GB1563337A

GB1563337A - Water-driven turbines

Info

Publication number: GB1563337A
Application number: GB32943/76A
Authority: GB
Original assignee: MOUTON W
Current assignee: MOUTON W
Priority date: 1975-10-15
Filing date: 1976-08-06
Publication date: 1980-03-26
Also published as: FR2360768A1; AU1668176A; NL7608634A; DE2635529A1; BE844971A; FR2360768B3

Description

(54) IMPROVEMENTS IN WATER-DRIVEN TURBINES (71) We, WILLIAM JOSEPH MOUTON, JR., of PO BOX 1075, New Orleans, Louisiana, 70181, United States of America, and DAVID FREEMONT THOMPSON, of 741 14th Avenue, Prospect Park, Pennsylvania, 19070, United States of America, both citizens of the United States of America, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed to be particularly described in and by the following statement:- This invention relates to a turbine adapted to be driven by a current of water, and has particular but not exclusive application to the generation of electrical power by means of river currents.

Power plants driven by river water stored by dams are well known, and where dams can be used and where a good supply of water is available, such power plants can be highly efficient, and are used throughout the world for the generation of electrical power.

There are many situations, however, where damming of the flowing water is prohibitively expensive, is impossible because of soil conditions, is impossible because of geographic conditions, or is impracticable because of navigational needs for the flowing water. Many efforts were made in the late 1800's and early 1900's to harness the flowing currents of rivers without using dams by attempting to recover kinetic energy from moving currents of river water, and to convert this energy to some other more useful form, by driving an electrical generator.

A study of this old art of river current driven motors reveals that they were all devised on the basis of a poor understanding of hydrodynamics and an apparent false premise that a river current driven motor can remove kinetic energy from the water and yet have the water proceed in the current without loss of velocity through ther motor. What actually happened upon introduction of a prior art river current driven motor into a stream, was that the motor acted as an obstruction to the flow of the stream, and the obstruction resulted in a build-up of pressure upstream of the motor.

As a consequence, part of the river flow that should flow through the motor, flowed instead around the motor. Since the path for flow of the water around the motor was not much longer nor more tortuous than the path through the motor, only a small fraction of the desired stream of water was passed through the motor; and this stream was moving more slowly than the main stream. Accordingly, little of the river's energy was extracted, and the prior art river current motors were extremely inefficient.

Little attention had been given in these prior art devices to obtaining smooth flow with least possible friction and turbulence from the mainstream, into the water wheel, and back into the mainstream. The turbines shown were highly inefficient, and many versions used ineffective screws or multiple wheels closely following one another; no attention was given to improving the downstream environment to ease the reentrance of the portion of the current from which energy was supposed to have been extracted.

The turbine of the present invention is adapted to be driven by a current of water and utilises a novel premise that in order to remove kinetic energy from a moving mass of water by means of a turbine without thereby reducing the mass rate of flow, it is necessary to provide downstream of the turbine's wheel, a region into which the water emanating from the turbine's wheel is impelled to move, and simultaneously, that the mainstream of water is impelled to move away from this region.

The present invention provides a turbine for being driven by a current of water, comprising a generally tubular nozzle with an internal water passageway in which a turbine wheel is mounted so as to be rotated by water passing through the passageway to a discharge end thereof upon the turbine being immersed in said current, the passageway having a gradually increasing cross section from the turbine wheel to the discharge end, and the exterior of the nozzle being of such a shape as to cooperate with the current to produce a diverging conical sheath of water, which sheath surrounds water emanating from said discharge end of the nozzle.

Thus, turbines in accordance with the invention utilise not only the energy in that portion of the river that actually passes through the turbine wheel, but also utilises part of the energy of the mainstream of the current to prepare a favourable downstream region for discharge of the portion of the current emanating from the turbine wheel.

One form of turbine of the invention is made up of a primary nozzle which in use has longitudinal horizontal axis and is immersed in a river current with its axis parallel to the river current direction, for collecting a portion of the river current from the mainstream of said current, the said primary nozzle having in sequence along its axis an entrance end connected to a through-going waterway, leading to a throat and then through a tailpiece to a discharge end, and coaxially supporting within the throat an axial-entrance turbine wheel to which is connected means for transferring mechanical rotational energy to external utilization means, the waterway being flared from the throat to the discharge end to initiate and establish a gradually increasing cross section of the collected portion of said river current from the time is passes said turbine wheel, and the exterior of said primary nozzle being so shaped to initiate and establish the formation of a diverging conical sheath of mainstream river current around the said collected portion as said portion discharges from the discharge end of said primary nozzle.

In one preferred form, the turbine wheel carries at its periphery a shroud ring, the throat of the waterway has a cooperating annular recess. receiving the shroud ring, and the inner diametrical surface of the shroud ring is an extension of the inner surface of the throat of the waterway.

In a preferred form of turbine of the invention, a debris screen is provided in the river upstream of the entrance end of the primary nozzle, the debris screen comprising a conical array of cables on a horizontal axis, the tip of the cone being attached to an upstream anchor cable and the base of the cone forming an open end of at least as large a cross section as the entrance end of the primary nozzle, to which the said open end is juxtaposed and attached.For minimum flow resistance, the included angle within the cone is preferably about 30". The waterway within the primary nozzle converges smoothly from an initial cross section at the mouth or entrance end to a smaller cross section at the throat, whereby the velocity of the portion of the river current intercepted by the nozzle is accelerated before impingement upon the turbine wheel blades, and the efficiency of energy transfer thereby increased. The area ratio for the said cross sections may be in the range of 2:1 to 4:1.

In one form, the turbine wheel is of the purely axial flow type, and the tail piece of the waterway downstream from the turbine wheel flares at an included angle of up to 15%, preferably about 7". With this form, the tail piece may have an axial length of at least one half of the diameter of the throat of the waterway.

The exterior of the primary nozzle is flared and structured with mechanical elements to promote the flow of a diverging conical sheath of mainstream water adjacent to and surrounding the collected portion as that portion discharges from the discharge end of the primary nozzle.

Thereby an environment is provided in the mainstream into which the collected portion is discharging, such that the collected portion can flow away under the impulse of its remaining static head pressure and remaining velocity head. Preferably, the mainstream sheath is formed and directed, and its total energy content so re-organized as to aid the flowing away of the collected portion.

To this end, the nozzle exterior may begin to flare outwardly in the water flow direction, at an angle as large as will be possible considering that the exterior surface should meet at the discharge end of the waterway with the waterway passage in a well faired thin trailing edge.

Also, structural elements can be added to the exterior surface to effect further the desired sheath formation. One such structural element is a vane, or set of vanes, extending radially outward from the surface of the primary nozzle, each such vane having a helically bent or tilted trailing edge. The trailing edge bend or tilt is for the purpose of initiating a rotational impulse in the sheath whereby the sheath develops motion, and a corresponding radially outward pressure gradient. The motion is as a helical sheath. The pressure gradient is distinctly helpful in aiding the discharge of the collected portion of the river current. Another such structural element, which may conveniently be supported on the outer extremities of the vanes just mentioned, is a coaxial secondary nozzle of inside dimensions such as to fit around the exterior surface of the primary nozzle, with clearance between the secondary and primary nozzles forming an annular passageway for the flow of mainstream water past the exterior surface of the primary nozzle. By providing more clearance at the front or entrance end of the annular passageway than at the back or discharge end, the water picked up at the front is accelerated and discharged at higher velocity, and lower pressure, in which condition the sheath formed is particularly effective in entraining and thereby aiding in the discharge of the collected portion of the river current.

Moreover, both the interior and the exterior surfaces of the secondary nozzle can be flared in the region near the trailing edge of this nozzle, such as to aid in the formation of the diverging conical sheath of mainstream current. Also, delta shaped vanes can be provided on the exterior of the secondary nozzle near its leading edge, the vanes extending outwardly from the surface, and formed into fragments of a helix or helices, whereby to generate a vertical motion of the mainstream on the outside of the secondary nozzle. It is also possible to form or position these vortex-generating vanes not to generate a single large vortex around the secondary nozzle, but rather to generate many small vortices or eddies along the surface of the secondary nozzle.

These eddies, in peeling away from the trailing edge of the nozzle aid in the maintenance of the diverging sheath of mainstream river current. One way of securing this eddy generation is simply the canting of adjacent vanes in opposite direction or hand-one canted to the counterclockwise spiral, the next to clockwise spiral, and so on around the periphery.

Further, a set of petal-like flaps can be arranged extending rearwardly from the trailing edge of the secondary nozzle, hingedly mounted thereto, provided with control means, whereby the flaps may be swung inwardly to reduce the flare of the mainstream sheath, or outwardly to increase the flare, as needed for control of the river current turbine output. In the case of no secondary nozzle, the flaps would be part of the primary nozzle trailing edge.

Further to the control of the previously mentioned external sheath, there may be provided adjustable aileron-like trailing edges on the vanes extending from the surface of the primary nozzle, whereby the strength of the helical motion of the sheath may be influenced.

In an alternative form of the turbine wheel and cooperating diverging waterway from the throat to the discharge end of the primary nozzle, the turbine wheel, rather than being of pure axial flow type, has vanes shaped to enable the portion of river current entering axially into the turbine, to exit with a considerable component of radial flow. In this form the waterway diverges immediately at the turbine discharge region of the throat, having a bell shape at this discharge point, whereby the region into which the partially de-energized water discharges may have a large cross section into which the water can flow at low velocity. Downstream from this region, the waterway flare will continue as already described.

In other forms of the axial-flow turbine wheel, its blades, rather than extending directly from hub to shroud ring, are preshaped into elements bowed in the flow direction which under load form catenaries, such that the main stresses in the blades are tensile stresses. In one catenary variation, each blade is bowed into an open U-shape, with axis of symmetry of the catenary between the two ends of the U, and parallel to the axis of the turbine wheel. In another catenary variation each blade constitutes nearly one half of the catenary, and the axis of symmetry is concentric with the turbine's axis. The blades may be bowed also in their rotational direction, as hereinafter detailed.

In order that the present invention may be more fully understood and more readily carried into effect, embodiments thereof will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is an isometric view of a pair of river turbines of the invention, mounted under a common float.

Figure 2 is a longitudinal section of one of the turbines of Figure 1; Figure 3 shows a primary nozzle of the invention in half section, this version having no preconvergence, and a full tailpiece; Figure 4 shows a version of primary nozzle with convergence and full tailpiece; Figure 5 shows a primary nozzle version with convergence, and minimum tailpiece; Figure 6 shows the addition of a secondary nozzle; Figure 7 shows a straight vane in the annular passageway between primary and secondary nozzle; Figure 8 shows a bent or canted vane in the annular passageway; Figure 9 shows a hinged "aileron" and a delta vane on the secondary nozzle; Figure 10 shows a detail indicating that the delta vane is bent or canted; Figure 11 shows a hinged petal flap at the rear edge of the secondary nozzle;; Figure 12 shows the rim of the turbine wheel, with its pulley groove, belt, and waterbearing; Figure 13 shows a detail of a means for steering or canting the strut vane upstream of the turbine wheel; Figure 14 shows a detail of the water bearing for the turbine wheel shaft; Figure 15 shows a turbine wheel with blades bowed into catenaries with axes of symmetry parallel to the turbine wheel axis; Figure 16 shows a turbine wheel with blades bowed into half catenaries with axes of symmetry coincident with the turbine wheel axis, and with the central bearing structure eliminated; Figure 16a is another catenary variation; and Figure 17 shows the rim of a radial-flow turbine wheel, and the adjacent bell-shaped waterway.

Referring now to Figures 1 and 2, two river turbines are shown mounted below a pontoon and machinery-deck structure, in a location within a river, where the river current flows from left to right. In all the Figures, corresponding elements carry the same designating numerals, even though their shapes may vary slightly from one specific version of the invention to another.

Where the differences are so substantial as to cause confusion, different reference numerals are used.

In Figures 1 and 2, the deck 1 of a boatlike structure is supported on a structural framework 3, above two or more pontoons 2, spread apart in catamaran-like fashion, with space between and below each pair of pontoons. In this space there is located a primary nozzle structure 5 connected through elements of the structural framework 3 to pontoons 2 and the deck 1.

Above the deck 1 is a cabin structure 25 and a transmission-line support tower 24.

Mounted on the deck are electrical generators 4a and 4b, their drive pulley 19a, an idler pulley 19b, electrical control gear 26 and a water pump arrangement 23.

The primary nozzle structure 5 as shown in Figures 1 and 2 is constituted of a shell 6 and a liner 7. The left, or front, end of shell 6 is smoothly joined to the entrance end 9 of liner 7, for low fluid flow resistance, both for entrance of a portion of the river current into a waterway through liner 7, and for the mainstream of river current passing around shell 6. Liner 7 continues from its entrance end 9 to a throat 8, which is the part of the waterway through the liner of minimum cross section. At the throat 8 is an annular recesses 30 occupied by a shrould ring 17; this arrangement will be described subsequently in detail with reference to Figure 12. Downstream of the throat, the liner 7 continues to a discharge section 10 at which the cross sectional area of the waterway through the nozzle has increased as the result of the flaring of the liner.In order to maintain attached flow of the river current portion through the waterway and to initiate and produce a diverging cone of this moving water portion, the liner is configured to flare with an included angle of less than about 15 and preferably about 7" In another form of the invention, as will be explained hereinafter, the liner downstream of the throat may enlarge immediately into a bell shape; after this enlargement, the rate of flare decreases to about 7 , as just mentioned; such an arrangement is shown in Figure 17.

The liner 7 has a circular cross section at the throat, but its cross section at other points along its length is not necessarily circular. The mouth 9 and also the discharge end 10, for example, may be rectangular, square, polygonal, or even trapezoidal in cross section. It is important, however, for minimum fluid flow resistance that all transitions from one shape to another, and from one section to another, be effected smoothly and not abruptly.

The external surface of the shell is smooth and has a cross sectional area that gradually decreases from the shell's front or entrance and towards its discharge end 12 but which then increases smoothly towards connection with the discharge end 10 of the waterway, the shape of the shell thus defining a smooth surface which near the exit end 12, has at least begun to flare away from the axis of the nozzle, whereby that layer of the mainstream of the river current passing along the shell's surface is deflected away from the axis into a generally conical diverging sheath of mainstream water surrounding the similarly diverging portion of river current passing out of the waterway.

This diverging sheath of water, as will be explained hereinafter, produces a substantial improvement of efficiency of operation of the river turbine.

In Figures 1 and 2, the divergence of the shell 6 at its discharge end 12 is slight and is hardly noticeable in the drawing. In this particular instance, such a slight divergence or flare is sufficient, because other structures surrounding the primary nozzle and shortly to be described also aid in the generation of the diverging sheath of mainstream water. In other forms of river turbine, the flaring of the primary nozzle is much larger, as in the arrangement of Figures 3, 4 and 5.

The primary nozzle 5 has a space or compartment between the surfaces defining the shell 6 and the liner 7, in which are located structural elements supporting the surfaces. In a preferred form of construction, the primary nozzle is comprised of eight segmental modules, to define a nozzle of octagonal cross section, each module having longitudinally extending side partitions which abut one another upon assembly of the nozzle. For very large river current turbines, where the turbine diameter might, for instance, exceed 60 ft., the modular construction greatly facilitates construction of the nozzle. The individual modules can be made in a boat yard from steel as in conventional barge manufacture. After construction, each module can be floated to the power generator site for assembly.

The primary nozzle's compartments provide buoyancy for the river turbine. The buoyancy can be made adjustable, and by pumping water out of upper compartments whilst leaving water in lower compartments, the centres of buoyancy can be adjusted for various river conditions.

Within the waterway of primary nozzle 5 is a turbine wheel 14 having a central shaft 13 (Fig. 14) coaxial with the waterway's throat 8 on which are mounted blades 29 having a shroud ring 17 attached to their outer ends. The turbine wheel is shown in more detail in Figure 14. In this form of the invention, the turbine is arranged for axial flow of river water. In another form shown in Figure 17, the turbine blades and shroud ring are so arranged that the flow enters the turbine wheel axially but leaves the wheel with a considerable radial flow component; this is the form of turbine wheel used with the bell shaped tail region in the waterway as previously mentioned.

In either case, as shown in Figure 14, the turbine shaft is mounted in bearings carried in bearing block 15, which is in turn supported centrally within the waterway by struts 16a and strut-vanes 16b. The strutvanes 16b as shown in Figure 13, not only support the bearing block but also constitute vanes that direct axially flowing water into a helical path such that the water impinges on the blades 29 of the turbine wheel with a radial component, thereby improving the efficiency of operation of the turbine wheel.

For control purposes, the strut vanes 1 6b can be rotated about their individual axes, to increase or decrease their effective pitch; the control means may be any of numerous kinds, such as hydraulic piston-cylinder actuators, operating through mechanical linkages, or may be hydraulic motors 16f operating on screws 16e meshing with pinions 16d on strut-vane shafts 16c, as shown in Figure 13.

To prevent water-logged logs and other foreign bodies entrained in the river flow from entering the nozzle and damaging the blades of the turbine, a debris screen 42 is provided upstream of the mouth of primary nozzle 5, the screen 42 being in the form of a cone of cables 43 and 44. The open end of the cone of cables is attached to the open end of the waterway entrance 9, and the tip of the cone is attached to anchor cable 41 leading from an upstream anchor 40. At the open end of the cone, each cable is individually shackled with devises to cable attachments (not shown) distributed around the periphery of the waterway mouth 9.

Some of the cables 43 are full length, extending the entire distance from the anchor cable 41 to the mouth devises. If all the cables extended the full length, however, and were spaced sufficiently close to prevent debris entering the large end of the cone, the cable density near the smaller end of the cone would be too great.

Accordingly. some of the cables, designated 44, extend only part of the way and are clamped, as at 46, to the full length cables.

Although only two lengths of cables are shown, those designated 43 being full length, several different lengths could be used with additional branches as desired. It will also be clear that should the size of the debris require it, the screen's open end could be attached to a secondary nozzle (to be described hereinafter), rather than to the primary nozzle 5.

The debris screen inevitably introduces some unwanted resistance to the flow of water through the waterway and turbine. In order to minimize the flow resistance of the screen, the cone of cables 43, 44 is arranged to have an interior included angle near 300 because near this angle, the tilt of the individual cable axis relative to the line of river flow offers an elliptical cable cross section rather than the actual circular cable cross section which we have found tends to minimise the flow resistance.

It was previously mentioned that the shrould ring 17 of turbine wheel 14 is let into an annular recess 30 in the throat 8 of the waterway. This feature and others related are shown in Figure 12. It is important for minimum water flow resistance that the inner face of the shroud ring 17 be a smooth extension of the adjacent waterway surface in the region of throat 8. The shroud ring is used not only as structural support for the outer ends of the turbine blades 29, but also for transferring the axial load from the blades to the surrounding nozzle structure.

For this purpose, the downstream side of the annular recess 30 is provided with a water bearing porous structure 27b, and a suitable pressurized supply of water 27a through jets 27, whereby deflection of the shroud ring under pressure of the river current against the turbine blades is prevented by a cusion of water maintained in the space between the edge of the shroud ring and the adjacent wall of the annular recess.

There may alternatively or additionally be a set of mechanical roller bearings disposed in this space. An advantage of the mechanical bearing is that in case of failure of water supply to the water bearing, catastrophic destruction of the river turbine would not result.

Figure 12 also shows that the outer face of the shroud ring 17 is provided with groove 21 in which a belt or belts 18 ride.

Conveniently, the belt 18 is a round, very long belt extending about 1 2/3 wraps around the shroud ring, and upward through two channels 20 to the driven pulley 19a and the idler pulley 19b, as shown in Figures 1 and 2. Of course, the load need not be taken in a single endless belt, and multiple belts may be used.

The tensions in the two parts of the belt 18 have their major vector components in the upward direction, tending to support at least part of the weight of the turbine wheel.

Thereby the load carried on the turbine wheel axial bearing is reduced, and a less costly bearing structure is possible.

The turbine wheel axial bearing as shown in Figure 14 may be of known construction utilizing for example water bearings 71, 72, 73 as practised in shafts for ships propellers.

Water bearing 71 is a porous block provided with a chamber and passageway 71, and a supply of pressurized water through line 74. Water bearing 71 is arranged at the front of the stationary bearing block 15 supported by strut's 16a and strut vanes 16b within the throat. The back surface of a nosepiece carried on shaft 13 bears against the water-bearing 71, whereby the axial thrust of the turbine wheel is absorbed. Water continuously supplied through the porous block maintains a cushioning film to prevent metal-to-metal contact in the structure.

Similarly porous blocks 72 and 73 are supplied with water, and act as radial water bearings. It is desirable of course, that the bearing be enclosed in a streamlined frontal enclosure as depicted in Figure 2. The stub shaft extending rearwardly of the turbine wheel should also be enclosed within a streamlined casing.

The turbine wheel 14 is made up of a hub on shaft 13, a shroud ring 17 and a set of blades 29 attached at one end to the hub and at the other to the inner side of the shroud ring. Following conventional hydrodynamic principles, each blade is set at an angle to the axis, at the hub, and because the blade is formed with a twist along its length, this angle changes along the length as indicated by the sections A-A, B-B and C-C on Figure 14.

The blade itself for highest efficiency of the turbine must be very carefully designed, with the most effective profile in each radial section, and changing profile from axis to shroud end. An important consideration is the avoidance of cavitation, because cavitation would not only increase the frictional drag (thereby converting mechanical energy into wasteful heat) but also might cause destructive erosion of the blade surface.

It is an advantage of the present invention that the turbine wheel will be rather deeply submerged below the water surface, and the differential head of water between the surface and the uppermost edge of the turbine will be of considerable magnitude; the greater this head, the greater the absolute pressure in the water, and the more that the pressure must be reduced before cavitation will take place.

However, even this advantage may not be sufficient, and the blades' profiles must be selected using known hydrodynamic principles so that the pressures on the back sides of the blades (where pressures are lowest) will not get so low as to permit cavitation to occur. Blades, which by their shape delay the formation of negative peaks of pressure are the best. Toward the outer ends of each blade the sections are accordingly thinner, and are tilted to cut into the water at a more acute angle.

Toward the axis end of each blade, the relative velocity is smaller for a given number of revolutions per minute of the wheel, and the section may both be thicker and be tilted more squarely to the rotational direction.

For the wheel structure shown in Figure 14, with the central ends supported in the hub and the radially outward ends supported in the shroud-ring 17, which is in turn supported in the recess 30 with water bearings 27b, each blade can be considered a complex beam, supported at both ends, and it must be designed accordingly.

In order to obtain the desired hydrodynamic blade shapes together with large strengths and reasonable cost, fibre reinforced plastics technology is preferably utilized and the blades are typically made of a fibre-glass/epoxy construction, with a rigid foam core in the thicker sections.

Continuous filaments of glass extend lengthwise of the blades to provide bending stiffness; for torsional strength, belts of filaments extend diagonally across the widths of the blades. Where a foam core is used, it may be of rigid polyurethane preshaped to establish the basic shape of the blade.

For very large turbine wheels, where the force of the river current exerts a large bending force on the blades, it may be difficult to obtain sufficient resistance to bending while maintaining desirable blade sections. One solution to this problem is to provide a catenary blade, as shown in Figures 15, 16 and 16a. In the construction of Figure 15, the blade is deliberately formed into a bowed U-shape in the direction toward which the current tends to force it. The pre-shaping is sufficient to make the blade when under load a catenary with axis of symmetry between its two ends; the forces in it are then mainly pure tension, and any tendency to further bending in the direction parallel to the axis is substantially eliminated. Such a construction takes full advantage of the excellent tensile strength characteristics of modern composite materials.

The above described catenary blade construction can be further developed, as shown in Figure 16. In this arrangement each blade can be designed to be (when under load) approximately one half of a symmetrical catenary with axis on the centre line of the wheel, and extending entirely across the diameter of the turbine wheel. By such a design, the forces parallel to the axis are transformed into tension in the catenary, and the thrust on the central shaft is eliminated; thus all of the load of the river current is transferred directly to the shroud ring and through its water bearings 27b to the surrounding primary nozzle structure.Having thus eliminated all of the axial thrust forces, it becomes possible also to eliminate the central support of the wheel, by locating trunnion bearings around the outside of the rim of the shroud, in order to support the turbine wheel radially as well as axially. These bearings are preferably water bearings like 27b, but may also be rollers supported in bearing blocks as conventionally in the support of large rotating horizontal structures such as ball mills and rotary kilns. With both the axial and the radial supports eliminated from the wheel, the entire central hub 15, its bearings 71, 72, 73 and its struts 16a and 16b are eliminated as indicated in Figure 16.

A further step in the use of catenary design of the blade is to curve the blade in the circumferential direction in which it is thrust by the impinging water currents, as well as in the axial direction. This design is indicated in Figure 16a which shows in fragmented fashion a face-on view of a turbine wheel. Only two complete blades 29 are shown, the others being indicated by the dotted lines extending from the central hub.

Each of the blades 29 has a catenary shape as seen from this viewpoint, as well as the catenary shape seen in Figure 16. Thereby all bending forces in any direction are eliminated, and the forces within the blade are tension. As in Figure 15, there being no axial thrust, the hub 13a serves only as a connector for attaching the central ends of the blades to one another. Accordingly no central bearing is needed, and none is shown.

Considering now features of the river turbine external to the primary nozzle, beginning with those shown in Figure 1 and Figure 2. Seen in side view in Figure 2, are two of a set of vanes 63 extending radially outward from the outside surface 6 of primary nozzle 5. These vanes in Figures 1 and 2 are not only vanes as such for directing the flow of mainstream river current past the exterior of the nozzle, but in this form of the invention are also structures supporting an annular secondary nozzle 60, coaxial and in partial overlap with the primary nozzle 5. Thus supported, the mouth 61 of the secondary nozzle forms with the exterior of the primary nozzle 5, the beginning of an annular passageway between the primary and secondary nozzles.

The vanes 63 extend longitudinally through this annular passageway. While vanes 63 may be straight as depicted in Section EE of Figure 7, they preferably are all bent in a helix, as in Section EE of Figure 8, whereby the passing mainstream current is directed to flow as a vortex. The bent downstream edge of the vane is depicted in Figure 2 at 64, and in Figure 9. It is in some circumstances desirable to be able to change the intensity of this helical motion, and this change is provided for, by making the trailing edge 64 not as a simple bent fixed edge, but rather as an adjustable aileron as in the section in Figure 9, with adjustment means not detailed.Such means can include cables extended from levers on the pivot shafts of the ailerons, or push-pull slides on bent tracks with hydraulic piston actuators, or even worm-and-pinion drive on the pivots, with hydraulic motors to drive the worms, similarly to Figure 13, and Figure 11.

The secondary nozzle 60, in a manner similar to the primary nozzle, has a liner forming an inside surface and defining a periphery of the aforesaid annular passageway. The secondary nozzle also has an exterior surface, and a space between the liner and the exterior surface containing struts and braces, and constituting a watertight compartment, or plurality of compartments, which can be utilized in obtaining the desired buoyancy characteristics of the entire river turbine.

Like the primary nozzle, the secondary nozzle is made in segments with segmental walls as well as liner and exterior surface. It is prefabricated, floated to the site as individual barge-like segments and there assembled into the nozzle.

The inside surface of the liner converges from its mouth 61 toward the adjacent primary nozzle's exterior surface, so that the annular passageway is of decreasing cross sectional area as it approaches the discharge end of the primary nozzle, so that the mainstream water flowing through this passageway is accelerated to a higher velocity, at the region 62.

Where the secondary nozzle's liner passes downstream beyond the adjacent discharge end of the primary nozzle, its cross sectional area begins to increase; in other words, the high velocity sheath of mainstream water now is guided by the flaring of the liner into a diverging conical sheath around the portion of the river current emitted from the primary nozzle.

From hydrodynamic principles it is known that the energy of a flowing water system is made up principally of two components, namely kinetic energy which varies as the square of the linear velocity, and potential energy, which is measured by the static head relative to any preselected datum level. By careful attention to streamlining and fairing of guiding surfaces, and avoidance of separation of flow by maintenance of the earlier stated 7" flare, it is possible with only minor loss of energy into heat due to turbulence and friction, to transform kinetic energy into potential energy, and vice versa. This transformation is expressed in the well known Bernouilli's theorem.

The portion of the water which is accelerated to high velocity, then flows through the turbine vanes and gives up energy as mechanical output through the turbine's belt 18, and emerges from the turbine vanes at reduced energy. The reduction may be in the velocity, in the static pressure, or both, depending upon the turbine and waterway design. In the straight-through axial turbine wheel, with the same flow cross section immediately downstream as at immediately upstream of the wheel and for a constant river flow rate, the water velocity achieved by acceleration through the converging primary nozzle entrance section is constant, because the total volumetric flow through the primary nozzle is constant.Accordingly, the static pressure, which is lowered considerably due to the converging section of the primary nozzle producing a higher water velocity, is further reduced as a result of the passage of the water through the turbine wheel, by transfer out of the water into the turbine's mechanical output. As the water flow in the primary nozzle passes from the turbine wheel into the portion of the primary nozzle which has an increasing cross section, its residual kinetic energy is partially transformed back into a higher static pressure before being blended with the surrounding mainstream water.

With the turbine wheel of the radial discharge type shown in Figure 17, it is possible for at least a portion of the kinetic energy to be converted directly to mechanical energy, with less reduction in pressure. The reason is that the radial discharge and bell shaped tailpiece to the waterway allows the high linear velocity water passing through the turbine to drop to a lower linear velocity because it is flowing from a smaller to a larger cross section, the mass flow of course being constant throughout the waterway for a given river flow rate. To the extent that the linear velocity can be dropped, the mechanical energy can be removed without change of pressure.This analysis neglects for the moment, that any feature introducing more turbulence into the flowing liquid will thereby increase the frictional losses, by transformation of some of the system's kinetic and potential energy into heat.

Effective use of the radial discharge turbine and bell shaped waterway requires careful design to minimize the frictional losses.

However, it may be difficult to maintan the flaring cone of water sufficiently separate from the surrounding mainstream, unless special steps are taken and in the embodiments described herein, a protective high velocity sheath of mainstream water is provided by means of the annular passageway between the primary and secondary nozzles to surround the flow emanating from the primary nozzle and aid in conversion of the energy of the water flow passing through the turbine wheel from kinetic to potential energy.The high velocity sheath developed by acceleration of mainstream water through the annular passageway between the primary and secondary nozzles, is, as a result of its acceleration, of reduced static pressure, thereby reducing the tendency of the mainstream river current to flow into the axial region downstream of the primary nozzle, and providing a favourable environment for the continued expansion in cross section in the flaring conical flow portion from the primary nozzle.

The exterior surface of the secondary nozzle 60 is also structured to favour the formation and protection of the diverging conical sheath of mainstream water.

Proceeding rearwardly from the mouth end 61, the exterior surface gradually and smoothly moves radially inward toward the turbine axis, but as the tail end 67 is approached, the curvature reverses, still gradually, and begins to flare outward, away from the axis, such that the mainstream river flow passing over this surface is directed outwardly, to conform generally with the exterior of the conical sheath emitting from the inside of the secondary nozzle.

To the same end, near the forward part of the exterior surface of the secondary nozzle there may be attached a set of radially extending delta-shaped vanes 65, the rear edges of which are bent to deflect the passing mainstream into a vortex, preferably in the same direction of rotation as the rotation of the sheath as impelled by vanes 63.

The secondary nozzle shown in Figure 2 has an exterior surface that decreases in diameter in the flow direction for some considerable distance, before its diameter then flares as earlier described. It is important that the mainstream flowing past the region of decreasing diameter should remain "attached" (in the parlance of the hydrodynamicist) and although the limiting angle of about 7" has been specified for the rate of convergence of this part of the nozzle, circumstances may prevent this small angle being achieved. Should this be the case, the delta vanes 65 can be set at a steeper "cant", or angle of attack, whereby each will cause a small vortex to develop in the wake of the vane.These small vortices will tend to keep the mainstream flow "attached" by replacing the boundary layer energy all the way to the nozzle's beginning of flare, or even to its trailing edge.

In the preceding discussions it has been mentioned that this invention may be practised with only a primary nozzle flaring from the throat toward the discharge end. It has also been pointed out that greater efficiencies may be achieved through the use of the exterior vanes, secondary nozzle, and other structures, as well as through the flaring external surface of the primary nozzle. There are some other variations of primary nozzle configuration to which the invention is also applicable.

Figure 3 shows in half section a version in which no pre-converging section of input water to the turbine wheel is utilized, the throat of the nozzle being immediately adjacent in the mouth. In this version, the turbine wheel receives an intercepted portion of the river current essentially at the prevailing river flow rate, removes energy from it, then diffuses the portion as already taught into a conically diverging stream of decreasing velocity and increasing pressure, before blending with the mainstream.

In Figure 4 a preconverging section is used with the primary nozzle, which distinguishes Figure 4 from Figure 3.

However, the nozzles of both Figures 3 and Figures 4 have an elongated flaring tail section, the advantage of which is to maintain smooth diffusion of the diverging stream until substantial pressure equalization is secured.

In Figure 5 is shown a primary nozzle having a relatively large preconverging section and a relative short tail section. This version has its exterior surface contoured in principle like the primary nozzle in Figure 2.

In Figures 3, 4 and 5 only the primary nozzle forms have been presented, both as to inside and exterior. In Figures 6, 7 and 8 are shown the stepwise additions of structure which may be made within the scope of this invention, for further improving the control of mainstream flow and sheath formation on the outside. Each aspect of the structures has already been discussed. These additions may be made to any of the forms of primary nozzle, as already described.

As previously mentioned, the deck 1 carries certain auxiliaries, and these will now be dealt with in more detail. Above the cabin supported from the platform is a transmission tower 24 for the support of electrical transmission cables for conducting power generated with this river current turbine. If submarine cable of suitable voltage and power specification be available, it may be substituted for all or part of the overhead cable.

Generator 4a is provided to generate large amounts of electrical power for utilization on shore. Since most power grid systems are based on either 50 or 60 Hertz, this generator will preferably be such a one, with output voltage and number of phases suitable to the particular utilization. In order that the produced power may be fed into existing grids into which other generating sources are also feeding, it will be essential that the synchronization and frequency, as well as the voltage produced, be of highly precise values. To this end, suitable electrical control gear 26 is provided. Signals showing any unwanted deviations will be provided by this control gear, and fed back to the generator speed and excitation control system, to cause the generator to keep in step with the power grid.

Generator 4a is shown as a single unit, but it will be entirely clear additional generators could be provided and with suitable clutches (not shown) and electrical controls, driven from the same energy source, being brought on line when demand for power requires. In this manner each generator when running will be producing power at operating conditions near its optimum efficiency.

Also shown on the platform 1, is the generally smaller generator 4b, which may be used to provide low voltage power for immediate utilization in connection with water pumps 23, air compressors (not shown), control systems including 26 and other needs for electrical power upon and near the platform. For idle and start up purposes, in general it will be necessary to have a supplemental engine-driven generator, and suitable fuel tanks, which are not shown in the drawings.

One of the means for speed control of generator 4a is by way of pulley 19a, which may be a variable diameter pulley with means for adjusting its diameter in use and in response to signals from the control system 26. Other means will be discussed later. At 19b is shown an idler pulley, by which the tightness of belt 18 may be held constant, despite changes in diameter of pulley 19a and despite stretching of the belt.

Idler pulley 19b may be continuously and automatically reset by conventional drive means and control means not shown.

Water pumps 23 are designated generally, but in actuality may be of more than a single specification. For example, some will be suitable for pumping water out of the compartments of the nozzles, other for pumping water into water-bearing devices such as 15 and water jets such as 27.

Whereas Figure 1 shows two river turbine units of this invention in side by side arrangement, it is obvious that single units, or multiple units of more than two turbine units can be used without departing from the scope of the invention. Indeed, when two or more units are coupled side by side, it is possible to dispense with the pontoons 2, or at least to reduce their number, because adequate flexibility in adjustment of buoyancy is available through the compartment-alization of the several nozzles.

By way of example to illustrate the ability of river turbines of this invention some typical dimensions that would apply to a single turbine for use in a river of at least 100 ft. depth and breadth are tabulated below. Rivers such as the Mississippi River in the United States of America have reaches of such a depth, and many times this breadth.

Primary Nozzle: Mouth Diameter 0066 ft.

Throat Diameter 40 ft.

Exit Diameter 48 ft.

Overall Length 60 ft.

Tailpiece Flare 7" Tailpiece length, throat to exit 28 ft.

Exterior Flare last 8 ft.

Secondary Nozzle: Mouth Diameter 90 ft.

Throat diameter (at primary exit) 68 ft.

Exit Diameter 76 ft.

Vortex Vanes (65) height 5 ft.

Overall Length 70 ft.

Tailpiece Flare 7" Tailpiece Length throat to exit 40 ft.

Exterior Convergence 60 ft.

Exterior Flare 10 ft.

Overlap of Primary and Secondary nozzles 30 ft.

Sheath thickness at departure from primary exit 9 ft.

With a river flow rate of 7 knots, the mechanical power delivery to the electrical generators is expected to be equivalent to the order of 7500 KVA.

WHAT WE CLAIM IS: 1. A turbine for being driven by a current of water, comprising a generally tubular nozzle with an internal water passageway in which a turbine wheel is mounted so as to be rotated by water passing through the passageway to a discharge end thereof upon the turbine being immersed in said current, the passageway having a gradually increasing cross section from the turbine wheel to the discharge end, and the exterior of the nozzle being of such a shape as to cooperate with the current to produce a diverging conical sheath of water, which sheath surrounds water emanating from said discharge end of the nozzle.

2. A turbine in accordance with claim 1 and including means on the exterior of the nozzle to induce a helical rotation of said sheath.

3. A turbine in accordance with claim 1 or 2 and including a debris screen arranged to prevent ingress of debris into said passageway.

4. A turbine in accordance with claim 3, wherein said debris screen comprises an arrangement of cables each attached at one end thereof to the periphery of the water inlet to said passageway, the cables being connected together at the other ends thereof.

5. A turbine in accordance with any preceding claim, wherein the discharge end of the nozzle is arranged within a secondary generally tubular nozzle.

6. A turbine in accordance with claim 5, wherein said secondary nozzle has an exterior surface of such a shape as to cooperate with said current to produce a secondary diverging conical sheath of water surrounding said first mentioned sheath.

7. A turbine in accordance with claim 5 or 6, wherein the exterior surface of the secondary nozzle is provided with a set of delta-shaped vanes extending outwardly from said surface and constituting fragments of the surface of at least one helix, each such helix rotating in the same sense.

8. A turbine in accordance with any preceeding claim in which the turbine wheel includes at its outer periphery a shroud ring contiguous with said water passageway and received within an annular recess therein, the shroud ring being supported by radial and thrust bearings within the recess.

9. A turbine according to claim 8, wherein said bearings are water bearings, and including means for supplying water under pressure to said bearings.

10. A turbine in accordance with claim 8

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. later. At 19b is shown an idler pulley, by which the tightness of belt 18 may be held constant, despite changes in diameter of pulley 19a and despite stretching of the belt. Idler pulley 19b may be continuously and automatically reset by conventional drive means and control means not shown. Water pumps 23 are designated generally, but in actuality may be of more than a single specification. For example, some will be suitable for pumping water out of the compartments of the nozzles, other for pumping water into water-bearing devices such as 15 and water jets such as 27. Whereas Figure 1 shows two river turbine units of this invention in side by side arrangement, it is obvious that single units, or multiple units of more than two turbine units can be used without departing from the scope of the invention. Indeed, when two or more units are coupled side by side, it is possible to dispense with the pontoons 2, or at least to reduce their number, because adequate flexibility in adjustment of buoyancy is available through the compartment-alization of the several nozzles. By way of example to illustrate the ability of river turbines of this invention some typical dimensions that would apply to a single turbine for use in a river of at least 100 ft. depth and breadth are tabulated below. Rivers such as the Mississippi River in the United States of America have reaches of such a depth, and many times this breadth. Primary Nozzle: Mouth Diameter 0066 ft. Throat Diameter 40 ft. Exit Diameter 48 ft. Overall Length 60 ft. Tailpiece Flare 7" Tailpiece length, throat to exit 28 ft. Exterior Flare last 8 ft. Secondary Nozzle: Mouth Diameter 90 ft. Throat diameter (at primary exit) 68 ft. Exit Diameter 76 ft. Vortex Vanes (65) height 5 ft. Overall Length 70 ft. Tailpiece Flare 7" Tailpiece Length throat to exit 40 ft. Exterior Convergence 60 ft. Exterior Flare 10 ft. Overlap of Primary and Secondary nozzles 30 ft. Sheath thickness at departure from primary exit 9 ft. With a river flow rate of 7 knots, the mechanical power delivery to the electrical generators is expected to be equivalent to the order of 7500 KVA. WHAT WE CLAIM IS:

1. A turbine for being driven by a current of water, comprising a generally tubular nozzle with an internal water passageway in which a turbine wheel is mounted so as to be rotated by water passing through the passageway to a discharge end thereof upon the turbine being immersed in said current, the passageway having a gradually increasing cross section from the turbine wheel to the discharge end, and the exterior of the nozzle being of such a shape as to cooperate with the current to produce a diverging conical sheath of water, which sheath surrounds water emanating from said discharge end of the nozzle.

10. A turbine in accordance with claim 8

or 9 wherein the turbine wheel includes a plurality of turbine blades extending outwardly to the shroud ring, each of the blades being bowed in a shape at least approaching a section of a catenary with an axis of symmetry parallel to the axis of the turbine wheel.

11. A turbine according to claim 10, in which the axis of symmetry of the said catenary is located between the axis of the wheel and the rim at the point of attachment of the blade.

12. A turbine according to claim 10, in which the axis of symmetry of the said catenary is located on the axis of the wheel.

13. A turbine according to claim 10, in which each turbine blade is bowed into catenary shape not only in the direction of water flow but also in the direction of rotation of the turbine wheel.

14. A turbine in accordance with any preceding claim and mounted beneath a buoyant float structure.

15. A turbine in accordance with claim 14 and including electrical generator means on the float structure and a mechanical coupling between the turbine wheel and the generator such that the generator is driven upon rotation of the turbine wheel.

16. A turbine in accordance with claim 4 and immersed in a current of water, the ends of the cables that are connected together being secured to an anchor to moor the turbine in said current.

17. A turbine in accordance with claim 16 wherein said cables define a cone having an apex angle of 30 .

18. A turbine in accordance with claim 16 or 17 wherein some of said cables are terminated downstream of the apex of the cone formed thereby.

19. A turbine in accordance with claim 7 and including flaps on the downstream end of said secondary nozzle.

20. A turbine adapted to be driven by a current of water substantially as herein described with reference to Figures 1 and 2 or as modified as described with reference to the other Figures of the accompanying drawings.

21. A turbine in accordance with any preceding claim and moored in a river current.