Wind turbine blade with multiple spar caps

Abstract

The present invention relates to wind turbine blade and a method of manufacturing the wind turbine blade. An aerodynamic shell is provided with a recess (70) at its inner surface, the recess (70) extending with-in the shell along a spanwise direction of the blade. A first region of the recess (70) has a first width and a second region of the recess (70) has a second width exceeding the first width. A transition region is provided between the first region and the second region of the re-cess. A first and a second spar cap (80, 82) are arranged within the shell.

Claims

1. A wind turbine blade comprising: an aerodynamic shell (62) having an outer surface (64) forming at least part of an exterior surface of the wind turbine blade and an inner surface (66); a recess (70) at the inner surface (66) of the aerodynamic shell, the recess (70) extending within the shell along a spanwise direction of the blade, wherein the recess (70) comprises a first region (72) having a first width, a second region (74) having a second width exceeding the first width, and a transition region (73) connecting the first region (72) with the second region (74) of the recess (70), wherein a width of the transition region (73) tapers from the second region (74) towards the first region (72); and a load carrying structure comprising a first and a second spar cap (80, 82) extending within the shell (62) along a spanwise direction of the blade, wherein the first spar cap (80) is arranged at least partly in the recess (70) of the aerodynamic shell, and wherein the second spar cap (82) is arranged on top of at least part of the first spar cap (80).

2. The wind turbine blade according to claim 1, wherein the second spar cap (82) is wider than the first spar cap (80).

3. The wind turbine blade according to claim 1, wherein the shell comprises a pressure side shell half and a suction side shell half, each of the shell halves comprising a recess (70) and a load carrying structure according to claim 1.

4. The wind turbine blade according to claim 1, wherein the first and second spar caps (80, 82) each comprise a fabric, wherein the fabric of the first spar cap (80) is different from the fabric of the second spar cap (82).

5. The wind turbine blade according to claim 1, wherein the first width of the first region is within a range of 35-90% of the second width of the second region.

6. The wind turbine blade according to claim 1, wherein the difference between the first width of the first region and the second width of the second region is in a range of 50-800 mm.

7. The wind turbine blade according to claim 1, wherein the spanwise extent of the transition region is 0.5-5 meters.

8. The wind turbine blade according to claim 1, wherein the first and/or second spar cap (80, 82) comprise a hybrid carbon/glass fibre material.

9. The wind turbine blade according to claim 1, wherein the recess (70) is substantially bottle-shaped.

10. The wind turbine blade according to claim 1, wherein the aerodynamic shell comprises a first thickened portion laterally adjoining the recess (70) at a first side of the recess (70) and a second thickened portion laterally adjoining the recess (70) at a second side of the recess (70).

11. The wind turbine blade according to claim 10, wherein the first thickened portion and/or the second thickened portion are formed as a sandwich structure comprising a number of outer skin layers, a number of inner skin layers, and an intermediate sandwich core material.

12. The wind turbine blade according to claim 1, wherein the recess (70) has a base (71) and two opposing side walls (76a, 76b), each side wall having a respective upper edge (76a, 76b), wherein the transition region (73) of the recess has a proximal end and a distal end, seen in the spanwise direction, wherein an angle (Δ) is formed between the base (71) of the recess (70) and a line extending from the upper edge (76a) of a side wall (70a) at the proximal end of the transition region to an intersection between the base (71) and the respective sidewall (70a) at the distal end of the transition region (73), wherein said angle is between 0.2-20 degrees.

13. The wind turbine blade according to claim 12, wherein the side walls (76a, 76b) of the recess (70) are chamfered.

14. The wind turbine blade according to claim 1, wherein the first spar cap (80) and the second spar cap (82) each are pre-manufactured as a fibre-reinforced object comprising a fibre reinforcement material and a matrix material.

15. A method of manufacturing a wind turbine blade, wherein the method comprises the steps of: manufacturing an aerodynamic shell comprising a recess (70) at the inner surface of the aerodynamic shell, the recess (70) extending within the shell along a spanwise direction of the blade, wherein the recess (70) comprises a first region having a first width, a second region having a second width exceeding the first width, and a transition region connecting the first region with the second region of the recess (70), wherein a width of the transition region tapers from the second region towards the first region; arranging a first spar cap (80) in the shell such that it extends within the shell along a spanwise direction of the blade, wherein the first spar cap (80) is arranged at least partly in the recess (70) of the aerodynamic shell; bonding the first spar cap (80) to the shell; arranging a second spar cap (82) on top of at least part of the first spar cap (80); and bonding the second spar cap (82) to the first spar cap (80).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention is explained in detail below with reference to embodiments 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,

(4) FIG. 3 shows a schematic view of a cross-section of a wind turbine blade,

(5) FIG. 4 is a partial perspective view of a shell part of a wind turbine blade of the present invention,

(6) FIG. 5 is a schematic top view of a shell part of a wind turbine blade according to the present invention,

(7) FIG. 6 shows various cross sections through the lines I, II and III of FIG. 4, and

(8) FIG. 7 is a cut-out partial perspective view of a recess in a shell part of a wind turbine blade according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

(9) 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 farthest from the hub 8. The rotor has a radius denoted R.

(10) FIG. 2 shows a schematic view of a wind turbine blade 10. 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 farthest 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.

(11) 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.

(12) 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.

(13) 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.

(14) The blade is typically made from a pressure side shell part 36 and a suction side shell part 38 that are glued to each other along bond lines at the leading edge 18 and the trailing edge of the blade 20.

(15) FIG. 3 shows a schematic view of a cross section of the blade along the line I-I shown in FIG. 2. As previously mentioned, the blade 10 comprises a pressure side shell part 36 and a suction side shell part 38. The pressure side shell part 36 comprises a spar cap 41, also called a main laminate, which constitutes a load bearing part of the pressure side shell part 36. The spar cap 41 comprises a plurality of fibre layers 42 mainly comprising unidirectional fibres aligned along the longitudinal direction of the blade in order to provide stiffness to the blade. The suction side shell part 38 also comprises a spar cap 45 comprising a plurality of fibre layers 46. The pressure side shell part 38 may also comprise a sandwich core material 43 typically made of balsawood or foamed polymer and sandwiched between a number of fibre-reinforced skin layers. The sandwich core material 43 is used to provide stiffness to the shell in order to ensure that the shell substantially maintains its aerodynamic profile during rotation of the blade. Similarly, the suction side shell part 38 may also comprise a sandwich core material 47.

(16) The spar cap 41 of the pressure side shell part 36 and the spar cap 45 of the suction side shell part 38 are connected via a first shear web 50 and a second shear web 55. The shear webs 50, 55 are in the shown embodiment shaped as substantially I-shaped webs. The first shear web 50 comprises a shear web body and two web foot flanges.

(17) The shear web body comprises a sandwich core material 51, such as balsawood or foamed polymer, covered by a number of skin layers 52 made of a number of fibre layers. The second shear web 55 has a similar design with a shear web body and two web foot flanges, the shear web body comprising a sandwich core material 56 covered by a number of skin layers 57 made of a number of fibre layers. The sandwich core material 51, 56 of the two shear webs 50, 55 may be chamfered near the flanges in order to transfer loads from the webs 50, 55 to the main laminates 41, 45 without the risk of failure and fractures in the joints between the shear web body and web foot flange. However, such a design will normally lead to resin rich areas in the joint areas between the legs and the flanges. Further, such resin rich area may comprise burned resin due to high exothermic peeks during the curing process of the resin, which in turn may lead to mechanical weak points. In order to compensate for this, a number of filler ropes 60 comprising glass fibres are normally arranged at these joint areas. Further, such ropes 60 will also facilitate transferring loads from the skin layers of the shear web body to the flanges.

(18) The blade shells 36, 38 may comprise further fibre-reinforcement at the leading edge and the trailing edge. Typically, the shell parts 36, 38 are bonded to each other via glue flanges in which additional filler ropes may be used (not shown). Additionally, very long blades may comprise sectional parts with additional spar caps, which are connected via one or more additional shear webs.

(19) FIG. 4 is a partial perspective view of a shell part 62, such as a shell half, for example a pressure side shell half, of a wind turbine blade according to the present invention. FIG. 4a is an exploded view, whereas FIG. 4b shows the assembled structure. The aerodynamic shell 62 has an outer surface 64 forming at least part of an exterior surface of the wind turbine blade and an opposing inner surface 66. A recess 70 is provided at the inner surface of the aerodynamic shell 62, wherein the recess generally extends within the shell 62 along the spanwise direction L of the blade.

(20) FIG. 4 also illustrates a first spar cap 80 and a second spar cap 82 extending within the shell along the spanwise direction L of the blade. The first spar cap 80 is arranged at least partly in the recess 70 of the aerodynamic shell 62. The second spar cap 82 is wider than the first spar cap 80 and is arranged on top of part of the first spar cap 80, as shown in FIG. 4b. The first spar cap 80 may be made from a different material than the second spar cap 82

(21) As best seen in FIG. 5, the recess 70 may be substantially bottle-shaped. It comprises a first region 72 extending over a spanwise length Ia and having a first width w1 and a second region 74 extending over a spanwise length Ic and having a second width w2 exceeding the first width w1. The first region 72 and second region 74 are connected by a transition region 73 extending over a spanwise length Ib and having a variable width over its length. As seen in the spanwise direction, the transition region 73 has a proximal end 92 and a distal end 94 (as seen from the tip end of the blade).

(22) FIG. 6 shows various cross sections taken along lines I (FIG. 6c), II (FIG. 6b) and III (FIG. 6a) of FIG. 4. In the embodiment shown in FIG. 6, a shell half 62, for example a pressure side shell half, is manufactured in a mould 90. The mould 90 comprises a moulding surface defining an outer surface of the finished wind turbine blade. The aerodynamic shell half 62 may be manufactured by applying a waxy substance to the moulding surface in order to be able to remove the shell part after moulding. Then a gelcoat may be applied to the moulding surface.

(23) The shell half comprises one or more outer skin layers 63, e.g. made of fibre glass layers, and one or more inner skin layers 65. A first thickened portion 67 and a second thickened portion 69 are formed by a sandwich core material such as balsawood, which is arranged between the skin layers 63, 65. The recess is formed between the two thickened portions 67, 69 such that the first thickened portion 67 laterally adjoins the recess 70 at a first side 70a of the recess and the second thickened portion 69 laterally adjoins the recess 70 at a second side 70b of the recess 70. As seen in FIGS. 6 and 7, the sides 70a, 70b of the recess are advantageously chamfered.

(24) The partial perspective view of FIG. 7 further illustrates the recess 70 as having a base 71 and two opposing side walls 70a, 70b, each side wall having a respective upper edge 76a, 76b. It is preferred that the transition region 73 of the recess 70 has a proximal end 92 and a distal end 94 as seen in FIG. 5. FIG. 7 illustrates an angle Δ formed between the base 71 of the recess 70 and a hatched line (see hatched line) extending from the upper edge 76a of sidewall 70a at the proximal end to an interface or intersection between the base 71 and sidewall 70a at the distal end. Said angle is preferably as low as possible, such as below 3 degrees to minimize wrinkle formation.

(25) The invention has been described with reference to advantageous embodiments. However, the scope of the invention is not limited to the illustrated embodiment, and alterations and modifications can be carried out without deviating from the scope of the invention. While the invention has been described referring to a first spar cap and a second spar cap, it is recognised that the two parts may also be parts of a single spar cap or load-carrying structure.

LIST OF REFERENCE NUMERALS

(26) 4 tower

(27) 6 nacelle

(28) 8 hub

(29) 10 blades

(30) 14 blade tip

(31) 16 blade root

(32) 18 leading edge

(33) 20 trailing edge

(34) 30 root region

(35) 32 transition region

(36) 34 airfoil region

(37) 36 pressure side shell part

(38) 38 suction side shell part

(39) 40 shoulder

(40) 41 spar cap

(41) 42 fibre layers

(42) 43 sandwich core material

(43) 45 spar cap

(44) 46 fibre layers

(45) 47 sandwich core material

(46) 50 first shear web

(47) 51 core member

(48) 52 skin layers

(49) 55 second shear web

(50) 56 sandwich core material of second shear web

(51) 57 skin layers of second shear web

(52) 60 filler ropes

(53) 62 shell part

(54) 63 outer skin layer

(55) 65 inner skin layer

(56) 64 outer surface of shell

(57) 65 inner surface of shell

(58) 67 first thickened portion

(59) 69 second thickened portion

(60) 70 recess

(61) 70a,b sides of recess

(62) 71 base of recess

(63) 72 first region of recess

(64) 73 transition region

(65) 74 second region of recess

(66) 76 upper edges of recess

(67) 80 first spar cap

(68) 82 second spar cap

(69) 90 mould

(70) 92 proximal end of transition region

(71) 94 distal end of transition region

(72) Ia spanwise length of first region

(73) Ib spanwise length of transition region

(74) Ic spanwise length of second region

(75) L spanwise direction

(76) r distance from hub

(77) R rotor radius

(78) w1 width of first region

(79) w2 width of second region