Patent Application
20210164436
The invention relates to a protective cover system for protecting a leading edge of a wind turbine rotor blade from erosion, to a wind turbine rotor blade comprising such a protective cover system, and to a method for mounting such a protective cover system to a wind turbine rotor blade.
Nowadays rotor or turbine blades e.g. blades for wind, gas or steam turbines are made of fibre reinforced plastic composite materials. Erosion of the leading edge of such blades is known to occur in operation. Erosion of the leading edge of a turbine blade may reduce the efficiency of the blade and thus the power output by the turbine.
Wind turbine rotor blades, and in particular those of offshore wind turbines, are specially affected by wear which occurs where interacting with particles or droplets result in degrading of their leading edge. Erosion of the leading edge of wind turbine blades by droplet impingement wear may reduce the blade aerodynamic efficiency and thus the maximum output power of the wind turbine.
Erosion on a turbine blade may penetrate into the structural fibre reinforced laminate leading to severe failure of the turbine blade requiring repair which can prove very costly to turbine operators. This holds especially true for offshore wind turbines because their maintenance costs are extremely high.
This is why generally a surface system is foreseen on the leading edge of a wind turbine blade.
Repair procedures typically include a re-establishment of the surface systems mostly comprising filler and paint. In case of severe degradation, a lamination may be required. Different solutions are used for protecting and/or repairing leading edges of composite blades, including adhesive plastic tapes.
EP2497943 A1 discloses a wind turbine blade with an improved surface, wherein a plastic tape is arranged at specific locations of the blade to reinforce the blade surface.
The lift time of erosion protection tapes will last approximately between 5-8 years, depending on the environmental conditions of the location of the wind turbine, as well as the turbine operating conditions. In general an erosion protection tape will rupture due to heavy erosion, causing the layer left on the rotor blade to freely flutter in the wind. This fluttering will result in a loss of aerodynamic performance of the blade, as well as in the generation of additional aerodynamic noise.
Other solutions suggest erosion protection coatings applied by brush, roller, spatula or spray can. Generally, such coatings have to be applied at a certain humidity level and within a special temperature window, e.g. 20 and 25 degree Celsius. Thus, these solutions may not be used in the field, e.g. at offshore wind farms.
Further solutions suggest attaching a protective cap made of a polymer material to the forefront of a wind turbine blade during manufacturing of the blade. One drawback of these solutions is that due to the length of the protective cap needed for a larger wind turbine blade, the mounting of such a protective cap in the field is impossible or at least very difficult, especially offshore. The transport and mounting of such protective caps are extremely cost intensive.
It is an object of the present invention to overcome the aforementioned drawbacks. A further object of the present invention is to provide a solution which allows for significantly reducing the required maintenance of the wind turbine and thus for reducing the maintenance costs compared to known protective solutions.
These objects are solved by the features of the independent claims. Further advantageous developments are subject of the dependent claims.
The invention relates to a protective cover system (10) for protecting a leading edge (59) of a wind turbine rotor blade (55) from erosion comprising a first protective cover (1) and a second protective cover (2). The first protective cover (1) and the second protective cover (2) comprise a polymer material. Both protective covers (1, 2) are pre-formed into a curved shape so as to accommodate at least a part of a wind turbine blade (55). Each of the first and second protective covers (1, 2) has a tip end (3) and a root end (4).
The first protective cover (1) comprises a first overlap portion (4a) at the root end (4) and the second protective cover (2) comprises a second overlap portion (3a) at the tip end (3).
The shape of the first overlap portion (4a) at the root end (4) of the first protective cover (1) is substantially complementary to the shape of the second overlap portion (2) at the tip end (3) of the second protective cover (2) such that when overlapping these first and second overlap portions (4a, 3a), the resulting cross section of the overlapped overlap portions (4a, 3a) substantially corresponds to the cross sections of at least one of the first and second protective covers (1, 2) outside the overlap portions (4a, 3a).
The resulting cross section of the overlapped overlap portions (4a, 3a) has and ensures a substantially continuous development of the cross section throughout the first and second protective covers (1, 2). As a result thereof, the aerodynamic properties of a wind turbine blade comprising this arrangement correspond substantially to those comprising a single protective cover with a continuous cross section development between its tip and root ends.
Smooth transitions between the first (1) and the second protective cover (2) are achieved when the protective cover system (10) is mounted on a leading edge of a blade (55).
An advantage thereof is that the protective cover system (10) does not peel off and erosion of the blade may not arise or is extremely limited where the protective covers (1, 2) overlap.
Advantageously, the protective cover system according to the present invention when mounted to a wind turbine blade avoids replenishing the leading edge protection of the wind turbine blade repeatedly during the operational life of the blade. Tests have shown that the protective cover system according to the invention may last on a wind turbine blade a lifetime of the blade.
In contrast to other erosion protection shields, like tapes or coatings, a protective cover (1, 2) of the protective cover system (10) according to the present invention do not only adapt to a curved shape of a leading edge of a blade when attached to the blade but it has the curved shape already before being mounted to a curved surface. Thus the handling of the protective covers (1, 2) during repair or manufacturing of blades (55) is easier than the handling of other erosion protective elements or shields like tapes or coatings. In addition, a tape could have the same Youngs Modulus, but not the same elongation at break as a protective cover 1, 2 according to the present invention.
The shapes of the first and the second overlap portions (3a, 4a) are substantially complementary such that the protective cover system (10) has a substantially closed surface even if the overlap portions (3a, 4a) do not engage with each other but only touch each other. Thus, in case the first and the second protective covers (1, 2) are disposed next to one another and their overlap portions (3a, 4a) are disposed one on top of the other but not as close as possible, a very little recess will arise on the surface of the protective cover system. However, due to the substantially complementary shapes of the overlap portions (3a, 4a), the protective cover system (10) has no interruption and will still protect the blade (55) underneath.
In an embodiment of the invention, the first overlap portion (4a) tapers at least partly towards the root end (4) of the first protective cover (1) and the second overlap portion (2) tapers at least partly towards the tip end (3) of the second protective cover (2). Such a tapered overlap portion will easier forgive any mounting variances.
In a further embodiment of the invention, each of the first overlap portion (1) and the second overlap portion (2) comprises at least one step (5).
In yet a further embodiment of the invention, the step (5) is at least partly rounded.
According to another embodiment of the invention, one of the first and second protective covers (1, 2) comprises a protruding element (6) in the respective first or second overlap portion (4a, 3a) and the other one of the first and second protective covers (1, 2) comprises a recess (7) in the other respective first or second overlap portion (4a, 3a),
wherein the recess (7) is arranged to accommodate the protruding element (6). Allows for guiding the covers when being mounted.
According to another embodiment of the invention, the recess (7) may be a hole and the protruding element (6) may be nipple-shaped.
According to a further embodiment of the invention, at least one of the protective covers (1, 2) comprise an Elastomer, e.g. comprising Polyurethane or Polyethylene, preferably a Polyurethane based Elastomer.
Each of the first and second protective covers (1, 2) comprises four corners (8). At least one of these corners (8) may be rounded. A rounded corner prevents the corner of the respective protective cover from peeling off.
According to yet a further embodiment of the invention,
the first and second protective covers (1, 2) are
pre-formed into a curved shape in a lateral direction and
extend from their tip end (3) to their root end (4) in a longitudinal direction, wherein at least one of the first and second protective covers (1, 2) has a centerline (C) running in the longitudinal direction, and this centerline is curved such that the first and second protective covers (1, 2) have a sagitta height (Hp).
According to another embodiment of the invention, the first and second protective covers (1, 2) are pre-formed into a curved shape in a lateral direction and extend from their tip end (3) to their root end (4) in a longitudinal direction,
wherein each of the first and second protective covers (1, 2) has a centerline (C) running in the longitudinal direction, and a first outer edge (9a) and a second outer edge (9b), both running in parallel to the centerline (C). The first and second protective covers (1, 2) have a thickness along their centerline (C) which tapers off towards the respective first and second outer edges (9a, 9b).
Avoiding peeling off of covers.
According to a further embodiment of the invention, the first and second protective covers (1, 2) are pre-formed into a curved shape in a lateral direction and extend from their tip end (3) to their root end (4) in a longitudinal direction,
wherein at least one of the first and second protective covers (1, 2) is curved in the longitudinal direction and/or tapers in the longitudinal direction, preferably towards its tip end (3). Advantage: This avoids that the protective covers wrinkle when mounted to a blade. The tapering also avoids peel-off of the protective cover and provides for a continuous transition between the protective covers.
According to another embodiment of the invention, a length of at least one of the first and second protective cover (1, 2) amounts to about 2000 mm at maximum, preferably to about 1000 mm. Advantage: This avoids that the protective covers wrinkle when mounted to a blade. The tapering also avoids peel-off of the protective cover and provides for a continuous transition between the protective covers.
According to a further embodiment of the invention, at least one of the first and second protective cover (1, 2) comprises a printed centerline (C) on its outer surface (11) to facilitate the mounting onto a leading edge (59) of a wind turbine blade (55). This facilitates the alignment of shells and enables a quality check by optical means as well as allows for documenting quality-related information, e.g. photographs.
The wind turbine blade (55) according to the present invention comprises a protective cover system (10) which is connected to the wind turbine blade (55) along a leading edge (59) of the blade (55). An advantage thereof is that less repair work is needed and the maintenance costs are reduced. In addition, a combination with a de-icing or LPS is possible because of the electrical insulation property of the covers 1, 2.
The method for mounting a protective cover system (10) according to the present invention comprises the steps of:
An embodiment of the invention comprises a protective cover system (10) according to claim 1 further comprising
Possible for some blades—first set true copy of second set!—Depending on shape and/or shorter length;
depending on repair length
Another embodiment of the invention comprises a protective cover system according to claim 6, wherein the LE radius of the first protective cover (1) is different from the LE radius of the second protective cover (2).
bending rate->LE radius
more open curvature vs., more closed curvature
only 4 diff cover types->
A further embodiment of the invention comprises a protective cover system according to claim 6 or 7, wherein the first protective cover (1) has a chord length between 0.5 (2 m from tip/1 m-3 m) and 1.3 (12 m from tip/pref. 9-24 m/more pref. 10-14 m) meters and the second protective cover (2) has a chord length of about 1.3 meters or more.
Outer ⅓ (−½ to) of the length of LE −50%/50% for diff sets of shells
A further embodiment of the invention comprises a protective cover system according to claim 6 or 7, wherein the first protective cover (1) has a chord length between 0.5 and 1.3 meters and the second protective cover (2) has a chord length of about 1.3 meters or more.
Another embodiment of the invention comprises a protective cover system according to anyone of claims 6 to 8, wherein the protective tip cover has a swept end to cover and fit the blade tip.
Pre-bend—more curved than other shells
not exact copy of blade tip but more curved—so it is stretched when mounted to the blade
Valid for all shells, but more exaggerated for tip shell
Tip covered or not covered/
open tip—easier fit to all variations of blade tips, but less erosion protection performance than closed one
close tip—better protection, but requires little variance in blade tips therefore more shell variants are needed
Another embodiment of the invention comprises a protective cover system according to anyone of claims 6 to 9, wherein the protective root cover features a smooth transition towards the leading edge on the root side.
smooth transition towards the leading edge on the root side
Option: root shell is same as first set of shells
Advantages:
for claim 6
Compared to a rigid protection shell that can be only mounted on a predefined part of the leading-edge surface, the material of which the protective covers according to the present invention are built has a certain flexibility which allows their mounting along a much greater surface area along the leading-edge. As a result, the total number of individually designed protective covers can be reduced to a strict minimum. The resulting economic advantages with respect to production costs and logistic are quite obvious and important. Since in many cases, the surface shape along the leading-edge of a wind turbine blade changes only smoothly, it's even possible to use just two different sets of protective covers, plus a protective tip cover and a protective root cover. It is even possible to do with just two one set of protective covers, plus a protective tip cover.
for claim 7:
As stated before, the surface shape, and more precisely the leading edge radius, along the leading-edge of a wind turbine blade changes only smoothly. Therefore, the same manufacturing process can be used to build the protective covers of the different sets. Same 3D-mould may be used for multiple blades types. This is be advantageously used to reduce furthermore the associated production costs.
A “wind turbine rotor blade” may also be referred to as “wind turbine blade”. A “protective cover” for protecting a leading edge of a wind turbine blade from erosion may also be referred to as “shell” or “shield”.
The “protective cover” according to the present invention is preformed. The protective cover is brought into a curved shape before being mounted. It may be machined. Preferably, it is pre-casted. The term “preformed” may also be referred to as pre-shaped. According to the present invention, the “protective cover” is pre-shaped into a curved shape so as to accommodate at least a part of a wind turbine blade (55). The “curved shape” referred to in claim 1 may also be described as a channel-like shape or as a substantially parabolic channel.
It is known in the art to cast a male part on the blade by use of a male mould. The resulting bond may be of superior quality. In contrast to this concept, a female mould may be used in addition to the male mould to pre-cast the first and second protective covers (1, 2) instead of casting over the blade (55) with one or more protective covers (1, 2).
Covers of an Elastomeric Polyurethane are preferred. This may be a rubbery, elastic and flexible material to allow the protective shell to be easily form-fitted to a wind turbine blade surface and to provide it with sufficient elasticity so as to dampen the impact of erosive influences.
The protective cover may be flexible. In other words, it may have some flexibility. That means the protective cover may be flexible in such a way that it is less flexible than a tape but more flexible than a stiff component. The advantage of a preformed but flexible protective cover is on the one hand a curved shape which facilitates handling of the cover and provides for a good fit to a curved surface, and on the other hand the fact that the protective cover may easily adapt to a range of differently curved surfaces, e.g. at different locations along a leading edge of a wind turbine blade. In other words, a preformed and flexible protective cover, e.g. made of a Polyurethane based Elastomer, may adapt to different curved surfaces having a range of different bending rates (angle) in a predetermined range of bending rates.
In order to keep the protective covers (1, 2) on the blade 55 even after being struck by a relatively large foreign object, such as a bird or an ice fragment, without a protective cover (1, 2) peeling off, the protective cover system (10) is bonded to the blade (55), e.g. by means of a heat-activatable adhesive. In so doing, the adhesive may be heated, e.g. by a heating blanket or a vacuum heating blanket.
The wind turbine blade comprises a protective cover system according to the invention, wherein the protective cover system is connected to the wind turbine blade along a leading edge of this blade.
The method for mounting a protective system to a leading edge 59 of a wind turbine rotor blade 55 from erosion,
the method comprises the steps of:
The invention is directed towards having a plastic shell 1, 2 that is bonded to the outer surface of the blade 55, more specific of the leading edge 59. The shell 1, 2 is referred herein to as protective cover 3. It may have a width W of +/−100 mm with respect to the leading edge 59 of the wind turbine blade 55, see
The shell may be made of a polymer comprising polyurethane and a further component. The shell is a curved protective plate in the shape of a parabolic channel. It is designed to be mounted lengthwise along the leading edge of a wind turbine blade. The shell is moulded in a moulding process. The shell is pre-moulded but still pliable enough to provide a tight fit to the turbine blade.
The shell system comprises a first shell and a second shell. Each shell has two short edges, herein also referred to as tip end and root end (3, 4) and two long edges, herein also referred to as outer edges. The long edges are longer than the short edges. The first short edge 4 is located at one end of the parabolic channel, and the second short edge 3 is located at the opposite end of the parabolic channel. The two long edges 9 are perpendicular to the two short edges 3, 4.
The shell has a centerline C running lengthwise along the substantially parabolic channel in parallel to the long edges 9. The thickness Tn of the shell is greatest along the centerline C and gradually diminishes toward the two long edges 9. The thickness Tn may be 3 mm at the centerline C, see
Overlap section: A shell system comprises at least two of above-mentioned shells 1, 2 touching one another at their short edges 3, 4. The shells may be connected to each other or interconnected by various means, e.g. by edge chamfer and guiding nipple 6, see
The overlap portions 3a, 4amay have a length Lo of 30 mm in longitudinal direction of the protective cover 1, 2. The protrusion 6 may have a diameter Dp of 2 mm and the recess 7 may also have diameter Dr of 2 mm. The length Lp of the protrusion may be 3 mm, see
The shells may be interconnected by means of connecting elements 5, 20, 21 that serve for a guiding/connecting of the two shells 1, 2. Mechanical Interlocking between the shells 1, 2 is achieved by having connecting elements 5, 20, 21 that have a nipple shape. This shape reduces stress concentration for the connecting element 5, 20, 21.
Transition consideration: Camfered interna—no exposure for the blade. Stepwise decline transition—provide thickness and strength which prolong the lifetime.
Different decline transitions at different positions of the leading edge are possible, e.g. step-like connecting elements 5 at the leading edge (that means at the Centerline C) of the shell 1, 2), step-like connecting elements 20 having rounded edges onto a width of the shell of +/−50 mm from the Leading edge (Centerline C) and tapered connecting elements 21 from +/−50 mm on to a width of +/−100 m (that means until the outer edges 9, 9a, 9b), see
The blade chord length is decisive of the aerodynamic property—therefore it needs to be as thin as possible. The thickness Tne at an end 4 of the shell may be around 0.05 mm. Corner rounding of corner 8 with a radius R5 help avoiding peeling off of the shell, see
At an end 3, 4 in lengthwise direction of the shell, the overlap area 3a, 4amay have a length of 20-40 mm, preferably 30 mm. The thickness of the shell may diminish in the overlap area to a very small thickness in the range of 0.03 mm to 0.07 mm, preferably to about 0.05 mm.
The shell may have a peel height Hp, referred to in Danish language as Peelhejde (in English language Sagitta height). That means the shell 1, 2 may be curved with a radius R2, that means the centerline C is curved. see
It is from other technology to extrude plastic elements. This invention is directed towards overcoming the disadvantage of having an extrude element.
Having a sagitta height Hp enables the shells to be drapable. The height difference between an outer end of the shell and a position at the centerline in the middle of the shell may be 3 to 7 mm, preferably about 5 mm.
The sagitta height Hp is achieved during the manufacturing of the shell. Each of the shells will be moulded as one piece. Another advantage of casting the shells is that each shell can be tailored.
The protective cover system 10 comprising a first and a second protective cover 1, 2 (first and second shell) may have an open angle at the Overlap OV. That means the angle between centerline C and root or tip end 3, 4 is smaller than 90 degrees and the angle between outer edge 9 and root or tip end 3, 4 is greater than 90 degrees. At the outer edge 9 the distance Dd may be 3 mm, see
Each overlap influences the aerodynamic performance of the blade. It is import to avoid excess overlap and thereby material. Therefore the overlap is less than 30 mm.
Bondline Features: Indentation, e.g with 20 mm spacing inbetween the indentations, on the inner surface ensure a better bonding due to the fact that the indentation entrap glue, see
A tailored tip as shown in
Enclosing the tip of the blade is an option, as also shown in
As an alternative, the tip shell 1, may be designed to leave the tip of the blade 30 blank, that means not covered, see
Advantages
Further Aspects of Invention
The length of at least one of the first and second protective cover (1, 2) may amount to about 2000 mm at maximum, preferably to about 1000 mm.
Advantage: good length blade, in view of operational window (1.7 m). w/o repositioning worker himself
Method for mounting a protective cover system (10) according to one of claims 1-4 to a leading edge (59) of a wind turbine blade (55),
the method comprises the steps of:
The protective cover system (10) according to claim 1 further comprising
Possible for some blades—first set true copy of second set!—Depending on shape and/or shorter length;
depending on repair length
The protective cover system according to claim 6, wherein the LE radius of the first protective cover (1) is different from the LE radius of the second protective cover (2).
bending rate->LE radius
more open curvature vs., more closed curvature
only 4 diff cover types->
The protective cover system according to claim 6 or 7, wherein the first protective cover (1) has a chord length between 0.5 (2 m from tip/1 m-3 m) and 1.3 (12 m from tip/pref. 9-24 m/more pref. 10-14 m) meters and the second protective cover (2) has a chord length of about 1.3 meters or more.
Outer ⅓ (−½ to) of the length of LE −50%/50% for diff sets of shells
The protective cover system according to claim 6 or 7, wherein the first protective cover (1) has a chord length between 0.5 and 1.3 meters and the second protective cover (2) has a chord length of about 1.3 meters or more.
The protective cover system according to anyone of claims 6 to 8, wherein the protective tip cover has a swept end to cover and fit the blade tip.
Pre-bend—more curved than other shells
not exact copy of blade tip but more curved—so it is stretched when mounted to the blade
Valid for all shells, but more exaggerated for tip shell
Tip covered or not covered/
open tip—easier fit to all variations of blade tips, but less erosion protection performance than closed one
close tip—better protection, but requires little variance in blade tips therefore more shell variants are needed
The protective cover system according to anyone of claims 6 to 9, wherein the protective root cover features a smooth transition towards the leading edge on the root side.
smooth transition towards the leading edge on the root side
Option: No root shell
Advantages
for claim 6
Compared to a rigid protection shell that can be only mounted on a predefined part of the leading-edge surface, the material of which the protective covers according to the present invention are built has a certain flexibility which allows their mounting along a much greater surface area along the leading-edge. As a result, the total number of individually designed protective covers can be reduced to a strict minimum. The resulting economic advantages with respect to production costs and logistic are quite obvious and important. Since in many cases, the surface shape along the leading-edge of a wind turbine blade changes only smoothly, it's even possible to use just two different sets of protective covers, plus a protective tip cover and a protective root cover. It is even possible to do with just two one set of protective covers, plus a protective tip cover.
for claim 7:
As stated before, the surface shape, and more precisely the leading edge radius, along the leading-edge of a wind turbine blade changes only smoothly. Therefore, the same manufacturing process can be used to build the protective covers of the different sets. Same 3D-mould may be used for multiple blades types. This is be advantageously used to reduce furthermore the associated production costs.
| Number | Date | Country | Kind |
|---|---|---|---|
| 16190944.5 | Sep 2016 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2017/074568 | 9/27/2017 | WO | 00 |
