Method for creating a transition from the edge of an additional part mounted on the outer surface of a rotor blade

Abstract

Method for creating a transition from the edge of an additional part mounted on the outer surface of a rotor blade. The invention describes a method for creating a transition from the edge (3E) of an additional part (3) mounted on the outer surface (2) of a rotor blade (1), the method comprising the following steps: - defining, with a thin and smooth masking tape (8), the application area on the rotor blade surface (2) and on the additional part (3) to be covered with a sealant compound (LS), - dispensing the sealant (LS) on the application area, - performing the distribution of the sealant (LS), - removing the masking tape (8), - smoothing the sealant (LS) transition step with a flexible tool (7). The invention further describes a corresponding wind turbine rotor blade.

Description

TECHNICAL FIELD

[0001] A method for creating a transition from the edge of an additional part mounted on the outer surface of a rotor blade, i.e. providing an edge seal for a rotor blade add-on, or a method for edge sealing of a wind turbine blade is described. In particular, the present invention relates to an aerodynamic edge seal for a step on the surface of a wind turbine blade and a method of applying such an edge seal. BACKGROUND

[0002] The aerodynamic performance of a wind turbine rotor blade is highly sensitive to surface imperfections, especially surface imperfections in close proximity to the leading edge of the rotor blade. This poses a challenge when there is a step or obstacle on the surface of the rotor blade, for example after applying a leading edge protection (LEP) cover, also known as a corrosion protection cover, and / or vortex generator (VG) panels, trailing edge (TE) panels, for example serrated trailing edge panels, spoiler plates mounted on the panels and placed on the blade surface, etc. The LEP cover is also known as a corrosion protection cover or LEP shell. The step or obstacle present on the surface due to leading edge protection is especially a problem for more intrusive solutions like protection covers or protection tapes attached to the blade surface.

[0003] There can be a sharp step at the edge of a panel or cover attached to a rotor blade, for example a leading edge protection cover. This sudden height difference causes the airflow to transition from laminar to turbulent, which will negatively impact the annual energy production (AEP) of the wind turbine and can also contribute to wind turbine noise.

[0004] It is known from the prior art to grind the edge of an already mounted add-on to a slope or bevel in order to reduce the AEP (annual energy production) impact. However, this grinding procedure is time-consuming and cost-intensive. In addition, it is difficult to obtain a uniform edge along the entire edge of the add-on, for example a cover or plate or panel, and there is a risk of grinding into the rotor blade itself. The grinding procedure can also be difficult to perform as the material of the add-on can be flexible and thus difficult to grind.

[0005] Another way to reduce the turbulence caused by the step along the edge of the add-on is to manufacture the add-on with a thin edge. However, mounting an add-on such as a LEP cover with a long thin edge can cause wrinkling along the edge, which contributes to scrap costs and reduces the aerodynamic performance.

[0006] In another approach, the add-on such as a LEP shell can be manufactured to fit into a built-in recess on the blade surface. However, this approach is associated with strict requirements regarding production tolerances and quality and significantly increases the manufacturing costs while also being more prone to defects.

[0007] The edges of the sealing front edge protection tape are further known. The purpose of the sealing is to smooth the edges of the tape and to protect them. No aerodynamic performance requirements are made for this tape sealing. SUMMARY

[0008] It is therefore the object of the present invention to provide a way to overcome the negative impact of the additional part on the aerodynamic performance of the rotor blade.

[0009] This object is achieved by the method for creating a transition from the edge of an additional part mounted on the outer surface of a rotor blade according to claim 1 and by the wind turbine rotor blade according to claim 12.

[0010] As mentioned above, the shell or panel edge creates a transition step between e.g. the shell and the blade surface when mounted on the blade. This will cause a disturbance of the airflow across the blade and thus accordingly induce an aerodynamic performance decrease as well as possible noise generation. In order to maintain the best performance and lower acoustic impact of such a transition step, a smooth surface finish is required at such an interface.

[0011] The method for creating a transition from the edge of an additional part mounted on the outer surface of a rotor blade according to the present invention, especially for providing such a smooth surface finish, comprises the following steps:

[0012] - defining the application area on the rotor blade surface and on the additional part to be covered by the sealant compound with a thin and smooth masking tape,

[0013] - dispensing the sealant on the application area,

[0014] - performing the distribution of the sealant,

[0015] - removing the masking tape,

[0016] - smoothing the sealant transition step with a flexible tool.

[0017] As will be further explained below, the term "sealant" can also be interpreted as "adhesive".

[0018] By way of example, the method preferably comprises the use of the following tools:

[0019] a toothed squeegee, preferably made of a flexible material, for levelling the sealing agent or adhesive sealant material after it has been dispensed to the sealed application area on the blade / panel (additional part).

[0020] A second doctor, made for example from a flexible material (e.g. silicone material) characterized by a Shore A hardness of 30 to 80, preferably 40 to 60, having a cross sectional profile adapted to the application. A low energy surface (surface free energy) preventing adhesion of the sealing material would provide a further advantage, but is not a prerequisite. The angle between the soft doctor and the blade surface at the point of contact with the blade surface (during use) should (will) be lower than in the case of a hard doctor.

[0021] The application process is designed to minimize and ideally prevent AEP loss due to steps between the blade surface and the attached and bonded cover / plate.

[0022] The method for creating such a transition from the edge of the plate / cover (add-on) to the blade surface comprises the following steps:

[0023] - Defining the area on the blade surface and the plate / cover (add-on) to be covered by the adhesive / sealant compound with a thin and smooth masking tape, for example having a thickness of less than 0.2 mm.

[0024] - Dispensing the adhesive / sealant, for example by bead or spray application or by roller application or using the so-called "spinning flow" process. By way of example, applying the adhesive / sealant in a serpentine line overlapping (25 / 50 or 20 / 50) the transition on both the plate / cover (add-on) and the blade surface and in straight lines along the plate / cover (add-on) and / or on the blade surface.

[0025] - Carrying out the adhesive / sealant distribution, for example using a flexible toothed doctor blade.

[0026] - (Optional) Smoothing the adhesive / sealant with a preferably flexible tool moving in the longitudinal direction of the blade. The tool is preferably designed to meet the profile of the blade, for example having a curvature matching the curvature of the blade leading edge profile.

[0027] - Removing the masking tape.

[0028] - After removal of the masking tape, smoothing the adhesive / sealant transition step with a (flexible) tool, for example preferably the same as in the two steps above. This leads to a further reduction of the step height between the adhesive / sealant and the blade surface.

[0029] Thus, if a plate / cover (add-on) is mounted on a blade with the edge seal described herein, i.e. using the edge seal design and its creation method, a wind turbine comprising a blade with an add-on attached thereon, such as a plate / cover (add-on), will benefit, for example in terms of performance.

[0030] Thus, the invention describes a method of providing an edge seal along a longitudinal edge of an additional piece mounted on an outer surface of a rotor blade.

[0031] Additionally, the inventors of the present invention have found that a seal width set between 2 to 5 millimeters is not sufficient to achieve the aforementioned improvement of the aerodynamic performance of a wind turbine and have provided other ranges in accordance with their findings.

[0032] For example, a flexible protective cover having a limited thickness is applied on the leading edge, but the general idea is applicable to any kind of step on the surface of a wind turbine blade, such as vortex generator panels, trailing edge panels or covers, sensors mounted on a plate, etc.

[0033] In the context of the present invention, the longitudinal edge at the additional piece can be assumed to have the appearance of an abrupt step. When using the inventive method of mounting the additional piece to the rotor blade, it is not necessary to manufacture the additional piece with a longitudinal edge that is gradually thinner, so that the manufacturing of such additional pieces can advantageously be economical. Since the additional piece is typically attached or bonded to the rotor blade in some way (e.g. by an adhesive bonding layer, including in particular a double-sided pressure sensitive adhesive tape), the height at the longitudinal edge of the additional piece can be assumed to include the height of the additional piece at that longitudinal edge as well as the height of any adhesive layer used to bond the additional piece to the rotor blade.

[0034] One main aspect in all embodiments is the extent of the edge. Theoretically, it can have a long extent on a flat surface, but practically, the length of the extent can be limited, since it obviously becomes thinner further away from the shell edge.

[0035] The improved step finish solution minimizes the AEP loss potentially to a negligible impact compared to a rotor blade without an edge seal, and also significantly reduces any noise generated when the rotor blade is in operation.

[0036] The edge seal width can be understood as extending outwardly from the longitudinal edge of the additional piece. Since the edge seal width is significantly larger than the additional piece height, the improved edge seal advantageously reduces or even eliminates the AEP loss associated with the additional piece. The edge seal obtained by the inventive method also significantly reduces the noise generation of the wind turbine blade when the wind turbine is in operation compared to a rotor blade along which a piece such as a LEP cover is not provided with such an edge seal.

[0037] The inventive method can be used during the manufacturing of a wind turbine rotor blade and also when maintaining, repairing or upgrading already installed rotor blades, e.g. for attaching a leading edge protection cover and / or a vortex generator panel, a trailing edge panel (e.g. a serrated trailing edge panel), or a spoiler mounted on a panel and placed on the surface of the blade as a retrofit solution for an existing blade. The inventive method can likewise be applied to existing blade add-ons, for which the contribution to the AEP will be improved when provided with the inventive edge seal.

[0038] According to the present invention, a wind turbine rotor blade comprises at least one additional part mounted to the outer surface of the rotor blade, and such an "extended" edge seal as described above formed along at least one longitudinal edge of the additional part.

[0039] A wind turbine rotor blade according to the present invention comprises at least one additional part mounted to the outer surface of the rotor blade, and an edge seal formed with the method according to the present invention.

[0040] In summary, the present invention relates to a wind turbine blade comprising a protective cover or plate or panel or other kind of additional part attached to the surface of the blade, especially along the longitudinal extension of the blade. The additional part is typically attached by an adhesive. An edge sealer is placed at the outer edge of the additional part (cover, panel, plate) on the surface of the blade, either overlapping or not overlapping the additional part.

[0041] Particularly advantageous embodiments and features of the present invention are given by the dependent claims, as disclosed in the following description. Features of different claim categories can be combined as appropriate to give further embodiments not described herein.

[0042] In this description, without limiting the invention in any way, the term "additional part" can be understood to mean any of a protective cover, plate or panel attached to the surface of the blade, especially along the longitudinal extension of the blade. The terms "edge seal" and "edge sealer" are used interchangeably.

[0043] The tool kit can be used to apply the sealant material, whether or not the sealant material is formed to overlap the additional part edge or step, comprising several spatulas with different properties. In a preferred embodiment of the invention, the step of forming an edge sealer comprises the steps of depositing the sealant material onto the surface of the rotor blade at least alongside the longitudinal edge of the additional part. The sealant material is then spread in the area delimited by the longitudinal edge of the additional part and the chosen edge sealer width, using a preliminary spatula. The preliminary tool preferably has a flexibility and shape that facilitates the initial spreading of the sealant.

[0044] In a subsequent step, a finishing doctor is used to finish the shape of the sealant spread by the preliminary tool. Preferably, the finishing tool has a lower hardness than the preliminary tool.

[0045] A preferred finishing doctor comprises several grooves running parallel to the tip of the doctor (perpendicular to the smoothing direction), particularly preferably on the side of the doctor that is intended to come into contact with the sealing material. Preferably, at least one groove is in the front half of the doctor, where the contact area is located. The advantage of these grooves is that the doctor is rigid in the direction of the grooves, but can easily be bent when sweeping over the surface. For better grip, a preferred finishing doctor has two fins at the opposite end of the tip, wherein the fin at the contact area side is preferably thinner than the fin at the other side. The rear half of the doctor (i.e. the part where the doctor is held) can be more rigid than the other part, and can in particular comprise another material than the other part.

[0046] The inventive method can preferably comprise the step of using a smooth, thin masking tape to define the area of the intended edge seal. One tape can extend a distance outwardly from the edge step along the outer edge of the intended edge seal. The distance is at least 20 times the edge step height. The thickness of the tape is as small as possible, preferably at most 0.2 mm. The other boundary of the edge seal can be defined by the edge step. Alternatively, if an overlap is to be formed on the edge step, a second tape can be applied to the surface of the add-on parallel to the longitudinal edge of the add-on. Then, the sealant is applied within these boundaries. The sealant can initially be roughly deposited on the rotor blade (and add-on), e.g. in the form of a bead from a dispenser nozzle, by spraying or another suitable method. Then, a preliminary shaping tool (e.g. a flexible, toothed doctor blade) is used to spread the roughly applied sealant.

[0047] Thus, according to a preferred method, the distribution of the sealant is achieved by using a toothed doctor blade, preferably made of a flexible material, for levelling the sealant after it has been dispensed to the application area, preferably wherein the teeth of the toothed doctor blade have a distance of between 1 and 2 mm and / or a height of between 0.2 and 5 mm.

[0048] The spreading can be done by guiding a toothed doctor blade along the longitudinal direction of the rotor blade surface between the border of the edge seal. After this preliminary step is done, one or more adhesive tapes are removed. Then, the still liquid sealant is smoothed to its final shape by dragging a softer flexible doctor blade over the spread sealant. This finishing or smoothing step with a second tool serves to further reduce the height of the "wedge" of the edge seal between the edge step and the outer border of the edge seal. The second flexible doctor blade is preferably made of a material such as silicone to ensure a relatively low Shore A hardness (e.g. 50 ± 10).

[0049] According to a preferred method, the flexible tool is a second doctor blade having a Shore A hardness between 30 and 70, in particular between 40 and 60, in particular between 48 and 52. The preferred Shore A hardness is preferably greater than 30, in particular greater than 40, in particular greater than 45, and / or the preferred Shore A hardness is preferably less than 70, in particular less than 60, in particular less than 55.

[0050] According to a preferred method, the flexible tool comprises a silicone material, preferably having a cross-sectional profile adapted to the application and a low-energy surface preventing the sealant from sticking.

[0051] According to a preferred method, the flexible tool comprises a tip at which the intended contact area with the sealant is present, and preferably a number of grooves running parallel to the tip (perpendicular to the smoothing direction). The advantage of these grooves is that the finishing doctor blade is rigid in the direction of the grooves, but can easily bend when swept over the surface. For better grip, the preferred finishing doctor blade has two fins at the opposite end of the tip, wherein the fin at the contact area side is preferably thinner than the fin at the other side.

[0052] According to a preferred method, the masking adhesive tape has a thickness of less than 0.2 mm. The advantage of this is that the sealant edge to be minimized is small during the finishing step.

[0053] According to a preferred method, the dispensing of the sealant is achieved by bead or spray application, preferably by applying the sealant in a serpentine line on both the add-on and the blade surface overlapping the transition, in particular 25 / 50 or 20 / 50 overlapping the transition, or in a straight line on the add-on and / or the blade surface.

[0054] According to a preferred method, after the distribution of the sealant and after the removal of the masking adhesive tape, the sealant is smoothed with a tool moving in the longitudinal direction of the blade, preferably with a flexible tool (as mentioned above), wherein the tool is preferably designed to meet the profile of the blade, in particular having a curvature matching the curvature of the blade leading edge profile.

[0055] A sealing formulation (sealant) or adhesive is used to form an edge seal along one or more edges (edge step) of the add-on, with or without overlap, as will be explained below. The geometry of the edge seal is adjusted and optimized in order to reduce the aerodynamic impact of the step due to the interfacing surface (i.e. the front edge solution). The terms "sealant", "edge sealant" and "sealing formulation" can be used to refer to such an adhesive. Preferably, the adhesive used to fix the add-on comprises the same material as the edge sealant, or vice versa. Thus, the sealant can be an adhesive, which is not necessary in each case. In this application, the term "sealant" also includes the term "adhesive".

[0056] Preferably, the seal is formed using a specific liquid sealant (especially adhesive material) which solidifies at a certain time after application and which, while being liquid, has a specific rheology (especially adhesive viscosity) which provides a good balance between sag resistance and flowability. The rheological properties and specific viscosity of the sealant are preferably tailored to the specific geometry and position of the seal. On the one hand, the viscosity must be low enough to allow the sealant to spread easily and to run off any streaks that can occur during spreading. But, on the other hand, the yield point (sag resistance) of the sealant must be high enough to avoid gravity-induced running off of the sealant, which would adversely affect the seal profile created by the application process.

[0057] Preferably, the solidified sealant is (highly) flexible, abrasion resistant and preferably adheres well to the surface on which it is applied and also has good resistance to UV light exposure.

[0058] In general, any liquid sealant material which solidifies after application by either a physical process, a chemical reaction or a combination of both is suitable for the purpose of the present invention. Reactive two-component sealants are preferred due to their faster curing response and thus faster occurring process. Preferably, physically hardening sealants (such as hot melt sealants which become firm when cooled) and / or sealants which cure by chemical reaction can be used. From the group of chemically curing sealants, two part sealants are preferred due to their faster curing response and thus faster occurring process.

[0059] It is preferred to use a sealant having such a solidification speed (open time) which on the one hand allows sufficient time for the application process, i.e. dispensing, levelling and creating the profile according to the application. On the other hand, in order to shorten the process time, a fast curing allowing further processing as quickly as possible is preferred. Here, in particular, chemically cross-linking two-component adhesives offer an advantage, especially since their curing can be accelerated after the profile according to the application has been formed by moderate heating (for example by means of an IR emitter), thus allowing further reduction of the process time.

[0060] Exemplary materials can be epoxy resins, polyurethanes, polyureas, silicones, silane modified polymers (SMP), methyl methacrylate (MMA) and hybrid solutions etc. selected in view of the desired properties in the liquid or solidified state, especially in view of the sag resistance and flowability as indicated above. For example, the sealant material can be selected to have a specific adhesive viscosity which provides a good balance between sag resistance and flowability as well as a highly flexible, thus high fatigue resistance in its solidified state. The integrity of the edge seal formed along the longitudinal edge of the LEP using such a material will not suffer from the repeated torsional bending of the rotor blade.

[0061] Preferably, a two-component sealant material is used, wherein the two components are mixed by means of a static or dynamic mixer just before application on the surface of the blade, wherein preferably the viscosity of the two components is between 40.000 - 110.000 mPas for the first component and between 100.000 - 380.000 mPas for the second component. However, sealants showing different viscosities can also be suitable as long as the rheological properties are well balanced.

[0062] The surface tension of the preferred sealant is lower than the surface free energy of the surface on which it is applied in order to allow (as a prerequisite for the formation of adhesive forces) sufficient wetting of this surface. Increasing the surface free energy by suitable methods such as but not limited to cleaning, abrasion, application of primers or adhesion promoters, and activation methods such as but not limited to plasma activation, corona activation, flame activation, VUV (vacuum-ultraviolet) is explicitly part of the application. In addition to the above-mentioned ability to wet the surface, good adhesion of the adhesive / sealant to the blade surface and the respective add-on also contributes to meeting the demanding requirements regarding service life, especially under the harsh conditions of offshore installations.

[0063] In addition to good adhesion, the mechanical properties of the sealant are also important. Both high resistance to weathering, which is required to withstand rain erosion conditions, and sufficient fatigue strength to withstand blade vibrations during operation. Thus, the preferred sealant has sufficient resistance to peel forces occurring on the respective surface over the entire service life of the blade, in particular peel forces greater than 2 N / mm. The test method for long-term resistance is, for example, the procedure described in ISO 20340.

[0064] Since the possible range of applications of the seal as subject matter of the present invention is very broad, the sealant is preferably customized for the respective application in terms of the materials involved, the size of the respective add-on and its position on the blade.

[0065] The tensile strength (according to DIN EN ISO 527) of the preferred sealant is greater than 4 MPa and / or less than 8 MPa, particularly preferably 5 MPa ± x < 0.5 MPa, in particular 5 MPa. After 1000 h at 80°C, the tensile strength can change to about 9 MPa or more.

[0066] Alternatively or additionally, the elongation at break (according to DIN EN ISO 527) is greater than 80% and / or less than 130%, particularly preferably 90% ± x < 5%, in particular 90%. After 1.000 h at 80°C, the elongation at break can change to a value of 100% or more.

[0067] Alternatively or additionally, the Young's modulus (according to DIN EN ISO 527) is greater than 8 MPa and / or less than 15 MPa, particularly preferably between 9 and 13 MPa, in particular 11 MPa. After 1.000 h at 80°C, the Young's modulus can have a value of 11 MPa or more.

[0068] Exposure to 80°C for 1000 hours refers to an accelerated aging test to imitate higher blade surface temperatures as a result of air temperature and sunlight radiation during the lifetime of a turbine. The maximum surface temperature under actual offshore conditions is estimated to be 60°C. Preferably, the sealant is chosen such that the mechanical properties (Young's modulus, tensile strength and elongation at break) remain constant and / or as such, wherein the combination of all three requirements is very advantageous for the long-term durability of the sealant.

[0069] Thus, according to the preferred method, the sealant is sufficiently flowable to flow into the gaps and surface cavities formed during the application of the add-on and to ensure a smooth finish.

[0070] Preferably, the sealant provides one or more of the following properties: the sealant has:

[0071] - a surface tension which is lower than the surface free energy of the surface of the blade, and / or

[0072] - sufficient resistance to peeling forces, in particular peeling forces greater than 2 N / mm, which occur on the respective surface over the entire service life of the blade, and / or

[0073] - a tensile strength greater than 4 MPa and / or less than 8 MPa, and / or

[0074] - an elongation at break greater than 80% and / or less than 130%, and / or

[0075] - a Young's modulus greater than 8 MPa and / or less than 150 MPa, and / or

[0076] - the maximum particle size of the filler particles, filler agglomerates and / or gel particles contained is limited to a maximum of 200 pm.

[0077] According to a preferred method, the filler is first applied along the edge of the additional part in the longitudinal direction before the sealant is dispensed in the application region, wherein the filler is preferably a fast-curing adhesive and / or a high- viscosity adhesive, and the sealant is applied on the cured or hardened filler.

[0078] According to a preferred method, the sealant comprises the same material as the adhesive used to fix the additional part on the surface of the rotor blade.

[0079] The preferred sealing material has good sandability, so that a smooth, aerodynamically advantageous surface can be produced. The maximum size of the solid particles in the sealing material, for example filler particles, agglomerates of filler particles, gel particles, is preferably limited to a maximum of 200 pm, preferably to a maximum of 100 pm, particularly preferably to a maximum of 60 pm, or even to a maximum of 50 pm, in both the liquid state and the hardened or crosslinked state of the sealing material, in particular determined according to DIN EN 21 524 or ISO 1524.

[0080] The inventive method of aerodynamically optimizing the edge of the additional part is not limited to aerodynamic devices such as LEP covers. The additional part can be a plate comprising sensors, for example a flexible plate which preferably conforms to the curved surface of the rotor blade. The fixing of such a sensor plate to the surface of the rotor blade benefits from the sealing concept of the present invention, thus achieving improvements with regard to AEP and noise generation. Such a plate can be attached to the surface of the rotor blade at any position between the leading edge and the trailing edge of the rotor blade and can be mounted on the suction side or the pressure side of the rotor blade.

[0081] Preferably, using the inventive method, an edge seal is formed along the longitudinal edges of such a plate. In this way, neither the upwind or windward edge of such a plate (i.e. the edge closer to the rotor blade leading edge) nor the downwind edge (the edge closer to the rotor blade trailing edge) will adversely affect the laminar flow of air over the rotor blade surface. Thus, the present invention is not limited to shells or aerodynamic devices, but also includes any kind of sensor mounted on a floor (e.g. a flexible plate) on the surface of a blade, for example. Thus, for a plate like a sensor plate, improvements regarding AEP are also possible, as well as a reduction of the noise generated when mounting such a plate on the surface of a blade.

[0082] As an example, the edge step height of the add-on (shell height) can be anywhere between 0.7 to 1 mm. The edge step height of the add-on is the sum of the thickness at the outer edge of the add-on plus the thickness of any adhesive or bonding layer used to attach the add-on to the rotor blade. In this case, the minimum width (range) of the edge seal for this add-on would be between 14 to 20 mm. For an edge step height of 0.7 mm, the minimum width of the edge seal is e.g. 14 mm. For an edge step height of 1.0 mm, the minimum width of the edge seal is e.g. 20 mm.

[0083] The ratio of edge seal width to step height can vary between 20:1 to 100:1. For an example edge step height range of 0.5 mm - 1.5 mm, the edge seal would be at least 10 mm wide and up to 150 mm wide. This relatively wide edge seal for rotor blade add-on parts has been observed to result in improved aerodynamic behavior (in wind tunnel tests).

[0084] A further preferred embodiment of the present invention is based on the insight that by forming an edge seal on the longitudinal edges of the add-on, i.e. by having the edge seal "overlap" the outer surfaces of both the add-on and the rotor blade, the laminar nature of the airflow over the rotor blade surface can be maintained. Thus, in a further preferred embodiment of the present invention, the method comprises the step of determining an overlap width of the edge seal in the area of the add-on surface next to its longitudinal edges. The term "overlap width" is to be understood to mean the width of the portion of the edge seal that extends onto the add-on surface. The overlap width is determined based on the add-on height.

[0085] The step of forming the edge seal then preferably comprises applying the sealant material also onto the overlap area of the add-on part. The overlap of the edge seal can advantageously form a smooth layer on the edge of the add-on. Thus, according to the preferred method, the sealant is formed to overlap the edge of the add-on.

[0086] In the inventive method, the edge seal width and the overlap width of the edge seal are preferably "adjusted" for the particular add-on to prevent or at least significantly delay the onset of the flow transition from laminar to turbulent flow on the blade surface behind (i.e., downwind of) the edge of the add-on. Preferably, the extent (i.e., width) of the edge seal and any overlap will be governed by the edge step height at the longitudinal edge of the add-on.

[0087] The ratio of overlap width to step height can vary from 10:1 to 50:1. For an example edge step height of 0.5 mm, the overlap width would be 5 mm - 25 mm wide. For an edge step height of 1.5 mm, the edge seal width would be 15 - 75 mm wide. The recommended ratios described above are significantly greater than those typically used by solutions known in the art. The maximum possible width or extent of the edge seal can also be determined or limited by the curvature of the rotor blade.

[0088] The edge seal presented herein can be achieved by using a sealing formulation (sealant) or adhesive that has sufficiently low viscosity to be sufficiently flowable to flow into any gaps and surface cavities formed during application of the add-on and to ensure a smooth finish to the blade surface. However, since the viscosity of the adhesive / sealant will determine the minimum height of the edge seal along its outer boundary, the sealant material is preferably also selected so as to ensure a smooth transition to the blade surface.

[0089] At the same time, the viscosity of the adhesive / sealant drives the step in a simple edge seal as well as in an overlapping edge seal. By forming a smooth layer over the shell edge, the overlapping edge seal can be able to eliminate the step. The edge seal material is selected so as to ensure a smooth transition to the blade surface.

[0090] For large edge steps, a filler material can be used to augment the edge seal. In this preferred embodiment of the invention, a filler material is initially applied along the edge of the add-on to reduce the edge step, i.e., to form a compact wedge or bevel that extends outward from the edge of the add-on. Then, a sealant material is applied over the filler. The filler material can have a higher viscosity than the sealant material to facilitate easy build-up of the filler or underlayer to a limited thickness. The extent (width) of the filler is preferably less than the width of the edge seal width so as to ensure a uniform layer of edge seal material on the surface, thereby achieving a smooth edge at the end of the edge seal (i.e., a smooth transition to the rotor blade surface). The volume occupied by the filler material can be less than half of the intended volume of the edge seal.

[0091] In preferred wind turbine rotor blades, the additional part comprises any of a leading edge protection cap, a trailing edge panel, a vortex generator panel, a plate or a sensor panel. Other possibilities are listed above.

[0092] In preferred wind turbine rotor blades, the thickness of the additional part at its longitudinal edge is in the range of 0.5 mm to 1.5 mm.

[0093] Advantageously, the inventive arrangement and method reduce the aerodynamic performance impact of steps or other obstacles on the surface of the blade (e.g. occurring due to the application of LEP) by reducing / avoiding edge steps. The solution also enables the use of LEP shells or LEP caps with higher edge thickness. This enables a significant opportunity for cost reduction of the shells, as the requirement of thin edges is a cost driver for manufacturing these shells. Avoiding thinner shell edges also reduces the risk of wrinkling during application, which further contributes to a reduction of scrap costs and improves aerodynamic performance.

[0094] The edge sealing method described above contributes to aerodynamic performance improvements of the LEP solution. The edge seal indirectly enables the use of shells with thicker edges and contributes to a reduction of shell and scrap costs.

[0095] Creating an overlapping finish with the right material to make the transition to the blade surface smooth. BRIEF DESCRIPTION OF DRAWINGS

[0096] Other objects and features of the present application will become apparent from the following detailed description considered in conjunction with the accompanying drawings. It is to be understood, however, that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the application.

[0097] Figure 1 An embodiment of the inventive edge seal applied to the longitudinal edge of a rotor blade add-on, which is a panel, is shown;

[0098] Figure 2 A further embodiment of the inventive edge seal sealing a plate is shown;

[0099] Figure 3 A further embodiment of the inventive edge seal sealing a cap is shown;

[0100] Figure 4 A further embodiment of the present application comprising an overlapping edge seal is shown;

[0101] Figure 5 An embodiment of the present application comprising an overlapping edge seal and a filler material is shown;

[0102] Figure 6A toothed squeegee is shown;

[0103] Figure 7 Another view of the toothed squeegee is shown;

[0104] Figure 8 A smooth tool is shown;

[0105] Figure 9 A profile of the smooth tool is shown Figure 8

[0106] Figure 10 Smoothing and distribution of sealant with soft and hard tools is shown;

[0107] Figure 11 Smoothing and distribution of sealant with soft and hard tools is shown to seal the edge of a finished add-on part;

[0108] Figure 12 An example of smoothing of an edge seal is shown;

[0109] Figure 13 A final smoothing of an edge seal is shown;

[0110] In the drawings, like numerals refer to like objects throughout the several views. Objects in the drawings are not necessarily to scale. DETAILED DESCRIPTION

[0111] Figure 1 An embodiment of the inventive edge seal S applied to an add-on part 3, which can be any of a LEP cover, a shell, a TE cover, a VG panel, a TE panel, a sensor panel, etc., is shown. The add-on part 3 is attached to the outer surface 2 of a rotor blade 1 by an adhesive bond layer 4. For the purposes of discussion, the adhesive layer 4 can be considered an element of the add-on part 3. The height t of the add-on part 3 at its edge step 3E is the sum of the thickness of the add-on part 3 and the thickness of the adhesive layer 4. The add-on part edge 3E can be assumed to extend in the longitudinal direction of the rotor blade 1. This figure clearly shows the “step” shape at the edge 3E of the add-on part 3. Using the inventive method, an edge seal S is formed along the add-on part edge 3E. The edge seal S begins at a first point J1 at the edge 3E of the add-on part 3 and extends to a second point J2, whereby the height t of the seal S gradually decreases from a maximum at point J1 to a minimum at point J2. The ratio of the height t to the width δ of the edge seal S, δ:t, is preferably at least 20:1. In this case, the volume of the edge seal S is the cross-sectional area of the edge seal S (i.e., (t•δ) / 2) multiplied by the length of the seal S (e.g., the length of the longitudinal edge 3E of the add-on part 3).

[0112] Figure 2 An embodiment of the inventive edge seal S applied to an add-on part 3, which can be any of a LEP cover, a shell, a TE cover, a VG panel, a TE panel, a sensor panel, etc., is shown. The add-on part 3 is attached to the outer surface 2 of a rotor blade 1 by an adhesive bond layer 4. For the purposes of discussion, the adhesive layer 4 can be considered an element of the add-on part 3. The height t of the add-on part 3 at its edge step 3E is the sum of the thickness of the add-on part 3 and the thickness of the adhesive layer 4. The add-on part edge 3E can be assumed to extend in the longitudinal direction of the rotor blade 1. This figure clearly shows the “step” shape at the edge 3E of the add-on part 3. Using the inventive method, an edge seal S is formed along the add-on part edge 3E. The edge seal S begins at a first point J1 at the edge 3E of the add-on part 3 and extends to a second point J2, whereby the height t of the seal S gradually decreases from a maximum at point J1 to a minimum at point J2. The ratio of the height t to the width δ of the edge seal S, δ:t, is preferably at least 20:1. In this case, the volume of the edge seal S is the cross-sectional area of the edge seal S (i.e., (t•δ) / 2) multiplied by the length of the seal S (e.g., the length of the longitudinal edge 3E of the add-on part 3). Figure 1 ​An embodiment of the inventive edge seal S applied to an add-on 3, where the add-on 3 here is a sensor panel covered with sensors 5.

[0113] Figure 3 An embodiment of the inventive edge seal S applied to an add-on 3, where the add-on 3 here is a sensor panel covered with sensors 5. Figure 1 An embodiment of the inventive edge seal S applied to an add-on 3, where the add-on 3 here is a sensor panel covered with sensors 5.

[0114] Figure 2 An embodiment of the inventive edge seal S applied to an add-on 3, where the add-on 3 here is a sensor panel covered with sensors 5.

[0115] The extent δ and the overlap extent h of the edge seal S thus depend on the height t of the edge step 3E at the junction J1. The ratio of δ to h with respect to t can vary anywhere between 20:1 to 100:1 (δ) and 10:1 to 50:1 (h), respectively. The edge seal S and the overlap extent are adjusted so as to prevent / delay the onset of the flow transition from laminar to turbulent flow on the surface of the rotor blade 1 due to the edge step 3E. The recommended ratios are longer than those commonly used by solutions known in the art.

[0116] By way of example, with respect to the figures (in particular Figure 4 ), the height t of the edge step 3E can be anywhere between 0.5 to 1.5 mm, preferably anywhere between 0.7 to 1 mm, which means that the minimum extent of the edge seal S will be at least 12 mm, for example between 12 to 70 mm, preferably between 14 to 50 mm, more preferably between 14 to 40 mm, and most preferably between 14 to 20 mm.

[0117] The extent δ of the edge seal depends on the curvature of the rotor blade 1, which causes the extent of the edge seal S to reach a maximum.

[0118] A preferred edge seal S can use a sealant with a certain viscosity so that the adhesive / sealant is sufficiently flowable to flow into the gaps and surface cracks created by the application and to ensure a smooth finish. At the same time, the viscosity of the adhesive / sealant 4 pushes against the step at the joint J2 in a simple edge seal S and at J0 and J2 in an overlapping edge seal S0. The overlapping edge seal S0 can be able to eliminate the step at J1, thereby creating a smooth layer on the shell edge 3E. The sealant is chosen so that a smooth transition to the blade surface 2 is ensured.

[0119] Figure 5 Further embodiments of the inventive edge seal S are shown. Similar to the edge seal S of Figure 4 , in this case the edge seal S extends over a filler material F (also referred to herein as filler F), which is applied first along the longitudinal edge 3E of the add-on 3. The filler F can be a fast-curing adhesive and / or a high- viscosity adhesive / sealant. The filler F can be applied to form a wedge, the straight edge of which is shorter than the height of the add-on 3. In a subsequent step, a sealant material is applied over the cured or hardened filler F so that the resulting edge seal S overlaps the longitudinal edge 3E of the add-on 3, starting at point J0 and extending to point J2. Also in this case, the total width δ of the edge seal S is measured from point J0 to point J2. As described above in Figure 2 , the height of the seal S gradually increases from a minimum at point J0 to a maximum at point J0 and gradually decreases from a maximum at point J1 to a minimum at point J2. The filler F shown here can also be used in other embodiments.

[0120] Thus, for large edge steps, a filler F can be used initially to reduce the edge step, and subsequently an edge seal can be applied. The filler material F can have a higher viscosity than the material of the edge seal S in order to enable the underlying layer to be built up to a limited thickness easily. The range of the filler F will be less than δ in order to ensure that there is a uniform layer of edge seal on the surface to achieve a smooth edge at the joint J2. Figures 3 to 5 The embodiments shown in

[0121] Figure 6A flexible toothed scraper 6 with a row of teeth 6a is shown. This toothed scraper 6 serves as a preliminary tool 6 to spread sealant material in the area defined by the longitudinal edge of the attachment 3 and the selected edge seal width δ. The preliminary tool 6 preferably has a flexibility and shape that facilitates the initial spreading of the sealant. This is achieved through the teeth 6a. The tooth pitch is preferably between 1 and 2 mm, and the tooth height is about 0.2 to 5 mm.

[0122] Figure 7 As shown Figure 6 Another view of the toothed scraper shown, which is made of a flexible material and is used for adhesive leveling.

[0123] Figure 8 A smoothing tool 7 in the form of a finishing scraper 7 is shown, which is used to finish the shape of the sealant spread by the preliminary tool 6. Preferably, the finishing tool has a lower hardness than the preliminary tool.

[0124] Figure 9 It shows Figure 8 The outline of the smoothing tool indicates the contact area 7e with the sealant / adhesive during smoothing (arrow).

[0125] Figure 8 and Figure 9 A preferred scraper is shown, having a plurality of grooves 7a extending parallel to the scraper tip 7d (perpendicular to the smoothing direction). The advantage of these grooves 7a is that the finishing scraper 7 is rigid along the direction of the grooves 7a, but can be easily bent when sweeping across a surface. For better grip, the preferred finishing scraper 7 has two fins 7b, 7c at opposite ends of its tip 7d, wherein the fin 7c on the contact area 7e side is preferably thinner than the fin on the other side.

[0126] Figure 10 The smoothing and distribution of sealant using a soft scraper / tool ​​7 and a hard scraper / tool ​​are illustrated. When using a soft finishing scraper 7, the resulting edge seal S will be smoother than that obtained using a hard tool. H (Dashed line) is flatter and wider (solid line).

[0127] Figure 11 It shows Figure 10 The smoothing effect at the edge seal S of attachment 3. Again, the dashed line shows the edge seal S produced by a hard tool. H The solid line shows the edge seal S produced by the soft finishing scraper 7 (for the scraper, see example...). Figure 8 The figure shows the angle (θ) between blade surface 2 and the seal created by the hard scraper. H), and the angle between the blade surface 2 and the seal produced with the soft finishing blade 7 (angle Θ S ). It can be easily seen that the angle Θ H between the blade surface 2 and the seal produced with the hard blade is much larger than the corresponding angle Θ S .

[0128] It has been observed from wind tunnel measurements that the angle Θ (seal edge angle) between the blade surface 2 and the edge seal S plays a crucial role in the performance of the sealing concept. The lower the seal edge angle Θ, the better the performance of the seal.

[0129] The soft blade produces a lower seal edge angle compared to a harder (more rigid) blade, since the blade is able to bend more locally towards the point where the seal ends and the blade surface begins. The influence on the seal edge angle Θ is thus a direct function of the hardness (rigidity) of the blade. Therefore, a blade with a suitably low hardness is preferably chosen.

[0130] Figure 12 and Figure 13 The attachment of the add-on 3 to the rotor blade surface 2 as well as the formation of the edge seal S with the method according to the present application is shown. The add-on 3 can be attached using an adhesive 4 as explained above (adhesive not shown here). The liquid sealant LS is applied on the surface 2 of the blade 1 in the area of the edge step 3E of the add-on 3.

[0131] Figure 12 The steps of spreading the liquid sealant LS using the preliminary shaping tool 6 and smoothing the sealant with the flexible tool 7 are shown. Figure 13 The final smoothing of the sealant LS is shown.

[0132] Before applying the sealant LS, the area of the intended edge seal is defined by using a smooth, thin masking tape 8. One tape 8 can extend along the outer edge of the intended edge seal S1 outwardly from the edge step 3E by a distance. This distance is at least 20 times the height of the edge step. The thickness of the tape 8 is as small as possible, preferably at most 0.2 mm. The other boundary of the edge seal S1 can be defined by the edge step 3E. Alternatively, if an overlap on the edge step 3E is to be formed, a second tape 8 can be applied to the surface of the add-on 3 parallel to the longitudinal edge of the add-on 3. Then, the sealant LS is applied within these boundaries. The sealant LS can initially be deposited roughly on the surface 2 of the rotor blade 1 and the add-on 3, e.g. in the form of beads from a dispenser nozzle or by spraying.

[0133] Then, the roughly applied sealant LS is spread using a preliminary shaping tool 6, e.g. a flexible toothed doctor blade 6. This can be done by guiding the toothed doctor blade 6 along the longitudinal direction of the rotor blade surface 2 between the edge seal boundaries. The flexibility of the preliminary shaping tool 6 is preferably such that it can bend in both axial directions to facilitate spreading of the sealant S.

[0134] After distribution of the sealant LS (before removal of the masking tape 8), the sealant LS is smoothed with a tool 7 (preferably flexible) that is moved along the longitudinal direction of the blade 1.

[0135] After completion of this preliminary step (see Figure 12 ), the tape 8 is removed (see Figure 13 ). Then, the still liquid sealant LS is smoothed to its final shape by dragging a softer finishing tool 7, e.g. a flexible finishing doctor blade 7, over the spread sealant LS. This finishing or smoothing step with the smoothing tool 7 serves to further reduce the height of the "wedge" of the edge seal S1 between the edge step 3E and the outer boundary of the edge seal S. The finishing doctor blade 7 is preferably made of a material such as silicone to ensure a relatively low Shore A hardness (e.g. 50 ± 10) so that it can be bent as needed during spreading of the sealant in order to obtain the desired edge seal profile shape.

[0136] By using the finishing tool 7, the still soft liquid sealant LS is shaped according to the desires, e.g. as shown in Figure 4 or Figure 5 to form an overlap So next to the long edge 3E of the add-on 3.

[0137] While the application has been disclosed in its preferred embodiments with variations and modifications, it will be understood that numerous additional modifications and variations could be effected, without departing from the scope of the application.

[0138] For the sake of clarity, it will be understood that the use of "a" or "an" throughout refers to "one or more" and that the use of "comprise" does not exclude other steps or elements.

Claims

1. A method for creating a transition from the edge (3E) of an additional part (3) mounted on the outer surface (2) of a rotor blade (1), said method comprising the steps of: - defining, with a thin and smooth masking tape (8) applied on the additional part (3) and on the outer surface (2) of the rotor blade (1), an application area on the outer surface (2) of the rotor blade (1) and on the additional part (3) to be covered with a sealant compound (LS) with said masking tape (8), - dispensing said sealant (LS) on said application area, - the distribution of the sealant (LS) is performed by using a toothed doctor blade (6) so as to form a first sealant edge angle (Θ H ) between the outer surface (2) of the rotor blade (1) and the edge seal (S) formed by the toothed doctor blade (6), - removing said masking tape (8), - smoothing the sealant (LS) transition step with a second doctor blade so as to form a second sealant edge angle (Θ S ) between the outer surface (2) of the rotor blade (1) and the edge seal (S) formed by the second doctor blade, the second doctor blade being made of a flexible material and having a hardness less than that of the toothed doctor blade (6), wherein the second sealant edge angle (Θ S ) is less than the first sealant edge angle (Θ H ), wherein said edge seal (S) overlaps the outer surface of the additional part (3) and said edge seal (S) has an overlap width (h) extending onto the outer surface of the additional part (3), and wherein said overlap width (h) is determined based on a step height (t) at the edge (3E) of the additional part (3).

2. The method of claim 1, wherein, Said toothed blade (6) is made of a flexible material for levelling the sealant (LS) after it has been dispensed on the application area.

3. The method of claim 2, wherein, The teeth (6a) of said toothed blade (6) have a distance between 1 and 2 mm and / or a height between 0.2 and 5 mm.

4. The method of any one of claims 1 to 3, wherein, The Shore A hardness of said second blade is greater than 30 and / or less than 70.

5. The method of claim 4, wherein, The Shore A hardness of said second blade is greater than 40.

6. The method of claim 4, wherein, The Shore A hardness of said second blade is less than 60.

7. The method of any one of claims 1 to 3, wherein, Said second blade is made of a silicone material.

8. The method of claim 7, wherein, Said second blade has a cross-sectional profile adapted to said application and a low-energy surface preventing the sealant material from adhering.

9. The method of any one of claims 1 to 3, wherein, Said second blade comprises a tip (7d) at which there is an expected contact area with the sealant (LS).

10. The method of claim 9, wherein, Said second blade comprises several grooves (7a) extending parallel to the tip (7d) and / or several fins (7b, 7c) at opposite ends of the tip (7d).

11. The method of any one of claims 1 to 3, wherein, Said masking tape (8) has a thickness less than 0.2 mm.

12. The method of any one of claims 1 to 3, wherein, Said dispensing of the sealant (LS) is achieved by bead or spray application or by roll application or using a "cyclone” process.

13. The method of any one of claims 1 to 3, wherein, Said dispensing of the sealant (LS) is achieved by a serpentine line with 25 / 50 or 20 / 50 overlap with the transition on both the additional part (3) and the outer surface (2) of the rotor blade (1), or by applying the sealant (LS) in a straight line on the outer surface (2) of the additional part (3) and / or the rotor blade (1).

14. The method of any one of claims 1 to 3, wherein, Said sealant (LS) is smoothed with said second blade moving along the longitudinal direction of the blade (1).

15. The method of claim 14, wherein, Said second blade is designed to meet the profile of the blade (1).

16. The method of claim 15, wherein, Said second blade has a curvature matching the curvature of the blade (1) leading edge profile.

17. The method of any one of claims 1 to 3, wherein, Said sealant (LS) is sufficiently flowable to flow into the gaps and surface cracks formed during the application of the additional part and to ensure a smooth finish.

18. The method of claim 17, - wherein, the sealing agent (LS) has a surface tension which is lower than the surface free energy of the outer surface (2) of the rotor blade (1), and / or - wherein the sealing agent (LS) has sufficient resistance to peeling forces occurring on the respective surfaces over the entire service life of the blade, and / or - wherein the sealing agent (LS) has a tensile strength which is greater than 4 MPa and / or less than 8 MPa, and / or - wherein the sealing agent (LS) has an elongation at break which is greater than 80% and / or less than 130%, and / or - wherein the sealing agent (LS) has a Young's modulus which is greater than 8 MPa and / or less than 150 MPa, and / or - wherein the maximum size of the solid particles, agglomerates of filler particles, gel particles of the sealing agent (LS) is limited to a maximum of 200 μιη in the liquid state as well as in the hardened or crosslinked state of the sealing material.

19. The method of claim 18, wherein, The peeling force is greater than 2 N / mm.

20. The method of claim 18, wherein, The solid particles are filler particles.

21. The method of any one of claims 1 to 3, wherein, Before the sealing agent (LS) is dispensed on the application area, a filler (F) is first applied along the longitudinal edge (3E) of the additional part.

22. The method of claim 21, wherein, The filler (F) is a fast-curing adhesive and / or a high-viscosity adhesive, and the sealing agent (LS) is applied on the cured or hardened filler (F).

23. The method of any one of claims 1 to 3, wherein, The sealing agent (LS) comprises the same material as the adhesive (4) used to fix the additional part (3) on the outer surface (2) of the rotor blade (1).

24. A wind turbine rotor blade (1) comprising at least one additional part (3) mounted to an outer surface (2) of the rotor blade (1), and an edge seal (S) formed with a method according to any one of claims 1 to 23.

25. A wind turbine rotor blade according to claim 24, wherein, The additional part (3) comprises any one of a leading edge protection cap, a trailing edge panel, a vortex generator panel, a spoiler, a plate or a sensor panel.

26. A wind turbine rotor blade according to claim 24 or 25, wherein, The thickness of the additional part (3) at its longitudinal edge (3E) is in the range of 0.5 - 1.5 mm. The sealing agent (LS) has a surface tension which is lower than the surface free energy of the outer surface (2) of the rotor blade (1), and / or - wherein the sealing agent (LS) has sufficient resistance to peeling forces occurring on the respective surfaces over the entire service life of the blade, and / or - wherein the sealing agent (LS) has a tensile strength which is greater than 4 MPa and / or less than 8 MPa, and / or - wherein the sealing agent (LS) has an elongation at break which is greater than 80% and / or less than 130%, and / or - wherein the sealing agent (LS) has a Young's modulus which is greater than 8 MPa and / or less than 150 MPa, and / or - wherein the maximum size of the solid particles, agglomerates of filler particles, gel particles of the sealing agent (LS) is limited to a maximum of 200 μιη in the liquid state as well as in the hardened or crosslinked state of the sealing material. The peeling force is greater than 2 N / mm. The solid particles are filler particles. Before the sealing agent (LS) is dispensed on the application area, a filler (F) is first applied along the longitudinal edge (3E) of the additional part. The filler (F) is a fast-curing adhesive and / or a high-viscosity adhesive, and the sealing agent (LS) is applied on the cured or hardened filler (F). The sealing agent (LS) comprises the same material as the adhesive (4) used to fix the additional part (3) on the outer surface (2) of the rotor blade (1).

24. A wind turbine rotor blade (1) comprising at least one additional part (3) mounted to an outer surface (2) of the rotor blade (1), and an edge seal (S) formed with a method according to any one of claims 1 to 23. The additional part (3) comprises any one of a leading edge protection cap, a trailing edge panel, a vortex generator panel, a spoiler, a plate or a sensor panel. The thickness of the additional part (3) at its longitudinal edge (3E) is in the range of 0.5 - 1.5 mm.

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