GB2503089A

GB2503089A - Device for recovering kinetic energy from a flowing fluid, eg from tidal or river currents

Info

Publication number: GB2503089A
Application number: GB1307159.2A
Authority: GB
Inventors: Hugh Malcolm Ian Bell
Original assignee: Individual
Current assignee: Individual
Priority date: 2012-04-19
Filing date: 2013-04-19
Publication date: 2013-12-18
Anticipated expiration: 2033-04-19
Also published as: GB201307159D0; GB2503089B; GB201206842D0

Abstract

A device for recovering kinetic energy, eg from tidal or river currents or from wind, comprises a rotatable frame 1 supporting hydrofoils or aerofoils. The foils have a leading edge and a trailing edge and are arranged to maintain their leading edge/ trailing edge orientation with respect to a direction of fluid flow and to change their profiles twice per rotation of the frame. The forces generated as fluid passes over the foils act on the frame to cause it to rotate. The foils can be oriented through gearing, each foil being rotated about an axis A. Alternatively, the profile of a foil 50 may be adjusted by inflating a membrane 55 surrounding a central plate 51, 52; by transferring fluid from one side of the central plate to the other the foil changes shape at the top and at the bottom of each rotational cycle. In a modification the profile is changed by a series of parallel semi-cylindrical tubes rotated in unison inside the membrane 55. The device may be fully submerged.

Description

Improvements In or Relating to Kinetic Energy Recovery

FIELD OF THE INVENTION

The present invention relates to kinetic energy schemes for recovering energy from natural resources and in particular, but not necessarily restricted thereto, relates to a scheme for converting the energy of tidal and river currents into electrical energy and, more particularly, the present invention can relate to a submerged device for recovering kinetic energy from a river or tidal current. The present invention can also comprise a device for recovering kinetic energy from a wind.

BACKGROUND OF THE INVENTION

To harness a small fraction of the energy of tides and currents from waterways and convert it into electricity, many innovative methods have been conceived. When compared with wind energy and solar energy power systems a fundamental problem is that of a total lack of predictability; to date such power supplies only augment the "ordinary" coal fired, oil fired and nuclear power stations. In contrast, tidal systems operate during four distinct periods of flow every day, associated with each tidal phase, each period being followed by an ebb period, when the tidal flow changes direction, there is no effective tidal flow. Whilst the ebb periods of tidal systems may cause local troughs in output of electrical energy, a number of tidal power stations acting in tandem across a region could ameliorate such troughs in supply; river current flow may also be employed to assist in such hydro-electric schemes.

Whilst it is well known that tidal currents can indeed be used to reliably generate electrical energy, the cost of generation can be prohibitively expensive, the initial capital cost of the structure and the manoeuvring of the structure to a desired location where it can remain, relatively maintenance free in extreme conditions; tidal currents, sea swell, low temperature, marine growth and the like all contribute to conditions where reliability must be high and ease of conducting even minimal maintenance must be good.

The net energy in a tidal stream can be very large. When a tidal stream is restricted, for example, between two land masses, the flow velocity can be increased considerably, condensing the net energy through the constricting points of land. To extract a significant amount of energy from this relatively slow moving body of water, a large cross-section of the tidal stream needs to be harnessed. In addition to tidal currents, prevailing sea and ocean currents also exist.

Known systems for deriving kinetic energy and/or producing electrical energy from river and ocean currents and tidal flows have been shown to be expensive to manufacture, install and maintain. Typical systems have employed turbines of the propeller type.

Simply put, known systems are uneconomic because the cost of producing kinetic energy I electrical energy from such systems since the market price for electricity is insufficient to cover the set-up and maintenance costs relative to other well established technologies or subsidised technologies.

Current systems under development employ turbines coupled to high-torque reduction gearboxes. Existing turbines, however, by the nature of their configuration are typically limited as to the depth of water they can operate by the rotor diameter. A turbine is most efficient at a specific water speed. If the velocity changes, the efficiency falls dramatically.

Such systems are mounted upon piles driven into the seabed or attached to templates similarly placed upon the seabed or river bed at great cost in terms of equipment and procedure. As can be realised, installation and maintenance is a major cost because the systems are situated in relatively deep water, as they require a homogeneous flow of water. Whilst there are many offshore paces suitable, access can be difficult and expensive, whilst transfer & transmission of energy / transmission of electricity can be expensive. It will also be appreciated that suitable sites will be necessarily subject to high water currents -it is to be borne in mind that energy to be derived from any wind or water flow is proportional to the cube of the velocity of the respective fluid. High currents are to be found in and around the many islands and inlets about the coast of the United Kingdom.

OBJECT TO THE INVENTION

The present invention seeks to provide an improved scheme for recovering energy form natural resources such as tidal currents and the wind. In particular the present invention seeks to provide a new configuration of turbine with improved efficiency, which can be fully submerged.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the invention, there is provided a device for recovering kinetic energy from a flowing fluid, wherein the device comprises a frame mounted about an axis for rotation and the frame having foils mounted thereon, the foils having a leading edge and a trailing edge, the foils being arranged to maintain their leading edge -trailing edge orientation with respect to a direction of fluid flow and to change their profiles twice per rotation of the frame; wherein, in use and when placed within a flowing fluid, fluid passing over the foils cause the foils to generate forces which act upon the frame to cause the frame to rotate about the axis.

In use, the profile of the foil switches about the hydrofoil axis for each foil at the top of the rotation cycle and again at the bottom of the rotation cycle, whereby to effect rotation. That is to say, the foil profiles are arranged so as to change their profile every half revolution as the foils are at the limit of perpendicular motion with respect to the direction of fluid flow. The foils, to maintain their leading edge -trailing edge orientation with respect to a direction of fluid flow must be mounted for continuous rotational movement with respect to the frame, as the Frame rotates.

The foil profiles can be caused to change by one of a means of mechanical, hydraulic or under electronic or electrical control. The foil profiles can be caused to move individually or in diametrically opposed pairs about the frame. Where the fluid is water, the foil is a hydrofoil; where the fluid is air the foil is an aerofoil. Where the fluid is water, the foil profile can be changed by use of water acting as a hydraulic profile actuator. By appropriately varying the profile it may be capable of rotating in both directions. In one alternative, an elongate cam system of parallel-spaced apart cylindrical cams can be employed.

The fluid can be water and the device can be mounted to a bed of a watercourse within which the device is situated. The device can be attached via piling or to a template which is attached to the bed of the watercourse. The device could be tethered above a bed of a watercourse within which the device is situated.

The outputs of a number of separate devices can be connected by several methods to drive a single power-take-off unit, such as an electrical generator. The kinetic energy could be transferred by means of a rotatable shaft, a flexible rotatable arrangement, a belt drive, a chain and sprocket arrangement or a hydraulic arrangement.

Preferably, when the arrangement is attached to a sea-bed or to a rock base, for example, the arrangement is rotatable in azimuth, whereby optimum current flow through the device can be achieved, in the event the azimuthal direction of fluid flow changes.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, reference will now be made, by way of example only, to the Figures as shown in the accompanying drawing sheets, wherein:-Figure 1 shows a plan view of an installation in accordance with the invention; Figure 2 shows a partial cross-sectional view of the installation shown in Figure 1; Figure 3 shows first and second oppositely directed paddles in accordance with the invention; Figure 4 is a show the two profiles of a foil in accordance with one aspect of the invention; Figure Sa & Sb show two configurations of a foil; Figure 6a shows a hydraulic fluid flow arrangement in plan; Figure 6b shows a hydraulic fluid flow manifold (as seen in profile in Figure 6a) in plan view; and, Figures 7a & 7b show a foil wherein the foil is defined by a parallel arrangement of cam profiles.

DETAILED DESCRIPTION OF THE INVENTION

In order to provide a better understanding of the present invention an embodiment of the invention will now be described. lit will be apparent, however, to one skilled in the art, that the present invention may be practised without these specific details. This should not be construed to limit the present invention, but should be viewed merely as an example of a specific way in which the invention can be implemented. Well known features have not been described in detail so as not to obscure the present invention.

Referring now to Figure 1, there is shown a frame 1 which is mounted for rotation upon an axle 3. Conveniently, the axis of rotation is horizontal, whereby supports for rotation can be placed upon a frame based upon the land/sea-bed, with the frame conveniently comprising two supports, providing support for rotation of the frame. The frame 1 supports paddles or hydrofoils which can be driven by movement of a fluid through the frame, perpendicular to an axis defined by the axle 3. By means of the axle, kinetic energy can be transferred to an energy converter, for example an electrical generator 2.

Figure 2 shows a frame 1 in accordance with the invention which supports eight hydrofoil paddles (hydrofoils) about a central axis; arms extending from the hub 12 allow a rotation of the hydrofoils as the frame rotates about its axis. The direction of rotation is anti-clockwise, as indicated by arrow 11. It will be appreciated that there are eight hydrofoils for illustrative purposes and fewer or more hydrofoils could be situated upon the frame. A limit on the spacing will be determined by the need for the hydrofoils to rotate about their axes 8, without hitting any adjacent hydrofoils.

In this first embodiment, a fluid, such as water, flowing through the frame in a direction indicated by arrows 4, will impinge upon the hydrofoils 20 and cause the frame 1 to rotate about its hub 12 by the forces that act upon the hydrofoil surfaces -using the principles of lift as known from aircraft wings for example. Referring in particular to Figure 3, two hydrofoils 9 and 10 are shown. Hydrofoil 9 is representative of the hydrofoils to the right of the hub and the bottom-most hydrofoil of Figure 2; Hydrofoil 10 is representative of the hydrofoils to the left of the hub 12 and the top-most hydrofoil of Figure 2. As the current flows in direction 4 over hydrofoil 9, a force acts upon the lower side of the hydrofoil surface (with respect to Figure 3) and is indicated by arrow 6. Similarly, as the current flows in direction 4 over hydrofoil 10, a force acts upon the upper side of the hydrofoil surface (with respect to Figure 3) and is indicated by arrow 7. As can be seen with reference to Figure 2, arrows 7 act from the hydrofoils to the left of the hub 12 and from the top-most hydrofoil onto the frame 1 and arrows 8 act from the hydrofoils to the right of the hub 12 and from the upper-most hydrofoil onto the frame 1. The resultant forces acting through the axles 8 cause the frame 1 to rotate, as indicated by arrow 11. Flow of a fluid over the hydrofoils will cause a negative force on one side of the hydrofoil and a positive force to act on the other side, in a similar fashion to the manner of aerofoils in a wind. If the direction of flow was from the right hand side, then the hydrofoils would need to be oriented oppositely to that shown and the direction of rotation would be clockwise, in a direction opposite to that indicated by arrow 11. Figure 4 shows how a single foil 15 can adopt separate profiles, 13, 14. A stop will be provided to prevent, if necessary, the foil interfering with other foils etc..

It will be realised that the foils can be oriented in a number of ways through gearing and the like so that a leading edge of the foil is presented forwardmost to the fluid flow, the foil being rotated about an axis A (see Figure Sa). Equally, the means by which the profile of the hydrofoil is changed can be numerous, as will be realised by those skilled in the art.

For example, a medium can be introduced into a membrane forcing the surface of the hydrofoil on either side of the hydrofoil to adjust its profile and the shape can be controlled by stiffening in that membrane.

Specifically, with reference to Figures Sa and Sb a foil 50 is shown with first and second profiles, respectively. In each case, the foil 50 comprises a central two-ply planar member having an upper ply 51 comprising a first honey-combed panel or perforated (on one side -the fluid not being passed to the other layer of the basic two-ply structure) or corrugated with apertures on its outside surface which has an inlet feed 53 and an outlet feed 54 with respect to a hydraulic source and drain (not shown).

When hydraulic fluid is allowed to enter the feed 53, then the hydraulic fluid enables the hydraulic fluid-filled honeycomb I perforated /corrugated and apertured structure to flow outside of the panel 51 (but not to the other, lower ply 52, with respect to which the panel 51 is fluid-tight), which fluid inflates a diaphragm member 55, which when inflated defines a foil which causes lift in a first direction with respect to a perpendicular flow of fluid which passes over the foil. The diaphragm member is conveniently of a formed plastics skin which inflates to a predetermined form, conveniently optimal for a particular set of flow velocities, the plastic membrane of the diaphragm having different degrees of elasticity to create the desired profile required under pressure. It will be appreciated that each diaphragm will be sealed at the edges of the foil.

When the foil reaches the end of its movement in a first direction perpendicular to the fluid flow over the foil, as the frame rotates, then the hydraulic fluid is emptied via outlet 54. Simultaneously, the foil then seeks to adopt the reverse profile, so that the "lift" or forces arising from the foil are generated is in an opposite direction, to cause the frame to continue its rotation. As will be appreciated in so doing, then the lower ply -also of a general honeycomb material I perorated I corrugated and apertured material fills with hydraulic fluid and causes the diaphragm member associated with the lower ply 52 to fill and adopt a profile reverse to the profile associated with the upper ply member 51, as shown in Figure Sa. Thus by alternatively transferring fluid from one side of the central plate to the other, the hydrofoil shape is changed at the top and at the bottom of each rotational cycle. It will be appreciated that a number of techniques can be adopted, using different technologies to achieve the same result. In a simplistic embodiment, the leading edge 56 may have a member which alternates between two positions and can move a membrane between two positions, whereby to provide first and second profiles per Figure 3.

Referring now to Figure 6a, there is show one system where fluid can be pumped to enable the foil profile to be achieved. The hydraulic fluid, in a marine or water-based environment may, conveniently, be the water in which the foils rotate. Equally, the hydraulic fluid may be a closed system relative to the fluid which drives the foils and frame. The hydraulic fluid may be pumped through the force of the water flowing, for example a rotation of the frame drives a pump; in the alternative a separate hydraulic pump, for example electrically powered hydraulic pump, may be provided. Figure 6a shows a pump 61 which drives fluid output along pipe 64 towards a manifold switching arrangement 62, wherein there are provided arcuate channels, to enable fluid flow -in this case channel 611 connects with channel 68 in the second part of the manifold switching arrangement 63, leading (through conduit not shown, for clarity of diagram) to a first one way-valve 66 towards a first inlet 6T associated with one foil, with a suction port 6B associated with the same foil for drainage purposes; in suction mode, the port 6B connects with channel 69 (again the conduit is not shown, for clarity) and via channel 612 and pipe returns to the pump 61. Other lines associated with other foils are similarly connected, but not shown for clarity: e.g. a first alternative inlet 6T' associated with a second foil, receives fluid from the pump 61, via channels 613, 610; the same foil, having a suction port 6B' in drainage or suction mode, connects with channel 615 and via channel 614 and pipe 65 returns to the pump 61 (noting that the pipe from channel 614 to pipe 65 is not shown for purposes of clarity). Switching manifold 63 rotates about axis A with respect to switching manifold component 62; the arcuate channels determining the filling characteristics (duration of operation over a cycle). It will be appreciated that there are many variations possible; the inlet orifice of one diaphragm associated with a foil could act as a suction orifice when the opposite diaphragm of the same foil is being pumped. It will be appreciated that the method utilised to maintain the angle of the foil with respect to the flow of fluid is the same for all the foils and could be enabled by pulleys, chains, gearing, hydraulics or chains, to name just some of the most readily available techniques. Figure 6b shows how the arcuate channels 611 -614 could be arranged for one configuration; again the skilled man will realise how to alter the length and spacing of arcuate channels for a particular configuration.

The fluid can be conveyed from one side of a divide in the hydrofoil.

Mechanical devices can change the profile of the hydrofoils not described here. A hydraulic system can be employed with a fluid pipe from the axles and metered through rotary valves, whereby to cause the alternative stiffening membranes to be actuated. The fluid could pass through a pipe separate to or integral with the frame 1.

In accordance with another embodiment, a reversal of the hydrofoil profile can be effected about the axis of the foil and that would use a series of tubes of a cylindrical section running parallel to the leading edge of the hydrofoil. Each tube would act as a cam being flat on one side and round on the other. The tubes could be solid cylindrical sections. Each successive cam would reduce in diameter from the leading edge of the foil and they would all rotate in unison being linked together, preferably by gears. As each foil reached the top and bottom positions the cam could be rotated using a mechanical device reacting with the structure of the wheel. This would cause the profile to switch from one side of the foil axis to the other. Specifically, with reference to Figures 7a and 7b, there is shown a further variant 70, wherein a number of elongate, parallel-spaced apart cams 71, 72, 73 and 74 are arranged upon a support 75 for rotation of 180° about axes 78 (or 1800 pivot between a first position and a second position). The cam lobes bear upon an associated plastics stretch cover 55, which is attached at a leading edge 76 and a trailing edge 77 of the support 75; the flats of the cams define the reverse side of the foil.

Figure 7b shows the cams per Figure 7a following a partial rotation of 1800 (or pivot through the same angle). The skilled man will be knowledgeable of many systems which can enable the cams to operate; a gear system, drive rod, hydraulic control etc. It is important to mention that the variation of the profile of the hydrofoil is not only restricted to its physical shape, but also its attitude to the impinging fluid flow. It would also be possible to restrict power generation by variation of the profile, which could be important in a vertically oriented set of foils.

The structure 1 can be suitably mounted in a number of different fashions within the current, by means of a physical support, by tethers, not shown.

The arrangement may allow for orientation of the structure, where the current is likely to come from different directions. In a non-tidal river, the direction of flow will be the same and no variable orientation would be necessary, but it will be appreciated that in certain areas, sea currents will vary, dependent upon the tide and upon the time of year.

Figure 1 shows how a rotatable single frame is connected to an electrical generator. Conveniently, the generator may be remotely mounted above water, whereby to enable service tasks to be determined simply and easily. In an arrangement of kinetic recovery devices, the devices may be arranged in a row; alternatively, they may be arranged in two rows, the second row being offset/displaced relative to the first row, whereby to maximise the use of the current, the second row generators being positioned to take advantage of currents flowing in-between the first row of generators. Other arrangements are possible.

Claims

CLAIMS1. A device for recovering kinetic energy from a flowing fluid, wherein the device comprises a frame mounted about an axis for rotation and the frame having foils mounted thereon, the foils having a leading edge and a trailing edge, the foils being arranged to maintain their leading edge -trailing edge orientation with respect to a direction of fluid flow and to change their profiles twice per rotation of the frame; wherein, in use and when placed within a flowing fluid, fluid passing over the foils cause the foils to generate forces which act upon the frame to cause the frame to rotate about the axis.
2. A device according to claim 1, wherein the foil profiles are caused to change by means of mechanical control.
3. A device according to claim 1, wherein the foil profiles are caused to change by means of hydraulic control.
4. A device according to claim 1, wherein the foil profiles are caused to change by means of electronic or electrical control.
5. A device according to any one of claims 1 -4, wherein the foil profiles are caused to move individually or in pairs.
6. A device according to any one of claims 1 -5, wherein the kinetic energy drives an electrical generator.
7. A device according to any one of claims 1 -5, wherein the kinetic energy is transferred by means of a rotatable shaft, a flexible rotatable arrangement, a belt drive, a chain and sprocket arrangement or a hydraulic arrangement.
8. A device according to any one of claims 1 -7, wherein the fluid is water and the foil is a hydrofoil.
9. A device according to any one of claims 1 -5, wherein the fluid is air the foil is an aerofoil.
10. A device according to any one of claims 1 -7, wherein the fluid is water and the device is mounted to a bed of a watercourse within which the device is situated.
11. A device according to any one of claims 1 -7, wherein the fluid is water and the device is tethered above a bed of a watercourse within which the device is situated.
12. A plurality of devices according to any one of claims 1 -11, wherein the outputs of the separate devices are connected to drive one or more power-take-off units, such as an electrical generator.14. An arrangement according to claim 10, wherein the device is attached via piling to the bed of the watercourse.15. An arrangement according to claim 10, wherein the device is attached to a template which is attached to the bed of the watercourse.16. An apparatus substantially as described herein, with reference to any one or more of the accompanying Figures.17. The use of any one or more of the above configurations to generate electricity, with reference to any one or more of the accompanying Figures.