Patent Description:
The vertical axis wind turbine (VAWT) exists in many variants, the "Darrieus" type is characterized by its curved blades attached to the central rotating axis, whereas the "H-type" utilizes separate struts and blades. The struts hold the blades at a distance from the central axis. Each VAWT-type has its advantages and disadvantages, one disadvantage with the "H-type" is the connection required between blade and strut. This connection is often at a relatively straight angle, to keep down aerodynamic drag the available volume or area to transfer loads between blades and struts is relatively limited. At the same time the connection is in the outermost part of the rotating turbine, subject to high centrifugal forces.

Further requirements on the blade-to-strut connection is that it should be easy to install and de-install when assembling the complete turbine, and that the connection should not be expensive, in order for the VAWT to compete successfully with the horizontal axis wind turbine (HAWT), which do not require any struts.

Current solutions to this design problem typically utilize some variant of metallic fastener (bolts and nuts) to solve this mechanical problem. Since the blade-to-strut connection is subject to high fatigue loading (loads are varying as the VAWT rotates), the resulting bolted design often requires a significant number of bolts - a both heavy and expensive solution.

It would thus be desirable to provide an improved VAWT, in particular a VAWT with a blade-to-strut connection with improved properties.

<CIT> discloses a VAWT in which a blade connecting fastener connects a blade with one end of a radial arm. The blade connecting fastener has a clamp portion and a hinge portion. The clamp portion slides over the blade.

In view of the above-mentioned and other drawbacks of the prior art, it is an object of the present invention to provide an improved VAWT, having an improved blade-to-strut connection.

According to a first aspect of the present invention, it is therefore provided a vertical axis wind turbine as defined by claim <NUM>.

That the pliable fastening member is "pulling" the blade towards the second end of the strut should be understood to mean that the pliable fastening member is arranged in such a way that tensile forces in the pliable fastening member give rise to contact forces at the interface between the blade and the strut.

The present invention is based on the realization that a blade-to-strut connection using a pliable fastening member can be made lighter and less prone to fatigue failure than a conventional bolted connection. Furthermore, disassembly of the blade-to-strut connection can be facilitated, which may simplify the procedure of assembling the complete wind turbine. This may be of particular importance for vertical axis wind turbines for offshore deployment, which may be very large, such as more than <NUM> meters in diameter.

In addition, the use of a pliable fastening member may enable the design of a fastening arrangement in which the load on the blade can be distributed across a relatively large area, as compared to a bolted connection. This may be particularly advantageous for vertical axis wind turbines in which the blades are made of composite materials, since such blades may exhibit a desired combination of low weight and high strength, but be relatively sensitive to point loads.

In various embodiments, the pliable fastening member may be at least partly made of textile material. In a textile material, fibers, wires, strands or bands are combined by textile-forming techniques such as weaving, braiding, or knitting etc. Thereby, the pliable fastening member can be provided with desired properties through a suitable combination of fiber material and/or configuration, and textile forming technique(s). It is known from, for example, the use of textiles in mooring systems or in sailing etc, that a mechanical connection using a textile-based fastening member can be made more lightweight and less prone to failure by fatigue than conventional metallic connections.

Although it may in many cases by advantageous to use a textile-based pliable fastening member, it should be noted that the pliable fastening member may, in embodiments, alternatively be made using other material configurations that are not fiber-based. For instance, the pliable fastening member may be formed by one or more bands, such as metal bands, that may not be combined by any textile-forming technique.

According to a second aspect of the present invention, it is provided a method as defined by claim <NUM>.

The steps of the methods according to various embodiments of the present invention need not necessarily be performed in any particular order, except where this is technically required.

<FIG> schematically shows an offshore wind farm <NUM> including a plurality of wind turbines <NUM>, here in the form of vertical axle wind turbines (VAWTs) according to an example embodiment of the present invention, floating in the sea <NUM>. These floating VAWTs <NUM> are shown to each have three blades <NUM>, where each blade <NUM> is coupled to the wind turbine body <NUM> using two struts 11a-b. It should be noted that the scope of the claims is not limited to this particular type of VAWTs, but additionally encompasses, for example, land-based VAWTs, VAWTs with a smaller or larger number of blades and/or a smaller or larger number of struts per blade.

In <FIG>, one of the VAWTs <NUM> in <FIG> is shown in a schematic side view, revealing an example configuration of the full VAWT <NUM>, including the portion that is submerged in <FIG>. As can be seen in <FIG>, each of the struts 11a-b has a first end 13a coupled to the wind turbine body <NUM> and a second end 13b coupled to the blade <NUM> using a fastening arrangement (in <FIG>, the first and second ends are only indicated by reference numerals for one of the struts 11b to avoid cluttering the drawings).

The fastening arrangement, which is not visible in <FIG>, will be described with reference to <FIG>, which are enlarged views of a portion of the VAWT <NUM> in <FIG>, as indicated in <FIG>.

<FIG> is a partial side view, in which the strut 11b is partly opened to reveal an example configuration of the above-mentioned fastening arrangement <NUM> that is used to couple the second end 13b of the strut 11b to the blade <NUM>. As can be seen in <FIG>, the fastening arrangement comprises a pliable fastening member <NUM> pulling the blade <NUM> towards the second end 13b of the strut 11b. In the example configuration of the fastening arrangement <NUM> in <FIG>, the pliable fastening member <NUM> is illustrated in the form of a textile sling passing around the entire circumference of the blade <NUM>. In embodiments where the pliable fastening member <NUM> is made of a textile material, it will be straight-forward for the skilled person to find a suitable material that is commercially available. Known from the maritime field are, for example, various kinds of polyester, such as UHMwPE, and Kevlar, etc..

In <FIG>, it is indicated by arrow <NUM> that a pulling force is acting on the pliable fastening member <NUM>, so that the pliable fastening member <NUM> in turn pulls the blade <NUM> towards the second end 13b of the strut 11b. The contact forces at the contact interface between the blade <NUM> and the second end 13b of the strut 11b will give rise to friction forces.

In embodiments, the fastening arrangement <NUM>, including the configuration of the contact interface, may be configured to provide sufficient friction to prevent relative movement between the blade <NUM> and the second end 13b of the strut 11b, even when various forces may act together to reduce the contact forces at the contact interface. Such forces may include the centrifugal force, wind force, and a component of the gravitational force acting on the blade <NUM>, especially when wind and/or waves cause the VAWT <NUM> to deviate from a vertical orientation of the wind turbine body <NUM>.

Through the use of a pliable fastening member <NUM>, the substantial force required to prevent relative movement between the blade <NUM> and the strut 11b can be made to act on a relatively large area, reducing the stress on the blade <NUM> and/or strut 11b as compared to conventional bolted connections. Furthermore, a pliable fastening member <NUM> can be made considerably more resilient to fatigue than rigid connections.

The pulling force represented by the arrow <NUM> in <FIG> is provided by a tensioning arrangement. An example configuration of such a tensioning arrangement will be described below with reference to <FIG>.

As is indicated in <FIG>, a tensioning arrangement <NUM> is provided for tensioning the pliable fastening member <NUM>. The tensioning arrangement <NUM> is shown in <FIG> as being attached to the strut 11b at a position <NUM> spaced apart from the second end 13b of the strut 11b, to allow the tensioning arrangement <NUM> to provide the above-mentioned pulling force to the pliable fastening member <NUM>.

In the example configuration of <FIG>, the tensioning arrangement <NUM> for tensioning the pliable fastening member <NUM> comprises a tensioning actuator <NUM> in the form of a screw. Various suitable screws are, per se, known, including roller screws, ball screws, lead screws etc. It should, however, be noted that other kinds of tensioning actuators may be beneficial depending on the requirements of the particular installation. Examples of such other kinds of tensioning actuators include a hydraulic cylinder, a spring, a bolt, etc. It should also be noted that the tensioning arrangement <NUM> could alternatively be arranged in or on the blade <NUM>.

<FIG> is a flow-chart schematically illustrating an example embodiment of the method according to the present invention of joining a blade and a strut of a VAWT. <FIG> are schematic illustrations of different steps in the flow-chart in <FIG>.

Referring to <FIG> and <FIG>, the blade <NUM> and the strut 11b are arranged, in step <NUM>, in such a way that a joining surface <NUM> of the blade <NUM> faces an end 13b of the strut 11b. As is schematically indicated in <FIG>, the VAWT <NUM> may be provided with a positioning structure configured to define a relative positional arrangement of the blade <NUM> and the end 13b of the strut 11b. In the example configuration in <FIG>, the positioning structure is indicated as an area <NUM> with a number of recesses <NUM> (only one indicated by a reference numeral in <FIG>) comprised in the blade <NUM>, and an area <NUM> with complementary protrusions <NUM> at the end 13b of the strut 11b. The provision of the positioning structure may facilitate relative positioning of the blade <NUM> and the strut 11b, and may also assist in maintaining the desired relative positioning while applying tension to the pliable fastening member <NUM>, as will be described below with reference to <FIG>.

As will be immediately obvious to the skilled person, many different configurations of the positioning structure will be possible, and may be beneficial depending on various circumstances, such as the material of the blade <NUM> and/or strut 11b and the method used for manufacturing the blade <NUM> and/or strut 11b. One example of an alternative configuration could be a guiding pin attached to one of the blade <NUM> and the strut 11b and a corresponding hole arranged to accommodate the guiding pin formed in the other one of the blade <NUM> and the strut 11b.

In <FIG>, the pliable fastening member <NUM> is indicated as surrounding the blade <NUM>. Depending on the assembly facilities, and the size of the VAWT <NUM>, etc, the pliable fastening member <NUM> may be installed before or after the positioning of the blade <NUM> and the strut 11b in relation to each other. According to one approach, the blade <NUM> and the strut 11b may first be arranged adjacent to each other, as shown in <FIG>, and then the pliable fastening member <NUM> may be pulled around the blade <NUM> before coupling both ends of the pliable fastening member <NUM> to the tensioning arrangement <NUM>. According to another approach, the pliable fastening member <NUM> may first be coupled to the tensioning arrangement <NUM>, and then the blade <NUM> may be inserted in the loop formed by the pliable fastening member <NUM>, or the loop may be moved along the length of the blade <NUM> to the correct relative position of blade <NUM> and strut 11b.

After having arranged the blade <NUM> and the strut 11b in relation to each other and having passed the pliable fastening member <NUM> around at least a portion of the blade <NUM>, regardless of how this is done, the blade <NUM> is then pulled, in step <NUM> towards the end 13b of the strut 11b until the joining surface <NUM> of the blade <NUM> is pressed against the end 13b of the strut 11b, by operating the tensioning arrangement <NUM>. The tensioning arrangement <NUM> may be operated until the pliable fastening member <NUM> has been subjected to a predefined tensile force. This predefined tensile force may, for example, be determined using simulation, and may be selected to ensure none or limited relative movement between the blade <NUM> and the strut 11b, at the contact interface, when the VAWT <NUM> is in operation.

So far, embodiments of the VAWT <NUM> according to the present invention have been shown and described where the pliable fastening member <NUM> passes around the periphery of the blade <NUM>. There are, however, many other ways to arrange the pliable fastening member <NUM> so that it can pull the blade <NUM> towards the end 13b of the strut 11b. Some of these other ways will be described below with reference to <FIG>.

Turning first to <FIG>, the blade <NUM> is shown to comprise internal passages 35a-b accommodating the pliable fastening member <NUM>. In the example configuration of <FIG>, the internal passages 35a-b pass through the blade <NUM> from the proximal side <NUM> of the blade <NUM> facing the wind turbine body <NUM> (see <FIG>) to the distal side <NUM> of the blade <NUM> facing away from the wind turbine body <NUM>.

According to another example configuration, which is schematically shown in <FIG>, the blade <NUM> comprises an internal passage <NUM> with both openings towards the proximal side <NUM> of the blade <NUM>.

According to yet another example configuration, an end portion of the strut 11b may be provided with side-facing openings 41a-b for the pliable fastening member <NUM>.

Claim 1:
A vertical axis wind turbine (<NUM>), comprising:
a wind turbine body (<NUM>);
a blade (<NUM>); and
a strut (11a-b) having a first end (13a) coupled to the wind turbine body and a second end (13b) coupled to the blade using a fastening arrangement (<NUM>),
wherein the fastening arrangement comprises a pliable fastening member (<NUM>) pulling the blade (<NUM>) towards the second end (13b) of the strut (11a-b) with a force pressing the blade (<NUM>) against the second end (13b) of the strut (11a-b),
wherein the pliable fastening member (<NUM>) passes around at least a portion of the blade (<NUM>),
wherein the fastening arrangement (<NUM>) comprises a tensioning arrangement (<NUM>) tensioning the pliable fastening member (<NUM>), and
wherein the tensioning arrangement (<NUM>) is attached to the strut (11a-b) at a position along the strut spaced apart from the second end (13b) of the strut (11a-b).