DK201970484A1 - Wind Turbine Blades - Google Patents

Abstract

In a first aspect of the invention, there is provided a method of making a wind turbine blade having a geometry tailored for a particular design objective. The method comprises: providing a main blade part shaped to define a main portion of an aerodynamic profile of the blade, the main blade part being adapted to connect to at least one edge module; and providing at least one edge module shaped to define an edge portion of the aerodynamic profile of the blade, the edge module being adapted to connect to the main blade part. The method further comprises connecting the at least one edge module to the main blade part to form the aerodynamic profile of the blade, and is characterized in that the method further comprises selecting the at least one edge module from a set of edge modules each having a different geometry, wherein the at least one edge module is selected based upon a particular design objective, such that the resulting aerodynamic profile of the blade has a geometry tailored for the particular design objective.

Description

DK 2019 70484 A1 1 Wind Turbine Blades Technical field The present invention relates generally to wind turbine blades, and more specifically to an improved method of making wind turbine blades and to wind turbine blades made according to the improved method. Background Modern utility-scale wind turbine blades are very large structures, in some cases having lengths of 80 metres or more. They are typically made from composite materials, such as glass-fibre reinforced plastic (GFRP), and are fabricated in large blade moulds shaped to define the complex geometry of the blades. A blade mould requires significant capital expenditure to produce and occupies a significant proportion of factory floor space. Accordingly, most blade manufacturing facilities tend to have only a small number of moulds, typically just one or two. Before a blade goes into production, a significant amount of research and development is required to determine the structural and aerodynamic properties of the blade. Most modern blades have an aerodynamic profile that transitions between a series of precisely-defined airfoil profiles along the length of the blade. The geometry is usually further complicated by twist and pre-bend. The geometry and dimensions of the blade are always a compromise between aerodynamic and structural constraints.

Wind turbine blades are usually designed to perform well in a wide range of conditions, since the operating conditions will vary markedly between different wind turbine sites. It would be desirable to use a blade designed for a particular wind class in a different wind class. Even within the same wind farm, the individual wind turbines may experience different operating conditions depending upon their location (‘pad’) within the farm. Accordingly, there remains room for further optimisation of the design of wind turbine blades to maximise their performance for a given site or to cater for particular constraints of a given site, such as the local climate conditions. However, the cost and size of the blade moulds, together with the significant lead time involved in building new moulds,

DK 2019 70484 A1 2 makes it economically prohibitive to modify the moulds or to produce further moulds once the blade design has been finalised.

Against this background, it is an object of the present invention to provide a new method — of making wind turbine blades that can readily accommodate changes in blade design.

Summary of the invention In a first aspect of the invention, there is provided a method of making a wind turbine blade having a geometry tailored for a particular design objective.

The method comprises: providing a main blade part shaped to define a main portion of an aerodynamic profile of the blade, the main blade part being adapted to connect to at least one edge module; and providing at least one edge module shaped to define an edge portion of the aerodynamic profile of the blade, the edge module being adapted to connect to the main blade part.

The method further comprises connecting the at least one edge module to the main blade part to form the aerodynamic profile of the blade, and is characterized in that the method further comprises selecting the at least one edge module from a set of edge modules each having a different geometry, wherein the at least one edge module is selected based upon a particular design objective, such that the resulting aerodynamic profile of the blade has a geometry tailored for the particular design objective.

The at least one edge module may comprise a trailing edge module shaped to define a trailing edge portion of the airfoil profile and/or a leading edge module shaped to define a leading edge portion of the airfoil profile.

Each edge module in the set may have a geometry optimised for a particular design objective and may result in the blade having a different aerodynamic performance in comparison to a baseline performance.

In cases where the main blade part is adapted to connect to a trailing edge module, the main blade part may define a leading edge portion of the airfoil profile.

In cases where the main blade part is adapted to connect to a leading edge module, the main blade part may define a trailing edge portion of the airfoil profile.

In other cases, the main blade part may be adapted to connect to both a leading edge module and a trailing edge module.

In such cases, the method may comprise selecting a trailing edge module from a set of trailing edge modules each having a different

DK 2019 70484 A1 3 geometry, and selecting a leading edge module from a set of leading edge modules each having a different geometry.

The set of edge modules may comprise a baseline edge module having a baseline geometry and one or more further edge modules having a geometry that differs from the baseline geometry. The geometry of the one or more further edge modules may differ from the geometry of the baseline edge module in terms of one or more of thickness, chord length, twist, curvature and camber.

One or more of the relative thickness, chord length, twist and camber of the resulting aerodynamic profile may be tailored for the particular design objective. The design objective may be to provide one or more of increased lift, reduced lift, reduced load, reduced thrust, reduced noise, optimised stall characteristics, optimised angle of attack, optimised wake effects.

The method may further comprise selecting the at least one edge module based upon site conditions at a location where the blade is to be installed. The method may further comprise selecting the at least one edge module based upon a pad location of a wind turbine within a wind farm.

In another aspect of the invention there is provided a wind turbine blade comprising a main blade part shaped to define a main portion of an aerodynamic profile of the blade, and an edge module shaped to define an edge portion of the aerodynamic profile, the edge module being connected to the main blade part such that the main blade part and the edge module in combination at least partially define an airfoil profile of the blade, wherein the edge module has a geometry that is tailored in accordance with a particular design objective.

In yet another aspect of the invention there is provided a kit of parts for producing a plurality of wind turbine blades having different geometries, the kit comprising a plurality of main blade parts each having substantially identical geometries and a plurality of edge modules, each adapted for connection to any of the respective main blade part, wherein each edge module has a different geometry tailored for a particular design objective.

In yet another aspect of the invention there is provided a blade production process for producing wind turbine blades having a range of different geometries. The blade

DK 2019 70484 A1 4 production process comprises: providing a main blade mould shaped to form a main part of an aerodynamic profile of the blade; producing a plurality of main blade parts using the main blade mould, the plurality of main blade parts being of substantially identical geometry and adapted to connect to a respective edge module; providing a set of edge modules each adapted to connect to a main blade part and shaped to define an edge portion of the aerodynamic profile of the blade, wherein each edge module has a different geometry optimised according to a particular design objective; and connecting each edge module to a respective main blade part to produce a plurality of wind turbine blades with different respective geometries, wherein each wind turbine blade has an aerodynamic profile optimised for a particular design objective.

The edge modules may be designed to tailor the lift coefficient of a blade such that it is optimised for a given site.

Alternatively, the edge modules may be designed to optimise other characteristics of the blade profile.

For example, the edge modules may be designed to optimise the lift to drag ratio.

A different edge module may be selected to change the design angle of attack and to reduce or increase lift and drag, depending upon the requirements.

For example, an edge module may be selected to provide a more slender airfoil design (where “more slender” means a smaller chord length) to minimise blade loads (i.e. a low load design). In other examples, a reduced camber may be selected to minimise blade loads, and a thinner trailing edge thickness may be selected to minimise noise.

The edge modules may also be designed to allow tailoring of the stall characteristics of the blade.

For example, edge modules may be designed that enable the blade to operate further from stall.

This can avoid stability issues, and/or may usefully provide a low-noise design (as the blade operates further away from stall), where site requirements require noise to be minimised.

Blade geometry may therefore be easily adjusted for different scenarios (e.g. different markets, different sites, different locations in the same wind farm etc.) by introducing edge modules of varying geometry that can be replaced depending on the scenario.

A number of different design scenarios may be envisaged where a baseline edge module could be substituted in the factory for a different shape module to achieve a particular effect.

Such design scenarios may include: performance boosting design; high wake performance; low noise design; optimised stall design; optimisation of the inboard section of modular blades; rotor stretch enabling.

Each of these scenarios will be briefly discussed below.

DK 2019 70484 A1 Performance boosting design — this may be used, for example, in cases where a site is under-loaded and could accept a more highly loaded blade design. In such cases, a relatively high-camber edge module may be selected for use near the tip of the blade to increase the camber towards the tip and thereby increase the induction and improve the 5 performance of the wind turbine. The edge modules therefore can be used to tailor the blade design to provide increased lift in regions of sub-optimal induction (load tailored blades). High wake performance — this may be used in cases where a site is subject to higher- than-normal wake losses. In such cases, some of the turbines in a wind farm could have their airfoil profiles modified using suitably-shaped edge modules to reduce the rotor thrust coefficient (Cr) to improve the overall performance of the wind farm. Accordingly, an edge module may be selected to provide a reduced rotor Cr for sites with high wake losses. Pad-specific tailoring may be used whereby only the turbines causing the highest losses are optimised in this way.

Low noise design — this may be used for sites that are noise constrained. In such cases, a trailing edge module of reduced thickness, in particular having a reduced thickness at the trailing edge thereof, may be selected to provide a more noise optimised airfoil profile. Alternatively, or additionally, a de-cambered edge module may be selected for optimal noise performance. Such low-noise designs may come at the cost of a slight reduction in annual energy production (AEP) in comparison to the baseline design. Optimised stall design - this may be used in situations where a given blade is operating too close to stall. In such cases, an edge module could be selected that either increases the margin to stall or that reduces the aggressiveness of the stall angle. Therefore, suitably-designed edge modules may be used to tailor the stall characteristics of the blade for stability improvements.

Shape constrained rotor — edge modules may be used to re-optimise split blades, where the blade shape is constrained by splits in the blade mould. Split blades are formed of spanwise-extending blade modules that are joined end-to-end. These blade modules must have the same aerodynamic profile at the blade joint in order to fit together. However, this profile shape may not be optimal for one or both of the modules. A — suitably-shaped edge module can be selected to re-optimise the shape of one or both modules without affecting the main mould tooling, and without affecting the structural

DK 2019 70484 A1 6 joint between blade modules.

For example, an edge module may be selected to change the effective twist distribution.

It is known for split blades to use a standard inboard module in conjunction with tip modules of different lengths.

In such cases, the inboard module may be designed to incorporate interchangeable edge modules such that an edge module can be selected to optimise the angle of attack for the inboard blade module depending upon the selection of the tip module.

Rotor stretch enabling — it is known to increase the length of an existing wind turbine blade by using a longer tip, for example a tip extension or longer outboard tip module in the case of a split blade.

However, there may be cases where the amount of stretch is limited by the loads of the blade in-board of the tip region.

In this case these inboard regions could be "de-loaded" by adjusting the aerofoil characteristics to potentially enable the rotor stretch.

Accordingly, edge modules on inboard sections of a blade may be selected to provide a reduced load, for example by reducing the design angle of attack on these parts.

By de-loading inboard sections of a blade, edge modules can be used to permit rotor stretches that may otherwise not have been possible.

The edge modules in this scenario may therefore be selected for a low load design.

The edge modules described herein may preferably be made from a thermoplastic material.

Examples of suitable thermoplastic materials include, without limitation, polyethylene, polyetheretherketone (PEEK), thermoplastic polyurethane, thermoplastic polyester, acrylic, ABS, Nylon and polyvinyl chloride (PVC). The edge modules may be formed using any suitable manufacturing method, but may preferably be injection moulded.

Injection moulding is advantageous because it is a relatively inexpensive process, with relatively low tooling costs, and provides highly accurate parts, with low dimensional tolerances.

If additional strength is required, the edge modules may be reinforced with fibres, for example with chopped glass fibres.

This can be achieved as part of an injection moulding process.

Alternatively, if very high strength is required, the edge modules may be moulded from the same materials as the main blade part, e.g. from fibre-reinforced plastic (FRP). The main blade part may preferably provide all, or at least a majority, of the structural strength of the blade.

The main blade part may preferably comprise a shell made from composite materials, for example FRP, such as glass-fibre reinforced plastic (GFRP) and/or carbon-fibre reinforced plastic (CFRP). The main blade part may include one or

DK 2019 70484 A1 7 more spar structures, such as a box spar, spar caps, shear webs etc, all of which will be familiar to the skilled person. The shell of the main blade part may preferably be made in a main blade mould. The main blade part may be moulded using any suitable composite fabrication technique suitable for making wind turbine blades. Such techniques may include vacuum-assisted resin transfer moulding (VARTM), resin infusion, resin transfer moulding etc. These techniques are all commonly used for manufacturing wind turbine blades, and are well known to persons skilled in the art.

Optional features described above in relation to a particular aspect of the invention are equally applicable to other aspects of the invention, repetition of such features is avoided purely for reasons of conciseness.

— Brief description of the drawings Embodiments of the present invention will now be described by way of non-limiting example only, with reference to accompanying figures, in which: Figure 1 is a schematic perspective view of a wind turbine blade comprising a main blade part and a trailing edge module; Figure 2 is a schematic cross-sectional view of a wind turbine blade, showing a main blade part and a trailing edge module connected to the main blade part; Figure 3 is similar to Figure 2, but shows a set of trailing edge modules having various geometries; Figure 4 is an illustrative plot of the lift coefficient (C.) versus angle of attack (a) for two of the profiles shown in Figure 3; Figure 5 is a schematic cross-sectional view of a wind turbine blade comprising a main blade part and a leading edge module; and Figure 6 is a schematic cross-sectional view of a wind turbine blade comprising a main blade part, a trailing edge module and a leading edge module.

DK 2019 70484 A1 8 Detailed Description Figure 1 is a schematic perspective view of a wind turbine blade 10 comprising a main blade part 12 and an edge module 14 connected to the main blade part 12. In this example, the edge module 14 is a trailing edge module 14a. The blade extends in a spanwise direction (S) between a root end 16 and a tip end 18, and in a chordwise direction (C) between a leading edge 20 and a trailing edge 22. In the example shown in Figure 1, the edge module 14 extends along a spanwise portion of the blade 10 outboard — of the blade shoulder 23. In other examples, an edge module 14 may extend along a different spanwise portion of the blade 10, and may, for example, extend further inboard to encompass the blade shoulder 23 and/or root of the blade 10. In yet other examples, the edge module 14 may extend along substantially the entire length of the blade 10. The blade 10 may be considered as a modular blade 10, wherein the main blade part 12 constitutes a main blade module 12 to which an edge module 14 is connected.

Figure 2 is a schematic cross-sectional view of the wind turbine blade 10 comprising a main blade part 12 and a trailing edge module 14a as shown in Figure 1. The main blade part 12 is adapted to connect to the edge module 14a. To this end, the main blade part 12 may comprise a connection part 24 such as a flange, which may project from a rear edge 26 of the main blade part 12. Likewise, the edge module 14a is adapted to connect to the main blade part 12. To this end, the edge module 14a may comprise a corresponding connection part 28, such as a slot or mouth, which fits over the flange 24.

The edge module 14a is preferably adhesively bonded to the main blade part 12. In this example, the edge module 14a is adhesively bonded to the flange 24. In other examples, any suitable means of attachment may be provided between the main blade part 12 and the edge module 14a, e.g. mechanical fasteners, interference fit etc.

The main blade part 12 is shaped to define a main portion 30 of an aerodynamic profile 32 of the blade 10. The edge module 14a is shaped to define an edge portion 34 of the aerodynamic profile 32 of the blade 10. The edge module 14a is connected to the main blade part 12 to complete the aerodynamic profile 32 of the blade 10. The aerodynamic profile 32 of the blade 10 is therefore defined in part by the geometry of the main blade part 12, and in part by the geometry of the edge module 14a.

DK 2019 70484 A1 9 When the edge module 14a is attached to the main blade part 12, the main blade part 12 and the edge module 14a together define an airfoil profile 32 in cross section. A chord line Chis shown in Figure 2, which extends in a straight line between the leading edge 20 and the trailing edge 22. A camber line Ca is also shown, which is a line or curve that is equidistant from upper and lower surfaces 32a, 32b of the airfoil profile 32. Both the chord Ch and camber Ca of the profile 32 are influenced by the geometry of the edge module 14a as well as the geometry of the main blade part 12. Similarly, the relative thickness of the profile 32 is determined by the geometry of the edge module 14a, and the twist and general curvature of the blade 10 can also be influenced by the geometry of — the edge module 14a.

The main blade part 12 preferably comprises a majority of the aerodynamic profile 32 of the blade 10. Conversely, the edge module 14a preferably comprises a minority of the aerodynamic profile 32 of the blade 10. The vertical line T in Figure 2 represents a surface transition 36 between the main blade part 12 and the trailing edge module 14a. Preferably, this surface transition 36 is located at a distance X from the leading edge 20 which is in the range of 60% to 80% of the length of the profile chord Ch (i.e. X/Ch = 60% to 80%).

In this example, the main blade part 12 defines the leading edge 20 of the blade 10, and the trailing edge module 14a defines the trailing edge 22. In another example, the edge module 14 may be a leading edge module 14b, and the main blade part 12 may define the trailing edge 22 (see Figure 5). In yet another example, the blade 10 may comprise both a trailing edge module 14a and a leading edge module 14b connected to a main blade part 12 (see Figure 6). In this case, the trailing edge module 14a defines the trailing edge 22, and the leading edge module 14b defines the leading edge 20. In all examples, the edge module(s) 14 may extend along the whole or part of the blade 10. Furthermore, the edge module(s) 14 may be formed as a single unit, or as a plurality of spanwise-extending sections.

Referring now to Figure 3, this schematically shows a set of three different trailing edge modules 14a, which may be connected, interchangeably, with the main blade part 12. Each trailing edge module 14a has a different geometry. Specifically, in this example, there is a baseline trailing edge module 14ai, which corresponds to the trailing edge module 14a shown in Figure 2. There is also a high-camber trailing edge module 14aii, and a de-cambered trailing edge module 14aiii. Each trailing edge module 14a is

DK 2019 70484 A1 10 adapted in the same way to connect to the main blade part 12. Specifically, in this example, each module 14a includes a similar slot or mouth 28 shaped to fit over the flange 24.

As mentioned above, the geometry of the trailing edge module 14a affects the overall geometry of the airfoil profile 32. When the baseline trailing edge module 14ai is connected to the main blade part 12, the resulting airfoil profile 32 has a baseline profile, with a baseline camber. When the high-camber module 14aii is connected to the main blade part 12, the resulting airfoil profile 32 (referred to as a ‘high camber profile’) has a comparatively higher camber than the baseline profile. Conversely, when the de- cambered module 14aiii is connected to the main blade part 12, the resulting airfoil profile 32 (referred to as a ‘low camber profile’) has a comparatively lower camber than the baseline profile.

— Each of the different airfoil profiles 32 has different attributes and different performance characteristics. The baseline profile 32 may be designed as a default profile that provides good performance in most circumstances. However, the ability to select from a range of different edge modules 14 allows individual blades 10 to be tailored according to specific requirements. For example, blades 10 may be customised for a particular site (referred to as ‘site specific tailoring’) or even the blades 10 of different turbines in a wind farm may be customised for their particular position within said wind farm (referred to as ‘pad specific tailoring’).

Referring now to Figure 4, this shows an illustrative plot of the lift coefficient (CL) versus angle of attack (a) for the baseline profile (solid line) shown in Figure 3, and for the high camber profile (dashed line) shown in Figure 3. It can be seen that the high camber profile has a higher maximum lift coefficient (Cv) than the baseline profile. In addition, the maximum lift coefficient (Cv) of the high camber profile occurs at a lower angle of attack (a) than the maximum lift coefficient of the baseline profile. Therefore, the high-camber trailing edge module 14aii shown in Figure 3 may be selected to achieve an increased lift coefficient (Cv). This high thrust / high performance design may be selected, for example, when wake effects are not important. This might be the case, for example, when wind turbines of a wind farm are arranged in a single row alongside one another. In such cases, there are no downstream turbines to consider.

DK 2019 70484 A1 11 Whilst the edge modules 14a shown in Figure 3 each have a different camber line (not shown), in other examples a set of edge modules 14 may be designed that differ in other respects. For example, thickness, slenderness, chordwise dimensions, curvature, and/or twist are all parameters of the edge modules 14 that may be used to tailor the aerodynamic characteristics of the wind turbine blade 10. In the case of the leading edge module 14b, a set of leading edge modules 14b can be designed so that performance of the blade 10 is optimised by changing the profile of the leading edge 20. In an example, a radius of the leading edge 20 can be increased so that the blade 10 is less sensitive to leading edge roughness (e.g. soling, erosion or manufacturing defects). The leading edge modules 14b can also be designed so that a leading edge on each module is at a given position on each of the modules 14b, so that the lift and drag characteristics of the blade 10 will be altered.

A particular advantage of wind turbine blades 10 comprising edge modules 14 as described above, is that it is possible to produce blades 10 having a tailored or customised profile 32 using a single main blade mould, without requiring modifications to the main blade mould. This is because all of the possible blade profiles 32 utilise the same main blade part 12, with just the edge module(s) 14 being used to provide the requisite tailoring of the blade geometry. The tooling costs for the edge modules 14 represent only a fraction of the tooling costs for the main blade parts 12. Therefore, producing blades 10 comprising edge module(s) 14 does not require significant additional capital expenditure in tooling and hence provides an economically efficient process for producing tailored/customised wind turbine blades 10. As only a single main blade mould is required, tailored blades 10 can be produced without requiring additional factory floor space to house additional blade moulds.

The ability to tailor the shape of a blade 10 by selecting edge modules 14 of different shapes provides a significant amount of flexibility to the blade production process.

Previously, once the blade design had been fixed and the mould tooling produced, it would not have been possible to modify the profile 32 of the blade 10. The above described method allows the blade design to be adapted to site requirements and to customer requirements even after the main blade design is fixed and after the main mould tooling has been created.

Claims (12)

DK 2019 70484 A1 12 Claims

1. A method of making a wind turbine blade having a geometry tailored for a particular design objective, the method comprising: providing a main blade part shaped to define a main portion of an aerodynamic profile of the blade, the main blade part being adapted to connect to at least one edge module; providing at least one edge module shaped to define an edge portion of the aerodynamic profile of the blade, the edge module being adapted to connect to the main blade part; and connecting the at least one edge module to the main blade part to form the aerodynamic profile of the blade, characterised in that the method comprises: selecting the at least one edge module from a set of edge modules each having a different geometry, wherein the at least one edge module is selected based upon a particular design objective, such that the resulting aerodynamic profile of the blade has a geometry tailored for the particular design objective.

2. The method of Claim 1, wherein the at least one edge module comprises a trailing edge module shaped to define a trailing edge portion of the airfoil profile and/or a leading edge module shaped to define a leading edge portion of the airfoil profile.

23. The method of Claim 1 or Claim 2, wherein the set of edge modules comprises a baseline edge module having a baseline geometry and one or more further edge modules having a geometry that differs from the baseline geometry.

4, The method of Claim 3, wherein the geometry of the one or more further edge modules differs from the geometry of the baseline edge module in terms of one or more of thickness, chord length, twist, curvature and camber.

5. The method of any preceding claim, wherein one or more of the thickness, chord length, twist and camber of the resulting aerodynamic profile is tailored for the particular design objective.

DK 2019 70484 A1 13

6. The method of any preceding claim, wherein each edge module in the set has a geometry optimised for a particular design objective and results in the blade having a different aerodynamic performance in comparison to a baseline performance.

7. The method of any preceding claim, wherein the design objective is to provide one or more of increased lift, reduced lift, reduced load, reduced thrust, reduced noise, optimised stall characteristics, optimised angle of attack, optimised wake effects.

8. The method of any preceding claim, further comprising selecting the at least one edge module based upon site conditions at a location where the blade is to be installed.

9. The method of any preceding claim, further comprising selecting the at least one edge module based upon a pad location of a wind turbine within a wind farm.

10. A wind turbine blade comprising a main blade part shaped to define a main portion of an aerodynamic profile of the blade, and an edge module shaped to define an edge portion of the aerodynamic profile, the edge module being connected to the main blade part such that the main blade part and the edge module in combination at least partially define an airfoil profile of the blade, wherein the edge module has a geometry that is tailored in accordance with a particular design objective.

11. A kit of parts for producing a plurality of wind turbine blades having different geometries, the kit comprising a plurality of main blade parts each having substantially identical geometries, and a plurality of edge modules each adapted for connection to any of the respective main blade parts, wherein each edge module has a different geometry tailored for a particular design objective.

12. A blade production process for producing wind turbine blades having a range of different geometries, the blade production process comprising: a) providing a main blade mould shaped to form a main part of an aerodynamic profile of the blade; b) producing a plurality of main blade parts using the main blade mould, the plurality of main blade parts being of substantially identical geometry and adapted to connect to a respective edge module; c) providing a set of edge modules each adapted to connect to a main blade part and shaped to define an edge portion of the aerodynamic profile of the blade, wherein

DK 2019 70484 A1 14 each edge module has a different geometry optimised according to a particular design objective; and d) connecting each edge module to a respective main blade part to produce a plurality of wind turbine blades with different respective geometries, wherein each wind turbine blade has an aerodynamic profile optimised for a particular design objective.