CA1051748A - River ocean turbine - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A turbine wheel on a horizontal shaft is coaxially mounted within a primary nozzle, for support in a river current below a platform carrying electrical power generations equipment. The turbine shaft and primary nozzle are submerged and oriented to enable flow of a portion of river current through the nozzle and the past the turbine wheel.
The external surface of the nozzle is shaped and has structure to accelerate and/or direct the flow of the adjacent surrounding mainstream river current in a manner to generate a sheath which aids the efflux of that portion of the river current which has passed through the turbine. Part of the said structure is a secondary nozzle is arranged to accentuate the control of the surrounding mainstream river current. Bearing means, support means, power take-off means, speed control means and blade shapes are disclosed.

Description

4~3 OBJECTS
nbjects of the present invention include the following:
(1) Harnessing some of that part of the sun's energy repre-sented in the rainfall collected in the flowing streams ofwater in rivers.

(2) Extracting energy from flowing river streams without the construction of expensive dams.

(3) Extracting energy from rivers in places where soil and geographic conditions make the use of dams impossible.

(4) Extracting energy from a part of river currents without foreclosing the use of the river for navigation.

(5) Enabling the shifting and re-shifting of energy ex-traction means to those parts of a river where the currents lS are optimum.

(6) Application of modern technology and materials of con- -` struction for the building of large navigable power plants of high efficiency and moderate cost.

(7) Enabling the production of electrical power in large ~ 20 quantities, with precise control of frequency and synchroni-1 zation such that the power can be merged with conventional electrical power generation systems, despite fluctuations in river flow.
, FIGURES
Figure 1 is an isometric view of a pair oF river ~-~ turbines of the invention, mounted under a common float.
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~ Figure 2 is a longitudinal section oF a single i '~ turbine of the invention.
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~ Figure 3 shows a primary nozzle of the invention in i 30 half section, this version having no preconvergence, and a full tailpiece.
Figure 4 shows a version of primary nozzle with ;I

~ ~ 5~ ~4 converger and full tailpiece.
Figure 5 shows a primary nozzle version with con-verger~ and minimum tailpiece.
Figure 6 shows the addition of a secondary noz~le.
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 no~zle.
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 I 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 catenarles 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 16b is another catenary variation.
; Figure 17 shows the rim of a radial-flow turbine ~ ~ wheel, and the adjacent bell-shaped waterway.
, GENERAL DESCRIPTION OF PRIOR ART SITU~TION
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Water power plants associated with the use of dams to .

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impound the water, and pass 1t through waterwheels, (and in later times through turbines) have undergone centuries of development. As a result, where dams can be used, and where a good fall of water is available, such power plants can be highly efficient, and are used throughout the world for the generation of electric power.
There are many situations~ however, where (l) damming of the flowin~ water is proh;bitively expensive, (2) is impossible because of soil conditions, (3) is impossible because of geographic conditions, or (4) is impracticable because of navigat;onal needs for the Flowing water. Among the situations preventing the successful use of impounded water for hydroelectric purposes are the following:
(1) Deep layers of alluvial soil overlaying impossibly deep bed rock, whereby construction of foundations for dams is totally impractical.
~ (2) Broad flat valleys, such that small rises in water level i would inundate`huge acreages of valuable land, and small drops in water level would lay bare large areas of mud flats.
(3) Related to the above, lack of nearby mountain ridges between which dams could be built.
The Mississippi River, is an outstanding example, exh;biting all of the above situations, yet at the same tîme represents the loss of huge amounts of solar energy. This solar energy is that which was used by Nature in moving the water through the sequence from ocean to cloud to sky above the Mississippi's watershed. Once in the rlver, the energy of the river shows up in two forms, namely, (1) the hydraulic gradient of the water as it flows downhill from sources to .
` 30 outlet, and (2) the kinetic energy of the moving mass of `' water.
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~5~ 8 The hydraulic gradient of the natural Mississippi River is very slight, being for much of the riYer lower than two inches per mile.
If one considers an appropriate machine for extract-ing energy from the potential energy in the static pressuredrop of a stream of water travelling at about 5 mph, and falling 0.0~2 ft. in a 100 ft. machine length it can be calcu-lated that the stream is conveying energy at the rate of only about 0.60 ft. lb./sec. for each square foot of stream, equivalent to about 1/1000 horsepower.
On the other hand, the kinetic energy of this stream is very much larger. It can be calculated that the same square foot of stream will be bringing kinetic energy into the machine at a rate of about 380 ft. lb./sec., which is about 0.7 horsepower, or 700 times larger.
Many efforts were made in the late 1800's and early l900's to harness the flowing currents of rivers without using dams. These river current motors were supposed by their inventors to recover energy from the velocity of the moving currents of water, and to convert this energy to some other more useful form. The driving of a generator of electricity was one commonly envisioned form.
Study of this old art of river current motors reveals that they were all invented on the basis of a poor under-standing of hydrodynamics, and a consequent false premise.The prior art seems to indicate that a river current motor, inserted into a river current, can remove part of the kinet;c energy from the water and yet have the ~ater proceed wlthout loss of velocity through the motor.
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1 30 ~ Such a situatlon is no more possible than is per-., ~ .
: petual motion. What actually happened upon\introduction oF a .

~5~t7~8 prior art river current 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, by a local rise in river level. As a consequence, part of the river flow that formerly went through the region of 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 ex-tracted, and the prior art river~current motors were extremely inefficient.
Little attention had been given in these prlor 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 re-entrance of the portion of the current from which energy was supposed to have been extracted.
SUMMARY OF THE PRESENT INVENTION
The river current motor of the present invention is based on the principal premise that in order to remove kinetic energy from a moving mass of water, without thereby reducing the mass rate of flow, it is necessary to provide immediately downstream of the energy removal device, a region intd which the mass of treated water is impelled to move, and simultane-ously, that the mainstream of water ~s impelled to move awayfrom this region. Subsidiary to this principal premise, the . 5 ':
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~ 8 present invention also employs novel configurations using accepted hydrodynamics principles, to take fullest possible advantage of the passing river stream, utilizing and recover-ing not only part of the energy in that portion of the river stream actually intercepted by t;his river turbine, but also utilizing part of the energy of the mainstream to prepare a favorable downstream region for the discharge of the inter-~ cepted portion.
; The objects of the invention, and others, are ac-complished in a river current motor of the type made up of a primary nozzle with longitudinal horizontal axis, immersed in ; said river with 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 ~o external utilization means, the improvement comprising the . following:
(a) the flarlng of the waterway from the throat to the dis-charge end to initiate and establish a gradually increasing j cross section of the collected portion oF said river current ;~. 25 from the time it passes said turbine wheel, and (b) the flaring and structuring of the exterior of said ~'. primary nozzle to initiate and establish the formation of adiverging conical sheath of mainstream river current around the said collected portion as said portion exits the discharge end o~ said primary nozzle.
In one preferred form, the turbine wheel carries at . . , .~ - 6 -. ., : .. . . . -; - -, . ~ . ., ~ . ~ . . .. . . . .
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-7~L8 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.
Also in preferred form, the outer rim of the shroud ring is a pulley on which is carried at least one endless belt leading through channels in the structure of the primary nozzle to energy utilization means.
And in preferred form, a trash screen is provided in the river upstream of the entrance end of the primary nozzle, the trash screen comprising a conical array of cables on hori-zontal 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 nozzle9 to which the said open end is juxtaposed and attached. For minimum flow resistance, the included angle within the cone is preferably about 30.
Preferably, the waterway within the primary nozzle converges smoothly from an initial intercepting 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 1:1 to 4:1.
In one form, the turbine wheel is of the purely axial - flow type~ and the tailpiece of the waterway downstream from the turbine wheel flares at an included angle of up to 15, preferably about 7. With this form the tailpiece may have an axial length of at least one half of the diameter oF the ; throat of the waterway.

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It is important to the success of this invention not only that the waterway of the primary nozzle have the charac-teristics enumerated above~ but also that the exterior be 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 exits the discharge end of the primary nozzle. There-by 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 reorganized as to aid the flowing away of the collected portion. The forming, directing, and reorgan-`' 15 izing are provided for by one or more of the following features of the exterior of the primary nozzle:
- (1~ As aforesaid, 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.
(2) Structural elements are added to the exterior surface further to effect the desired sheath formation.
(3) 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 radi-i 30 ally outward pressure gradient. The motion is as a helical .~
;l sheath. The pressure gradient is distinctly helpful in aiding

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the discharge of the collected portion of the river current.
(4) A further structural element, which may conveniently be supported on the outer extremities of the vanes just men-tioned, 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 nozzle forming 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.
(5) A further structural feature is the flaring of the interior and the exterior surfaces of the secondary nozzle 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.
(6) Yet another structural feature is the provision on the exterior of the secondary nozzle near its leading edge of a set of delta - shaped vanes, extending outwardly from the sur~ace, and Formed into ~ragments of a helix or helices, whereby to generate a vortical motion o~ the mainstream on the outside of the secondary nozzle, in the same manner and for the same reasons as in item (3) above.
~ ,1 It is also possible to form or position these vortex-generating vanes not to generate a single large vortex around ; 30 the secondary nozzle, but Yat~e~ to generate many small vortices or eddies along the surface of the secondary nozzle. `

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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.
(7) Yet another structural feature is a set of petal-like flaps extending rearwardly from the trail1ng 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.
(8) 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 the cooperating diverging waterway from the throat to the dis-charge end of the primary nozzle, the turbine wheel, rather than being of pure axial flow type, has vanes shaped to enable ~i the portion of river current entering axially into the tur-'t 25 bine, to exit with a considerable component of radial flow.
In this form the waterway diverges immediately at the turbine ~; discharge region of the throatl having a bell shape at this discharge point, whereby the region into which the partially ' de-energized water exits may have a large cross section into which the water can flow at low velocity. Downstream from this regîon, the waterway flare will continue as already , - 10 -,~

1~5~'74g3 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 that under load form catenaries~ such that the main stresses in the blades are tensile stresses. In one catenary vari-ation9 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 cate-nary variation each blade constitutes nearly one halF of thecatenary, 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.
DETAILED DESCRIPTION OF THE INVENTION
Figure 1 shows an isometric view of two of the nozzle and turbine arrangements of this invention in side-by-side arrangement. Figure 2 shows a single nozzle of Figure 1, in longitudinal section, mounted below a pontoon and machinery-deck structure, in a location within a river, where the river current impinges from the left, and flows away toward the rlght. 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. ~here the differences are so substantial as to cause confusion, separate designators are used.~
In Figures 1 and 2, item 1 designa~tes the deck of a boat-like structure, which is supported on structural - framework 3, aboYe two or more pontoons 2 9 spread apart in -` catamaran-like fashion, with space between and below each pair or pontoons. In thls`space there is located a primary nozzle structure 5 9 connected through elements nf 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 3 electrical control gear 26 and water pump means generally designated as 23.
The primary n~z~le 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 ~rom its entrance end 9 to a throat 8, which is the part of the waterway through the liner of least cross section. At the throat 8 is an annular recess 30 occupied by a shroud ring 17, which inter-relationship will be detailed subsequently and in Figure 12.
Downstream of the throat the liner 7 continues to a discharge section 10, at which section the cross section o~ the waterway through the nozzle has increased as the result of the flaring of the liner. As in known venturi practise, the liner should - flare with an included angle of less than about 15, prefer~
~ably about 79 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.
In another form of the invention~ as will be ex-plained hereinafter, the liner downstream of the throat may enlarge immediately into a bell shapei after this enlargement, 2 the rate of ~lare decreases to about 7, as just mentioned.
This is shown in Figure 17.
The liner 7 has a clrcular cross section at the , throat, but its cross section at other points along its len~th .~';

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is not necessarily circular. The mouth 9, for example, may be rectangular, square, polygonal, or even trapezoidal in cross section, and likewise may be the discharge end 10. 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 shell 6, has an external shape in the form of a long gradual change from the connection at its front or entrance end to its discharge end 12, which is joined smoothly into connection with the discharge end 10 of the waterway.
The gradual change is such that shortly before the junction, the surface of the shell, near its 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 this surface is deflected away from the axis into the be-ginning of a generally conical diverging sheath of mainstream water surrounding the similarly diYerging portion of river current passing out of the waterway.
In Figures 1 and 2, the divergence of the shell 6 at its discharge end 12 is slight, being hardly noticeable in the drawing. In this particular instance, such a slight di-vergence or flare is sufficient, because the other structures surrounding the primary nozzle and shortly to be described are the main causes of the generation of the flaring sheath of malnstream water. In other forms the flaring of the primary nozzle is much larger, as in Figures 3, 4, and 5.
The primary nozzle 5, having the previously described ;` outslde shell 6 and the inside liner 7, has a space or com-partment between these surfaces in which are located structur-al elements supporting the surfaces. In a preferred form of construction, the primary nozzle is comprised of ~ segmental ,.,. . , : .. r " ' ' ' ~. . ' ; ; ' ' ' ' " ' ' 5~7413 modules, each a segment of an octagon, each module carries not only 1/8 of the shell 6 and 1/8 of the liner 7, but also side partitions where the modules after assembly meet one another.
Especially for very large river current turbines, where the turbine wheel 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, using steel plate fabrication technology well known in barge manufacture. After construction, each module can be floated to the power generator site, and there they can be assembled.
The primary nozzle's compartments constitute an important source of adjustable buoyancy for the river turbine.
By pumping water out of upper compartments, but leaving more or less water in lower compartments, a range of centers of buoyancy can be established, as needed for various river conditions.
Nithin the waterway o~ primary nozzle 5 there is a turbine wheel 14 ? having a central sha~t 13 coaxial with the ` waterway's throat 8, blades 29, and a shroud ring 17 attached - 20 to the outer ends of blades 29. The turbine wheel is more easlly seen in Figure 14. In this form of the invention, the turbine is arranged for straight-through axial flow. In another form shown in Figure 17 the turbine blades and shroud ring are so arranged that the flow enters axially, but turns and exits outwardly, with a considerable radial component of .i ~
~, flow. This is the form of ~urblne wheel used with the bell shaped tail region in the waterway as previously mentioned.
In e~ther case, as shown in Figure 14 the turbine shaft is mounted in bearings carried in bearing block 15, which is in turn supported centrally withln the waterway with struts 16a and strut-vanes 16b. The strut-vanes 16b as shown : ~ .

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in Figure 13, are, as their name indicates, both struts sup-porting the bearing block, and vanes directing the axially flowing water into a helical path, the better to impinge on the blades of the turbine wheel in direction to achieve the highest efficiency of energy extraction. For control pur-poses, these strut-vanes can be rotated on 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 the strut-vane shafts 16c, as shown in Figure 13.
It is well known that river currents may entrain water-logged logs and other massive objects. Such objects, if carried into the blades of the turbine, could cause serious damage. In order to prevent such damage, it is a feature of ; the present invention, to provide upstream of the mouth of the waterway through primary nozzle 5, a trash screen 42 in the form of a cone of cables 43 and 44. The open end of the cone of cables is juxtaposed 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 clevises to cable attachments (not detailed) distributed around the periphery of $he waterway mouth 9. Some of the cables desig-nated 43 are full length, extending the entire distance from the anchor cable 41 to the mouth cl~vises. If all the cables extended the full length, however, and were spaced sufficient-.: j ly close to prevent trash entrance at 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) . -, .
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~ 5:~7~151 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 length1 it is within the spirit of this facet of the invention to use several lengths with additional branches as desired. It will also be clear that should the size of the trash require it, the trash screen's open end could attach to the secondary nozzle, rather than to the primary nozzle.
The cone-of-cables trash screen inevitably introduces some resistance to the flow of water through the waterway and turbine, which is an undesirable situation. In order to minimize the flow resistance, the trash screen is built with an interior included angle near 30, because near this angle the tilt of the individual cable axis relative to the line of ; 15 river flow offers an elliptical cross section from the actu-ally ~ound cable, at which section the fluid flow resistance is a minimum.
It was previously mentioned that the shroud ring 17 of turbine wheel 14 is let into an annular recess 30 in the throat 8 of the waterway. This detail 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.
An aspect of the present invention is the use of the shroud ring, not only as structural support for the outer ends of the turbine blades 29, but also for transfer of 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, : ' ~O ~ 7 ~
whereby deflection of the shroud ring under pressure of the river current against the turbine blades is cushioned in a layer 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. ~n 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 bPlts 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 l9a and the idler pulley l9b, as shown in Figure 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 i reduced, and less costly bearing structure is possible.
The kurbine wheel axial bearing as shown in~Figure 1 may ~e of known construction utilizing for example water 25 bearings 71, 727 73 as practised in shafts fur ships pro~
pellers.
I Water bearing 71 is a porous block provided with a -' chamber and passageway 71a, and a supply of pressurlzed water through line 74. Water bearing 71 is arranged at the ~ront surface o~ the stationary bearing ~lock 15 supported by struts 16a and strut vanes 16b within the throat. The back surFace ,' ' .

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of a nosepiece carried on sha-Ft 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 waterbearings. It is desirabie of - course, that the bearing be enclosed in a well streamlined frontal enclosure as depicted in Figure 2. The stub shaft extending rearwardly of the turbine wheel should also be well streamlined.
The turbine wheel l4 is made up of a hub on shaft l3, ; a shroud ring l7 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 l4.
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 con,sideration is the avoidance of cavitation, because cavitation would not only ' 25 increase the ~rictional 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 wlll be rather deeply ~submerged below the water surface~ and the differential head of water between the surface and the uppermost edge of the turblne will be of considerable magnitudei the greater this :

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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, : 5 and the blades' profiles must be selected using known hydro-dynamic principles so that the pressures on the back si~es 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 numi~er of revolutions per minute of the wheel, and the section may both be thicker and ~- be tilted more s~uarely 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-rîng 17, which is ~n turn sup ported 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 shapes -together with large strengths and reasonable cost, it is almost essential that modern fiber reinforced plast~cs tech-~, nology be utiliz:ed. Preferably, the blades are made with fiberglass/epoxy construction, with rigid foam core in the .j .
, ~ thicker`sections. Continuous filaments of glass extend . : lengthwise of the blades, for bending stiffness; for torsional strength, ~elts of filaments extend diagonally across the widths of the blades. ~here a core is used, it may be of - : 1 9 _ :, .

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S~5L'7~L8 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. Some solutions to this problem are forms of a catenary blade, as shown in Figures 15, 16, and 16b. In construction of Figure 15 the blade is deliberately formed into a bowed U-shape, ln the direction toward which the current tends to force it. The preshaping 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 .15 elim~nated~ Such a construction takes full advantage of the -~excellent strength characteristics of modern composite materi-als.
The above described catenary blade construction can :`be carried a further step, as shown in Figure 16. In this 20 version each blade can be designed to be (when under load) .approxlmately one half of a symmetr7cal catenary with axis on the centerline of the wheel, and extending entirely across the .`idiameter of the turbine wheel. By such a design, the forces parallel to the axis are transformed into tension in the .25 catenary, and the thrust on the central shaft is eliminated;
all of the load of the impulse of the river current is trans-ferred directly to the shroud ring and through its water bearings 27b to the surrounding primary nozzle structure.
Having thus eliminated all of the axlal thrust forces, ~t becomes posslble also to eliminate the central support of the wheel, by locating trunnion bearings around the outside of the ~, ' - 20 - :

~ '74~
rim of the shroud, in order to support the turbine wheel radi-ally 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. ~lth 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 is 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 d1rection - in which it is thrust by the impinging water currents, as well as in the axial direction. This design is ind~cated in Figure 16b which shows in fragmented fashion a face-on view of a turbine wheel. Only two complete blades 29 are shown, the others being ind~cated by the dotted lines extending from the ` central hub. Each of the blades 29 has a catenary shape as ~een from this v1ewpo1nt, as well as the catenary shape seen in Figure 16. Thereby all bending forces 1n any direct10n are elim1nated, and the forces within the blade are tension. As in Figure 16, 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.
This discuss10n w111 now cover the structures external to the primary nozzle, beginn1ng with those shown in -~ Figure l and Fiyure 2. Seen in side view in Figure 2 are two , of a set of vanes 63 éxtending radially outward from the outside surface 6 of primary nozzle 5. These vanes 1n Figures l~and 2 are not only vanes as such for directing the Flow of mainstream river current past the exterior of the nozzle, but .

~ 7 ~ 8 in this form of the invention are also structures supporting the annular secondary nozzle 60, coaxial and in partial over-lap 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 past the remaining surface of the primary nozzle. 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 Sect EE of Figure 8, ~hereby the passing mainstream current is directed to begin to flow as a vortex. The ~ent downstream edge of the vane is depicted in Figure 2 at 64, and in Figure 9. Tt is in some c~rcumstances deslrable to be able to change the intensity of this helical motion, and this change is provided for, by ; 15 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 conventi~nal adjustment means not detailed. - -Such means might include as some of the possible alternatives the following: (1) cables exten~ded from levers on the pivot shafts of the ailerons (2) push-pull slides on bent tracks, with hydraulic piston actuators (3) worm-and-pinion drive on the pivots, with hydraulic motors to drive the worms, simi-larly to Figure 13, and Figure 11.
- The secondary nozzle 60, in a manner similar to the primary nozzle, is designed with a liner forming an inside surface and deflnlng the aforesaid annular passageway outside i;~ the primary nozzle. The secondary nozzle also has an exterior -,~ surface, and a space between the liner and the exterior surface containing struts and braces9 and constituting a ` 30 watertight compartment, or plural~ty of compartments, which can be utilized in obtaining the desired buoyancy character-5~79~

istics of the entire 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 lndividual 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 exterlor 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.
` As the secondary nozzle's liner passes downstream beyond the adjacent discharye end of the primary nozzle, its cross section begins to increase; ln other words, the high velocity sheath of mainstream water now is guided by the flaring of the liner into a diverging cGnical 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, t~e kinetie energy, which varies as the square of the linear velocity, and the potentiaZ ene~gy, which is measured by the static head relative to any preselected datum.
By careful attention to streamlining and flaring o~ 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 because of turbulence and friction, to transform kinetic energy into potential energy, and vice versa. This transformation is expressed in the well known : .
Bernouilli's theorem, which is simply one form of the energy ~ S3L~
balance on the flowing water.
The portion of the water which was accelerated to high velocity, then flowed through the turbine vanes and gave up energy as mechanical output through the turbine's belt 18, comes out of 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, with the same flow cross section immediately downstream as at immediately upstream, the velocity achieved by acceleration through the converging primary nozzle entrance section can not change, because the total volumetric flow is constant. Accordingly, the static pressure, which was already considerably lowered because of the conversion in the converging section into additional kinetic energy of the higher velocity, is further reduced in passage through the turbine, by transfer out of the liqu'id into the turbine's mechanical output. As the portion of river current downstream of the turbine increases in cross section in the diverging section its residual kinetic energy is partlally transformed back into higher static pressure po-tential energy. ~hen the pressure has thus been raised suf-ficiently in the flaring downstream cone o~ water, it may again be blended with the surrounding mainstream water.
With the turbine wheel of the radqal 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 ~n 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 eo drop to a lower linear velocity because it is flowing from a smaller to a larger cross section, the mass :~ .

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~ 3Ç5 ~a~8 flow of course being constant throughout the waterway. To the extent that the linear velocity can be dropped, the equivalent mechanical energy can be removed without change of pressure.
This analysis neglects for the moment, that any feature intro-ducing more turbulence into the flowing liquid will therebyincrease the frictional losses, by transformation of some of the system's kinetic and potential energy into heat. Ef-fective use of the radial discharge turbine and bell shaped waterway requires careful design to minimize the frictional losses.
However, it may be difficult to maintain the flaring cone of water sufficiently separate from the surrounding mainstream, unless special steps are taken. These special steps are the result of the shaping and structures on the out-side of the primary nozzle. The formation of the protectingsheath of mainstream water enables the continued conversion of the portion passing through the turbine from kinetic to pressure energy.
The high velocity sheath developed by acceleration of mainstream water through the annular passageway between primary and secondary nozzle, has, as a result of its acceler-ation, a reduction in static pressure, so that there is reduced tendency of the mainstream river current to flow into the axial region downstream of the nozzle, whereby the environment for the continued expansion in cross section in the flaring conical portion is favorable.
The exterior surface of the secondary nozzle 60 is also structured to favor the formation and protection of the diverging conical sheath of mainstream water. Proceeding rearwardly from the mouth end 61, the exterior surface gradu-ally and smoothly moves radially inward, toward the turbine : ~ - 25 -, .

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~0 S~ 8 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 passing this surFace is directed outwardly, to conform generally with the exterior of the conical sheath emitting from the inside of the second-ary nozzle.
To the same end, near the forward part of the exterior surFace of the secondary noz~le 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 sur~ace that decreases in diameter in the flow direction for some considerable distance, before its diameter then flares as earlier described. It is important ~hat the mainstream flowing past the region of decreasing diameter should remain "attached" (in the parlance of the hydro-dynamicist) 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 vor~ices 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 a simple primary nozzle flaring from the throat toward the discharge end. It .
has also been pointed out that greater efficiencies may be .. . : , . .. .. . . . . .. .. . . ..

~95~7~
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 preconverger is utilized, the throat of the nozzle falling immediately adjacent to the mouth. In this version, the turbine wheel receives the intercepted portion of the river current essentially at its prevailing velocity, removes energy from it, then diffuses the portion as already taught into a conically diverging stream of decreasing velocity and in-creasing pressure, before blending with the mainstream.
- In Figure 4 a preconverger is used with the primary nozzle, which distinguishes Figure 4 from Figure 3. However5 the nozzles of both Figure 3 and Figure 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.
` 20 In Figure 5 is shown a primary nozzle having a rela-tively 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 ha~ve 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 in-vention, in further improving the control of mainstream flow and sheath formation on the outside. Fach aspect of the ,~ 30 structures has already been discussed. These additions may be made to any of the forms of primary nozzle, as already , . .
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described.
It was earlier mentioned that the deck 1 carries certain auxiliaries, and these will now be dealt with in more detail. Abo~e the cabin supported from the platform is a transmission tower 24 for the support of electrical trans-mission 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 for the main purpose of this ~; invention, namely, to generate large amounts of electrical power for utilization cn shore. Since most po~er grid systems ~ are based on ~0 herz, this generator will preferably be such a - one, with output voltage and number o~ phases suitable to the ; 15 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 synchroni-zation and frequency, as well as the voltage produced, be of highly precise values. To this end, conventional electrical control gear is provided at 26. Signals showing any unwanted deviations will be developed 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 such as 4b could be provided and with suitable clutches (not shown) and electrical controls, driven from the same energy source, being bro~ught `~ "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 .

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~ 15~8 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 neces-sary to have a supplemental engine-driven generator, and suitable fue1 tanks. These are conventional, and are not shown in the drawings.
One of the means for speed control on generator 4a is by way of pulley l9a, wh;ch may be a variable diameter pulley with means for adjusting its diameter "on the fly" as required - in response to signals from the control system 26. Other : means will be discussed later. At l9b is shown an idler pulley, by which the tightness of belt 18 may be held constant, despite changes in diameter of pulley l9a, and despite stretching of the belt. Idler pulley l9b may be con-tinuous1y and automatically reset by conventional drive means and control means not shown.
- Water pumps 23 are designated generally9 but in actu-`, 20 ality may be of more than a single specification. For example, some will be suitable for pumping water out of the compartments of the nozzles, others 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 ; 25 this invention in side by side arrangement, it is obvious that single units, or multiple units of more than two turbines can be used without departin~ from the spirit of the invention.
~' Indeed, when two or more units are coupled side by sidea it ispossible to completely eliminate the pontoons 2, or at least to reduce their number, because adequate flexibility in adjustment of buoyancy is available through the compartmental-' .

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~L~S~ 4E3 ization at the several nozzles.
EXAMPLE
By way of example to illustrate the ability of river turbines of this invention, there are tabulated below some typical dimensions that would apply to a single turbine for use in a river of at least 100 ft. depth and breadth. Many reaches of the Mississippi River have such a depth, and many times this breadth.
; PRIMARY NOZZLE: Mouth Diameter........................ 66 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.
20 Overall Length....................... 70 ft.
Tailpiece Flare.......................... 7 Tailpiece Length throat to exit.................... 40 ft.
Exterior Convergence............................... 60 ft.
Exterior Flare..................................... 10 ft.
25 Overlap of Primary and secondary nozzles.............................. 30 ft.
Sheath thickness at departure from primary exit......................... 9 ft.
With an upstream river velocity of 7 knoks, the mechanical power delivery to the electrical generators is i 1 expected to be equivalent to 7500 KVA.
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Several modes of operation of the invention have been disclosed in the foregoing specification, and others will be - evident. It will be understood that various modifications may be made within the scope of the claims, without departing from ; 5 the spirit of the invention.

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Claims (14)

CLAIMS:

1. In a river current motor of the type made up of a primary nozzle with longitudinal horizontal 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 improvement comprising the following:
(a) the flaring of the waterway 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 it passes said turbine wheel, and (b) the flaring and structuring of the exterior of said primary nozzle having means to initiate and establish the formation of a diverging conical sheath of mainstream river current around the said collected portion as said portion exits the discharge end of said primary nozzle, (c) the provision in the said structuring of a set of radially extending vanes on the exterior surface of said primary nozzle, each vane of said set having a helically bent trailing edge, all said bent trailing edges being turned in the same helical direction, whereby to induce helical rotation into said diverging conical sheath.

2. The river current motor of Claim 1, with which a trash screen is provided in the river upstream of the en-trance end of the primary nozzle, the trash screen comprising a conical array of cables on 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.

3. The river current motor of Claim 2, in which the cone has an included angle of about 30°.

4. The river current motor of Claim 1, having a second-ary nozzle with a passageway having a mouth, throat and exit coaxially supported in partially overlapping and surrounding relationship with the tailpiece of the said primary nozzle, with clearance between the lining of the passageway of the secondary nozzle and the exterior surface of the primary nozzle forming an annular passageway for the flow of mainstream water past the overlapped exterior surface of the primary nozzle.

5. The river current motor of Claim 4 , in which the exterior surface of the secondary nozzle is provided with a set of delta-shaped vanes extending outwardly from the surface and formed into fragments of at least one helix, each such helix rotating in the same direction as any other.

6. The river current motor of Claim 1, positioned in a river current, and (1) tethered from an upstream anchor through (2) an anchor cable connecting from said anchor to the tip of a trash screen in the form of a horizontal con-cal array of cables extending over at least part of the slant length of said array from said tip to an open end forming the base of said array, each cable terminating in an at-tachment around the periphery of (4) the mouth of the said primary nozzle of Claim 1, said primary nozzle having (5) a waterway converging from said mouth to (6) a throat of lesser cross section than said mouth, said throat provided with (7) an annular recess, said waterway flaring from said throat to (8) a discharge end removed from said throat by a distance of at least one half diameter of said throat, the angle of flare being less than 15°, preferably about 7°, (9) an axial-flow turbine wheel coaxially mounted in (10) a water-bearing structure supported on (11) struts and (12) strut-vanes within said waterway at said throat, said turbine wheel having vanes extending from hub to (13) a shroud-ring rim positioned with the said annular recess of the throat and rotatable against (14) water bearings located downstream of said rim and bearing against it, said rim carrying at least (15) one pulley groove in its exterior face, (16) an endless belt riding in said groove and proceeding through (17) channels extending upwardly to (18) variable-diameter pulley means driving (19) electrical generators, said primary nozzle having (20) an exterior surface coaxial with said waterway, said exterior surface having (21) a mouth joined in watertight fashion to the said mouth of the waterway, and (22) a discharge end likewise joined in water-tight fashion to the said discharge end of the waterway whereby (23) a watertight compartment is formed between said waterway and said exterior surface, (24) pump means connected to said compartment for controllably removing water therefrom, said exterior surface of the primary nozzle having (25) a smoothly curved surface that flares adjacent to its discharge end at an angle approaching the aforesaid angle of flare of the waterway, (26) a set of strut-vanes extending radially outward from said exterior surface, said strut vane being provided with (27) aileron-like flaps hingedly attached to the trailing edges of said strut vanes and with (28) control means for adjusting the angle of set of said flaps, (29) a secondary nozzle mounted externally to said strut-vanes, coaxial with the primary nozzle and in partially overlapping relation with the discharge end of the exterior surface of the primary nozzle, said secondary nozzle having (30) a mouth, (31) a throat and (32) a discharge end and together with the overlapped primary nozzle forming (33) an annular passageway there between, said annular passageway having a cross section at its mouth greater than the cross section at its throat in the area ratio of 1:1 to 3:1, said passageway from its throat to the discharge end flaring outwardly at an (34) angle like the angle of flare of the waterway within the primary nozzle, (35) the exterior surface of said secondary nozzle being joined in watertight fashion to the mouth and discharge end thereof and forming therebetween a watertight compartment (36) pump means connected to said compartment to control its water content (37) the exterior surface of said secondary nozzle proceeding smoothly from the mouth to the discharge end of the secondary nozzle, and flaring at least in the region near the discharge end, with an angle of flare approaching the angle of flare of the adjacent passageway, said secondary nozzle carrying at its discharge end (38) a set of petal flaps hingedly attached to said discharge end and provided with (40) control means for establishing a desired degree of flare and said secondary nozzle carrying adjacent its mouth end on its exterior surface (41) a radially standing set of delta-shape vanes canted to fall within at least a single helix around the exterior surface.

7. The improved river current motor of Claim 1, in which the turbine wheel carries at its outer periphery a shroud ring, the throat of the waterway has a cooperating annular recess receiving the shroud ring, the said ring being positioned within the said recess and rotatably supported therein on radial and thrust bearings positioned within the said recess.

8. The structure of Claim 7, in which the said bearings areof water bearing type and in operation are supplied with pressurized water lubricant.

9. The river current motor of claim 7, with which a trash screen is provided in the river upstream of the entrance end of the primary nozzle, the trash screen comprising a conical array of cables on 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 secondary nozzle, to which the said open end is juxtaposed and attached.

10. The river current motor of Claim 9, provided with a trash screen comprising a conical array of cables, in which array some of the cables extend the full length of the array from the tip of the cone to the base of the cone, whereas some others extend only part of the way from the base of the cone toward the tip and are clamped at their upstream ends to the adjacent full length cables, whereby to improve the distribution of cable density.

11. The river current motor of claim 1, in which the turbine wheel is mounted for rotation on a generally horizontal axis concentric within the diameter of the throat of the nozzle, the throat having a concentric annular recess, the wheel being comprised of a shroud-ring rim and a set of turbine blades extending from the said axis to the said rim, the said rim being positioned within the said recess and rotatably supported therein on radial and thrust bearings wherein each blade of the said set has a configuration in a plane through the blade and the axis of the wheel that is bowed in the direction of river current motion in a shape approaching at least a section of a catenary figure with axis of symmetry parallel to the axis of the wheel, said axis of symmetry being within the diameter of the shroud-ring rim.

12. The turbine wheel of claim 11 in which the axis of symmetry of the said catenary figure is located between the axis of the wheel and the rim at the point of attachment of the blade.

13. The turbine wheel of claim 11 in which the axis of symmetry of the said catenary figure is located on the axis of the wheel.

14. The turbine wheel of claim 11, 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.