GB2620958A

GB2620958A - Turbomachine

Info

Publication number: GB2620958A
Application number: GB2210980.5A
Authority: GB
Inventors: Normington Christopher; Amy Paris; Wild Philip; Seeburrun Vishal
Original assignee: Cummins Ltd
Current assignee: Cummins Ltd
Priority date: 2022-07-27
Filing date: 2022-07-27
Publication date: 2024-01-31
Also published as: GB202210980D0

Abstract

A turbomachine is disclosed. The turbomachine comprises a shaft 12, a housing 11 supporting the shaft, a turbine wheel 14 comprising a plurality of blades 15, and a stator assembly 16 mounted upstream of the fan 15. The stator assembly comprising first 18a and second 18b vane sets provided concentrically about a central axis. The blade sets 18a,18b are configured to receive respective first and second flows. The second vane set is disposed radially outwards of the first vane set. The stator assembly may define first 19a and second 19b annular stator channels that are fluidically sealed from each other. The housing 11 may define a volute 30 downstream of the turbine, having an outlet passage 32 that may be divided into first and second channels. The turbomachine is configured to transfer energy from first and second fluid flows with different physical properties, with the vanes designed to operate in the different conditions.

Description

I

TURBOMACHINE

Field of the invention

The present invention relates to a turbomachine. Particularly, but not exclusively, it may relate to an axial power turbine for use in a waste heat recovery system.

Background of the invention

As legal requirements regarding emissions, across the world, become more stringent, solutions are required which result in reduced fuel consumption, in particular for medium/heavy duty commercial vehicles.

It is known that emissions from vehicles can be reduced in a number of ways, which may include using cleaner fuels and altering the design of the vehicle itself to have improved aerodynamic properties to reduce fuel consumption. However, as one of the biggest losses of energy is heat, through the exhaust, the intercooler, exhaust gas recirculation cooler (EGR) and the radiator, recovery of heat losses continues to be sought in order to further reduce energy consumption and emissions.

Many medium/heavy duty commercial vehicles comprise a waste heat recovery system, generally an exhaust heat recovery system. Exhaust heat recovery systems often comprise a closed-loop system which captures high grade exhaust heat thought a heat exchanger, where a working fluid can be heated and driven through a Rankine cycle, whose output can be harnessed mechanically or electrically. Nevertheless, low to medium and in some cases high-grade heat is still lost.

A conventional turbine, which may be used as part of a waste heat recovery system allows for the transfer of energy between a rotor and a fluid. It essentially comprises a turbine wheel mounted on a rotatable shaft within a turbine housing, where rotation of the shaft is driven by the fluid acting on the turbine wheel. The rotational energy of the shaft may be used to do useful work, such as, generating electricity in a power turbine, or to compress fluids by driving a compressor. The turbine shaft is conventionally supported by journal and thrust bearings, including appropriate lubricating systems, located within a bearing housing.

The design and operating of turbines of this kind, including for use in jet engines, axial power turbines, steam turbines, in turbochargers, is well known, and said turbines are usually designed to operate as efficiently as possible for a given design point. As known in the art, the design of the turbine itself is heavily influenced by the properties of the fluid that it is expected to receive together with the expected or desired operating conditions.

As a result, a turbine receiving a fluid with differing properties and characteristics to what it is designed for will not operate as efficiently.

There exists a need to provide an improved turbine, which overcomes one or more of the disadvantages of known turbines whether set out above or otherwise.

According to a first aspect of the invention, there is provided a turbomachine comprising a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel; the stator assembly comprising first and second vane sets provided concentrically about the central axis; the first vane set configured to receive a first fluid flow and the second vane set configured to receive a second fluid flow; wherein the second vane set is disposed radially outwards of the first vane set.

The turbomachine encompasses a machine which is configured to transfer energy from the first and second fluid flows to a rotor. The turbomachine may be, but not limited to a jet engine, an axial power turbine, a steam turbine, and a turbocharger. The turbine wheel is a rotor, as it is configured to rotate about the central axis. It will be appreciated, that the shaft may also rotate about the central axis. Accordingly, the turbine wheel may be considered to extract energy from the first and second fluids. The shaft may be connected to a generator, or it may be connected to another system or assembly which may be configured to harness the kinetic energy of the shaft.

The stator assembly being provided upstream of the turbine wheel, encompasses, the stator assembly, relative to the central axis, being axially upstream of the turbine wheel. The stator assembly may also be axially upstream of an end of the shaft relative to the central axis.

The term The first vane set being configured to receive a first fluid flow and the second vane set configured to receive a second fluid flow" encompasses the first and second fluids passing through the first and second vane sets respectively. In particular, the first and second fluids may pass through passages defined between adjacent vanes of the first and second vane sets. As the first and second fluids pass through first and second vane sets, the vanes may cause the respective first and second fluid flows to be turned and directed onto the blades of the turbine wheel. Controlling and directing the flow of the first and second fluids onto the blades of the turbine wheel increases the efficiency of the turbine. It will be appreciated that the first and second fluids may be turned different amounts by the first and second vane sets respectively.

The second vane set being disposed radially outwards of the first vane set encompasses the first and second vane sets being concentric vane sets, meaning that the vanes of the first vane set are circumferentially disposed around the central axis, and the vanes of the second vane set are also circumferentially disposed around the central axis but are provided radially outwards of the first vane set. The first and second vane sets may be axially offset from one another, or they may be provided at the same axial location along the central axis.

Preferably, the center of the first and second vane sets is provided at the same axial location along the central axis. By the first and second vane sets being concentric and not axially offset from one another provides a compact design, and allows energy from two fluid flows with different properties to be efficiently harnessed by the turbine wheel downstream.

The first and second fluids may be gaseous. The first and second fluid flows may be the same fluid flows or they may be different. If the first fluid flow is different to the second fluid flow, it may have the same chemical make-up or composition but different physical properties. For example, if the first and second fluids are gaseous fluids, they may have the same chemical composition; and by way of example they may comprise the same concentrations of oxygen, hydrogen and carbon dioxide, but have different physical properties. Physical properties, are intended to refer to any of at least the temperature, energy, pressure, velocity and/or the density of the first and second fluid flows.

The turbomachine may be a full admission turbomachine, meaning that both the first and second fluids are received over an entire circumferential annulus of each of the first and second vane sets respectively.

The vanes of the first vane set may be designed to operate at a first condition. For example, the profile of the vanes of the first vane set may be designed around physical and chemical properties of the fluid flow that it is expected to receive, which may be referred to as a design condition. Tailoring the design of the vanes is advantageous, as it allows the flow of the fluid to be directed at the correct angle and velocity for the turbine wheel, thus increasing the efficiency of the turbine wheel. However, if in use, the fluid that passes through the vanes is not at the condition the vanes were designed to receive (off-design condition), the fluid may not be as well directed onto the turbine wheel and hence the turbine wheel will not operate as efficiently as it was designed to do.

Therefore, providing a second vane set that is designed to receive a fluid with different physical properties to the first vane set is advantageous. Energy may be recovered from multiple heat sources simultaneously, or energy can be harnessed from a single source but at different times.

By way of example, if the fluid flow is an exhaust gas from an engine, at engine start-up the exhaust gas is relatively cool compared to when the engine has been running for a prolonged period. As such, it may be advantageous to for the fluid to be directed through the second vane set at start-up, and when the exhaust gas is hotter it may pass through the first vane set, or vice versa.

The turbomachine may receive exhaust gases that have passed through a turbocharger. In particular, the turbomachine may receive exhaust gases that have passed through a waste-gated turbocharger, whereby some exhaust gases have passed through a turbine wheel of the turbocharger and some exhaust gas has been diverted around the turbine wheel of the turbocharger. Exhaust gas that has passed through the turbine wheel of the turbocharger may have different physical properties to exhaust gas that bypassed the turbine wheel of the turbocharger. The exhaust gas that has passed through the turbine wheel of the turbocharger may be considered to be a lower grade than exhaust gas that has not passed through the turbine wheel of the turbocharger. Accordingly, the low grade exhaust gas may pass through one of the first or second vane sets of the turbo machine, and the higher grade exhaust gas may pass through the other of the first or second vane sets of the turbomachine. This is advantageous as the profile and design of the vanes does not need to be compromised in order to accommodate both exhaust gas streams, or does not require the use of partial admission.

One of the first or second vane sets may be configured to receive a fluid flow with high grade energy, and the other of the first or second vane sets may be configured to receive a fluid flow with a lower grade energy.

The first and second fluids may exit the first and second vane sets with approximately the same flow angle, relative to the central axis, thus allowing both the first and second fluid flows to be directed onto the turbine wheel, where the turbine wheel comprises a single blade set, each blade having the same profile.

The first vane set and the second vane set of the stator assembly may be angled in the same direction. In other words, the vanes of the first and second vane set may all appear to be angled in a clockwise direction, or they may appear to be angled in an anti-clockwise direction.

If energy were to be harnessed from two fluid flows with different properties without providing concentric vane sets. To efficiently harness the energy at least two vane sets each with a corresponding turbine wheel, and hence two shafts would be required, taking up significantly more room; or a compromise in the efficiency of the turbine would have to be realized, and therefore less heat would be recovered.

The first and/or second vane sets may be axially extending channels. In particular, the first and/or second vane sets may be conically shaped channels.

The stator assembly may define a first annular stator channel and a second annular stator channel. The first vane set may be provided in the first annular stator channel and the second vane set may be provided in the second annular stator channel; and the first and second annular stator channels may be fluidically sealed from each other.

The first and second annular stator channels encompass passages or conduits through which the first and second fluids can pass though. The first and second vane sets may be provided in the first and second channels respectively so that the first and second fluids pass through only the first and second vane sets respectively.

The first and second annular stator channels being fluidically sealed from each other is intended to mean that fluid in the first channel is substantially prevented passing from the first channel to the second channel; and that fluid in the second channel is substantially prevented passing from the second channel to the first channel. Because the first and second fluids may have different properties, by sealing the first and second annular stator channels, the first and second fluids are substantially prevented from mixing; mixing of the fluids may reduce the effectiveness of the vanes on turning the flow of the fluids as they pass through the vanes.

The first and second annular stator channels may be fluidically sealed from each other through means of one or more 0-rings or any other suitable seal or sleeve.

The housing may define or partially define at least one of the first and second annular stator channels.

The turbine wheel may be configured to receive fluid from the first and second annular stator channels substantially simultaneously.

The turbine wheel receiving fluid from the first and second annular channels simultaneously, in use, encompasses the first fluid flow which exits the first annular stator channel travelling towards the turbine wheel and passing through the passages provided between adjacent blades of the plurality of blades; and the second fluid flow which exits the second annular stator channel travelling towards the turbine wheel and passing through the passages provided between adjacent blades of the plurality of blades at the same time.

The turbine wheel being configured to receive fluid flow from both the first and second channels, simultaneously, may increase the amount of waste heat that can be recovered from multiple sources. Because the turbine wheel receiving the first fluid flow and the second fluid flow simultaneously allows for energy to be harnessed from multiple sources. Said sources may be exhaust gas flows, which otherwise would be emitted into the atmosphere, thus recovering waste heat energy. Advantageously, the waste heat energy can be recovered from the first and second fluid flows without the need to provide an additional turbine wheel and shaft, thus reducing the overall weight of the system while still recovering waste heat from more than one source at the same time.

The number of vanes in the first vane set may be the same as, or may be different to, the number of vanes in the second vane set.

In some embodiments, the vanes of the first vane set and the second vane set may be designed almost independently of one another to operate at different conditions that are suitable for the fluid flow they are designed to receive.

By not having to restrict the number of vanes in the first vane set to be the same as the number of vanes in the second vane set allows for greater freedom in the design parameters, and allows for the first and second fluid flows with different properties to be utilized efficiently.

The second vane set may comprise more vanes than the first vane set.

It will be appreciated, that in some embodiments, it may be desirable to have an equal number of vanes in the first and second vane sets.

The expansion ratio across the first vane set may be the same as, or may be different to, the expansion ratio across the second vane set.

The expansion ratio across the first vane set encompasses the ratio of the volume of exhaust gas at a location immediately upstream of the first vane set and the volume of exhaust gas at a location immediately downstream of the first vane set. The expansion ratio across the second vane set encompasses the ratio of the volume of exhaust gas at a location immediately upstream of the second vane set and the volume of exhaust gas at a location immediately downstream of the second vane set. The expansion ratio may be the inverse of the pressure ratio As described above, the present invention is advantageous in that the turbomachine is configured to receive a first fluid flow and a second fluid flow. The first and second fluid flows may have different physical properties, such as temperature, energy, pressure, velocity and density. Accordingly, it may be desirable for the pressure drop across the first vane set to be different to second vane set.

The radially outer vane set may be configured to receive a higher volume of fluid in comparison to the radially inner vane set.

The first vane set may have an expansion ratio of 18:1. The second vane set may have an expansion ratio of 18:1.

The first vane set may have an expansion ratio of 2.5:1. The second vane set may have an expansion ratio of 2.5:1.

The first vane set may have a different expansion ratio to the second vane set. The first vane set may have a higher expansion ratio than the second vane set. The first vane set may have a lower expansion ratio that the second vane set.

By way of example, the first vane set may be a higher pressure design with an expansion ratio of 10:1. The second vane set may be a lower pressure design with an expansion ratio of 4:1.

The first and second vane sets having different expansion ratios allows for fluid streams of different energy, temperature and pressure levels to be utilized. Each vane set may be sized and designed for the optimum running conditions associated with the properties of that fluid flow. This may obviate the need to compromise on the size and design of a vane set or resort to partial admission, as would be required if receiving the first and second fluid flow through a single vane set.

Each vane of the first vane set may have a chord length V1 and each vane of the second vanes set may have a chord length V2, wherein V2 and V1 may not be equal.

The profile of each vane in the first vane set may be the same as or may be different to the profile of each vane in the second vane set.

The term "vane profile" encompasses the geometric and structural properties of the vane and may include but is not limited to: - The twist of the geometry of the vane relative to the vane root (i.e. excluding any vane pitch). Where a vane may have a positive twist rotating in an anticlockwise direction about a vane axis, and a negative twist defining an anticlockwise rotation about a vane axis; The chord length of the vane, which may be the distance between a trailing edge of the vane and a leading edge of the vane; The vane thickness, which may be the maximum thickness of the profile; The camber of the vane, where the camber is a measure of the curvature of the vane. In particular, of comparing cambers of the first and second vane set, the mean camber may be compared.

The vanes of the first vane set may all have the same profile, and the vanes of the second vane set may all have the same profile. The vane profile of the first vane set and the second vane set may be optimized for a given design condition, thereby, increasing the efficiency of the downstream turbine wheel.

The vane profiles of the first vane set and the second vane set may be compared at the mid-height radius of each vane set. The mid-height radius being the distance that is half way from the base of the vane to the tip of the vane. The profile of the vane is considered to be the plan view of the vane at the mid-height of the vane, from a cascade view.

Differences in vane profiles may include at least one of the chord length, the camber length, the maximum camber, the maximum vane thickness and the angle of attack. Where all of these terms are taken as their usual meaning in the field of turbomachinery vane and blade design.

The housing may define a volute positioned downstream of the turbine wheel, the volute may be in fluid communication with the turbine wheel.

The term "volute" encompasses a spiraled or scrolled conduit that is in fluid communication with the turbine wheel. As fluid exits from the turbine wheel it flows into the volute. The volute may allow for controlled expulsion of the fluids that have passed through the turbine wheel, rather than the fluids being directly emitted into the atmosphere.

Fluid exiting the turbine wheel into the volute is also advantageous, in that it may provide greater design flexibility as to where the turbomachine may be installed. By way of example, the turbine wheel does not need to be proximate a location where the fluids can be immediately emitted into the atmosphere.

Further, by the housing defining the volute, the number of components required, and hence the number of joints between components is reduced. The reduction in joints between components helps to mitigate against any fluid or gas leakage. The mitigation of fluid and gas leakage may help to prevent any sudden or rapid pressure drops which may have a negative impact on the turbine efficiency.

In some embodiments, the housing may be a multipart housing such that different volutes can be connected to different housings. Thereby providing greater flexibility of the turbomachine to suit the end-user's requirements.

The volute may define an outlet passage having an inlet and an exit; the outlet passage may be configured, in use, to receive fluid in a generally axial direction at the inlet and for fluid to leave the outlet passage at the exit in a generally radial direction.

The volute may define at least part of the outlet passage. The inlet of the outlet passage defined by the volute may be provided directly downstream of the turbine wheel. In use, fluid may exit the turbine wheel, and immediately flow into the outlet passage of the volute at the inlet in a generally axial direction relative to the central axis. Because the outlet passage is at least in part defined by the volute, the outlet passage diverges away from the central axis in a radial direction, such that it can be considered to provide a curved passageway.

As fluid exits the turbine wheel and enters the outlet passage the fluid may be considered to be an axial flow, meaning the flow is generally parallel to the central axis. As the fluid flows along the outlet passage, from the inlet to the exit, the fluid follows a curved path. When at the exit, the fluid flow can be considered to be in a generally radial direction, meaning that the fluid flow is generally perpendicular to the central axis.

By directing the flow in a generally radial direction at the exit of the outlet passage, allows for the turbine shaft to be directly or indirectly coupled to a generator, or to another system which can utilize the kinetic energy of the shaft, without the need to provide room for the fluid flow exiting the turbine.

In some embodiments, the cross sectional area of the outlet passage may increase along its length from the inlet to the exit. This change in cross sectional area may cause the velocity of the fluid in the outlet passage to decrease and the pressure of the fluid to increase. The increase in pressure, may provide a useful back pressure, to the upstream turbine wheel and increase the efficiency of the turbine wheel.

The volute may further define a discharge port which is downstream of the exit of the outlet passage. The discharge port may be a region where the cross sectional area of the volute rapidly increases, which in turn causes rapid expansion of the fluid flow in the volute after exiting the outlet passage. The rapid expansion of fluid flow may further increase the efficiency of the turbine wheel by providing a useful back pressure.

The housing may define a dividing wall extending along the outlet passage from the inlet to exit, and wherein the outlet passage and the dividing wall may define a first outlet channel and a second outlet channel.

The first and second channels of the outlet passage may be concentric channels.

The channels may be fluidically sealed from one another. The fluidic sealing of the channels may substantially prevent fluid from the first outlet channel passing into the second outlet channel and vice versa.

In some embodiments, the first and second fluid flows may remain separated as they pass through and exit the turbine wheel. Accordingly, the first fluid flow may remain separated from the second fluid flow downstream of the turbine wheel and pass through the first outlet channel and the second fluid flow may pass through the second fluid channel.

The volute may further define a discharge port. The discharge port may be a region of the volute, where the cross sectional area of the volute rapidly increases, causing fluid flow which passes into it to rapidly expand. The discharge port may be downstream of the first and second outlet channels.

The dividing wall may not extend into the discharge port such that the first and second fluid flows may be configured to mix in the discharge port of the volute after exiting the outlet passage. In some embodiments, the first and second outlet channels may extend beyond the exit of the outlet passage and into the discharge port of the volute. Keeping the first and second fluids separated after passing through the turbine wheel may mitigate against the mixing of the fluids immediately downstream of the turbine wheel exit, where the kinetic energy and rotational kinetic energy is higher than at the exit of the outlet passage. Restricting the mixing of the first and second fluids to downstream of the outlet passage exit may aid in reducing the occurrence of turbulent flow, which could result in an unwanted or uncontrolled back pressure on the turbine wheel, and thereby reduce the efficiency of the turbine wheel.

The cross sectional areas of the first and second outlet channels may increase from the inlet of the outlet passage to the exit of the outlet passage.

The first and second outlet channels may at least be partially defined by the housing The plurality of blades may comprise a first blade portion and a second blade portion, the second blade portion may be provided radially outwards of the first blade portion.

In some aspects, the first and second blade portions may be distinct blades that form the plurality of blades. An interface may be provided between the first and second blade portions.

In other aspects, a single monolithic blade may comprise a first and second blade portion.

The first blade portion may extend from a radially innermost point of the blade, i.e. at the root of the blade and extend radially outwards towards the second portion of the blade. The second portion of the blade may start at a radial height of the blade where the first blade portion ends and extend to the radially outermost point of the blade, i.e. the blade tip.

The first blade portion may have a first profile, and the second blade portion may have a second profile. The geometry of the blade may change rapidly in the area proximate where the first portion ends and the second portion starts. Where the geometry of the blade rapidly changes from the first portion to the second portion, the area of the rapid change may define where the first portion ends and the second portion starts. Alternatively, the profile of the blade in the first portion may gradually transition to the profile of the blade in the second portion. Where the first profile gradually transitions to the second profile, there may be third area referred to as a transition portion. The radial extent of the transition portion will vary depending on the similarities or differences between the profiles of the first and second blade portions. The radial extent of the transition portion will be smaller when the first and second blade profiles are similar, and will be greater when the first and second profiles have greater differences The first blade portion may be designed for a design condition corresponding to the first fluid flow exiting the first annular stator channel. The second blade portion may be designed for a design condition corresponding to the second fluid flow exiting the second annular stator channel. By a blade comprising a first blade portion which is designed and configured to receive a first fluid flow and a second blade portion which is designed and configured to receive a second fluid flow is advantageous in that that first and second portions of the blades can cause the first and second fluid flows to respectively turn by differing amounts, relative to the central axis, if desired, thereby providing the ability to increase the power output of the turbine compared to if the first and second fluid flows were to pass through a single blade profile.

Each blade of the plurality of blades may extend in a radial direction from an innermost radius of the first blade portion to an outermost radius of the second blade portion.

That is to say, relative to the central axis, the first blade portion may extend from a root of the blade to a height which is radially outer of the root of the blade, and the second blade portion may extend from the height at which the first blade portion ends to a tip of the blade. Where the tip of the blade is radially outer of the height at which the first blade portion ends.

Each of the plurality of blades may be equally angularly distributed about the central axis.

Each of the plurality of blades may be orientated in the same direction as the vanes of the stator assembly (e.g. a clockwise or anticlockwise direction).

The first blade portion of each blade of the plurality of blades may collectively define a first blade set, and the second blade portion of each of the plurality of blades may collectively define a second blade set.

The term "blade set" encompasses a plurality of blades, which relative to the central axis, are axially aligned and circumferentially spaced from one another. The second blade set may be radially outwards and concentric to the first blade set. The second blade set may be axially offset from the first blade set, meaning that the center of the second blade set is not at the same axial location along the central axis as the center of the first blade set. Preferably, the center of the second blade set is at the same axial location along the center line as the center of the first blade set. The first blade set and the second blade set being axially aligned provides a compact arrangement of the turbomachine.

A support structure may be provided between the first blade set and the second blade set.

The support structure may extend around a perimeter of a radially outermost region of the first blade set. The support structure may define an interface from which the second blade set extends radially outwards from.

The support structure may be formed from a single structure, such that it forms a ring.

The support structure may be formed from at least two structures. The at least two structures may be supported by the blades of the first blade set. The at least two structures may be joined together to form a ring. The at least two support structures may be considered to be discontinuous support structures, whereby the at least two structures are supported by the first blade set, but there exists at least one gap in a circumferential plane between the at least two support structures.

The support structure may be a shrouded ring, from which blades extend.

The blades and the support structure may be manufactured and machined from a solid. Alternatively, the blades and support structure may be manufactured separately and then assembled. For example, the blades and/or support structure may be formed used metal injection molding, and casting processes including lost wax assembly. The blades and the support structure may be addifively manufactured.

In some embodiments, the support structure may form part of the first and/or second blade sets.

The first blade set may comprise a shrouded blade portion, in that a shroud extends circumferentially around a radially outer edge of the first blade set. The second blade set may be fixed to the shroud. For example, the shroud may comprise radially extending recesses or protrusions, and the second blade portion may comprise complementary protrusions or recesses such that the second blade portion and the shroud can be brazed together, or engaged to form an interference fit; the first blade set and/or the second blade set may be press fit to the shroud. The first and/or second blade set and the shroud may comprise anti-rotation features, so as to prevent relative rotational movement between the second blade set and the shroud, and/or the first blade set and the shroud, and/or the first and second blade sets.

The support structure, first blade set, and second blade set may all be formed as a single integral component.

The support structure and first blade set may be formed as an integral component; and the second blade set may be joined to the support structure The support structure and the second blade set may be formed as an integral component; and the first blade set may be joined to the support structure.

The first blade set may be configured to receive the first fluid flow. The second blade set may be configured to receive the second fluid flow.

The support structure, may provide a fluidic seal between the first and second blade sets. The first fluid flow may not be able to pass through the second blade set. and the second fluid flow may not be able to pass through the first blade set.

The first blade set may be designed with a design condition around the properties of the first fluid flow as it exits the stator assembly. The second blade set may be designed with a design condition around the properties of the second fluid flow as it exits the stator assembly.

The blades of the first blade set may be equally angularly distributed about the central axis The blades of the second blade set may be equally angularly distributed about the central axis The first blade portion of each blade of the plurality of blades may collectively define a first blade set, and the second blade portion of each of the plurality of blades may collectively define a second blade set.

The number of blade portions in the first blade set may be different to the number of blade portions in the second blade set.

The blade portions of the first blade set and of the second blade set may be designed almost independently of one another to operate at different conditions that are suitable for the fluid flow they are designed to receive. Operating at different conditions encompasses the first blade set being configured to receive a first fluid flow and the second blade set being configured to receive a second fluid flow where the first and second fluid flows have different physical properties; and the blade portions of the first blade set may be configured to turn the first fluid flow by a first angle relative to the central axis and the blade portions of the second blade set may be configured to turn the second flow relative to the central axis by a second angle, where the second angle is different to the first angle.

By not having to restrict the number of blade portions in the first blade set to be the same as the number of blade portions in the second blade set allows for greater freedom in the design parameters, and allows for the first and second fluid flows with different properties to be utilized efficiently.

It will be appreciated, that for some design conditions, it may be desirable to have an equal number of blades portions in the first and second blade sets.

The number of blade portions in the first blade set may be less than the number of blade portions in the second blade set Each blade portion of the first blade set may have a chord length B1 and each blade portion of the second blade set may have a chord length B2. Wherein B2 and B1 may not be equal.

A profile of the blade portions in the first blade set may be the same, or may be different to, a profile of the blade portions in the second blade set.

The term "a profile of the blade portions" encompasses the geometric and structural properties of the blade and may include but is not limited to: - The twist of the geometry of the blade relative to the blade root (i.e. excluding any blade pitch). Where a blade may have a positive twist rotating in an anticlockwise direction about a blade axis, and a negative twist defining an anticlockwise rotation about a blade axis; The chord length of the blade, which may be the distance between a trailing edge of the blade and a leading edge of the blade; The blade thickness, which may be the maximum thickness of the profile; The camber of the blade, where the camber is a measure of the curvature of the blade. In particular, of comparing cambers of the first and second blade set, the mean camber may be compared.

The blade portions of the first blade set may all have the same profile, and the blade portions of the second blade set may all have the same profile. The blade portion profiles of the first blade set and the second blade set may be optimized for a given design condition, thereby, increasing the efficiency and/or power output of the turbine wheel.

The blade portion profile of the first blade set and the second blade set may be optimized for a predetermined design condition.

The blade portion profiles of the first blade set and the second blade set may be compared at the mid-height radius of each blade set. The mid-height radius being the distance that is half way from the base of the blade portion to the tip of the blade portion. The profile of the blade portion is considered to be the plan view of the blade at the mid-height of the blade portion, from a cascade view.

Differences in blade portion profiles may include at least one of the chord length, the camber length, the maximum camber, the maximum blade thickness and the angle of attack. Where all of these terms are taken as their usual meaning in the field of turbomachinery vane and blade design.

The turbine wheel comprise may comprise a hub and a support structure. A first annular turbine channel may be defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel may be defined, at least in part, by the support structure and the housing The hub encompasses a central component of the turbine wheel and in use is configured to rotate about the central axis. In some embodiments the hub may be mounted to the shaft, and in other embodiments the hub may be defined at least in part by the shaft. The term support structure encompasses an annular structure which may extend generally around the tips of the first blade portions and the roots of the second blade portions and provides an interface between the first and second blade portions The support structure may extend around the entire circumference of the interface between the first and second blade portions. The support structure may comprise a shrouded ring. The blades and the support structure may be manufactured and machined from a solid. Alternatively, the blades and support structure may be manufactured separately and then assembled. For example, the blades and/or support structure may be formed used metal injection molding, and casting processes including lost wax assembly. The blades and the support structure may be additively manufactured. The first and/or second blade portions may be joined to the support structure by an interference fit, the first and/or second blade portions may be brazed to the support structure. The first and/or second blade portions may be welded to the support structure. The first and/or second blade portions may be joined to the support structure using any suitable means, for example mechanical fittings, sintering, brazing, welding.

The first and second annular turbine channels encompass passages or conduits through which the first and second fluids can pass though. The first annular turbine channel may be configured to receive the first fluid flow, and the second annular turbine channel may be configured to receive the second fluid flow. The first and second annular turbine channels may be configured to direct the first and second fluids through the turbine wheel, from an upstream turbine wheel inlet to a downstream turbine wheel outlet.

The first and second annular turbine channels may be fluidically sealed from each other such that fluid in the first annular turbine channel is substantially prevented passing from the first turbine channel to the second turbine channel; and that fluid in the second turbine channel is substantially prevented passing from the second turbine channel to the first turbine channel. Because the first and second fluids may have different properties, by sealing the first and second annular turbine channels, the first and second fluids may be substantially prevented from mixing; mixing of the fluids may cause the power output of the turbine to be reduced.

The first and second annular turbine channels may be fluidically sealed from each other through means of one or more 0-rings or any other suitable seal or sleeve.

The second radially outward annular turbine channel being defined by the housing and the turbine wheel is advantageous in that the weight of the turbomachine may be reduced through use of the housing to partly define the second annular turbine channel, rather than through use of an additional component.

It will be appreciated, that in other embodiments, additional components, for examples sleeves and skins may be used in combination with the turbine wheel and/or the turbine housing to define the first and second annular turbine channels.

The first blade portions may be provided in the first annular turbine channel and the second blade portions may be provided in the second annular turbine channel.

The first and second annular turbine channels encompass conduits through which the first and second fluid flows can pass though. The first and second blade sets may be provided in the first and second channels respectively so that the first and second fluids pass through only the first and second blade sets respectively.

The first and second annular turbine channels may be fluidically sealed from each other.

That is to say, the first fluid flow may be substantially prevented from passing through the second annular turbine channel, and the second fluid flow may be substantially prevented from passing through the first annular turbine channel. It will be appreciated, that it may not be possible to entirely prevent fluid leakage between the first and second annular turbine channels. Because the first and second fluid flows may have different properties, by sealing the first and second annular turbine channels, the first and second fluids are substantially prevented from mixing; mixing of the fluids may reduce the effectiveness of the first and second fluid flows on the blade sets and thereby reduce the efficiency and/or power output of the turbine wheel.

The first annular stator channel may be in fluid communication with the first annular turbine channel, and the second annular stator channel may be in fluid communication with the second annular turbine channel.

The first annular stator channel being in fluid communication with the first annular turbine channel allows for the first fluid through to pass through the first annular stator channel, and be turned by the first vane set such that it has the desired flow conditions for the first blade set in the first annular turbine channel.

The second annular stator channel being in fluid communication with the second annular turbine channel allows for the second fluid through to pass through the second annular stator channel, and be turned by the second vane set such that it has the desired flow conditions for the second blade set in the second annular turbine channel.

The first and second annular stator channels together with the respective vane sets are configured to condition the first and second fluid flows respectively, such that the first and second fluid flows can efficiently turn the turbine wheel.

The first annular stator channel may have the same outermost diameter as the first annular turbine channel.

The second annular stator channel may have the same outermost diameter as the second annular turbine channel.

The vane height of the vanes in the first vane set may be equal to the blade height of the blades in the first blade set.

The vane height of the vanes in the second vane set may be equal to the blade height of the blades in the second blade set.

The first outlet channel may be in fluid communication with the first annular turbine channel, and the second outlet channel may be in fluid communication with the second annular turbine channel. The first and second outlet channels may be fluidically sealed from one another.

Sealing the first and second outlet channels from one another, is intended to mean that the fluid flow between the first and second outlet channels is substantially prevented. It will be appreciated, that dependent upon the chosen sealing method between the two channels, there may be small fluid leakages between the channels, in particular, this may occur at the outlet passage inlet and exit, but otherwise, fluid is generally blocked from passing between the first and second outlet channels.

The first outlet channel being in fluid communication with the first annular turbine channel allows the first fluid flow to pass through the first blade set and directly into the first outlet channel. Similarly, the second outlet channel being in fluid communication with the second annular turbine channel allows the second fluid flow to pass through the second blade set and directly into the second outlet channel. This advantageous as it mitigates against mixing of the first and second fluid flows immediately downstream of the turbine wheel. In other words, the first and second fluid flows remain separated after exiting the respective blade sets of the turbine wheel. By mitigating against the first and second fluid flows mixing immediately downstream of the turbine wheel, turbulent mixing between the first and second fluid flows reduced; this is advantageous, as turbulent mixing between the first and second fluid flows immediately downstream of the turbine wheel could lead to an undesirable and unwanted back pressure on the turbine wheel, which in turn may reduce the efficiency of the turbine wheel or an upstream system, for example an internal combustion engine, to which the turbomachine may be connected to.

According to a second aspect of the invention, there is provided a turbomachine comprising a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel, the stator assembly comprising first and second vane sets provided concentrically about the central axis, the first vane set configured to receive a first fluid and the second vane set configured to receive a second fluid; the second vane set being disposed radially outwards of the first vane set; the stator assembly defining a first annular stator assembly channel and a second annular stator assembly channel; the first vane set provided in the first annular stator assembly channel and the second vane set provided in the second annular stator assembly channel; and the first and second annular stator assembly channels being fluidically sealed from each other; wherein the turbine wheel comprises a hub and a support structure; wherein a first annular turbine channel is defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel is defined, at least in part, by the support structure and the housing; wherein the plurality of blades of the turbine wheel comprise a first blade portion and a second blade portion, the second blade portions are provided radially outwards of the first blade portions; and wherein the first blade portions are provided in the first annular turbine channel and the second blade portions are provided in the second annular turbine channel.

According to a third aspect of the invention, there is provided a turbomachine comprising a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel, the stator assembly comprising first and second vane sets provided concentrically about the central axis, the first vane set configured to receive a first fluid and the second vane set configured to receive a second fluid; wherein the second vane set is disposed radially outwards of the first vane set; wherein the stator assembly defines a first and a second annular stator assembly channel; the first vane set is provided in the first annular stator assembly channel and the second vane set is provided in the second annular stator assembly channel; and the first and second annular stator assembly channels are fluidically sealed from each other; wherein the turbine wheel comprises a hub and a support structure; wherein a first annular turbine channel is defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel is defined, at least in part, by the support structure and the housing; wherein the plurality of blades of the turbine wheel comprises a first blade portion and a second blade portion; wherein the second blade portions are provided radially outwards of the first blade portion; wherein the first blade portions are provided in the first annular turbine channel and the second blade portions are provided in the second annular turbine channel; and wherein the housing defines a volute positioned downstream of the turbine wheel; wherein the volute is in fluid communication with the turbine wheel; and wherein the volute comprises an outlet passage having an inlet and an exit; and the housing defines a dividing wall extending along the outlet passage from the inlet to outlet; wherein the outlet passage and the dividing wall define a first outlet channel and a second outlet channel.

It will be appreciated that any of the above-discussed aspects of the invention may, where appropriate, be combined with one or more other aspects of the invention. Furthermore, an optional feature described in relation to one aspect of the invention may, where appropriate, be an optional feature of another aspect of the invention.

Brief description of the drawings

The invention may now be described by way of example, with reference to the accompanying figures in which: Figure 1A shows a cross-sectional side view of a turbomachine according to a first embodiment of the present invention; Figure 1B shows a detailed cross-sectional side view of the stator assembly according to Figure 1A; Figure 2 shows an end view of the turbomachine of Figure 1A; Figure 3 shows a cross-sectional end view of a turbine wheel for use in the turbomachine according to Figure 1A; Figure 4A shows a cross-sectional side view of a turbomachine according to a second embodiment of the present invention; Figure 4B shows a detailed cross-sectional side view of the stator assembly and turbine wheel according to Figure 4A; Figure 5 shows an end view of a turbine wheel for use in the turbomachine according to Figure 4A; Figure 6 shows a variant of the turbomachine according to Figure 4A. Detailed description of the embodiments Figure 1A shows a cross-sectional side view of an axial turbomachine 10 according to a first embodiment of the present invention. The axial turbomachine 10 may be interchangeably referred to as a turbomachine, axial turbine or turbine.

The axial turbine 10 comprises a housing 11 which supports a shaft 12 for rotation about a central axis A-A. The shaft 12 is further supported by a bearing housing 13. A turbine wheel 14 is fixedly connected to the shaft 12. The turbine wheel 14 is disposed proximate a first end of the shaft 12, upstream of the bearing housing 13 (shown to the left-hand side of the bearing housing in Figure 1). The turbine wheel 14 is configured to rotate about the central axis A-A. When the turbine wheel 14 rotates about the central axis A-A the shaft 12 also rotates about the central axis A-A. Rotation of the turbine wheel 14 can be considered to drive the shaft 12.

A second end of the shaft 12, that is opposite the first end of the shaft 12, may be connected to a generator (not shown), or it may be connected to another system or assembly which can harness the kinetic energy of the shaft 12 either mechanically or electrically.

The turbine wheel 14 is shown in Figure 1A as a component that is fixedly attached to the shaft 12. Alternatively, the turbine wheel 12 and the shaft 14 may be formed as a single integral component.

The turbine wheel 14 comprises a plurality of blades 15. The blades 15 are equally circumferentially spaced about the central axis A-A and are shown in more in detail in Figure 3.

Provided upstream of the turbine wheel 14 and supported by the housing 11 is a stator assembly 16 (sometimes referred to as a 'stator ring'). The stator assembly 16 comprises a plurality of guide vanes 17 configured to receive fluid from an upstream location, usually in the form of a gas, and direct said fluid on to the blades 15 of the turbine wheel 14, thus driving the turbine wheel 14.

In the embodiment according to Figure 1A, the stator assembly 16 comprises a first guide vane set 18a and a second guide vane set 18b. Each guide vane set 18a, 18b comprises a plurality of guide vanes. The second guide vane set 18b is disposed radially outwards of and concentric to the first guide vane set 18a relative to the central axis A-A. The first and second guide vane sets 18a, 18b are positioned at the same axial location, in other words the first and second guide vane sets 18a, 18b are axially aligned with respect to the central axis A-A. In other embodiments the first and second guide vane sets 18a, 18b may be axially offset from one another.

The vanes of the first guide vane set 18a and of the second guide vane set 18b are equally circumferentially spaced about the central axis A-A, shown more clearly in Figure 2. The first and second guide vane sets 18a, 18b are stationary with respect to the central axis A-A. In other words, the first and second guide vane sets 18a, 18b differ from the turbine wheel in that they do not rotate about the central axis A-A.

The stator assembly 16 further defines a first annual stator channel 19a and a second annular stator channel 19b. The second annular stator channel 19b is disposed radially outwards and concentric to the first annular stator channel 19a with respect to the central axis A-A. The first annular stator channel 19a and the second annular stator channel 19b each define a fluidic conduit, through which a fluid may pass, and can be seen more clearly in figure 1B.

Figure 1B shows a detailed cross-sectional view of the stator assembly 16 of Figure 1A.

The first annular stator channel 19a has a radial thickness and the first guide vane set 18a is disposed in the first annular stator channel 19a. The radial thickness, in the embodiment shown is equal to the diameter of the first annular stator channel 19a. Each vane of the first guide vane set 18a extends across the radial thickness of the first annular stator channel 19a. The second guide vane set 18b is disposed in the second annular stator channel 19b. The second annular stator channel 19b has a radial thickness, and each vane of the second vane set 18b extends across the radial thickness of the second annular stator channel 19b. In Figures 1A and 1B the radial thicknesses of the first and second annular stator channels 19a, 19b are equal. It will be appreciated that in other embodiments, the radial thickness of the first and second annular stator channels 19a, 19b need not be equal, and in some instances it is desirable for the respective radial thicknesses of the annular stator channels 19a, 19b to be different. For example, the radial thickness of the first annular stator channel 19a may be greater than the radial thickness of the second annular stator channel 19b. Alternatively, the radial thickness of the first annular stator channel 19a may be less than the radial thickness of the second annular stator channel 19b.

In use, the first annular stator channel 19a receives a first fluid flow 20a from a source (not shown) upstream of the stator assembly 16. Similarly, the second annular stator channel 19b receives a second fluid flow 20b from a source (not shown) upstream of the stator assembly 16.

The first fluid flow 20a flows through the first annular stator channel 19a, and passes between adjacent vanes of the first vane set 18a. As the first fluid flow 20a passes between the adjacent vanes, the vanes cause the flow angle of the first fluid flow to change. In other words, the vanes of the first vane set 18a can be considered to turn the first fluid flow 20a relative to the central axis A-A. After the first fluid flow 20a has passed through the first vane set 18a, the fluid exits the stator assembly 16 and impinges upon the blades 15 of the turbine wheel 14.

Likewise, as the second fluid flow 20b flows through the second annular stator channel 19b, and passes between adjacent vanes of the second vane set 18b the vanes cause the flow angle of the second fluid flow 20b to change. In other words, the vanes of the second vane set 18b can be considered to turn the second fluid flow 20b. After the second fluid flow 20b has passed through the second vane set 18b, the fluid exits the stator assembly 16 and impinges on the blades 15 of the turbine wheel 14.

The first annular stator channel 19a is fluidically sealed from the second annular stator channel 19b. Such that, once the first fluid flow 20a enters the stator assembly 16 and the first annular stator channel 19a, it generally cannot pass into the second annular stator channel 19b. Similarly, once the second fluid flow 20b enters the stator assembly 16 and the second annular stator channel 19b, it cannot pass into the first annular stator channel 19a.

The first fluid flow 20a and the second fluid flow 20b may come from different sources. In some instances, they may come from the same source. In Figure 1B, it is shown that the first and second fluid flows 20a, 20b flow simultaneously through the first and second annular stator channels 19a, 19b. It will, however, be appreciated, that in some instances, one of the first or second annular stator channels 19a, 19b may not be used. By way of example, a first fluid flow 20a may pass through the first annular stator channel 19a, but no fluid flow is directed through the second annular stator channel 19b. Alternatively, a second fluid flow 20b may pass through the second annular stator channel 19b, but no fluid flow is directed through the first annular stator channel 19a.

The first vane set 18a and the second vane set 18b may turn the first and second fluid flows 20a, 20b by different amounts. This is because the first fluid flow 20a may have different physical properties to the second fluid flow 20b upstream of the stator assembly 16. The first vane set 18a and the second vane set 18b may be designed such that the first fluid flow 20a and the second fluid flow 20b exit the stator assembly 16 with approximately the same flow angle and/or velocity, or may be designed such that the first and second fluid flows 20a, 20b exit the stator assembly 16 with different flow angle and/or velocity.

A leading edge of the turbine blades 15 of the turbine wheel 14 is provided proximate the exit of the stator assembly 16. Providing the blades 15 of the turbine wheel 14 immediately downstream of the stator assembly 16 reduces as far as possible any mixing of the first and second fluid flows 20a, 20b before the they impinge on the blades 15 of the turbine wheel 14.

After exiting the stator assembly 16, the first fluid flow 20a generally impinges on the blades 15 of the turbine wheel 14 generally radially inwards of the second fluid flow 20b. The first and second fluid flows 20a, 20b pass between adjacent blades 15 of the turbine wheel 14, thus causing the turbine wheel 14 and, hence, the shaft 12 to rotate about the central axis A-A.

The blades 15 of the turbine wheel 14 are single monolithic blades, as discussed in more detail below and seen more clearly in Figure 4.

Returning to Figure 1A, the turbomachine 10 further comprises a volute 30 defined by the housing 11 of the turbomachine 10. The volute 30 comprises an outlet passage 32 and a discharge port 34. The discharge port 34 having a cross-sectional area that is larger than the cross sectional area of the outlet passage 32.

The outlet passage 32 can be considered to have an inlet 36 which is immediately downstream of a trailing edge of the turbine blades 15. The outlet passage 32 can be further considered to have an exit 38 located proximate where the cross-sectional area of the volute 30 increases between the outlet passage 32 and the discharge port 34.

When the first and second fluid flows 20a, 20b exit the turbine wheel 14, the flows can be considered to travel in a generally axial direction, i.e. generally parallel to the central axis A-A. Thus, as the fluid flows 20a, 20b enter the outlet passage 32 at the inlet 36 they are still considered to be in a generally axial direction.

The outlet passage 32 diverges away from the central axis A-A from the inlet 36 to the exit 38 in a radial direction, thereby defining a curved passageway.

As fluid flows along the outlet passage 32, from the inlet 36 to the exit 38, the fluid follows the curvature of the outlet passage 32. When at the exit 38, the fluid flow can be considered to be in a generally radial direction, meaning that the fluid flow is generally perpendicular to the central axis A-A.

Directing the fluid flow in a generally radial direction at the exit 38 of the outlet passage 32 allows the shaft 12 to be directly or indirectly coupled to a generator, or to another system which can utilize the kinetic energy of the shaft 12, without needing to provide room for the fluid flow exiting the turbine wheel 14.

The first and second fluid flows 20a, 20b are not prevented from mixing when passing through the blades 15 of the turbine wheel 14 or when passing through the outlet passage 32. Some mixing between the first and second fluid flows 20a, 20b may occur as the flows pass through the turbine wheel 14. However, the majority of the mixing will occur in the volute 30 and in particular, in the discharge port 34 and in the outlet passage 32 proximate the exit 38.

Figure 2 shows an end view from the stator assembly 16 end of the turbomachine 10 according to Figure 1A and 1B, where it can be seen more clearly that the first vane set 18a is radially inwards of, and concentric with, the second vane set 18b.

The vanes of the first vane set 18a extend across the radial thickness of the first annular stator channel 19a; and the vanes of the second vane set 18b extend across the radial thickness of the second annular stator channel 19b.

In Figure 2, the number of vanes in the second vane set 18b is greater than the number of vanes in the first vane set 18a. It will be appreciated that the number of vanes in the first and second vane sets 18, 18b will vary depending on the design conditions of the turbomachine.

It can be seen that the vanes of the first vane set 18a and the vanes of the second vane set 18b are generally orientated in the same direction. In other words, the first and second vane sets 18a, 18b in Figure 2 may be considered to have a clockwise orientation. A clockwise orientation is intended to mean that a tip (i.e. a radially outermost point) of a vane is positively circumferentially displaced relative to the circumferential location of a base (i.e. a radially innermost point) of the same vane.

In other embodiments, the first and second vane sets 18a, 18b may both be orientated in an anti-clockwise direction; and in other embodiments one of the first or second vane sets 18a, 18b may be orientated in a clockwise direction, and the other of the first or second vane sets 18a, 18b may be orientated in an anti-clockwise direction.

Figure 3 shows a schematic cross-sectional end view of an exemplary turbine wheel 14 comprising a plurality of blades 15 that can be used in the turbomachine 10 according to Figure 1A.

Each of the blades 15 may be a single monolithic blade, meaning that the blade is a unitary structure, and which is designed around a particular design condition for use in the turbomachine.

A theoretical dashed circular line 40 is shown in Figure 3. The circular line 40 intersects each blade 15 above the radial mid-height of each blade 15, but is radially inwards of each blade tip. The circular line 40 may correspond to a radial height that is equal to the radially outmost point of the first vane set 18a in Figure 1A. Such that, the first fluid flow 20a, after exiting the first vane set 18a, would impinge on the blades 15 radially inwards of the theoretical circular line 40; and the second fluid flow 20b, after exiting the second vane set 18b, would impinge on the blades 15 radially outwards of the theoretical circular line 40. As such, the blades 15 may be considered to have a first portion 15a that is radially inwards of the theoretical circular line 40, which in use, the first fluid flow 20a impinges upon, and a second portion 15b that is radially outwards of the theoretical circular line 40, which in use, the second fluid flow 20b impinges upon.

In some embodiments, the first and second vane sets 18a, 18b, may be configured such that the first and second fluid flows 20a, 20b, although entering the stator assembly 16 with different flow characteristics, leave the assembly with similar flow characteristics, this may include similar temperature; pressure; mass flow rate; and/or whirl angle, including any combination. For example, the first and second fluid flows 20a, 20b may exit the stator assembly 16 with mean velocities within a 5 % tolerance of each other, and/or flow angles within a 5 % tolerance of each other. The first and second fluid flows 20a, 20b may exit the stator assembly 16 with a similar whirl angle (the term whirl angle may be interchangeably referred to as swirl angle). Where the whirl angle can be defined as Whirl Angle = tan-1 IVaxiati adiail Where V, is the axial component of the velocity vector of the fluid flow relative to the central axis and Vrad,a, is the radial component of the velocity vector the fluid flow. Although it may be desirable for the first and second fluid flows 20a, 20b to exit the stator assembly with the same whirl angle, it will be appreciated that the whirl angle of the first fluid flow 20a after exiting the stator may differ from the whirl angle of the second fluid flow 20b after exiting the stator assembly by around 5%, more preferably by around 2%.

The stator assembly may be designed to condition the first and second fluid flows 20a, 20b such that they exit the stator assembly with the same temperature and/or pressure. It will be appreciated that the when referring to the fluid flows 20, 20b having the same temperature and/or pressure conditions, these conditions may deviate from one another by around 5%, preferably by around 2%.

The stator assembly 16 is designed such that the first and second fluid flows 20a, 20b are conditioned to be received by the turbine wheel 14. The stator assembly may be designed to match specific user requirements, dependent upon from where the first and second fluid flows 20a, 20b originate.

The first and second fluid flows 20a, 20b may be pre-conditioned prior to passing through the stator assembly. For example, the first and/or second flows may be heated or cooled prior to reaching the stator assembly 16. In particular, the turbomachine may comprise a water jacket, or labyrinth passage resulting in transfer of heat energy away from the first and/or second fluid flows 20a, 20b and resulting in a decrease in temperature.

When the first and second fluid flows 20a, 20b exit the stator assembly 16 with approximately the same flow characteristics, the blades 15 of the turbine wheel 14, may have a single blade profile, and accordingly a conventional turbine wheel may be used. As such, the theoretical circular line 40 simply delineates the portions 15a, 15b of each of the turbine blades 15 upon which the first and second flows 20a, 20b will impinge during use.

In other embodiments, instead of the first and second flows 20a, 20b exiting the stator assembly 16 with approximately the same flow conditions, the first and second vanes sets 18a, 18b may be designed such that the first and second fluid flows 20a, 20b exit the stator assembly 16 with differing flow conditions. For example, in use, the first and second fluid flows may exit the stator assembly 16 with mean velocities which differ from each by more than 10 %, and/or flow angles which differ from each other by more than 10 %. In this case, the design of the first blade portions 15a are optimized with respect to the intended flow conditions of the first fluid flow 20a exiting the stator assembly 16; and the design of the second blade portions 15b are optimized with respect to the intended flow conditions of the second fluid flow 20b exiting the stator assembly 16. As such, when the first and second fluid flows 20a, 20b exit the stator assembly 16 with differing flow conditions, the portions 15a and 15b of the blades 15 may not have a single blade profile. Instead, the first blade portion 15a, which is radially inwards of the circular line 40, will define a first profile configured to receive the first fluid flow 20a; and the second blade portion 15b, which is radially outwards of the circle 40, will define a second blade profile configured to receive the second fluid flow 20b. By designing the first and second blade portions 15a, 15b to have respective first and second profiles which are configured to receive the first and second fluid flows 20a, 20b with differing flow properties, it is possible to extract more energy from the first and second flows 20a, 20b. If the first and second blade portions 15a, 15b define a single blade profile, the first and second flows 20a, 20b may not turn the turbine wheel with the same level of efficiency, and accordingly, less energy may be extracted from the first and second fluid flows 20a, 20b by the turbine wheel 14.

In further embodiments, where the first and second fluid flows 20a, 20b also exit the stator assembly 16 with differing fluid properties, the region of the first blade portion 15a proximate the circular line 40 and the region of the second blade portion 15b proximate the circular line 40 may form a transition region. The transition region is a location of the blade 15 where the profile of the first portion 15a transitions to the profile of the second portion 15b. Providing a gradual transition between the first and second portions 15a, 15b, avoids any undesirable sudden discontinuities across the blade profile which might disrupt efficient fluid flow across the blade 15. Sudden discontinuities or sudden changes in blade geometry could lead to excessive and undesirable stresses and strains in the blades, in turn leading to sudden and premature failure, and could cause localized regions of high turbulence, which could reduce the efficiency of the turbine wheel 14.

For completeness, the term blade profile is intended to take its usual meaning in the field of blade design for turbomachinery, and may include, but is not limited to, chord length, camber length, maximum thickness and maximum camber.

In further embodiments, the stator assembly 16, instead of comprising a plurality of vanes, may instead be a disc like member, with an axial extent, which comprises a plurality of axially extending passages. The axially extending passages may be channels, and in particular may be tapered or angled channels which are designed to change in part the radial velocity of a fluid flow received in the channel. The axially extending passages may be generally conically shaped. The stator assembly 116 may comprise a first radially inner row of axially extending passages for receiving a first fluid flow 20a and a second radially outer row of axially extending passages for receiving a second fluid flow 20b. The first and second rows of axially extending passages, may be equally circumferentially spaced about a central axis of the stator assembly 16. Each axially extending passage may be fluidically sealed from other axially extending passages in the stator assembly. The axially extending passages/channels may be drilled or machined into the stator assembly.

Figure 4A shows a cross-sectional side view of a turbomachine 110 according to a second embodiment of the present invention. The turbomachine 110 may be interchangeably referred to as an axial turbine, axial turbomachine or tudoine.

The turbomachine 110 comprises a housing 111 which supports a shaft 112 for rotation about a central axis A-A. The shaft 112 is further supported by a bearing housing 113. A turbine wheel 114 is fixedly connected to the shaft 112. The turbine wheel 114 is disposed proximate a first end of the shaft 112, upstream of the bearing housing 113 (shown to the left-hand side of the bearing housing in Figure 4A). The turbine wheel 114 is configured to rotate about the central axis A-A. When the turbine wheel 114 rotates about the central axis A-A, the shaft 112 also rotates about the central axis A-A. Rotation of the turbine wheel 114 can be considered to drive the shaft 112.

A second end of the shaft 112, that is opposite the first end of the shaft 112, may be connected to a generator (not shown), or it may be connected to another system or assembly which can harness the kinetic energy of the shaft 112 either mechanically or electrically.

The turbine wheel 114 is shown in Figure 4A as a component that is fixedly attached to the shaft 112. Altemafively, the turbine wheel 114 and the shaft 112 may be formed as an integral component.

The turbine wheel 114 comprises a plurality of blades 115. The blades 115 are equally circumferentially spaced about the central axis A-A and are shown in more in detail in Figure 4B and 5.

Provided upstream of the turbine wheel 114 and supported by the housing 111 is a stator assembly 116 (sometimes referred to as a 'stator ring'). The stator assembly 116 comprises a plurality of guide vanes 117 configured to receive fluid, usually in the form of a gas, and direct said fluid on to the blades 115 of the turbine wheel 114, thus driving the turbine wheel 114.

As with the embodiment shown in Figure 1A and 1B, in the embodiment according to Figure 4A, the stator assembly 116 comprises a first guide vane set 118a and a second guide vane set 118b. Each guide vane set 118a, 118b comprises a plurality of guide vanes. The second guide vane set 118b is disposed radially outwards of and concentric to the first guide vane set 118a. The first and second guide vane sets 118a, 118b are positioned at the same axial location. In other embodiments the first and second guide vane sets 118a, 118b may be axially offset from one another.

The first and second guide vane sets 118a, 118b are disposed about the central axis AA. The vanes of the first guide vane set 118a and of the second guide vane set 118b are equally circumferentially spaced about the central axis A-A, as shown in Figure 2 in relation to the first embodiment. The first and second guide vane sets 118a, 118b, do not rotate about the central axis A-A. Each vane of the first and second guide vane sets 118a, 118b is in a fixed angular position relative the central axis A-A.

The stator assembly 116 further defines a first annual stator channel 119a and a second annular stator channel 119b. The second annular stator channel 119b is disposed radially outwards and concentric to the first annular stator channel 119a.

Figure 4B shows a detailed cross-sectional view of the stator assembly 116 and the turbine wheel 114 of Figure 4A. The first guide vane set 118a is disposed in the first annular stator channel 119a. The first annular stator channel 119a has a radial thickness, and each vane of the first guide vane set 118a extends across the radial thickness of the first annular stator channel 119a. The second guide vane set 118b is disposed in the second annular stator channel 119b. The second annular stator channel 119b has a radial thickness, and each vane of the second vane set 118b extends across the radial thickness of the second annular stator channel 119b. In Figures 4A and 4B the radial thickness of the first and second annular stator channels 119a, 119b are equal. It will be appreciated that in other embodiments, the radial thickness of the first and second annular stator channels 119a, 119b need not be equal, and in some instances it is desirable for the respective radial thicknesses of the annular stator channels 119a, 119b to be different.

In use, the first annular stator channel 119a receives a first fluid flow 120a from a source (not shown) upstream of the stator assembly 116. Similarly, the second annular stator channel 119b receives a second fluid flow 120b from a source (not shown) upstream of the stator assembly 116.

The first fluid flow 120a flows through the first annular stator channel 119a, and passes between adjacent vanes of the first vane set 118a. As the first fluid flow 120a passes between the adjacent vanes, the vanes 118b cause the flow angle of the first fluid flow 120a to change. In other words, the vanes of the first vane set 118a can be considered to turn the first fluid flow 120a. After the first fluid flow 120a has passed through the first vane set 118a, the fluid exits the stator assembly 116 and impinges on the blades 115 of the turbine wheel 114.

The second fluid flow 120b flows through the second annular stator channel 119b, and passes between adjacent vanes of the second vane set 118b. As the second fluid flow 120b passes between the adjacent vanes, the vanes 118b cause the flow angle of the second fluid flow 120b to change. In other words, the vanes of the second vane set 18b can be considered to turn the second fluid flow 120b. After the second fluid flow 120b has passed through the second vane set 118b, the fluid exits the stator assembly 116 and impinges on the blades 115 of the turbine wheel 114.

The first annular stator channel 119a is fluidically sealed from the second annular stator channel 119b, such that once the first fluid flow 120a enters the stator assembly 116 and the first annular stator channel 119a, it cannot pass into the second annular stator channel 119b. Similarly, once the second fluid flow 120b enters the stator assembly 116 and the second annular stator channel 119b, it cannot pass into the first annular stator channels 119a.

The first fluid flow 120a and the second fluid flow 120b may come from different sources.

In some instances, they may come from the same source. In Figure 4B, it is shown that the first and second fluid flows 120a, 120b flow through the first and second annular stator channels 119a, 119b, respectively, simultaneously. It will, however, be appreciated that in some instances, one of the first or second annular stator channels 119a, 119b may not be used. By way of example, a first fluid flow 120a may pass through the first annular stator channel 119a, and no fluid flow is directed through the second annular stator channel 119b, or vice versa.

The first vane set 118a and the second vane set 118b may turn the first and second fluid flows 120a, 120b respectively by different amounts. This may be desirable because the first fluid flow 120a may have different physical properties to the second fluid flow 120b upstream of the stator assembly 116. The first vane set 118a and the second vane set 118b may be designed such that the first fluid flow 120a and the second fluid flow 120b exit the stator assembly 116 with approximately the same flow angle and/or velocity.

The turbine wheel 114 differs from the turbine wheel 14 of the first embodiment in that the blades 115 of the turbine 114 are not single monolithic blades. Discussed in more detail below in relation to Figure 5, the turbine wheel 114 comprises a plurality of first blade portions 115a, which collectively define a first blade set, and a plurality of second blade portion 115b, which define a second blade set. The second blade set is radially outwards and concentric to the first blade set.

Turning to Figure 5, which shows an end view of a turbine wheel 114 for use in the turbomachine 110 according to Figures 4A and 4B, the turbine wheel comprises a plurality of blades 115 having a first blade portion 115a, which collectively define a first blade set, and a second portion 115b, which collectively define a second blade set. The first and second blade sets are both equally circumferentially distributed about the same center.

The second blade set is radially outwards of, and concentric to, the first blade set.

Provided between the first and second blade sets is a support structure 150. Support structure 150 in an annular structure that extends around the tips of the first blade set. The support structure 150 also extends around the root of the blades of the second blade set. In other words, the support structure 150 extends around a perimeter of the radially outermost region of the first blade set; and extends around a perimeter of the radially innermost region of the second blade set. The support structure 150 provides an interface between the first and second blade sets. The support structure 150 may be a shrouded ring, from which blades 115 extend from.

The blades 115 and the support structure 150 may be manufactured and machined from a solid. Alternatively, the blades 115 and support structure may be manufactured separately and then assembled. For example, the blades 115 and/or support structure may be formed using metal injection molding, and casting processes including lost wax assembly. The blades 115 and/or support structure may be addifively manufactured.

The purpose of having the first blade portion 115a and the second blade portion 115b is so that energy can be efficiently extracted from two different flows having different flow characteristics. In some embodiments, the support structure 150 may form part of the first and/or second blade portions 115a, 115b.

The first blade portion 115a may be a shrouded blade portion, in that a shroud extends circumferentially around a radially outer edge of the first blade portion 115a. The second blade portion 115b may be fixed to the shroud. For example, the shroud may comprise radially extending recesses or protrusions, and the second blade portion 115b may comprise complementary protrusions or recesses such that the second blade portion 115b and the shroud can be brazed together, or engaged to form an interference fit.

The blades 115a of the first blade set extend across a radial thickness between hub 112 of the turbine wheel 114 and the support structure 150. The blades 115b of the second blade set extend across a radial thickness between the support structure 150 and the turbine housing 111. The blades 115a of the first blade set are axially aligned, with respect to the central axis A-A with the blades 115b of the second blade set; in other embodiments the blades 115a of the first blade set may be axially offset from the blades 115b of the second blade set.

In some embodiments the support structure 150, the blades 115a of the first blade set, and the blades 115b of the second blade set f may all be formed as a single integral component. In another embodiment the support structure 150 and the blades 115a of the first blade set may be formed as an integral component, and the blades 115b of the second blade set may be joined or attached to the support structure 150; and in another embodiment the support structure 150 and the blades 115b of the second blade set may be formed as an integral component, and the blades 115a of the first blade set may be joined to the support structure.

The turbine wheel 114 defines a first annular turbine channel 160a and a second annular turbine channel 160b. The second annular turbine channel 160b is radially outwards of, and concentric to, the first annular turbine channel 160a.

The first annular turbine channel 160a is defined by the hub of the turbine wheel 114 and the support structure 150. The second annular turbine channel 160b is defined by the support structure 150 and the turbomachine housing 111. The first and second annular channels 160a, 160b extend from a location downstream of the stator assembly 116 to an inlet 136 of the outlet passage 132. The first blade set is provided in the first annular turbine channel 160a and the second blade set is provided in the second annular turbine channel 160b.

The first annular turbine channel 160a is fluidically sealed from the second annular turbine channel 160b. In that way, fluid is substantially prevented from passing between the first annular turbine channel 160a and the second annular turbine channel 160b.

In the turbine wheel 114 as shown in Figure 5, the number of blades 115b in the second blade set is greater than the number of blades 115a in the first blade set. In other embodiments the number of blades 115a in the first blade set may be greater than the number of blades 115b in the second blade set. In other embodiments, the number of blades 115a, 115b in the first and second blade sets may be the same. It will be appreciated that the number of blades 115a, 115b provided in the first and second blade sets will depend upon the design conditions of the turbomachine, and the flow properties of first and second fluid flows 120a, 120b.

The first blade set and the second blade set may be designed independently of one another to optimize fluid handling of the first and second flows 120a, 120b separately.

Because of this, the fluid flows 120a, 120b do not need to exit the stator assembly 116 with approximately the same flow conditions. Allowing the first and second blade sets to be designed independently, i.e. around a different design points, enables the efficiency of the turbine to be increased, when compared to the first and second flows 120a, 120b passing through a blade defining a single profile.

It will be appreciated that the turbine wheel embodiment shown in Figure 5 is an exemplary embodiment. In other embodiments, the turbine wheel 114, may be a wheel which comprises a plurality of axially extending passages. The axially extending passages may be channels, and in particular may be conical channels. The turbine wheel 114 may comprise a first radially inner row of axially extending passages which define a first annular turbine channel 160a, and a second radially outer row of axially extending passages which defines a second annular turbine channel 160b. The channels 160a and 160b function in principle the same as the channels 160a, 160b provided between the turbine blades 115 described in relation to Figure 5 above. The first and second rows of axially extending passages, may be equally circumferentially spaced about the turbine wheel axis. Each axially extending passage may be fluidically sealed from other axially extending passages in the turbine wheel 114.

Returning to Figures 4A and 4B, the first turbine annular channel 160a is in direct fluid communication with the first annular stator channel 119a. The second turbine annular channel 160b is in direct fluid communication with the first annular stator channel 119b.

In use, when the first fluid flow 120a has passed through the first annular stator channel 119a and exits the stator assembly 116, it immediately enters the first annular turbine channel 160a. Likewise, when the second fluid flow 120b has passed through the second annular stator channel 119b and exits the stator assembly 116 it immediately enters the first annular turbine channel 160b. Because the first annular turbine channel 160a is in direct fluid communication with the first annular stator channel 119a, and because the second annular turbine channel 160b is in direct fluid communication with the first annular stator channel 119b, mixing between the first and second fluid flows 120a, 120b is minimized. Mitigating against the first fluid flow 120a and the second fluid flow 120 from mixing as they leave the stator assembly 116 is beneficial, in that if mixing were to occur between the two fluid flows, turbulent vortices may develop, causing energy dissipation and losses in the flows and, in turn, reduce the power output of the turbine wheel 114. The support structure 150 can be considered to provide a fluidic seal between the first annular turbine channel 160a and the second annular turbine channel 160b. It will be appreciated that, in use, there may be small leakage paths proximate the stator assembly exit and, as such, mixing between the first and second fluid flows 120a, 120b cannot be said to be completely inhibited, but nevertheless, mixing between the fluid flows 120a, 120b before entering the turbine wheel 114 is minimized.

The first fluid flow 120a impinges on the first blade set 115a and the second fluid flow 120b impinges on the second blade set 115b as the first and second flows 120a, 120b pass through the respective annular turbine channels 160a, 160b. The first and second fluid flows 120a, 120b pass between adjacent blades of the first and second blade sets 115a, 115b respectively. As the first and second fluid flows 120a, 120b impinge on the respective blade sets 115a, 115b the turbine wheel 114 and hence the shaft 112 rotate about the central axis A-A. Providing a turbine wheel 114 that is specifically configured to receive two fluid flows with different fluidic properties increases the amount of energy which can be recovered from the fluid flows.

The turbomachine 110 further comprises a volute 130. The volute 130 is defined by the housing 111 of the turbomachine 110. The volute 130 comprises an outlet passage 132 and a discharge port 134. The discharge port 134 having a cross-sectional area that is larger than the cross sectional area of the outlet passage 132.

The outlet passage 132 defines an inlet 136 that is immediately downstream of the trailing edge of the turbine blades 115, and hence downstream of the first and second annular turbine channels 160a, 160b. The outlet passage 132 further defines an exit 138 located proximate where the cross-sectional area of the volute increases between the outlet passage 132 and the discharge port 134.

When the first and second fluid flows 120a, 120b exit the turbine wheel 114, the flows can be considered to travel in a generally axial direction, i.e. parallel to the central axis A-A. Thus, as the fluid flows 120a, 120b enter the outlet passage 132 at the inlet 136 they are still considered to be flowing in a generally axial direction.

The outlet passage 132 diverges away from the central axis A-A from the inlet 136 to the exit 138 in a radial direction, defining a curved passageway.

As the fluids 120a, 120b flow along the outlet passage 132, from the inlet 136 to the exit 138, the fluids follow the curved path of the outlet passage 132. When at the exit 138, the fluid flow can be considered to be in a generally radial direction, meaning that the fluid flow is generally orthogonal to the central axis A-A.

Directing the fluid flow in a generally radial direction at the exit 138 of the outlet passage 132, allows for the shaft 112 to be directly or indirectly coupled to a generator, or to another system which can utilize the kinetic energy of the shaft, without needing to provide room for the fluid flow exiting the turbine wheel 114.

As described above, the first and second fluid flows 120a, 120b are substantially prevented from mixing when passing through the first annular turbine channel 160a and the second annular turbine channel 160b of the turbine wheel 114. When the fluid flows 120a, 120b exit the turbine wheel 114 and flow into the outlet passage 132, the fluid flows 120a, 120b may mix.

Figure 6 shows a variant of the turbomachine 110 according to Figure 4A; like reference numerals will be used for like features.

The turbomachine 110 of Figure 6 differs from the turbomachine 110 of Figure 4A in that the outlet passage 132 of the volute 130 comprises a dividing wall 133, which partly defines a first outlet channel 137a and a second outlet channel 137b which is concentric with the first outlet channel 137a. The diving wall 133 extends along the outlet passage 132 from the inlet 136 to the outlet 138, and comprises an inner surface that partly defines the first outlet channel 137a, and an outer surface which partly defines the second outlet channel 137b.

The first outlet channel 137a extends along the outlet passage 132 from the inlet 136 to the exit 138, and the second outlet channel 137b extends along the outlet passage 132 from the inlet 136 to the outlet 138. The first and second outlet channels 137a, 137b are fluidically sealed from each other, in that fluid is substantially prevent from passing between the first outlet channel 137a and the second outlet channel 137b.

The first outlet channel 137a is in direct fluid communication with the first annular turbine channel 160a. The second outlet channel 137b is in direct fluid communication with the second annular turbine channel 160b.

In use, as the first fluid flow 120a exits the turbine wheel 114 and exits the first annular turbine channel 160a, the fluid flow passes into the first outlet channel 137a. Likewise, as the second fluid flow 120b exits the turbine wheel 114 and exits the second annular turbine channel 160b, the second fluid flow 120b passes into the second outlet channel 137b. The first and second fluid flows 120a, 120b remain separated as they pass through the first and second outlet channels 137a, 137b respectively. The first and second fluid flows 120a, 120b are permitted to mix when they reach the discharge port 134 portion of the volute 130. Substantially preventing the first and second fluid flows 120a, 120b from mixing until after exiting the outlet passage 132 may increase the efficiency of the turbine wheel 114. Without wishing to be bound by any particular theory, this may be because, the first and second fluid flows may exit the turbine wheel 114 with different fluidic properties, and if permitted to mix with one another immediately downstream of the turbine wheel 114, unwanted turbulent regions may be generated due to the mixing of flows with different fluidic properties. The generation of unwanted turbulent regions may negatively impact the ability of the turbine wheel 114 to rotate and decrease the efficiency of the turbine wheel 114, reducing the amount of energy that is recovered by the turbine wheel 114 from the first and second fluid flows 120a, 120b. Avoiding or reducing the likelihood of such turbulence developing should improve the performance of the turbine.

The described and illustrated embodiments are to be considered as illustrative and not restrictive in character, it being understood that only preferred embodiments have been shown and described and that all changes and modification that come within the scope of the inventions as defined in the claims are desired to be protected. In relation to the claims, it is intended that when words such as "a", "an" or "at least one" are used to preface a feature there is no intention to limit the claim to only one such feature unless specifically stated to the contrary in the claim.

Optional and/or preferred features as set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional and/or preferred features for each aspect of the invention set out herein are also applicable to any other aspects of the invention, where appropriate.

Claims

CLAIMS: 1. A turbomachine comprising: a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel, the stator assembly comprising first and second vane sets provided concentrically about the central axis, the first vane set configured to receive a first fluid flow and the second vane set configured to receive a second fluid flow; wherein the second vane set is disposed radially outwards of the first vane set.
2. A turbomachine according to claim 1, wherein the stator assembly defines a first annular stator channel and a second annular stator channel; the first vane set is provided in the first annular stator channel and the second vane set is provided in the second annular stator channel; and the first and second annular stator channels are fluidically sealed from each other.
3. A turbomachine according to claim 2, wherein the turbine wheel is configured to receive fluid from the first and second annular stator channels substantially simultaneously.
4. A turbomachine according to any preceding claim, wherein the number of vanes in the first vane set is the same as, or is different to, the number of vanes in the second vane set.
5. A turbomachine according to any preceding claim, wherein the expansion ratio across the first vane set is the same as, or is different to, the expansion ratio across the second vane set.
6. A turbomachine according to any preceding claim, wherein each vane of the first vane set has a chord length V1 and each vane of the second vanes set has a chord length V2; wherein V2 and V1 are not equal.
7. A turbomachine according to any preceding claim, wherein the profile of each vane in the first vane set is the same as or is different to the profile of each vane in the second vane set.
8. A turbomachine according to any preceding claim, wherein the housing defines a volute positioned downstream of the turbine wheel, the volute being in fluid communication with the turbine wheel
9. A turbomachine according to claim 8, wherein the volute defines an outlet passage having an inlet and an exit; the outlet passage being configured, in use, to receive fluid in a generally axial direction at the inlet and for fluid to leave the outlet passage at the exit in a generally radial direction.
10. A turbomachine according to claim 9, wherein the housing defines a dividing wall extending along the outlet passage from the inlet to exit, and wherein the outlet passage and the dividing wall define a first outlet channel and a second outlet channel.
11. A turbomachine according to any of claims 2 to 10, wherein the plurality of blades comprises a first blade portion and a second blade portion, the second blade portion being provided radially outwards of the first blade portion.
12. A turbomachine according to claim 11, wherein each blade of the plurality of blades extend in a radial direction from an innermost radius of the first blade portion to an outermost radius of the second blade portion.
13. A turbomachine according to claim 11 or claim 12, wherein the first blade portion of each blade of the plurality of blades collectively define a first blade set, and the second blade portion of each of the plurality of blades collectively define a second blade set.
14. A turbomachine according to claim 13, wherein the number of blade portions in the first blade set is different to the number of blade portions in the second blade set.
15. A turbomachine according to claim 13 or claim 14, wherein the number of blade portions in the first blade set is less than the number of blade portions in the second blade set.
16. A turbomachine according to any of claims 13 to 15, wherein each blade portion of the first blade set has a chord length B1 and each blade portion of the second blade set has a chord length B2; wherein B2 and B1 are not equal.
17. A turbomachine according to any of claims 13 to 16, wherein a profile of the blade portions in the first blade set is the same, or different to, a profile of the blade portions in the second blade set.
18. A turbomachine according to claim 11, wherein the turbine wheel comprises a hub and a support structure, wherein a first annular turbine channel is defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel is defined, at least in part, by the support structure and the housing.
19. A turbomachine according to claim 18, wherein the first blade portions are provided in the first annular turbine channel and the second blade portions are provided in the second annular turbine channel.
20. A turbomachine according to claim 18 or claim 19, wherein the first annular stator channel is in fluid communication with the first annular turbine channel, and the second annular stator channel is in fluid communication with the second annular turbine channel.
21. A turbomachine according to claim 20, dependent directly or indirectly on claim 10, wherein the first outlet channel is in fluid communication with the first annular turbine channel, and the second outlet channel is in fluid communication with the second annular turbine channel; and wherein the first and second outlet channels are fluidically sealed from one another.
22. A turbomachine comprising: a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel, the stator assembly comprising first and second vane sets provided concentrically about the central axis, the first vane set configured to receive a first fluid and the second vane set configured to receive a second fluid; the second vane set being disposed radially outwards of the first vane set; the stator assembly defining a first annular stator assembly channel and a second annular stator assembly channel; the first vane set provided in the first annular stator assembly channel and the second vane set provided in the second annular stator assembly channel; and the first and second annular stator assembly channels being fluidically sealed from each other; wherein the turbine wheel comprises a hub and a support structure; wherein a first annular turbine channel is defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel is defined, at least in part, by the support structure and the housing; wherein the plurality of blades of the turbine wheel comprise a first blade portion and a second blade portion, the second blade portions are provided radially outwards of the first blade portions; and wherein the first blade portions are provided in the first annular turbine channel and the second blade portions are provided in the second annular turbine channel.
23. A turbomachine comprising: a shaft positioned about a central axis; a housing supporting the shaft; a turbine wheel comprising a plurality of blades supported by the shaft; a stator assembly mounted upstream of the turbine wheel, the stator assembly comprising first and second vane sets provided concentrically about the central axis, the first vane set configured to receive a first fluid and the second vane set configured to receive a second fluid; wherein the second vane set is disposed radially outwards of the first vane set; wherein the stator assembly defines a first and a second annular stator assembly channel; the first vane set is provided in the first annular stator assembly channel and the second vane set is provided in the second annular stator assembly channel; and the first and second annular stator assembly channels are fluidically sealed from each other; wherein the turbine wheel comprises a hub and a support structure; wherein a first annular turbine channel is defined, at least in part, by the hub and the support structure, and a second radially outward annular turbine channel is defined, at least in part, by the support structure and the housing; wherein the plurality of blades of the turbine wheel comprises a first blade portion and a second blade portion; wherein the second blade portions are provided radially outwards of the first blade portion; wherein the first blade portions are provided in the first annular turbine channel and the second blade portions are provided in the second annular turbine channel; and wherein the housing defines a volute positioned downstream of the turbine wheel; wherein the volute is in fluid communication with the turbine wheel; and wherein the volute comprises an outlet passage having an inlet and an exit; and the housing defines a dividing wall extending along the outlet passage from the inlet to outlet; wherein the outlet passage and the dividing wall define a first outlet channel and a second outlet channel.