Introduction

The present disclosure relates to a turbine and in particular to a vertical axis turbine suitable for use in the generation of electricity from the flow of a fluid past the turbine blades such as occurs when sea and river water surges during the rise and fall of tides.

Background

There are two main types of turbine, defined by the orientation of the axis of rotation of the components driven by a fluid. Horizontal axis turbines have one or more blades attached to a central rotor whose axis is horizontal and aligned with the direction of the fluid. Drag and lift forces on the blades, usually dominated by the latter, produce motion perpendicular to the direction of the fluid, resulting in rotation. The speed at the tips of the blades usually exceeds the speed of the fluid, typically by a factor of about six.

In a horizontal axis turbine the axis of rotation must be aligned, actively or passively, with the direction of the fluid. In the case of wind turbines, if the wind direction shifts, the rotor/blade assembly must rotate to the new direction. The fact that wind direction changes frequently, makes the design of vertical axis wind turbines complex because a mechanism must be designed to efficiently move the blades into the correct orientation with respect to the wind.

The second main type of turbine has a vertical axis with blades arranged around the axis in an asymmetrical manner. Drag and lift forces on the blades produce rotation in a preferred direction about the vertical axis. Most vertical axis turbines produce rotation regardless of the fluid direction and are therefore advantageous when the fluid direction shifts frequently or is turbulent. A vertical axis is convenient because the electrical generator or other equipment using the rotational energy can easily be located at ground level, or at least below the blades. The disadvantage of most vertical axis wind turbines is that the blades gain energy on the downwind half of their rotation but lose it on the upwind half. This can result in low efficiency of extraction of the energy of the wind in the area swept by the blades. This inefficiency is the primary reason why horizontal axis turbines are favoured at present despite their drawbacks.

A feature of many vertical axis turbines which is both advantageous and disadvantageous is that they rotate slowly, with the blades moving at a speed no higher than the fluid speed. Thus they are safe and produce modest noise and vibration. As they do not experience high blade rotation speeds which can cause damage in horizontal axis wind turbines, the structures themselves need not be constructed to withstand excessive speed and vibration and they can continue to generate electricity when the wind speed is high. This feature is particularly valuable given that the energy in the wind is proportional to the cube of wind speed.

A well-established vertical axis design is the Savonius turbine, which uses two or more blades curved in such a way as to experience a high drag force when moving downwind, but not too much drag when moving upwind. The blades move at a speed somewhat lower than the wind speed, and the efficiency is low.

Some vertical axis turbines try to address the issue of low efficiency by keeping the blades slim and shaping them so they experience lift rather than drag forces once they are rotating at speed. The Darrieus design has blades which resemble an egg-beater, which rotate at a speed higher than the wind speed. Further variants with straight vertical blades exhibit improved start-up torque but reduced efficiency.

Tides may be defined as the rise and fall of sea and river levels in a predictable manner. Tides cause the periodic movement of water into and out from a shore. Consequently, tide tables can be used for any given locale to fairly accurately predicted tide times and amplitude. Predictions are influenced by many factors including the alignment of the Sun and Moon, the phase and amplitude of the tide (pattern of tides in the deep ocean), the amphidromic systems of the oceans, and the shape of the coastline and near-shore bathymetry. The actual time and height of the tide is affected by wind and atmospheric pressure.

Therefore, tidal flow has the potential to provide an available and predictable source of fluid flow past a turbine blade for the generation of energy.

Tidal power may be generated by tidal barrages which exploit the potential energy in the difference in height between high and low tides. When the sea level rises and the tide begins to come in, the temporary increase in tidal power is channelled into a large basin behind a dam. With the receding tide, this energy is then converted into mechanical energy as the water is released through large turbines.

Tidal stream generators make use of the kinetic energy of moving water to power turbines, in a similar way to wind turbines that use the wind to power turbines. Some tidal generators can be built into the structures of existing bridges or are entirely submersed, thus avoiding concerns over aesthetics or visual impact. Land constrictions such as straits or inlets can create high velocities at specific sites, which can be captured using turbines. These turbines can be horizontal, vertical, open, or ducted.

Summary

It is an object of the present disclosure to create an improved turbine

In accordance with a first aspect of the disclosure there is provided a turbine comprising at least two blades and a turbine axis of rotation, wherein: each blade extending radially outwards from the turbine axis of rotation, wherein the blade comprises a first end at the axis of rotation a second end remote from the first end and a central recessed portion which is offset from the first end and second end; and a blade extension, attached to a surface of blade along at least part of its length, the blade extension being shaped to extend in a direction substantially parallel to the blade axis, wherein, the blade is moving with the direction of fluid motion and the blade extension is retracted to substantially within the profile of the blade when the blade is moving against the direction of fluid motion.

Preferably, the blade extension is biased to extend when the blade is moving about the axis with the direction of fluid flow and biased to retract when the blade is moving about the axis against the direction of fluid flow.

Preferably, the turbine blade is made from a thin flexible material.

Preferably, the turbine blade is made from a fabric.

Preferably, the turbine blade comprises one or more internal pocket.

Preferably, the internal pocket is sealable.

Preferably, the internal pocket is adapted to receive a filler material.

Preferably, the filler material controls the buoyancy of the device.

Preferably, the filler material is water.

Optionally, the filler material is air.

Optionally, the filler material is water and air.

Optionally, the filler material is ballast.

Optionally, the amount and composition of the filler may be altered to vary the buoyancy of the device. Optionally, the turbine comprises two blades.

Optionally, the turbine comprises three or more blades.

Optionally, the turbine blade is shaped as a Savonius turbine blade.

Preferably, the blade extension acts to increase the surface area of the turbine blade when the blade is with the direction of fluid motion to increase the force exerted on the blade by the fluid.

Preferably, the blade extension is made from a thin flexible material.

Preferably, the blade extension is made from a fabric.

Preferably, the turbine further comprises a power take-off device.

Preferably, the power take-off device comprises an electrical generator.

Preferably, the fluid is water.

Preferably, the fluid is tidal sea water.

Optionally, the turbine is coupled to a tether which is connected to the seabed.

Optionally, the turbine blades may be stacked on top of each other on the same tether.

Optionally, the turbines may be stacked on top of each other on the same shaft.

Preferably, the turbine is a vertical axis turbine.

Optionally, the blade comprises two straight pieces supported by an angle. Optionally, the angle is less than 180 degrees and more than 90 degrees.

In accordance with a second aspect of the disclosure there is provided a method of generating electricity using the turbine of the first aspect.

Brief Description of the Drawings

The present disclosure will be described by way of example only with reference to the accompanying drawings in which: figure 1 is a plan view of an embodiment of a turbine in accordance with the present disclosure; figure 2 is a perspective view of the embodiment shown in figure 1 ; figure 3 is a side view of the embodiment shown in figure 1 ; figure 4 is a perspective view of the embodiment shown in figure 1 ; figure 5 is another perspective view of the embodiment shown in figure 1 ; figure 6 is a schematic diagram of a second embodiment of the present disclosure; figure 7 is a schematic diagram of a third embodiment of the present disclosure; figure 8 is a front view of an embodiment of the present disclosure, in use; figure 9 is a front view of an embodiment of the present disclosure, in use; and figure 10 is a side view of an embodiment of the present disclosure, in use; Detailed Description of the Drawings

The present disclosure comprises a turbine which is designed to have a larger blade surface area when the blade is moving with the direction of fluid motion and a smaller blade surface area when the blade is moving against the direction of fluid motion.

The turbine as exemplified herein is of particular utility when the fluid is water and the flow of water is tidal. One reason is that tidal water flow is predictable and in one direction when the tide is coming in and in the opposite direction when the tide is going out.

In one example, the turbine is made from a fabric or textile material and filled with water and/or air to form the shape of a Savonius turbine with a plurality of blades or arms typically 2 or 3. The use of a flexible material such as a fabric allows for easy transportation and deployment of the turbine. In addition, when empty, the turbine can be more easily stored.

The fabrics which are used to make the turbine blades and extension can be chosen for the ease of recycling or re-purposing.

The turbine blades and/or blade extensions may be formed from a fluid- impermeable material. The fluid-impermeable material may comprise a plastics material. The plastics material may be flexible polyvinyl chloride (PVC). The fluid-impermeable material may be polyurethane coated fabric.

As is shown in the following examples, the blade extension is attached to a surface of blade along at least part of its length and in a direction substantially parallel to the blade axis. The blade extension acts to collect the fluid over a larger area than the blade alone. In at least one embodiment of the disclosure the blade extension acts like a parachute or sail to collect flow from a larger area that the blade alone, causing the blade turn with greater energy than if the turbine blade alone was deployed. In at least one embodiment, the blade extension comprises a membrane which expands or contracts with the flow of the water. This increases the size of the section that is open to the current to extract more energy from the flow while also decreasing the size of the closed section.

In at least one embodiment, the turbine is tethered to the seabed to keep its position. This tether may be a physical fitment into the sea bed, a weight or any combination of the two.

More than one tether may be used for individual turbines and the turbine may be tethered to a buoy on the surface instead, or in addition.

A generator is attached to the turbine and held steady by the tether so that rotation of the turbine generates electricity.

In at least one embodiment, the turbine blades contain pockets which may be filled with air and/or water. The ratio of air to water within the structure can be altered to attain the desired level of buoyancy. This mix can be changed to increase buoyancy and raise the turbine to the surface for repairs or the buoyancy can be reduced to lower its place in the current flow.

In at least one example, a number of turbines may be stacked on top of each other on the same tether to generate more power. In addition, the turbines may be placed in arrays to generate more power.

Figures 1 to 5 described below illustrate a first embodiment of the present disclosure. Figure 1 is a plan view, figure 2 a perspective view, figure 3 a side, figure 4 a perspective view and figure 5 another perspective view.

Figures 1 to 5 show a turbine 1 which comprises a first blade 3 and a second blade 5. The blades 3, 5 are attached to a blade axis of rotation 11 at a first end 13 and are shaped such that the central portion 17 is recessed with respect to the first end and the second, free end of the blade 15. In this example the blade has the well-known shape of a Savonius turbine. The blade extensions 7 and 9 are attached to a top surface of the blades 3 and 5 respectively. The blade extensions 7 and 9 are, in this example, identical and are shaped and coupled to the blades in order to bias the blade extension to extend and open when the blade is moving about the axis 11 with the direction of tidal water flow and biased to retract or close when the blade is moving about the axis 11 against the direction of tidal water flow. In a specific embodiment, the turbine 1 may be a fabric structure that is inflatable/fillable with water in order to form a Savonius turbine.

Figure 6 is a schematic diagram of a second embodiment of the present disclosure. Figure 6 shows a turbine 21 which comprises a first blade 23 and a second blade 25. The blades are attached to a blade axis of rotation 31 at a first end 33 and are shaped such that the central portion 37 is recessed with respect to the first end and the second, free end of the blade 35. In this example the blade comprises two straight pieces supported by an angle of around 160 degrees. The blade extensions 27 and 29 are attached to a top surface of the blades 23 and 25 respectively. The blade extensions 27 and 29 are shaped and coupled to the blades in order to bias the blade extension to extend and open when the blade is moving about the axis 31 with the direction of tidal water flow and biased to retract or close when the blade is moving about the axis 31 against the direction of tidal water flow.

Figure 7 is a schematic diagram of a third embodiment of the present disclosure. Figure 7 shows a turbine 41 which comprises a first blade 43, a second blade 45 and a third blade 53. The blades 43, 45, 53 are attached to the blade axis of rotation 55 at a first end 57 and are shaped such that the central portion 60 is recessed with respect to the first end 57 and the second, free end of the blade 59. In this example each blade comprises two straight pieces supported by an angle of around 160 degrees. The blade extensions 49, 51 and 53 are attached to a top surface of the blades 43, 45 and 47 respectively. The blade extensions 49, 51 and 53 are shaped and coupled to the blades in order to bias the blade extension to extend and open when the blade is moving about the axis 55 with the direction of tidal water flow and biased to retract or close when the blade is moving about the axis 55 against the direction of tidal water flow.

Figure 8 is a front view of an embodiment of the present disclosure, in use. It shows a turbine 61 which comprises a first blade 63 and a second blade 65. The blades are attached to the shaft 71 which is the blade axis of rotation. As with other embodiments, the blade is shaped such that the central portion is recessed with respect to the first end and the second, free end of the blade, this feature nor being shown in this view. The blade extensions 67 and 69 are shown such that blade extension 67 is extended because it is moving about the axis shaft 71 in the clockwise direction 73 with the direction of tidal water flow. Blade extension 69 is retracted because it is moving about the axis shaft 71 in the clockwise direction 73 against the direction of tidal water flow. Pockets 77 which contain a water/air mix are also shown. The ratio of air to water within the structure can be altered to attain the desired level of buoyancy. This mix can be changed to increase buoyancy and raise the turbine to the surface for repairs or the buoyancy can be reduced to lower its place in the current flow.

Figure 9 is a front view of an embodiment of the present disclosure, in use. The embodiment of figure 9 is similar to that of figure 8, except that the turbine blades 63, 65 and respective extensions 67, 69 are rotating anticlockwise 75 about the shaft 71 . The blade extensions 67 and 69 are shown such that blade extension 69 is extended because it is moving about the axis shaft 71 in the anticlockwise direction 75 with the direction of tidal water flow. Blade extension 67 is retracted because it is moving about the axis shaft 71 in the anticlockwise direction 75 against the direction of tidal water flow.

Figure 10 is a side view of an embodiment of the present disclosure, in use. It shows a turbine 81 , with a first blade 83, a second blade 85, blade extensions 87, 89 a shaft 91 and pockets 95. In addition, the tidal flow direction 93 is shown. Blade extension 87 is extended because it is moving about the axis shaft 91 in the direction of tidal water flow. Blade extension 89 is retracted because it is moving about the axis shaft 91 against the direction of tidal water flow.

The embodiments shown are connectable to a power take-off mechanism, typically a generator which converts the rotation of the shaft into electrical energy.

Improvements and modifications may be incorporated herein without deviating from the scope of the disclosure.