U.S. patent application number 10/508379 was filed with the patent office on 2005-08-18 for wind turbine blade with carbon fibre tip.
Invention is credited to Andersen, Lars Fuglsang, Grabau, Peter.
Application Number | 20050180853 10/508379 |
Document ID | / |
Family ID | 27837991 |
Filed Date | 2005-08-18 |
United States Patent
Application |
20050180853 |
Kind Code |
A1 |
Grabau, Peter ; et
al. |
August 18, 2005 |
Wind turbine blade with carbon fibre tip
Abstract
The invention relates to a wind turbine blade (14) of
fibre-reinforced polymer. The blade (14) is divided into an inner
end portion (15) including the blade root and made substantially
from fibre glass-reinforced polymer, and an outer end portion (17)
including the blade tip and made substantially from carbon
fibre-reinforced polymer.
Inventors: |
Grabau, Peter; (Kolding,
DK) ; Andersen, Lars Fuglsang; (Odense, DK) |
Correspondence
Address: |
Cooper & Dunham
1185 Avenue of the Americas
New York
NY
10036
US
|
Family ID: |
27837991 |
Appl. No.: |
10/508379 |
Filed: |
September 20, 2004 |
PCT Filed: |
March 19, 2003 |
PCT NO: |
PCT/DK03/00185 |
Current U.S.
Class: |
416/241R |
Current CPC
Class: |
Y02E 10/72 20130101;
F05B 2240/30 20130101; B29L 2031/085 20130101; Y02P 70/50 20151101;
Y02P 70/523 20151101; Y02E 10/721 20130101; F03D 1/065
20130101 |
Class at
Publication: |
416/241.00R |
International
Class: |
B63H 001/26 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 19, 2002 |
DK |
PA 2002 00424 |
Claims
1. Wind turbine blade (14) of fibre-reinforced polymer
characterised in that it is divided into an inner end portion (15)
including the blade root and made substantially from fibre
glass-reinforced polymer, and an outer end portion (17) including
the blade tip and made substantially from carbon fibre-reinforced
polymer.
2. Wind turbine blade (14) according to claim 1, characterised in
that the outer end portion (17) constitutes between 25 and 50% of
the entire length of the blade (14).
3. Wind turbine (14) according to claim 1, characterised in that
the outer end portion (17) opposite the blade tip includes a
transition zone (16) in which the carbon fibres are gradually
replaced by glass fibres.
4. Wind turbine blade (14) according to claim 3, wherein the length
of the transition zone (16) is between 0.5 and 1 metre.
5. Wind turbine blade (14) according to claim 3, characterised in
that the two types of fibres are distributed such in the polymer
matrix that carbon fibres or carbon fibre bundles (1) with varying
lengths extend from a first end of the transition zone (II) and
glass fibres or glass fibre bundles (2) extend from the opposite
end of the transition zone (II).
6. Wind turbine blade (14) according to claim 3, characterised in
that the transition zone (II) is formed of a laminate of several
fibre layers (6,7), in which each fibre layer has a boundary
surface (10) at a position in the longitudinal direction, the fibre
layer including carbon fibres (6) on one side of the boundary
surface and glass fibres (7) on the other side of the boundary
face, the boundary surfaces (10) of each fibre layer being
displaced in relation to each other in the longitudinal direction
of the blade (14).
7. Wind turbine blade according to claim 6, wherein the boundary
surfaces (11) are serrated in a sectional view parallel to the
fibre layers (3, 4, 5).
8. Wind turbine blade according to claim 7, wherein the tips (12)
of the serrated boundary surfaces (11) are displaced in relation to
each other in the transverse direction of the blade (14).
Description
TECHNICAL FIELD
[0001] The invention relates to a wind turbine blade according to
the preamble of claim 1.
[0002] Wind turbine blades are typically made by means of two blade
shell halves of fibre-reinforced polymer. When moulded the two
halves are glued together along the edges and via two bracings,
which prior thereto have been glued to the inner face of one the
blade shell halves. The other blade shell half is then arranged on
top of bracings and glued thereto and along the edges.
[0003] The blade shell halves per se are typically made by vacuum
infusion, in which evenly distributed fibres, rovings, which are
fibre bundles, bands of rovings or mats which may be felt mats of
single-fibres or woven mats of fibre rovings, are layered in a
mould part and cover by a vacuum bag. By creating vacuum (typically
80-90%) in the cavity between the inner face of the mould part and
the vacuum bag resin is sucked into and fills the cavity containing
the fibre material. In order to obtain the optimum distribution of
resin, so-called distribution layers and distribution channels are
often used between the vacuum bag and the fibre material.
[0004] The used polymer is typically polyester or epoxy, and the
fibre reinforcement is usually based on fibre glass. It is,
however, also known to use carbon fibres which are stiffer than
glass fibres, but have a smaller elongation at breakage than glass
fibres. The carbon fibres may be added to obtain a higher degree of
stiffness and/or a lower weight. It is thus possible to let a
portion of the fibre reinforcement be formed of carbon fibres to
reduce the weight of the blade without the blade loosing too much
of its stiffness. Carbon fibres are, however, encumbered by the
drawback of being significantly more expensive than glass fibres,
which is one of the reasons why wind turbine blades of carbon
fibre-reinforced polymer are not widely used.
BACKGROUND ART
[0005] From WO 00/14405 it is known to reinforce a wind turbine
blade of fibre glass polymer with longitudinal bands of carbon
fibre-reinforced polymer.
[0006] U.S. Pat. No. 6,287,122 discloses the manufacture of
elongated composite products, wherein a variation in the stiffness
of the product along its length is obtained by altering the fibre
content or the angle orientation of braided fibres.
[0007] U.S. Pat. No. 5,520,532 discloses a mould part of
fibre-reinforced polymer of a varying stiffness, said stiffness
being obtained by varying the number of fibre mat layers.
[0008] U.S. Pat. No. 4,077,740 discloses a helicopter rotor blade
of a fibre composite material, the stiffness of the blade varying
when seen in longitudinal direction. This feature is obtained by
varying the fibre orientation so as to obtain an enhanced vibration
dampening.
[0009] The dead load of modern fibreglass blades constitutes a
problem in that a high dead load moment requires a high fatigue
resistance in the edgewise direction of the blade. This problem
increases with the length of the blades.
BRIEF DESCRIPTION OF THE INVENTION
[0010] The object of the invention is to solve the above problem in
a simple and inexpensive manner.
[0011] According to the invention the object is obtained in that
the blade is divided into an inner end portion including the blade
root and made substantially from fibre glass-reinforced polymer and
an outer end portion including the blade tip and made substantially
from carbon fibre-reinforced polymer. The weight is thus reduced in
the outermost part, whereby the dead load moment is minimised. Less
material and/or a smaller cross section is thus required at the
innermost portion of the blade and the load on the turbine hub is
reduced. The outermost portion of the blade may furthermore be
provided with an increased stiffness, whereby the risk of the blade
deflecting so heavily that the blade tip hits the turbine tower is
reduced. Such a wind turbine blade is more inexpensive to produce
than a blade made solely of carbon-fibre-reinforced polymer.
[0012] At a certain degree of stiffness, the dead load may be
reduced by using carbon fibres in the outer end portion, whereby
the dynamic loads on the blade shell and the blade root may also be
reduced, said parts being particularly sensitive to dynamic
loads.
[0013] By changing the carbon fibre content in the outer end
portion or the length thereof, the stiffness as well as the natural
frequencies may be varied. The stiffness and the natural
frequencies may thus be optimised to the specific conditions.
[0014] A comparatively stiff outer end portion and a comparatively
less stiff inner end portion result in an advantageous deflection
shape as regards aerodynamic damping, the damping depending on the
integrated deflection along the blade during a vibration. An
increased aerodynamic damping is advantageous in that the
aerodynamic load thus is reduced.
[0015] Compared to a blade made solely of fibre glass-reinforced
polymer or a blade made solely of carbon-fibre-reinforced polymer,
a blade according to the invention renders an optimum stiffness to
costs ratio.
[0016] According to an embodiment the outer end portion may
constitute between 25% and 50% of the entire length of the
blade.
[0017] The outer end portion may, however, constitute 5%, 10%, 15%,
20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%,
85% or even 90% of the blade's length.
[0018] According to a preferred embodiment the outer end portion
opposite the blade tip may include a transition zone in which the
carbon fibres are gradually replaced by glass fibres. As a result
an abrupt change in the blade stiffness in the transitional area
between the carbon fibres and the glass fibres is avoided. At heavy
dynamic or static stresses, an abrupt transition between the carbon
fibres and the glass fibres causes a concentration of stress, the
carbon fibres typically being 3-4 times stiffer than the glass
fibres. This may involve a risk of destroying the blade. By using
such a transition zone a heavy stress concentration is avoided at
the boundary surface between the carbon fibres and the glass
fibres.
[0019] According to an embodiment the length of the transition zone
may be between 0.5 and 1 metre. A length of up to 10 metres or of
even more than 10 metres may, however, also be preferred.
[0020] According to the invention the two types of fibres may be
distributed such in the polymer matrix that carbon fibres or carbon
fibre bundles of varying lengths extend from a first end of the
transition zone, and glass fibres or glass fibre bundles extend
from the opposite end of the transition zone, whereby a
particularly smooth transition in stiffness is obtained.
[0021] According to another embodiment the transition zone may be
formed of a laminate of several fibre layers, in which each fibre
layer has a boundary surface at a position in the longitudinal
direction, the fibre layer including carbon fibres on one side of
the boundary surface and glass fibres on the other side of the
boundary face, the boundary surfaces of each fibre layer being
displaced in relation to each other in the longitudinal direction
of the blade. As a result a gradual change in stiffness in the
transition zone is obtained in a particularly simple manner.
[0022] According to an embodiment the boundary surfaces may be
serrated in a sectional view parallel to the fibre layers. An even
smoother transition in the stiffness is thus obtained in the
transition zone. The tips of the serrated boundary surfaces may be
displaced in relation to each other in the transverse direction of
the blade. As a result an additional smooth variation in the
stiffness is obtained in the transition zone.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] The invention is explained in greater detail below by means
of various embodiments of the invention in diagrammatical views in
the drawings, in which
[0024] FIG. 1 shows a wind turbine with three blades,
[0025] FIG. 2 shows a blade according to an embodiment of the
invention,
[0026] FIG. 3 shows a continuous variation of the quantitative
ratio of carbon fibre to glass fibres according to a particular
embodiment of the invention,
[0027] FIG. 4 shows a continuous variation of the quantitative
ratio of carbon fibre to glass fibres according to another
particular embodiment of the invention,
[0028] FIG. 5 shows a continuous variation of the quantitative
ratio of carbon fibre to glass fibres according to a third
particular embodiment of the invention,
[0029] FIG. 6 shows diagrams illustrating how the quantitative
ratio of carbon fibres to glass fibres may be varied in the
transition zone.
BEST MODES FOR CARRYING OUT THE INVENTION
[0030] FIG. 1 shows a modern wind turbine including a tower 12 with
a hub 13 and three wind turbine blades 14 extending from the
hub.
[0031] FIG. 2 illustrates an embodiment of a wind turbine blade
according to the invention, in which an inner end portion 15
including the blade root is made substantially from fibre
glass-reinforced polymer, and in which an outer end portion 17
including the blade tip is made substantially from carbon
fibre-reinforced polymer. Bordering on the inner end portion 15 the
outer end portion 17 includes a transition zone 16, in which the
carbon fibres are gradually replaced by glass fibres such that a
gradual change in the stiffness of the blade is obtained.
[0032] FIG. 3 is a sectional view of the transition zone, in which
the quantitative ratio of carbon fibres to glass fibres gradually
changes. The carbon fibres 1 extend from the left-hand side of the
sectional view in form of bundles or single-fibres of different
lengths. The glass fibres 2 are not visible in FIG. 3, but they
complement the carbon fibres 1. The transition between the two
types of fibres are thus diffuse such that a smooth transition is
obtained from the outer end portion 17, which is substantially
reinforced with carbon fibres 1, to the inner end portion 15, which
is substantially reinforced with glass fibres 2.
[0033] FIG. 4 illustrates a second embodiment in which fibre mats
of non-woven fibres or knitted fibre bundles have been punched,
whereby they are provided with serrations in one of their ends. Two
mats of carbon fibres and glass fibres, respectively, in the same
fibre layer have correspondingly shaped serrations and thus mesh
with each other. Two stacked fibre layer serrations may be
displaced in relation to each other, as shown in FIG. 4, whereby a
smooth transition is obtained between the stiffness in the area
with carbon fibres shown on the left-hand side and the stiffness in
the area with glass fibres shown on the right-hand side. FIG. 4 is
a diagrammatic view of two stacked carbon fibre layers 3, 4 and
corresponding glass fibre layers are provided in the area 5. As
also shown in FIG. 4 the tips 12 of the serrations 11 of the two
carbon fibre layers 3, 4 are displaced in transverse direction to
ensure a smooth stiffness transition. A transition zone between the
area with carbon fibres and the areas with glass fibres is thus
determined by the length of the serrations. Accordingly the
transition zone may vary according to need by either shortening or
extending the length of the serrations.
[0034] FIG. 5 shows a particularly simple provision of the
transition zone between the outer end portion and the inner end
portion. FIG. 5 is a diagrammatic view of four stacked fibre layers
including a carbon fibre layer 6 and a glass fibre layer 7. Each
fibre layer has a boundary surface 10, where the carbon fibres are
replaced by glass fibres, a transition zone of some length being
obtained, since the boundary faces 10 are displaced in relation to
each other. The length of the transition zone may of course be
varied according to need by displacing the boundary faces more or
less in relation to each other and/or by using more fibre
layers.
[0035] FIG. 6 is a diagrammatic view of the quantitative ratio of
the carbon fibres to the glass fibres in the longitudinal direction
of the blade. The first zone I corresponds to the outer end portion
17 and the second zone III corresponds to the inner end portion 15
of the blade. A transition zone II is provided between the two
zones, the ratio of glass fibres 9 in said zone steadily increasing
from the level in the first zone I to the level in the second zone
III.
[0036] FIG. 6a thus shows an embodiment, in which the first zone I
is formed solely of carbon fibres 8 and the second zone III is
formed solely of glass fibres 9.
[0037] FIG. 6b shows an embodiment, in which the first zone I is
formed solely of carbon fibres 8 and the second zone III includes a
constant minority amount of carbon fibres 8 and a constant majority
amount of glass fibres 9.
[0038] FIG. 6c shows an embodiment, in which the first zone I
includes a constant majority amount of carbon fibres 8 and a
constant minority amount of glass fibres 9, and in which the second
zone III is formed solely of glass fibres 9.
[0039] FIG. 6d shown an embodiment, in which the first zone I
includes a constant majority amount of carbon fibres 8 and a
constant minority amount of glass fibres 9, and in which the second
zone III includes a small constant amount of carbon fibres and a
large constant amount of glass fibres 9.
[0040] FIG. 6a thus diagrammatically illustrates a preferred
embodiment of a wind turbine blade, wherein the first zone I
corresponds to the outer end portion of the blade including the
blade tip and wherein the second zone III corresponds to the inner
end portion of the blade including the blade root. The
reinforcement material for the outer end portion is thus made
solely of carbon fibres, while the inner end portion of the blade
root is made solely of glass fibres. Consequently the outer end
portion may include a transition zone II, in which the carbon
fibres and the glass fibres gradually substitute each other. This
transition zone II may have a restricted length of for instance
0.5-1 metre. The blade may, however, also be provided with the
embodiments shown in FIGS. 6b-6d.
[0041] A transition zone may be provided in the blade during the
fibre lay-up per se in the mould parts. It is, however, also
possible to use prefabricated transitional laminates produced
according to the principles shown in FIGS. 3, 4 and 5. Such
prefabricated transitional laminates are advantageous in relation
to production in that the fibre lay-up process time is
substantially the same as at the production of conventional wind
turbine blades, in which the same material is used in the entire
longitudinal direction of the blade.
[0042] If an existing wind turbine is to be provided with longer
blades, this may be obtained by replacing the outermost portion of
the blade by a transition zone including one or more transitional
laminates and a carbon fibre tip. The weight of the blade is not or
only slightly increased compared to the original blades made
completely from fibreglass-reinforced polymer. Optionally
completely new blades may be made for an existing wind turbine or
the outermost portion blades may be cut off and replaced by a
carbon fibre tip with or without a transition zone.
[0043] The advantages according to the invention are particularly
obtained by making the load-bearing portions of the outer end
portion substantially from carbon fibre-reinforced polymer. The
load-bearing portions include the main laminates in form of
longitudinal fibre-reinforced polymer bands provided in the areas
of the suction and pressure sides of the blade shell being furthest
from the centre of the blade cross section. The laminates
reinforcing the blade in edgewise direction at the leading and
trailing edges of the blade may also advantageously be made of
carbon fibre-reinforced polymer in the outer end portion of the
blade.
[0044] The main laminates may advantageously be provided as hybrid
mats in which evenly distributed rovings or bundles of either glass
fibres or carbon fibres are distributed over the cross-sectional
area.
[0045] For lightning reasons it may be advantageous to make the
outermost portion of the blade tip entirely out of fibre glass so
as to ensure that strokes of lightning hit a purpose-built
lightning receptor and not the electrically conducting carbon fibre
material.
[0046] Tests have shown that the outermost portions of the carbon
fibres in the transition zone may break at deflection of the
transition zone, but this is not an entirely undesirable effect, as
it contributes to a further smoothing of the stiffness transition.
The frequency of broken fibres may thus be high but not critical,
as they are surrounded by more compliant glass fibres. However, the
broken fibres still contribute to reducing the deflection and thus
the breakage of additional fibres. The gradual and even transition
between the properties of the composite material, which is based on
glass fibres and carbon fibres, is thus obtained by means of two
factors. The first factor is the distribution of stiff and
compliant fibres to obtain a smooth transition from the stiff to
the compliant area. The second factor is the non-critical breakage,
which further smoothens the transition. An additional not shown
embodiment of a wind turbine blade according to the invention may
be obtained by means of a so-called spray-up process. In this
process a spray gun is used for the polymer material and a mixture
of chopped fibres of the two types are ejected into a resin stream
and sprayed into the mould. By varying the mix ratio during the
spray-up process, the intended transition zone may be obtained.
[0047] The elongation at breakage for glass fibres is typically
about 4.8%, while it typically ranges between 0.3% and 1.4% for
carbon fibres. Young's Modulus of glass fibres is about 73,000 MPa,
while Young's Modulus of carbon fibres (means modulus) typically is
about 245,000 MPa. Carbon fibres are typically 3-4 times stiffer
than glass fibres. The density of glass is about 2.54 g/cm.sup.3,
while the density of carbon is about 1.75 g/cm.sup.3.
* * * * *