WO2010004286A1

WO2010004286A1 - Water turbine

Info

Publication number: WO2010004286A1
Application number: PCT/GB2009/001710
Authority: WO
Inventors: James Mowat
Original assignee: Mowat Technical & Design Services Ltd
Priority date: 2008-07-09
Filing date: 2009-07-09
Publication date: 2010-01-14
Also published as: BRPI0915880A2; CL2011000033A1; US20110142625A1; GB0812524D0; CA2730266A1; EP2310669A1

Abstract

A turbine for use in extracting energy from within a water flow comprises: an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first, driving, configuration when moving with the direction of water flow, to a second, return, configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration.

Description

Water Turbine

The present invention relates to the provision of a water powered turbine for extracting energy from flowing water.

A very large number of water-powered devices have been proposed to provide power, for example in the form of electricity, from flowing water. However, devices that are successful in meeting the requirements of acceptable convenience in use, cost, robustness and efficiency of energy conversion can be difficult to provide.

It is an object of the present invention to provide a water-powered turbine that avoids or minimises at least one of the aforementioned disadvantages of known devices.

According to a first aspect the present invention provides a turbine for use in extracting energy from within a water flow comprising: an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first, driving, configuration when moving with the direction of water flow, to a second, return, configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration. In use the turbine may rotate as a consequence of a greater force of water flow acting on the turbine blade when in the said driving condition.

The turbine blades may rotate about an axis substantially normal to the water flow. Rotation may be by turbine blades fitted to a shaft rotating in suitable bearings. The rotating movement of the shaft may be converted into usable power by any suitable means. For example, the rotating shaft may drive a gearbox to provide power to a device such as a pump or electrical generator. Alternatively the turbine blades may be fitted to a central hub, which rotates about a fixed shaft passing there through. In this case rotational motion of the hub can be converted into useable power.

Whilst an array of turbine blades directly connected to a central shaft or a central hub can operate satisfactorily it has been found advantageous to provide a turbine where the blades of the array are spaced radially outwardly from the centre of rotation of the turbine in order to provide a central space, radially inward of the turbine blades. This central space allows through flow of water. The central space may be free of any components for maximum flow through, or may have a component such as the main shaft for the rotation of the turbine passing through it.

Tests have shown that in some configurations of the invention providing a central space can reduce the drag on the turbine by 15% or more, thus providing a significant gain in efficiency. Furthermore the flow through the central space can be advantageous when the turbine blades, or cover flaps fitted to the turbine blades, are formed and arranged to extract energy from the water when on the return as described hereafter.

In operation water may flow through the central space.

The turbine blades may be arranged so that in operation water contacts at least one of the turbine blades after flowing through the central space. Said at least one turbine blade may be arranged to generate lift from contact with water that has flowed through the central space.

An array of turbine blades can be provided with a central space by various means. For example the blades may be mounted on a plate, which is itself mounted on a central shaft. The plate rotates about the turbine axis by the action of water flow on the turbine blade array. The turbine blades may be mounted on the plate radially outward of the centre leaving a central space. With such an arrangement the blades may generally be mounted normal to the plate .

In some arrangements there may be a first set of circumferentially spaced turbine blades each mounted at the same radially outward distance from the centre. There may also be a second or even more sets of blades mounted radially outwardly of the first.

In some arrangements it is convenient to mount the blades of the array between two parallel opposed plates, spaced apart on the turbine axis .

The turbine blades may be adjustable in various ways. For example the turbine blades may be adjustable in angle by being rotatable about their join to the centre of the turbine, where they are directly joined to a central shaft or hub. In use an adjustable blade may be rotated to a first configuration where the blade presents its full face to the water flow (i.e. the blade surface is in alignment with the axis of rotation) so as to be driven with the flow. On the return, when the blade is rotating against the water flow the blade may be rotated to present a much reduced surface area to the direction of the flow, in a manner akin to feathering an oar. By reducing the angle of attack of the turbine blade in this way the force of the flow on the returning blade is reduced and the drag of the blade through the water is also reduced. The turbine is thus powered by the water flow acting on the blade when in the first driving configuration.

Alternatively the turbine blade may be adjustable in other ways. For example, the blade may be provided with one or more flap portions, which move to increase or decrease the surface area of the turbine blade presented to the direction of water flow when moving from the driving configuration to the return configuration.

Preferably the said at least one turbine blade is provided with at least one aperture therethrough, said aperture having at least one cover flap movable from a first closed position where water flow through the aperture is restricted to a second open position where water flows more freely through the said aperture. For such a turbine blade the first, driving configuration is when the cover flap or flaps are closed and the second, return configuration is when the cover flap or flaps are in their open positions.

The water flow that can be used to drive the turbine may be of any suitable form, for example river current, tidal movement or ocean current. The turbines of the invention can therefore find use in a wide range of locations and applications. For example turbines may be placed in rivers making use of the normal flow or a tidal flow to provide power for any purpose. Conveniently the turbines be used to extract additional energy from the watercourse below a hydroelectric dam. In an ocean use can be made of tidal flows or currents to provide power for onshore uses offshore uses, for example to power desalination plant or provide power on an oilrig. The turbines may be fitted beneath a vessel and used, for example when the vessel is at anchor, to produce power from water flow for battery recharge .

In use the turbine of the invention may rotate about an axis that is substantially normal to the direction of water flow i.e. for half of its rotation each turbine blade moves with the direction of flow and for the other half it moves against the direction of flow. In order to provide rotation with the maximum extraction of energy, when fitted, the cover flaps of a turbine blade should be in their first

(closed) positions during the part of a rotation that is with the direction of water flow and in their second positions or some intermediate open position when the blade is rotating against the direction of water flow ( 'on the return' ) . This arrangement allows maximum interaction between the turbine blade and the water flow when the flow is pushing the turbine blade. The turbine blade, with covered apertures presents a maximum surface area to the flow.

Conversely, the apertures may be open (not covered by the closed cover flaps) when the blade is moving against the flow, minimising the forces acting against the desired rotation of the turbine i.e. the water flow can pass through the apertures of a turbine blade when it is rotating against the flow.

The turbine blades may be of any shape or form suitable for interacting with a water flow. Preferably the principal plane of the turbine blade (i.e. the blade face) is substantially aligned with the axis of rotation of the turbine, i.e. the turbine blade projects radially outwardly from the axis of rotation, when in the driving configuration. This means that the turbine blades present their full face to the direction of water flow during rotation, when in the driving configuration.

If desired the turbine blades may be adjustable in angle as well as having apertures and cover flaps. For example when directly joined to a central hub or shaft the turbine blades may be rotatable about their join to the centre of the turbine. This has the effect of reducing the interaction with the water flow and reducing the power extracted. Such an arrangement can be advantageous where the water flow may become excessive, potentially leading to damage to the turbine or associated energy extraction/conversion equipment. Alternatively adjustable turbine blades may be used as a means to control the power output.

The array of turbine blades may comprise any number of blades. An array of from three to nine blades distributed circumferentially around the turbine axis is preferred. An array with several turbine blades has the advantage that it provides a smoother transfer of energy from the water flow to the turbine. An odd number of blades, for example an odd number of blades distributed circumferentially and equidistantly about the turbine axis, may be most preferred. Where the turbine blades are provided with apertures and cover flaps, preferably all the turbine blades are provided with at least one aperture and corresponding cover plate (s) . Advantageously each turbine blade has a substantial portion of its surface area formed as an aperture or a plurality of apertures, which can be covered by corresponding cover flaps.

Advantageously the cover flaps may cover the apertures completely when in the first position so that no water can flow through the apertures. This means that when the cover flaps are in their first positions the turbine blade can present a continuous surface to the forces of water flow.

The turbine blades may be adjustable from the first to the second configuration. Movement of the blades, flap portions or cover flaps, where fitted may be by any means. For example, by means of hydraulic or electric motors.

Where fitted cover flaps are moveable from the first closed position to the second open position. Movement of the cover flaps covers (or partially covers) an aperture and then uncovers it. Powering the cover flaps by motor allows complete control of cover flap motion and can be used if desired to control the power output of the turbine, for example reducing power output by opening the cover flaps by a selected amount when a turbine blade is being driven by the water flow. However powered cover flaps require the expenditure of some energy and increase the complexity of the turbine construction.

Advantageously the cover flaps, where fitted, or the turbine blades themselves are formed and arranged to move from their first to their second positions by the force of the same water flow that rotates the turbine.

For example, a cover flap may be attached to a turbine blade by being freely mounted on a pivot at the side of a corresponding turbine blade aperture . When the turbine blade is being driven by a water flow, the cover flap is pushed shut (against an edge of the aperture, for example) to cover its corresponding aperture . When the turbine blade is on the return, rotating against the direction of water flow, the flap is pushed open by the water, allowing water to flow more or less freely through the aperture, greatly reducing the force of the water flow acting against the desired direction of turbine rotation. The cover flap, when not forced closed against the aperture, will naturally adjust and align with the direction of water flow as the blade rotates. This reduces the drag forces of the flap through the water .

The cover flap may therefore operate entirely automatically, opening and closing as the turbine rotates. Similarly if it is the turbine blade itself that is moved by the flow of water on rotation of the turbine it can move from the first configuration to the second configuration entirely automatically. If desired, the movement of the flap or of the turbine blade may be damped or biased. For example, spring loading the pivot to hold the cover flap shut until a desired opening force is applied by the force of water. For example holding the turbine blade in the driving configuration by means of a latch, that is only released at a pre-determined position during rotation of the turbine.

A turbine blade that operates automatically in a manner akin to that of the cover flap described above can be formed, for example, as follows. The blade may be mounted on a plate by means of a pivot shaft normal to the plate. The pivot shaft allows the blade to pivot about an axis at or near one end of the turbine blade. The flow of water acting on the turbine causes the blade to rotate until it is pushed against a stop, for example mounted on the plate.

The stop is positioned so as to hold the turbine blade in the first, driving configuration. As the turbine rotates further the angle of the force of water flow on the blade changes and at some point acts on the opposite face of the blade, pushing it away from the stop, towards the second, return, configuration. When not forced closed against the stop, the blade, because it is pivoted at one end, will naturally adjust and align with the direction of water flow as the blade rotates. This reduces the drag forces of the blade through the water .

Advantageously the turbine may also be provided with at least one flow deflector. The flow deflector may be located in use in front of the turbine (i.e. 'upstream' of the turbine) to deflect the water flow away from the turbine blades when they are on the return, rotating against the direction of water flow. A flow deflector acting in this way may increase the efficiency of power extraction by reducing or even eliminating the force of the water flow, downstream of the deflector. The deflector may produce a Mead zone' of reduced or no flow where the turbine blades are on the return. Alternatively or additionally a flow deflector may be formed and arranged to increase the force of water acting on the turbine blades when they are being driven by the water flow. For example the flow deflector or a portion of the flow deflector may have the form of an open-ended cone or narrowing funnel that may be located upstream of the turbine blades in use and placed so as to gather and direct the water flow onto the turbine blades when they are in their first, driving configuration. The effect of a cone or narrowing funnel is to concentrate the flow of water from a large cross sectional area of the flow onto the blades .

A single flow deflector may be formed and arranged to both deflect flow away from turbine blades on the return and concentrate flow onto turbine blades when being driven.

The flow deflector may simply be a suitably rigid plate placed to deflect flow away from the returning blades of the turbine. Advantageously the flow deflector takes the form of a shroud or housing, which surrounds part or all of the turbine. Preferably the housing surrounds substantially half of the turbine. In use, the turbine may be placed in the water with the housing surrounding turbine blades when on the return. This may minimise the effect of the water flow acting against the desired direction of turbine rotation. More preferably the flow deflector takes the form of a housing, which surrounds all of the turbine and is formed and arranged both to deflect flow away from turbine blades on the return and also to concentrate flow onto turbine blades being driven.

The flow deflector or housing may be moveable . This allows adjustments to be made, for example, when the direction of a river flow alters slightly or when a tidal flow reverses completely. In a tidal situation the deflector or housing (if fitted) is moved when the tide turns if power is to be extracted in both directions of tidal flow.

Alternatively the flow deflector may have moveable portions which, when moved, change the amount and/or direction of water flow deflected. For example the flow deflector may be a plate or a housing fitted with opening and closing deflector flaps that open to allow flow through corresponding apertures and close to prevent flow therethrough .

In a preferred flow deflector the flow deflector is provided with at least one deflector flap and corresponding aperture both on the upstream and on the downstream side of the turbine. Preferably the deflector flaps operate in response to the force and direction of water flow in a manner akin to that of the cover flaps of turbine blades as described above .

For example the flow deflector may be a housing placed around the turbine and provided with deflector flaps and apertures both on the upstream and downstream sides of the turbine. If the turbine is placed in a tidal (i.e periodically reversing) flow, the deflector flaps when upstream of the turbine may be forced closed by the flow and a continuous deflecting surface is presented to the flow. When downstream of the turbine the deflector flaps are opened by water flow to allow water to flow through the apertures, relatively unhindered. When the tide turns the upstream deflector flaps become downstream deflector flaps and vice versa. This arrangement is described more fully hereafter and with reference to a specific embodiment.

Advantageously, for use in a tidal or other reversing flow, the flow deflector or flow deflectors is/are formed and arranged so that the direction of rotation of the turbine remains the same even when the flow reverses i.e. the flow deflector (s) move or are formed to direct the flow of water onto the same face of each turbine blade irrespective of the direction of the tide. This has the advantage of simplifying power extraction means, which otherwise have to be arranged to operate with a turbine that periodically reverses rotational direction. Furthermore, when the turbine blades are fitted with cover flaps or turbine blades that operate automatically, in response to the force of the water flow as the turbine rotates as described before, then the turbine can only be driven efficiently in one rotational direction. If the turbine were to rotate in the opposite direction then cover flaps if used would tend to be opened when the turbine blades were moving in the direction of flow or the turbine blades would tend to be moved away from their stops thereby reducing the force on the driven blades, thus tending to stop turbine rotation.

The flow deflector or housing may be moved or moveable portions of the flow deflector or housing may be moved to provide optimum power output from the turbine. In some circumstances, where the flow rate is too high, the flow deflector may be used to deliberately reduce efficiency, slowing the turbine down, avoiding damage caused by excessive flow speed.

Whilst the above arrangements can provide satisfactory power for many circumstances, researches by the inventor have shown that further significant improvements can be made. Making use of flow deflectors that deflect flow away from the part of the turbine that is on the return results in some losses of available energy. In some arrangements of flow deflector the water flow intended to act on the turbine blades in the driving configuration can be reduced, as the deflector can disturb the direction and force of flow to the driven blades.

Greater power extraction can be obtained where the turbine blades, or cover flaps fitted to apertures in the turbine blades, are formed and arranged to extract power from the water flow when on the return. This can be achieved by providing that at least one of the blades comprises at least one hydrofoil. The blades or cover flaps for blades may be shaped as hydrofoils and may pivot about an axis that is parallel to the turbine axis as the configuration changes from first to second. The hydrofoil shapes may be pivoted near their leading edges.

A hydrofoil shape is similar in form to and behaves in water akin to an aerofoil in the air. Cover flaps or blades that are hydrofoils generate "lift" forces, forces at an angle to the direction of travel of the blade or cover flap, as water flows past them. When the blade or cover flap is at an appropriate angle to the direction of rotation of the turbine the lift forces generated have a force component that acts in the direction of rotation thus adding to the power extracted by the turbine from the flow as illustrated hereafter with reference to specific embodiments .

The benefits of using cover flaps or moveable turbine blades of hydrofoil cross section can be enhanced by constraining their movement in operation of the turbine. By this means the power output of otherwise automatically operating cover flaps or turbine blades such as described above can be significantly improved when using hydrofoil blades or cover flaps. Improvements of 10% or more can be achieved when using hydrofoil shapes .

Advantageously the cover flaps or moveable blades may be latched into place when in the first configuration and released to allow movement to the second configuration at an optimum point during the rotation of the turbine e.g. when energy extraction of water flow in the driving configuration is no longer significant.

The or each hydrofoil may be arranged so that in operation the hydrofoil generates lift during at least part of the rotation of the turbine. The or each hydrofoil may be arranged to generate lift in operation when in the return configuration .

Advantageously the motion of the hydrofoil cover flaps or turbine blades when moving from the first configuration may be constrained during at least part of the rotation. The turbine may further comprise constraining means for constraining movement of the or each hydrofoil. The constraining means may be configured to constrain the or each hydrofoil to have a desired orientation during at least part of each rotation of the turbine. The desired orientation may be a desired orientation relative to the direction of water flow. Alternatively or additionally, in the desired orientation the or each hydrofoil may be held substantially tangential to the direction of rotation of the turbine.

Preferably the hydrofoil cover flap or turbine blade is held tangential to the direction of rotation of the turbine during part of the return. This generates a lift force with a component in the direction of rotation thus adding to the power extracted. As the rotation of the turbine continues the cover flap or turbine blade may be released from constraint to pivot more or less freely in response to the force of water flow and thus be moved back to the first configuration .

Constraining the motion of the hydrofoil cover flaps or turbine blades can be achieved in a number of ways . For example by powering a pivot shaft of the flap or blade. The constraining means may comprise at least one guide device attached to or forming part of the or each hydrofoil, and the at least one guide device may be arranged to engage with at least one track during at least part of the rotation of the turbine. For example, conveniently, the cover flaps (or the turbine blades themselves, if they move) may be fitted with an extension that fits into a shaped groove or slot in a guide plate that remains fixed relative to the rotation of the turbine. The shaped groove in the guide plate may dictate the allowable movement of the cover flap or blade as the turbine rotates.

By this means the hydrofoil cover flap or turbine blade is constrained to a selected or optimum path of motion about its pivot as the turbine rotates. The cover flaps or turbine blades can be held at the optimum angle with respect to the water flow and to each other throughout some or all of each rotation of the turbine. The path of motion can include being held with the plane of the cover flap or blade tangential to the circular motion of the turbine on at least part of the return.

Preferably the extension that fits into the groove or slot of the guide plate is at or towards the trailing edge of the hydrofoil cover flap or turbine blade i.e. away from the leading edge. Conveniently the extension may be fitted with a roller or other friction-reducing device to allow smooth movement along the groove.

Said at least one turbine blade may be formed and arranged to generate lift in operation to rotate the turbine. Said at least one turbine blade may be formed and arranged to generate lift when in the return configuration to rotate the turbine.

Said at least one turbine blade may be formed and arranged to experience in operation a drag force from water flow acting on the turbine blade when in the first, driving configuration, the drag force acting to rotate the turbine.

In operation the drag force acting on the turbine blade in the first, driving configuration may be greater than a drag force acting on the turbine blade when in the second, return configuration.

Turbines of the invention may be manufactured of any suitable materials such as are well known in the art, for example, metals such as steel, plastics or composites such as carbon fibre composites. Possible materials include so- called sheet moulding compounds (SMC) , which typically are fibreglass-reinforced thermosetting plastics compositions. These can be used to make structural components (by compression moulding techniques) that are thin, lightweight and require complex shaping, such as the turbine blades or blade components .

The turbine may be provided with some buoyancy. This assists in moving the turbine into place on installation and a turbine that is buoyant to at least some extent has reduced weight acting on its supports when placed in water allowing less heavy duty support structures and bearings to be used. Buoyancy may be provided, for example, by means of turbine blades, which have sealed air, gas or foam filled chambers within their structure. Alternatively or additionally a hub to which the turbine blades are attached may have sealed air, gas or foam filled chambers. A neutral buoyancy, at the depth of water where the turbine is located in use, is preferred. Buoyancy may also be provided in a housing for the turbine (where fitted) . For example, the housing may comprise air, gas or foam filled chambers. Optionally these chambers and/or like chambers of other buoyant members of the turbine may be arranged to provide sufficient buoyancy to float the turbine assembly. The turbine can then be easily moved, as it floats, to its selected location.

Adding mass to the turbine may then cause it to sink into its operational position. Preferably flooding or partially flooding some or all of the buoyancy chambers with water is used to allow the turbine to sink into its operational position. Replacing the water in the flooded chambers by, for example pumping in compressed air, refloats the turbine allowing its recovery for repair, maintenance or relocation.

Turbines of the invention can be built to any desired scale to suit the water flow conditions and desired power output. Relatively small scale units, which may be supplied as complete units built in a frame for easy transport and then lowering into a body of water can be supplied on the back of a road vehicle. Such portable units may be provided ready fitted with a power converter such as a pump unit or an electricity generator for immediate delivery of energy at a selected location.

The turbines of the invention may rotate about an axis substantially normal to the water flow. Advantageously they may rotate about a substantially vertical axis. This arrangement allows a turbine with relatively long turbine blades to be located in shallow waters. In some locations a turbine rotating about a vertical axis has the advantage that it can be located in a body of water whilst still allowing shipping to pass freely above without risk of collision.

Advantageously for some applications the turbine may further comprise at least one additional array of turbine blades formed and arranged for rotation about the same axis as the first array. This arrangement increases the size of the turbine as the arrays are stacked one after the other, along the rotational axis, but can provide more power. Preferably where additional arrays of turbine blades are fitted the blades of adjacent arrays are offset in radial angle by between 15 and 30 degrees.

The turbines of the invention and associated power conversion devices can be fitted with suitable control systems, which may be computer controlled, to adjust the power uptake. The control system may control, for example, adjustable turbine blades, moveable flap portions, moveable flow deflectors and/or powered cover flaps as discussed above. Other mechanisms such as a gearbox, a braking device or an electrical generator can also be operated by a suitable control system.

According to a second aspect, the present invention provides a method of extracting energy from within a water flow comprising: locating at least one turbine in a body of water; and extracting energy from the rotation of the said turbine, wherein the said turbine comprises an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first driving configuration when moving with the direction of water flow, to a second return configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration; whereby in use the turbine rotates as a consequence of the greater force of water flow acting on the turbine blade when in the said driving condition. The turbine provided for use in the method of the invention may comprise any or all of the features described above in relation to the turbines of the first aspect of the invention. For example, additional arrays of turbine blades, a flow deflector, or turbine blades that are adjustable in angle, have moveable flap portions, or have apertures and corresponding cover flaps, in order to adjust from the first to the second configuration.

The method may include the step of providing an electrical generator coupled to the turbine to produce electrical power .

The method of the invention can be applied to almost any situation where water flows, with the turbine employed being sized to suit the body of water and water flow found. Where the body of water is large, for example a large river or an estuary, then the method may include locating an array of turbines in the body of water. Conveniently when more than one turbine is employed at a given location the power take off and control devices may be combined or grouped in an economic fashion. For example, a single control system may be used to monitor and control the array of turbines. For example electrical power produced by generators attached to each turbine may be combined to produce a single power output from the array, which can be smoothed or otherwise adjusted for delivery to an electrical grid system, for example.

Any feature in one aspect of the invention may be applied to other aspects of the invention, in any appropriate combination. For example, apparatus features may be applied to method features and vice versa.

Further preferred features and advantages of the present invention will appear from the following detailed description of embodiments illustrated with reference to the accompanying drawings in which: Fig. 1 shows in schematic perspective view a turbine of the invention;

Fig. 2 shows the turbine of Figure 1 in plan view; Fig. 3 shows a detail of a turbine blade; Figs. 4 and 4a show a turbine of the invention fitted with a flow deflector in the form of a housing,- Figs. 5a to 5d, show in perspective, elevation and cross section views a turbine of the invention fitted with a flow deflector in the form of a housing with moveable flaps; Figs . 6a to 6c, show a turbine hub for a turbine of the invention which includes buoyant chambers;

Figure 7 shows in plan view a turbine according to an alternative embodiment; Figure 8 illustrates the turbine of Figure 7 in operation;

Figures 9a to 9c show a further embodiment in which a roller guide is provided on each hydrofoil flap of the turbine ; Figures 10a to 10c illustrate another embodiment in which a fin guide is provided on each aerfoil flap of the turbine;

Figures 11a and lib illustrate a turbine unit for use in, for example, tidal currents,- Figures 12a and 12b illustrate a turbine unit for use in, for example, a river; and

Figure 13 is a cross sectional view of a hydrofoil that is used in various embodiments of the turbine.

Figure 1 shows a turbine 1 of the invention. The turbine 1 is fitted with five turbine blades 2 each extending radially from a central hub 4 which has a bearing 6 formed for rotation about a suitable shaft (not shown) . Each turbine blade 2 has five apertures 8 and each aperture has a corresponding cover flap 10. The flaps 10 are generally free to rotate about pivots 12 except that they are slightly larger than their corresponding apertures 8 and so cannot pass through them. In addition, the opening of the flaps 10 is limited by the provision of stops (see Figure 3) . The cover flaps 10 are shown in both their first closed positions 14 and in second open positions 16.

The plan view of Figure 2 shows the operation of the turbine 1 of Figure 1. The direction of water flow is indicated by the broad arrow 18. The direction of rotation of the turbine 1 is shown by the curved arrow 19. Turbine blades 2 that are rotating in the direction of flow are in their first driving configuration and have their cover flaps 10 in their first closed positions 14 so that the turbine blades 2 present a continuous surface to the water flow and are driven round by it. Turbine blades 2 that are rotating against the direction of water flow are in their second, return configuration and have their cover flaps 10 opened 16 by the action of the water flow and drag through the water. The apertures 8 are therefore open 20 reducing the effect of water flow and drag on these blades. Figure 3 shows in detail a part of a turbine blade 2 with a cover flap 10 in an open second position with respect to its corresponding aperture 8. A stop 22 fitted in the pivot 12 prevents over rotation of the flap past its desired second position, ensuring closure of the flap in the correct direction, over the aperture 8, as rotation continues. The aperture 8 has a surround 23 against which the cover flap 10 rests when closed.

Figure 4 shows in schematic plan view a turbine 1 of the same form as in figures 1 and 2 fitted with a housing 24. The housing 24 is semi-circular in form and surrounds half of the turbine see perspective view figure 4a of the housing 24. The -housing 24 acts as a flow deflector 26 preventing the flow 18 acting on those turbine blades 28 that are on the return, rotating against the flow direction. The forces acting on these blades are therefore reduced only to the drag of the blades 28, with their open apertures 8, as they are moving through effectively still water 30.

Figures 5a to 5d show a portable turbine unit 32 of the invention suitable for use in a tidal reversing water flow. As shown in the perspective view of figure 5a the portable unit 32 comprises a housing 24 fitted with lifting eyes 34 to facilitate location of the unit in a water flow by means of a crane or other lifting apparatus. The housing includes a power take off housing 36, which incorporates a gearbox and electrical generator driven by a turbine 1 fitted inside the housing (see cross section 5c) .

Appropriate cabling 38 connects from the power take off housing 36 to the water surface to allow extraction of electricity and passage of control and monitoring signals to and from the unit 32. The housing 24 is formed to act as a flow deflector 26 in both directions of a tidal flow.

Both the upstream 40 and downstream 42 faces of the housing 24 have the form of a narrowing funnel 44 with a generally rectangular cross section. See also rear view perspective, figure 5d. The elevation 5b shows the upstream face 40. The funnels 44 are formed to concentrate and direct water flow 18 onto the turbine 1 when they are upstream of the turbine. The flow is directed specifically onto the turbine blades 2 in the driving configuration, moving in the direction of the flow.

The narrowing funnels 44 have deflector flaps 46, which can cover corresponding apertures 48 in a surface of the funnels 44. The deflector flaps 46 operate in a similar fashion, in response to water flow, to the turbine cover flaps 10 as described above with reference to figure 2.

The operation of the unit 32 is best described with reference to the cross section view of figure 5c along A-A of figure 5b. At the upstream face 40 of the housing 24 the flow 18 is directed and concentrated by the narrowing funnel 44, as indicated by arrows 50, through the funnel opening 51 onto the turbine blades 2 which are thereby driven anti-clockwise in the direction shown by curved arrow 19.

The flow acts on the deflector flaps 46, on the upstream face 40, to force them closed over their corresponding apertures 48 preventing flow from acting directly on the turbine blades when on the return 28 and thus improving power output by reducing the forces acting against the desired direction of turbine rotation 19.

Conversely the deflector flaps 46 on the downstream face 42 are forced open by the flow allowing water to flow as indicated by the arrows 52, through the apertures 48 on the downstream face 42 as well as through the opening 54 of the funnel 44. Thus a substantially free flow of water is allowed through most of downstream face 42 of the housing 24. This avoids unwanted deflection of flow by the funnel 44 on the downstream face 42, which would cause a loss of power uptake by the turbine 1. (Perspective view figure 5d and its magnified detail shows the downstream face 42 of the housing 24 with its flaps 46 in their open position, uncovering the apertures 48) .

When the tidal flow reverses (arrow 18 reversed) the upstream face 40 of the housing will become the downstream face 42 and vice versa. The deflector flaps 46 on both faces 40,42 will automatically open and close in accordance with the flow direction allowing the turbine to continue to operate in the same fashion. As the openings 51,54 in the funnels 44 are diagonally rather than directly opposite, the direction of rotation 19 of the turbine 1 will remain the same. The water flow will continue to be directed onto the same face of each turbine blade 2, causing the cover flaps 10 to close when the blades 2 are driven and to open when the blades 2 are on the return 28. This arrangement also avoids the complications associated with power take off from a turbine whose direction of rotation reverses in use.

Figure 6a shows in perspective a hub 4 for a turbine of the invention, which has attachment points 56 for turbine blades (not shown) . The hub is of steel all welded construction. A cross section on B-B (from the elevation, figure 6b) is shown in figure 6c. The sealed chamber 58 is air filled to provide buoyancy to a turbine fitted with the hub 4. If desired the chamber 58 may be filled with an inert gas or a foam instead of air. Alternative or additional buoyancy can be provided by the provision of similar air, gas or foam filled chambers in parts of turbine blades fitted to the hub or indeed to a hub that is not provided with buoyancy.

Figure 7 shows a turbine device 100 of an alternative embodiment in plan view. The turbine 100 is fitted with seven turbine blades 102. Other numbers of turbine blades may be provided, but it has been found to be advantageous to provide an odd number of turbine blades .

The turbine blades 102 are positioned between a bottom plate 104 and a top plate (not shown in Figure 7) , and comprises a pair of hydrofoil flaps 110. The turbine blades are rotatable about a central axis 109. It should be noted that the term aerofoil when used herein in the figures refers to components that, when in water, operate as hydrofoils.

Each flap 110 is free to rotate about a pivot 112. As was the case with the embodiment of Figures 1 and 2, the hydrofoil flaps are able to rotate between a first, closed position 114 and a second, open position 116. Each hydrofoil flap 110 is hollow and has neutral buoyancy.

Each hydrofoil flap includes a guide device, for example a guide pin, guide roller or guide plate, on its base. Each guide device 105 is located in a machined track 107 in a rotatable portion of the bottom plate 104 that is attached to and rotates with the turbine blades, and in operation constrains the range of motion of the hydrofoil flap 110 and the orientation of the flap 110. Stops 122 are fitted to the top plate to prevent over-rotation of the hydrofoil flaps 110 past their second, fully closed positions 114. Each track 107 is machined to have a shape that keeps the hydrofoil flap 110 tangential to the water flow at substantially all positions between the closed 114 and fully open 116 positions.

In the embodiment of Figure 7, at least part of the bottom plate 104 is rotatable around a central, fixing axis 109. The turbine blades are not mounted on a large central hub 4 as was the case for the embodiment of Figures 1 and 2, but instead can be mounted on the rotatable part of the bottom plate 104, or an a framework linked to the axis 109, and in operation rotate around the axis 109, which is of much smaller diameter than the hub 4 of Figures 1 and 2. A central space is thus provided, radially inwards of the turbine blades. Water is able to travel through the device via the central space .

A variant of the turbine device 100 of Figure 7 is illustrated in operation in Figure 8, in which the direction of water flow is illustrated by solid arrows.

The turbine device 100 is shown mounted within a housing

124. In the variant of Figure 8 , instead of a separate machined track 107 for each hydrofoil flap being provided on the bottom plate 104, a pair of tracks 130, 132 are provided in a stationary base plate portion. The guide device 105 of each hydrofoil flap 110 enagages one of the tracks 130, 132 during a portion of its rotation. The tracks 130, 132 operate similarly to the tracks 107 in Figure 1 in ensuring that the hydrofoil flaps 110 are maintained in a tangential position to the water flow when passing between the open 114 and closed 116 positions.

In operation, turbine blades 102 that are rotating in the direction of water flow are in their first, driving configurations and have their hydrofoil flaps 110 in their first closed positions 114 so that the hydrofoil flaps 110 present a continuous surface to the water flow and are driven round, in a similar fashion to the embodiment of Figure 1 and 2. However, driving of the rotation of the turbine by such drag effects on flaps in their closed positions 114 only provides for a contribution from each flap during a limited portion (for example 90°) of each 360° rotation of the turbine.

It is a feature of the embodiments of Figures 7 and 8 that, due to the provision of hydrofoil flaps, and the omission of the central hub thus allowing water flow through the central space of the device, each turbine blade can contribute to the driving of rotation of the turbine throughout substantially all of each rotation of the turbine .

Each turbine blade contributes to the driving of the rotation of the turbine by each of three different effects, at different points in its rotation, namely drag, cross- flow and lift effects.

The drag effects, when the hydrofoil blades are in their closed positions 114 have been described above.

The cross flow effects occur when water passes through the turbine (which is possible due to the absence of the hub 4) and hits the hydrofoils 110 on the far side of the turbine to the origin of the water flow causing lift and/or drag on those hydrofoils, and thus providing a contribution to the driving of the rotation of the turbine.

Lift effects are also provided by the hydrofoil flaps 110 that are in positions tangential to the water flow. As the water flows over the hydrofoil flap 110 in such a position it speed up as it passes the blade, causing lift, which produces forward movement. As described above the location of the guide device of each flap in a corresponding machined track on the base plate 104, and the shaping of each machined track and hydrofoil flap ensures that each hydrofoil is maintained in a position that is tangential to the water flow at positions intermediate between the fully open 116 and fully closed 114 positions.

It has been found that allowing the water to flow through the centre of the turbine unit can cut down on drag by approximately 15% and can create the cross flow which enhances the return leg of the turbines revolution. Furthermore it has been found that approximately 10% extra lift can be created by a suitable hydrofoil profile of the flaps, which increases the turbine performance and the proportion of each turbine revolution during which a flap does positive work. It has also been found that the profiles and angles at which the hydrofoils are sitting relative to each other can be optimised to provide a larger impact area. In addition, it has been found that the use of the guide devices 105 and the machined tracks can provide an increase in power performance by maintaining the hydrofoils at a desired, for example substantially optimum, angle to each other and the flow of water.

Various types of guide devices 105 can be used to guide the hydrofoil flaps during rotation of the turbine. Figures 9a to 9c illustrate one embodiment in which each guide device 105 comprises a roller guide 140 rotatably mounted on an axis 142. It can be seen in Figure 9b that the roller guide 140 engages the track 130 in a stationary portion of the bottom plate during rotation of the turbine. Figure 9b also shows the top plate 144 of the turbine. In the embodiment of Figure 9b the stop 122 is provided on the bottom plate 104.

A further embodiment is illustrated in Figures 10a to 10c, in which the guide device 105 for each flap 110 comprises a fin guide 150 including a brass bushing 152. As shown in Figure 10b, the fin guide 150 engages the track 130 of a stationary portion of the bottom plate during rotation of the turbine, to maintain the hydrofoil in a desired position. As illustrated in Figures 10 and 10b, each hydrofoil flap 110 can also include an electromagnet 154. Electromagnetic coils can be provided on the top plate 144 that can be energised to exert a force on the electromagnets 154 at the appropriate point in the rotation of the turbine, thus helping to constrain the movement of the flaps 110. Thus, the electromagnets 154 can complement operation ' of the guide device 105 and track 130. However, it is more usual for only one rather than both of the electromagnets 154 and associated coils, and the guide devices 105 and track arrangements, to be provided.

The turbine 100 can be used, for example, in rivers or in tidal stream currents.

Figures 11a and lib show, in cross-section and perspective view, a portable turbine unit 160 that is particularly suitable for use in tidal stream currents. The portable turbine unit 160 is similar in construction to that shown in Figures 5a to 5d, and includes a housing 162 fitted with lifting eyes 34, and a power take-off housing 36, which incorporates a gearbox and electrical generator driven by a turbine 100 fitted inside the housing. The turbine housing 100 is hollow and can be flooded with water to sink the device or pumped with air to allow the device to float to the surface. In operation in tidal sea currents, the device is completely sunk beneath the water surface. One significant difference between the housing 162 of the embodiment of Figures 11a and lib and that of the embodiment of Figures 5a to 5d is that the housing 162 does not include any flow deflectors 26. In certain embodiments, the turbine 100 or the turbine unit 160 is instead placed within a larger pipe or funnel to intensify the flow of water to the turbine 100, although effective operation can nevertheless be obtained without such pipe or funnel .

A portable turbine unit 170 that is particularly suitable for operation in rivers is illustrated in Figure 12a and 12b. The turbine 100 is located within a turbine device housing 172 is suspended by pods 174 that float on the river surface.

Figure 13 shows in cross-section a hydrofoil that is suitable for use with embodiments described herein.

It will be understood that the present invention has been described above purely by way of example, and modifications of detail can be made within the scope of the invention. Each feature disclosed in the description, and (where appropriate) the claims and drawings may be provided independently or in any appropriate combination.

Claims

1. A turbine for use in extracting energy from within a water flow comprising: an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first, driving, configuration when moving with the direction of water flow, to a second, return, configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration.

2. A turbine according to Claim 1, wherein in use the turbine rotates as a consequence of a greater force of water flow acting on the turbine blade when in the driving configuration .

3. A turbine according to Claim 1 or 2 , wherein said at least one turbine blade comprises at least one hydrofoil.

4. A turbine according to Claim 3 , wherein the or each hydrofoil is arranged so that in operation the hydrofoil generates lift during at least part of the rotation of the turbine.

5. A turbine according to Claim 4, wherein the or each hydrofoil is arranged to generate lift in operation when in the return configuration.

6. A turbine according to any of Claims 3 to 5, further comprising constraining means for constraining the movement of the or each hydrofoil.

7. A turbine according to Claim 6, wherein the constraining means is configured to constrain the or each hydrofoil to have a desired orientation during at least part of each rotation of the turbine.

8. A turbine according to Claim 7, wherein the desired orientation is a desired orientation relative to the direction of water flow.

9. A turbine according to Claim 7 or 8, wherein in the desired orientation the or each hydrofoil is held substantially tangential to the direction of rotation of the turbine.

10. A turbine according to any of Claims 6 to 9 wherein the constraining means comprises at least one guide device attached to or forming part of the or each hydrofoil, wherein the at least one guide device is arranged to engage with at least one track during at least part of the rotation of the turbine.

11. A turbine according to any preceding claim, wherein said at least one turbine blade is formed and arranged to generate lift in operation to rotate the turbine.

12. A turbine according to Claim 11, wherein said at least one turbine blade is formed and arranged to generate lift when in the return configuration to rotate the turbine.

13. A turbine according to any preceding claim, wherein said at least one turbine blade is formed and arranged to experience a drag force from water flow acting on the turbine blade when in the first, driving configuration, the drag force acting to rotate the turbine.

14. A turbine according to Claim 13, wherein in operation the drag force acting on the turbine blade in the first, driving configuration is greater than a drag force acting on the turbine blade when in the second, return configuration .

15. A turbine according to any preceding claim, wherein the turbine blades are spaced radially outwardly from the centre of rotation of the turbine, thereby providing a central space radially inward of the turbine blades.

16. A turbine according to Claim 15, wherein in operation water flows through the central space.

17. A turbine according to Claim 15 or 16, wherein the turbine blades are arranged so that in operation water contacts at least one of the turbine blades after flowing through the central space.

18. A turbine according to Claim 17, wherein said at least one turbine blade is arranged to generate lift from contact with water that has flowed through the central space.

19. A turbine according to any preceding claim, wherein at least one adjustable turbine blade is provided with one or more flap portions, which in operation move to increase or decrease the surface area of the turbine blade presented to the direction of water flow when moving from the driving configuration to the return configuration.

20. A turbine according to Claim 19 as dependent on any of Claims 3 to 10, wherein at least one of the flap portions is shaped to form at least one of the hydrofoils.

21. A turbine according to any preceding claim, further comprise latching means for releasably holding the or each turbine blade in the first configuration during at least part of rotation of the turbine.

22. A method of extracting energy from within a water flow comprising: locating at least one turbine in a body of water; and extracting energy from the rotation of the said turbine, wherein the said turbine comprises an array of turbine blades formed and arranged for rotation, in use, about an axis substantially normal to the direction of water flow; wherein at least one turbine blade of the array is formed to be adjustable, in use, from a first driving configuration when moving with the direction of water flow, to a second return configuration when moving against the direction of water flow, and wherein the surface area of the turbine blade presented to the direction of water flow is reduced when in the return configuration.