The present invention relates to a turbine apparatus and method, and in particular to a vertical-axis turbine apparatus and method.

A number of designs of vertical-axis turbine have been proposed for generating power from moving bodies of water, including in rivers and in marine applications. The present invention aims to solve a number of problems in these existing designs.

The invention provides a turbine, a ballasted turbine-blade or foil assembly, and a method for operating a turbine as defined in the appended independent claims, to which reference should now be made. Preferred or advantageous features of the invention are set out in dependent sub-claims.

In a first aspect, the invention may thus provide a turbine for operation in a moving body of water, comprising a hub for rotation about a vertical axis, an arm extending outwardly from the hub, and a ballasted turbine-blade or foil assembly connected to or mounted on the arm, spaced from the hub.

Typically, a turbine may comprise two or more arms extending outwardly from the hub, each connected to a ballasted turbine-blade assembly.

Embodiments of the invention may advantageously be larger and slower moving than many types of turbine. For example, a preferred embodiment may provide a turbine of greater than 50m, 75m, 100m or 200m in diameter, for example for use in medium-strength tidal-stream applications. For example, embodiments of the invention may advantageously be designed to operate in water flows of between 1.5 and 6 ms ^"1 , or preferably between 2 and 4 ms ^"1 , The large size of the turbine may be enabled by the use of the buoyancy of the blades or foils to support the arms, so that the hub and the arms may not need to be sufficiently rigid to support all of the weight of the arms or the blade assemblies.

Each blade assembly is movable relative to the hub in a direction substantially parallel to the axis of rotation of the hub. During operation of a vertical-axis turbine, this means that the blade assembly is movable in a substantially vertical direction. A turbine blade of the blade assembly may be movable in other directions, for example to vary the pitch or angle of attack of the turbine blade relative to the fluid within which it is moving. In the invention, however, the blade assembly is movable so that at least a component of its motion is relative to the hub, in a direction parallel to the axis of rotation of the hub.

The blade assembly can be ballasted so that its buoyancy in the water is sufficient to support at least a portion of the weight of the arm and/or of the blade assembly. Advantageously, the blade or foil itself may be ballasted, for example by means of a ballast chamber positioned within the blade or foil. Preferably, the blade assembly is ballasted only by ballasting of the blade or foil, and comprises no other buoyant elements for supporting the weight of the arm and/or of the blade assembly during operation of the turbine. In a preferred embodiment, at least a portion of the arm and/or of the blade assembly may thus be supported above a surface of the water. In a preferred embodiment, during operation of the turbine to generate power, the blade assembly may be ballasted so that a turbine-blade, or foil, portion of the blade assembly is immersed in the water, while at least a portion of the arm and/or of the blade assembly is positioned above the surface of the water. This may advantageously reduce drag which would be generated by motion of the arm and the entire blade assembly through the water as the turbine rotates, if the arm and the entire blade assembly were submerged. In addition, supporting at least a portion of the arm or of the blade assembly above the surface of the water during operation of the turbine may advantageously reduce drag, reduce loads applied to these components, and reduce wear of these components.

Preferably, the blade assembly, or the blade, may be ballasted so that only the blade or foil, or a portion of the blade or foil, is below the water surface.

A further advantage is that supporting a portion of the arm or of the blade assembly above the surface of the water enables these components of the turbine to be visible, and easily accessed for servicing. Although the blade assembly is allowed to move parallel to the axis of rotation of the hub, it is constrained from moving tangentially to the hub, or

perpendicular to the axis of rotation of the hub, so that forces applied by the moving body of water to the blade assembly are transmitted as torque to the hub.

In a preferred embodiment, the arm is constructed so as to allow the vertical movement of the blade assembly parallel to the turbine axis, while tangential movement of the blade assembly perpendicular to the turbine axis is constrained. For example, the arm may comprise a pivot so as to allow the movement of the blade assembly parallel to the turbine axis. The pivot advantageously has a pivot axis which is perpendicular to the turbine axis, and so is substantially horizontal in a vertical-axis turbine. The pivot is preferably mounted on or adjacent to the hub, but may be at any convenient position along the length of the arm. Advantageously, the pivot should be closer to the hub than to the blade assembly, and should preferably be close to the hub. Further, any arm portion between the hub and the pivot should extend substantially rigidly from the hub, and may therefore effectively form part of the hub. For example, the pivot is preferably at a radius from the turbine axis of less than 25%, and particularly preferably less than 20% or 10% or 5%, of the radius of the blade assembly from the turbine axis. Alternatively, the arm may be flexible such that the blade assembly can move parallel to, but not perpendicular to, the turbine axis.

Where the arm is pivotably connected to the hub, the vertical movement of the blade assembly may be in an arc around the pivot rather than moving only vertically, or parallel to the turbine axis. Nevertheless, a component of the motion of the blade assembly around the pivot is then vertical, or parallel to the turbine axis. In addition, as described above, in a preferred embodiment of the invention the diameter of the turbine, and therefore the length of each arm, is very large and may be 50m, 100m or more. In such a structure, the motion of the blade assembly in an arc around the pivot will have a very large vertical component, parallel to the turbine axis. In a further alternative design, the blade assembly may be vertically movable relative to the arm, for example using a sliding or pivoting arrangement, to enable the movement of the blade assembly parallel to the turbine axis. A turbine of this design may provide a number of advantages. In many applications, the surface of the water may not be smooth. In marine applications in particular, the surface of the sea may be disturbed by waves of variable height, which may be very large, powerful and even destructive in stormy weather. The ballasted blades, or foils, of a turbine embodying the invention may advantageously be able to move parallel to the turbine's axis of rotation so as to follow disturbances of the water surface, such as waves, so as both to optimise power output from the turbine at all times and to reduce the risk of damage to the turbine in heavy seas. A further advantage is that a turbine embodying the invention may be able to operate efficiently and effectively in water of varying depth, such as in tidal applications. As the depth of the water changes, the hub of the turbine may remain at a fixed position but the ballasted blades may move parallel to the turbine axis and remain immersed to a substantially constant depth below the water surface. Thus, for example, if a blade assembly is ballasted such that its buoyancy positions only a blade portion of the blade assembly below the water surface, then only that blade portion may remain below the water surface even if the water level varies or if there are waves on the surface of the water. Also, if the buoyancy of each blade assembly is used to support at least a portion of the blade assembly and/or the arm linking it to the hub above the surface of the water, then this may be achieved even if there are waves on the water surface or if the water depth varies. This may advantageously reduce drag at all times.

For these reasons, a turbine embodying the invention may advantageously optimise power generation even in rough seas or in water of varying depth.

These advantages may be achieved in a turbine in which the ballasting of each blade assembly is fixed. For example, when a turbine is constructed or installed, the ballasting of each blade assembly may be adjusted so that the buoyancy of each blade assembly retains a desired portion of the blade assembly (such as a blade or foil portion) below the water surface and a desired portion of the blade assembly (such as a mounting for securing the blade assembly to an arm of the turbine) above the water surface.

In a further aspect of the invention, the ballasting of the blade assembly may advantageously be controllable, or adjustable. During operation of the turbine, the ballasting of the blade assembly may then be controlled to position a turbine-blade, or foil portion of the blade assembly beneath the surface of the water, in order to optimise the transfer of power between the moving water and the turbine blade or foil, while the buoyancy of the blade assembly supports at least a portion of the arm or of the blade assembly above the surface of the water. As described above, this may advantageously increase power output, and reduce drag and reduce wear of the turbine components.

In a further aspect of the invention, the ballasting of the blade assembly may be controlled, or adjusted, to raise the blade assembly to a position higher than its position during normal, power-generating operation of the turbine. For example, in this position, an increased portion of the arm or of the blade assembly (optionally including an increased portion of the blade or foil itself as described below) may be raised above the surface of the water. This process may provide a number of advantages, including ease of inspection of the arm and blade assembly, and ease of servicing. In addition, in some applications of the turbine the step of increasing the buoyancy of the blade assembly may form part of the normal operation of the turbine. For example, if the turbine operates in shallow water, and the depth of the water reduces for any reason, then the buoyancy of the blade assembly may increased to raise the arm and blade assembly out of the water. This may, for example, enable a turbine to operate in shallow tidal water, where the maximum depth of the turbine blades may be reduced as the depth of water reduces during the tidal cycle. Such a turbine may be installed, for example, on a sand bank where rapid tidal flows are available, but where the depth of the water varies with the tide. The blade assembly may advantageously comprise a ballast chamber, in which the volume of water can be controlled in order to control or adjust the ballasting of the blade assembly. The volume of the water in the ballast chamber may be varied using, for example, compressed air or a pump, in known manner.

The blade assembly comprises a turbine blade or foil, and the ballast chamber(s) may conveniently be positioned within the blade or foil.

The shape and positioning of the turbine blade may be implemented by the skilled person in known manner. For example, the turbine may be a Darreius turbine, a Vort-Schneider propellor or other vertical-axis turbine operable in moving water. In a number of known turbine designs, the turbine blades are not held in fixed position but are movable, for example to vary the angle of attack or pitch of the blade, or to vary the tilt of the blade. The turbine blade assembly of the present invention may be constructed so as to implement these control parameters in known manner, without affecting the features of the invention described above.

Description of Specific Embodiments and Best Mode of the Invention

Embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, in which;

Figure 1 is a perspective view of a turbine embodying the invention; Figure 2 is an enlarged perspective view of the hub of Figure 1 ;

Figures 3, 4 and 5 are schematic side views of the turbine of Figure 1 in various operating conditions; and Figure 6 is an enlarged perspective view of one of the turbine blades or foils of the turbine of Figure 1.

As noted above, turbines embodying the invention may be of large diameter, of 50m or 100m or more. As the skilled person would appreciate, the drawings are schematic and show, for clarity, a turbine with arms of shorter length than this.

The turbine 2 shown in Figure 1 comprises a hub 4 mounted for rotation about a vertical axis. It is supported on a vertical shaft 6 which is secured in position in known manner, for example being supported on the sea bed.

The turbine comprises four arms 8, extending from the hub at 90° intervals. As shown in Figure 1 , the arms extend substantially horizontally from the hub, and are secured to the hub at pivots 10. An enlarged view of the hub and pivots is shown in Figure 2. Each pivot comprises a spaced pair of sleeves 12 welded to the hub, and a horizontal pin 14 extending between the sleeves. Each arm 8 is pivotably engaged with one of the pins 14, between a pair of sleeves.

As shown in Figure 1 , a turbine-blade assembly 16 is connected to or mounted on an end of each arm 8, spaced from the hub. Each turbine-blade assembly comprises a turbine-blade support 8, and a blade or foil 20. The blades 20 depend substantially vertically below the arms 8, when the arms are in a substantially horizontal position as illustrated in Figure 1. As can be seen by comparing Figures 3, 4 and 5, which are side views of a turbine in various operating conditions and which show the angle between each arm and its blade or foil in a substantially vertical plane in each operating condition, each blade assembly retains or holds its blade or foil at a substantially constant angle to the corresponding arm. As shown in the Figures, this angle is retained as the arm pivots up or down. The angle may be substantially perpendicular or may be less than 90°, for example being less than 85° or 80°, and/or more than 70° or 75°, such as about 70°, 75°, 80° or 85°. For a turbine of large radius, this may advantageously retain the blade or foil at an approximately constant angle to the water at all times because the angle through which the arms pivot vertically may be advantageously small.

Figure 6 shows an enlarged view of one of the turbine blades, or foils. The blade 20 is of hollow, or partially hollow, construction and contains one or more ballast chamber(s) (not shown). A control system, which may be located at the hub or within the blade support 18, enables the volume of water in the ballast chamber to be varied or controlled, in order to control the buoyancy of the blade. Valves 26, 28 are provided for admitting or expelling water or air into or out of the ballast chamber(s) as required. The volume of water in the ballast chamber(s) may be controlled by means of any known ballast-control system, including, for example, a pump or a compressed air system, which may be housed within the blade support 18 or within the blade 20 itself.

Figure 3 is a side view of the turbine of Figure 1 in its normal operating condition, for generating power. (In Figures 3, 4 and 5, which show the turbine in various operating conditions, two of the arms and turbine-blade assemblies have been omitted for clarity.)

As shown in Figure 6 the shaft 6, on which the hub 4 is mounted, is secured at its base to the sea bed 24. The surface 22 of the water is just beneath the hub 4. The arms 8 extend substantially horizontally from the hub, above the surface 22 of the water. The turbine blades or foils 20 depend downwardly from the ends of the arms into the water, so that substantially all of the length of each blade or foil 20 is beneath the water surface. As shown in Figure 3, only an advantageously small portion of each blade or foil may remain above the surface, such as less than 5% of the length of the blade or foil. In addition, as shown in Figure 3, the portion of the blade assembly above the foil may advantageously remain above the surface of the water. The ballast within each blade is controlled, such that the buoyancy of each blade is sufficient to support the weight of the arm and the turbine-blade apparatus in this position.

As the water flows past the turbine, the interaction of the blades or foils with the moving water causes rotation of the turbine about the shaft 6. This rotation can be used to generate power in known manner. For example an electrical generator (not shown) may be mounted at the hub 4. The generator may conveniently be mounted above the water surface, which may simplify the construction of the generator.

In this operating condition, it should be noted that the arms are free to pivot at the hub, and that the weight of the arms is therefore supported by the buoyancy of the blades or foils 20. This may advantageously reduce the loads applied to the arms during operation of the turbine, as the arms do not need to support their own weight or the weight of the blades. The arms only need to transmit to the hub the rotational forces generated by the passage of the water past the blades. Vertical movement of the blade assemblies also allows the blade assemblies to follow the surface of the water if waves pass the turbine, and keeps the blade assemblies immersed in the water to a constant depth even if the depth of the water changes, for example due to tides.

In an alternative, simplified embodiment, in order to achieve these advantages, the ballasting of the blade assemblies need not be controllable but may be fixed. In the alternative embodiment, the ballasting may therefore be preset during manufacture, or during installation of the turbine. In the latter case, a turbine may be installed in a body of water and then the ballast chamber(s) of each blade assembly filled or partially filled in order to adjust the buoyancy of each blade assembly so that desired portions of the blade assembly and its arm are positioned above and below the water surface. As described above, this may be with substantially all of the length of each foil beneath the water surface. The ballast chambers may, for example, be filled or partially filled with water or concrete or other suitable ballast, and then sealed.

Reverting to the embodiment of Figures 1 to 3 and 6, in which the ballasting of the blade assemblies is controllable, Figure 4 illustrates the turbine in a condition suitable for servicing or inspection. In this operating condition, the ballasting of the blades has been controlled, for example by expelling water from one or more ballast chambers, to increase the buoyancy of the blades, causing the arms to pivot upwards and the blades themselves to rise out of the water. A portion of each blade remains beneath the surface of the water, and the buoyancy of this portion of each blade supports the weight of the turbine- blade apparatus and its supporting arm.

Increasing the buoyancy of the blades in this way, in order to raise the arms of the turbine, may advantageously permit access to the arms and the blade apparatus. In addition, this mode of operation may be useful in order to reduce the forces exerted by the moving water on the turbine, for example in stormy weather.

Figure 5 shows a further operating condition of the turbine. In this case, the turbine is operating in water which becomes shallow at low tide. The reduced water level 22 is shown in Figure 5. In this operating condition, the ballasting of the blades has been controlled to increase the buoyancy of the blades and to reduce the portion of each blade which is beneath the surface of the water. The buoyancy of the blades in Figure 5 is therefore similar to that in Figure 4. As shown in Figure 5, however, the purpose of increasing the buoyancy of the blades is to protect the blades from striking the sea bed 24 at low tide.

If the water level reduces further, the turbine may effectively become beached on the sea bed 24, with the turbine blades resting on the sea bed. In this case, the ability to increase the buoyancy of the blades before the turbine blades come into contact with the sea bed may advantageously reduce the loading on the turbine, exerted by the moving water, before the turbine becomes beached.

A turbine of this design could therefore be used in tidal water, for example on a sand bank or in an estuary, where there is not sufficient depth of water to operate the turbine at all stages of the tide.

In summary, these advantages may be achieved by enabling the portion of each blade or foil that is beneath the surface of the water to be varied

(preferably being continuously variable) by controlling the ballasting of the blades, between the operating condition shown in Figure 3 where substantially all of the length of each blade (e.g. >95%) is immersed, to the conditions of Figures 4 and 5 where half or less, such as less than 30%, of the length of each blade is immersed beneath the surface of the water.

The drawings of the turbine shown in the Figures are schematic only, and are not drawn to scale. It is envisaged that a turbine embodying the invention may be larger and slower moving than many types of turbine design. For example, it is envisaged that turbines embodying the invention may be as much as 50m, 75m, 100m or 200m in diameter, for use in medium-strength tidal-stream applications. The large size of the turbine is enabled by the use of the buoyancy of the blades or foils to support the arms, so that the hub and the arms do not need to be sufficiently rigid to support the weight of the blade assemblies.

Also, the blade design shown in the Figures is schematic. As the skilled person would appreciate, any suitable vertical-axis turbine-blade design may be used, such as a Darreius rotor or a Vort-Schneider propeller. The Figures illustrate a turbine having four blades. It is envisaged that a turbine embodying the invention may have any suitable number of blades, such as between three and eight blades.