TURBINE BLADE FOR A WATER TURBINE WITH BI-DIRECTIONAL FLOW

Abstract

The invention relates to a turbine blade for a water turbine, comprising, at least over part of its length, a curved profiled element having a median line created point-symmetrically in relation to a point of symmetry on the chord of the profiled element, half-way down, in such a way as to form an S-shaped curve. The median line splits the profiled element into a first side and a second side. The invention is characterised in that the turbine blade comprises an overflow device between the first side and the second side of the profiled element.

Description

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.

As another alternative for creating a water turbine for a bi-directional flow, it is proposed in WO 2006/125959 A1, 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 A1, 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.

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 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:

FIG. 1 a shows a profile section, cut along the line A-A in FIG. 1b, 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.

FIG. 1 b shows a partial section of a turbine blade from above, for the profile from FIG. 1a, having an overflow device applied in the central region of the profile, with a limited extension along the longitudinal axis of the turbine blade.

FIG. 2 a shows as a profile section, an alternative embodiment example of the invention having numerous overflow channels.

FIG. 2 b shows a top view of a partial section of a turbine blade having a profile in accordance with FIG. 2a.

FIG. 3 a shows another profile section according to the invention, having off-center, passively controllable overflow channels.

FIG. 3 b shows a top view of a partial section of a turbine blade having a profile in accordance with FIG. 3a.

FIGS. 4 a 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.

FIGS. 5 a and 5b show active, adaptive wall components in the overflow device in different settings for the first and the second flow directions.

FIG. 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 FIG. 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.

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 FIG. 1a, 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 central region 26, which is defined as that part of the profile that extends from ⅜ to ⅝ 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 FIG. 1b, which depicts a top view of the turbine blade 13 having the profile according to the invention depicted in FIG. 1a. 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 FIG. 2a, cut along the line B-B in FIG. 2b. A number of overflow channels 2, 2.1, 2.2, . . . , 2.n are depicted for defining the overflow opening 1. According to FIG. 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 FIGS. 3a and 3b. The profile section C-C in FIG. 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 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 FIG. 3b, a top view of a turbine blade 13 having a profile according to FIG. 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.

FIGS. 4 a 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 FIG. 1a. For this, the first adaptive wall component 3 is disposed in that part of the overflow device 1, that is dedicated 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 FIGS. 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 FIGS. 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 FIG. 5a, the second active, adaptive wall component 17 is extended, and corrects the overall contour of the second profile half 25. The first active, 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 FIG. 5b.

The embodiment according to FIGS. 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.

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
• 31 Second profile tip
• 32 Median line
• w camber

Claims

1. A turbine blade for a water turbine, having a cambered profile with a median line (32) in at least a portion of its length, that is designed to be symmetrical about a point in relation to a point of symmetry (27) lying at the midpoint of the profile length on the profile chord (20), and forming an S-curve, wherein the median line (32) divides the profile into a first profile surface (21) and a second profile surface (22), and wherein the profile comprises a midline (23) that depicts aright angle to the profile chord (20) having the symmetry point (27) as its starting point, and which divides the profile into a first profile half (24) and a second profile half (25), characterized in that the turbine blade comprises an overflow device (1), which establishes a fluid connection between the first profile surface (21) and the second profile surface (22), wherein the overflow device (1) comprises a first off-center overflow channel (5, 5.1, . . . , 5.n), which establishes a fluid connection between the first profile surface (21) and the second profile surface (22) in the first profile half (24), and a second off-center overflow channel (6, 6.1, . . . , 6.n), which establishes a fluid connection between the first profile surface (21) and the second profile surface (22) in the second profile half (25), and the first off-center overflow channel (5, 5.1, . . . , 5.n) has a dedicated first channel closing component (7.1, 7.2) and the second off-center overflow channel (6, 6.1, . . . , 6.n) has a dedicated second channel closing component (10.1, 10.2), which are configured for the selective closing of the respective off-center overflow channels, depending on the direction of flow.

2. The turbine blade according to claim 1, characterized in that the selective closing of the first off-center overflow channel (5, 5.1, . . . , 5.n) and the second overflow channel (6, 6.1, . . . , 6.n) are caused by passive means.

3. The turbine blade according to claim 2, characterized in that a first elastic profile component (8, 8.1, . . . , 8.n) on the second profile surface (22) is used for the passive control of the first channel closing component (7, 7.1, 7.2), and a second elastic profile component (11) on the first profile surface (21) is used for the passive control of the second channel closing component (10.1, 10.2).

4. The turbine blade according to claim 1, characterized in that the overflow device (1) comprises a first adaptive wall component (3) and a second adaptive wall component (4), which are disposed symmetrically about a point of symmetry (27).

5. The turbine blade according to claim 4, characterized in that the first adaptive wall component (3) and the second adaptive wall component (4) function as passive components, the contours of which are affected by the flow forces.

6. The turbine blade according to claim 4, characterized in that the first adaptive wall component (3) comprises a first active, adaptive wall component (16), and the second wall component (4) comprises a second active, adaptive wall component (17).

7. A method for operating a turbine blade for a water turbine with bi-directional flow, having a cambered profile with a median line (32) in at least a portion of its length, that is designed to be symmetrical about a point in relation to a point of symmetry (27) lying at the midpoint of the profile length on the profile chord (20), and forming an S-curve, wherein the median line (32) divides the profile into a first profile surface (21) and a second profile surface (22), and the turbine blade comprises a first off-center overflow channel (5, 5.1, . . . , 5.n), which establishes a fluid connection between the first profile surface (21) and the second profile surface (22) in the first profile half (24), and a second off-center overflow channel (6, 6.1, . . . , 6.n), which establishes a fluid connection between the first profile surface (21) and the second profile surface (22) in the second profile half (25), and wherein the first off-center overflow channel (5, 5.1, . . . , 5.n) comprises first channel closing component (7.1, 7.2) and the second off-center overflow channel (6, 6.1, . . . , 6.n) comprises second channel closing component (10.1, 10.2), and wherein, by means of the respectively dedicated channel closing component, depending on the direction of flow, the upstream off-center overflow channel is closed, and the downstream off-center overflow channel is opened.

8. The turbine blade according to claim 2, characterized in that the overflow device comprises a first adaptive wall component and a second adaptive wall component, which are disposed symmetrically about a point of symmetry.

9. The turbine blade according to claim 3, characterized in that the overflow device comprises a first adaptive wall component and a second adaptive wall component, which are disposed symmetrically about a point of symmetry.