Wind turbine blade assembly and method for producing a wind turbine blade

Disclosed is a wind turbine blade assembly and a method for its manufacture. The wind turbine blade assembly comprises a leading edge, a trailing edge, a blade shell with a trailing portion, and a flatback profile component. The trailing portion has an outwardly curving arc shape and the flatback profile is positioned so as to cover the trailing portion of the blade shell.

This is a National Phase Application filed under 35 U.S.C. 371 as a national stage of PCT/EP2020/072583, filed Aug. 12, 2020, an application claiming the benefit of Great Britain Application No. 1911619.3, filed Aug. 14, 2019, the content of each of which is hereby incorporated by reference in its entirety.

The present invention relates to a wind turbine blade assembly and to a method of its production. The wind turbine blade assembly comprises blade shell and a flatback profile component. The profile of the wind turbine blade assembly is embodied as a flatback profile.

BACKGROUND

As wind turbines and wind turbine blades increase in size, the blade loads, i.e. strains, bending moments, peel loads etc., in particular along the trailing edge, increase. For this and other reasons, the design of the trailing edge is an important factor for the efficiency of the wind turbine.

Wind turbine blades comprising a flatback profile at the trailing edge may have an increased efficiency in some circumstances. An optimized profile comprises a varying geometry of the trailing edge along the airfoil region of the blade. A rounded corner may be required in a flatback profile which is produced as an integral part of the shell parts. This is disadvantageous for the aerodynamic properties.

Document EP 2 341 241 A1 shows a wind turbine blade with a leading edge, a trailing edge and pressure and suction shells between the leading edge and the trailing edge, wherein edges of the pressure and suction shells are configured to provide a flatted trailing edge with sharp corners can be provided. However, considerable manufacturing time is spent in configuring the joint of the pressure shell and the suction shell. Furthermore, substantial reinforcement material has to be applied in order to sustain high loads, especially for long blade lengths.

A general desire in the field of flatback wind turbine blades is to provide a flatback blade structure which sustains high mechanical forces, especially for long blade lengths.

Another general desire in the field of flatback wind turbine blades is to provide a method of assembling such a flatback blade profile which is scalable in geometry and strength.

SUMMARY

On this background, it may be seen as an object of the present disclosure to provide a wind turbine blade assembly with a flatback profile resulting in good aerodynamic properties and which sustains high mechanical loads.

Another object of the present disclosure is to provide an improved method of manufacturing a flatback wind turbine blade assembly which is scalable in geometry and strength.

One or more of these objects may be met by aspects of the present disclosure as described in the following.

A first aspect of this disclosure relates to a wind turbine blade assembly having a longitudinal axis extending between a root end to a tip end, a chord extending transversely to the longitudinal axis between a leading edge and a trailing edge, the wind turbine blade assembly comprising:a blade shell having a upwind shell side, a downwind shell side, a leading portion defining the leading edge of the wind turbine blade assembly, and a trailing portion arranged opposite to the leading portion and connecting the upwind shell side with the downwind shell side, wherein a cross-section of the trailing portion perpendicular to the longitudinal axis has an outwardly curving arc shape, convexly rounded shape, outwardly curving circular arc shape, outwardly curving elliptical arc shape, and/or outwardly curving C shape; anda flatback profile component having an upwind side positioned substantially flush with the upwind shell side, a downwind side positioned substantially flush with the downwind shell side, and a substantially planar flatback side connecting the upwind side with the downwind side, the flatback side defining the trailing edge of the wind turbine blade assembly and being shaped so as to provide the wind turbine blade assembly with a flatback airfoil shape;
wherein the flatback profile component is positioned to cover the trailing portion of the blade shell.

This may provide the advantage that the blade shell can be provided to sustain high mechanical loads as the outwardly curving arc shape of the trailing portion is a geometrical strong shape, while simultaneously providing a wind turbine blade assembly with the aerodynamic benefits associated with a flatback profile.

Furthermore, this may provide the advantage that functions of the wind turbine blade is separated so that the blade shell provides the mechanical strength to the wind turbine blade assembly and the leading portion of the airfoil shape, and the flatback assembly provides improved aerodynamic properties to the trailing portion of the airfoil shape but does not provide significant strength to the wind turbine blade assembly. This may provide the advantage that the flatback profile component can be adapted with low cost to the specific wind regime of the intended wind turbine location, and that the same blade shell can be used for multiple wind regimes thus increasing production volume and lowering costs.

Such a wind turbine blade assembly may also improve manufacturing as time spent configuring the trailing edge is minimized since the flatback profile component can be configured to be fairly simple to attach to the blade shell.

In some embodiments, the flatback profile component and the blade shell may be formed as separate components. For instance, the blade shell and the flatback profile component may be manufactured at two separate production lines or even at two different geographical locations.

This may provide the advantage that a single blade shell geometry can be utilised in multiple different wind regimes as the flatback profile component can be modified to accommodate the specific wind regime.

In some embodiments, the upwind side of the flatback profile component may be attached, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, to an outer surface of the upwind shell side, and/or the downwind side of the flatback profile component may be attached, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, to an outer surface of the downwind shell side. The outer surface of either shell side may be the surface in contact with wind.

This may be a particularly simple way of attaching the flatback profile component to the blade shell and allows the manufacture of a separate blade shell with full structural integrity before attaching of the flatback profile component.

In some embodiments, the flatback profile component may comprise a first edge between the flatback side and the upwind side of the flatback profile component and/or a second edge between the flatback side and the downwind side, wherein the first and/or the second edge may be aerodynamically sharp. In this case, the term “aerodynamically sharp” in relation to an edge may be understood as an edge adjacent to a surface wherein wind flowing along the surface substantially instantaneously separates from the surface at the aerodynamically sharp edge.

This may improve the aerodynamic properties of the wind turbine blade assembly, and since the mechanical strength is primarily provided by the blade shell, having one or more sharp edges on the flatback profile component does not compromise the mechanical strength of the wind turbine blade assembly in a significant way.

In some embodiments, the upwind shell side and the downwind shell side are formed as separate upwind and downwind shell parts, the blade shell further comprises a joint portion having an upwind joint portion formed integrally with the upwind shell part in one piece, a downwind joint portion formed integrally with the downwind shell part in one piece, and a flange adhering to an inner surface of the upwind joint portion and to an inner surface of the downwind joint portion, so as to structurally join the upwind shell part to the downwind shell part.

This may be a particularly simple and cost-effective way of joining the upwind shell side with the downwind shell side to be able to sustain high mechanical loads.

In some embodiments, in a cross-section perpendicular to the longitudinal axis, the perimeter of the trailing portion of the blade shell from the attachment of upwind side of the flatback profile component to the attachment of the downwind side of the flatback profile component may be outwardly arc shaped, convexly rounded, circular arc shaped, elliptical arc shaped, and/or C-shaped. In some embodiments, the trailing portion of the blade shell may be curving non-abruptly.

This may provide the advantage of a particularly strong geometric shape thus reducing the need for additional reinforcement at the trailing portion.

In some embodiments, the flatback profile component consists essentially of a fibre-reinforced composite material.

This may provide the advantage of a strong and light flatback profile component, furthermore this may allow the flatback profile component to be plastic welded onto the blade shell.

In some embodiments, the flatback profile component or a matrix material of the flatback material comprises or consist essentially of a thermoplastic material or a thermoset material.

This may provide the advantage of easier plastic welding the flatback profile component onto the blade shell, especially a thermoplastic material.

In some embodiments, the thickness of the upwind, downwind, and/or the flatback side of the flatback profile component is/are equal to or less than the thickness of the blade shell.

This may provide the advantage that material and thus cost is saved since the flatback profile component is primarily for improved aerodynamical properties instead of providing mechanical strength to the wind turbine blade assembly.

In some embodiments, the flatback profile component covers the trailing portion of the blade shell at least along 10%, 20%, 30%, 40%, 50%, 60%, or 70% of the distance from the root end to the tip end of the wind turbine blade assembly.

Such an extent of the flatback profile component has been found to be especially advantageous.

Some embodiments of the first aspect relate to a kit of parts for a wind turbine blade assembly, the kit of parts may comprise:a blade shell having a upwind shell side, a downwind shell side, a leading portion defining the leading edge of the wind turbine blade assembly, and a trailing portion arranged opposite to the leading portion and connecting the upwind shell side with the downwind shell side, wherein the trailing portion has an outwardly curving arc shape, convexly rounded shape, outwardly curving circular arc shape, outwardly curving elliptical arc shape, and/or outwardly curving C shape; anda flatback profile component having an upwind side configured for being attached substantially flush with the upwind shell side, a downwind side configured for being attached substantially flush with the downwind shell side, and a flatback side connecting the upwind side with the downwind side, the flatback side being configured to provide the wind turbine blade assembly with a flatback airfoil shape, the flatback profile component being configured for covering the trailing portion of the blade shell.

In some embodiments, a wind turbine may comprise a wind turbine blade assembly according to the first aspect of this disclosure.

In some embodiments, a wind turbine farm may comprise a plurality of wind turbines comprising a wind turbine blade assembly according to the first aspect of this disclosure.

A second aspect of this disclosure relates to a method for manufacturing a wind turbine blade assembly according to the first aspect of this disclosure, the wind turbine blade assembly having a longitudinal axis extending between a root end to a tip end, a chord extending transversely to the longitudinal axis between a leading edge and a trailing edge, the method comprising the steps of:providing a blade shell having an upwind shell side, a downwind shell side, a leading portion defining the leading edge, and a trailing portion arranged opposite to the leading portion and connecting the upwind shell side with the downwind shell side, wherein the trailing portion has an outwardly curving arc shape, convexly rounded shape, outwardly curving circular arc shape, outwardly curving elliptical arc shape, and/or outwardly curving C shape;providing a flatback profile component having an upwind side, a downwind side, and a flatback side connecting the upwind side with the downwind side;positioning the flatback profile component to cover the trailing portion of the blade shell so that the flatback side defines the trailing edge of the wind turbine blade assembly;attaching, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, the upwind side of the flatback profile component to the upwind shell side, so that the upwind side of the flatback profile component is positioned substantially flush with the upwind shell side; andattaching, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, the downwind side of the flatback profile component to the downwind shell side, so that the downwind side of the flatback profile component is positioned substantially flush with the downwind shell side.

This may provide the advantage that the blade shell can be provided separately from the flatback profile component and thus increases manufacturing flexibility, for instance the flatback profile component may be attached to the blade shell after the blade shell has been moved from the mould allowing lowering production time for the blade shell.

A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects of this disclosure and embodiments thereof.

DETAILED DESCRIPTION

FIG.1illustrates a conventional modern upwind wind turbine2according to the so-called “Danish concept” with a tower4, a nacelle6, and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub8, and three blade assemblies10extending radially from the hub8, each having a blade root16nearest the hub and a blade tip14furthest from the hub8.

FIG.2shows a schematic view of an exemplary wind turbine blade assembly10. The wind turbine blade assembly10extends along a longitudinal axis L with a root end17and a tip end15and has the shape of a conventional wind turbine blade with comprises a root region12closest to the hub, a profiled or an airfoil region11furthest away from the hub and a transition region13between the root region12and the airfoil region11. The blade assembly10comprises a leading edge18facing the direction of rotation of the blade assembly10, when the blade is mounted on the hub, and a trailing edge20facing the opposite direction of the leading edge18.

The airfoil region11(also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region12due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade assembly10to the hub. The diameter (or the chord) of the root region12may be constant along the entire root area30. The transition region13has a transitional profile gradually changing from the circular or elliptical shape of the root region12to the airfoil profile of the airfoil region11. The chord length of the transition region13typically increases with increasing distance r from the hub. The airfoil region11has an airfoil profile with a chord extending between the leading edge18and the trailing edge20of the blade assembly10. The width of the chord decreases with increasing distance r from the hub.

A shoulder40of the blade assembly10is defined as the position, where the blade assembly10has its largest chord length. The shoulder40is typically provided at the boundary between the transition region13and the airfoil region11.

It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

The trailing edge20may be embodied as a flatback trailing edge, wherein the trailing edge20is flattened in order to achieve better aerodynamic properties. This construction may increase the aerodynamic efficiency of the wind turbine blade in comparison with a sharp trailing edge design.FIG.3shows a wind turbine blade assembly10with a flatback profile at the trailing edge20in more detail. The wind turbine blade assembly10comprises a blade shell22including two blade shell parts, a first blade shell part24and a second blade shell part26, typically made of fibre-reinforced polymer. The first blade shell part24is typically a pressure or upwind blade shell part. The second blade shell part26is typically a suction or downwind blade shell part. The first blade shell part24and the second blade shell part are typically glued together along bond lines or glue joints28extending along the trailing edge20and the leading edge18of the blade assembly10as shown in more detail onFIG.5. Typically, the root end17of the blade shell parts24,26have a semi-circular or semi-oval outer cross-sectional shape.

The trailing edge20has a flattened profile. The flattened profile may increase the aerodynamic efficiency and also helps to reduce the chord width. The flatback profile is provided by a flatback profile component30which connects the upwind side shell part24to the downwind side shell part26. In the present embodiment, the flatback profile component30extends substantially along the entire length of the trailing edge20, however in other embodiments, the flatback profile component30may extend at least along 10%, 20%, 30%, 40%, 50%, 60%, or 70% of the distance from the root end17to the tip end15of the wind turbine blade assembly10. Details of this flatback profile component30and the method for manufacturing the wind turbine blade assembly10will be explained in more detail with reference to the following drawings.

FIG.4shows a flatback airfoil profile of the wind turbine blade assembly10in a cross-section perpendicular to the longitudinal axis L along lines I-I shown inFIG.3. The wind turbine blade assembly10comprises the upwind blade shell part24, the blade shell part26, and the flatback profile component30which were formed as separate components. The blade shell parts24,26has been joined at a trailing portion21of the blade shell parts24,26to form an integral blade shell24,26which will be discussed in more detail in connection withFIG.6. A leading portion19of the blade shell includes the leading edge18of the blade assembly10and a trailing portion21of the blade shell24,26is covered by the flatback profile component30which shaped so as to provide the wind turbine blade assembly10with a flatback airfoil shape with a flattened trailing edge20.

FIG.5shows the trailing portion21of the blade shell24,26and the flatback profile component30in more detail. The trailing portion21of the blade shell24,26has an outwardly curving arc shape substantially in the shape of a C. This geometric shape sustains loads much better relative to a more typical airfoil with an aerodynamically sharp trailing edge which substantially has the shape of a >. The flatback profile component30has an upwind side31positioned substantially flush with the upwind shell side24, a downwind side32positioned substantially flush with the downwind shell side26, and a substantially planar flatback side33connected to the upwind side31at an upwind edge34and to the downwind side32at a downwind edge35. The flatback side33defines the trailing edge20of the wind turbine blade assembly10. The upwind edge34and the downwind edge35are aerodynamically sharp so that wind traversing the edges34,35substantially instantaneously separates from the respective flatback side33at the aerodynamically sharp edge34,35.

The blade shell parts are made of fibre-reinforced plastic, typically a thermoplastic or thermoset polymer with carbon or glass fibre-reinforcement, usually wrapped around a core, often of balsa wood, to form a sandwich structure. The flatback profile component30advantageously consist essentially of the same material as the blade shell parts24,26, however typically the flatback profile component30is formed as a non-sandwich structure. In particular, the thickness of the upwind31, downwind32, and/or the flatback side33of the flatback profile component30is/are usually equal to or less than the thickness of the blade shell24,26.

Typically, the upwind side31of the flatback profile component30is adhered to an outer surface25of the upwind shell side part24, and the downwind side32of the flatback profile component30is adhered to an outer surface27of the downwind shell side26. In other embodiments, the upwind31and downwind32side are plastic welded onto the respective outer surfaces25,27.

The blade shell24,26comprises a joint portion28having an upwind joint portion28aformed integrally with the upwind shell part24in one piece, a downwind joint portion28bformed integrally with the downwind shell part26in one piece, and a flange29extending in parallel by and slightly offset to the trailing portion21of blade shell parts24,26. The flange29adheres to an inner surface of the upwind joint portion28aand to an inner surface of the downwind joint portion28b, so as to structurally join the upwind shell part24to the downwind shell part26. In the present embodiment, the joint portion28is positioned at the trailing portion21, but in other embodiments, the joint portion28may be positioned away from the trailing portion21, for instance on the upwind or downwind side of the blade shell24,26.

FIG.6is a flowchart showing the steps of producing a wind turbine blade according to a detailed embodiment.

Firstly100, a blade shell24,26is provided, typically in an upwind blade shell part24and a downwind blade shell part26joined at a joint portion28. The blade shell24,26has an upwind shell side24, a downwind shell side26, a leading portion19defining a leading edge18, and a trailing portion21arranged opposite to the leading portion19and connecting the upwind shell side24with the downwind shell side26. The trailing portion21has an outwardly curving arc shape.

Secondly101, a flatback profile component30is provided. The flatback profile component30has an upwind side31, a downwind side32, and a flatback side33connecting the upwind side31with the downwind side32.

Thirdly102, the flatback profile component30is positioned to cover the trailing portion21of the blade shell24,26so that the flatback side33defines the trailing edge20of the wind turbine blade assembly10.

Fourthly103, the upwind side31of the flatback profile component30is attached, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, to the upwind shell side24, so that the upwind side31of the flatback profile component30is positioned substantially flush with the upwind shell side24.

Fifthly104, the downwind side32of the flatback profile component30is attached, preferably by thermoplastic welding, plastic welding, adhesive, and/or glue, to the downwind shell side26, so that the downwind side32of the flatback profile component30is positioned substantially flush with the downwind shell side26.

Due to the fact, that the blade shell24,26is manufactured in a different step than the flatback profile component30, the blade shell24,26can form the structural basis of many different wind turbine blade assemblies since a number of different flatback profile components30can be produced to correspond to different wind regimes.

The invention has been described with reference to preferred embodiments. However, the scope of the invention is not limited to the illustrated embodiments, and alterations and modifications can be carried out without deviating from the scope of the invention.

LIST OF REFERENCES