Note: Descriptions are shown in the official language in which they were submitted.
CA 02783997 2012-06-11
Turbine Blade for a Water Turbine with Bi-Directional Flow
The invention concerns a bi-directional flow turbine blade for a water
turbine, which preferably
is used in an immersing power generation facility for the production of energy
from a bi-
directional flow of water.
For energy production from a flow having a variable direction, such as a tidal
current, for
example, by means of a free standing, propeller shaped designed turbine,
normally a tracking
mechanism is used, which turns a gondola having the turbines attached thereto
towards the
current. If two substantially opposing main flow directions are present, such
as is the case with
the ebb and flow of a tidal current, then a directional tracking of this type
can be obtained with a
shuttered or rotating device, which rotates the gondola from a first position
to a second position.
The disadvantage, however, is that for a tracking mechanism of this type,
massive rotational or
shutter blinder systems must be used. Furthermore, if it is the case that the
water turbine drives
an electric generator, a device must be provided that prevents a twisting of
the power cable
emerging from the electric generator.
In order to circumvent this problem, an overall tracking of the water turbine
by means of a pitch
adjustment device, which causes a rotation of the turbine blades through 180
at the hub, can be
used instead to create a device for bi-directional flow. However, a design of
this type also has
disadvantages, because, with a propeller shaped turbine having turbine blades
extending radially
outwards, typically lying on the upstream side of the retaining structure of
the gondola for at
least one flow direction, there is a flow impediment reducing the degree of
efficiency.
Furthermore, a pitch adjustment mechanism is structurally elaborate and is
disadvantageous,
with respect to the necessity of maintenance, for immersing power production
facilities for
obtaining energy from an ocean current.
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As another alternative for creating a water turbine for a bi-directional flow,
it is proposed in WO
2006/125959 Al, that a double symmetrical profile be selected as the profile
contour for the
turbine blades of a rotary water turbine. For this, the chord line represents
a first axis of
symmetry. In addition, the profile is symmetrical along a midpoint line, which
is defined as
being perpendicular to the profile chord at 50% of the length of the chord.
The result is a lens-
shaped profile, which ensures identical profile contours for a bi-directional
flow. It is
disadvantageous, however, that due to the doubled symmetry selected for the
profile contour in
comparison with a cambered profile that is subject to flow from one side,
there is a lower degree
of efficiency. Furthermore, there are disadvantages due to downstream flow
separations and an
increased flow resistance of the turbine blades.
Furthermore, from document US 2007/0231148 Al, profiles that are symmetrical
about a point,
having a camber, are known. These are characterized by a point of symmetry,
which at the
midpoint of the profile length, lie on the profile chord, such that the point-
symmetry designed
median line follows an S-curve. The thickness distribution of the profile is
selected such that it
is symmetric to the midline. In this manner, the S-curve shaped profile
improves the
performance coefficients and limits the thrust coefficients.
The invention assumes the objective of designing a turbine blade such that a
bi-directional flow
can be accommodated. This turbine blade should also be suitable for use in a
propeller shaped
turbine of an immersing power production facility, wherein the turbine blade
per se should be
characterized by a high degree of efficiency and limited longitudinal torsion
for a flow arriving
from both sides.
The invention builds on the known point-symmetrical profiles having an S-curve
shaped median
line and a thickness distribution that is symmetrical over the midline of the
profile. This profile
is then further developed such that an overflow device from one profile
surface to the second
profile surface is provided.
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Due to the point-symmetrical profile shape, there is the risk for S-curve
profiles of a flow
separation at the downstream profile components. In addition, strong torsion
forces act on a
turbine blade having a profile of this type. Through an overflow from the
first to the second
profile surface in the middle portion and/or the downstream surface region of
the profile, there is
the possibility of reducing the tendency towards flow separation, and due to
the reduced torsion
forces, of structurally simplifying the reinforcing of the turbine blade
against twisting.
In addition, the turbine blade profile can be substantially adjusted to the
technical properties of
the flow, without the need for following competing structural mechanical
requirements in the
construction of the turbine blade. For this, elongated, slender profiles may
be used, which result
in a high glide ratio. In addition, the attachments of the turbine blade at
the hub of the rotating
unit have to accommodate reduced torques and can be correspondingly simplified
structurally
and in terms of the production technology.
According to a first embodiment, the overflow device comprises numerous
overflow channels,
whose orientation is adjusted to the bi-directional flow direction. For
another embodiment
variation, which can be used as an alternative or in addition to the overflow
channels, the
overflow device is formed by a divided blade profile. For this, there is at
least one partial section
in the central region of the overall profile, at which point the thickness
distribution along the S-
curve shaped median line assumes the value of zero.
For a further development, the overflow device may comprise adaptive wall
components, which,
depending on the direction of flow, change from a first setting to a second
setting, thus creating
deviations in the point-symmetry of the profile. By this means, a targeted
overflow to the back,
downstream side region of the profile can be effected, without resulting in a
serious loss in
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efficiency. In this case, the adaptive wall components can be displaced by
means of a dedicated
actuator, either actively, or said components can be designed as passive,
elastic components,
whose contour changes with the flow.
In another design alternative of the invention, the overflow device comprises
overflow channels,
which can be closed, depending on the flow direction. By this means, overflow
channels can
also be disposed outside of the central region of the profile. The closing of
the overflow
channels can be effected either passively or actively. For a passive
execution, there is preferably
a coupling of channel closing components in the overflow channels having
elastic profile
components, which are disposed along the exterior of the profile that the
current is flowing over,
and become deformed by means of the flow forces. If a hydraulic or pneumatic
working
substance is accommodated in the elastic profile components, then pressure for
actuating the
channel closing components can be generated and at the same time, an adaptive
profile is created
thereby.
In the following, the invention shall be explained more precisely based on
embodiment examples
in connection with the drawings, in which the following is depicted:
Figure 1 a shows a profile section, cut along the line A-A in figure I b, for
a profile
according to the invention, having a symmetry about a point, with an overflow
device from the first to the second profile surface.
Figure lb shows a partial section of a turbine blade from above, for the
profile from figure
1 a, having an overflow device applied in the central region of the profile,
with a
limited extension along the longitudinal axis of the turbine blade.
Figure 2a shows as a profile section, an alternative embodiment example of the
invention
having numerous overflow channels.
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Figure 2b shows a top view of a partial section of a turbine blade having a
profile in
accordance with figure 2a.
Figure 3a shows another profile section according to the invention, having off-
center,
passively controllable overflow channels.
Figure 3b shows a top view of a partial section of a turbine blade having a
profile in
accordance with figure 3a.
Figures
4a and 4b show a further development of the invention have a paired and point-
symmetrical
configuration of elastic components for influencing the profile in the
overflow
device from the first profile surface to the second profile surface.
Figures
5a and 5b show active, adaptive wall components in the overflow device in
different settings
for the first and the second flow directions.
Figure 6 shows a point-symmetrical, cambered profile corresponding to the
prior art, for
the creation of a bi-directional flow turbine blade.
For the purpose of explaining the terminology used in the following, first a
profile section
corresponding to the prior art, depicted in figure 6, shall be examined. A
profile is shown,
designed such that it is point-symmetrical in relation to the symmetry point
27. For this, the
symmetry point 27 is disposed on the profile chord 20 at the midpoint of the
profile, and is,
accordingly, covering the intersection of the profile chord 20 at the midline
23, whereby the
latter is defined as running perpendicular to the profile chord 20.
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For the S-curve shaped profile, the median line 32, applied symmetrically in
relation to the
symmetry point 27, exhibits a camber w. Furthermore, the aforementioned
condition of
symmetry results in a symmetrically applied profile thickness distribution
with respect to the
midline 23. Other embodiments for bi-directional flow, point-symmetrical
profiles are
conceivable (not shown), such as a median line having at least one linear
course in sections, in
the central profile section and profile tips 30, 31 designed such that they
are point-symmetrical to
one another.
For the following explanation, a conceptual division of the profile through
the median line 32 is
assumed, resulting in a first profile surface 21, and a second profile surface
22. In addition, a
division of the profile through the midline 23 into a first profile half 24
and a second profile half
25, is to be assumed. For this, the first profile half 24 extends from the
first profile tip 30 to the
midline 23, and the second profile half 25, accordingly, extends from the
midline 23 to the
second profile tip 31.
Furthermore, for the indicated first flow direction 28, wherein an effective
flow is assumed, there
is a suction effect in at least the first profile half 24 on the first profile
surface 21, and there is a
pressure effect to the second profile surface 22. However, due to the S-curve
in the region of the
downstream edge of the second profile half 25 on the first profile surface 21,
i.e. in the vicinity
of the second profile tip 31, a pressure node may occur for the observed first
flow direction 28,
which reduces the efficiency of the profile, and further increases the torsion
acting on the S-
curve profile. For the second flow direction 29, the pressure and suction
surface configuration is
reflected over the symmetry point 27.
For the profile according to the invention, depicted as a profile section in
figure 1 a, there is a
point-symmetrically applied overflow device 1, which is symmetrical in
relation to the symmetry
point 27. In the embodiment example depicted, the overflow device 1 interrupts
the profile at a
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central region 26, which is defined as that part of the profile that extends
from 3/8 to 5/8 of the
profile length.
The overflow device 1 can extend, according to a first design, longitudinally
over the entire
turbine blade 13, such that there is a divided profile over the entire length.
According to an
alternative, presently depicted design, the overflow device 1 extends over a
limited section of the
length of the turbine blade 13. This design is illustrated in figure ib, which
depicts a top view of
the turbine blade 13 having the profile according to the invention depicted in
figure I a. For this,
numerous overflow devices 1 can be provided along the length of the turbine
blade 13, which are
separated from one another by cross-bars, which improve the structural
stability. These are not
shown in detail in the figures.
The effect of an overflow device 1 provided according to the invention for a
point-symmetrical,
bi-directional S-curve profile subjected to flow is as follows: the
substantial lift effect is caused,
for the first flow direction 28, by the front profile section, i.e. the first
profile half 24.
Correspondingly, for a flow direction in the opposite direction, i.e. in the
direction of the second
flow direction 29, the substantial effect of the profile is provided by the
second profile half 25,
which is then upstream. By means of the overflow device 1 according to the
invention, an
overflow from the pressure side to the downstream region of the opposite
profile surface is
caused. Accordingly, a portion of the profile current is guided along the
first profile half 24 on
the second profile surface 22, via the overflow device 1, to the second
profile half 25 on the first
profile surface 21 for the first flow direction, thereby reducing the danger
there of flow
separations on the one hand, and torque being applied to the turbine blade 13,
on the other hand.
Another design example of the invention is evident from the profile section
depicted in figure 2a,
cut along the line B-B in figure 2b. A number of overflow channels 2, 2.1,
2.2,..., 2.n are
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depicted for defining the overflow opening 1. According to figure 2b, the
individual overflow
channels 2, 2.1, 2.2, ..., 2.n are disposed over the length of the turbine
blade 13, parallel and
offset to one another. For this, designs are also conceivable for the adjacent
channels, oriented at
angles to one another, or provided with branches. In addition, the cross-
sections of the overflow
channels 2, 2.1, 2.2,..., 2.n can be modified. An embodiment alternative
having slit shaped
overflow channels 2, 2.1, 2.2,..., 2.n is preferred. Embodiments of this type
are not depicted in
detail in the figures.
Another design of the invention is depicted in figures 3a and 3b. The profile
section C-C in
figure 3a shows a first, off-center flow channel 5 and a second off-center
flow channel 6, which
at least for portions of their lengths are disposed outside of the central
region 26. The first
channel closing components 7.1, 7.2 are provided for closing the first off-
center overflow
channel 5. For the illustrated first flow direction 28, these are closed, such
that no overflow
occurs through the first off-center overflow channel 5, and thereby in the
region of the first
profile half 24, from the first profile surface 21 to the second profile
surface 22. This is different
in the case of the second, off-center overflow channel 6. In this case, the
second channel closing
components 10.1, 10.2, designated for the illustrated first flow direction 28,
are open, such that
in the second profile half, the desired overflow from the first profile
surface 21 to the second
profile surface 22 results.
For the depicted design, a passive control of the first and second channel
closing components,
7.1, 7.2, 10.1, 10.2 occurs. For this, a first elastic profile component 8,
comprising a pressure
accommodating working substance, is compressed for the illustrated first flow
direction 28, by
means of which, a connection is provided between the first channel closing
components 7.1, 7.2
and the first elastic profile component 8 via the first coupling channel 9.
Accordingly, a
compression of the first elastic profile component 8, due to its location on
the pressure side for
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the flow direction 28, results in an expanding of the bellows shaped channel
closing components
7.1, 7.2 applied thereto, and thereby to the aforementioned flow interruption
in the first off-
center overflow channel 5. This is different in the case of the second elastic
profile component
11, which lies point-symmetrically opposite the first elastic profile
component 8, in relation to
the symmetry point 27, and therefore is on the suction side for the first flow
direction 28.
Accordingly, the second channel closing components 10.1, 10.2 are contracted
due to the liquid
coupling via the second coupling channel 12, and not impeding the second off-
center flow
channel 6. For the, not depicted, second flow direction 29, the first elastic
profile component 8 is
on the suction side, and the second elastic profile component 11 is on the
pressure side, as a
result of which, the first channel closing components 7.1, 7.2 open the first
off-center overflow
channel 5, and the second channel closing components 10.1, 10.2 close the
second off-center
overflow channel 6.
In figure 3b, a top view of a turbine blade 13 having a profile according to
figure 3a is shown. It
is evident that the first elastic profile components 8, 8.1, ... 8.n, which,
in each case, are
dedicated to a first off-center overflow channel 5, 5.1, ..., 5.n, have a
limited extension in the
longitudinal direction of the turbine blade, in order to prevent a
transporting of the working
substance through centrifugal force.
As a result of the deformation of the elastic profile components 8, 8.1, ...,
8.n, 11 caused by
current forces, an adaptive adjustment of the profile results, dependent on
the direction of flow.
This is understood to be a breakdown of the point-symmetry as a result of the
deformation of the
profile, wherein the deformation direction is reversed with a change in the
direction of flow.
Figures 4a and 4b show another design alternative of the invention, for which
a first adaptive
wall component 3 and a second adaptive wall component 4 are provided for a
further
development of an overflow device 1 corresponding to that in figure I a. For
this, the first
adaptive wall component 3 is disposed in that part of the overflow device 1,
that is dedicated
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to the first profile half 24 on the first profile surface 21. Respectively,
the second adaptive wall
component 4, dedicated to the second profile half 25 on the second profile
surface 22, is located
in a point-symmetrical manner to this, reflected over the symmetry point 27.
The passive adjustment of the contour of the first and the second adaptive
wall components 3, 4
is shown in figures 4a, 4b, which are constructed as elastic components, or
contain a filling that
can adapt to the current, or can be compressed. Due to the deformation of the
adaptive wall
components 3, 4, a symmetry breakdown of the contour of the overflow device 1
occurs when
the profile is subjected to a flow, which results in an improvement of the
flow guidance in the
overflow device 1. The basic contour of the profile, i.e. its state when not
subjected to flow, is
not changed, however, in the point-symmetry in relation to the symmetry point
27.
A design alternative having a first active, adaptive wall component 16 and a
second active,
adaptive wall component 17 is shown in figures 5a and 5b. For this, the first
active adaptive wall
component 16 is dedicated to the first profile half 24 of the first profile
surface 21, and the
second active, adaptive wall component 17 is a part of the second profile half
25 on the second
profile surface 22. For the execution of a rotational movement about a first
center of rotation 14,
which lies in the vicinity of the outer edge of the overflow device 1, the
first adaptive wall
component 16 has a dedicated first actuator 18, which may comprise a hydraulic
cylinder, for
example. For small adjustments, piezo components can also be used as actuators
18.
Accordingly, the second adaptive wall components 17 have a dedicated second
actuator and a
second center of rotation 15.
For the first flow direction 28, depicted in figure 5a, the second active,
adaptive wall component
17 is extended, and corrects the overall contour of the second profile half
25. The first active,
CA 02783997 2012-06-11
adaptive wall component 16 remains in the retracted state. When the flow is
changed to the
second flow direction 29, then, accordingly, the first active, adaptive wall
component 16 is
extended and corrects the associated profile region. On the suction side, the
second active,
adaptive wall component 17 remains in its original state. This situation is
depicted in figure 5b.
The embodiment according to figures 5a and 5b uses active, added, adaptive
wall components in
the region of the overflow device 1 according to the invention, wherein an
increased technical
expenditure is necessary for the control in contrast to a purely passive
system. Compared to the
active devices for the adaptation to a change in the direction of flow by
means of a complete
rotation of the turbine blade 13 using a pitch adjustment device applied at
the intersection with
the hub, that have been used until now, there is the advantage that by means
of numerous
adaptive components that can be activated separately, an adaptation of the
profile contour to the
direction of flow can be caused, that can be distributed to numerous
individual components for
the flow forces. In addition, if individual adaptive components cease to
function, this does not
result in a complete loss of function to the turbine blade 13.
Other designs of the invention are conceivable. As such, a channel structure
having an intake
opening in the region of a profile tip can be applied within the profile, for
example, which
displaces the flow parts along the median line within the profile to an output
opening in the
region of a downstream and suction side section of the profile. Other design
variations can be
derived from the following Claims.
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List of Reference Symbols
1 Overflow device
2, 2.1, 2.2, 2.m Overflow channel
3 First adaptive wall component
4 Second adaptive wall component
5, 5.1, ..., 5.n First off-center overflow channel
6, 6.1,..., 6.n Second off-center overflow channel
7.1, 7.2 First channel closing component
8, 8.1,..., 8.n First elastic profile component
9 First coupling channel
10.1, 10.2 Second channel closing component
11 Second elastic profile component
12 Second coupling channel
13 Turbine blade
14 First center of rotation
15 Second center of rotation
16 First active, adaptive wall component
17 Second active, adaptive wall component
18 First actuator
19 Second actuator
20 Profile chord
21 First profile surface
22 Second profile surface
23 Midline
24 First profile half
25 Second profile half
26 Central region
27 Point of symmetry
28 First direction of flow
29 Second direction of flow
30 First profile tip
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31 Second profile tip
32 Median line
w camber
13
