Rotary fluid propulsion devices are used for imparting movement to watercraft and aircraft, and also have applications in circulating pumps and hydro-electric power generation.

Conventional propellers have a number of disadvantages.

These include a lack of integral strength due to the blades being unsupported at the outer diameter. There are also a number of safety concerns due to the exposure of the blades to the surrounding area. Indeed, the exposed tips of conventional propeller blades presents a major safety problem. Many thousands of accidents are reported in a typical year, involving people and wildlife being injured by the unprotected blades of conventional

propellers used in the majority of powered boats and dinghies.

A further problem of conventional propellers is that they will tend to produce a degree of undesirable tangential fluid flow, in addition to the axial flow required to impart movement. Furthermore, the tips of the propeller blades can cause eddy currents and vortices, which tend to reduce the efficiency of the unit and in some cases can cause environmental damage, particularly in sensitive shallow water ecosystems.

The tangential component of the flow also causes a reaction force on the propeller, which tends to increase friction losses.

A further disadvantage is that the lack of rigidity of the propeller causes a degree of blade flexing when a load is applied. The energy required for this flexing would be better used for creating fluid flow.

Attempts have been made to improve upon conventional propellers by mounting the propeller blades in a sheath or shroud. This goes some way to improving the axial flow properties of the propeller, and alleviates some of the safety concerns. However, such arrangements do not provide the overall efficiency desired for many applications.

Further attempts are described in US 5,181, 868, US 5,383, 802, and JP 63195093. These documents disclose vane arrangements fixedly mounted to the inner surface of a cylinder, thereby providing additional structural

strength. These propulsion units do not adequately solve the above-described problems.

Significantly, the prior art arrangements include central throughbores. That is, the vanes do not cover the entire cross section of the cylinder. In use, this results in turbulence in a central area of the cylinder, creating vortex losses and reducing the axial flow components.

This turbulence can cause erosion damage to the environment.

In addition, the throughbore will tend to pull foreign objects, or even limbs, into the unit, which clearly can be harmful to any equipment and individuals present in the vicinity of the unit.

It would therefore be desirable to provide an energy conversion device that obviates or mitigates at least some of the drawbacks associated with the prior art.

It is one object of one aspect of the invention to provide a propulsion unit or turbine which provides improved safety from injury to third parties and wildlife.

It is further object of one aspect of the invention to provide an energy conversion device that reduces the impact on the surrounding environment.

It is a further object of the invention to provide a propulsion unit that generates substantially axial fluid movement.

Further aims and objects of the invention will become apparent from reading the following description.

According to the first aspect of the invention, there is provided a rotor assembly for an energy conversion device, the rotor assembly comprising: - a tubular member having an inner surface and an outer surface defining a fluid inlet, a fluid outlet, and a longitudinal axis; - a central shaft; - at least two vanes, each vane having an inner edge, an outer edge, wherein the inner edge of the vanes are fixed in relation to the central shaft, and the outer edge of the vanes are fixed to the tubular member; - and wherein the outer surface of the tubular member is coupled to a drive mechanism such that motion of the drive mechanism is coupled to rotational motion of the tubular member.

Preferably, rotational motion of the tubular member is driven by the drive mechanism.

Alternatively, rotational motion of the tubular functions to drive the drive mechanism.

The tubular member is preferably cylindrical.

Alternatively, it may be frusto-conical.

The vanes are preferably helical about the central shaft of the tubular member.

Preferably, the vanes extend along a part-length of the tubular member. Alternatively, the vanes may extend along the entire length of the tubular member.

Optionally, the vanes may extend beyond the length of the tubular member.

Preferably, the central shaft extends along a part-length of the tubular member. Alternatively, the central shaft may extend along the entire length of the tubular member.

Optionally, the central shaft may extend beyond the length of the tubular member.

In one embodiment the tubular member, central shaft and vanes are moulded as a single piece.

Preferably, the rotor assembly comprises N vanes, and each vane extends in the longitudinal axis and twists through a twist angle @, wherein the twist angle 0 is greater or equal to 360/N.

Alternatively, the rotor assembly comprises N vanes, and each vane extends in the longitudinal axis and twists through a twist angle 6, wherein the twist angle 6 is less than 360/N.

Optionally, each vane has a first surface and a second opposing surface, with the first and second surfaces defining radial edges of the cross sectional profile of the vane.

Optionally, the radial edges are parallel to one another.

Optionally, the radial edges are straight, and the vanes extend radially from the central shaft to the tubular member.

Alternatively, the radial edges are non-parallel to one another. The radial edges may be converging biconvex, planoconvex, diverging biconcave, meniscus converging, planoconcave, or meniscus diverging.

The vanes may be located at regular angular intervals about the central axis.

Optionally, the propulsion unit comprises four vanes.

The vanes may twist through an angle of 180 degrees.

Optionally, the tubular member is rotatably mounted within an outer sheath.

Alternatively, the propulsion unit may be driven by means acting on the outer surface of the jacket.

According to a second aspect of the invention, there is provided a propulsion unit incorporating the rotor assembly of the first aspect.

According to a third aspect of the invention, there is provided a turbine unit incorporating the rotor assembly of the first aspect.

There will now be described, by way of example only, various embodiments of the invention with reference to the following drawings, of which:

Figure 1 shows a perspective view of part of a propulsion unit in accordance with an embodiment of the invention; Figure 2 shows a plan view of the part of the propulsion unit of Figure 1; Figures 3a to 3f show a variety of cross sectional profiles of vanes that may be incorporated into various embodiments of the invention; Figure 4 is a perspective view of rotor assembly showing an example of an external driving mechanism; Figures 5a and 5b are front and rear views of a rotor assembly mounted within a housing; Figures 6 to 8 show examples of propulsion units with alternative vane arrangements in accordance with various embodiments of the invention.

Figures 9a and 9b show multi-stage impellers in accordance with embodiments of the invention.

Figure 1 shows a perspective representation of part of a propulsion unit 10. The propulsion unit comprises a tubular member 12, having fluid inlet 13a and fluid outlet 13b. The tubular member 12 is in the form of a cylinder, and defines a longitudinal axis. Within the tubular member 12 is a rotor assembly 14 comprising a number of helical vanes 15 and a central shaft 11. The central shaft extends along the longitudinal axis and is concentric with the tubular member.

In this example, the rotor assembly comprises four vanes.

Each of the vanes is fixedly mounted to the inner surface of the tubular member 12 and is fixed to the central shaft 11. The vanes twist around the central shaft.

Each vane 15 extends along the longitudinal axis of the tubular member and has a twist angle of 90°.

Figure 2 is a plan view of the unit of Figure 1. The Figure shows that the vanes 15 are mounted such that the leading edges of the vanes are regularly displaced about the central axis of the cylindrical tubular member. In addition, the leading edges of the blades meet at the central shaft such that the radial width of the vane is approximately equal to the difference between the outer radius of the central shaft and the inner radius of the cylindrical tubular member.

Figure 2 most clearly shows the cross sectional profile of the vanes of the unit, which is defined by the opposing surfaces of the vanes. The surfaces are parallel to give the vanes a flat profile at any plane perpendicular axis.

The vane arrangement of the propulsion unit of this example is such that the vanes each twist through 90 degrees. Since there are four such vanes, separated at 90 degree intervals, the four vanes cover all 360 degrees of the circular cross-section of the tubular member. The vanes therefore cover the entire cross-sectional profile of the cylinder. As such, there is no axis passing from the inlet to the outlet that is not obstructed by either the vanes or the central shaft. When the unit is rotated, the vanes impart a resultant axial force on the

fluid at all points across the internal cross section of unit.

This arrangement provides a number of advantages over known devices. For example, the resultant axial flow generally produces less turbulence, and hence less energy loss. The unit has a lower tendency to flex and less slippage at low revolutions. The unit has increased safety because the inner edges of the vanes are not exposed. The symmetry of the vane structure means that the unit is equally effective when rotated in either direction.

Figures 3a to 3f show alternative vane profiles that may be employed in alternative embodiments of the invention.

In these examples, the vane is no longer a flat, twisted planar sheet, as shown in Figures 1 and 2. Rather, the opposing surfaces of each vane are non-parallel. The Figures show a cross section of the vane, taken perpendicularly to the longitudinal axis of the tubular member.

Figure 3a shows a converging biconvex profile, where both surfaces are curved such that the central portion of the vanes is thicker than the inner and outer edges.

Figure 3b shows a planoconvex profile, where only one surface of the vane is curved in a convex manner, the other remaining planar.

Figure 3c shows a diverging biconcave profile, where both surfaces are curved such that the central portion of the vanes is thinner than the inner and outer edges.

Figure 3d shows a meniscus converging profile where both surfaces are curved in the same sense, but with differing curvature, such that the central portion of the vanes is thicker than the inner and outer edges.

Figure 3e shows a planoconcave profile, where only one surface of the vane is curved in a concave manner, the other remaining planar.

Figure 3f shows a meniscus diverging profile where both surfaces are curved in the same sense, but with differing curvature, such that the central portion of the vanes is thinner than the inner and outer edges.

The alternative vane profiles shown in Figures 3a to 3f effect the flow of fluid through the tubular member. The shaping of the surfaces of the vanes affects the pressure exerted by the fluid on the vanes, and has a corresponding effect on the flow and rotation characteristics of the device. Different shaped profiles may be used in different applications.

Although Figures 3a to 3f show cross-sections of the vane profiles, it is possible for the vanes to similarly shaped along their length. That is, taking a section through the vane from its leading edge to its trailing edge, the resulting profile may be converging biconvex, planoconvex, diverging biconcave, meniscus converging, planoconcave, or meniscus diverging.

Figure 4 shows an example of how the propulsion unit of Figure 1 can be externally driven. The unit is provided

with a gear 16 mounted on the outer surface of the cylinder 12. The gear engages with means for driving the propulsion unit, such a driving gear (not shown).

Various implementations may be adopted. There may be an intermediate gearbox provided between the propulsion unit and a power source. A pair of bearing rings (not shown) may be fixed to the outer surface of the jacket on either side of the gear 16, with the area defined by the bearing rings filled with a suitable lubricant.

It is envisaged that several different mechanisms could be used to drive the units described above. These include electric motors, hydraulic motors, or any suitable engine. The externally driven rotor assemblies could for example be driven by gears, v-belt pulleys, or chains. Alternatively, the rotor assembly itself could form the rotor of an electrical motor.

Figures 5a and 5b shows an assembly with the propulsion unit being mounted within a casing 20. The casing is attached to a substantially vertical support 21 that contains equipment for controlling the operation of the unit. The casing encapsulates the driving mechanism for the unit. The assembly as a whole may be used in place of a conventional outboard motor.

It should be noted that the rotor assembly 22 shown in Figures 5a and 5b differs from the example of Figures 1 and 2. Firstly, the vanes extend longitudinally beyond the volume defined by the tubular member. Secondly, the central shaft of the rotor assembly is mounted on a pivot mounting 24. The pivot mounting is fixed to a rear

support member 24, which is part of the casing 20. The pivot mounting provides additional support and rigidity to the unit.

The above-described embodiments include helical vanes coiled around a central shaft and fixedly mounted to the inner surface of a jacket. The central shaft gives structural support and additional rigidity to the unit.

The vanes then coil around the central shaft, being attached thereto along the length of the shaft. The shaft extends along the entirety of the inner edge of the vanes, or may only be present along a part-length of the unit. In this manner, the shaft can be used to provide additional strength only at those parts of the unit most in need.

In the event that the cylinder length exceeds the length of the central shaft, the part of the vanes that protrude beyond the length of the central shaft but not beyond the length of the tubular member will be in free space on their inner edges, but firmly attached to the inside of the cylinder wall along their outer edges.

The embodiments described herein should in no way be considered to be limiting. It will be appreciated that many changes could be made to the twist angle, the number of vanes, and the particular dimensions of the units.

In addition, the degree of twist of the vanes can be varied along the axial length of the unit. This variation of twist can be regular, or the rotor assembly could be composed of two distinct portions, each having a different twist angle. Furthermore, it is not necessary

for the vanes to be regularly displaced about the central axis of the cylinder.

The vanes can be set perpendicular to the inside surface of the tubular member or at any angle dependent on operating conditions.

The vanes can also be tilted along their length so that the contact angle on the inside cylinder surface is different to the contact angle of the vane on the central shaft.

The vanes or blades will normally be continuous, but not limited to being continuous. In some applications two or more stages of vanes or blades may be attached to the inside of a cylinder and/or axis, with designed spaces/spacers between the sets of vanes/blades. The vanes can also have slots in them such as to give a Venetian blind effect if so desired.

The inside diameter and thickness of the cylinder in which the vanes/blades are located can be of any value and not necessarily constant along the length of the cylinder so as to make the cylinder parallel. In addition the cylinder could be parallel but the vanes may taper both along the central axis length and or any free length space. Alternatively, or in addition, the central shaft may be tapered along the longitudinal axis of the tubular member.

For some applications the cylinder may represent a frustrum of a cone with one end of the cylinder larger than the other. The taper of the cylinder can either be uniform or variable.

In addition, sections of the vanes can be removed to form curved blade-shaped sections, analogous to a conventional propeller.

The vanes may have movable flaps along all or part of their edges. The vanes can be attached to the cylinder and the central axis in such a way as to allow their pitch to be changed either manually or otherwise. The rotor assembly can be produced as a single integral form or fabricated from separate prepared elements.

Figures 6 to 8 show examples of propulsion units with alternative vane arrangements in accordance with various embodiments of the invention. It should be noted that the central shaft of the rotor assemblies in the following examples has not been shown, in order that the vane shape is displayed with greater clarity.

Figure 6 shows a rotor assembly 60 having four helical vanes, each vane having a twist angle of 90 degrees. In this example, the twist occurs over a shortened length, such that the length/diameter ratio is approximately 1: 4.

Figure 7 shows a rotor assembly 70 having four helical vanes, each vane having a twist angle of 180 degrees. In this example, the length/diameter ratio is approximately 1: 2.

Figure 8 shows a rotor assembly 80 having three helical vanes, each vane having a twist angle of 120 degrees.

Figure 9a shows a propulsion unit being formed from a series of rotor assemblies of varying radius and twist angle, and a nozzle 91. Each rotor assembly in this example is of the type illustrated in Figure 1, but with different twist angles. Various combinations may be used, but for non-compressible fluids, each stage must be carefully matched with regard to its flow characteristics. Thus, for a decrease in twist angle, moving from Stage 4 to Stage 3 as shown, the radius of the rotor assembly must be decreased by a spacer 92. The difference in radius accounts for the difference in volumetric flow rates produced by rotor assemblies with varying twist angles.

In the example shown in Figure 9a, the rotor assemblies are chosen as follows: Stage 1-90 degree twist angle Stage 2-180 degree twist angle Stage 3-270 degree twist angle Stage 4-360 degree twist angle Figure 9b shows an alternative multi-stage propulsion unit suitable for use with gases. For compressible fluids, the same degree of flow matching is not necessary. In the example of Figure 9b, the rotor assemblies are as follows: Stage 1-90 degree twist angle

Stage 2-180 degree twist angle Stage 3-270 degree twist angle Stage 4-360 degree twist angle The foregoing description relates primarily to the propulsion units and impellers, particularly for marine craft such as in outboard or inboard motors, jet pumps, or in ROVs. However, it will be apparent to a skilled reader that the invention has applications in a variety of fields. For example, it is envisaged that various aspects of the invention could be utilised in pumping applications, for imparting flow to slurries and liquids as an alternative to centrifugal or axial flow pumps.

Embodiments of the invention could be deployed in any type of conduit, and in a downhole environment.

It will also be appreciated that the present invention can be used to impart flow to air or other gases.

Embodiments could therefore be used in the propulsion of aircraft.

Furthermore, a turbine in accordance with embodiments of the invention could be rotated by flowing fluid in order to generate electricity, and thus the invention could be used in wind, tidal, or hydroelectric energy generation systems. The angle of twist and the dimensions of the unit can be carefully selected to generate electricity at the desired frequency.

Aspects of the invention could be used to measure the flow of gases, liquids or slurries as an alternative to conventional flowmeters.

Aspects of the present invention provide a propulsion unit and/or turbine with improved efficiency of operation, and with a wide range of possible app lications.

Aspects of the invention offer improved axial flow characteristics, improved rigidity, and reduced environmental impact.

Various modifications from the above-described embodiments may be made within the scope of the invention herein intended.