WO2008100158A1

WO2008100158A1 - Means for exploiting kinetic energy from water

Info

Publication number: WO2008100158A1
Application number: PCT/NO2008/000062
Authority: WO
Inventors: Espen Ekeland
Original assignee: EULER AS
Current assignee: EULER AS
Priority date: 2007-02-16
Filing date: 2008-02-15
Publication date: 2008-08-21
Anticipated expiration: 2009-08-16

Abstract

The invention relates to a turbine (10) for power production by extracting energy from a fluid flow, the turbine (10) being intended to be submerged in a body of water. The turbine comprises a centrally arranged column (26) which is rotationally supported by a housing (14) for rotation around a primary axis, arranged perpendicular to a direction of water flow, and two or more, typically three curved elastic profiles (12) which are rigidly attached to the column (26) at their upper end and rotatably attached at their lower end with respect to stay (20), the stays (20) being perpendicularly attached to the column (26). Said profiles (12) are stiffened against the column (26) at least on an intermediate level by means of stays (19). The support of said curved elastic profiles (12) is configured in such way that the profiles (12) at their lower end are supported only on the stays (20) in the region of each profiles (12) leading edge, each profile (12) being allowed to more or less to twist back and fro around an angle of twist (28) dependent upon the direction of water flow (S) and the position of said profiles (12) in the rotation in the water flow (S).

Description

MEANS FOR EXPLOITING KINETIC ENERGY FROM WATER

Technical Field of the Invention.

The present invention relates to a device for extraction of energy from fluid flows, e.g. alluvial or marine current.

Background for the Invention

For generation of wind power horizontal turbines are very commonly used. Use of vertical turbines has been attempted as well, but they have not become widespread. A problem associated with early designs of vertical turbines was that dynamic loads are not constant over a rotation. When such unevenness happens to hit a resonant frequency in the structure, harmful resonances tended to occur.

For generation of power from rivers and oceans designs belonging to a type of turbine that may be designated free-turbines has been applied to a very limited degree only. Free-turbines are distinguished by the feature of not being enclosed in a pipe or a housing. There have been done small-scale tests by different types of submerged turbines. In the ocean it is, as of 2005, installed a turbine in the Kvalsundet in Norway. This installation is of the horizontal type. It lacks the option of rotation about its secondary axis, i.e. about its vertical axis. To compensate for the resulting inability to orient itself to the current direction it can pitch its blades 180 degrees for thereby to be able to operate on current in two directions. The resulting pitching mechanism is complex. In addition it is required to equip the turbine with a gearbox to achieve an RPM sufficient to drive a generator of the necessary- compactness. Thus, this type of design requires both complex mechanical equipment and electrical high-voltage gear placed permanently submerged. This is undesirable indeed. Furthermore, the center of gravity and the center of buoyancy in this type of design do not lie on the same vertical axis. Consequently, lift out of the sea becomes difficult because of the tilting that occurs in the splash zone crossing. This significantly increases handling problems by lifting and lowering for maintenance.

There is a subgroup of turbines where tubular casings or housings are not introduced. These can be designated free-turbines. Among the free-turbines that have been applied for exploitation of wind energy, there is two main types. One type is characterized in that the primary- rotational axis for the blades is oriented parallel to the wind direction. This is the more widespread concept. Such turbines are called horizontal turbines. They are commonly used as windmills. In many cases it is possible to twist the blades individually for pitch changes to adapt to changing wind speeds .

There is also a subset of free-turbines has the primary rotational axis perpendicular to the wind direction. These may be called vertical turbines. The best known of these is the Darreius turbine. Designs of this type involve two or more blades. The blades can be straight or curved. A characteristic trait of the original Darreius design is that the blades are fixed and do not twist during a revolution about the primary axis.

NO 319.880 describes a method to produce energy by means of one or more rotating submerged turbines that produce hydraulic energy, wherein each individual turbine drives a rotary pump for hydraulic fluid. This can be done in closed or open circuits of pipes or hoses. The energy transferred to the hydraulic fluid is then utilized to drive a hydro-electric generator set producing electricity. According to this concept a hydraulic fluid or water is pumped to a base station onshore or submerged.

NO 320 286 describes a concept of using a vertical turbine of "Darrieus" type. This particular design involves two or more profiles, made from a flexible material. These profiles rotate about a vertical axis. Each individual profile is controlled by a governing rod. All rods are collected centrally near the main rotational axis from where they are controlling the pitch of the individual flexible blades.

Summary of Invention.

An object of the present invention is to produce a device to improve energy output from turbines compared to prior art turbines.

A second object of the invention is to produce a turbine submerged in a body of water wherein the direction of rotation of the turbine is independent of direction of water flow.

Still further object of the present design is to provide a turbine that does not depend on separate mechanical mechanisms to change the turbine direction of rotation.

A still further object of the invention is to exploit the rotation in the fluid flow S which is the consequence of the deflection of a flow by an airfoil, inducing a moment from this reaction force.

The present invention involves a turbine of the basic "Darreius" type, but differs from this in significant aspects. According to the invention the blades in the turbine can be twisted without separate mechanisms to produce such twist. The desired effect is achieved according to the invention by means of hydrodynamic forces acting on the elasticity on the blades. Thereby is achieved additional efficiency and improvement of the self-starting performance of the turbine. According to the invention the objects are achieved by a concept that is specifically defined in the independent patent claim, whereas different embodiments are defined in the dependent patent claims.

According to the invention the desired twist of the blades is achieved by means of the forces in the fluid flow action upon elasticity in the turbine blades.

An advantage in the concept according to the invention is that the rotational direction of the turbine is independent of the flow direction. This involves the feature that the turbine will function independent of the direction of the flow in which it operates.

According to the invention additional efficiency and enhanced performance are achieved.

Brief Description of the Drawings.

One embodiment of the invention shall be described below, referring to the drawings, where:

Figure Ia shows a free-turbine where the primary axis of rotation for the blades is arranged to be parallel with the flow direction of the fluid;

Figure Ib shows a turbine of the Darrieus type with a rotational axis perpendicular to the direction of flow and where the blades are curved and fixed and do not twist during rotation about the primary axis;

Figure 2 shows a schematic perspective sketch of a turbine according to the present invention;

Figure 3 shows schematically a view in perspective of a turbine according to the invention shown in the Figures 3a and 3b, where the main features of the pattern of flow around a generic airfoil in a Darreius turbine is shown, and

Figure 4 indicate different positions of a blade in a turbine according to the invention. Detailed Description of the Invention

Figure Ia and Ib describe two varieties of turbines lOaccording to prior art technology of the so called free- turbine type. Figure Ia show a turbine 10 where the primary axis 11 of rotation of the turbine 10, i.e. the rotational axis of the blades 12, is arranged in parallel to the direction of flow S. The embodiment shown in Figure Ia is of the type commonly applied in windmills. As indicated in the Figure the blades are rotationally attached to a housing 13 that is rotationally arranged on a secondary rotational axis 14. In addition the blades 12 are also rotationally arranged on a hub 15, so that the angle of the blades 12 can be varied and/or be adjusted about a pitch axis 17, thereby achieving a maximum exploitation of the at any time occurring fluid flow. The blades 12, the housing 13, the hub 15 as well as the rotational axis 14 is supported by a tower 16 that for instance can be fixed to a foundation on the ground or on . a sea floor.

Figure 1 b shows another embodiment of a free-turbine 10. According to this embodiment, the primary axis of rotation is vertical and is perpendicular to the fluid' s direction of flow S. The turbine 10 shown in Figure Ib is of the prior art Darreius type. It is equipped with arched blades 12 which span between an upper and lower fixation point 18. The blades 12 are rigid and stiffened at a number of levels by means of stiffeners 19, arranged at a number of levels, arranged perpendicular to the primary- rotational axis 11 of the turbine 10. This embodiment is without a secondary rotational axis and also without any twist axis for the blades.

Figure 2 show a schematic view of a turbine 10 according to the present invention. The turbine 10 is of the general Darreius type and involves a vertical column 26 provided with arched blades 12 that can rotate about the axis of rotation of the column 26. The blades 12 are attached at their upper ends at the top of the column 26. Furthermore, the lower ends of the blades 12 are affixed to the lower part of the column 26 by mean of plates 20 or stays. Hence, the turbine 10 is independent of the direction of flow S. The column 26 and the blades 12 are rotationally arranged for rotation about a primary- rotation axis 11. Said lower plates or stays 20 and stays 19 are arranged perpendicularly onto the primary- rotational axis 11 of the turbine 10. The blades 12 are in turn kept in a stayed-out position by means of intermediate stays, also arranged perpendicular to the primary rotational axis 11 of the turbine 10. According to the embodiment shown in Figure 2, two sets of intermediate stays 19 are applied.

Turbine blades 12 are rotationally arranged on a plinth 21 forming a foundation that contains a pump housing. The foundation is fixed to a seafloor 22 by means of anchoring bodies 23 that preferably may be in the form of suction anchors, forced down into the seafloor 22. To obtain the maximum achievable stability, the anchors 23 are placed in a lateral distance from the housing 21, the anchors 23 being connected to the housing by means of rigid arms 24. The pump inside the housing 21 is fluid communication with pipes 25 for circulation of a fluid such as seawater, between the pump at the seafloor and a generator (not shown) , for example placed onshore for generation of electrical power.

Consequently, the power transmission from the turbine 10 is achieved by direct connection to a pump supplying a conventional hydro-electrical aggregate with kinetic energy. Hence the turbine 10 can be retrieved to surface without the need of breaking electrical connections. The connection between turbine 10 and pump can be direct such that submerged, complex gearboxes can be avoided. This feature distinguishes the invention for example from the embodiment described in NO 319 880.

Furthermore, the rotational direction of the turbine is independent of the direction of the surrounding flow. The turbine starts in a predetermined direction without other external influences than the fluid flow from which it is extracting energy. The hydraulic communication between the pump and the hydro-electric generating set can advantageously be without direction-changing valve trains. This distinguishes the invention from NO 320 286.

Independent of the direction of flow, the turbine will rotate in the same direction, even if the direction of flow changes 180°.

As shown in Figure 2, the blades are attached to the plates 20 in proximity of the front edge of the blades 12, allowing the blades to swing or pivot more or less sideways, backwards and forwards, about the fore edge, dependent upon the direction of flow and the angle of attack of the blades in a rotation cycle.

In the following, the principle of functioning of the invention shall be described, referring to Figures 3 and 4. It is commonly known that any airfoil 12 produces lift by deflection of a fluid flow. The deflection causes a change in the momentum of the flow, which sets up a force component laterally to the original direction of flow. This force component is commonly designated lift. In addition, the flow will have to travel a longer distance on what is in conventional arrangement will be the upper surface of the airfoil 12. This causes a small increase in velocity in this part of the flow, which in turn leads to a small reduction in pressure. This is known as the Bernoulli effect. This increases the lift somewhat. In all actual flows frictional forces acting in the direction of flow, is also produced. Inherent in the deflection of the fluid flow S is also a rotation of the fluid. As its reaction, this leads to a significant a rotational moment on the airfoil. This is the reason why practically all aircrafts have horizontal flight surfaces in their tails. These are to counterbalance said rotational moment. In horizontal turbines this moment only sets up some extra, undesirable, loads on the blades 12. In vertical turbines these moments give an advantageous contribution to the energy extraction. This is utilized in the present invention.

In the original Darreius concept is was the rotational moment on the foils 12 that gives rotation in the turbine 10. When a conventional Darreius turbine is not rotating, this moment is acting equally but in opposite directions on opposite sides of the rotational axis 11. Hence it will not start by itself from a standstill. Not until it is set in rotation, the moment on the wings 12 will be different on the two sides of the axis and rotation will be sustained and energy can be extracted. If the circumferential speed of the wings 12 is larger than the wind speed, the moment will be positive on both sides of the axis 11 of the turbine, even if it still is less on the tailwind side. On the tailwind side, however, the drag component is less, which to an extent will compensate for the weaker moment.

The blade 12 is provided with a rounded leading edge with an integral leading edge stiffener 30, making the profile less sensitive to changes in the flow angle of attack. The blade 12 may be flexible, and/or elastic and may possibly be hollow or massive, possibly reinforce by steel cords or textile cords. The blade may for example be made of rubber, an elastomer, such as NBR, plastic materials or corresponding materials. Alternatively, the blade 12 may be in the form of a fine-meshed netting of metal or very thin metal plates. According to the invention the properties of such an airfoil can be utilized without introducing textile membranes. Hence, the abrasive wear be reduced. The blade 12 is at its leading edge 27 equipped with an axis of rotation 28. Due to the placement of this axis near the leading edge of the blade 12, the angle of attack of the flow S will decline as the flow velocity increases. An airfoil 12 with an elastic profile can be suspended elastically in a fluid flow such that by adjusting the axis of rotation along the cord of the airfoil it can be brought to twist in advantageous directions. If the axis of rotation of the airfoil is adjusted towards the trailing edge the flow will tend to increase the angel of attack. It is desirable at it is somewhat forward of the neutral center 29.

Figure 4 shows the blade 12 in three different, typical positions. The top part of the picture, Figure 4a, shows the blade 12 in a neutral position. In this position the blade profile is symmetric about the profile' s longitudinal axis. In the mid part of the picture, Figure 4b, the blade is hit by a fluid flow that approaches angled to one side. In this position the leading edge of the profile will tend to orient itself towards the flow direction, while the overall profile will twist about its rotational axis 28, whereas the neutral point of the profile will tend to move in the opposite direction of the leading edge. In this position the blade 12 has a convex upper surface and a concave lower surface. In the lower part of the picture, Figure 4c, the blade is shown in a position where the fluid flow is coming laterally angled in from the opposite side of what is indicated in Figure 4b. In this position the movements and rotations are identical but opposite.

A profile 12 that is somewhat curved will readily be brought to be more concave on the side that is more exposed to the flow (its "bottom surface") . The invention uses this advantageously. The blades 12 are preferably fixed to the column at the upper end and are elastic such that they twist about the axis 28 of twist into the flow at high angles of attack. This is achieved without torsionally stiff or springy end bearings in the ordinary sense of the concept, but rather by the proper curve of the ached design of the blade 12. In the leading edge of the wing 12 it can advantageously be arranged a structural element 30, such as a cylindrical pipe. The structural element 30 is intended to give both local torsionally stiffness and local lateral stiffness. The trailing edge of the blade 12 can also advantageously be equipped with a structural element 31 with a somewhat higher stiffness than the blade 12 otherwise have, bur still less than the leading edge stiffener 30. By this means the blade 12 will, by large angles of attack, form a concave surface towards the flow. This will give both benign lift and moment. The absence of such mechanical devices is particularly advantageous for submerged installations. This separates the invention from NO 319 880.

The turbine 10 according to the invention is basically symmetric about the vertical axis 11. That in itself lends itself to vertical running and retrieval to and from a submerged environment. Vertical lifting is an essential operation by all sub sea installations.

Power transmission from the turbine proper is done in that it is directly connected to a pump that supply a conventional hydro electrical generator set. By this means the turbine can be pulled to the surface without having to break any electrical power connections. The connection between turbine and pump can be direct and fixed such that the complexity of sub sea gearboxes is avoided. This separates the invention from NO 319 880.

The turbine 10 has the feature of a direction of rotation that is independent of the flow direction. It starts in a predetermined direction without other external influences than the flow from which it extracts power. The hydraulic communication between pump and hydroelectric generator set can thus with advantage be without direction-changing valves. This separates the invention's claim 2 from NO 320 286.

Above, it is specified that the upper end of the blades 12 are rigidly attached to the column. It should be appreciated, however, that this is not a condition for achieving the desired results. The fact is that the blades being curved, contributes to the desired torsional resistance .

Claims

C l a i m s

1. Turbine (10) for power production by extracting energy from a fluid flow, the turbine (10) being intended to be submerged in a body of water, comprising a centrally arranged column (26) which is rotationally supported by a housing (14) for rotation around a primary axis, arranged perpendicular to a direction of water flow, and two or more, typically three curved elastic profiles (12) which are rigidly attached to the column (26) at their upper end and rotatably attached at their lower end with respect to stay (20), the stays (20) being perpendicularly attached to the column (26), and that said profiles (12) being stiffened against the column (26) at least on an intermediate level by means of stays (19), c h a r a c t e r i z e d i n that the support of said curved elastic profiles (12) is configured in such way that the profiles (12) at their lower end are supported only on the stays (20) in the region of each profiles (12) leading edge, each profile (12) being allowed to more or less to twist back and fro around an angle of twist (28) dependent upon the direction of water flow (S) and the position of said profiles (12) in the rotation in the water flow (S) .

2. Turbine (10) for power production according to claim 1, wherein each profile (12) being provided with a rigid, rounded stiffening means (27) at their leading edge, extending along the entire vertical length of the profile (12) and that each profile (12) is provided with a point of twisting (28) positioned downstream of said stiffening means (27) along the leading edge.

3. Turbine (10) for power production according to claim 1 or 2, wherein the axis of twist (28) is positioned between said leading edge stiffening means (27) and the neutral point (29) of the profile (12) .

4. Turbine (10) for power production according to one of the claims 1-3, wherein said profile (12) is configured such that the angle of attack and the curvature of the profile assume the most beneficial position with respect to the direction of water flow (S) at any time, so that the turbine (12) in a better manner may exploit the kinetic energy of the water flow and also become self staring in a varying flow.

5. Turbine (10) for power production according to one of the claims 1-4, wherein said profile (12) is covered by an elastic material provided with internal stiffening means so that the trailing edge of said profiles (12) is allowed to pivot back and fro.

6. Turbine (10) for power production according to one of the claims 1-5, wherein said profiles (12) at their trailing ends are provided with an element (31) having a higher stiffness than the remaining parts of the profile

(12) .

7. Turbine (10) for power production according to one of the claims 1-6, wherein the power transmission is obtained by means of a pump for pumping sea water, water or oil to a hydro-electrical generator without the use of valves.