Introduction

The current invention relates to water wheels and hydrostatic pressure converters used to harvest energy from flowing liquids such as rivers and streams, which when suitably configured can be used to provide mechanical or electrical power.

It is particularly relevant to Hydrostatic energy converters, but also has application to other water wheel forms wherein such devices are configured so that blades pass through bodies of water for a significant proportion of their rotation.

Basic Hydrostatic Pressure Converters

In such devices, blade geometries are chosen to occupy the maximum cross section of the fluid channel to maximise the flow from which energy is captured and minimise the losses due to leakage between blades and flow constraining geometries.

However, this gives rise to three significant compromises in performance. The first is that fixed blades experience considerable drag forces arising as the blades pass through the fluid either before or after the point of rotation when energy is extracted from the flow, leading to significant energy losses. The second is that fixed blades tend to allow air to remain trapped in each cell as it fills with fluid, reducing both the flow capacity of the device and the efficiency of energy extraction. The third is that since clearances between blade edges and the fixed constraining channel walls are kept small to minimise leakage losses, these devices can be vulnerable to damage or jamming from foreign objects carried by the fluid flow becoming trapped between the rotating blades and the fixed structure. This latter issue can also give rise to environmental damage to fish and aquatic life forms entering the device which potentially reduces the number of sites at which deployment of such devices can be permitted.

A typical installation of a basic Hydrostatic Pressure Machine is shown in Figure 1 and an explanation of the terminology used to describe its' features follows. A central hub of the device acts as a weir separating the up and downs stream flows and has a diameter equal to the nominal head difference between those fluid levels. For typical devices of this type, hub diameters fall in the range of 0.5 to 2.5 meters. A number of blades are mounted around the circumference of the hub. The length of these blades is selected to match the down stream water depth at a particular site, but are typically is in the range of 0.4 to 2.5 meters. These blades may be flat, curved or inclined to the axis of rotation of the device as required by the installation.

A pair of blades acting together with the surface of the hub forms what is termed a "Cell" into which fluid flows into and out off, during rotation. The lower gap between the circumference of the device and the channel bed is largely sealed by a curved "shoe", leaving a minimal operating clearance between fixed and rotating elements. These devices are capable of processing large volumes of fluid. For example, at 2 meters head, up to 4.3 cubic meters per second, per meter width of the rotor, can pass through the device. Since the hub and blades presents very little obstruction to the passage of sediments, the width of the rotor may extend over a large proportion of the fluid channel, enabling significant amounts of energy to be harvested. Peak hydraulic energy conversion efficiencies have been measured for basic devices at 82% and the construction of the device permits it to be readily scaled, with cost effective installation possible from power outputs as low as 6 Kilowatts, to whole river flows with power outputs of up to 1 Megawatt.

Potential locations for deployment include, streams, reactivated mills, level-control structures on rivers or canals and in some types of coastal and tidal energy installations. The power extracted with the device can by suitable means be applied to electricity generation, fluid pumping, or used for the direct drive of mechanical processing equipment such as mills, oil extractors or crushers.

Prior Art

Several previous workers have suggested the use of mechanical mechanisms to change the geometry of rigid blade forms during rotation to ameliorate these performance deficiencies in water wheels (for example: Brewer J.J (1976) Waterwheel Driven Electrical Generator, United States Patent No.3984698). The present invention employs the properties of flexible materials to enable blade geometry to conform to the optimum shape for drag reduction or power extraction during rotation, through the action of fluid forces alone and without the need for external mechanical means.

While flexible blades have been previously proposed for pumps and motors where the rotor operates within a completely enclosing housing, (Stenild E.I., (1995) Positive Displacement Fluid Motor with Flexible Blades, United States Patent No. 5456585), the present invention represents the first application of such blades to the open rotors of waterwheels and hydrostatic pressure machines.

Summary of the Present Invention

The present invention provides a hydraulic energy converter for harvesting energy from a flowing liquid using flexible blades to reduce energy losses that would otherwise occur, comprising of a rotatable hub, a plurality of support ribs mounted circumferentially around the hub, and a plurality of flexible blades mounted circumferentially around the hub fixed along the edge attaching to the hub by suitable means, other edges not being attached to the hub or ribs to permit deflection of the flexible blade in response to fluid forces.

The membrane of the said flexible blades may be constructed from such materials (although not exclusively so), as natural rubber, synthetic rubbers of various kinds, or synthetic polymer materials such as polythene with or without the inclusion of reinforcing fibres, fabrics or filaments. The thickness, tensile strength, flexural stiffness, abrasive resistance and modulus of membrane material may be matched to the size, flow conditions, fluid type, operating conditions and particular purpose for which the device is employed.

In applications where high pressure forces are encountered, the flexible blade may be constructed from rigid materials such as (although not exclusively) steel, aluminium or rigid polymer composites. In such cases, flexibility of the blades shall be effected through the use of hinge connections between adjacent segments which constitute the said blade, each hinge having an axis of rotation substantially parallel to rotational axis of the hub. A single blade may consist of a singular or plurality of such segments so configured, attached one to another in series by suitable means.

Preferably, the plurality of ribs is mounted, in a mutually spaced annular array around the outer circumferential surface of the hub and may be either fixed in position, or movable.

Preferably if such ribs are movable, attachment to the outer circumferential surface of the hub shall comprise of a hinge and stop. Preferably each rib is movable from a first position which is substantially radially outward directed, and to a second position at which the blade is substantially tangential to the outer circumferential surface of the hub. The stops shall be so arranged to prevent rotation of the rib past the first position when forces are applied to it in the direction of rotation of the whole device, while allowing the rib to move to the second position when forces are applied in the opposite direction to that of the rotation of the whole device.

Preferably attachment of the flexible blades at the hub shall be via a supporting plate, itself fixed to the circumferential surface of the hub, by suitable means. Said plate will provide substantially continuous support to the edge of the flexible blade adjacent to the attachment parallel to the hub, along the whole width of the device. Said plate may occupy a lesser or substantial proportion of the radial length of the blade.

Preferably, the load carrying capacity of each flexible blade is enhance by a single or plurality of support beams running broadly parallel to the edge of the blade attached to the hub, either mechanically fixed, moulded within the flexible blade material itself, or formed by suitable isotropic shaping of the flexible blade material or elements. Said support beams are of sufficient length to bear against the support ribs when the resultant fluid forces act on the blade in the direction of rotation of the device, transferring the torque so produced to the hub and thence by suitable mechanical means, to the power take off.

Brief Description of the Drawings

Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 schematically shows a typical installation of a basic hydrostatic pressure machine;

Figure 2 schematically shows the operating principle of a hydraulic energy converter incorporating flexible blades in accordance with the present invention;

Figure 3 is a schematic drawing representing a hydraulic energy converter incorporating flexible blades and fixed support ribs in accordance with a first embodiment of the present invention; and

Figure 4 is a schematic drawing representing a hydraulic energy converter incorporating flexible blades and movable support ribs in accordance with a second embodiment of the present invention.

Detailed Description of the Preferred Embodiments

Operating Principle of the Present Invention

Referring to Figure 2, as blades enter the upstream fluid, rotation of the wheel is moving the blades against or across the prevailing flow resulting in drag forces being exerted on the blade. Since the blade is flexible, these drag forces cause the blade surface to deflect, reducing the projected area of the blade presented to the flow and as a result, the magnitude of drag losses exerted on the wheel. As blade rotation continues towards the lower portion of the wheel, a point is reached where hydrostatic pressure forces acting on the upstream face of the blade become greater than opposing drag forces and the blade is pushed in the direction of rotation until it bears against the support spokes. This is the portion of rotation in which energy is extracted from the flow, and the pressure forces acting on the blade surface is transmitted via the spokes to the hub, hence yielding mechanical power. As wheel rotation continues, the blades are pulled upwards through the downstream fluid, at which stage blades again deflect away from the spokes once forces arising from drag and fluid lift, become greater than the forces extracted from the flow.

The material properties of the flexible blade may be selected to optimise the performance of the device over a specific range of flow rates and operating conditions as required by the application. The present invention typically increases peak efficiency compared with a conventional blade design by up to 5%, but enables this efficiency to be obtained over higher flow rates, improving power out put and energy capture by up to 20%. Under very high flow rates (corresponding for example to winter floods), the present invention is able to continue extracting power, beyond the point at which a conventional device would have to be shut down, greatly increasing the potential for energy capture from seasonal flow conditions. In addition the present invention presents little or not obstruction to excess flows overtopping the device, minimising upstream flood risks presented by such an installation.

Embodiment #1

Referring to Figure 3, the machine comprises a bearing or axle 1, about which the device rotates. In this Figure the device rotates counter-clockwise when viewed on axle 1, with fluid flowing from left (upstream) to right. A Hub 2, runs coaxial to the axis of rotation presenting a continuous circumferential surface to the fluid flow and of a diameter equal to the nominal difference in up and downstream fluid levels. A plurality of ribs 3, are mounted in a mutually spaced annular array around the cylindrical surface of the hub 2. Depending on the size of the device and the nature of the flexible blade materials employed, additional arrays of ribs to those shown in the figure may be spaced along the length of the hub as required. Flexible material forms the surface of the blades 4, on which fluid pressure and drag forces act. This material is supported along the edge adjacent to the cylindrical surface of the hub 2, by one or more support plates, extending between ribs 3, and attached to the hub surface by suitable means. Said support plates may represent a greater proportion of the radial length of the blade to that shown in the illustration. The side of the blade material 4, adjacent to the surface of the hub 2, is fixed to the support plates 5, by suitable means with other edges remaining free to deflect. In the illustration, this is achieved with an upper clamp plate 6. The flexible blade 4, is of low stiffness in a direction broadly parallel to the axis of the hub 2, but is supported either externally or internally by one or more edge beams 7 increasing the stiffness of the flexible blade 4 in a direction perpendicular to the hub axis. These edge beams 7, serve to transfer forces from the flexible blades to the support ribs at suitable periods during the rotation of the complete device. The principle of operation of the flexible blades is shown in Figure 2, as discussed above. When the blade is passing through a segment of rotation experiencing high fluid drag forces, the flexible blades, co-acting with the edge beams, deflect away from the drag forces applied 8, reducing the projected area presented to the flow and thus the drag losses transmitted to the hub 2. As blade motion continues to the lower portion of rotation, fluid hydrostatic pressure and flow forces are greater than those arising from fluid drag, which cause the flexible blade 4, co-acting with the edge beams 7 to extend and move into contact with the support ribs 3. This is the portion of rotation in which energy is extracted from the fluid 9, with pressure forces acting on the flexible blades 4, being transferred via edge beams 7, support plates 5, and ribs 3, to the hub 2, and thence by suitable mechanical means enabling mechanical power take off for either direct mechanical use, or for conversion to electricity.

Embodiment #2

Referring to Figure 4, the addition of moveable ribs to this embodiment offer a potential increase in tolerance to damage from large objects passing through the device and contacting the rib elements.

The machine comprises a bearing or axle 1 , about which the device rotates. In this Figure, the device rotates counter-clockwise when viewed on axle 1, with fluid flowing from left (upstream) to right (downstream). A Hub 2, runs coaxial to the axis of rotation presenting a continuous circumferential surface to the fluid flow and of a diameter equal to the nominal difference in up and downstream fluid levels. A plurality of movable rib assemblies comprising items 4, 5 and 7, are mounted in a mutually spaced annular array around the cylindrical surface of the hub 2. These assemblies consist of a lug 7, fixed by suitable means to the cylindrical surface of the Hub 2, to which the rotating portion of the rib 4 is attached by pin, bolt or other means to form a hinge joint 5. A rotation stop 8, is provided by suitable shaping of the rib, lug or by other means to prevent the moving portion of the rib 4 from moving significantly passed the radial position (compared to the cylindrical surface of the hub 2), when rotated in the same direction as the rotational movement of the whole device. However, the rib is free to attain a substantially tangential position relative to the cylindrical surface of the hub 2, when subjected to forces acting in the opposite direction to that of the rotation of the whole device.

Depending on the size of the device and the nature of the flexible blade materials employed, additional arrays of ribs to those shown in the figure may be spaced along the length of the hub as required. Flexible material forms the surface of the blades 12, on which fluid pressure and drag forces act. This material is supported along the edge adjacent to the cylindrical surface of the hub 2, by one or more support plates 3, extending between ribs 4, and attached to the hub surface by suitable means. Said support plates may represent a greater proportion of the radial length of the blade to that shown in the illustration. The side of the blade material 12, adjacent to the surface of the hub 2, is fixed to the support plates 3, by suitable means with other edges remaining free to deflect. The flexible blade 12, is of low stiffness in a direction broadly parallel to the axis of the hub 2, but is supported either externally or internally by one or more edge beams 6 increasing the stiffness of the flexible blade 12 in a direction perpendicular to the hub axis. These edge beams 6, serve to transfer forces from the flexible blades to the support ribs at suitable periods during the rotation of the complete device.

When the blade is passing through a segment of rotation experiencing high fluid drag forces, the flexible blades, co-acting with the edge beams, deflect away from the drag forces applied, reducing the projected area presented to the flow and thus the drag losses transmitted to the hub 2. In the event of the rib 4, striking an obstruction, the rib rotates in the opposite direction to that of the whole device 10, until the projected length of the rib is sufficiently reduced for the obstruction to be cleared. As blade motion continues to the lower portion of rotation, fluid hydrostatic pressure and flow forces acting on the blade are greater than those arising from fluid drag, which causes the flexible blade 12, co-acting with the edge beams 6, to extend and move into contact with the support ribs 4, returning the deflected rib 10 back to the fully extended position 1 1. This is the portion of rotation in which energy is extracted from the fluid, with pressure forces acting on the flexible blades 12, being transferred via edge beams 6, support plates 3, and ribs 4, to the hub 2, and thence by suitable mechanical means enabling mechanical power take off for either direct mechanical use, or for conversion to electricity.