GB2487448A

GB2487448A - Hydro-kinetic Water Turbine Duct

Info

Publication number: GB2487448A
Application number: GB1117705.2A
Authority: GB
Inventors: Alan Saunders
Original assignee: Individual
Current assignee: Individual
Priority date: 2011-05-13
Filing date: 2011-10-13
Publication date: 2012-07-25
Anticipated expiration: 2031-10-13
Also published as: GB2487448B; GB201108027D0; GB2490729A; GB201117705D0

Abstract

A hydro-kinetic water turbine 1 for tidal rivers and shallow tidal areas houses a cross flow turbine 19 to drive a generator. The turbine is ducted 3 and may use two symmetrical converging ducts when used for reversing tidal flow. The assembly 1 is provided with non-moving disrupters (31 figures 3-4) that cause the average flow through the turbine 19 to be constant above a certain free stream flow rate. The ducts are radiused at entry and discharge and an external fairing is provided to optimise the acceleration achieved. Various means of installation are presented depending on the site conditions, including the use of floats where necessary. The turbine-generator module may be easily removable as a single subÂassembly. A mesh basket may be provided at the openings to prevent large fish and debris entering the turbine 19.

Description

A HYDRO-KINETIC TURBINE ASSEMBLY

AND A DUCT FOR SUCH AN ASSEMBLY

The present invention relates to a hydro-kinetic turbine assembly and a duct for such an assembly, and particularly but not exclusively relates to a turbine assembly for use in flowing water in rivers, estuaries or shallow tidal waters.

The use of hydro-turbine assemblies, which incorporate a turbine and an electricity generator, to extract energy from flowing water is well known. In the current climate of increasing renewable energy provision, it is generally noted that hydro-turbine assemblies lag behind the technology of other types of renewable energy source such as wind turbines for example. One of the reasons for this is that the wet environment in which the hydro-turbine assembly is installed is relatively harsh. The cost of installation per unit of electricity produced can therefore be relatively high.

Any hydro-turbine assembly used where the working flow rate varies requires a control system in order to maintain the correct rotational speed for the electrical generator, taking into account its capacity and the available energy in the flowing fluid. Control systems are either mechanical or electronic. Any mechanical system can be unreliable and tends to require a relatively high degree of maintenance especially where moving parts are immersed in water in use. Electronic control systems tend to be complex adding both cost and a higher likelihood of failure to the system.

In addition to flow control there is the problem of overcoming the practicalities of providing a turbine assembly suitable for use in flowing water in rivers, estuaries or shallow tidal waters.

GB 259558 A of Darrieus discloses a hydro-kinetic turbine assembly comprising a cross-flow turbine in a duct to optimise the fluid flow rate. However, no control system is disclosed, and control of such a turbine has been a problem for turbines US 2006008351 discloses a two bladed Darrieus turbine in a duct. Here the generator is connected to the turbine via a complex arrangement using a 90° gearbox to allow all machinery to be above the water. The speed control is achieved by using the generator as a brake, which has the disadvantage that during this period no electricity is generated.

EP 1430220 of Clean Current Power Systems describes a cylindrical duct used to generate a venturi effect of the water flow around an axial flow turbine.

The invention as defined in the appended claims uses a cross flow turbine rather than an axial turbine.

By cross flow turbine' we mean a turbine in which the flow of water is substantially perpendicular to the rotational axis of the turbine.

The water passes through the turbine transversely to the rotational axis, across the turbine blades. The turbine preferably consists of a blade or blades mounted on a shaft, the blade or blades being radially spaced from the shaft and extending substantially parallel thereto. Alternatively, the blades may extend between two end plates, a central shaft being omitted.

The turbine blade or blades are elongate and extend along the axis of rotation whilst being radially spaced therefrom, and may be generally straight with an aerofoil shaped profile, or may be twisted along their length to be of helical, or part helical, form.

The cross flow turbine is preferably of hydro-dynamic type, such as a Darrieus turbine for example, comprising a blade or blades arranged to rotate due to the difference in pressure between the faces of the blade(s).

According to a first aspect of the invention there is provided a hydro-kinetic turbine assembly comprising an elongate duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar walls, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, and an increasing cross section outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion of the duct comprising a fluid inlet defined by a leading edge extending circumferentially around the inlet portion, the leading edge being radiused, an intersection of the inlet portion with the reduced cross section mid portion being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending S circumferentially around the outlet portion, the trailing edge being radiused, the duct being housed within an exterior fairing of oblong transverse cross section defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duct comprising a turbine housing of oblong transverse cross section, a cross flow turbine being mounted in the turbine housing with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duct, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of detritus into the duct in use.

According to a second aspect of the invention there is provided an elongate hydro-kinetic turbine duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar walls, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, and an increasing cross section outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion of the duct comprising a fluid inlet defined by a leading edge extending circumferentially around the inlet portion, the leading edge being radiused, an intersection of the inlet portion with the reduced cross section mid portion being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending circumferentially around the outlet portion, the trailing edge being radiused, the duct comprising an exterior fairing of oblong transverse cross section defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duct comprising a turbine housing of oblong transverse cross section being adapted to mount a cross flow turbine with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duct, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of detritus into the duct in use.

According to a third aspect of the invention there is provided a turbine array comprising a plurality of the hydro-kinetic turbine assemblies of the first aspect of the invention.

S Other aspects of the present invention may include any combination of the features or limitations referred to herein.

The present invention may be carried into practice in various ways, but embodiments will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a perspective view from the front and one side of a hydro-kinetic turbine assembly in accordance with the present invention; Figure 2 is a perspective view from the front, one side and above of the hydro-kinetic turbine assembly of Figure 1; Figure 3 is a sectional side view of a duct of the turbine assembly of Figures 1 and 2; Figure 4 is a sectional side view of the turbine assembly of Figures 1 to 3; Figure 5 is an enlarged sectional side view of a duct of the turbine assembly of Figures 1 to 4; Figure 6 is an end view of a modified turbine assembly in accordance with the present invention; Figure 7 is a sectional side view of a further modified turbine assembly in accordance with the present invention; Figures 8a to 8e are end views of a turbine assembly in accordance with the present invention on various different mounting structures; FIgure 9 is a graph showing a relationship between the radius of part of a duct of a hydro-kinetic turbine assemble, and the performance of a turbine mounted in the duct; and FIgure 10 is an end view of another turbine assembly in accordance with the present invention.

Referring to Figures 1 to 4 a hydro-kinetic turbine assembly 1 comprises an elongate duct 3 housed within an exterior cuboidal fairing 5 of oblong transverse cross section, the fairing 5 being defined by four orthogonal planar fairing walls 7.

The duct 3 is defined by two opposed parallel, planar duct walls 9, and two opposed varying profile duct walls 11. The non planar duct walls 11 comprise a first pair of opposed, non parallel, sub walls 1 1A arranged to define a reducing cross section inlet portion 13 where the sub walls 1 1A converge into a reduced cross section mid portion 15 defined by a second pair of opposed, parallel sub walls 1 lB that are relatively close together. A third pair of opposed, non-parallel, sub walls 1 1C are arranged to define an increasing cross section outlet portion 17 where the non-planar sub walls 11 C diverge from the mid portion 15. The duct 3 is thus of elongate form extending from front to back of the turbine 1 and is of varying oblong transverse cross section along its length. That is, the duct 3 is oblong along its entire length, but the size of the oblong changes along the duct's length.

The sub walls 1 1A, 11 C may each be substantially planar, as per the example of Figures 3 and 4, or curved as per the example of Figures 1 and 2.

The mid portion 15 of the duct 3 functions as a turbine housing in which a cross-flow turbine 19 is mounted, with the rotational axis 21 of the turbine 19 extending transversely across the duct between the opposed planar walls 9 of the duct 3. In the example illustrated the rotational axis 21 is horizontal with the opposed planar faces 9 vertical. However, the turbine 1 may equally well be used in any other orientation, such as with the turbine rotational axis 21 vertical for example.

The cross flow turbine 19 in the illustrated example comprises a Darrieus type turbine comprising a plurality of turbine blades 23 spaced along the longitudinal axis 21, each blade being radially spaced from the axis 21 and being substantially straight and parallel to the axis 21, with an aerofoil shaped cross section. Any number, type or form of blades 23 could alternatively be used and indeed a plurality of blades could be used that are radially spaced from the axis 21 and extend from one end of the S turbine 19 to another.

The turbine 19 is connected to a suitable electricity generator (not shown) driven by rotation of the turbine 19 in use. The generator could be directly mounted on the end of the turbine shaft, or have its axis parallel to the turbine shaft but spaced from it.

Joining the turbine and generator shafts may be via a device that incorporates a speed increaser if required.

The inlet portion 13 of the duct 3 comprises an inlet 1 3A defined by a circumferential leading edge 25 extending around the inlet portion 13 and comprising the front margins of the walls 9, 11 of the duct 3. This leading edge 25 is radiused RL.

Likewise the outlet portion 17 of the duct 3 comprises an outlet 17A defined by a circumferential trailing edge 27 extending around the outlet portion 17 and which is radiused Rr. Finally, the intersections 29, 31 between the inlet portion 1 3 and the mid portion 15, and between the outlet portion 17 and the mid portion 15, are also radiused R1 The radii RL, R1 and R1 are determined according to the overall dimensions of the duct 3 and in particular the cross sectional area of the inlet portion 13 and outlet portion 17 at their largest, the length of the duct 3 between the leading and trailing edges 25, 27, the distance D between the leading and trailing edges 25, 27 and the turbine 19, and the volume of the duct 3. The radii RL, R and R1 are determined in order to maximise the overall efficiency of the turbine assembly 1, the efficiency being the ratio of the water speeds divided by the ratio of the geometric cross sectional areas of the duct 3. It is a measure of how good the duct 3 is at accelerating the water. Referring additionally to the graph of Figure 9, the relationship between duct efficiency, or coefficient of performance, and the Radii RL, R is shown.

As an example only, for a turbine assembly 2.Sm tall, 3.Om wide and 5.Sm long, an optimum RL, Rr is 0.1 Sm, with R1 being equal to the distance between the second pair of opposed parallel sub walls 11B of Figure 3.

The duct 3 is thus designed so that it causes the water flow to alter its characteristics above a certain inlet fluid flow rate. The key part of the fluid flow is where it enters the part of the duct 3 having the smallest cross sectional area, that is, the mid portion 15, where the turbine 19 is situated. The ideal flow would be in streamlines parallel to each other without eddies or reverse flows or other disruptions of any kind.

This is achieved by first increasing the velocity at which the flow changes characteristic by incorporating the radius R1 at the joint between the converging inlet portion 13 and the parallel mid portion 15 housing the turbine 19.

In a classical venturi a "vena contracta" is incorporated in the flow so that the performance of the venturi is predictable. However, to ensure this, the included angle of the contraction of the duct is limited, typically to about 22 degrees or so, and the discharging duct has to have a very shallow angle indeed, typically 7 degrees. As a result a classical venturi is typically relatively long.

Incorporating the radius B.1 increases the velocity at which the flow comes away from the duct walls and becomes disrupted. The angle of the walls of the inlet portion 13 of the duct 3 can then be increased so that at the chosen fluid flow rate the fluid becomes disrupted, with the result that the average flow rate through the duct 3 remains the same.

It has been discovered that for the rates of flow likely to be encountered in average tidal rivers that this effect takes place where the ratio of the hydraulic diameter H of the inlet portion 13 to the hydraulic diameter h of the mid portion 15 housing the turbine 19 is greater than 1.6, and the ratio of the orthogonal distance D between these areas to the hydraulic diameter h of the mid portion 15 housing the turbine is less than 1.8. This can give an acceleration of the stream fluid flow to the mid portion 15 housing the turbine 19 of about two.

Mesh grids 29, or any equivalent detritus bathe; cover each end of the duct 3 to resist the ingress of detritus into the duct 3.

In use, with the duct 3 submerged in a body of water with the leading edge 25 facing the direction of flow, water flows into the inlet portion 13, over the blades 23 the turbine 19, and out of the duct 3 via the outlet portion 17, the water flow driving rotation of the turbine 19. If the direction of water flow reverses, the water flow can enter the duct 3 via outlet portion 17 to maintain the rotation of the turbine 19.

The radii RL, R and R1 the converging inlet portion 13 to the turbine 19, and the fairing S around the duct 3, improve the acceleration of the water into the turbine duct 3. It has been discovered that the use of the correct radii improves the overall efficiency of the unit, increasing the acceleration of the water. The use of the fairing S improves the fluid flow and helps prevent backflows and eddying as these reduce the acceleration of the water achieved by the duct 3. The fairing S also allows the angle of the converging and diverging inlet and outlet portions 13, 17 to be maximised which allows the maximum acceleration to be achieved for a given size of turbine assembly 1.

A duct 3 of oblong (square or rectangular) transverse cross section maximises the cross sectional area open to the incoming water flow.

Having two of the walls 9 of the duct 3 as parallel, planar walls reduces the cost of tooling and manufacture of the turbine 1, and makes the heavier components easier to assemble.

A Darricus type cross flow turbine is preferred because its efficiency is about twice that of other types of cross flow turbine that could be suitable for this application.

With additional reference to Figure 5, the fluid flow can be further controlled because the turbine 19, generator (and associated housing) are mounted in the central, narrow, mid portion 15 of the duct 3 so that it may be removed easily for maintenance. By the nature of the duct design in conjunction with a removable turbine there is a disrupter in the form of a slot 30, gap or step 32 around the joint between the turbine 19 and duct 3. This will have little effect when the fluid flow rate is low, but will be more disruptive as the flow rate increases. Arrows 30A, 32A illustrate the diverting of fluid streamlines caused by the slot 30 and step 32. Any combination of slot(s) and step(s) can be used as required.

With additional reference to Figure 6, the fluid flow can also be controlled using disrupters 3 1 in the form of hydrodynamic spoilers, designed to have little effect when the flow rate is low but to become more disruptive as the flow rate increases. These spoilers may be finger-like projections projecting into the fluid flow from the duct walls 9, 11. These disrupters 3 1 may cross the duct 3 entirely, rather like a large mesh. They may have an aerofoil section, or deliberately have sharp edges in order to disrupt the flow. The exact number and design of the disrupters 31 depends on the fluid flow velocities that are being targeted in the particular design.

If the duct 3 is intended for use in water flowing in one direction, then, with reference to Figure 7, the sub walls 11 C of the diverging outlet portion 17 may diverge at a greater angle than the angle of the sub walls hA of the converging inlet portion 13, in order to optimise the accelerating effort. In a reversing tidal flow, the duct 3 should be symmetrical.

With additional reference to Figures 8a-8e, the turbine assembly 1 can be installed using one of many different techniques which will depend on the details of the particular site.

For example, cantilevered brackets 33 may be fixed to a steel or concrete river wall, bridge stanchion or similar upon which the turbine assembly 1 is mounted. The height of the brackets 33 would be such that the turbine assembly 1 is underwater at all states of all tides when a significant flow is running to ensure that the maximum amount of energy is captured.

Alternatively, the turbine assembly 1 may be constrained by rings 35, or similar, around spaced apart posts 39 to allow vertical movement up and down with the tide without any lateral movement which could both disrupt the flow of water into the turbine assembly 1 and cause damage to it and/or its surroundings if it was impacting on, as an example, a pontoon. The posts 39 may be on both sides of the turbine assembly 1 as shown, or on one side only.

The turbine assembly 1 may be mounted so as to be constrained between upright constraints external to the turbine assembly 1, such as, for example, right-angled posts (for example of L' shaped cross section) 41 at each corner which will allow the turbine assembly 1 to rise and fall but prevent lateral movement.

If the turbine assembly 1 is constrained to move vertically with the tide then it could be fitted with a float or floats (not shown) which would ensure that it does indeed rise and fall with the tide but keeps the inlet portion 13 of the duct 3 under water at all times. Typically the top of the inlet portion 13 of the duct 3 would be 0.5m below the S surface of the water. Similarly, the turbine assembly 1 could be mounted beneath a pontoon or similar structure which itself floats up and down with the tide.

The turbine assembly 1 could be mounted on legs or a stand 43 which is itself fixed to the river or sea bed. The legs or stand 43 may comprise feet of relatively large surface area to resist the legs or stand 43 sinking into the river or sea bed. The legs or stand 43 serve to space the underside of the outer fairing 5 from the river or sea bed.

This serves to prevent any suction effect preventing the turbine assembly 1 from refloating as the tide rises, and also serves to prevent any debris being moved along the river or sea bed by the water flow from entering the duct 3. This also prevents any bottom feeding fish or eels from sheltering inside the duct 3 which would give risk of damage to them when the turbine restarts.

Other installation methods include the use of mooring lines to a pontoon, wharf or dock wall or to pier or bridge legs.

In addition the turbine assembly 1 could be fixed to a mooring weight 45, or equivalent, and allowed to turn with the tide, or between mooring weights or buoys or equivalent to prevent turning with the tide.

A turbine assembly 1 of this type could also be fitted to, or under, a raft or other boat or floating apparatus which could then be moored using conventional methods.

The nature of the design also allows the turbine assembly 1 to be fixed together laterally in a "fence" and then installed across waterways, or partially across waterways, for example under bridges or from a river wall out to a pontoon. The turbine assemblies 1 may be installed in a string spaced out appropriately according to local conditions.

In order to simplify the design, reduce costs and improve reliability the turbine bearings, when situated under water, are to be lubricated by that water which flows through or around the machine. Materials are available that will give a good life time if the components are designed and manufactured to the state-of-the-art by those skilled in the practice.

For the same set of reasons the turbine 19 and generator can be mounted on the same shaft.

The hydro-kinetic turbine assembly 1 may be manufactured from at least one of a rotationally moulded polymer, fibre reinforced concrete (GRC or FRC), and fibre reinforced polymer (GRP or FRP), and may optionally comprise an integrally incorporated float.

With reference to Figure 10, the turbine assembly 1, and the duct 3, may be of any oblong transverse cross section including rectangular for example.

Hydro-turbines can suffer from fouling by marine organisms. If internal to the duct fouling will reduce the fluid flow velocity thereby reducing the power extracted from the fluid. If the fouling is on the turbine itself it will reduce the efficiency by a relatively large amount. Conventional methods would include painting the duct with a poisonous anti-foul paint such as that used on most marine craft. This would require annual maintenance and does put some poison into the local marine environment, which is undesirable. Another option is to use a copper based paint which appears to have a longer life, probably of the order of 10 years. This too, works by poisoning the organisms, but is kinder to the environment. Other options are becoming available, but to date have not been used in turbine assemblies 1 as described above but only on marine craft for which they have been invented and are being commercialised. These include the use of ultrasonic frequencies, seawater electrolysis and the use of a naturally occurring microscopic fungus called streptomyces avermitilis' that exists in some large fish and prevents small organisms such as barnacles from adhering to the surface. These three latter options are preferred for use in these turbine assemblies 1.

The first two of these require a small electrical current in order to operate. This can be derived from the generator output.

The duct 3 could be damaged if large objects such as tree branches, weed, bundles of fishing line and other river debris entered the duct and went into the turbine. Thus the turbine assembly 1 comprises a mesh basket that projects from the inlet area having sides as well as a frontal area so that it is unlikely to get blocked up, and in any case when the tidal flow reverses the revised flow direction will clear the mesh basket of any debris. The mesh will also have the effect of preventing any swimmers or other S river users from getting injured due to the rotating parts of the turbine.

It is essential that fish are protected and a combination of an inlet mesh and a gap between the turbine and the housing slightly larger than the mesh size to allow free passage of those fish that are smaller than the mesh size will ensure the minimum amount of damage. Others have in any event reported that fish are not drawn towards a rotating Darrieus turbine but turn away from it.

The duct 3 may be subject to the ingress of small amounts of weed, fishing line and light rope despite the mesh baskets fitted. Thus it may incorporate rope cutters between the end plates of the turbine and the turbine housing. These are typically stainless steel protuberances or fixed stainless steel blocks or folded steel sheet fixed to both the end plates of the turbine and the turbine housing such that as the turbine rotates these cutters pass each other at an angle neither orthogonal or parallel and the clearance between them is of the order of 0.5 mm or so. Any weed or similar caught in this area will be chopped and then pass harmlessly through the machine.

The turbine assembly 1 described above comprises a ducted turbine suitable for use in rivers, both rural and urban, harbours and other man-made areas as well as shallow off-shore tidal areas. In such areas it is common for the water flow to be disrupted by either natural or man-made objects in the water. These would include trees, rocks, pontoons, bridge piers, water craft, etc. By using a ducted turbine, it is possible to control and straighten the fluid streamlines, making the assembly 1 more efficient than an open turbine. In addition by designing the duct inlet and discharge correctly the duct 3 can accelerate the water from the average free-stream velocity to a higher velocity, perhaps up to two times. As the power extracted by the turbine is proportional to the cube of the water flow, a much smaller turbine (of lower cost) can be used. In addition it will rotate faster than a turbine of a larger diameter such that any generator or speed increasing device can be reduced in size and also be lighter weight and lower cost. By nature of being ducted, grids or a mesh across the ends of the duct 3 in order to prevent the entry of foreign objects such as large fish and debris of the various types that are encountered in rivers, particularly in the urban environment, and even human beings.

The turbine assembly 1 is appropriate for both rivers where the water is running in one direction only and for tidal, i.e. reversing flows. Generally the former will generate about three times the amount of electricity compared to the latter. Thus there is a greater need for a tidal turbine to be efficient in order to make it cost effective. Any tidal turbine has to cope with a varying velocity of water from zero at the turn of the tide to a maximum midway between the extremes of the tidal levels. In addition tidal heights vary from a minimum at neap tides to a maximum at spring tides. The turbine and generator could be sized to cope with the maximum velocity and hence maximum power. However, this is only required for about an hour once every two weeks, whilst for the rest of the time the velocity and power is substantially less. As is well known, for a fluid turbine, the power is related to the fluid velocity by the cubic power. Thus for a typical tidal flow where the spring tidal flow rate may be twice that of the neap tidal flow the power could be eight times larger. In order to capture the energy at a reasonable cost the turbine and generator have to be sized to be smaller than the peak flow and power, but large enough to give enough power to pay back the investment in the device.

Claims

CLAIMS1. A hydro-kinetic turbine assembly comprising an elongate duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar walls, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, the varying profile walls further defining an increasing cross section outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion of the duct comprising a fluid inlet defined by a leading edge extending circumferentially around the inlet portion, the leading edge being radiused, an intersection of both the inlet and outlet portions with the reduced cross section mid portion each being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending circumferentially around the outlet portion, the trailing edge being radiused, the duct being housed within an exterior fairing of oblong transverse cross section defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duct defining a turbine housing of oblong transverse cross section, a cross flow turbine being mounted in the turbine housing with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duct, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of foreign objects into the duct in use.
2. The hydro-kinetic turbine assembly of claim 1 wherein the duct comprises power limiting means having no moving parts and being located at the inlet portion, and operative, in use in flowing water, to cause the average water speed to remain substantially constant once the water speed is above a predetermined level.
3. The hydro-kinetic turbine assembly of claim 2 wherein, the power limiting means comprises a disrupter in the duct at or adjacent the turbine housing.
4. The hydro-kinetic turbine assembly of claim 3 wherein the disrupter comprises at least one of a slot, a gap or a step where the duct walls meet the turbine.
5. The hydro-kinetic turbine assembly of claim 3 or claim 4 wherein the disrupter is located at a position at the inlet portion or outlet portion, adjacent the turbine housing.
6. The hydro-kinetic turbine assembly of any one of claims 3 to 5 wherein the disrupter comprises a projection projecting into the interior of the duct.
7. The hydro-kinetic turbine assembly of claim 6 wherein the projection projects entirely across the duct.
8. The hydro-kinetic turbine assembly of claim 6 wherein the projection projects only partially across the duct.
9. The hydro-kinetic turbine assembly of any one of the preceding claims wherein the ratio of the hydraulic diameter of the inlet of the inlet portion to the hydraulic diameter of the turbine housing is greater than or equal to 1.6, and the ratio of the orthogonal distance there between to the hydraulic diameter of the turbine housing is less than or equal to 1.8.
10. The hydro-kinetic turbine assembly of any one of the preceding claims wherein the inlet and outlet portions of the duct are symmetrical to allow the turbine assembly to be fixed in orientation whilst in a reversing tidal flow.
11. The hydro-kinetic turbine assembly of any one of claims 1 to 9 wherein the inlet and outlet portions of the duct are asymmetrical.
12. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising a mounting bracket operative to mount the turbine assembly to a fixed structure such as a dock wall, pier leg or equivalent such that at least the turbine housing is underwater at all states of the tide.
13. The hydro-kinetic turbine assembly of claim 12 wherein the turbine assembly and bracket are arranged to constrain the turbine assembly to move in a vertical direction only, the turbine assembly being provided with at least one float to ensure that the duct operates below the water surface by a fixed amount.
14. The hydro-kinetic turbine assembly of claim 12 or claim 13 wherein the bracket comprises at least one leg operative to support the duct on a river or sea bed or the like.
15. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising at least one mooring lines adapted to connect the turbine assembly to a fixed structure.
16. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising a mooring weight.
17. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising wherein the turbine and generator comprise a module removably mounted in the duct, the module being secured to the duct by a fixing, a part of the fixing that is arranged to be manipulated in order to release the module being arranged to be above water level in use.
18. The hydro-kinetic turbine assembly of claim 17 wherein at least one of the turbine and the generator module comprises water lubricated bearings.
19. The hydro-kinetic turbine assembly of claim 17 or claim 18 wherein the turbine and generator are mounted on the same shaft.
20. The hydro-kinetic turbine assembly of any one of the preceding claims wherein an ultrasonic device is provided to prevent fouling by marine growth, the device taking its operating electrical current as a by-product of the generator.
21. The hydro-kinetic turbine assembly of any one of the preceding claims wherein a seawater electrolysis device is provided to prevent fouling by marine growth, the electrolysis device taking its operating electrical current as a by-product of the generator.
22. The hydro-kinetic turbine assembly of any one of the preceding claims comprising a paint finish incorporating a microscopic fungus called streptomyces avermitilis' to prevent fouling by marine growth.
23. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising at least one float arranged such that, in use, the duct is always beneath the water level.
24. The hydro-kinetic turbine assembly of any one of the preceding claims manufactured from at least one of a rotationally moulded polymer, fibre reinforced concrete (GRC or FRC), and fibre reinforced polymer (GRP or FRP), and integrally incorporating a float.
25. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising rope cutters between the turbine and the duct to cut debris such as weed, fishing line and light rope that may have entered the duct and which would otherwise prevent the turbine from rotating.
26. An elongate hydro-kinetic turbine duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar walls, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, and an increasing cross section outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion of the duct comprising a fluid inlet defined by a leading edge extending circumferentially around the inlet portion, the leading edge being radiused, an intersection of the inlet portion with the reduced cross section mid portion being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending circumferentially around the outlet portion, the trailing edge being radiused, the duct comprising an exterior fairing of oblong transverse cross section defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duct comprising a turbine housing of oblong transverse cross section being adapted to mount a cross flow turbine with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duct, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of detritus into the duct in use.
27. A plurality of hydro-kinetic turbine assemblies of any one of claims 1 to 25 fixed laterally together to form a fence.
28. A hydro-kinetie turbine assembly substantially as described herein and as shown in Figures 1 to 4.Amendments to the claims have been filed as follows:CLAIMS1. A hydro-kinetic turbine assembly comprising an eEongate duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar wails, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, the varying profile walls further defining an increasing cross section outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion of the duet comprising a fluid inlet defined by a leading edge extending eireumferentially around the inlet portion, the leading edge being radiused, an intersection of both the inlet and outlet portions with the reduced cross section mid portion each being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending eireumferentially around the outlet portion, the trailing edge being radiused, the duct being housed within an exterior fairing of oblong transverse cross section r defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duet defining a turbine housing of oblong transverse cross section, a cross flow o turbine being mounted in the turbine housing with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duet, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of foreign objects into the duet in use, and wherein the duet comprises power limiting means having no moving parts and being located at the inlet portion, and operative, in use in flowing water, to cause the average water speed to remain substantially constant once the water speed is above a predetermined level.2, The hydro-kinetie turbine assembly of claim 1 wherein, the power limiting means comprises a disrupter in the duet at or adjacent the turbine housing.3. The hydro-kinetie turbine assembly of claim 2 wherein the disrupter comprises at least one of a slot, a gap or a step where the duet walls meet the turbine.4. The hydro-kinetie turbine assembly of claim 2 or claim 3 wherein the disrupter is located at a position at the inlet portion or outlet portion, adjacent the turbine housing.5. The hydrokinetic turbine assembly of any one of claims 2 to 4 wherein the disrupter comprises a projection projecting into the interior of the duct.6. The hydro-kinetic turbine assembly of claim 5 wherein the projection projects entirely across the duct.7. The hydro-kinetic turbine assembly of claim 5 wherein the projection projects only partially across the duct.8. The hydro-kinetic turbine assembly of any one of the preceding claims wherein the ratio of the hydraulic diameter of the inlet of the inlet portion to the hydraulic diameter of the turbine housing is greater than or equal to 1.6, and the ratio of the orthogonal distance there between to the hydraulic diameter of the turbine housing is less than or equal to 1.8.r 9. The hydro-kinctic turbine assembly of any one of the preceding claims wherein the inlet and outlet portions of the duct arc symmetrical to allow the turbine assembly o to be fixed in orientation whilst in a reversing tidal flow.10. The hydro-kinetic turbine assembly of any one of claims 1 to 8 wherein the inlet and outlet portions of the duct are asymmetrical.11. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising a mounting bracket operative to mount the turbine assembly to a fixed structure such as a dock wall, pier leg or equivalent such that at least the turbine housing is underwater at all states of the tide.12. The hydro-kinetic turbine assembly of claim 11 wherein the turbine assembly and bracket arc arranged to constrain the turbine assembly to move in a vertical direction only, the turbine assembly being provided with at least one float to ensure that the duct operates below the water surface by a fixed amount.13. The hydro-kinetic turbine assembly of claim 11 or claim 12 wherein the bracket comprises at least one leg operative to support the duct on a river or sea bed or the like.14. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising at least one mooring lines adapted to connect the turbine assembly to a fixed structure.15. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising a mooring weight.16. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising wherein the turbine and generator comprise a module removably mounted in the duct, the module being secured to the duct by a fixing, a part of the fixing that is arranged to be manipulated in order to release the module being arranged to be above water level in use.17. The hydro-kinetic turbine assembly of claim 16 wherein at least one of the turbine and the generator module comprises water lubricated bearings.18. The hydro-kinetic turbine assembly of claim 16 or claim 17 wherein the turbine o and generator are mounted on the same shaft.19. The hydro-kinetic turbine assembly of any one of the preceding claims wherein an ultrasonic device is provided to prevent fouling by marine growth, the device taking its operating electrical current as a by-product of the generator.20. The hydro-kinetie turbine assembly of any one of the preceding claims wherein a seawater electrolysis device is provided to prevent fouling by marine growth, the electrolysis device taking its operating electrical current as a by-product of the generator.21. The hydro-kinetic turbine assembly of any one of the preceding claims comprising a paint finish incorporating a microscopic fungus called streptomyees avermitilis' to prevent fouling by marine growth.22. The hydro-kinetie turbine assembly of any one of the preceding claims further comprising at least one float arranged such that, in use, the duet is always beneath the water level.23. The hydro-kinetic turbine assembly of any one of the preceding claims manufactured from at least one of a rotationally moulded polymer, fibre reinforced concrete (GRC or FRC), and fibre reinforced polymer (GRP or FRP), and integrally incorporating a float.24. The hydro-kinetic turbine assembly of any one of the preceding claims further comprising rope cutters between the turbine and the duct to cut debris such as weed, fishing line and light rope that may have entered the duct and which would otherwise prevent the turbine from rotating.25. An elongate hydro-kinetic turbine duct of oblong transverse cross section, the duct being defined by two opposed parallel, planar walls, and two opposed varying profile walls arranged to define a reducing cross section inlet portion where the varying profile walls converge into a reduced cross section mid portion where the varying profile walls are relatively close together, and an increasing cross section r outlet portion where the varying profile walls diverge from the mid portion, the duct thus being of varying oblong transverse cross section along its length, the inlet portion o of the duct comprising a fluid inlet defined by a leading edge extending circumfcrentially around the inlet portion, the leading edge being radiused, an intersection of the inlet portion with the reduced cross section mid portion being radiused, the outlet portion of the duct comprising a fluid outlet defined by a trailing edge extending circumfcrentially around the outlet portion, the trailing edge being radiuscd, the duct comprising an exterior fairing of oblong transverse cross section defined by four orthogonal planar fairing walls, the reduced cross section mid portion of the duct comprising a turbine housing of oblong transverse cross section being adapted to mount a cross flow turbine with the rotational axis of the cross flow turbine extending between the two opposed parallel planar walls of the duct, a respective mesh barrier being positioned at the inlet portion and at the outlet portion to resist the ingress of detritus into the duct in usc, wherein the duct comprises power limiting means having no moving parts and being located at the inlet portion, and operative, in use in flowing water, to cause the average water speed to remain substantially constant once the water speed is above a predetermined level..26. A plurality of hydro-kinetic turbine assemblies of any one of claims 1 to 24 fixed laterally together to form a fence.27. A hydro-kinetic turbine assembly substantially as described herein and as shown in Figures ito 4. c\J rLU r