Note: Descriptions are shown in the official language in which they were submitted.
CA 02914727 2015-12-08
Rotor blade deicing
Description
The invention relates a rotor blade of a wind turbine,
the rotor blade extending from a blade root to a blade
tip and having a cavity, in which a web is arranged in
the longitudinal extent of the rotor blade, separating
a first region of the rotor blade comprising a rotor
blade nose from a second region of the rotor blade
comprising a rotor blade trailing edge.
The invention also relates to a deicing system for a
wind turbine. Moreover, the invention relates to a
method for deicing a rotor blade of a wind turbine.
During the operation of wind turbines, there is the
problem at cold sites that the rotor blades ice up,
which leads on the one hand to a deterioration in the
aerodynamics, and with that the efficiency, of the
rotor blades and on the other hand to undesired loading
problems.
For this reason, systems by means of which the rotor
blades can be heated in order to provide deicing have
been developed.
DE 10 2010 030 472 Al discloses a rotor blade of a wind
turbine with a first and a second channel running
inside the rotor blade for directing an air stream
through. Also provided is a method for deicing a rotor
blade of a wind turbine. The rotor blade according to
DE 10 2010 030 472 Al has a separating device, which
separates the channels from one another, so that the
first channel is arranged on a first side of the
separating device, toward the pressure side of the
rotor blade, and the second channel is arranged on a
second side of the separating device, toward the
suction side of the rotor blade. The method described
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provides that, at least in portions of the rotor blade,
the flow velocity of the air stream provided in the
first channel and the second channel is prescribed.
The fundamental problem with hot air systems is that a
significant proportion of the thermal energy is lost in
the region near the blade root and, as a result,
deicing in the outer region of the blade, in particular
in the region of the blade tip, is only made possible
with great expenditure of energy and mass flows. Since
the material of rotor blades, that is usually glass-
fiber reinforced plastic, does not withstand all that
high a temperature, and consequently the temperature of
the heating air is limited, and moreover pressure
losses increase disproportionately with the mass flow,
some electrical systems have been developed. These
however have problems with respect to the lightning
protection concept of a rotor blade. Moreover, they
involve greater maintenance expenditure, since
corresponding heating foils are typically adhesively
attached to the outside of the rotor blades and are
correspondingly exposed to the effects of the weather.
The object of the present invention is to provide an
effective and low-maintenance deicing system, the
intention being in particular to provide a rotor blade
of a wind turbine and a method for deicing a rotor
blade of a wind turbine that makes more efficient
deicing of the rotor blade possible.
This object is achieved by a rotor blade of a wind
turbine, the rotor blade extending from a blade root to
a blade tip and having a cavity, in which a web is
arranged in the longitudinal extent of the rotor blade,
the web separating a first region of the rotor blade,
comprising a rotor blade nose, from a second region of
the rotor blade, comprising a rotor blade trailing
edge, which rotor blade is developed in such a way that
a thermally insulated channel is arranged in the first
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region of the rotor blade on the web, in order to
conduct hot air in the direction of the blade tip in an
air stream, openings, which are formed in such a way as
to direct hot air to the rotor blade nose, being
provided in the channel, with a return of the hot air
to the blade root taking place in the first region of
the rotor blade. By providing a thermally insulated
channel, the hot air can be transported very far in the
direction of the blade tip without great heat losses.
Moreover, an arrangement of the thermally insulated
channel on the web, in particular the web that is
arranged toward the rotor blade nose, is conducive to
achieving short paths for the air stream from the
channel to the inner wall of the rotor blade nose. Also
as a result of this, very efficient and effective
deicing is made possible. In particular, the first
region of the rotor blade and the second region of the
rotor blade are to be understood as meaning a first
region of the cavity or interior space and a second
region of the cavity or interior space of the rotor
blade.
A closed air stream is preferably provided. The
components of the rotor blade are consequently
redesigned in such a way that a closed air stream is
made possible. By providing a closed air stream, very
effective deicing is possible, since no air is lost and
in particular the air may possibly contain residual
heat, which does not have to be re-heated to be re-
admitted into the rotor blade as hot air. This ensures
high energy efficiency.
The openings in the channel are preferably formed as
nozzles, whereby an increase in the velocity of the hot
air as it leaves the openings is achieved, and
consequently a corresponding air stream directly onto
the inner wall of the rotor blade nose is made
possible.
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The thermally insulated channel preferably tapers in
the direction of the blade tip. As a result, an
increase in the velocity is achieved or a loss of
velocity caused by hot air being discharged via the
openings in the channel is compensated. The tapering of
the channel preferably takes place continuously, at
least in certain portions, or alternatively in the form
of stages, at least in certain portions.
The thermally insulated channel preferably has at its
end toward the blade tip an opening, which points
toward the blade tip and is formed in particular as a
nozzle. As a result, the inner wall of the blade tip
can be very efficiently subjected to hot air, and the
blade tip consequently deiced.
The first region is preferably formed as a front box.
The front box then comprises the web, which is arranged
toward the rotor blade nose, and also the parts of the
rotor blade shell, which comprise the rotor blade nose
and reach up to the web.
It is particularly preferred if an air-stream directing
device, which directs the heated air stream along the
rotor blade nose in the direction of the blade root, is
provided in the first region. The air-stream directing
device may comprise directing plates or directing
angles. These are preferably arranged on the inner side
or the inner wall of the rotor blade nose. The channel
is preferably formed as a tube.
The channel or the tube is formed in a thermally
insulating or thermally insulated manner in order to
avoid great heat losses. Being formed in a thermally
insulated manner or a thermally insulated channel or
tube should be understood as meaning a channel or a
tube on the wall of which there is a corresponding
thermal insulation, which has a low thermal
conductivity. The thermal conductivity is preferably
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below 1 W/(m*K), in particular below 0.8 W/(m*K), in
particular below 0.4 W/(m*K). It is particularly
preferred for the thermal conductivity to be below 0.11
W/(m*K), in particular below 0.1 W/(m*K). The thickness
of the wall of the thermally insulated channel is
preferably between 1 cm and 10 cm, in particular
between 3 cm and 8 cm, in particular between 4 cm and 6
cm. At least in certain portions, the wall of the
thermally insulated channel is preferably made of an
insulating material and a stabilizing material, such as
for example glass-fiber reinforced plastic. A sandwich
structure is preferably provided for the wall, a
stabilizing material respectively enclosing an
insulating material. The following structure is
consequently obtained from the inside to the outside:
stabilizing material insulating material
stabilizing material. Further plies or layers may also
be provided, for example as follows: stabilizing
material / insulating material / stabilizing material /
insulating material/stabilizing material. Polyurethane,
mineral wool, glass wool and/or PVC foam preferably
come into consideration as insulating material.
The channel or the tube is preferably adhesively
attached to the web. This is particularly efficient
during production, since the tube or the channel can be
mounted on the web outside the main mold of the rotor
blade during production, and consequently the mold
occupancy time is preferably not increased and the mold
also does not have to be modified.
As an additional measure, it may preferably be
envisaged to provide a device for sealing off a leak in
the thermally insulated channel. This device may be
designed in the manner of a lance, in particular in the
form of a tube, and serve the purpose of introducing an
adhesive or a resin into the region of a leakage
location of the thermally insulated channel.
Particularly preferably, an injection head may be
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provided, by means of which injection of the adhesive
or the resin into the leakage location is provided. The
injection head may be designed in the form of a brush,
the bristles of the brush touching the inner wall of
the thermally insulated channel and bringing about a
transport of the adhesive or the resin to the leakage.
It may in particular be envisaged to provide hollow
bristles, through which the adhesive or the resin can
then be conducted from the device formed as a lance or
from the interior of this device through the bristles
to the inner surface of the thermally insulated
channel. As a result, corresponding material can be
introduced quite specifically only in the region of a
leakage, in order to eliminate the leakage.
Other methods of repair may also be used, such as for
example the feeding of glass-fiber reinforced plastic
mats into the region of the leakage, these preferably
being plastic mats that have already been provided or
impregnated with resin or adhesive, which are then
stuck onto the leakage location. Adhesive tapes may
also be correspondingly applied, or particularly
preferably thermally insulating materials that are
provided with adhesive at least on one side.
The object is also achieved by a deicing system for a
wind turbine with a rotor blade that is described
above, according to the invention or preferred. The
deicing system provides a hot air stream or a heated
air stream, in order to make deicing possible.
In the deicing system, an air-heating device is
preferably provided in the region of a nacelle, a rotor
hub or the blade root. The air-heating device
preferably also comprises an air-stream generating
device. Particularly preferably, the air-heating device
is formed as a heating fan.
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The object is also achieved by a method for deicing a
rotor blade of a wind turbine that has the following
method steps:
- conducting a heated air stream from a blade root
of the rotor blade in the direction of a blade
tip,
- the heated air stream being conducted in a
thermally insulated channel, which is arranged on
a web, the web delimiting a first region of the
rotor blade, comprising a rotor blade nose, from a
second region, comprising a rotor blade trailing
edge,
- the heated air stream being at least partially
branched off from the channel on the way to the
blade tip and conducted in the direction of the
rotor blade nose, and
- the branched-off air stream subsequently being
conducted in a cavity, which is provided between
the rotor blade nose and the web and also the
channel, back to the blade root.
The term or the feature in the direction of the rotor
blade nose comprises the meaning in the direction of
the inner wall of the rotor blade nose. Part of the air
stream is consequently directed directly onto the inner
wall of the rotor blade nose.
The branched-off air stream is preferably returned to
the blade root on the inner wall of the rotor blade
nose. As a result, residual heat can also be put to
further use, in order to deice the rotor blade
correspondingly at the rotor blade nose.
The variant that the velocity of the air stream is
increased during the branching off from the channel is
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particularly preferred. This involves exploiting a
nozzle effect or the Bernoulli effect, in order to
direct the air stream directly onto the inner wall of
the rotor blade nose.
Part of the heated air stream is preferably directed
onto the inner wall of the blade tip and subsequently
returned to the blade root in the cavity, in particular
at the rotor blade nose. As a result, the blade tip of
the rotor blade can also be heated very efficiently.
It is particularly preferred for a closed air-stream
circulation to be provided.
It is also preferred to direct the air stream onto the
inner wall of the rotor blade nose and/or the inner
wall of the rotor blade tip by means of an air-stream
directing device. This involves preferably exploiting a
Coanda effect. The directing device may for example be
formed in such a curved manner that the hot air stream
remains in close contact with the air-stream directing
device and subsequently remains in close contact with
the inner wall of the rotor blade nose and/or the inner
wall of the rotor blade tip. A directing wall or a
directing angle, which extends in the longitudinal
extent of the rotor blade and confines a significant
part of the hot air stream to an intended region of the
inner wall of the rotor blade nose or the rotor blade
tip, may also be provided as the air-stream directing
device.
Preferably only a region of 40% to 100%, in particular
50% to 95%, of the length of the rotor blade, measured
from the blade root to the blade tip, is subjected to
the heated air stream directly from the channel.
Consequently, it is preferably only from 40%, measured
from the blade root, preferably only from 50%, measured
from the blade root, that the channel is provided with
openings from which hot air then flows out and subjects
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the inner wall of the rotor blade nose to hot air. A
preferred way of carrying out the method according to
the invention envisages using additional measures of
the operating control system to assist the deicing
here. Turning the rotor out of the wind, for example by
moving the nacelle on the tower, changing the position
of the rotor, for example setting the blade
horizontally with the nose downward or the blade axis
perpendicularly downward, changing the blade angle
(pitch) by 1800 and/or additional vibrational
excitation for shaking off ice that has begun to thaw
are preferred here.
The method for deicing is preferably only carried out
in the case of one rotor blade, which is arranged on
the rotor in such a way that no other rotor blade is
arranged under the rotor blade that is to be deiced. In
the case of wind turbines with rotors that have three
rotor blades, this is usually always the case when the
rotor blade to be deiced is arranged in the lower half
of the circle traced by the rotor. This avoids damage
to another rotor blade being caused by ice falling off.
Furthermore, for deicing, a rotor blade trailing edge
is preferably positioned in or adjusted into the
direction of the incident wind. The rotor blade
trailing edge of the rotor blade that is adjusted into
the direction of the incident wind, i.e. on which the
wind first acts, has the effect that no convection is
produced at the rotor blade nose. The rotor blade nose
is then on the downwind side and the rotor blade
trailing edge is on the upwind side. The wind flow
consequently breaks away before the nose, so that no
further ice can form there, which makes the deicing of
the rotor blade nose easier.
In the event of a defect of the thermally insulated
channel, the channel is preferably repaired by means of
an injection of a resin or an adhesive at the defective
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location or at a leakage location. This involves using
for example a lance-like device, which may in
particular be configured in the form of a tube and has
an injection head. The injection head is brought into
the region of a leakage location or damaged location,
so that adhesive or resin can be specifically
introduced there.
It is particularly preferred if a brush-like injection
head is provided, particularly preferably in operative
connection with the entire circumference of the inner
surface of the thermally insulated channel. By means of
the brush-like injection head, adhesive can then be
brought to the leakage location very efficiently.
It may also be envisaged to provide on the injection
head a brush that is only provided to one side, so that
only a small region of the inner side of the thermally
insulated channel can be provided with an adhesive or a
resin at a time, so that the leakage location can be
sealed off in a specific manner with little material
consumption.
Alternatively, a thermally insulating material that is
provided with an adhesive or layer of adhesive on one
side may also be stuck onto the leakage location.
Moreover, a monitoring may also take place, for example
by means of a camera robot, which is brought into the
region of the leakage location in order to check the
precise nature of the leakage location and which repair
measure appears to be most appropriate.
Further features of the invention are evident from the
description of embodiments according to the invention
together with the claims and the accompanying drawings.
Embodiments according to the invention may implement
single features or a combination of a number of
features.
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The invention is described below on the basis of
exemplary embodiments with reference to the drawings,
without restricting the general concept of the
invention, reference being expressly made to the
drawings with respect to all details according to the
invention that are not explained more specifically in
the text. In the drawings
Figure 1 shows a schematic sectional representation in
a plan view of a rotor blade,
Figure 2 shows a schematic detail 25 from Figure 1 in
a plan view,
Figure 3 shows a schematic cross section through a
part of a rotor blade according to the
invention, to be precise transversely in
relation to the longitudinal extent and
Figure 4 shows a detail of a further rotor blade
according to the invention in a schematic
representation.
In the drawings, elements and/or parts that are the
same or similar are in each case provided with the same
reference numerals, and so they are not described from
the beginning each time.
Figure 1 schematically shows a rotor blade 10 according
to the invention in a sectional representation and in a
plan view. The rotor blade 10 has a blade root 11,
which is usually attached to a rotor hub. On the side
opposite from the blade root 11, a blade tip 12 is
provided. The longitudinal extent of a rotor blade 10
may be for example up to 60 or more meters.
A rotor blade nose 15, that is to say a forward region
of the rotor blade, i.e. the region that is exposed to
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the flow of air during use of the rotor blade as
intended, and a trailing edge 16 are represented.
Arranged in the rotor blade are for example two webs 13
and 14, the web 13 being the forward web or the web
5 that is arranged toward the rotor blade nose 15.
A rotor blade 10 is usually formed as hollow with a
cavity 31. According to the invention, the cavity 31 or
the rotor blade 10 is divided into a first region 19
and a second region 20, the first region 19 being the
region between the forward web 13 and the rotor blade
nose 15. According to the invention, provided in this
region is a channel or tube 18, which extends
substantially from the blade root 11 to substantially
the rotor blade tip 12. In this exemplary embodiment,
the tube begins at a distance from the blade root 11
and ends at a distance from the blade tip 12. A
connection of the tube 18 to a heating fan 22 exists by
way of a connector tube 21, which is preferably
configured as flexible, in order to compensate for
tolerances and decouple vibrations and noise
transmission.
The tube 18 is tapered in stages, to be precise in the
longitudinally axial direction of the rotor blade
toward the blade tip 12. This may preferably take place
by tubes of different diameters pushed into one another
with suitable rubber seals, so that at the same time
simple thermal expansion compensation or axial movement
compensation is made possible. Provided at the blade
root 11 is a bulkhead 23, which closes off the cavity
31 from the rotor hub. Provided through the bulkhead 23
is a lead-through, through which the connector tube 21
is led.
By means of the heating fan 22, hot air 24 is conducted
through the tube 18. Ice 17 is indicated on the rotor
blade nose. The hot air 24 is directed through the tube
18 and from the tube 18 through openings 26, which are
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not represented in Figure 1 but are represented in
Figure 2, onto the inner wall of the rotor blade nose
32 and at the end of the tube 18 in the direction of the
inner wall 33 of the blade tip 12. As a result, deicing
can be performed efficiently.
Figure 2 schematically shows the region of a detail 25
from Figure 1. Here, the openings 26 and the
corresponding hot air stream 24, which may be referred
to as a partial hot air stream, are represented. In one
embodiment, the openings 26 may be formed as nozzles.
The tube 18 is attached to the web 13. The attachment
may take place for example by adhesive bonding, in
particular over a surface area or by means of adhesive
tabs, or in the case of the tubes that are pushed into
one another for length adjustment by means of rubberized
clips, which are for their part adhesively bonded. In
Figure 2 it is also shown especially that a nozzle 27
is provided at the end of the tube 18 on the blade tip
side, in order to make an increased velocity of the hot
air stream 24 possible as it leaves the tube 18. Deicing
in the region of the blade tip, where the cross section
of the front box is very narrow, is thereby made possible
in an efficient way.
Figure 3 schematically shows in a cross-sectional
representation transversely in relation to the
longitudinal axis of the rotor blade 10 a part of the
rotor blade 10, that is the front part of the rotor
blade 10, and in particular the front box of the rotor
blade 10. The rotor blade nose 15, on which ice 17 is
located, is represented. The channel 18 has been applied
to the web 13 by means of an adhesive bond 28. Also
represented are the first region 19 of the cavity 31 and
corresponding directing angles 29, which provide that
the air stream forms substantially between the two
directing angles 29, so that there substantially the
heating of the rotor blade nose 15 takes place from the
inner wall 32 of the rotor blade nose 15.
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Figure 4 shows a further embodiment of a rotor blade 10
according to the invention, in which the connecting
tube 21', which ends in the heating fan 22, is also
additionally provided for the return of the air stream
24'. Moreover, a closing-off element 30, through which
the returned air stream 24' is conducted, is provided
for the reliable return of the air stream, and in order
that no air stream is lost. The closing-off element may
also be configured very simply in the form of a
flexible sheet, for example a truck tarpaulin. As a
result, a closed air-stream circulation can be achieved
particularly efficiently. A mesh or the like should
preferably be provided in the region of the return of
the air stream 24', in order to prevent dirt or clumps
of resin from being sucked in. In Figure 4, the
corresponding air mass flows are represented by ti and
ri12. For a closed air circulation it holds that Mi 1112.
By providing a corresponding deicing system, which has
in a rotor blade a thermally insulated tube which, with
decreasing cross section, is fastened on the front box
of the rotor blade and to the forward web, a design
that is particularly compatible in terms of production
is possible, since the tube can be mounted on the web
outside the main mold in production. The tube conducts
heating air up to the blade tip. Provided in the region
of the blade tip are a multiplicity of simply drilled
openings, which generate corresponding hot air streams
or hot air jets.
Within the scope of the invention, the term blade outer
region includes in particular a region of the rotor
blade 10 that lies over more than 50% of the radius.
The blade outer region may therefore make up 50% to
100% of the length of the rotor blade, measured from
the rotor blade root. Part of the blade outer region is
defined within the scope of the invention as the blade
tip. The blade tip is defined as 85% to 100% of the
length of the rotor blade. The rotor blade tip
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preferably comprises a region of 90% to 100% of the
rotor blade with respect to the length of the rotor
blade, measured from the rotor blade root.
The hot air streams point directly at the leading edge
to be deiced and correspondingly transfer the amount of
heat optimally to there. Corresponding directing angles
direct the mass flow along the leading edge. The tube
tapers further toward the blade tip and serves there as
a nozzle. This generates an additional hot air stream,
which can be transferred with corresponding thermal
energy into the last meters of the blade tip, since
there is no corresponding installation space left there
for a tube.
The deicing system or hot air system is preferably
closed, i.e. hot air flows in the blade root region
through the insulated tube into the front box and is
conducted to the leading edge via the hot air jets.
Then the air flows via the front box back into the
blade root, where a heating fan is positioned.
It is moreover preferably envisaged to provide the
front box as completely closed. In this case, two
openings, in which corresponding flexible pipelines or
connecting tubes 21, 20' are provided, serve for the
connection to the heating fan. The heating system or
the rotor blade and the method for deicing a rotor
blade are very low-maintenance and preferably do not
have any metal components apart from the rotor hub.
Metal components may of course be provided in the form
of lightning arresters and/or be incorporated in the
blade shell in order to conduct heat better to the ice.
Consequently, thermal energy is optimally transferred
and the ice can preferably deice in the critical blade
outer region.
According to the invention, reduced structural
expenditure is provided in comparison with DE 10 2010
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030 472 Al, and moreover less frictional losses occur
as a result of the more direct conduction of the flow.
In spite of a very simple structure, very efficient
functionality and consequently deicing is possible. By
providing corresponding arrangements of the openings
that can be prescribed, it is possible to provide
desired temperature profiles at the specific regions of
the rotor blade nose, in particular in the blade outer
region. It is possible in particular to make allowance
for variations in the structure and thickness of the
blade shell in the nose region that have been made on
the basis of optimizing the structure from aspects of
strength. The deicing system or the rotor blade may be
adapted by displacing or adding or omitting openings.
The system or the rotor blade can be optimized such
that mainly the critical outer region of the rotor
blade, that is 50% to 95% of the length of the blade,
i.e. from 50% to 95% of the length of the blade,
measured from the blade root, can be deiced.
All of the features mentioned, including the features
that can be taken from the drawings alone and also
individual features that are disclosed in combination
with other features, are regarded as essential to the
invention on their own and in combination. Embodiments
according to the invention may be implemented by single
features or a combination of a number of features.
Within the scope of the invention, features that are
characterized by "in particular" or "preferably" are to
be understood as optional features.
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List of designations
rotor blade
11 blade root
12 blade tip
13 web
14 web
rotor blade nose
16 rotor blade trailing edge
17 ice
18 tube
19 first region
second region
21, 21' connector tube
22 heating fan
23 bulkhead
24, 24' air stream
region of detail
26 opening
27 nozzle
28 adhesive bond
29 directing angle
closing-off element
31 cavity
32 inner wall
33 inner wall
