WO2007107505A1

WO2007107505A1 - Turbine assembly and generator

Info

Publication number: WO2007107505A1
Application number: PCT/EP2007/052489
Authority: WO
Inventors: George Robert Lee; Benjamin Rimmer; Antonios Tourlidakis
Original assignee: Shell Internationale Research Maatschappij B.V.; Shell Canada Limited
Priority date: 2006-03-21
Filing date: 2007-03-16
Publication date: 2007-09-27
Also published as: CN101389853A; GB0812132D0; GB2446765A; AU2007228835B2; AU2007228835A1; CA2645258A1; BRPI0708262A2

Abstract

A turbine unit comprises a housing (20) a turbine rotor (10), and a diffuser (70), which is located downstream of said turbine rotor (10) to receive fluid discharged from the rotor, which tapers outwardly in the downstream direction, and which comprises means (72, 74) for introducing supplemental fluid from exteriorly of the housing (20) to the flow discharged from the rotor (10). Furthermore a turbine generator unit is provided of which the rotor (10) comprises a plurality of rotor blades and the unit further comprises an electrical generator (80) coupled to the turbine rotor (10) to be driven thereby, the generator comprising a rotor assembly and a stator assembly, one of the rotor assembly and the stator assembly comprising one or more coils (86) and the other of the rotor assembly and the stator assembly comprising one or more magnets (84) for magnetically coupling to the one or more coils (86) for the inducing of electric current therein as the turbine rotor rotates, wherein the rotor assembly is carried to the turbine rotor blades (12).

Description

TURBINE ASSEMBLY AND GENERATOR

FIELD OF THE INVENTION

This invention relates to a turbine assembly for powering an electrical generator. The invention also relates to a combined turbine assembly and electrical generator.

BACKGROUND OF THE INVENTION

The need arises in various locations for a local source of electrical power, free from mains or other conventional power line supplies and not requiring an energy source such as the conventional petrol-driven or gas-driven electrical generator. A primary source of energy that may be available is wind or water. Water power may be available in flow bodies of water on land and found in rivers and streams or in moving currents in lakes for example. Water power may also be found in currents in the sea.

The extraction of energy to generate electrical power from moving natural bodies of water may be differentiated from conventional hydro-electric power generation in which a head of water is deliberately engineered to power a turbine which drives the electrical generator .

The use of natural currents of air is applied in wind powered turbines. A wind turbine is a fixed structure having a set of blades on which the wind impinges and which is constructed to orient itself to face into the wind.

The development of the present invention has been particularly directed to a unit capable of extracting energy from natural or forced movements of bodies of water with a view to providing a local source of electrical power. It is contemplated that the teachings of the invention may be applied over a scale ranging from a hand-portable generator to a substantial unit located on the sea-bed for example. However, the teaching of the invention is not limited in scale. It could be applied in what is known as microengineering for example. The invention is also applicable to extracting energy from air flows. Reference herein to fluid flow is to be understood to encompassing liquid and gas flows. The invention will be particularly described and discussed with relevance to extracting energy from flowing water.

One form of small turbine generator is described in US patent 4746808. The turbine is of the Pelton wheel type requiring activation by a set or injectors connected to a pressurized source of water. It cannot take advantage of a natural flow of water. The rotary motion of the turbine is communicated to the rotor of an electrical generator which is of the type using permanent magnets.

US Patent 6013955 discloses an axial flow turbine which is mounted in a housing intended for submersion in a stream. The turbine is mounted in a conduit extending through the housing and through which water flows to rotate the turbine. The turbine unit is provided with a tail fin to maintain the unit headed into the stream. The turbine is mechanically coupled to a separate electrical generator .

The design of the turbine housing and conduit described in the '995 patent does not provide for self alignment with a flowing stream. Furthermore, the flow paths associated with the housing and the conduit therethrough do not have a particularly high efficiency of extraction of energy to power the turbine from the flowing water. The efficiency with which the available potential energy of the water flow is extracted is a function of both the structure of the turbine itself and the flow path in which it operates . One deficiency of the inlet to the flow path provided by the housing disclosed in the '955 patent is that it has a symmetric configuration. The significance of this will be explained subsequently. It is generally desirable to provide a turbine generator (turbine unit plus generator) which is capable of operating at a relatively high efficiency in slow- moving current of water or other fluid (including air) . In the embodiments of the invention described below, the only energy available for doing work is that of the free stream in which the turbine unit is submersed. A first objective, therefore, has been the design of a turbine which extracts energy efficiently from a free flowing current of fluid. The fluid flow may be a relatively unconstrained flow, such as a natural stream of water: It may be a constrained flow such as is found in a pipe. The turbine arrangement to be described is applicable in any orientation, horizontal, vertical or inclined. It is usable over a wide range of flow rates and is scalable from very small up to large devices. SUMMARY OF THE INVENTION

In one aspect, the present invention is concerned with the design of a turbine unit as a converter of fluid flow to mechanical power. The particular use to which the mechanical power so developed is put in the preferred embodiments of the invention is powering an electrical generator. The generator may be separate from the turbine unit or may be have its rotor made integral with or part of a unitary structure with the rotor of the turbine unit .

Another aspect of the invention is concerned with an electrical generator the rotor of which employs a turbine rotor as an integral element or in which at least the turbine rotor and generator are combined in a unitary assembly.

In connection with the foregoing one aspect, the invention provides a turbine unit as set forth in Claim 1.

A preferred turbine unit is provided with the inlet portion and the diffuser in accordance with Claim 6. Still more preferred is to have the turbine rotor as part of a unitary structure with the rotor of an electrical generator as set forth in Claim 10, Claim 11 or 12.

The above-mentioned other aspect of the invention concerned with an electrical generator is applicable to a turbine generator unit comprising: a housing defining a conduit for the flow of fluid therethrough, a turbine rotor located in the conduit for rotation by the flow of fluid therepast, the rotor comprising a plurality of rotor blades, and an electrical generator coupled to the turbine rotor to be driven thereby, the generator comprising a rotor assembly and a stator assembly. In accordance with this other aspect of the invention the rotor assembly is made integral with or a unitary structure with the turbine rotor.

In connection with this other aspect, the invention also provides a turbine generator as set forth in Claim 13.

These and other features, embodiments and advantages of the turbine unit and turbine generator according to the invention are described in the accompanying claims, abstract and the following detailed description of preferred embodiments in which reference is made to the accompanying drawings .

The invention and its practice will be described in detail with reference to the preferred embodiments thereof illustrated in the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

Figs. Ia and Ib show perspective external views of a turbine generator unit embodying the invention; Fig. 2 shows in a diagrammatic representation, an axial cross-section of the turbine generator unit;

Fig. 3 shows a schematic half-axial view of the successive stages of the turbine unit and their interfaces ; Figs. 4a and 4b show respectively absolute flow velocity (C) and static pressure (P) as a function of distance (x) as fluid flows through the successive stages of the turbine unit;

Fig. 5 shows vector velocity relationships pertaining to the inlet guide vane (IGV) and turbine rotor stages, velocity triangles a) and b) referring to interfaces 92 and 93 respectively;

Fig. 6 is a normalised vector diagram combining diagrams a) and b) of Fig. 5; Fig. 7 illustrates a section through the inlet stage of the turbine unit and the streamlines associated with fluid intake into the inlet stage;

Fig. 7a illustrates the pressure and velocity differentials established between the inner and outer surfaces of the inlet stage;

Fig. 8 shows a cross-section through the turbine generator unit to show a face view of the rotor stage forming part of an electrical generator, only one rotor blade being shown;

Fig. 9 shows a diagrammatic axial cross-section through a modified embodiment of the turbine generator unit of Fig. 2; and

Fig. 10 shows a diametric cross-sectional view through the generator unit of Fig. 9 to a larger scale. DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention will be described in relation to a turbine generator which includes a turbine unit that is made as part of a unitary combination with an electrical generator or dynamo. The embodiment to be described includes elements of the generator as a unitary part of the turbine rotor. However, the design of the turbine unit itself as a converter of the energy of a fluid flow to mechanical power, specifically rotary power, is applicable to turbine generators in which the generator is a separate entity to the turbine to which the generator is coupled to be driven the rotation of the turbine. The following description will describe the major elements of the turbine generator unit, followed by a more detailed consideration of the turbine unit, and thereafter a more detailed discussion of a generator incorporated into the turbine generator unit. The Turbine Generator Unit

Figs. Ia and Ib each show an external view of a turbine unit embodying the invention and shows main elements of the structure. The electrical generator within the unit is not seen in these figures. As will be described below, the complete turbine unit has a succession of stages. It will be assumed that the unit is to be powered by a flowing body of fluid in which the unit is submersed. Specifically a flowing body of water will be assumed.

The turbine unit has a turbine rotor 10 rotatable about a longitudinal axis of the unit. The rotor 10 is disposed for rotation in a circularly annular housing 20 which provides a conduit for a generally axial flow path therethrough. Housing 20 includes an inlet stage 30 having an inlet opening 32. Water enters the inlet stage flowing in a general axial flow direction F. The inlet stage 30 is flared to narrow in the flow direction F towards the rotor 10.

Between the inlet stage 30 and the turbine rotor 10 are a set of inlet guide vanes 40 (conveniently referred to as the IGV 40) the outer ends 42 of which are affixed to the inner surface of the housing 20 and the inner ends 44 of which are affixed to an axial boss 50, whereby the boss is supported in an axially centred position in the flow conduit. The inlet guide vanes provide a stage by which a whirl component is given to the axial flow of water entering IGV stage 40. The whirl component drives the turbine rotor 10 as an reaction turbine as will be more fully explained below. The blades 12 of the turbine rotor 10 are secured to a rotor hub 60 that is rotatably mounted to boss 50 to rotate about the common longitudinal axis. The construction will be described later with reference to Fig. 2. The downstream side of rotor 10 leads to a diffuser 70 which is mounted to the rear of housing 20 by supports (not shown) . The diffuser 70 flares outwardly in the rearward or downstream direction. It is an important feature of the diffuser that it provides for supplementary flow of water drawn from externally of the unit into the interior diffuser chamber. The means for enabling supplementary flow of surrounding water into the diffuser 70 is shown as a pair of annular slots 72, 74 in Figs. Ia and Ib. Thus the total flow of water leaving the rear of the diffuser is the flow through housing 20 and past rotor 10 plus the additional flow drawn in through the annular slots. This enables an important operational benefit to be gained as will be explained below.

Many ways of providing a supplementary flow intake can be envisaged. Some are mentioned subsequently. The illustrated slot arrangement shown provides a first slot 72 between the rear of housing 20 and a first diffuser part 70a, and a second slot 74 between part 70a and a second diffuser part 70b. The slots face toward the flow. The first diffuser part 70a overlaps the rear of housing 20 in the axial direction and is of greater diameter to form forward-facing slot 72. Similarly the second forward-facing slot 74 is formed by the overlap of parts 70b and 70a. The housing 20 and part 70a and the parts 70a and 70b can be connected by radial struts 73 and 75 in the overlap regions. It is not essential that the slots are defined by overlapping parts as will become apparent from the modified embodiment described hereinafter .

The internal structure of the turbine unit is better seen in Fig. 2 which shows a diagrammatic axial section which is essentially circularly symmetrical about longitudinal axis A-A. Like reference numerals denote the like parts of Figs. Ia and Ib.

As will become apparent from the later description, aspects of the external design of the unit and the external flow are of considerable importance to the provision of a unit that efficiently extracts energy (power) from the water flowing through and around the unit. The direction of water flow is indicated by arrows F, upstream being at the left of the figure.

Fig. 2 illustrates more of the internal structure of the turbine generator unit in which the rotor of the turbine unit is formed as a unitary structure with the rotor of an electrical generator 80. In Fig. 2 the annular housing 20 has a first intermediate portion 20a in which the IGV 40 is supported (the vanes are shown schematically as a block) and a second intermediate portion 20b of greater internal diameter in which the turbine rotor 10 rotates (the turbine blades are shown schematically as a block) . The outward stepping of the housing portion 20b is provided to accommodate the rotor element of the generator 80 as will be described. The flared inlet stage 30 is formed in a forward portion 20c of the housing 20 and leads into the IGV 40. The rearward portion 2Od of the housing provides the flow connection between the turbine rotor 10 and the diffuser 70.

As noted above, IGV 40 is mounted between boss 50 and the inner surface of housing (portion) 20a and thereby supports the boss aligned on axis A-A. The rotor hub 60 carries the rotor blades 12 (Figs. Ia and Ib) to rotate within the intermediate portion 20b of housing 20. As illustrated the boss 50 supports axially-projecting spindle 52 about which hub 60 rotates on ball-race 62. It will be appreciated that many ways of rotatably supporting the rotating hub 60 to the fixed boss 50 can be devised.

Mention has been made of the greater internal diameter of housing portion 20b as compared with the portion 20a in which IGV 40 is supported. The rotor 10 has an outer diameter (at the tips of the rotor blades) essentially equal to the internal diameter of housing portion 20a to receive the flow delivered through IGV 40. The rotor tips are thus spaced from the inner surface 2Oe of housing portion 20b and in this space is received an annular structure which forms the rotor part of a generator 80. The annular structure comprises a ring 82 affixed to the tips of the rotor blades and in which are embedded magnets 84 that move closely adjacent surface 2Oe as the rotor 10 rotates. The inner surface of ring 82 forms a continuation of the inner surface of housing portion 20a to which IGV 40 is attached. If the boss 50 and hub 60 are of uniform diameter between the inlet to the IGV 40 and exit from the rotor 10, and likewise the outer diameter of the conduit formed by housing portion 20a and surface 82 is uniform, then a smooth flow path is provided which is of constant cross- sectional area (omitting the vanes and the rotor blades). The magnets 84 provide magnetic flux linking with a set of coils 86 supported in an annular assembly in housing portion 20b and extending to or closely adjacent surface 2Oe, whereby maximum linkage or magnetic coupling between the coils and the magnets is obtained. The generator 80 is discussed further below. It will also be seen that the rear inner surface 88 of ring 82 is flared outwardly toward the inner housing surface 2Oe to assist in a smooth flow of fluid along the surfaces.

The section 2Od of housing 20 rearward of the turbine rotor provides the input portion of the diffuser 70 which extends in the downstream direction as represented by outwardly flared parts 70a and 70b with first inlet slot 72 provided between housing section 2Od and the first diffuser part 70a and the second diffuser slot 74 provided between parts 70a and 70b. The supports between parts 2Od and 70a and between 70a and 70b are not shown .

As described above the slots 72 and 74 face toward the fluid flow F exteriorly of the turbine generator unit to which end the forward edge portion 71a of diffuser part 70a axially overlaps the rear edge portion of housing portion 2Od; and likewise the forward edge portion 71b of diffuser part 70b overlaps the rear edge of part 70a. The forward edges 71a and 71b are shaped to channel flow into the diffuser interior in a manner similar to the shaping of the inlet stage 30 provided by housing portion 20c as will be further discussed below.

Another feature of the slots is that the slot 72 directs supplementary addition flow obliquely toward the axis as shown by arrow Sl: slot 74 directs flow at a lesser or more shallow angle to be more nearly parallel to the axis as shown by arrow S2. The operation of the diffuser is more fully discussed below.

The description thus far has outlined the major elements of the turbine generator unit and individual stages of the complete turbine unit will now be considered in greater detail. The Turbine Unit

The operation of the turbine unit in relation to the flow through it can be considered in terms of the successive stages of the unit together with the respective interfaces between adjacent stages. The stages of the unit and the interfaces are indicated in Fig. 3. Inlet stage 30 provides the intake inlet interface 90 with the flowing stream and an inlet stage/guide vane interface 91 with the IGV stage 40. IGV 40 leads to an interface 92 with the inlet side of rotor 10. The outlet side of rotor 10 has an interface 93 with the inlet of diffuser 70 and the diffuser has an outlet interface 94 back into the flowing stream. The supplementary intake into the diffuser 70 is not indicated in Fig. 3 and is discussed subsequently. More detailed consideration will first be given to the combination of the inlet guide vanes and the turbine rotor. The design of the guide vanes and the rotor blade shape employs techniques known in the art. The inlet guide vanes 40 receive an axially-directed flow at interface 91 and introduce into it a tangentially- directed or whirl component at interface 92. This whirl component acts on the rotor blades 12 to rotate the rotor as an reaction turbine .

The following description introduces various parameters which may have different values at different interfaces. The appending of the subscript 0, 1, 2, 3 or 4 to a parameter (e.g. C, V, h or H) denotes the value of the parameter at the interface 90, 91, 92, 93 and 94 respectively . As already noted the hydraulic turbine unit being described is of the reaction type. The relevant stages of the unit presently being considered are IGV 40 and rotor 10 involving interfaces 91, 92 and 93. The datum for measuring angles is the direction of axial flow A-A. Angle α pertains to vectors denoting absolute flow velocity C: angle β pertains to vectors denoting flow velocity V relative to the rotor blades at the mean rotor blade radius r_m. It is assumed that the flow into IGV 40 at interface 91 is axial (α = 0), and that the flow exiting the rotor to enter the diffuser at interface 93 is also axial (α = 0). In addition to the velocities C and V, reference is made of the tangential velocity U of the rotor blades at the mean radius r_m so that U = Ωr_m, where Ω is the angular speed of rotation of the rotor 10.

Two other parameters that are utilised are a non- dimensional (normalised) flow parameter φ = C_n/U (1) where n relates to the relevant interface, and the head ψ acting on the turbine unit given by ψ = ΔH/U² (2) where ΔH represents a change in total enthalpy of the fluid flow between interfaces 91 and 93.

Thus ΔH = Hi - H₃ (3)

The reaction R of the turbine unit (IGV40 plus rotor 10) can be expressed as follows:

where h denotes static enthalpy and H denotes total enthalpy.

Referring now to Fig. 5, the axial direction through the stages 40 and 10 is vertical, top-to-bottom. The velocity triangles to be discussed relate to flow at the mean blade radius r_m. Water enters IGV 40 at an absolute velocity C₁. It is then gently accelerated as the angle of the vane increases to α₂, the guide vane exit angle, so that the absolute velocity of the flow at interface 92 is represented by C₂. C₂ can be expressed as C₂ ² = Ci² + V_w ² (5) where V_w is the whirl or tangential velocity component imparted by IGV 40. Ci and V_w are shown in dashed line on diagram a) .

The water now enters the rotor 10 to impinge on its blades 12 and rotate the rotor at speed Ω.

The water exiting the rotor 10 is desirably flowing in the axial direction with an absolute velocity C₃, and a velocity V₃ relative to the rotor at an angle β₃. Ideally, the whirl or tangential velocity component V_w has been entirely dissipated in powering the rotor 10. It is also to be noted that C₃ = Ci and that the axial flow velocity through the turbine unit remains constant if flow continuity is maintained through the unit. This assumes that the cross-sectional areas Ai and A₃ of the flow path are equal. In the structure described with reference to Fig. 2, Ai = A₂ = A₃. The velocity triangles given in diagrams a) and b) of Fig. 5 can be combined as shown in Fig. 6 where the velocity vectors are normalised with reference to the rotor velocity U, and thereby become dimensionless . The rotor velocity vector U thus become unity (1.0) and the axial flow velocity can be normalised to φ = Ci/U = C₃/U. The normalised head ψ acting on the turbine unit is also seen in Fig. 6. Also shown is the angle ε_s, the flow deflection in the IGV 40, and the angle ε_R, the deflection of the flow in passing through the rotor. By using these dimensionless velocity triangles, the following relations are used to define the angles and velocities :

β₂ = arctan — —

I Φ )

ε _R = β₂ + β₃ = arctan ^ '

Φ - ψ+ K

γ

To summarise what has been discussed above, the IGV 40 imparts a whirl component of rotation to the fluid and this motive energy is converted to torque on the rotor blades. The power extracted by the turbine is proportional to the whirl velocity acting on the rotor. For minimum energy wastage, the flow exiting the turbine rotor should have minimal whirl. Losses such as skin friction and sheer losses have been ignored in this discussion . In terms of the total enthalpy at interfaces 91 and

93 the efficiency η_Tτ can be expressed as

where ζ_s and ζ_R are the loss coefficients for the inlet guide vanes (stator) and the turbine rotor respectively. These coefficients take into account profile friction losses and secondary flow losses.

The static and total pressure variation from the inlet interface 90 to the outlet interface 94 of the complete system may be carried by using the Bernoulli equation and by using the absolute velocity components at the various interfaces .

Hydraulic losses in the turbine stage can also be taken into account .

The foregoing discussion of design parameters relating to the IGV and rotor stages has referred to parameters identified with the mean rotor blade radius r_m. To realise a complete design prototype the hydrodynamic design of it was carried out in three stages . Firstly a one-dimensional model was used in order to define the basic dimensions, the velocity components and the inlet and outlet blade angles at a mid-span cross- section. The flow was assumed to be axial upstream of the rotor and one of the design objectives was to minimise the secondary (whirl) flow at the rotor discharge thus assuming axial flow entering the diffuser. The hydrodynamic losses due to the friction on the blade surfaces and due to the secondary flows were taken into account. A free vortex design was considered assuming a uniform distribution of the work along the blade span. This assumption was utilised to specify the blade angles at the hub and the tip sections of the inlet guide vanes and the rotor . In the second step, the geometrical design of the blades was carried out. Customised blade profiles were used in the near-hub, near-tip and mid-span sections and they were linked together in order to form the three- dimensional blade shape. In the third step, a three-dimensional computational fluid dynamics analysis of the turbulent flow was carried out in order to assess the hydrodynamic performance of the turbine stage and to predict the detailed flow phenomena inside the IGV and the rotor passages. This analysis provided a detailed description of the pressure and velocity distribution together with global performance parameters such as power output, efficiency and torque .

A number of iterations of the second and third steps was necessary in order to accomplish the target hydrodynamic performance parameters. The detailed performance of these steps is considered to be within the competence of those skilled in the art of turbine design. The three design steps were preceded by a parametric investigation in order to identify the parametric space that would produce useful turbine designs. It was found that in order to generalise the design procedure, the non-dimensional flow Φ and Ψ coefficients should be selected as independent variables. This procedure is what has been discussed above.

In order to further consider the operation of the complete turbine unit from inlet to outlet including the inlet stage 30 and diffuser 70, reference will again be made to Fig. 3 and to the velocity and pressure curves of Figs . 4a and 4b which diagrammatically illustrate the velocity and pressure variations through the complete unit. It will be understood that these figures are for illustrative purposes and like Fig. 3, they are not intended to be to scale.

Attention will now be given to the design of the input stage 30. Because the unit is to be submersed in flowing water, it has to be recognized that the water is as likely to find a flow path around the exterior of the unit as to find a flow path through the unit. The shaping of the input stage is such as to provide a funnelling of water to the input guide vanes 40 and rotor 10. The input stage has a greater effective input or collection area A₀ at interface 90 (Fig. 3a) than the area Ai at interface 91 so that the flow velocity at Al is increased by A₀/Ai. Thus, the purpose of the input stage is to collect as much flow as possible from upstream and accelerate it to a greater velocity Ci at the area Al of interface 91 given by

where C₀ is the axial flow velocity at interface 90 about which more is said below. One of the features of the shaping of input stage 30 is that the effective input area is greater than the physical area of the inlet opening 32.

Referring to the input stage 30 as illustrated in Figs. Ia, Ib and 2, the forward portion 20c of the housing has a flared or tapered interior surface 22, narrowing from the physical mouth 32 to the inlet guide vanes 40. The physical mouth is the circular forward edge or periphery of the housing. Furthermore, this flared surface is curved and has a greater curvature (lesser rate of change of angle mentioned below - curvature is an inverse function of the rate of change of angle) than does the exterior surface 24 of housing portion 20c which is flatter, that is nearer to a circular cylinder in shape. The periphery 32 at which the surfaces 22 and 24 merge should have a smooth transition to avoid introducing turbulence into the flow into and without the housing portion 20. The difference in curvatures of surfaces 22 and 24 introduces an asymmetry into the inlet stage 30 that has the effect of capturing water flow through a greater area than the physical area of mouth 32. This is equivalent in terms of Fig. 3 of defining the interface 90 as being effectively located upstream of the inlet periphery 32 in Fig. 2. The inlet mouth of the turbine unit disclosed in above-mentioned US patent 6,013,955 has a capture area which is no greater than the physical area of the mouth of the inlet.

The benefit of the asymmetric design of the mouth of the inlet stage is seen in Fig. 7 which shows a diagrammatic radial section through the annular housing portion 20c defining the inlet stage with its inner surface 22 and exterior surface 24 which meet at periphery 32 but diverge therefrom asymmetrically with respect to axis 26. Axis 26 is the notional circular cylinder axis A-A which contains periphery 32. As already mentioned the inner and exterior surfaces 24 and 26 should form a smooth curve or transition at peripheral point 32 as by sharing a common tangent at this point.

The surfaces 22 and 24 may be segments of ellipses though this is not essential with exterior surface 24 exhibiting a greater rate of change of angle of the tangent to the surface as it diverges from common tangent point 32 than does interior surface 22. As will be seen, the surface 24 becomes substantially flat parallel to the axis A-A relative quickly while surface 22 tapers inwardly more gradually to give a more rapid change of cross-sectional area. A consequence of this asymmetric design is that the pressure of the interior flow associated with surface 22 drops more rapidly from the periphery 32 (the stagnation point) than does that of the exterior flow. This is illustrated in Fig. 7a by the respective pressure (P) curves in full line related to surfaces 22 and 24, where the origin on the abscissa axis the mouth 32 and the abscissa is the axial distance in the direction of flow toward interface 91. Concomitantly, the water velocity at the inner and outer surfaces rises in an inverse manner to the pressure drop as indicated by the dash-line curves. The pressure differential causes water to flow into mouth 32 as indicated by stream lines 100. As can be seen from the streamlines 100, water is captured from an upstream region of extended area so that while interface 90 is directly associated with the physical area of mouth 32, it has an effective cross- sectional area that is great than A₀. Furthermore, the pressure differential assists in heading the turbine unit into the direction of flow F. The relative flatness of the outer surface gives least disturbance to the exterior flow and avoids causing unwanted pressure gradients and fluid accelerations/decelerations. The inner surface 24 is, of course, designed to provide the smoothest flow possible (lowest boundary layer drag) to accomplish the enhanced capture area described above.

As already indicated the flared inlet stage shape described in combination with the asymmetry with the outer surface of the housing body leads to the important feature that the unit "self-heads" into the flow of water. This makes the tethering or other securing of the unit at a required location simpler to arrange, particularly in circumstances where the orientation of the unit is required to follow a change in the direction of flow from time-to-time. This self-heading capability is a considerable advantage over the structure shown in U.S. patent 6013955 mentioned above and in which the turbine unit is supported on a vaned structure responsive to the flow direction and in turn rotatably supported on a substantial base structure.

Turning now to the diffuser 70, it will be initially considered as a continuous flared surface without provision for introducing supplementary flow into the diffuser chamber. This is the diffuser as illustrated in Fig. 3. The diffuser serves the function of pressure recovery by restoring the low pressure established at interface 93 to the ambient pressure at outlet interface 94. The diffuser should enable pressure recovery without undesirable effects such as cavitation or losing boundary layer stability.

The function of the diffuser will be described as one of the elements determining the overall flow parameters of velocity and pressure through the unit. The absolute velocity C and pressure P variations associated with the energy extraction by the turbine unit are illustrated in Figs. 4a and 4b respectively. They are shown as a function of axial distance along the turbine axis and the fine vertical lines indicate the positions of the interfaces 90-94 in Fig. 3a with respect to the velocity and pressure curves. The velocity C is the absolute flow velocity at a given axial location. The velocity vector is not necessarily axial. The pressure P is the static pressure at a given axial location. For convenience of explanation, the graphs of Figs. 4a and 4b are each shown somewhat simplified as a sequence of straight line segments . The subscripts 0-4 applied to parameters C and P in the following description relate to values at interfaces 90-94 respectively.

The two graphs commence at an upstream point from interface 80 and show an initial velocity C₀ and pressure P₀ related to the flowing stream or other body of water. As already described, due to the acceleration in the inlet stage 30, the velocity increases to a value Ci at interface 91 as set out in equation (4) above and seen in Fig. 3a. However as the velocity increases the pressure decreases. Between interfaces 91 and 92, the fluid velocity continues to increase as it passes through IGV 40. The velocity here is the absolute velocity of the fluid which now has the tangential or whirl component added by the guide vanes. This is noted in equation (5) above .

The power generated at the reaction turbine rotor 10 increases with the value of V_w (Fig. 5) . The angle turned by the guide vanes to impart the whirl velocity component is selected to optimise the value of V_w. However, the increase of the whirl velocity component V_w is accompanied by an increased drop in pressure at the inlet interface 92 to the rotor 10.

The velocity acceleration from Ci to C₂ is accompanied by a pressure drop from Pi to P₂ at the inlet to the rotor 10. The pressure at interface 92 is given by:

P₂ = Pi - y .V_w ² (8) where/7 is the density of the fluid, i.e. water.

The velocity of the fluid exiting the rotor blades will have dropped to a value C₃ at which point the whirl component imparted at the rotor inlet will ideally have reduced to zero. At interface 93 the absolute flow velocity C₃ is axial and equal to Ci as explained with reference to Fig. 5 (neglecting losses). The pressure will have dropped significantly lower to a low value P₃. The power W extracted ideally by the turbine rotor is proportional to the pressure drop Pd in the rotor and the volume flow rate Q, that is W = Q. Pd =p .C₂-A₂(P₂ - P₃) (9) It follows from equation (9) that ideally, the value of P₃ should be minimised to maximise the value of Pd. However, the minimum value practicably achievable for P₃ is limited by the pressure recovery limitation in the downstream diffuser 70, and the need to avoid cavitation (more especially in high speed flows) . The implementation at the diffuser of a measure that eases the pressure recovery limitation is thus of value. The performance of the diffuser will now be given fuller consideration. As has been described, the water exiting the rotor 10 has kinetic energy at a low pressure. The pressure recovery provided by the diffuser entails transformation of the kinetic energy of the water leaving the rotor into a pressure rise. Assuming the velocity C₃ is entirely axial and neglecting pressure losses from interface 93 to interface 94, the pressure recovery in the diffuser 70 can be expressed as follows. At interface 93, the energy (static and kinetic) available is:

At interface 94, the energy (static and kinetic) available is:

P₄ +— C₄ ²; and 2 as these energies are equal, the pressure recovery, Pr, achieved in the diffuser 70 is P₄ - P₃ so that from the expression of energy at interfaces 93 and 94 given above, Pr can be expressed as Pr = P₄ - P₃ =^.(C₃ ² - C₄ ²) (10).

Also assuming a mass balance of water flow at each of interfaces 93 and 94, C₃. A₃ = C₄. A₄, where A₃ and A₄ are the respective flow cross-section areas at the interfaces.

Consequently, the pressure recovery Pr can be expressed as

Pr =^■£ .C₃ ² (1 - A₃ ²M₄ ²) (11) .

It will be seen that the pressure recovery approaches its maximum value — P .C₃7 when A₃ << A₄. The taper of the diffuser to enlarge the flow cross-section from A₃ to A₄ has to be maintained low enough to establish a stable boundary layer condition along the diffuser surface and to avoid introducing turbulence between the flow through interface 93 and the surrounding water into which the flow finally merges.

Referring again to Figs . 4a and 4b, the decrease in the flow velocity C along the diffuser is matched by a rise in pressure P, the diffuser having a sufficient length to provide a smooth transition to the flow of the surrounding water, that is the values of C and P at interface 94 are close to those at the inlet interface 90. The diffuser of Fig. 3 has so far neglected the slots 72, 74 (Figs. Ia, Ib and 2) for introducing a supplementary flow into the diffuser. Fig. 2 indicates the introduction of supplementary flow into the diffuser 70 at points 72 and 74 by arrows Si and S₂ respectively. The additional fluid entering the upstream slot 72 is directed into the flow exiting rotor 10 at an angle. The additional fluid entering the downstream slot is directed into the flow adjacent the outlet of the diffuser at an angle substantially parallel to that flow. It will be recalled from equation (11) that the maximum pressure recovery is

Pr (max) = -C₃ ² 2

What the diffuser slots 72 and 74 provide by the supplementary flow is the introduction of an additional kinetic energy term from which pressure recovery can be obtained. Taking the case of just one slot which introduces supplementary flow at a velocity C₃, it adds an additional term— P .C₃7. For two or more slots this can

be expressed as — P .∑C₃? where ∑ indicates the net result of the individual slot contributions. Thus the maximum pressure recovery can be expressed as :

Pr (max) =— . (C₃ ² + ∑C_S ²)

This additional factor enables : 1) the pressure drop, Pd, in the rotor to be made greater than it might otherwise be

2) the flow velocity at the rotor outlet (at interface 93) to be made lower than it might otherwise be

3) the length of the diffuser (and with it the final outlet cross-section) to be reduced on what it would otherwise need to be.

The possibilities can be realised individually or in a selected combination.

It will be appreciated that, as already indicated, the means for introducing the supplementary flow can be other than slots. Other forms of aperture can be utilised, preferably maintaining a substantially uniform introduction of fluid around the axis of the diffuser. One or more perforated or mesh sections can be included in the diffuser.

Preferred features of the slots are: the inward flow Si through upstream slot 72 (or other equivalent means) should be directed inwardly towards the axis A-A (i.e. at an angle to the axis) as indicated by the arrow Si, while the inward flow through downstream slot 74 (or other equivalent means) should be more nearly parallel to the axis A-A. It is also preferred to shape the leading edge portions 71a and 71b of diffuser parts 70a and 70b in a manner similar to that described for the leading edge portion of the inlet stage 30 with reference to Fig. 2 and to Fig. 7. That is the inner surface is given a greater curvature than the outer surface. The shaping of the overlapping parts of the rear housing portion 2Od and the forward edge portion 71a of the diffuser part 70a, and of the rear edge portion of diffuser part 70a and the forward edge portion 71b of the diffuser part 70b should be such as to produce the desired inward flow direction Sl and S2 respectively while at the same time maintaining the stability of the internal flow including keeping the boundary layers attached to the surfaces of the diffuser chamber.

The self-heading design of the inlet stage to align with the inward direction of flow has already been mentioned. This characteristic considerably assists the supporting or tethering of the complete assembly in a flowing fluid. Tethering can be effected by an attachment toward the front of the housing 20 so that the unit tends to act as a vane, even without taking the additional self-heading measures. It will be understood that the design described does not preclude the provision of an external vane if desired.

The foregoing description has been directed to the motive power being derived from a flowing liquid, specifically water. The teachings herein are also applicable to a turbine unit powered by a flowing gas such as air. The Electrical Generator One obvious use of the mechanical power available from the turbine unit is electrical power generation but application is not restricted to this field. The electrical generator (dynamo) may be a separate entity coupled to the rotor though it may still be housed within the overall unit. For example, an electrical generator could be housed in the boss/rotor hub assembly 50, 60 seen in Figs . Ia, Ib and 2. An alternative which is illustrated in Fig. 2 is to use the turbine rotor to also provide the rotor component or part of an electrical generator so that no separate transmission coupling from the rotor to the generator is required. One possibility is to embed a respective permanent magnet in each rotor blade tip to rotate past a set of circumferentially (angularly) spaced coils supported in the portion 20b of housing 20.

A more preferred construction is that already outlined with reference to Fig. 2 in which a ring 82 in which permanent magnets 84 are embedded is affixed to the turbine rotor 10 to rotate therewith as the rotor of the electrical generator. This unitary construction should be such as to maintain a balanced rotation. Fig. 8 illustrates a face view of the turbine rotor 10 with the housing portion 20b. The ring 82 is affixed to the tips of the rotor blades, only one of which is shown. The magnets 84 are embedded in ring 82 depending from the outer surface thereof. For protection the magnets may not emerge at the outer surface but could be protected by a thin sleeve surrounding ring 82. One advantage of separating the magnets from the rotor blades 12 is that the number of magnets can be chosen independently of the number of rotor blades. While Fig. 2 shows the generator coils embedded in the housing portion 20b, Fig. 8 shows a more preferred arrangement in which the housing portion 20b is formed in two annular parts. An outer part denoted 20b in Fig. 8 is integral with the remainder of the housing 20. Snugly seated within the outer part is an insertable part 88 which may extend to and be inserted from the rear of the housing 20 or a stator assembly encircling the rotor ring 82 located in placed by a rearward extending inner portion of the housing. It may be keyed to the housing to secure it against rotation. The insertable part 88 thereby provides the stator component of the generator having the internal surface 2Oe previously mentioned with reference to Fig. 2. Part 88 contains the coils 86 which project inwardly to terminate at or adjacent surface 2Oe so as to magnetically engage the magnets 84 across air- gap G. The number of coils is normally equal to the number of magnets, typically 6-8. The number of turbine rotor blades may be in the range 4-10. The coils 86 are supported on ferromagnetic pole pieces which may be magnetically integral with a ferromagnetic annulus 87 encircling the axis A to form a complete magnetic circuit. The whole ferromagnetic structure is preferably laminated to reduce eddy currents so that it can be formed as a stack of stampings .

Many permanent magnet generator configurations are known and are well within the purview of those versed in the generator field. An important feature of the design for the present application is to ensure that the generator parts are well protected from the flowing water, or other fluid, which may be corrosive. Thus techniques involving embedding components in corrosion- resistant plastic material or sealing sleeves may be employed.

The magnets should be of high performance materials, such as rare earth magnets . Magnet performance is often quoted by the energy-product of the material. For example, sintered Neodymium is a high energy-product rare earth-based magnetic material though the composite has a high ferrous content. Samarium Cobalt is another candidate and is without ferrous content. The rotor 10 may be made of various materials. Corrosion resistance is one factor to be borne in mind, together with strength. The rotor should be non-brittle to avoid shattering from water-borne debris. It should be light and of a material that is malleable or mouldable into the complex curve that characterizes a turbine rotor blade design. The rotor should also be cheap to replace. As the major moving part of the unit, it is likely to be the first to break. Materials that can be considered for meeting these requirements are carbon fibre, cast or machined aluminium, silicon bronze or expoxy resin composite and stainless steel. These concerns apply both to a turbine unit with separate electrical generator and to a turbine unit in which the rotor is made part of the generator. The inlet stage 30 may be provided with a grill to restrict access into the unit of at least larger items of debris without unduly affecting the flow.

It will be understood that the frequency of the alternating voltage induced in the coils is a function of rotor speed. If the generator output is rectified to produce a D. C. supply then speed variations are of small importance provided the rotor is rotating above some lower speed.

The stator part (88) of the generator 80 in which electrical currents flow should be protected from the water flowing through the conduit of the turbine unit and impinging on the rotor. It is preferred therefor to provide an inner water-impervious lining or casing 90 for the stator of the generator and thereby extending about the rotor. The lining should be kept as thin as possible to allow the closest passage of the rotor magnets 84 to the coil pole members. The lining should not affect the magnetic flux emanated by the magnets 84. While it is possible to have the coils on the rotor and the magnets on the stator, there is considerable advantage in having the rotor support components not involving current flow and to consign the current flows to the stator. Figures 9 and 10 of the drawings show sections, generally corresponding to Figs. 2 and 8, of a turbine generator unit constructed in accordance with the invention and incorporating some presently preferred features of construction. Parts like to those seen in Figs. 2 and 8 are given the same reference numerals increased by "100" .

As in the embodiment described above, the turbine generator unit of Fig. 9 comprises a housing 120, having a shaped inlet stage 130 funnelling or ramping the water flow F to a rotor 110 preceded by inlet guide vanes 140. The rotor 110 and IGV 140 are designed in accord with the considerations given above. The guide vanes 140 support an axially central boss 150 from which a spigot 152 extends rearwardly and terminates in a nose 200 that tapers inwardly to promote smooth flow of water therepast. The spigot 152 may be threaded to engage a threaded bore in the boss 150. The blades of rotor 10 are secured to a central hub 160 that is axially located between boss 150 and nose 200 and is freely rotatable about spigot 152.

The water flow exiting the rotor 110 flows through the rearward portion 12Od of the housing into the first part 170a of the diffuser 170 and thereafter into the downstream part 170b of the diffuser. Slot 172 is defined between housing portion 12Od and the upstream part 170a of the diffuser. Slot 174 is defined between parts 170a and 170b. However, it will be noted that in his embodiment the housing portion 12Od and diffuser part 170a do not overlap but the leading edge of the latter is of greater diameter than the trailing edge of the former while the outer surface of the housing portion 12Od is shaped to assist in funnelling an intake Sl of supplementary flow into the diffuser, Sl being toward the axis A-A. Likewise there is little overlap between diffuser parts 170b and 170a the leading edge of the former being of greater diameter than the trailing edge of the latter to promote an intake flow S2 substantially in the direction of the axis A-A.

Turning to the generator illustrated in Figs. 9 and 10 it follows the previously described embodiment in having a ring which is carried by the turbine blades and which supports the magnets. As better seen in Fig. 10, the ring 182 is supported at the tips of eight equiangularly disposed rotor blades 112 secured to hub 160. The ring 182 supports a plurality of equiangularly-disposed, arcuate radial magnets 184, eight in the illustrated embodiment. Each magnet is radially magnetised to present a North or South outer pole and the magnets alternate in polarity so that next-adjacent magnets are of opposite polarity. The housing portion 120b encircling the rotor assembly supports a plurality of equiangularly spaced coils 186 which in this case are equal in number to the number of magnets 184. Each individual coil 186 also has an arcuate shape to match the path travelled by the magnets. The coils are illustrated as being air-spaced, that is not wound on ferromagnetic core material. The addition of a ferromagnetic circuit to enhance efficiency is also contemplated as previously indicated. Test have shown that very useful amounts of power can be nonetheless generated, especially for lower power requirement applications. For efficient magnetic coupling of the magnets to the coils, the effective air gap between the magnets and the coils should be kept to a minimum. As will now be described with particular reference to Fig. 9, the construction adopted in this embodiment is effective in achieving this goal.

It is seen in Fig. 9 that the ring 182 carried by the rotor and carrying the magnets 184 enters an annular recess 202 in housing portion 120b. This recess extends outwardly from the fluid flow conduit through housing 120 and terminates in an annular chamber 204 in which the coils 186 are received. As previously explained the housing 120 can be made in separable pieces to allow placement and location of the generator components . The annular ring 182 is formed with an annular outer recess 212 in which the magnets 184 are received. It is preferred that a respective lip projects inwardly from the outer end of each wall of the recess 212 to retain the magnets 184 against centrifugal forces as the rotor rotates. The magnets can also be secured in place by adhesive and a water-proof coating - for example an epoxy coating - provided to protect the magnets.

The hub 160 may be made in more than one piece. It may comprise a main annular body 222 to which the rotor blades 112 are affixed. The body rotates about spigot 152 and to each side is a thinner slip ring 224a and 224b also mounted about spigot 152. The outer end of the spigot 152 comprises a head 226 which seats against a shoulder in nose 200 so that as the spigot is fastened in place, the nose, the body 222 and the slip rings 224a and 224b are all located in place on the spigot.

It will be understood that various features as described and/or claimed may be combined in various ways.

Claims

C L A I M S

1. A turbine unit comprising: a housing defining a conduit for the flow of fluid therethrough, said conduit having an inlet opening; a turbine rotor located in a portion of the conduit for rotation by the flow of fluid therepast; said housing being submersible in a flowing fluid for the flow of fluid both through the conduit and exteriorly of the housing; a diffuser located downstream of said turbine rotor to receive fluid discharged from the rotor, said diffuser tapering outwardly in the downstream direction, wherein said diffuser comprises means for introducing supplemental fluid from exteriorly of the housing to the flow discharged from the rotor.

2. A turbine unit as claimed in Claim 1 in which said means comprises at least one slot, perforations, a mesh structure or the like in a wall of the diffuser.

3. A turbine unit as claimed in Claim 1 in which said means for introducing supplemental flow is located in an upstream portion of the diffuser and is shaped to introduce a supplemental flow at an angle to the flow exiting the rotor.

4. A turbine unit as claimed in Claim 1 in which said means for introducing supplemental flow is located in a downstream portion of the diffuser and is shaped to introduce a supplemental flow substantially parallel to the direction of flow about to exit the diffuser.

5. A turbine unit as claimed in Claim 1 in which said means for introducing supplemental flow comprises an upstream part and a downstream part, the upstream part being shaped to introduce a supplemental flow at an angle to the flow exiting the rotor and the downstream part being shaped to introduce a supplemental flow substantially parallel to the direction of flow about to exit the diffuser.

6. A turbine unit as claimed in Claim 3 or 4 wherein said means comprises a slot, set of perforations, a mesh structure or the like in a wall of the diffuser.

7. A turbine unit as claimed in Claim 5 in which each of said upstream part and said downstream part comprises a slot, set of perforations, a mesh structure or the like in a wall of the diffuser.

8. A turbine unit as claimed in any one of Claims 1 to 7 in which said means is shaped to face forward into the flow exterior of said housing.

9. A turbine unit as claimed in any preceding claim in which said turbine rotor acts as an reaction turbine and the unit further comprises a guide vane assembly upstream of said turbine rotor to impart a whirl component into the flow directed to the rotor .

10. A turbine unit as claimed in any one of Claims 1 to

9 further comprising an electrical generator comprising a rotor assembly and a stator assembly, said rotor assembly being mounted to said rotor blades to rotate therewith and said stator assembly being mounted to said housing.

11. A turbine unit as claimed in any preceding claim in which said turbine rotor is encircled by a ring affixed to the rotor blades to rotate therewith, said ring carrying one of a plurality of magnets and a plurality of electrical coils, and the housing having a portion encircling said ring and supporting the other of said plurality of magnets and plurality of coils in a stator assembly, whereby the magnets magnetically couple to the coils as the turbine rotor rotates to provide an electrical generator.

12. A turbine unit as claimed in any one of Claims 1 to 11 in which said turbine rotor comprises plurality of blades, a respective magnet being disposed at or in each tip portion of a blade, and in which a plurality of interconnected coils are supported by a portion of the housing surrounding the turbine rotor to be influenced by the magnetic fields emanated by the magnets and thereby form an electrical generator therewith.

13. A turbine generator unit comprising: a housing defining a conduit for the flow of fluid therethrough, a turbine rotor located in a portion of said conduit for rotation by the flow of fluid therepast, the rotor comprising a plurality of rotor blades, an electrical generator coupled to the turbine rotor to be driven thereby, the generator comprising a rotor assembly and a stator assembly, one of the rotor assembly and the stator assembly comprising one or more coils and the other of the rotor assembly and the stator assembly comprising one or more magnets for magnetically coupling to the one or more coils for the inducing of electric current therein as the turbine rotor rotates, wherein : the rotor assembly is carried to the turbine rotor blades .

14. A turbine generator unit as claimed in Claim 13 in which the rotor assembly comprises a ring affixed to the turbine rotor blades to rotate therewith, said ring carrying one of said one or more coils or said one or more magnets .

15. A turbine generator unit as claimed in Claim 13 in which the rotor assembly comprises the one or more coils or the one or more magnets, the or each of the coils or the or each of the magnets being disposed at or in a tip portion of a turbine rotor blade.

16. A turbine generator unit as claimed in Claim 13, 14 or 15 in which the rotor assembly comprises the one or more magnets and the stator assembly comprises the one or more coils .

17. A turbine generator unit as claimed in any one of Claims 13 to 16 in which the stator assembly comprises an annular part inserted within said housing to encircle said rotor assembly.

18. A turbine generator unit as claimed in any one of claims 13 to 16 further comprising: a diffuser located downstream of said turbine rotor to receive fluid discharged from the rotor, said diffuser tapering outwardly in the downstream direction, which diffuser comprises means for introducing supplemental fluid from exteriorly of the housing to the flow discharged from the rotor.