Patent Description:
Modern wind turbines are commonly used to supply electricity into the electrical grid. Wind turbines of this kind generally comprise a tower and a rotor arranged on the tower. The rotor, which typically comprises a hub and a plurality of blades, is set into rotation under the influence of the wind on the blades. Said rotation generates a torque that is normally transmitted through a rotor shaft to a generator, either directly ("directly driven" or "gearless") or through the use of a gearbox. This way, the generator produces electricity which can be supplied to the electrical grid.

The wind turbine hub may be rotatably coupled to a front of the nacelle. The wind turbine hub may be connected to a rotor shaft, and the rotor shaft may then be rotatably mounted in the nacelle using one or more rotor shaft bearings arranged in a frame inside the nacelle. The nacelle is a housing arranged on top of a wind turbine tower that may contain and protect the gearbox (if present) and the generator (if not placed outside the nacelle) and, depending on the wind turbine, further components such as a power converter, and auxiliary systems.

Wind turbine blades are usually made of composite materials. For example, reinforcing fibers such as glass fibers or carbon fibers may be covered or embedded in resin in a mold and then cured for forming two longitudinal blade half shells, e.g. an upwind half shell for the pressure side and a downwind half shell for the suction side. The two half shells may then be joined to form the blade shell. In other examples, a blade shell may be formed in a single step, e.g. a single mold may be used to manufacture the blade shell, without the need to join two blade half shells.

Wind turbine blades made of composite materials may not have sufficient structural integrity to provide a safe and strong attachment to the hub on its own, and therefore the blade root may include a metal blade flange, and bushings are usually arranged at the blade root. The root of the wind turbine blade may include a plurality of bushings embedded in a rim of the root, the bushings extending in a tip-root direction of the blade. Bolts or studs may be used to secure the blade to the hub, or to a pitch bearing arranged with the hub.

The pitch bearing may comprise an inner ring, an outer ring and a plurality of roller elements between the inner ring and the outer ring. The wind turbine blade may be attached either at the inner bearing ring or at the outer bearing ring, whereas the hub is connected at the other bearing ring. Sometimes, an extender may be additionally arranged between the blade and the hub, e.g. between the blade and the pitch bearing.

As the pitch bearing is circular and the blade flange is circular or annular as well, the blade root should have a substantially circular cross-section for being mounted to the hub as well. However, the blade root may lose its circularity between the molding of the blade and the attachment of the blade root flange. As a wind turbine blade may weigh tens of tons, e.g. <NUM>, <NUM>, <NUM> tons or more, the root may deform and adopt a more elliptical cross-section when stored. It may also happen that if the resin is not totally cured before extracting a wind turbine half of its mold, and thus the blade is softer than it should be, or if the composite material shrinks during curing, the blade root will also lose its circularity. Prior art examples are disclosed in <CIT> and <CIT>.

The present disclosure aims at increasing a circularity of a blade root.

In an aspect of the present disclosure, a method for adapting a cross-sectional shape of a root of a wind turbine blade is provided. The method comprises providing a root flange configured to be mounted to the root of the wind turbine blade. The method further comprises arranging the root flange with the root of the wind turbine blade and joining a plurality of push elements to the root flange. The push elements are configured to push a wall of the root of the wind turbine blade. The method further comprises pushing the wall of the root of the wind turbine blade with one or more of the push elements.

According to this aspect, a root flange that is to be attached to a root of a wind turbine blade is used as a support for a plurality of push elements. When the root flange is in an appropriate position, e.g. sufficiently close or next to a root end, or inside the blade root, the push elements may be used to change the cross-section of the blade root. For instance, a more circular or a substantially circular cross-section may be obtained.

As a root flange installation process is combined with a de-ovalizing procedure, processing time may be reduced. Also, a finer control and more versatility may be obtained than with other methods for de-ovalizing a wind turbine blade root, for example if tools having a length of about a diameter of a blade root or tools configured to push towards an entirety of an inner wall of a blade root at a same time are used. Adaptation of the cross-section of the root of a wind turbine blade may also be easier and safer with respect to other de-ovalization methods, as the dimensions and weight of the push elements may be smaller than the tools used in other methods.

Throughout this disclosure, a root flange may be understood as an element to be attached to a root of a wind turbine blade, e.g. to a root end or to an inside wall at or near the root. The root flange has a strengthening or stiffening function, e.g. to avoid or limit blade root deformation, and/or may serve as a stopper for avoiding people or objects falling to an inside of a wind turbine blade. In some examples, a root flange may be a ring-shaped body or a disc-shaped body. In some examples, the root flange may be a bulkhead. The root flange may have at least one surface to which at least two push elements may be attached for pushing a wall portion of a blade root.

Throughout this disclosure, a push element may be understood as an element, e.g. a device or tool, that is configured to push a portion of a wall, e.g. an inner wall, of a root of a wind turbine blade. The push elements may be configured particularly for pushing a (portion of a) blade root radially outwards. The push elements may comprise a push surface for contacting such a wall and pushing it for changing a cross-sectional shape of the blade root. It may be understood that the push element is also configured to be attached to a root flange. In some examples, a push element may be any suitable type of jack. The push elements may be activated manually or may include a power source or may be connected to a power source for activating and/or driving a pushing action.

In a further aspect of the present disclosure, an assembly for adapting a cross-sectional shape of a root of a wind turbine blade is provided. The assembly comprises a root flange configured for a root of a wind turbine blade. The assembly further comprises a plurality of push elements attached to the root flange such that the push elements are arranged to push a wall of the root of the wind turbine blade radially outwards.

In yet a further aspect of the present disclosure, a method for de-ovalizing a root of a wind turbine blade is provided. The method comprises moving a root platform assembly comprising a root platform and a plurality of push elements secured to the root platform towards the root of the wind turbine blade. The method further comprises pushing an inner wall of the root of the wind turbine blade with one or more of the push elements.

Reference now will be made in detail to embodiments of the present disclosure, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation only, not as a limitation. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present disclosure. Thus, it is intended that the present disclosure covers such modifications and variations as come within the scope of the appended claims.

<FIG> illustrates a conventional modern upwind wind turbine <NUM> according to the so-called "Danish concept" with a tower <NUM>, a nacelle <NUM> and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub <NUM> and three blades <NUM> extending radially from the hub <NUM>, each having a blade root <NUM> nearest the hub and a blade tip <NUM> furthest from the hub <NUM>.

The airfoil region <NUM>, also called the profiled region, has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region <NUM>, due to structural considerations, has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade <NUM> to the hub. The chord length of the transition region <NUM> typically increases with increasing distance from the hub. The width of the chord decreases with increasing distance from the hub.

The wind turbine blade <NUM> comprises a blade shell comprising two blade shell parts or half shells, a first blade shell part <NUM> and a second blade shell part <NUM>, typically made of fiber-reinforced polymer. The wind turbine blade <NUM> may comprise additional shell parts, such as a third shell part and/or a fourth shell part. The first blade shell part <NUM> is typically a pressure side or upwind blade shell part. The second blade shell part <NUM> is typically a suction side or downwind blade shell part. The first blade shell part <NUM> and the second blade shell part <NUM> are fastened together with adhesive, such as glue, along bond lines or glue joints <NUM> extending along the trailing edge <NUM> and the leading edge <NUM> of the blade <NUM>. Typically, the root ends of the blade shell parts <NUM>, <NUM> have a semi-circular outer cross-sectional shape.

In an aspect of the present disclosure, a method <NUM> for adapting a cross-sectional shape of a root <NUM> of a wind turbine blade <NUM> is provided. The method <NUM> is schematically shown in the flow chart of <FIG>.

The method comprises, at block <NUM>, providing a root flange <NUM> configured to be mounted to the root <NUM> of the wind turbine blade <NUM>. The method further comprises, at block <NUM>, arranging the root flange <NUM> with the root <NUM> of the wind turbine blade <NUM>. The method further comprises, at block <NUM>, joining a plurality of push elements <NUM> to the root flange <NUM>, the push elements <NUM> being configured to push a wall <NUM> of the root <NUM> of the wind turbine blade <NUM>. The method further comprises, at block <NUM>, pushing the wall <NUM> of the root <NUM> of the wind turbine blade <NUM> with one or more of the push elements <NUM>.

The steps of this method may be performed at a factory, while the blade shell is being manufactured, or later on, e.g. after the blade has been stored during some days, weeks or months. In other examples, the steps of the method may be performed in the field, e.g. after the blade has been transported to its installation location.

With such methods, a cross-sectional shape of a blade root <NUM> may be improved. For instance, if a blade root has been deformed, e.g. after unmolding, a suitable cross-sectional shape may be obtained, e.g. for enabling a successful coupling of the blade to a wind turbine hub. In addition, an element which is to be attached to the blade root <NUM>, namely a root flange <NUM>, can be used as a support for the plurality of pushing elements <NUM>. A better and more efficient use of resources may be achieved, e.g. less time and less tools may be required. For example, attaching several relatively small pushing devices <NUM> to a root flange <NUM> that has to be joined to the blade root <NUM> and pushing with them may be more efficient than using one or a few large pushing devices for de-ovalizing the blade root and, separately, join the root flange <NUM>. In this example, a large pushing device may for example have a length of about a diameter of a cross-section of a blade root <NUM>. For example, if the blade shell has lost its circular shape in one or more relatively small portions of the root, smaller push elements may provide force and compensation of the deformation where it is needed.

<FIG> schematically shows an example of a deformed blade root <NUM> and a root flange <NUM> to be attached to the blade root. The blade root <NUM> of this figure may not be suitable to be joined to a hub of a wind turbine <NUM>, as a more circular cross-section of the root <NUM> may be required. An example of a root flange <NUM> may also be seen in this figure. The root flange <NUM> has a disc shape and a substantially circular cross-section, and it is to be attached to the blade root <NUM>, specifically to the root end <NUM>. As the cross-sectional shape of the blade root <NUM> is not circular in this example, the root flange <NUM> cannot be properly joined to the blade root <NUM>. In addition, it may be difficult or even impossible to mount such a blade to a wind turbine hub.

Although the root flange <NUM> has a substantially circular cross-section in the example of <FIG>, a root flange <NUM> may have other suitable shapes and cross-sections. For instance, if the root flange <NUM> is a bulkhead, the root flange may have a disc shape, but also a cylindrical shape or other appropriate shape depending on the bulkhead. Or if the root flange <NUM>, instead of being provided as an integral piece, is provided in separate portions, e.g. in an upwind portion <NUM> and a downwind portion <NUM> (see <FIG>), each portion may e.g. have a semi-circular cross-section.

<FIG> and <FIG> schematically illustrate a longitudinal cross-section of a blade root <NUM>. The root flange <NUM> is configured to be attached to a root end <NUM> of the blade <NUM> in <FIG>, e.g. with a plurality of bolts <NUM>, see <FIG>. The root flange <NUM> may comprise a plurality of through holes to this end. The root flange <NUM> is configured to be attached to an inner wall of the blade root <NUM> in <FIG>. A suitable sealant to be arranged between the inner wall of the blade and the root flange <NUM> may be used to attach the root flange to the inner wall.

The root flange may be configured to fill, in cross-section, a root <NUM> of a wind turbine blade <NUM> when the root has a suitable, e.g. circular, shape. For example, a root flange having a circular cross-section may have a diameter <NUM> of about an outer diameter <NUM> of the blade root, see <FIG>, or about an inner diameter <NUM> of the root flange, see <FIG>. A joining element, e.g. a sealant or an adhesive, may be used to join the root flange <NUM> to a wall <NUM> of the blade root <NUM> in the example of <FIG>. In other examples, a root flange <NUM> may have a size, in cross-section, much smaller than an inner diameter <NUM> of the blade root <NUM>.

When the root flange <NUM> has a circular cross-section, the root flange may comprise a hole <NUM> in a circle center of the root flange. A through hole in the root flange may be configured to allow passage to one side to the opposite side of the root flange. An operator may therefore be able to move between one side and the other side of the root flange <NUM>, going through the root flange. When the blade root <NUM> has a suitable cross-sectional shape, e.g. a circular cross-section, and the root flange <NUM> is attached to the blade root, the hole or opening <NUM> may provide passage in a root-tip direction of the blade. In this way, an operator may access an inside of the blade <NUM> by going through the opening <NUM> of the root flange. A hatch for covering or closing the hole or opening <NUM> may be provided with, or attached to, the root flange <NUM>. A root flange hole <NUM> for the passage of an operator may for example have a circular cross-section and have a diameter of about one meter. Such an opening <NUM> may be provided in a center of a root flange regardless a cross-sectional shape of the root flange <NUM>. It may also be possible to provide such a through hole <NUM> in another portion of the root flange, e.g. in a less centric position. In general, a hole for the passage of an operator may be provided in any suitable location of the root flange. Similarly, a root flange <NUM> does not need to include such a hole <NUM>. For example, the root flange <NUM> of <FIG> does not include it.

Arranging <NUM> the root flange <NUM> may, in some examples, comprise inserting the root flange in an inside <NUM> of the root <NUM> of the wind turbine blade. For instance, the root flange is inserted in an inside of the blade root <NUM> in the example of <FIG>. In some of these examples, the root flange may be a bulkhead. Depending on the type of root flange <NUM> to be used, the root flange <NUM> may be inserted into an inside <NUM> of the blade root or not.

In this example, the root flange may be circular or annular but with a diameter that is smaller than a local internal diameter of the blade root. The perimeter of the root flange may be connected to the inside of the blade root, specifically once the blade root has been given a substantially circular shape.

In some examples, joining <NUM> may comprise joining the plurality of push elements <NUM> to a surface <NUM> of the root flange <NUM> which, upon adapting (finishing the adaption) the cross-sectional shape of the root <NUM> of the wind turbine blade <NUM>, faces a tip <NUM> of the wind turbine blade <NUM>. This may allow to effectively push a wall <NUM> of blade root <NUM> and to appropriately approach and join the root flange <NUM> to the blade root <NUM>.

The push elements <NUM> may be specifically joined to a portion of that surface <NUM> which is configured to be adjacent to a root plane, e.g. to the wall <NUM> of the root <NUM>, of the wind turbine blade <NUM>. In the example of <FIG>, two push elements <NUM> are attached to surface <NUM> of the root flange <NUM>, but each push element <NUM> is closer, in cross-section, to an external edge of the root flange <NUM> than to a center of the root flange <NUM>. Therefore, a finer control of pushing may be achieved. Also, in comparison with other methods for de-ovalizing, a size of the push elements may be greatly reduced.

<FIG> schematically illustrates a side view of an inside of a wind turbine blade root, in particular of a region close to an inner wall <NUM> of the blade root <NUM>. The push elements may be jacks. In this specific example, a scissor jack having a ball joint <NUM> is used. The jacks <NUM> have a push surface <NUM> to contact a portion of a wall of blade shell. The push surface <NUM> may be configured to distribute the pushing forces over the inner surface of the root.

Any suitable type of jack may be used. In the example of <FIG>, the jacks are attached close to an edge, e.g. a circumferential outside edge, of a surface of the root flange <NUM> which will be facing a tip of the wind turbine blade once a suitable cross-section of the blade root is obtained. A fastener, e.g. a bolt, <NUM> is used to join the push element <NUM>, specifically an end of the push element opposite to the push surface <NUM>, to the root flange <NUM>. More than one fastener may be used. A screw <NUM> is provided for enabling the ball joint <NUM> of the jack be displaced horizontally. The horizontal movement changes the angle between the legs of the jack and therefore moves the push surface <NUM> close to a wall <NUM> of the root blade. Intermediate elements <NUM> such as a thrust bearing and one or more washers may be provided.

Pushing <NUM> may comprise pushing towards an outside <NUM> of the wind turbine blade <NUM>, e.g. radially outwards, see for example the arrows in <FIG>. In other examples, the push elements may push towards an inside <NUM> of the wind turbine blade, e.g. radially inwards, or both towards and inside and an outside of the blade. Depending on the dimensions of a root flange <NUM>, it may be possible to attach two or more push elements <NUM> to the root flange <NUM> such that one or more pushing devices <NUM> may be used to push towards an inside <NUM> of the wind turbine blade whereas one or more other pushing devices may be used to push towards an outside <NUM> of the blade. For example, if the root flange has a disc shape or a cylindrical shape, and therefore has two opposite axial surfaces <NUM>, <NUM> and a radial surface <NUM> extending between the two opposite axial surfaces <NUM>, <NUM>, one or more push elements <NUM> may be attached to a radial surface <NUM>. Additionally or alternatively, a push element <NUM> may be attached to an axial surface <NUM> which is to face away from a blade tip <NUM> once a desired blade root cross-section has been achieved. Attachment may be direct, e.g. without intermediate pieces or elements, or may be indirect, e.g. with an intermediate element such as an extendible arm connecting the root flange <NUM> and a push element <NUM>.

In some examples, pushing <NUM> may comprise actuating one of the push elements at a different time than another of the push elements <NUM>. One or more push elements <NUM> may be actuated during a first period of time, and one or more push elements may be actuated during a second period of time. The second period of time may be subsequent to the first period of time or may be partially overlapping with the first period of time. Control and adaptation over the de-ovalization process may be increased. An operator may actuate, e.g. directly actuate, one or more push elements. In other examples, actuation may be remote.

<FIG> schematically illustrates a perspective view of a root flange <NUM> being moved along a rod <NUM> comprised in a root end <NUM> of the blade root <NUM>. In some examples, the blade root may have a plurality of bushings configured to receive a plurality of studs through which the blade root is to be coupled to a wind turbine hub <NUM>. If the blade root has not a suitable cross-sectional shape, it may not be possible to insert the root flange in blade root studs already provided in the blade root. Therefore, only a few studs, e.g. one, two, three or more studs may be provided with the blade root <NUM> before the root flange <NUM> is moved towards the blade root. These studs may be inserted into bushings of the blade root before the root flange is moved towards the blade root and moved along the studs, and the remaining bushings may be left empty. The studs in this example have the function of arranging the flange with the blade root in a precise position. Other rods, e.g. guiding pins may be used to position a root flange with respect to the blade root.

Therefore, arranging <NUM> the root flange may, in some examples, comprise inserting one or more rods <NUM> in the root of the wind turbine blade and in corresponding holes <NUM> of the root flange <NUM>. The holes <NUM> are configured to receive the rods <NUM>. The rods <NUM> may be studs or guiding pins. Blade root studs may be shorter than the guiding pins. Once the blade root <NUM> has all its necessary studs, the blade <NUM> may be coupled to the wind turbine hub <NUM> (or pitch bearing) through the studs. A number of guiding pins, if used at all, may be much lower of a number of studs. Two or more guiding pins may be attached to the blade root end <NUM> for easing and better controlling an installation of the blade to the hub. During blade installation, the guiding pins may be inserted into the hub first, and the studs may be inserted afterwards, once the blade is closer to, and aligned with, the hub <NUM>. Rods <NUM> may therefore be one or more of studs and guiding pins.

The push elements <NUM> may be joined to the root flange <NUM> after the root flange has been moved close to the wind turbine blade <NUM>, or they may be joined before. In the example where the root flange <NUM> is slid through one or more rods <NUM>, the plurality of push elements <NUM> may be attached to the root flange before displacing the root flange along the rods, or may be attached after the sliding along the rods has begun, e.g. after the root flange is besides the root end <NUM>. Both options may also be combined, such that some push elements <NUM> may be joined before the root flange is slid along the rods, and some push elements <NUM> may be joined afterwards, e.g. once the root flange is closer to, or next to, the root end <NUM>. It is also possible to join one or more push elements to the root flange at any moment if deemed necessary. For example, if the root flange <NUM> is besides the root end <NUM>, one or more additional push elements may be joined if deemed suitable. Likewise, if may be possible to change a position of one or more push elements at any time, i.e. at what portion of the root flange <NUM> they are joined to, if deemed suitable. The reorganization of the push elements, both in terms of number and location on the root flange, may be performed regardless the root flange <NUM> is to be attached to a root end <NUM>, see <FIG>, or to an inside of the blade, see <FIG>.

In some examples, the method <NUM> may further comprise securing the root flange <NUM> to the wind turbine blade root <NUM> after the wind turbine blade root attains a suitable cross-sectional shape, e.g. a substantially circular cross-sectional shape. Securing elements <NUM> such as bolts, see <FIG>, may be used. Securing elements may also be non-mechanical. Bonding elements such as adhesive may be provided, e.g. for joining a bulkhead to an inner wall of a root blade. Also, both mechanical and non-mechanical securing elements may be used simultaneously.

The method may further comprise detaching the plurality of push elements <NUM> from the root flange <NUM>. When a desired cross-section of a blade root <NUM> has been achieved, the push elements may be removed. The dimensions of the root flange <NUM> may be such that, once that it has been attached to the blade root <NUM>, it confers rigidity to the blade root, e.g. to a root end <NUM>, and minimizes the deformation of the blade root. The push elements <NUM> may e.g. be removed through the central hole or opening <NUM> of the root flange. In other examples, the push elements, or at least some of them, may be left attached to the root flange. For instance, some or all the push elements may be kept attached to the root flange during transportation of the blade to a wind turbine installation site.

The wind turbine blade <NUM> may comprise an upwind blade shell, e.g. a pressure side blade shell, and a downwind blade shell, e.g. a suction side blade shell. <FIG> shows an example of root portion of an upwind blade shell <NUM> and a downwind blade shell <NUM>. It may be possible to attach a root flange to the blade shells before the shells <NUM>, <NUM> are joined. In these examples, deformation of the blade root <NUM> may be prevented as a root flange may keep a desired cross-sectional shape of the blade root already before the blade is removed from a mold and stored. In these examples, the root flange <NUM> may comprise an upwind root flange portion <NUM> and a downwind root flange portion <NUM>. Arranging <NUM> may comprise attaching the upwind root flange portion <NUM> to the upwind blade shell <NUM> and attaching the downwind root flange portion <NUM> to the downwind blade shell <NUM>. Joining <NUM> may be performed before attaching the upwind blade shell <NUM> and the downwind blade shell <NUM> to form the wind turbine blade <NUM>.

In a further aspect of the disclosure, an assembly <NUM> for adapting a cross-sectional shape of a root <NUM> of a wind turbine blade <NUM> is provided. The assembly <NUM> comprises a root flange <NUM> configured for a root <NUM> of a wind turbine blade <NUM>. The assembly <NUM> further comprises a plurality of push elements <NUM> attached to the root flange <NUM> such that the push elements <NUM> are arranged to push a wall <NUM> of the root <NUM> of the wind turbine blade <NUM> radially outwards. Examples of such an assembly <NUM> may be seen in <FIG>, <FIG> and <FIG>.

<FIG> schematically shows a top view of a root flange <NUM> with a plurality of push elements attached <NUM>. The root flange <NUM> may, in some examples, comprise a plurality of mounting points <NUM>. The mounting points may be spaced about a circumferential direction <NUM>. The mounting points may be provided radially outwards. Other locations of the mounting points may also be possible. The schematic example of <FIG> shows <NUM> mounting points <NUM>, four to which push elements <NUM> have been joined, and for which have been left free. In some examples, between <NUM> and <NUM>, e.g. <NUM> or <NUM> mounting points <NUM>, may be provided. In other examples, between <NUM> and <NUM>, e.g. <NUM> mounting points, may be provided.

A mounting point or mounting region <NUM> may be understood as a portion of a root flange to which a push element <NUM> may be attached. A suitable number and location of mounting points <NUM> may for example be determined by computer simulations. Visual marks may be provided on a root flange as indicators of the mounting points <NUM>. Paint or adhesive tape may for example be used as visual marks. Mounting points <NUM> may also be provided by holes or receptacles. For instance, a root flange may be provided with holes for the insertion of fasteners <NUM> and pins <NUM>, see <FIG>. Other suitable visual marks may be provided.

Depending on how a blade root <NUM> is deformed, a different number and a different location of push elements may be required. In some examples, a same number of push elements <NUM> than a number of available mounting points <NUM> may be provided. In other examples, a number of push elements <NUM> may be less than a number of mounting points <NUM>. That is to say, depending on how the blade root <NUM> is deformed, more or less push elements <NUM> may be attached to the root flange <NUM>, and its location may also be adjusted as required. Providing mounting points <NUM> in root flanges <NUM> may allow adaptability and efficacy for the de-ovalization process.

The plurality of push elements <NUM> may be arranged in pairs of push elements. In <FIG>, two pairs of opposing push elements may be seen attached to the root flange. Each pair is formed by two push elements <NUM> arranged in radially opposing mounting points <NUM> in this example. Each pair of push elements may comprise one push element to push against an upwind blade shell <NUM>, and another push element to push against a downwind blade shell <NUM>. The pairs of push elements may be arranged in diametrically opposite positions. A good balance between weight and effectivity in de-ovalizing may be obtained by providing between <NUM> and <NUM> pairs of push elements <NUM>. Thus, <NUM>, <NUM> or <NUM> pairs of push elements may be provided.

A dimension of the push elements <NUM>, in a direction of pushing, may be about or less than a <NUM>%, specifically about or less than a <NUM>%, of a diameter of the root of the wind turbine blade. Such a dimension of the push elements may e.g. be measured in a most compressed state of the push elements. An inner diameter of the de-ovalized blade root may be used as a reference in some examples. A dimension of the push elements <NUM>, in a direction of pushing, may similarly be about or less than a <NUM>%, specifically about or less than a <NUM>%, of a diameter <NUM> of the root flange <NUM>.

The description and explanations of the push elements <NUM> and the root flange <NUM> regarding method <NUM> also applies to assembly <NUM>, and vice versa. For example, a direction of attachment of the push elements <NUM> and the root flange <NUM> may be substantially perpendicular to a direction of pushing. In the example of <FIG>, the direction of attachment would be axial, i.e. perpendicular to plane of the figure, and the direction of pushing would be radial. Also, as shown in the example of <FIG>, the root flange <NUM> may comprise a through hole <NUM>, e.g. a central opening, for moving one or more push elements <NUM> from a side of the root flange to an opposite side of the root flange. The push elements may be scissor jacks.

A wind turbine blade <NUM> comprising an assembly <NUM> as described herein may also be provided.

In a further aspect of the disclosure, a method for de-ovalizing a root of a wind turbine blade is provided. De-ovalizing may be understood as increasing a circularity of a cross-section of a blade root <NUM>. Method <NUM> is shown in the flow chart of <FIG>. Aspects and explanations with respect to method <NUM> and assembly <NUM> may be combined and applied to method <NUM> and vice versa.

The method comprises, at block <NUM>, moving a root platform assembly <NUM> comprising a root platform <NUM> and a plurality of push elements <NUM> secured to the root platform <NUM> towards the root <NUM> of the wind turbine blade <NUM>. Moving the root platform assembly <NUM> may comprise sliding the root platform <NUM> along one or more studs of the root of the wind turbine blade. The root platform assembly may be moved towards the blade root until at least a portion of the root platform touches the blade root. The plurality of push elements may be a plurality of jacks.

In some examples, the plurality of push elements <NUM> may be secured to an outer portion, e.g. to an outer radial portion, of a surface <NUM> of the root platform which, after de-ovalizing, is perpendicular to a root-tip direction of the wind turbine blade. The platform <NUM> may have a circular cross-section, e.g. the platform may have a disc shape.

The method further comprises, at block <NUM>, pushing an inner wall <NUM> of the root <NUM> of the wind turbine blade <NUM> with one or more of the push elements <NUM>. Pushing may be performed after the platform assembly <NUM> is next to a root end <NUM>. One or more operators may manually act on one or more push elements for causing them to move towards the inner wall.

The method may further comprise bolting the platform <NUM> to the root of the wind turbine blade at least partly after de-ovalizing the root of the wind turbine blade. The platform <NUM> may therefore be attached to the root of the wind turbine blade.

Claim 1:
A method (<NUM>) for adapting a cross-sectional shape of a root (<NUM>) of a wind turbine blade (<NUM>), the method comprising:
providing (<NUM>) a root flange (<NUM>) configured to be mounted to the root (<NUM>) of the wind turbine blade (<NUM>);
arranging (<NUM>) the root flange (<NUM>) with the root (<NUM>) of the wind turbine blade (<NUM>);
joining (<NUM>) a plurality of push elements (<NUM>) to the root flange (<NUM>), the push elements (<NUM>) being configured to push a wall (<NUM>) of the root (<NUM>) of the wind turbine blade (<NUM>); and
pushing (<NUM>) the wall (<NUM>) of the root (<NUM>) of the wind turbine blade (<NUM>) with one or more of the push elements (<NUM>).