Wind turbine blade having an erosion shield

Abstract

The invention relates to a wind turbine blade having a leading edge erosion shield. The erosion shield comprises an inner layer of a first thermoplastic material, the inner layer being an integral part of the shell body of the wind turbine blade. The erosion shield further comprises an outer layer of a second thermoplastic material attached to the inner layer.

Claims

1. A method of manufacturing a wind turbine blade, comprising the steps of: placing a first thermoplastic material in a mould for moulding at least a part of a blade shell body of the wind turbine blade, wherein the first thermoplastic material forms at least part of a leading edge of an outer surface of the wind turbine blade; placing reinforcement fibres in the mould; contacting the first thermoplastic material and the reinforcement fibres with thermosetting resin; curing said resin to form at least a part of the blade shell body, the blade shell body comprising a composite material of the reinforcement fibres and the thermosetting resin, wherein the first thermoplastic material forms an inner layer of an erosion shield of the wind turbine blade; and following the moulding of the at least a part of the blade shell body and the curing of the resin, attaching to said first thermoplastic material a second thermoplastic material, the second thermoplastic material forming an outer layer of the erosion shield, wherein the erosion shield extends along at least a part of the leading edge of the outer surface of the wind turbine blade, the first thermoplastic material of the inner layer of the erosion shield being an integral part of the blade shell body.

2. A method of manufacturing a wind turbine blade, comprising the steps of: placing a first thermoplastic material in a mould for moulding at least a part of a blade shell body of the wind turbine blade, wherein the first thermoplastic material forms at least part of a leading edge of an outer surface of the wind turbine blade; placing reinforcement fibres in the mould; contacting the first thermoplastic material and the reinforcement fibres with thermosetting resin; curing said resin to form at least a part of the blade shell body, the blade shell body comprising a composite material of the reinforcement fibres and the thermosetting resin, wherein the first thermoplastic material forms an inner layer of an erosion shield of the wind turbine blade; and following the moulding of the at least a part of the blade shell body and the curing of the resin, attaching to said first thermoplastic material a second thermoplastic material by plastic welding, the second thermoplastic material forming an outer layer of the erosion shield, wherein the erosion shield extends along at least a part of the leading edge of the outer surface of the wind turbine blade, the first thermoplastic material of the inner layer of the erosion shield being an integral part of the blade shell body.

Description

DETAILED DESCRIPTION

(1) The invention is explained in detail below with reference to an embodiment shown in the drawings, in which

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows a schematic view of a wind turbine blade according to the invention,

(4) FIG. 3 shows a schematic view of an airfoil profile,

(5) FIG. 4 shows a schematic view of the wind turbine blade according to the invention, seen from above and from the side,

(6) FIG. 5 shows a schematic view of an airfoil profile having an erosion shield comprised of two layers of thermoplastic materials at the leading edge,

(7) FIG. 6 shows a schematic view of an airfoil profile of two shell body parts having an integrated first thermoplastic material in a recess at the leading edge,

(8) FIG. 7 shows a schematic view of an erosion shield comprised of 2 layers of thermoplastic materials joined together.

(9) FIG. 8 shows a schematic view of pre-formed parts of a first—and a second thermoplastic material, respectively.

(10) FIG. 9 shows a schematic view of two sheets/foils of a first—and a second thermoplastic material, respectively.

(11) FIG. 10 shows a schematic view of a pre-formed part of thermoplastic material, the part being thinner at the ends than in the middle,

(12) FIG. 11 shows a schematic view of an airfoil profile corresponding to the joining of the two shell body parts of FIG. 5,

(13) FIG. 12 shows a schematic view of a wind turbine blade with an erosion shield, serrations and a spoiler attached to the blade of FIG. 2 at the anchoring sites indicated.

(14) FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8. The rotor has a radius denoted R.

(15) FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

(16) The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

(17) A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

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

(19) An integrated thermoplastic anchoring site 61 for attaching, for example, a spoiler in the transition region 32 is shown. A further integrated site 63 for attaching, for example, noise reducing serrations is indicated at the trailing edge 20 in the airfoil region 34. At the leading edge 18, an attachment site 68 for a second thermoplastic material is shown, thereby completing an erosion shield. It is seen that the erosion shield may extend around the tip of the blade.

(20) It is clear that the blade can have more or fewer attachment sites than the three shown on FIG. 2.

(21) The attachments sites are integrated in the wind turbine blade during manufacturing of the blade. This integration may be achieved by placing a thermoplastic material in the mould for the blade body shell or parts of the blade body shell so that the thermoplastic material is facing the outer surface of the final blade, as indicated on FIG. 2. Different attachment sites may comprise the same or different thermoplastic materials. For example, attachment site 68 may be poly (acrylonitrile butadiene styrene) while attachment sites 61 and 63 are polycarbonate or all attachment sites are poly (acrylonitrile butadiene styrene).

(22) FIGS. 3 and 4 depict parameters, which are used to explain the geometry of the wind turbine blade according to the invention.

(23) FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use—i.e. during rotation of the rotor—normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

(24) Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position df of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position dt of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position dp of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

(25) FIG. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 3, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=Lw, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius ro and a minimum inner curvature radius ri, which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Δy, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

(26) FIG. 5 shows a schematic view of an airfoil profile having an erosion shield 64 comprised of two layers, one layer of a first thermoplastic material 65 and a second layer of a second thermoplastic material 66 at the leading edge. The erosion shield is situated in a recess 67 in the blade and it is indicated that the outer surface of the erosion shield is flush with the surface of the shell body.

(27) The leading edge is not strictly defined as a narrow edge but is indicated to extend to both suction side and pressure side of the airfoil. The leading edge is broadly understood as the part of the blade cutting through the air during rotation of the rotor of the wind turbine, this part of the blade thereby being most vulnerable towards erosion.

(28) FIG. 6 shows a schematic view of an airfoil profile of two shell body parts having an integrated first thermoplastic material 65 in a recess 67 at the leading edge. The first thermoplastic material acts as a site for attachment of a second thermoplastic material, the second thermoplastic material completing an erosion shield at the leading edge of the blade. The completed erosion shield corresponds to the shield 64 shown in FIG. 5.

(29) FIG. 7 shows a schematic view of an erosion shield comprised of 2 layers, one layer of a first thermoplastic material 65 and a second layer of a second thermoplastic material 66. joined together. Such a pre-fabricated erosion shield may be integrated in the shell body to provide a complete leading edge protection. The two layers in the erosion shield are preferably joined by plastic welding. In particular laser welding is a preferred method of joining the 2 layers of thermoplastic material. The first thermoplastic material 65 and the second thermoplastic material 66 are brought into close contact and a laser is used to melt the second thermoplastic material and the first thermoplastic material at the interface between the two materials whereby a bond is established between the two materials.

(30) It may be beneficial to pre-fabricate such two-layer erosion shield before integration with the shell body, because the joining of the two thermoplastic materials in some embodiments may be more conveniently done before integration with the shell body, for example, by placing the pre-fabricated erosion shield or part of a pre-fabricated erosion shield in a mould to form the shell body or a part thereof.

(31) FIG. 8 shows a schematic view of pre-formed parts of a first 65—and a second 66 thermoplastic material, respectively. Typically, the pre-formed part of the first thermoplastic material 65 is placed in the mould when moulding the shell body or part of the shell body of the wind turbine blade. The pre-formed part of the second thermoplastic material is then attached to the pre-formed part of the first thermoplastic material post-moulding to complete an erosion shield at the leading edge of the blade. When using pre-formed parts, both the correct placement of the pre-formed part of the first thermoplastic material in the mould and correct attachment of the second part post moulding may be easier compared to using flexible thermoplastic foils or sheets, because the pre-formed parts, due to narrow tolerances achievable during their manufacturing, are relatively easy to handle and fit together nicely when attached to one another.

(32) The pre-formed part of the first thermoplastic material shown here is applicable in a one-shot moulding process. It should be understood that, if, for example, the blade is formed from two shell body parts (see FIG. 6), the pre-formed part of the first thermoplastic material may also constitute two pre-formed parts, one to be placed in a first mould for moulding a first shell body part and another to be placed in a second mould for a second shell body part.

(33) FIG. 9 shows a schematic view of two sheets/foils of a first 65—and a second 66 thermoplastic material, respectively. Flexible sheets or foils may be advantageous to use according to these embodiments, to form an erosion shield. The sheet/foil of the first thermoplastic material may be placed in the mould together with fibre material. The sheet/foil may be flexible enough to follow the contour of the mould surface, especially when subjected to the weight of fibre plies or pre-preg material placed on top of the sheet/foil of first thermoplastic material. The vacuum applied when resin is injected may also help to fix the sheet/foil of first thermoplastic material in the mould.

(34) After moulding of the shell body, now comprising the first thermoplastic material exposed to the outer surface of the shell at the leading edge, the sheet/foil of the second thermoplastic material is attached on top of the first thermoplastic material. By choosing suitable thermoplastic materials, as explained above, it may be possible to attach the second thermoplastic material by plastic welding, such as laser welding.

(35) In a service situation, where the second thermoplastic material has been eroded from the erosion shield of the wind turbine blade, exposing the first thermoplastic material at the outer surface of the leading edge of the blade, the repair of the erosion shield may be done on-site by welding a new sheet/foil of the second thermoplastic material to the first thermoplastic material. If, for example, laser welding is used, the attachment process is more or less independent of the environmental conditions at the site of repair (temperature, humidity etc.).

(36) The repair can of course be performed with pre-formed parts of the second thermoplastic material as well.

(37) FIG. 10 shows a schematic view of a pre-formed part of thermoplastic material, the part being thinner at the ends than in the middle. Such a part may be advantageous if no recess is available at the leading edge. A first such part of the first thermoplastic material may be integrated in the shell body of the blade in the moulding process, as previously explained, and a second such part of the second thermoplastic material may be attached to the first part after moulding. The geometry having the thinner ends allows the resulting erosion shield to be substantially flush with the surface of the airfoil, even without a recess in the shell body, whereby aerodynamic disturbances from the erosion shield may be minimized.

(38) FIG. 11 shows a schematic view of an airfoil profile corresponding to the joining of the two shell body parts of FIG. 5.

(39) The recess 67 at the leading edge may accommodate a second thermoplastic material (not shown) on top of the shown integrated first thermoplastic material 65 and attached to the first thermoplastic material 65, for example by plastic welding. The second thermoplastic material may be in the form of a sheet or foil as shown in FIG. 9 or a pre-formed part as shown in FIG. 8.

(40) It may also be possible to attach a pre-formed sandwich part (see FIG. 7) already comprising a layer of a first—and a layer of a second thermoplastic material to the thermoplastic material in the recess, whereby a three-layer erosion shield may be formed.

(41) FIG. 12 shows a schematic view of a wind turbine blade with an erosion shield 69, and further surface mounted devices, serrations 71 and a spoiler 73, attached to the blade of FIG. 2 at the sites for attachment shown in FIG. 2. Attaching such add-ons or surface mounted devices via the sites of attachment integrated in the shell body may be performed by using adhesive. The adhesive may be chosen to provide better bond strength than can be achieved by gluing surface mounted devices to the shell body without having the dedicated sites for attachment. Preferably other methods of attachment may be used, such as plastic welding. It is only possible to use plastic welding if both the sites of attachment and the surface mounted devices are made of thermoplastic material. Due to the integration of the anchoring sites for attachment in the shell body, a superior attachment of the surface mounted devices may be achieved when compared to attaching surface mounted devices directly to the fibre reinforced material of a shell body for a wind turbine blade, for example, by using double-sided tape, because the material used for providing the anchoring site may be selected for optimal bonding, while fibre reinforced material typically is selected to provide stiffness and to resist stresses induced in the blade when subjected to different forces during rotation when mounted on the wind turbine.

(42) Accordingly, any add-ons suitable for attachment to thermoplastic sites of attachment may be used according to embodiments of the invention. Vortex generators (not shown), for example, may be made of thermoplastic material and attached to suitably placed sites of attachment.

LIST OF REFERENCE NUMERALS

(43) 2 wind turbine 4 tower 6 nacelle 8 hub 10 blade 14 blade tip 16 blade root 18 leading edge 20 trailing edge 22 pitch axis 30 root region 32 transition region 34 airfoil region 41 first airfoil profile 42 second airfoil profile 43 third airfoil profile 44 fourth airfoil profile 45 fifth airfoil profile 46 sixth airfoil profile 50 airfoil profile 52 pressure side 54 suction side 56 leading edge 58 trailing edge 60 chord 61 thermoplastic anchoring site in transition region 62 camber line/median line 63 thermoplastic anchoring site at trailing edge 64 first erosion shield 65 a first thermoplastic material 66 a second thermoplastic material 67 recess 68 thermoplastic anchoring site at leading edge 69 second erosion shield 71 surface mounted device, serrations 73 surface mounted device, spoiler c chord length dt position of maximum thickness df position of maximum camber dp position of maximum pressure side camber f camber L blade length P power output r local radius, radial distance from blade root t thickness vw wind speed □ twist, pitch Δy prebend