and its structure, during the tower-transportation or tower installation. The vortex shedding arrangement comprises vortex shed ^¬ ding elements and at least one shrink foil. The shrink foil is prepared to fix and to position the vortex shedding ele ^¬ ments at specific positions at the tower surface by heat ap ^¬ plied to the shrink foil.

The invention is especially directed towards wind turbine towers with a lower stiffness than usual, which are exposed to increased vibrations induced into the tower and its struc ^¬ ture due to wind vortexes.

The invention could be applied to offshore and onshore towers as well. The invention does not need a tower flange or a fixed point on the tower, to keep the tower during transportation in its respective place. The invention preferably uses the strength of the shrink foils (being used as wrapping material) and the circular shape around the tower to stay in place.

The invention preferably uses the conical shape of the tower to stay in place.

The claimed vortex shedding arrangement can be dismounted without a crane. Only a lowering mechanism is needed. The invention provides a temporarily mounted vortex shedding solution, which can be mounted on any tower quite easily with low efforts and costs.

The invention can be applied to any mast of a wind turbine regardless of the swinging mass and frequency.

The invention is shown in more detail by help of figures. The figures show preferred configurations and do not limit the scope of the invention.

FIG 1 shows a wind turbine tower with an attached vortex

shedding arrangement,

FIG 2 shows a detailed view to the vortex shedding arrange ^¬ ment in reference to FIG 1, and

FIG 3 shows further details of the vortex shedding arrange ^¬ ment according to the invention.

FIG 1 shows a wind turbine tower 1 with an attached vortex shedding arrangement 2.

The vortex shedding arrangement 2 is shaped in a way that Vortex induced vibrations (VIV) during the installation and transportation of the wind turbine tower are reduced. The wind turbine tower 1 comprises a top end 3 and a bottom end 4. The vortex shedding arrangement 2 is attached to the tower 1 from the top end 3 of the tower 1 towards the bottom end 4 of the tower 4.

Preferably the upper first third part of the length of the tower 1 is fitted with the vortex shedding arrangement 2. A wind turbine tower 1, which is used for an offshore wind turbine installation site, is transported in an upright posi ^¬ tion from the harbor towards the installation site of the wind turbine by ship.

As described above strong wind is acting on the wind turbine tower 1, which starts to vibrate. The wind flows along the sides of the wind turbine tower 1 in a non-laminate struc ^¬ ture. Thus vortexes are generated in the wind shadow of the wind turbine tower 1. This vortex wind structures lead to vortex induced vibra ^¬ tions, influencing the tower 1 and its structure. The vortex induced vibrations are reduced by vortex shedding arrangement 2, which is arranged and attached along the surface of the tower 1.

The vortex shedding arrangement 2 are only needed during transportation and installation of the wind turbine tower. They are disassembled from the tower 1 before the power- generating operation of the wind turbine is started.

FIG 2 shows a detailed view to the vortex shedding arrange ^¬ ment 2 in reference to the tower 1, referring to FIG 1.

The vortex shedding arrangement 2 is attached to a wind tur- bine tower 1. The vortex shedding arrangement 2 consists of three vortex shedding elements VSE, which are wrapped around the wind turbine tower 1 in an equally distributed manner. In a preferred configuration each of the vortex shedding elements VSE of the vortex shedding arrangement 2 show a trian ^¬ gular shaped cross-section. The angle of inclination of the longitudinal axis of the vor ^¬ tex shedding element VSE in respect to the longitudinal axis of the wind turbine tower is in a range between 10° and 80°.

FIG 3 shows further details of the vortex shedding arrange- ment according to the invention.

A tower section TS of the tower 1 is equipped with the vortex shedding arrangement 2. The tower 1 is shaped like a conical cylinder in this example.

In a first preferred configuration the vortex shedding arrangement 2 comprises two shrink foils SF1, SF2 as well as three elongated vortex shedding elements VSE. The vortex shedding elements VSE are preferably made of "Pol ^¬ yethylene, PE".

In another preferred configuration the vortex shedding elements VSE are made of foam, preferably made of light-weight foam.

The vortex shedding elements VSE are arranged between the two shrink foils SF1, SF2. The shrink foils SF1, SF2 are used as wrapping material or as an envelope of the vortex shedding elements VSE. The shrink foils SF1, SF2 are welded together thus the vortex shedding elements VSE are fixed in their re ^¬ spective positions.

The vortex shedding arrangement 2, comprising the shrink foils SF1, SF2 and the vortex shedding elements VSE, is put in place at the tower 1. The vortex shedding arrangement 2 is fixed by a first belt Bl close to the upper part of the tower 1, while the vortex shedding arrangement 2 is fixed by a second belt B2 close to the lower part of the tower 1.

Next heat is applied to the shrink foils SFl, SF2. Thus the whole vortex shedding arrangement 2 is put into shape in view to the surface of the tower 1 by the applied heat. The vortex shedding arrangement 2 is additionally secured tightly around the tower by the shrinking foils and the ap ^¬ plied heat.

For dismounting of the vortex shedding arrangement 2 from the tower both belts Bl, B2 may be removed by using respective releases Rl and R2, arranged in the belts Bl and B2.

Finally a cutting device (like a knife, a cutting string, etc.) is used to cut in vertical direction along the tower surface in a way that the vortex shedding arrangement 2 is split - its circular cross section is opened by the vertical cut and the vortex shedding arrangement 2 can be removed from the tower 1 easily by only one vertical cut. In another preferred configuration the vortex shedding elements are mounted on the shrink foil SFl by using an adhesive tape or by using welding.