U.S. patent application number 13/060746 was filed with the patent office on 2011-09-22 for wind turbine blade with device for modifying the blade aerodynamic surface.
This patent application is currently assigned to VESTAS WIND SYSTEMS A/S. Invention is credited to Nicolas Dudley Barlow, Mark Hancock, Dick Veldkamp.
Application Number | 20110229320 13/060746 |
Document ID | / |
Family ID | 41722016 |
Filed Date | 2011-09-22 |
United States Patent
Application |
20110229320 |
Kind Code |
A1 |
Hancock; Mark ; et
al. |
September 22, 2011 |
WIND TURBINE BLADE WITH DEVICE FOR MODIFYING THE BLADE AERODYNAMIC
SURFACE
Abstract
The invention further relates to a wind turbine blade comprising
at least one device for modifying the aerodynamic surface or shape
of the blade. The device is connected to a drive system for
operating the device, and the drive system is arranged such that it
is drivable by a pressure difference across the drive system. In
one embodiment of the invention the wind turbine blade further
comprises a number of conduits guiding a flow of air between an
outer surface of the wind turbine blade and the drive system. The
invention further relates to a method for operating an aerodynamic
device for modifying the aerodynamic surface or shape of a wind
turbine blade comprising the steps of exploiting a pressure
difference across a drive system, inside or around the wind turbine
blade in providing operating power for operating said device.
Inventors: |
Hancock; Mark; (Southampton,
GB) ; Barlow; Nicolas Dudley; (Southampton, GB)
; Veldkamp; Dick; (Houten, NL) |
Assignee: |
VESTAS WIND SYSTEMS A/S
Randers SV
DK
|
Family ID: |
41722016 |
Appl. No.: |
13/060746 |
Filed: |
August 28, 2009 |
PCT Filed: |
August 28, 2009 |
PCT NO: |
PCT/EP2009/061153 |
371 Date: |
June 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61092788 |
Aug 29, 2008 |
|
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|
61196144 |
Oct 14, 2008 |
|
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|
61159630 |
Mar 12, 2009 |
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Current U.S.
Class: |
416/1 ;
416/23 |
Current CPC
Class: |
F05B 2240/3052 20200801;
F05B 2240/31 20130101; F03D 1/0675 20130101; F03D 1/0683 20130101;
Y02E 10/72 20130101; F05B 2270/506 20130101; F05B 2270/60 20130101;
F03D 7/0232 20130101 |
Class at
Publication: |
416/1 ;
416/23 |
International
Class: |
F03D 7/00 20060101
F03D007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2008 |
DK |
PA 2008 01189 |
Oct 14, 2008 |
DK |
PA 2008 01436 |
Mar 12, 2009 |
DK |
PA 2009 00342 |
Claims
1. A wind turbine blade comprising at least one device for
modifying the aerodynamic surface or shape of the blade connected
to a drive system for operating said device, the drive system being
arranged such that it is drivable by a pressure difference across
the drive system.
2. The wind turbine blade according to claim 1 where said drive
system is placed interiorly in said wind turbine blade adjacent to
at least one of said devices.
3. The wind turbine blade according to claim 1 comprising one or
more conduits connecting said drive system to an outer surface of
the wind turbine blade for guiding a flow of air to or from said
drive system.
4. The wind turbine blade according to claim 3, where at least one
of said conduits terminates near the leading edge, on the suction
side, and/or near the trailing edge of said wind turbine blade.
5. The wind turbine blade according to claim 3, where at least one
of said conduits terminates at the tip of said wind turbine
blade.
6. The wind turbine blade according to claim 1 comprising at least
one conduit connecting said drive system to the root end of said
wind turbine blade.
7. The wind turbine blade according to claim 6, where said at least
one conduit is at least partly made up by one or more interior
surfaces of said wind turbine blade.
8. The wind turbine blade according to claim 1, where said drive
system is placed at least partly in an opening in a partition
between sections of the wind turbine blade.
9. The wind turbine blade according to claim 1, said drive system
comprising a vacuum and/or pressure drive system.
10. The wind turbine blade according to claim 1, where said drive
system is connected to a control unit via a signal communication
pathway for conveying control signals for said operating of said
device.
11. The wind turbine blade according to claim 10 where the at least
one communication pathway comprises a power link.
12. The wind turbine blade according to claim 10 where the at least
one communication pathway comprises a pressure tube for conveying
pressure control signals.
13. The wind turbine blade according to claim 12 where said
pressure tube comprises a gas such as air.
14. The wind turbine blade according to claim 12 where said
pressure tube comprises a gas of a lower molecular weight than 28.9
kg/kmol, such as Helium He, Ammonia NH.sub.3, Hydrogen H.sub.2,
Hydroxyl OH, Methane CH.sub.4, Natural Gas, Acetylene
C.sub.2H.sub.2, or Neon Ne.
15. The wind turbine blade according to claim 12 where said
pressure tube comprises a liquid such as water and/or hydraulic
oil.
16. The wind turbine blade according to claim 1, comprising a feed
back system from said device to said drive system for adjusting
said operation of said devices according to feed back signals from
said feed back system.
17. The wind turbine blade according to claim 1, comprising one or
more actuators connected to said drive system and to said device
for operating said device.
18. The wind turbine blade according to claim 1, where said device
comprises a movable trailing edge.
19. The wind turbine blade according to claim 1 comprising an
accumulator connected to said device.
20. The wind turbine blade according to claim 19 where said
accumulator comprises a pressure tank comprising a gas of a lower
molecular weight than 28.9 kg/kmol, such as Helium He, Ammonia
NH.sub.3, Hydrogen H.sub.2, Hydroxyl OH, Methane CH.sub.4, Natural
Gas, Acetylene C.sub.2H.sub.2, or Neon Ne.
21. The wind turbine blade according to claim 19 comprising a
pressure tank at least partly constituted by one or more sections
of beam walls of the wind turbine blade.
22. A wind turbine comprising at least one wind turbine blade
according to claim 1.
23. A method for operating one or more devices for modifying the
aerodynamic surface or shape of a wind turbine blade comprising the
steps of exploiting a pressure difference across a drive system
inside or around the wind turbine blade in providing operating
power for operating said device.
24. Use of a pressure difference for providing power to at least
partly operate a device for modifying the aerodynamic surface or
shape of a wind turbine blade.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a wind turbine blade
comprising at least one device for modifying the aerodynamic
surface of the blade. The invention furthermore relates to a method
for operating one or more of such devices.
BACKGROUND
[0002] Most modern wind turbines are controlled and regulated
continuously during operation with the purpose of ensuring optimal
performance of the wind turbines in all operating conditions, such
as at different wind speeds or subject to different demands from
the power grid. For instance, at lower wind velocities (typically
up to a nominal wind speed of 14 m/s) the turbine is regulated with
a view to maximize its power production, whereas the reduction of
the loads on the blades, in the bearings, on the tower etc becomes
the dominant purpose at higher wind velocities above the nominal
wind speed. Desirably, the wind turbine can also be regulated to
account for fast local variations in the wind velocity--the
so-called wind gusts. Also, as the loads on each of the blades vary
due to e.g. the passing of the tower or the actual wind velocity
varying with the distance to the ground (the wind profile), the
ability to regulate each of the wind turbine blades individually is
advantageous enabling the loads to be balanced reducing the yaw and
tilt of the rotor.
[0003] A well-known and effective method of regulating the loads on
the rotor is by pitching the blades which can also be performed on
the blades individually and cyclically. However, with the
increasingly longer blades on modern wind turbines (which of
present can be of 60 m or longer) pitching becomes a relatively
slow regulation method incapable of changing the blade positions
fast enough to account for e.g. wind gusts or other load variations
to be compensated for within relatively short periods of time such
as within one or half a rotation cycle.
[0004] Another way of regulating the blades is by changing their
aerodynamic surfaces or shapes over parts or the entire length of
the blade, thereby increasing or decreasing the blade lift or drag
correspondingly. Different means of changing the airfoil shape are
known such as different types of movable or adjustable flaps (e.g.
trailing edge flaps, leading edge slats or Krueger flaps, Gurney
flaps placed on the pressure side near the trailing edge, ailerons,
or stall inducing flaps), vortex generators for controlling the
boundary layer separation, adaptive elastic members incorporated in
the blade surface, means for changing the surface roughness,
adjustable openings or apertures, or movable tabs. Such different
means are here and in the following referred to in common as
aerodynamic devices or devices for modifying the aerodynamic
surface or shape of the blade. One important advantage of the
relatively small aerodynamic devices is a potentially faster
response due to less inertia than if the whole blade is being
pitched.
[0005] One drawback with the known different systems of various
aerodynamic devices of the above mentioned types is however how
they are powered. In order to reach the devices potential in the
regulation of wind turbines, the aerodynamic surface modifying
devices need to be able to operate quickly and repeatingly.
Therefore the power consumption could be considerable. In the known
systems, the aerodynamic devices are powered directly from the hub
via a power link. An electrical cable is however undesirable due to
the inevitable implications in relation to lightning. On the other
hand air power systems lead to considerable size demands.
DESCRIPTION OF THE INVENTION
[0006] It is therefore an object of embodiments of the present
invention to overcome or at least reduce some or all of the above
described disadvantages of the known systems for control,
regulation, and activation of devices for modifying the aerodynamic
surface of wind turbine blades.
[0007] It is a further object of embodiments of the invention to
provide a wind turbine blade with regulation means with reduced
power consumption. A yet further object of embodiments of the
invention is to avoid or at least reduce the need for electrical
wiring in the wind turbine blade due to the different regulation
means of the blade.
[0008] In accordance with the invention this is obtained by a wind
turbine blade comprising at least one device for modifying the
aerodynamic surface or shape of the blade connected to a drive
system for operating the device, and the drive system being
arranged such that it is drivable by a pressure difference across
the drive system.
[0009] Hereby is obtained a power supply for the operating of any
devices capable of modifying the aerodynamic surface of a wind
turbine blade which can be driven by energy tapped locally close to
the aerodynamic devices to be operated. The drive system capable of
using the dynamic pressure energy inside and outside the blade to
provide the energy for the actuation of the devices can thus be
placed locally optionally further out in the wind turbine blade
where the operational power is needed, whereby the need for power
links from the hub to the flaps etc is at least partly removed.
[0010] Further, the described wind turbine is advantageous in
enabling a faster yet robust activation and regulation of the
aerodynamic devices in the blade due to their low inertia and the
drive system being placed locally near the devices to be operated.
A fast regulation system is a prerequisite if the wind turbine
blades are to be regulated optimally taking into account fast
variations and fluctuations in the wind (e.g. wind gusts or due to
tower passage).
[0011] In one embodiment, the drive system is placed interiorly in
the wind turbine blade adjacent to at least one of the devices.
[0012] The wind turbine blade according to the invention may
comprise one or more conduits connecting the drive system to an
outer surface of the wind turbine blade for guiding a flow of air
to or from the drive system. Hereby the local pressure energy
around the blade may be guided into and exploited by the drive
system. The conduits may advantageously terminate in regions of
high or low pressure to provide for maximum power, such as near the
leading edge, on the suction side, and/or near the trailing edge of
the wind turbine blade. Alternatively, the conduit may terminate at
the tip of said wind turbine blade.
[0013] In a further embodiment of the invention, the wind turbine
blade comprises a conduit connecting said drive system to the root
end of said wind turbine blade thereby exploiting the air flow
present internally in the wind turbine blade in operation.
[0014] The conduits may be at least partly made up by one or more
interior surfaces of the wind turbine blade such that the blade
shell or beams etc in themselves constitute the conduit.
[0015] The internal air flow in the blade can be effectively guided
to the drive system by placing the drive system in a partition
opening between sections of the wind turbine blade thereby
enforcing a greater portion of the air flow to pass the drive
system.
[0016] In yet a further embodiment of the wind turbine blade, the
drive system may comprise a vacuum and/or pressure drive system
[0017] In a further embodiment of the invention, the drive system
may be connected to a control unit via a signal communication
pathway for conveying control signals control signals for said
operating of said device. This is advantageous in providing the
drive system with information for optimally active regulation and
control of the aerodynamic devices during operation, where the
devices may be regulated continuously according to the control
signals.
[0018] In an embodiment of the invention, the communication pathway
of the wind turbine blade according to the above comprises a power
link. The aerodynamic surface of the wind turbine blade may hereby
fast an effectively be regulated and modified continuously
according to the signals e.g. from a central control unit placed
for instance in the nacelle of the wind turbine. The control
signals in the power link are electrical or light or other
electromagnetic waves.
[0019] The communication pathway in the wind turbine blade
according to another embodiment comprises a pressure tube for
conveying pressure control signals. Here, the one or more pressure
tubes comprise a liquid such as water and/or hydraulic oil, or a
gas such as air. By the use of pressure tubes and hydraulics or
pneumatics for the control of the valve system, the use of
electrical wires in the wind turbine blade can be minimized if not
completely avoided.
[0020] In a further embodiment, the pressure tube comprises a gas
of a lower molecular weight than 28.9 kg/kmol, such as Helium He,
Ammonia NH.sub.3, Hydrogen H.sub.2, Hydroxyl OH, Methane CH.sub.4,
Natural Gas, Acetylene C.sub.2H.sub.2, or Neon Ne. Dry air has a
molecular weight of 28.96 kg/kmol (as determined e.g. in Chemical
Rubber Company, 1983. CRC Handbook of Chemistry and Physics. Weast,
Robert C., editor. 63rd edition. CRC Press, Inc. Boca Raton, Fla.,
USA) depending to some extend on the exact content of the different
gasses in the mixture. Because the molecular weight of the gas
according to the invention is lower than 28.9 kg/kmol and thereby
lower than air, the speed of sound in the gas is correspondingly
higher. Hereby is obtained a reduction in the delay of the control
signals when sent from the control unit to the valve system as the
pressure signals propagate with the speed of sound in the gas. The
reduction in the signal delay is correspondingly larger, the longer
the distance over which the signals are sent. The reduction of the
time needed for transporting the signals is even more advantageous
in view of the technological trend to increase the length of wind
turbine blades, and as many aerodynamic devices are placed some
distance from the blade root where the control signals are likely
to terminate. The use of Helium may be further advantageous due to
being light in combination with its non-corrosive, non-toxic, and
non explosive properties while on the same time being relative easy
to acquire.
[0021] Further, the wind turbine blade may comprise a feed back
system from the device to the drive system for adjusting the
operation of the devices according to feed back signals from the
feed back system. This further enables an optimal regulation where
the required position or operating conditions of the aerodynamic
devices can be ensured.
[0022] The wind turbine blade according to the former may further
comprise one or more actuators connected to the drive system and to
the device for operating the device. The actuator can for instance
be hydraulic, pneumatic or mechanical.
[0023] In a specific embodiment of the invention the device
comprises a movable trailing edge. Other possibilities are
mentioned in the description.
[0024] In yet a further embodiment of the invention the wind
turbine blade comprises an accumulator connected to the device.
This may be advantageous in working as a back-up system for the
drive system, ensuring that a device can be operated at all times
independent of the present wind conditions or even during start up
of the wind turbine. Such a system may in one embodiment of the
invention comprise a pressure tank comprising a gas of a lower
molecular weight than 28.9 kg/kmol, such as Helium He, Ammonia
NH.sub.3, Hydrogen H.sub.2, Hydroxyl OH, Methane CH.sub.4, Natural
Gas, Acetylene C.sub.2H.sub.2, or Neon Ne.
[0025] The pressure tank may at least partly be constituted by one
or more sections of beam walls of the wind turbine blade.
[0026] The invention further relates to a wind turbine comprising
at least one wind turbine blade according to any of above
mentioned.
[0027] According to another aspect, the invention relates to a
method for operating one or more devices for modifying the
aerodynamic surface or shape of a wind turbine blade comprising the
steps of exploiting a pressure difference across a drive system,
inside or around the wind turbine blade, in providing operating
power for operating the device. The advantages hereof are as
mentioned previously in relation the different embodiments relating
to the wind turbine.
[0028] Finally, the present invention relates to the use of a
pressure difference for providing power to at least partly operate
a device for modifying the aerodynamic surface or shape of a wind
turbine blade.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] In the following different embodiments of the invention will
be described with reference to the drawings, wherein:
[0030] FIG. 1 shows a sketch of a wind turbine blade according to
prior art and comprising movable aerodynamic devices in the shape
of a movable trailing edge and vortex generators,
[0031] FIG. 2 is a sketch of the pressure distribution around an
aerofoil according to prior art,
[0032] FIG. 3 shows in a perspective cross sectional view an
embodiment of a part of a wind turbine blade according to the
present invention,
[0033] FIG. 4 is a sketch illustrating the working principle of a
wind turbine blade according to an embodiment of the invention
exploiting an internal air flow.
[0034] FIG. 5 shows a sketch of an embodiment of a wind turbine
blade according to the invention illustrating the control system of
an aerodynamic device in the shape of a movable trailing edge,
[0035] FIG. 6 illustrates an embodiment of a wind turbine blade
according to the invention where the aerodynamic device is driven
by a gas of lower molecular weight than 28.9 kg/kmol and thereby
lower than air, and
[0036] FIG. 7 shows a sketch of a rotor for a wind turbine,
comprising three turbine blades with aerodynamic devices controlled
by a control unit and at least partly driven by pressure from
pressure tanks in each blade,
DETAILED DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 shows a blade 100 for a wind turbine according to
prior art and comprising some examples of so-called aerodynamic
devices 101. When manipulated, the aerodynamic devices change the
aerodynamic surface or shape 105 of the wind turbine blade 100
thereby altering the lift and/or drag coefficients of the wind
turbine blade during operation. In the examples illustrated in this
figure, the aerodynamic shape 105 of the wind turbine blade 100 can
be changed and regulated by changing the position of the movable
trailing edge flap 102 placed a distance out along the length of
the blade, or by the activation of a number of vortex generators
103 placed closer to the root end 104 of the wind turbine blade on
its suction side. As also mentioned in the background description,
examples of such aerodynamic devices 101 are: different movable or
adjustable flaps, e.g. trailing edge flaps 102, leading edge slats
or Krueger flaps, Gurney flaps placed on the pressure side near the
trailing edge, ailerons, or stall inducing flaps, vortex generators
103 controlling the boundary layer separation, adaptive elastic
members incorporated in the blade surface, means for changing the
surface roughness, adjustable openings or apertures, or movable
tabs.
[0038] Traditionally, the various aerodynamic devices 101 are
powered directly from the hub via some kind of power link 105 as
sketched in FIG. 1. An electrical cable is however undesirable due
to the inevitable implications in relation to lightning.
Alternatively, the various aerodynamic devices 101 may be powered
directly from the hub by means of air powered links which however
lead to considerable size demands for modern wind turbine blades of
60 m or longer.
[0039] According to the present invention, such problems are
reduced or solved by fully or partly (in time and/or in amount)
powering the operation of the aerodynamic devices 101 locally in
the blade by tapping dynamic pressure in different ways as will be
further explained in the following.
[0040] FIG. 2 illustrates a typical pressure distribution 200
around and on the surface 105 of an airfoil 201 corresponding to
the outer cross sectional geometry of a wind turbine blade 100 at
some position down the length of the blade. Typically, during
operation a positive pressure 203 is present on the pressure side
204 of the airfoil including at the leading edge 205 whereas a
negative pressure 206 is present on the suction side 207 of the
airfoil. The pressure distribution depends (apart from the
aerodynamic surface geometry) upon the actual angle of attack of
the blade and on the velocity of the wind.
[0041] As sketched in FIG. 3, these differences in pressure are
exploited to drive and energize a drive system 300 which in turns
operate the required devices 101 for altering the aerodynamic
surface 105 of the blade 100. FIG. 3 shows a part of a wind turbine
blade 100 seen in a perspective cross sectional view. Any internal
spars or beams or alternative stiffening structure of the blade are
not shown for clarity. A number of conduits 301 such as hoses or
pipes connect the exterior of the blade to the drive system 300
guiding ambient air as an air flow to and from the drive system due
to the pressure differences at the in- and outlets positions 303,
304. In FIG. 3 one first set of conduits or pipes 305 end on the
blade exterior or outer surface 302 near the blade leading edge 205
where a positive pressure is most often present during operation of
the wind turbine. Further, a second set of conduits or pipes 306
terminates on the suction side 207 of the blade airfoil where a
negative pressure is typically present during operation.
[0042] A pressure difference could of course alternatively be
realized with conduits ending at other positions on the outer
surface of the wind turbine blade with a view to the pressure
distribution around the wind turbine blade for different
aerodynamic surface geometries, different angles of attack, and
different wind velocities. Optionally, the pressure difference
across the drive system 300 could also be realized by exploiting
the difference in pressure from somewhere on the exterior surface
of the blade to a position within the blade. The drive system could
both work as a vacuum system or as a positive pressure system, the
latter having the advantage of being able to operate with larger
pressure differences whereby the same magnitude of forces can be
obtained with a physically smaller system.
[0043] The drive system 300 yields as output 310 an actuation power
to one or more aerodynamic devices 101 for modifying the
aerodynamic surface of the wind turbine blade as illustratively
exemplified with a movable trailing edge 102 in FIG. 3. The
actuation power could for instance be in the form of a pneumatic, a
hydraulic pressure, or a force link directly to the aerodynamic
device 101 or indirectly via one or more actuators 311. Different
types of actuators could be applied such as for example pneumatic,
hydraulic, and/or mechanical actuators.
[0044] All or some of parts (conduits, inlets, valves, cylinders
etc) in the described system for powering and controlling the
devices for modifying the aerodynamic profile of the wind turbine
blade can advantageously be made of lightweight and electrically
non-conductive materials such as for instance plastics. Hereby is
obtained both a system of low weight which is advantageous in
adding minimally to the undesirable loads in the rotor caused by
the weight of the wind turbine blade. Furthermore the use of
electrically non-conductive materials is advantageous from
lightning considerations. Further some of the parts in the
described system according to the invention may be fully or partly
embedded in the blade parts during manufacture improving the
durability of the system parts under use.
[0045] In a further embodiment of the invention, the drive system
300 is also connected via a signal communication pathway 320 to a
control unit 510 from which control signals 320 comprising
information on the desired operational parameters of the devices
for modifying the aerodynamic surface. The drive system 300 may be
connected to the actuator 311 via a valve system 504 which based on
the control signals 320 from the control unit 510 controls the
driving force and hereby the position and movement of the
aerodynamic device 101.
[0046] The signal communication pathway 320 conveying or sending
the control signals to the drive system and/or the valve system for
controlling the actuator(s) may for instance be a power link which
is advantageous in being simple and inexpensive to imbed or in
other ways establish within the blade body and in providing fast
signals over long distances.
[0047] In another embodiment the signal communication pathway may
comprise one or more pressure tubes for conveying pressure control
signals, --either pneumatic or hydraulic. In the latter case the
hydraulic fluid may be for instance water, or a type of hydraulic
oil. If the control signals are pneumatic, the pressure tubes may
comprise a gas such as air. Air is advantageous for the obvious
reasons of requiring no special safety provisions towards leaks,
inflammability etc. By sending the control signals 320 without the
use of electrical wires and electrically conductive materials,
--for instance by the use of pressure signals, --the risk of
damages from lightning is minimized.
[0048] The signal communication pathway may be connected directly
to the control unit or indirectly via a signal interface. The
control unit may be placed in the blade body 107 itself for
instance in a root portion 104 of the blade or it may be placed in
the hub or the nacelle of the wind turbine. The signals sent by the
control unit operating the valve system may be based on different
system parameters for the wind turbine such as rotational speed,
weather conditions (e.g. wind velocities, temperature, humidity),
the present and desired power yield, tower or nacelle accelerations
etc. The system parameters may be received from e.g. sensors placed
on the blades, nacelle or tower, from its surroundings, from other
wind turbines in the same wind park, from the power grid etc.
[0049] The control unit could be placed outside the wind turbine
blade such as in the hub and could optionally be connected to the
drive systems in all the blades of the wind turbine. Hereby all or
some of the blades could be regulated and controlled together as a
whole, for instance simultaneously or suitably delayed taking
cyclic effects into account in the regulation. Further, connecting
all the wind turbine blades to a common control unit makes it
possible to regulate the blades with a view to minimizing the yaw
of the rotor.
[0050] The drive system could in one embodiment of the invention
comprise a servomechanism optionally (but not necessarily) also
comprising a feed-back system to the movable or adjustable
aerodynamic device. The feed-back system then correlates some
actual condition parameter (such as e.g. the position) of the
aerodynamic device to the desired condition for the device for
instance being pre-defined or being given by some control signal.
In another embodiment the feed-back system could correlate the
actual condition of the aerodynamic device directly to the pressure
difference experienced by the drive system. In this way the system
could be designed to keep on adjusting the aerodynamic profile
until some given pressure differences were attained and thereby a
desired pressure distribution around the airfoil. Hereby is other
words obtained a passive and automatic operating and regulation
system where the aerodynamic device adapts itself according to the
pressure distribution profile around the wind turbine blade.
[0051] The servomechanism could for instance be a pressure servo or
a vacuum servo similar to the ones applied in many car braking
systems.
[0052] In a further embodiment of the invention, the wind turbine
blade could also comprise an accumulator of some sort acting as a
secondary back-up system for the power supply to the aerodynamic
device. The accumulator could for instance be a conventional
battery or an air accumulator using a pressure chamber for
accumulating vacuum or over-pressure. The accumulator could act to
supply part of or all of the driving power to the aerodynamic
device during some time periods, or could supplement the previously
described system in supplying a part of the needed power at all
times. The accumulator may be directly connected to the drive
system or may be connected directly to the actuator via a valve
system as sketched in FIG. 5.
[0053] A section of the spar or beams within the blade shell could
advantageously be closed off and used as an air pressure chamber in
which either vacuum or an over-pressure is built up continuously by
a further set of conduits guiding a pressure difference to the air
tank. Alternatively, the pressure chamber may be connected to and
pressurized by a pressure setting device such as e.g. a compressor
or a pump 503. The pressure setting device 503 may be placed in a
root portion 104 of the blade or alternatively in the nacelle or
the hub of the wind turbine.
[0054] By regulating the pressure from the pressure chamber or
reservoir by means of the valve system 504, a faster and a far more
precise and accurate control of the driving pressure can be
obtained instead of e.g regulating and adjusting the pressure in
the pressure chamber according to the driving pressure needed
without a controllable valve system.
[0055] Also, compared to the control system according to prior art
of FIG. 1 of air power links directly from the hub to the
actuators, the use of the pressure chamber or reservoir ensures a
large source of a more constant driving pressure to be present.
[0056] Additionally, the wind turbine blade 100 may comprise one or
more drainholes 231 for allowing water, small dirt particles etc to
escape from the interior of the blade body 107. Such drainholes may
advantageously be placed near the tip of the blade and/or near the
trailing edge. The wind turbine blade may also comprise a lightning
arrestor device 232 for catching lightnings and guiding them safely
to the ground without damaging the material or other devices in the
blade body 107.
[0057] The described drive system could also transform all or parts
of the pressure energy into electrical energy used to power for
instance a warning light near the tip of the blade. This requires
an electrical power link from the drive system which is
disadvantageous out of lightning consideration. However, as the
drive system according to the invention can be placed quite far out
in the blade, the electrical wiring needed to a warning light in
the tip of the blade would still be less than if the warning light
is powered directly from the hub.
[0058] In another embodiment of the invention the drive system 300
is driven by the air flow 400 from the blade root end 104 towards
the blade tip 401 which is naturally present within the wind
turbine blade when rotating 402. This is illustrated in FIG. 4
showing a wind turbine blade 100 with a device for changing the
aerodynamic surface of the blade which in the figure is illustrated
by a movable trailing edge flap 402. As in the previous
embodiments, the aerodynamic device 402 is operated by means of a
drive system 300 placed within the wind turbine blade 100. The
drive system 300 is powered by the pressure difference across the
drive system i.e. the difference in pressure from the root end 104
to some opening 403 in or near the tip 401 of the wind turbine
blade resulting in an outward air flow 400. The opening or outlet
403 near the tip 401 could simultaneously also function as a drain
hole allowing water and small dirt particles to escape the cavity
or cavities of the wind turbine blade. As sketched in FIG. 4 the
drive system could advantageously be placed in an opening in a wall
partition 404 between sections of the blade thereby maximizing the
extraction of energy from the air flow 400. The drive system 300
could in this embodiment comprise some sort of turbine converting
the fluid energy into a mechanical, electrical, pneumatic,
hydraulic, and/or electrical output for the operation of the
aerodynamic device 101. In the illustrated embodiment in figure,
the conduits guiding the air flow to the drive system are
constituted in whole by interior wall surfaces 405 of the blade
itself. Alternatively, air could be guided to and from the drive
system by means of e.g. hoses or flexible tubes. In one embodiment
of the invention air could also be guided to the blade root from
e.g. the spinner in the nacelle via special air intakes and
conduits whereby a flow is avoided or at least minimized within the
hub where the pitching systems, electronics, coolers, and other
equipment sensitive to dust, humidity etc. are present.
[0059] The operating speed of the aerodynamic devices and therefore
of the actuators affects the efficiency of the wind turbine in
enabling the wind turbine to be optimally controlled for a longer
period of its time in operation. Optimally controlled may in some
scenarios depending on the actual wind situation imply to maximize
the power output of the wind turbine or in other scenarios to
minimize the loads exerted by the wind on the different parts of
the wind turbine.
[0060] One parameter influencing the operational speed is the
length of the communication pathway between the valve system and
the control unit operating the valve system. If air is used as the
driving media in the pressure tubes for communicating the signals,
the information signals (being the pressure changes in the tubes)
propagate with the speed of sound in the air of approximately 344
m/s at 20.degree. C. For a 33 m long distance (corresponding to a
typical distance for many proposed blades with trailing edge flaps)
this yields a delay of the pressure signal of about 0.1
seconds.
[0061] According to an embodiment of the invention, a gas or a gas
mixture of a lower molecular weight than 28.9 kg/kmol and thereby
lower than air (having a molecular weight of 28.96 kg/kmol) is used
as the driving media in the pressure tube. Such a gas could for
instance by Helium (He) or Hydrogen (H.sub.2). Hereby is obtained
an increase in the operational time of the system. The speed of
sound in a gas squared is inversely proportional to the molecular
weight of the gas in question. Thus, the lower the molecular weight
of the gas, the higher the speed of sound. Examples of densities
and molecular weights of some different gases are shown in the
table below also including the data from dry air for comparison.
The gasses in the table all have a lower molecular weight than air
wherefore the speed of sound and thus the speed of the pressure
changes constituting the information signals in the communication
pathway according to the invention is higher yielding faster
operation times of the proposed control system. In the case of
Helium, the molecular weight is approximately 4.02 yielding a speed
of sound of around 927 m/s at 20.degree. C. or almost three times
as high as in air. For the same example as above of a 33 m long
distance this yields a significantly smaller delay of the pressure
signal of about 0.03 seconds.
[0062] In other embodiments the pressure tube comprises any of the
following gases or mixtures hereof: Helium He, Ammonia NH.sub.3,
Hydrogen H.sub.2, Hydroxyl OH, Methane CH.sub.4, Natural Gas,
Acetylene C.sub.2H.sub.2, or Neon Ne.
TABLE-US-00001 Molecular weight Density Gas Formula (kg/kmol)
(kg/m.sup.3) Acetylene C.sub.2H.sub.2 26.04 1.092 (ethyne) 1.170
Air 28.96 1.205 1.293 Ammonia NH.sub.3 17.031 0.717 0.769 Helium He
4.02 0.1664 Hydrogen H.sub.2 2.016 0.0899 Hydroxyl OH 17.01 Methane
CH.sub.4 16.043 0.668 0.717 Natural gas 19.5 0.7-0.9 Neon Ne 20.179
Water Vapour H.sub.2O 18.016 0.804
[0063] In one embodiment of the invention, air which is cheap and
non-complicated to use, is used as the powering medium in the
pressure chamber if present, while another medium with a lower
molecular weight (as e.g. suggested in the table above) is used for
the control signals. This other medium may be more expensive but on
the other hand only a very limited quantity is needed for the
control signals.
[0064] In one embodiment of the invention, a gas of lower molecular
weight than air as discussed above may also be used as pressure
medium in the pressure tank. In a further embodiment as illustrated
in FIG. 6, the devices for controlling the aerodynamic surface or
shape of a blade 101 may be controlled by a pneumatic actuator 311
driven by a gas of lower molecular weight than air and at least
partly driven directly or indirectly by a pressure setting device
503. The gas is then guided via pressure guiding means such as
pressure tubes or hoses 601 (and optionally via a pressure tank
501) to drive the actuator 311. The driving pressure on the
actuator 311 is in the embodiment of FIG. 6 controlled by a control
unit 610 acting on the pressure setting device 503. As the case in
the previous embodiments, the pressure setting device and/or the
control unit may be placed in the blade body 107 itself e.g. in a
root portion of the blade, or may be placed outside the blade in
the hub or nacelle of the turbine.
[0065] In FIG. 7 is shown an embodiment of the invention of a wind
turbine rotor 700 in this case comprising three blades 100. Each
blade 100 comprises one or more devices for modifying its
aerodynamical surface or shape of the blade 101 which are activated
partly or fully by pressure from a pressure tank 501 in this
embodiment placed a distance out in the blade. Here, one pressure
setting device such as a compressor or a pump 503 keeps the
pressure in all three pressure tanks within a desired level via
pressure hoses 601 from the compressor or pump to the pressure
tank. Similarly only one control unit 510 is in this example
coupled via communication pathways 320 to the valve systems (not
shown) in all three blades thereby controlling the pressure guided
from the pressure tanks to the pneumatic actuators of the
aerodynamic devices 101. The communication pathways may be directly
connected to the control unit or indirectly via signal interfaces.
By letting a central control unit operate all or some of the
aerodynamic devices in all the wind turbine blades, the control
unit may control and regulate all the blades in unison or
alternatively in dependence of each other taking for instance
cyclical effects into account such as the tower passage or the wind
velocity varying with the distance from the ground.
[0066] In one embodiment, sensors signals of e.g. velocities or
accelerations measured on one blade may be used in controlling the
aerodynamic devices on the following wind turbine blade 120 degrees
later in the rotor rotation, the blade in this way being optimally
operated according to its present and current conditions as
measured by the preceding blade. Further, connecting all the wind
turbine blades to a common control unit makes it possible to
regulate the blades with a view to minimizing the yaw of the
rotor.
[0067] While preferred embodiments of the invention have been
described, it should be understood that the invention is not so
limited and modifications may be made without departing from the
invention. The scope of the invention is defined by the appended
claims, and all devices that come within the meaning of the claims,
either literally or by equivalence, are intended to be embraced
therein.
* * * * *