GB2470020A

GB2470020A - Paddle wheel with vertical paddles

Info

Publication number: GB2470020A
Application number: GB0907715A
Authority: GB
Inventors: David Maurice Watson
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-05-06
Filing date: 2009-05-06
Publication date: 2010-11-10
Anticipated expiration: 2029-05-06
Also published as: GB2470020B; GB0907715D0

Abstract

A paddle wheel has paddles 6 which are able to rotate with respect to a rotating support member 4, e.g. so that they remain vertical throughout rotation of the support member 4. Orientation of the paddles 6 may be controlled by sprockets 11, 12 and chains 13, or by gears 14-16, or the paddles may be weighted. The blades 6 may have a flat face, and the wheel may be supported to float at the water surface 10. The wheel may be connected to a generator for electrical power generation, and may be mounted for vertical sliding movement with respect to posts (19, figure 9).

Description

POWER SYSTEM

Field of the Invention

The invention relates to improved paddle wheels, and especially such wheels for use in extracting energy from flowing water, and more especially from tidal currents. The invention also relates to apparatus and methods for extracting energy from flowing water, especially from tidal currents.

Background and Prior Art Known to the Applicant

The extraction of power from flowing water sources have been practiced for centuries, such as the use of water wheels to drive mechanical equipment. The generation of electrical power by use of flowing water -hydroelectric power -is also a known technology. Most of these systems are directed towards harnessing the power in flowing rivers by use of dams and turbine technology. Extraction of power from tidal sources is somewhat more recent, and many of the systems employed use submerged axial turbines.

Harvesting tidal power provides particular problems: water depth in regions where tidal flows are experienced is often quite shallow, posing problems for the use of axial turbines.

Furthermore, the availability of motive power is inherently cyclic, following the ebb and flow of the tide. Additional problems of maintenance also arise with submerged axial turbines, due to the inherently hostile environment of tidal flows where these devices must be situated.

It is among the objectives of the present invention to attempt a solution to these and other problems.

Summary of the Invention

Accordingly, in a first aspect the invention provides a paddle wheel comprising: a hub; a support member, mounted for rotation with respect to said hub about a generally horizontal (in use) axis; a blade, extending substantially perpendicularly from said support member, and mounted for rotation thereto about a generally horizontal (in use) axis. The provision of rotatable blades on the paddle wheel allows their orientation to adjust such that motive power from flowing water in which the wheel is partially submerged is transferred to the blades primarily by bluff body impaction, i.e. the blades act in a drag mode rather than using the aerofoil effect as found in turbine impellers.

Preferably, in a second aspect, the blade is weighted and mounted such that a face of the blade assumes a generally vertical orientation at rest. In this way, the blade presents a maximum surface area to the flowing water, thereby increasing energy transfer.

In relation to paddle wheels of the first aspect, it is particularly preferred that rotation of the support member with respect to the hub is coupled to rotation of the blade with respect to the support member such that as the support member rotates with respect to the hub, the blade rotates with respect to the support member in an opposite direction, thereby maintaining the orientation of the blade with respect to the hub. By providing a mechanical linkage to the blade (or blades) that maintains their orientation in the face of rotation of the support member, the wheel can be configured to ensure that the blades present a face oriented perpendicularly to flowing water when in use. A number of mechanisms for achieving this coupling are described herein, and a number of alternative configurations will be evident to the skilled addressee, e.g. the provision of active control systems to feather the blades as required.

In one envisioned embodiment, the rotational coupling is effected by means of a chain and sprocket arrangement. Such an arrangement is described in more detail below, and has advantages of being easy and cost-effective to manufacture, and requires no active control system. Chains and sprockets may be manufactured from material resistant to corrosion such as stainless steel, which is particularly important when the device is to be used to harvest energy from flowing tidal streams. Chain and sprocket technology is well understood, and allows for adequate power transmission between the blades and the drive spindle.

In an alternative embodiment, the rotational coupling is effected by means of intermeshing gears. Again, configurations such as this are described below.

In any aspect of the invention it is preferred that the paddle wheel comprises a plurality of such blades. In use, the paddle wheel is partially immersed in a flowing stream of water (such as a tidal stream) such that the lowermost blade is immersed, or at least partially immersed in the water. As the water impinges on the wheel, the support member is rotated by the action of the water. Clearly, once the blade has risen out of the water, the rotational forces no longer act, and the blade can only re-enter the water as a result of continued turning of the support member. Whilst this may occur as a result of the angular momentum of the wheel, it is preferable to provide multiple blades on the wheel. The provision of three such blades will ensure that at least one blade is always in contact with water, ensuring continuous energy transfer. The inventor has found, however, that four blades provide an ideal configuration, taking into consideration mechanical complexity, power smoothing (see below) and shadowing effects of each blade on its neighbour.

Accordingly, in preferred embodiments, the invention provides a paddle wheel comprising three or more blades, and most preferably comprising four blades.

In any aspect of the invention it is preferred that blades are provided with a substantially flat face. As the device operates in a drag mode, flat faces provide good energy transfer.

Preferably, and especially for tidal power systems, both opposite faces of the blades are flat. In this way, the paddle wheel can operate in with water flowing in opposite directions; as the flow of the tide reverses, the paddle wheel changes direction and can generate power from both a rising and a falling tide.

In any aspect of the invention it is preferred that the wheel comprises a hub and support member at each end of said blade(s). This provides greater stability to wheel.

Also in any aspect of the invention, it is preferred that the wheel is constructed so as to float in water. Whilst it is possible to mount the paddle wheel in a fixed position in relation to a water stream (e.g. for use a non-tidal river), it is particularly envisaged that the wheel will find application in tidal situations, where water levels rise and fall. The vertical positioning of the wheel must therefore be varied to maintain the desired partial submersion of the device in the water. By constructing the wheel to be buoyant, its vertical positioning with respect to the water becomes semi-automatic, with the device rising and falling in response to water levels.

In order to improve stability of the device, it is preferred that the paddle wheel is mounted for vertical movement to an anchoring. The anchoring maintains the wheel's horizontal position in a tidal stream, whilst allowing the device to rise and fall. Preferably, the anchoring comprises a substantially vertical post. The post, or posts, may have the form of piles, driven into the sea bed. Operable connection between the wheel and the anchoring may include a water level sensor and a linear drive arrangement (such as a rack and pinion drive) to enable the wheel's vertical position to be adjusted in response to changing water levels. In this instance, the buoyancy of the wheel is not essential, but has the advantage of reducing the mechanical forces required to move the wheel up and down.

In preferred embodiments, the wheel is mounted for vertical sliding movement with respect to said post.

Also included within the scope of the invention is a paddle wheel substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings, Figures 1-9.

In a further aspect, the invention provides a hydroelectric generator comprising a paddle wheel as described herein, operably coupled to a generator. By coupling the rotational movement of the support member to a generator, electricity may be produced by the paddle wheel when in flowing water. In order to optimise generation efficiency, a suitable gearbox may be operably interposed between the wheel and the generator.

Also included within the scope of the invention is a hydroelectric generator substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings, Figures 1-9.

Particular benefits of paddle wheels and generators disclosed herein are that electricity can be generated on a large scale by use of substantially sized and multiple devices. By way of an example, blades of the paddle wheel may be fabricated as steel box sections with blade lengths of, say, 30m, each blade being 5m high, and having an overall thickness of O.5m. For a paddle wheel of this size, a typical diameter for a circular supporting member would be approximately 1 Om, with blades mounted on the supporting member at a radius of approximately 4.7 m. In use, the wheel would be positioned with the centre-line of the supporting member approximately 2.5m above the water surface.

In alternative constructions, blades may be manufactured from e.g. carbon fibre or glass fibre. A number of such paddle wheel arrangements may positioned between successive anchor posts to create an array of paddle wheels in a generator system.

Unlike most axial turbine systems, the paddle wheels are capable of operating in either direction, thereby allowing energy to be captured from tidal streams flowing in both tidal directions. The wheels are easy to construct and maintain, and are expected to exhibit a high degree of reliability. The system has no requirement (at least in some embodiments) for underwater chains or gears, thereby reducing corrosion risk. As the wheel is only partly submerged (unlike submerged axial turbine systems) maintenance is easier, as operative parts of the wheel can always be accessed from above water by suitable positioning of the wheel.

As the system is expected to rotate relatively slowly (no faster than the tidal stream itself) in contrast to axial turbine systems that rotate at high speed due to the effects of their aerofoil-type construction, it is expected that such devices will have minimal impact on the marine environment, e.g. to marine flora and fauna.

Additionally, as the sub-water elements are of relatively simple construction, requiring no underwater bearings, the system will be more resilient to the presence of water-borne solids such silt which might otherwise damage sensitive engineering components.

The devices of the present invention offer advantages over more conventional axial flow turbines by sweeping a rectangular section of a tidal stream or river. By virtue of their generally circular geometry, axial flow turbines are limited to the capture area by the depth of water. The proposed devices can simply be expanded in both blade height and length to capture more energy.

Brief Description of the Drawings

The invention will be described by reference to the accompanying drawings, in which: Figure 1 is a schematic perspective view of a paddle wheel of the invention; Figures 2 and 3 are respectively end and side elevations of a blade according to an embodiment of the invention; Figure 4 is an end elevational view of an embodiment of a paddle wheel on the invention comprising a cam arrangement; Figure 5 is an end elevational view of an embodiment of a paddle wheel on the invention comprising a chain and sprocket arrangement; Figures 6 and 7 are end elevational views of an embodiment of a paddle wheel on the invention comprising a geared arrangement; Figures 8 and 9 are side elevational views of an embodiment of a hydroelectric generator according to the invention; Figure 10 is a side elevational view of an axial turbine array or the prior art.

Figures 11 and 12 are graphs of drag force and torque on a single blade of a paddle wheel of the invention; and Figures 13-15 are graphs of individual blade torque, total torque and total rotor power of a paddle wheel of the invention comprising four blades.

Description of Preferred Embodiments

Figure 1 illustrates, in schematic perspective view, a paddle wheel of the present invention, generally indicated by 1. The wheel comprises a hub 2 connected by means of a rotatable spindle 3 to a support member 4. Attached to the support member 4 by means of bearings 5 are two blades 6, each having a generally rectangular box form. The blades 6 are able to rotate relative to the support member 4 by means of the bearings 5. In this embodiment, the support member 4 is illustrated in the form of a disc, or wheel, but in any embodiment could equally be configured in another form in order to support the blades in a spaced-out configuration disposed around the axis of the spindle 3. For example, a cross-shaped member would serve the same function. In this configuration, two such blades are illustrated, for clarity, but in preferred embodiments to be described below, more blades may be provided. In the configuration illustrated in Figure 1, the axis of the bearings 5 is aligned lengthwise along the blades 6 which extend generally perpendicularly from the face of the support member 4. The bearings 5 are attached to the blade 6 near to the top (in use) edge of the blades, thereby causing the blades to hang in a generally vertical configuration with respect to the face 7 of the blade 6.

In use, the paddle 1 would be partially submerged in flowing water such that a blade in its lowermost configuration on the support member 4 would be immersed, or at least partially immersed, in the flowing water such that the water moves towards the blade face 7. In this way, motive force from the water is transferred into rotational movement of the support member 4 with the face 7 of the blade 6 remaining approximately perpendicular to the water flow. In this way, energy transfer between the flowing water and the blades is enhanced by contrast to e.g. solidly mounted and radially oriented blades as encountered on traditional paddle wheels. In the configuration shown in Figure 1, a small displacement of the face of the blade from a vertical position is inevitable when immersed in flowing water, but weighting of the blade will ensure that such deflection is minimal.

Figures 2-3 illustrate an alternative embodiment of a paddle wheel of the present invention comprising a further mechanism to maintain the faces of the blades in a general vertical orientation, in use. Figures 2 and 3 illustrate an end elevation and partial side view respectively of a blade 6 incorporated into a paddle wheel of the present invention.

In this embodiment, the blade 6 is rotationally mounted to a support member (not illustrated) again by means of a bearing 5. Located towards the lower edge (in use) of the blade 6 is a projecting lug 8 extending from the edge of the blade 6 and towards the supporting member. A cam 9 in the form of a circular arc is provided just above the projecting lug 8 mounted on the blade. The cam 9 is shown in cross-sectional view in Figure 3.

Figure 4 shows an end elevational view of part of a paddle wheel of the present invention, employing the blade and cam configuration illustrated in Figures 2-3. In this embodiment, four blades 6 are rotationally mounted by means of bearings 5 on a support member 4, the support member is rotationally attached to a hub (not illustrated). Figure 4 illustrates the positioning of the cam 9 that is mounted independently of the support member 4 -it may, for example, be attached to the hub.

In use, the paddle wheel may be partially submerged into flowing water. A typical water level b appropriate for the paddle is illustrated in Figure 4 by means of lines 10. As the flowing water impacts on the face 7 of a submerged blade (e.g. for water flowing from right to left as illustrated in Figure 4), the force of the water on the blade 6 causes the support member to rotate in a clockwise fashion. The blades 6 are generally free to pivot about the bearings 5 attached to the support member, but as the support member 4 rotates, a projecting lug 8 of the blade 6 comes into engagement with the cam 9 whilst the blade is partially submerged under the flowing water. Interaction between the lugs 8 and the cam 9 resists rotation of the blades 6 from their at-rest vertical orientation whilst submerged.

In preferred embodiments, therefore, the lug may comprise a wheel or a roller, to reduce frictional forces between the lug and the cam, although in some satiations, a low-friction contact surface may be employed. As the support member 4 rotates further, the lug 8 of the partially submerged blade 6 disengages from the cam 9 as the blade rises from the water.

Figure 5 illustrates, schematically, a further embodiment of the invention that maintains the blades 6 of the paddle in a substantially vertical orientation in the face of the rotation of the support member 4 to which they are attached. In this embodiment, a central, fixed sprocket 11 is provided centrally in a fixed position, i.e. not rotating with the support member (not illustrated for clarity). Disposed around the support member 4, are the blades 6, each of which is fixed to a peripheral sprocket 12, each of which blade and peripheral sprocket assemblies are rotatably mounted to the support member. The central sprocket 11 comprises a number of parallel-disposed like sprockets (one for each blade), each one of which central sprockets is connected to a corresponding peripheral sprocket 12 by a chain 13. In Figure 5, only two of such chains 13 are illustrated, for clarity. It can be seen that as the assembly of blades 6 rotate about the central axis of the support member, the sprocket and chain arrangements serve to keep the blades 6 at a constant orientation. It will be appreciated that such a sprocket and chain assembly may be readily replaced by a correspondingly functional arrangement, such as the use of a toothed belt and notched wheel. Also illustrated in Figure 5, is a typical water level 10 in which such a paddle wheel might be immersed.

Figures 6 and 7 illustrate a further embodiment of a paddle wheel of the present invention using an alternative mechanism to ensure that the paddle blades 6 maintain a constant orientation in the face of rotation of the support member.

In this embodiment, a central, static gear 14 is provided, arranged to maintain its orientation, and not rotate with the rotation of the support member. Each of the blades 6 of the paddle wheel is fixed to a peripheral gear 15 with each such blade-gear assembly being rotatably mounted to the supporting member 4. Intermediate gears 16 operably connect the central gear 14 to the peripheral gears 15, forming a gear train. It will be appreciated that an odd number of intermediate gears 16 is provided in between the central gear 14 and the peripheral gears 15 in order to produce the desired effect.

Figure 7 illustrates the arrangement of Figure 6 following rotation of the support member 4. It can be seen that as the support member 4 rotates, the action of the gear trains serve to maintain the blade 6 in a generally vertical orientation.

Figure 8 illustrates, schematically, an elevational view of a hydroelectric generator comprising a paddle wheel according to corresponding aspects the present invention. The hydroelectric generator, generally indicated by 17, comprises blades 6 rotatably mounted on a support member 4 at each end of the blade, thereby providing significantly improved stability of the blade assembly. The provision of support members at each end of the blades is a preferred configuration for any paddle wheels of the invention. The supporting members are themselves rotatably mounted to hubs 2, again at each end of the blade assembly. For clarity, the paddle wheel of Figure 8 is illustrated having just two blades, and any mechanism for maintaining the orientation of the blades is omitted, again for clarity. The central spindle 3 of the paddle wheel is operably coupled to an electrical generator 18 for the generation of electrical power via a suitable gear box. It is to be expected that, with variable rotational rates of the paddle wheel, an alternating current of varying frequency will be reduced by such a generator. In order to conveniently pass this into an alternating current (AC) grid system, a pair of back-to-back inverters may be employed to produce a stable frequency power source.

In this embodiment, each of the hubs 2 is mounted for vertical movement to an anchoring, comprising a substantially vertical post 19. Each post may then be anchored into e.g. the seabed 20 to provide a stable support.

The paddle wheel assembly may be moved up and down the anchoring posts 19 in order to maintain an optimal submersion of a lower blade 6 under the water level 10 in the face of rising and falling tides.

Movement of the paddle assembly up and down the supporting posts 19 may be carried out by means of a suitable linear actuator coupled to a level measuring device to measure the level of the sea 10.

In the particularly preferred embodiment of Figure 8, the paddle, supporting wheel and hub assembly is constructed to be buoyant such that the whole assembly floats at the correct level with respect to sea level 10. This may be effected by constructing the blades 2 of the paddle to be hollow, or filled with a closed cell foam, thereby giving the desired density characteristics. Other parts of the assembly such as the supporting members and hubs may be of a similar buoyant construction. In this way, the whole paddle wheel assembly may be mounted for vertical sliding movement with respect to the anchor posts 19, and will move up and down the posts in the face of changing water level 10 in a largely automatic fashion.

Figure 9 illustrates, schematically, a hydroelectric generator of the present invention for comparison with an axial turbine hydroelectric generator as illustrated schematically in Figure 10. Figure 9 illustrates a hydroelectric generator substantially the same as illustrated in Figure 8, and labelled accordingly. The Figure omits the generator 18 for sake of clarity.

Figure 10 illustrates, in schematic elevational view, an array of four axial turbines located beneath the water surface 10 and above the seabed 20 of a tidal flow. It can be seen that, in order to increase the area over which energy is captured, in the turbine case of Figure 10, multiple axial turbines must be provided to prevent them breaking through the surface of the water flow. The consequence of this is that the cost of the installation rises for each additional width of tidal flow to be captured. By contrast, with the hydroelectric generator of Figure 9, energy from an increasing width of water flow may be captured simply by extending the length of the blades 6 of the paddle wheel.

Figures 11 and 12 illustrate the drag force and torque respectively on a single blade 6 of a paddle wheel of the present invention with respect to rotor angle (i.e. rotational position of the support member 4). It can be seen that, in this example, four rotor angles between 0 and approximately 90 and approximately 270 and 360 degrees the blade is submersed or partially submersed in the flowing water and a drag force is evident on the blade. For angles between this range, the blade is out of the water and therefore experiences no drag force.

Figure 12 illustrates the corresponding torque curve for a single blade.

By mounting multiple blades on a support member, each offset from its neighbour by an angular displacement, the torque profile with respect to rotor angle for each blade is offset, as illustrated by the graph of Figure 13. Figure 14 illustrates the sum of the torque of each blade showing how the overall torque on the central shaft is smoothed out. Figure 15 is a graph of the corresponding rotor power as a function of rotor angle for a four blade paddle wheel assembly. The inventor has found that the provision of four blades provides an optimal compromise between power smoothing and energy capture.

In Figures 11-15, the numerical scales (apart from the angular displacement scale) are for illustrative example purposes only.

Claims

CLAIMS1. A paddle wheel comprising: ahub; a support member, mounted for rotation with respect to said hub about a generally horizontal (in use) axis; a blade, extending substantially perpendicularly from said support member, and mounted for rotation thereto about a generally horizontal (in use) axis.
2. A paddle wheel according to claim 1 wherein said blade is weighted and mounted such that a face of the blade assumes a generally vertical orientation at rest.
3. A paddle wheel according to claim 1 wherein rotation of the support member with respect to the hub is coupled to rotation of the blade with respect to the support member such that as the support member rotates with respect to the hub, the blade rotates with respect to the support member in an opposite direction, thereby maintaining the orientation of the blade with respect to the hub.
4. A paddle wheel according to claim 3 wherein rotational coupling is effected by means of a chain and sprocket arrangement.
5. A paddle wheel according to claim 3 wherein rotational coupling is effected by means of intermeshing gears.
6. A paddle wheel according to any preceding claim comprising a plurality of such blades.
7. A paddle wheel according to claim 6 comprising three or more blades.
8. A paddle wheel according to claim 6 comprising four blades.
9. A paddle wheel according to any preceding claim wherein blades are provided with a substantially flat face.
10. A paddle wheel according to any preceding claim comprising a hub and support member at each end of said blade(s).
11. A paddle wheel according to any preceding claim constructed so as to float in water.
12. A paddle wheel according to any preceding claim mounted for vertical movement to an anchoring.
13. A paddle wheel according to claim 12 wherein said anchoring comprises a substantially vertical post.
14. A paddle wheel according to claim 13 wherein said wheel is mounted for vertical sliding movement with respect to said post.
15. A paddle wheel substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.
16. A hydroelectric generator comprising a paddle wheel according to any preceding claim operably coupled to a generator.
17. A hydroelectric generator substantially as described herein, with reference to and as illustrated by any appropriate combination of the accompanying drawings.