A WIND TURBINE COMPONENT

Abstract

A wind turbine component, the wind turbine component comprising a laminate of layers with an outer side and an inner side, wherein the outer side faces an exterior of the wind turbine component and the inner side faces an interior of the wind turbine component, the laminate of layers being configured to reflect a radar wave impinging the outer side of the laminate of layers, wherein a reflection loss of the reflected radar wave is below a threshold at a frequency, the laminate of layers comprising: an attenuating layer comprising reinforcing fiberglass or reinforcing carbon fibers, a polymer matrix, and radar absorbing particles; a reflective layer arranged on the inner side of the attenuating layer, the reflective layer being configured to reflect a transmitted portion of the radar wave, the transmitted portion of the radar wave being a portion of the radar wave that has passed through the attenuating layer.

Claims

1. A wind turbine component, the wind turbine component comprising a laminate of layers with an outer side and an inner side, wherein the outer side faces an exterior of the wind turbine component and the inner side faces an interior of the wind turbine component, the laminate of layers being configured to reflect a radar wave impinging the outer side of the laminate of layers, wherein a reflection loss of the reflected radar wave is below a threshold at a frequency, the laminate of layers comprising: an attenuating layer comprising reinforcing fiberglass or reinforcing carbon fibers, a polymer matrix, and radar absorbing particles; and a reflective layer arranged on the inner side of the attenuating layer, the reflective layer being configured to reflect a transmitted portion of the radar wave, the transmitted portion of the radar wave being a portion of the radar wave that has passed through the attenuating layer.

2. The wind turbine component according to claim 1, the wind turbine component further comprising a phase shifting layer, the phase shifting layer being a layer between the attenuating layer and the reflective layer, the phase shifting layer comprising reinforcing fiberglass or reinforcing carbon fibers and a polymer matrix; wherein the phase shifting layer has a thickness configured to set a phase difference between a radar wave reflection from the attenuating layer and a radar wave reflection from the reflective layer, the phase difference being configured to give at least partially destructive interference between the radar wave reflection from the attenuating layer and the radar wave reflection from the reflective layer at the frequency.

3. The wind turbine component according to claim 1, wherein the radar absorbing particles of the attenuating layer comprise one or more of: carbon nanotubes, carbon black, or graphene.

4. The wind turbine component according to claim 1, wherein the radar absorbing particles of the attenuating layer comprise single-wall carbon nanotubes.

5. The wind turbine component according to claim 1, wherein the reflective layer comprises reinforcing fiberglass or reinforcing carbon fibers, a polymer matrix, and metal particles.

6. The wind turbine component according to claim 1, wherein the radar absorbing particles of the attenuating layer are attached to the reinforcing fiberglass or reinforcing carbon fibers of the attenuating layer.

7. The wind turbine component according to claim 1, wherein the radar absorbing particles of the attenuating layer are dispersed in the polymer matrix of the attenuating layer.

8. The wind turbine component according to claim 1, wherein the attenuating layer comprises a plurality of cured prepreg sheets, the prepreg sheets being sheets of reinforcing fiberglass or reinforcing carbon fibers, pre-impregnated with polymer resin and the radar absorbing particles, wherein the attenuating layer is formed by bonding the prepreg sheets together by curing the polymer resin to form the polymer matrix.

9. The wind turbine component according to claim 1, wherein the laminate of layers is configured to have a reflection loss below the threshold at a frequency in the L-band, in the S-band or in the Xband, the L-band being a frequency band between 1 GHz and 2 GHz, the S-band being a frequency band between 2 GHz and 4 GHz, the X-band being a frequency band between 8 GHz and 12 GHz.

10. The wind turbine component according to claim 1, wherein the laminate of layers is configured to have a reflection loss below the threshold at a frequency in the S-band as well as at a frequency in the X-band.

11. The wind turbine component according to claim 1, wherein the attenuating layer comprises a reinforcing fiber fabric comprising a plurality of reinforcing fibers onto which the radar absorbing particles are attached, the plurality of reinforcing fibers being the reinforcing fiberglass or the reinforcing carbon fibers, wherein the reinforcing fibers are intertwined to form the reinforcing fiber fabric.

12. The wind turbine component according to claim 11, wherein the radar absorbing particles are incorporated in a reinforcing fiber sizing attached to the reinforcing fibers, the reinforcing fiber sizing being a coating on the reinforcing fiber, the coating being configured to bond to a polymer matrix.

13. The wind turbine component according to claim 11, wherein the reinforcing fabric is a first reinforcing fabric, and wherein the plurality of reinforcing fibers are a plurality of first reinforcing fibers, the wind turbine component further comprising a radar attenuating layer comprising a second reinforcing fabric and a polymer resin suitable for resin infusion of the second reinforcing fiber fabric, wherein a reinforcing fiber sizing of second reinforcing fibers of the second reinforcing fiber fabric and the polymer resin are configured to bond to each other when cured.

14. A resin infusion method for producing a wind turbine component, the method comprising: placing a plurality of reinforcing fiber fabric sheets on top of each other on top of a mold, wherein the plurality of reinforcing fiber fabric sheets comprise reinforcing fiber fabric comprising a plurality of reinforcing fibers onto which the radar absorbing particles are attached, and wherein the mold forms a shape of at least part of the wind turbine component; placing a flexible film on top of the plurality of reinforcing fiber fabric sheets, wherein the flexible film is impermeable to air, the flexible film forming at least part of a vacuum bag which surrounds the plurality of reinforcing fiber fabric sheets; evacuating air from the vacuum bag such that a vacuum is formed within the plurality of fiberglass fabric sheets, thereby pressing the flexible film against the plurality of reinforcing fiber fabric sheets to force the plurality of reinforcing fiber fabric sheets to adapt the shape of the mold; admitting a polymer resin to the vacuum bag such that the vacuum pulls the resin into voids within the plurality of reinforcing fiber fabric sheets, thereby infusing the plurality of reinforcing fiber fabric sheets with the polymer resin; curing the polymer resin such that polymer resin solidifies to form a polymer matrix.

15. A prepreg method for producing a wind turbine component, the method comprising: placing a plurality of radar absorbing prepreg sheets on top of each other on top of a mold, wherein each of the radar absorbing prepreg sheets comprises reinforcing fiberglass or reinforcing carbon fibers, the reinforcing fiberglass or reinforcing carbon fibers being pre-impregnated with a polymer resin and radar absorbing particles, and wherein the mold forms a shape of at least part of the wind turbine component; pressing the plurality of radar absorbing prepreg sheets against the mold such that the plurality of radar absorbing prepreg sheets adapt the shape of the mold; curing the plurality of radar absorbing prepreg sheets such that the plurality of radar absorbing prepreg sheets bond together and the polymer resin solidifies to form a polymer matrix, the polymer matrix encasing the reinforcing fiberglass or reinforcing carbon fibers and the radar absorbing particles.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0114] The above, as well as additional objects, features and advantages of the present inventive concept, will be better understood through the following illustrative and non-limiting detailed description, with reference to the appended drawings. In the drawings like reference numerals will be used for like elements unless stated otherwise.

[0115] FIG. 1 is cross-section of a wind turbine rotor blade.

[0116] FIG. 2 is a laminate of layers.

[0117] FIG. 3 is a laminate of layers.

[0118] FIG. 4 is a fiberglass fabric.

[0119] FIG. 5 is a fiberglass fiber.

[0120] FIG. 6 is a fiberglass fiber.

[0121] FIG. 7 is a fiberglass fiber.

[0122] FIG. 8 is a prepreg.

[0123] FIG. 9 is a flow chart of a resin infusion method.

[0124] FIG. 10 is a resin infusion setup.

[0125] FIG. 11 is a flow chart of a prepreg method.

DETAILED DESCRIPTION

[0126] In cooperation with attached drawings, the technical contents and detailed description of the present invention are described thereinafter according to a preferable embodiment, being not used to limit the claimed scope. This invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness, and fully convey the scope of the invention to the skilled person.

[0127] In the following the inventive concept will be exemplified with structures wherein the reinforcing fibers are fiberglass fibers. However, it should be understood that the reinforcing fibers may also be carbon fibers.

[0128] A wind turbine component 1 may e.g. be a rotor blade, a nacelle or a nose cone. FIG. 1 illustrates a cross-section of a wind turbine rotor blade. The illustrated rotor blade is constructed as a shell with an outer side 2 and an inner side 4, wherein the shell comprises a laminate of layers 10.

[0129] FIGS. 2 and 3 illustrate laminate of layers 10. FIG. 2 illustrates a laminate of layers 10 comprising a reflective layer 12, a phase shifting layer 14, and an attenuating layer 16. FIG. 3 illustrates a laminate of layers 10 comprising a reflective layer 12 and an attenuating layer 16. In either case the thicknesses of the layers may be configured to give a reflective loss below a threshold at a frequency, the threshold may be −10 dB.

[0130] In FIG. 2 the layers within the laminate of layers 10 are arranged with the reflective layer 12 towards the inner side 4 followed by the phase shifting layer 14 and the attenuating layer 16 towards the outer side. However, it should be understood that further layers are possible both on the outer 2 and inner side 4. For example, on the inner side 4 of the reflective layer 12 there may be layers which do not affect the reflection loss of the laminate of layers 10 but serves to improve the structural integrity of the wind turbine component. In another example, there may be an outermost gel coat layer providing a high-quality finish, UV-resistance and/or improved aerodynamic properties.

[0131] In another example the laminate of layers 10 may comprise, from the inner side 4 to the outer side 2, a reflective layer 12, a first phase shifting layer, a first attenuating layer, a second phase shifting layer, and a second attenuating layer. The first and second phase shifting layers may herein have different thicknesses. The first and second attenuating layers may herein have different thicknesses. The thicknesses may be configured such that a radar reflection from the second attenuating layer into the air outside the second attenuating layer has an opposite phase to both a reflection from the first attenuating layer and the reflective layer 12 when these reflections emerge into the air outside the second attenuating layer. The thicknesses may also be configured such that the magnitudes of the three reflections allow the reflections to cancel each other out. It should also be understood that the thicknesses of the first and second phase shifting layers and the first and second attenuating layers may be configured to give a frequency dependence of the reflection loss wherein the reflection loss has at least two local minima. Thus, the reflection loss may be below a threshold, e.g. a threshold of −10 dB, at two different frequencies, e.g. two different frequencies in different radar bands.

[0132] FIG. 3 further illustrates a close-up view of the reflective layer 12 and the attenuating layer 16. The structure of the reflective layer 12 and the attenuating layer 16, described hereafter, may be valid for a number of embodiments of the laminate of layers 10. Regardless of whether there is a phase shifting layer 14 between or not. In FIG. 3 the reflective layer 12 comprises sheets of fiberglass fabric 20 and metal particles 44 in a polymer matrix 30. The metal particles may e.g. be attached to the fiberglass or dispersed in the polymer matrix 30. In FIG. 3 the attenuating layer 16 comprises sheets of fiberglass fabric 20 and single-wall carbon nanotubes 42 in a polymer matrix 30. The single-wall carbon nanotubes 42 herein functions as radar absorbing particles 40. The single-wall carbon nanotubes 42 may e.g. be attached to the fiberglass or dispersed in the polymer matrix 30.

[0133] FIG. 4 illustrates a fiberglass fabric 20 comprising a plurality of fiberglass fibers 22. In the illustrated fiberglass fabric 20 most of the fiberglass fibers 22 aligned along one direction. When the fiberglass fabric 20 is used to produce a wind turbine rotor blade the fiberglass fabric 20 may be laid out with this one direction along the length direction of the rotor blade.

[0134] FIGS. 5-7 illustrate fiberglass fibers 22. FIG. 5 illustrates a fiberglass fiber 22 with a sizing 24 in the form of a coating around a glass fiber. The fiberglass sizing 24 may comprise a film former and a coupling agent. FIG. 6 illustrates a cutaway view of a fiberglass fiber 22 with a sizing 24, wherein radar absorbing particles 40 are dispersed within the fiberglass sizing 24. FIG. 7 illustrates a cutaway view of a fiberglass fiber 22 with a sizing 24, wherein radar absorbing particles 40, in this case single-wall nanotubes 42, are distributed on the outer surface of the fiberglass sizing 24.

[0135] FIG. 8 illustrates a fiberglass prepreg 50. The prepreg 50 comprises a sheet of fiberglass fabric 20, in the illustrated case a woven sheet of fiberglass fabric 20, which is pre-impregnated with polymer resin. The polymer resin may be partially cured to allow easy handling. The prepreg 50 may further comprise radar absorbing particles 40 such that when the prepreg 50 is cured it may form part of an attenuating layer 16.

[0136] The wind turbine component 1 may be produced in many different ways, as readily understood by the skilled person. Two methods, encompassed by the inventive concept, may be particularly useful. The methods will in the following be described in conjunction with FIGS. 9-11.

[0137] A resin infusion method 100 for producing a wind turbine component will hereinafter be described in conjunction with FIGS. 9 and 10. FIG. 9 is a flow chart of the resin infusion method 100 comprising steps S102, S104, S106, S108 and S110. FIG. 10 illustrates a cross-section of a resin infusion setup 60 which may be used with the resin infusion method 100. The close-up view of the cross-section of the resin infusion setup 60 in FIG. 10 illustrates a stack of sheets of fiberglass fabric 20 that will form part of the laminate of layers 10 after resin infusion. The sheets of fiberglass fabric 20 may be sheets of fiberglass fabric 20′ with attached radar absorbing particles or sheets of fiberglass fabric 20″ without attached particles.

[0138] The illustrated resin infusion setup 60 comprises a mold 70, wherein the mold 70 forms the shape of half of a rotor blade which is divided lengthwise. The surface of the mold 70 may be covered with a gel coat. In step S102 a plurality of sheets of fiberglass fabric 20′ with attached radar absorbing particles are placed on top of each other on top of the mold. The number of sheets of fiberglass fabric 20′ with attached radar absorbing particles may herein define the thickness of the future attenuating layer 16. After the sheets of fiberglass fabric 20′ with attached radar absorbing particles have been laid out, a number of sheets of fiberglass fabric 20″ without attached particles may be stacked on top. The number of sheets of fiberglass fabric 20″ without attached particles may herein define the thickness of the future phase shifting layer 14. The sheets of fiberglass fabric 20″ without attached particles may of course be excluded if a phase shifting layer 14 is not needed. After the sheets of fiberglass fabric 20″ without attached particles have been laid out, a reflective film 62 may be placed on top. The reflective film 62 may e.g. comprise a metal film or one or more sheets of fiberglass fabric 20 with attached metal particles, a carbon textile is another alternative. In step S104 a flexible film 72, wherein the flexible film 72 is impermeable to air, is placed on top of the previously laid sheets and films. In FIG. 10 the flexible film 72 and the mold 70 together forms a vacuum bag. A resin inlet 74 is connected to a reservoir of polymer resin 52. A vacuum outlet 76 is connected to a vacuum pump with a resin trap. Air is evacuated from the vacuum bag via the vacuum outlet 76 with the resin inlet 74 closed, S106. Thus, the sheets of fiberglass fabric 20 and the reflective film 62 is pressed against the mold 70, thereby forcing them to adapt the shape of the mold 70. By opening the resin inlet 74, the polymer resin 52 is admitted into the vacuum bag, S108, thereby infusing the sheets of fiberglass fabric 20 with polymer resin 52. Finally, the polymer resin 52 is cured, S110, still under vacuum pressure, to form the polymer matrix 30. The result will be a laminate of layers 10 in the shape of the mold 70.

[0139] A prepreg method 200 for producing a wind turbine component will hereinafter be described in conjunction with FIG. 11. FIG. 11 is a flow chart of the prepreg method 200 comprising steps S202, S204, and S206. The setup for a prepreg method 200 may be similar to the setup illustrated in FIG. 10. However, for a prepreg method there may not be any need for any additional polymer resin 52 other than the polymer resin 52 which the prepreg is already pre-impregnated with. Consequently, the resin inlet 74 may not be needed. The prepreg method 200 may comprise the use of fiberglass prepregs 50. The fiberglass prepregs 50 may be fiberglass prepregs 50′ with radar absorbing particles and fiberglass prepregs 50″ without radar absorbing particles. However, the method may not necessarily make use of fiberglass prepregs 50″ without radar absorbing particles.

[0140] In step S202 of the prepreg method 200 a plurality of radar absorbing fiberglass prepregs 50′ are placed on top of each other on top of the mold 70, wherein each of the radar absorbing fiberglass prepregs 50′ comprises reinforcing fiberglass pre-impregnated with a polymer resin 52 and radar absorbing particles 40. The number of radar absorbing fiberglass prepregs 50′ may herein define the thickness of the future attenuating layer 16. A plurality of prepregs 50″ without radar absorbing particles may subsequently be stacked on top of the radar absorbing fiberglass prepregs 50′. The number of prepregs 50″ without radar absorbing particles may herein define the thickness of the future phase shifting layer 14. The prepregs 50″ without radar absorbing particles may of course be excluded if a phase shifting layer 14 is not needed. After the prepregs 50″ without radar absorbing particles have been laid out, a reflective film 62 may be placed on top. A flexible film 72, wherein the flexible film 72 is impermeable to air, may be placed on top of the previously laid sheets and films. The flexible film 72 and the mold 70 may together form a vacuum bag.

[0141] In step S204 the prepregs 50 may be pressed against the mold 70 by evacuating air from the vacuum bag via the vacuum outlet. Thus, the prepregs 50 and the reflective film 62 is pressed against the mold 70, thereby forcing them to adapt the shape of the mold 70.

[0142] Finally, the fiberglass prepregs 50 are cured, S206, still under vacuum pressure such that the fiberglass prepregs 50 bond together and the polymer resin 52 solidifies to form a polymer matrix 30. The result will be a laminate of layers 10 in the shape of the mold 70.

[0143] In the above the inventive concept has mainly been described with reference to a limited number of examples. However, as is readily appreciated by a person skilled in the art, other examples than the ones disclosed above are equally possible within the scope of the inventive concept, as defined by the appended claims. It should be understood that the examples may be combined in any number of ways.