WO2011042863A2

WO2011042863A2 - Bladeless working wheel useful as a turbomachine component

Info

Publication number: WO2011042863A2
Application number: PCT/IB2010/054501
Authority: WO
Inventors: Anatoly Soudarev; Mike Sassoon
Original assignee: CMT SYSTEMS-CERAMIC MICRO TURBINE TECHNOLOGIES Ltd
Current assignee: CMT SYSTEMS-CERAMIC MICRO TURBINE TECHNOLOGIES Ltd
Priority date: 2009-10-06
Filing date: 2010-10-05
Publication date: 2011-04-14
Anticipated expiration: 2012-04-06
Also published as: WO2011042863A3

Abstract

Disclosed are bladeless working-wheels suitable for use as components of a turbomachine, the working wheels comprising a plurality of hollow wheel tunnels, each wheel tunnel passing from a periphery opening of the working wheel to a face opening in a face of the working wheel, wherein each wheel tunnel has a substantially continuous smooth curved shape.

Description

BLADELESS WORKING WHEEL USEFUL AS A TURBOMACHINE COMPONENT

RELATED APPLICATION

The present application gains priority from U.S. Provisional Patent Application No. 61/249,156 filed 6 October 2009 which is included by reference as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The invention, in some embodiments, relates to the field of turbomachines such as gas turbines and compressors. More particularly, the invention relates to the field of bladeless working wheels of turbomachines.

Turbomachines are widespread, used for example as turbines in gas turbines to transform energetic gas flow into mechanical rotation of a shaft, or as compressors or pumps to employ mechanical rotation to generate pressurized fluid flow.

The efficiency of a bladed turbomachine is known to decrease with smaller size. One reason is the escape of part of the working fluid through gaps between the working wheel blade array and the turbomachine stator, the proportion of such escaping fluid becoming higher as the dimensions of the working wheel decrease. Another reason is that as the size of a blade array becomes smaller the open interblade area becomes a narrow slit with a small hydraulic diameter. This in turn leads to a small Reynolds number of the stream of working fluid, and to a corresponding increase in the energy losses in the blade array and, consequently, in the turbomachine as a whole.

Bladeless working wheels for turbomachines have been proposed, e.g. for small turbines, for example in US Patent 4,293,278 and PCT patent publication WO/2004/022921.

One of the Inventors describes a bladeless turbomachine concept for micro gas turbine engine applications in "Novel blade-free turbomachine concept for microgasturbine engine applications" A.Soudarev, A.Souryaninov, V.Tikhoplav, A.Molchanov, P.Avran, L.Lelait, TS-041, Proceedings of the International Gas Turbine Congress Tokyo, 2003, and also in "Pioneer concept of blade-free turbomachines for micro gas turbine engines" A.Soudarev, A.Souryaninov, V.Tikhoplav, A.Molchanov, P.Avran, L.Lelait TS-019, Proceedings of the International Gas Turbine Congress Tokyo 2007.

Figure 1 schematically depicts a bladeless gas turbine 10 similar to the described in PCT patent publication WO/2004/022921. Gas turbine 10 comprises a centripetal (radial inflow) turbine 12 and a centrifugal compressor 14, mounted on a common rotatable shaft 16, and joined together inside a casing 18. Turbine 12 comprises a turbine working wheel 20, a nozzle ring 22, a distribution volute 24 and a thrust bearing 26. Compressor 14 comprises a bearing 28, an impeller 30 (i.e., a compressor working wheel), a diffuser 32, and a sectional volute 34. Turbine working wheel 20 is rigidly connected to impeller 30 by shaft 16, together constituting a rotor 36 of gas turbine 10. Casing 18 rigidly connects distribution volute 24 and 5 sectional volute 34, together constituting a stator 38 of gas turbine 10. Commonly, nozzle ring 22 and/or diffuser 32 may also be components of stator 38. Turbine thrust bearing 26 and compressor bearing 28 interface between stator 38 and rotor 36, enabling rotor 36 to rotate with respect to stator 38.

When gas turbine 10 is operated, distribution volute 24 distributes hot gas from a

10 combustor (not depicted) around the circumference of nozzle ring 22, and nozzle guide vanes or nozzle tunnels (not depicted) of nozzle ring 22 direct the flow of the hot gas into wheel tunnels (not depicted) of turbine working wheel 20. The flow of hot gas through the wheel tunnels rotates turbine working wheel 20 and consequently all of rotor 36 relative to stator 38. Rotating impeller 30 compresses gas entering through an inlet (not depicted) through diffuser

15 32 into sectional volute 34. Sectional volute 34 collects the pressurized gas from the circumference of diffuser 32 into a pressurized gas pipe system (not depicted) that directs the gas into the combustor of gas turbine 10.

The term "turbomachine" as used herein means a device such as turbine 12 or compressor 14, having a static part (stator) and a rotating part (rotor). The term "working 0 wheel" as used herein means a rotating wheel in a turbomachine, such as turbine working wheel 20 of turbine 12 or such as impeller 30 of compressor 14.

SUMMARY OF THE INVENTION

Aspects of the invention, in some embodiments thereof, relate to bladeless working 5 wheels of turbomachines such as gas turbines and compressors. More specifically, aspects of the invention, in some embodiments thereof, relate to a working wheel including a plurality of hollow wheel tunnels passing through the working wheel for directing the flow of a working fluid between an inlet and an outlet, where the wheel tunnels have a substantially continuous smooth curved shape.

30 According to an aspect of some embodiments of the invention, there is provided a working wheel comprising a tunnel face, a back face, a periphery and an axis of rotation. The working wheel further comprises at least one rotationally- symmetrical disk arranged concentrically around the axis of rotation substantially between the tunnel face and the back face of the working wheel. The working wheel further comprises a plurality of hollow wheel tunnels, each wheel tunnel passing from a periphery opening in the periphery of the working wheel through the disk to a face opening in the tunnel face of the working wheel, thereby substantially defining a fluid flow path through the working wheel between the periphery opening and the face opening, where the wheel tunnels have a substantially continuous smooth curved shape through the working wheel.

In some embodiments the wheel tunnels have a spiral shape.

In some embodiments, proximal to the periphery of the working wheel, at least some of the wheel tunnels are directed in a direction in a plane roughly perpendicular to the axis of rotation. In some embodiments, proximal to the periphery of the working wheel, at least some of the wheel tunnels are directed in a direction in a plane roughly perpendicular to the axis of rotation and directed at an angle (φ) tangential to the axis of rotation. As used herein, the term "roughly perpendicular to a direction" as used herein means diverging from perpendicular to the direction by no more than about 30°, by no more than about 10°, and even by no more than about 5°.

In some embodiments, proximal to the tunnel face, at least some of the wheel tunnels are directed in a direction in a plane roughly parallel to the axis of rotation. As used herein, the term "roughly parallel to a direction" as used herein means diverging from the direction by no more than about 30°, by no more than about 10°, and even by no more than about 5°.

According to an aspect of some embodiments of the invention, there is also provided a turbomachine comprising a working wheel substantially as described above.

According to an aspect of some embodiments of the present invention, there is also provided a gas turbine comprising a turbine and a compressor mounted on a common rotatable shaft, where at least one of the turbine and compressor comprises a working wheel substantially as described above.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the patent specification, including definitions, takes precedence.

As used herein, the terms "comprising", "including", "having" and grammatical variants thereof are to be taken as specifying the stated features, integers, steps or components but do not preclude the addition of one or more additional features, integers, steps, components or groups thereof. These terms encompass the terms "consisting of and "consisting essentially of.

As used herein, the indefinite articles "a" and "an" mean "at least one" or "one or more" unless the context clearly dictates otherwise. BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the invention are described herein, with reference to the accompanying figures. The description, together with the figures, makes apparent how embodiments of the invention may be practiced to a person having ordinary skill in the art. The figures are for the purpose of illustrative discussion of embodiments of the invention and no attempt is made to show structural details of an embodiment in more detail than is necessary for a fundamental understanding of the invention. For the sake of clarity, objects depicted in the figures are not drawn to scale. In the Figures:

FIG. 1 (prior art) is a schematic depiction of a bladeless gas turbine;

FIGS. 2A and 2B (prior art) are two views of a 3-dimensional shape of an ideal spiral;

FIG. 3A is a schematic depiction of a first embodiment of a working wheel of a turbomachine as described herein, in side view;

FIG. 3B is schematic depiction of the working wheel of Figure 3 A, in front view;

FIG. 4A is a schematic depiction of the spatial arrangement of spiral wheel tunnels inside the working wheel of Figures 3 A and 3B in front view;

FIG. 4B is a schematic depiction of the spatial arrangement of spiral wheel tunnels inside the working wheel of Figures 3 A, 3B and 4A in back view;

FIG. 5 is a schematic depiction of an embodiments of a bladeless gas turbine as described herein comprising the working wheel of Figures 3 and 4 as a component of a centripetal turbine and as a component of a centrifugal compressor;

FIG. 6 is a schematic depiction of an embodiment of a periphery of a working wheel of a turbomachine as described herein;

FIG. 7A is a schematic depiction of an additional embodiment of a working wheel as described herein, in side cross-section;

FIG. 7B is a schematic depiction of the the working wheel of Figure 7A, in front cross section;

FIG. 8 is a schematic depiction of an additional embodiment of a working wheel as described herein, in side cross-section; and

FIG. 9 is a schematic depiction of an additional embodiment of a working wheel as described herein, in side cross-section. DESCRIPTION OF SOME EMBODIMENTS OF THE INVENTION

The invention, in some embodiments thereof, relates to bladeless working wheels useful, for example, as components of turbomachines and, more particularly, but not exclusively, to working wheels comprising wheel tunnels for directing the flow of a working fluid between an inlet and an outlet having a substantially continuous smooth curved shaped inside the working wheel, in some embodiments having spiral shape.

The principles, uses and implementations of the teachings of the invention may be better understood with reference to the accompanying description and figures. Upon perusal of the description and figures present herein, one skilled in the art is able to implement the teachings of the invention without undue effort or experimentation. In the figures, like reference numerals refer to like parts throughout.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its applications to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the Examples. The invention can be implemented with other embodiments and can be practiced or carried out in various ways. It is also understood that the phraseology and terminology employed herein is for descriptive purpose and should not be regarded as limiting.

According to an aspect of some embodiments of the invention there is provided a working wheel comprising a tunnel face, a back face, a periphery and an axis of rotation, and at least one rotationally- symmetrical disk arranged concentrically around the axis of rotation substantially between the tunnel face and the back face of the working wheel. The working wheel further comprises a plurality of hollow wheel tunnels, each wheel tunnel passing from a periphery opening in the periphery of the working wheel through the disk to a face opening in the tunnel face of the working wheel, thereby substantially defining a fluid flow path through the working wheel between the periphery opening and the face opening. The wheel tunnels have a substantially continuous smooth curved shape through the working wheel.

In some embodiments, the continuous smooth curved shape of the wheel tunnels is substantially a spiral. Generally, the shape of the wheel tunnel refers to the geometrical curve of the centerline of the tunnel. Thus, a wheel tunnel having a spiral shape means that the centerline of the wheel tunnel is substantially a spiral curve. The terms "centerline" and "median" of the wheel tunnels are used herein interchangeably.

In Figures 2A and 2B are two views of a 3-dimensional ideal spiral, a helix 5. A helix such as 5 is characterized by a constant pitch Is (Figure 2A) and by a constant diameter Ds, related to the helix curvature (Figure 2B). In some embodiments, the medians of wheel tunnels inside the working wheel have the shape of a helix such as 5, with a substantially constant pitch and a substantially constant curvature. In some embodiments the wheel tunnels deviate from the shape of a helix but retain a general shape of a spiral. A general shape of a spiral herein means the shape of a three-dimensional curve which winds around a given direction essentially in a same course, clockwise or anticlockwise, while progressing along that direction thus having curvature and torsion of unchanging sign.

In some embodiments, proximal to the periphery of the working wheel (substantially at the periphery openings), at least some, preferably all, wheel tunnels are directed in a direction in a plane roughly perpendicular to the axis of rotation, so that a fluid exiting such a wheel tunnel from a periphery opening is directed roughly parallel to a plane perpendicular to the axis of rotation.

In some embodiments, proximal to the periphery of the working wheel (substantially at the periphery openings) at least some, preferably all, wheel tunnels are directed at an angle (φ hereinbelow) of at least about 20°, at least about 25°, at least about 30°, at least about 40°, at least about 50° and even at least about 60° relative to a radial plane passing through the center of the respective periphery opening of the wheel tunnel so that fluid exiting a wheel tunnel from a periphery opening is directed tangentially from the working wheel. In some embodiments, at least some, preferably all, wheel tunnels are directed at an angle of not more than about 80° relative to a radial plane passing through the center of the respective periphery opening of the wheel tunnel.

In some embodiments, proximal to the tunnel face of the working wheel at least some, preferably all, wheel tunnels are directed in a direction in a plane roughly parallel to the axis of rotation so that a fluid exiting such a wheel tunnel from a face opening during operation is directed in a plane roughly parallel to the axis of rotation. In some such embodiments the tangential inclination (i.e., angle from parallel with the axis of rotation inside the plane roughly parallel to the axis of rotation) of at least some, preferably all, wheel tunnels proximal to the face openings is a function of the optimal working rotational velocity of the working wheel, in some embodiments helping provide substantially maximal turbomachine efficiency. For example, in such embodiment when a working wheel is configured to be a turbine working wheel of a centripetal turbine, the tangential inclination of a given wheel tunnel proximal to a respective face opening is such that when the working wheel is rotating at the optimal working rotational velocity, fluid exiting the wheel tunnel is directed substantially parallel to the axis of rotation with little or no swirl. A person having ordinary skill in the art is able to determine a desirable tangential inclination for a given wheel tunnel based on factors including the optimal working rotational velocity of the working wheel, and the tangential velocity of a given face opening at the optimal working rotational velocity. Since tangential velocity is a function of radius, the desirable tangential inclination is a function of the radial distance of a face opening from the axis of rotation of the working wheel.

In some embodiments, curved wheel tunnels, and particularly wheel tunnels having a spiral shape, are advantageous compared to wheel tunnels having other shapes: spiral shape can provide for large deflection of flow direction, in some embodiments up to about 90°, and in some embodiments even more, in a smooth and continuous flow path. All things being equal, the greater the deflection of a fluid when passing through the wheel tunnels from one opening to the other, the more efficient the turbomachine. Embodiments in which a spatial arrangement of spiral wheel tunnels incorporates a large total deflection in flow direction between the working wheel periphery the working wheel face are advantageous by allowing a higher efficiency of the turbomachine (either a turbine or a compressor) compared to spatial arrangements of wheel tunnels where the total deflection is considerably lower. In a wheel tunnel where the total deflection of flow direction is considerably less than 90°, either the tunnel has a considerable inclination departing from the plane perpendicular to the axis of rotation proximally to the periphery, or the tunnel has a radial inclination towards the axis proximally to the wheel face, both arrangements adversely affecting turbomachine efficiency.

Further, wheel tunnels having spiral shape provide a smooth and continuous flow path with gradual changes in direction and no sudden changes of direction such as with corners or elbow, thus having an advantageous flow regime inside the tunnel. Furthe, spiral wheel tunnels provide for a curved flow path essentially in a same course, clockwise or anticlockwise, throughout the flow path, significantly reducing turbulence and other sources of energy loss along the flow path, therefore increasing the turbine efficiency compared to turbines with working wheels comprising wheel tunnels having other shapes such as an S- shape. A spiral flow path further provides an even distribution of the required total curvature along the flow path, rather than restricting the total deflection to a small region as in an elbow or a corner, thus reducing mechanical and thermal stress on the tunnel walls compared to working wheels with wheel tunnels of other shapes.

In some embodiments, a spiral shape also allows dense packing of a larger number of tunnels inside a given volume of the working wheel so that a greater proportion of the working wheel is wheel tunnel void and the mass of the working wheel is thus reduced. Herein, by wheel tunnel void is meant the total volume of the wheel tunnels in a working wheel. In some embodiments, a working wheel is at least about 30%, at least about 40%, at least about 60%>, at least about 70%> and even at least about 80%> wheel tunnel void. In some embodiments, spiral wheel tunnels thus provide a higher flow rate, a higher volume of working fluid flowing through the working wheel per unit time for a given working wheel size, a higher specific power providing a relatively high rated capacity for a given working wheel dimension (e.g., relatively greater power for a turbine).

In this context, the fact that the spiral shape of wheel tunnels leads to a distribution of stress caused by the fluid flow, means that a relatively small amount of solid material may provide sufficient strength to maintain the structural integrity of the disk, even when a disk of a working wheel is a large percentage void. As a result, a greater proportion of void leads to a lower working wheel mass, in some embodiments particularly near the periphery of the working wheel, and consequently lower tensile stress when the working wheel is rotating at high speeds. In some embodiments the lower tensile stress allows a working wheel to be practically made (in whole or in part) of ceramic materials that are generally less able to withstand tensile stress compared with other materials such as metals.

In some embodiments, the working wheel includes at least two different types of wheel tunnels, each type having a different substantially smooth curved shape. In some embodiments, the working wheel includes two different types of wheel tunnels, each type having a different substantially smooth curved shape. In some embodiments the working wheel includes tunnels having two different spiral shapes. In some embodiments, the working wheel includes three different types of wheel tunnels, each type having a different substantially smooth curved shape. In some embodiments the working wheel includes tunnels having three different spiral shapes.

In some embodiments the periphery openings at the periphery of the working wheel are at a distance from the edge between the tunnel face and the periphery of the working wheel, and at a distance from the edge between the back face and the periphery of the working wheel. In some embodiments the periphery openings of each of the different types of wheel tunnels are at a different distance from the edge between the tunnel face and the periphery of the working wheel.

In some embodiments, the face openings of each different type of wheel tunnels are at a different distance from the axis of rotation in the tunnel face of the working wheel. As discussed above, in some embodiments, the distance from the axis of rotation influences the direction of the wheel tunnel proximal to a respective face opening. In some embodiments the periphery openings are substantially ellipsoids. In some embodiments the periphery openings are substantially circular. In some embodiments the face openings are substantially ellipsoids. In some embodiments the face openings are substantially circular.

In some embodiments, the face openings of least one type of wheel tunnels have a cross- sectional area greater than the cross-sectional area of the periphery opening of the same wheel tunnels. For example, in some embodiments where a working wheel as described herein is implemented as a turbine working wheel of a centripetal turbine of a gas-turbine, it is advantageous that the cross-sectional area of the face openings be greater than of the periphery openings so that the wheel tunnels be divergent.

In some embodiments, the working wheel comprises only one rotationally- symmetrical disk arranged concentrically around the axis of rotation and between the tunnel face and the back face of the working wheel. In some embodiments the working wheel comprises two rotationally-symmetrical disks, fixedly joined together and arranged concentrically around the axis of rotation and between the tunnel face and the back face of the working wheel. In some embodiments the working wheel comprises three rotationally- symmetrical disks, fixedly joined together and arranged concentrically around the axis of rotation and between the tunnel face and the back face of the working wheel.

In some embodiments, at least one disk of the working wheel is substantially made of a metal, especially metals suitable for high-temperature applications such as known in the art of gas-turbine manufacture, and include alloys such as Inconel® (Special Metals Corporation, New Hartford, New York, USA) or titanium and titanium alloys. Such metals are available, for example, from High Temp Metals, Inc., Sylmar, California, USA. In some embodiments, a metal disk is fashioned by free-forming methods, laser sintering, lost-wax methods or the stacking of a plurality of thin coaxial disks.

In some embodiments, the working wheel comprises hollow ceramic liners held inside the wheel tunnels. In some such embodiments, the ceramic liners help define a fluid flow path through the wheel tunnels. In some such embodiments, the ceramic liners are relatively heat resistant and protect other working wheel components from heat.

In some embodiments, at least one disk of the working wheel is made of a ceramic material. Ceramics are advantageous as material from which to fashion a disk of a working wheel as described herein due to relatively low density and/or relatively high stiffness and/or suitability for use in a high-temperature environment. A ceramic disk component of a working wheel including curved tunnels as described herein can be fashioned using many known manufacturing techniques, e.g. lost-wax, laser sintering and free-forming (e.g., as described in PCT publication WO 03/053102). Employing such methods has a further advantage of allowing the manufacture of a working wheel fashioned of a single disk comprising continuous and smooth curved tunnels having a desired deflection.

In some embodiments, the back face of the working wheel is configured as a fluid- bearing surface operable as part of a hydrostatic gas thrust bearing.

In some embodiments the working wheel comprises at least one hollow in at least one disk, in some embodiments reducing the mass (especially near the periphery) and moment of inertia of the working wheel.

According to an aspect of some embodiments of the invention there is also provided a turbomachine comprising a working wheel as described herein. In some embodiments the turbomachine is a centripetal turbine, and the working wheel is a turbine working wheel. In some embodiments the turbomachine is a centrifugal compressor and the working wheel is an impeller.

According to an aspect of some embodiments of the invention there is also provided a gas turbine comprising a turbine including a turbine working wheel and a compressor including an impeller, wherein at least one of the turbine working wheel and the impeller is a working wheel as described herein. In some embodiments a turbine working wheel is a working wheel as described herein and the turbine is a centripetal turbine. In some embodiments an impeller is a working wheel as described herein, and the compressor is a centrifugal compressor.

Figure 3A is a schematic depiction of a first embodiment of a working wheel 40 of a turbomachine (e.g., of a turbine or a compressor) as described herein. Working wheel 40 comprises a tunnel face 42, a back face 44, a periphery 45 and an axis of rotation 46. Periphery 45 is a cylindrical surface of revolution generated by a straight generatrix (generating curve), parallel to axis 46. Edges 47 separate periphery 45 from tunnel face 42 and from back face 44. Tunnel face 42 has a center face surface 48 incorporated in a plane perpendicular to axis 46, and a ring face surface 49 in the form a truncated cone.

Working wheel 40 further comprises a single rotationally- symmetrical disk 50, arranged concentrically around axis of rotation 46, substantially between tunnel face 42 and back face 44 and substantially constituting working wheel 40. Disk 50 is functionally divided into two sections, a tunnel section 52 and a back section 54, separated by a groove 56. Back section 54 of disk 50 functions as a component of a hydrostatic gas thrust bearing (not shown), where back face 44 is a fluid bearing surface of the hydrostatic gas thrust bearing.

Thirty-three hollow wheel tunnels 60 pass through tunnel section 52 of disk 50, each wheel tunnel passing from a respective periphery opening 62 in periphery 45 of working 5 wheel 40, to a respective face opening (not seen in Figure 3A) in tunnel face 42 of working wheel 40, in a substantially continuous smooth curved shape through working wheel 40.

Periphery openings 62 are ellipsoids, for example circular and oval. Centers 64 are the intersection points of the medians (not depicted) of wheel tunnels 60 with periphery 45. Periphery openings 62 are entirely included within periphery 45 at a distance CI from edge

10 47 between periphery 45 and tunnel face 42 and at a distance C2 from edge 47 between periphery 45 and back face 44.

Figure 3B is a front view of working wheel 40 (view A in Figure 3 A) depicting tunnel face 42 of working wheel 40. Face openings 66 of wheel tunnels 60 in tunnel face 42 are ellipsoids, for example, circular and oval, and are arranged in tunnel face 42 in three groups

15 68, 70 and 72. Centers 74 of face openings 66 are the intersection points of the medians (not depicted) of wheel tunnels 60 with tunnel face 42. Centers 74 of each group 68, 70 and 72 are distributed concentrically around circumferences 76, 78 and 80, respectively. As circumferences 76, 78 and 80 each have different radii, it is clear that the geometry of the associated wheel tunnels of the three groups is also different from group to group, as is 0 discussed herein.

Each of the three groups of openings 68, 70 and 72 consists of eleven face openings, associated with eleven respective wheel tunnels 60 having substantially identical shapes. A border line 82 is shown encircling a triplet 84 of face openings 66, one face opening 66 from each of the three groups 68, 70, and 72. Triplets 84 are designated so that the three hollow 5 wheel tunnels 60 associated with the face openings 66 of a triplet 84 have neighboring periphery openings 62 on periphery 45 (Figure 3 A).

Figure 4A is a schematic front view of the spatial arrangement of wheel tunnels 60 inside working wheel 40. Wheel tunnels 60 have a substantially spiral shape where wheel tunnels 60 of each group 68, 70 or 72 are substantially identical to each other, and different

30 from wheel tunnels of the other groups. Accordingly, the spiral shape of each of the three wheel tunnels 60 in a triplet 84 of wheel tunnels, is characterized by geometric parameters such as total length, curvature, pitch and periphery and face opening shapes, different from the respective geometric parameters of the other two wheel tunnels 60 in that triplet. Each wheel tunnel 60 in Figure 4A is spatially arranged inside working wheel 40 so that proximal to periphery 45 of working wheel 40, a wheel tunnel 60 is directed in a plane that is directed roughly perpendicular to axis of rotation 46 (in Figure 4A, the plane of the figure sheet) and at an angle φ (discussed below) with the radial direction. Further, proximal to tunnel face 42, a wheel tunnel 60 is directed in a direction in a plane roughly parallel to plane including axis of rotation 46. Such spatial arrangement provides a large deflection in flow direction of a fluid passing between a periphery opening 62 and a face opening 66 of a wheel tunnel 60. In some embodiments, such a large deflection in flow direction is advantageous as it allows a higher efficiency of the turbomachine (either a turbine or a compressor) compared to tunnel arrangement where the total deflection is less. In a working wheel having hollow wheel tunnels where the total deflection of flow direction is relatively low, the wheel tunnels proximal to the working wheel periphery 45 have a considerable inclination departing from the plane perpendicular to the working wheel axis of rotation 46, and/or the wheel tunnels proximal to the working wheel tunnel surface 42 have a radial inclination towards the working wheel axis of rotation 46, adversely effecting the turbomachine efficiency.

As noted above, spiral wheel tunnels as described herein such as wheel tunnels 60 of working wheel 40, provide a smooth and continuous flow path providing an advantageous flow regime inside the wheel tunnels. Spiral wheel tunnels provide for a flow path that curves in a same direction (clockwise or anticlockwise) along the flow path, having a curvature and a torsion of unchanging sign, thus significantly reducing the incidence of turbulence and other sources of energy-loss along the flow path in the wheel tunnel and increasing the turbomachine efficiency when compared to turbomachines having wheel tunnels with other shapes, such as S-shaped wheel tunnels.

As noted above, a spiral wheel tunnel further provides a gradual and even distribution of the required total curvature along the flow path, rather than restricting the total deflection to a localized region as in a corner or an elbow shape. A spiral wheel tunnel thus provides distribution of mechanical and thermal stress caused by fluid flow on a greater part of wheel tunnel walls. As a result, compared to working wheels having wheel tunnels of other shapes, the disk or disks of a working wheel as described herein, including spiral tunnels, can be fashioned from materials having lower material strength and/or increased turbine performance with a reduced incidence of material failure. As noted above wheel tunnels having a spiral shape allow a greater number of tunnels to be packed inside a given volume of working wheel, that is to say a greater proportion of the working wheel can be void, as can be qualitatively appreciated from Figure 4A. I

Figure 4B schematically depicts the spatial arrangement of wheel tunnels 60 inside working wheel 40 from a back view (direction B in Figure 3 A). Wheel tunnels 60 have circular transverse cross section 86 perpendicular to spiral centerlines 88. Proximal to periphery 45, wheel tunnels 60 of each of the three groups 68, 70 and 72 are directed at angles φ₆&, (f o and ψη, respectively, relative to the radial planes (planes containing axis 46 and the radial direction) passing through the respective centers of transverse cross section 86, as is indicated by the angles between the radial direction and the respective centerlines 88 of each wheel tunnel 60.

Figure 5 schematically depicts a bladeless gas turbine 90 generally similar to gas turbine 10 described in Figure 1, with the differences of having a working wheel 40 as described herein as the turbine working wheel 20, and a working wheel 40 as described herein as an impeller 30. In some embodiments, after a turbomachine including working wheel 40 as a component of the rotor of the turbomachine is assembled, it is possible to balance rotor 36 by removing material from inside groove 48 (in Figure 3A). It is noted that when a working wheel such as 40 is used as a turbine working wheel the turbine 12 is a centripetal turbine so that during operation fluid generally flows inside wheel tunnels 60 from periphery openings 62, which function as inlets, to face openings 66 which function as outlets. Conversely, when a working wheel such as 40 is used as an impeller, the compressor or pump is a centrifugal compressor or pump so that during operation fluid generally flows through wheel tunnels 60 from face openings 66 which function as inlets to periphery openings 62 which function as outlets.

As noted above, all things being equal, the greater the deflection of a fluid when passing through the wheel tunnels of a working wheel from one opening to the other, the more efficient the turbomachine.

For example, in gas-turbine 90 depicted in Figure 5, energetic gas from a combustor passes through a nozzle ring 22 to enter a wheel tunnel 60 from a periphery openings 62, passes through the wheel tunnel and out through a face opening 66.

The energetic gas undergoes a change of direction from substantially perpendicular to axis 46 in a plane that includes axis 46 to roughly parallel to axis 46. With reference to Figure 3A, the energetic gas undergoes a roughly 90° deflection, in some embodiments even substantially 90°, in the plane of the sheet from perpendicularly towards axis 46 to roughly towards the letter "A".

The energetic gas also undergoes an additional change of direction from inside a plane perpendicular to axis of rotation 46 to roughly parallel to axis 46. With reference to Figure 4A, the energetic gas undergoes a high degree of deflection in the plane of the sheet from an angle φ (as determined by the direction of a given wheel tunnel 60 at a respective periphery opening 62 to out if the sheet roughly towards the viewer, as determined by the direction of a given wheel tunnel 60 at a respective face opening 66.

As noted above, in some embodiments, the exact direction of a given wheel tunnel 60 at a respective face opening 66 is determined so that when the working wheel operates at an optimal working rotational velocity, the gas exiting a face opening 66 moves substantially parallel to axis 46 with little, if any swirl. As such a direction is a function of rotational velocity of a face opening 66, it is clear that in some such embodiments, each member of a triplet 82 of face openings 66 is directed in a different direction.

An analogous discussion can be made when a working wheel as described herein is an impeller of a centrifugal compressor or centrifugal pump, such as 40 in Figure 5.

It is important to note that Figures 3 A, 3B, 4A and 4B provide a non-limiting example of an embodiment of working wheel 40. Some embodiments of working wheel 40 comprise wheel tunnels 60 having different geometrical parameters, different shape or different structure from wheel tunnels 60 in Figures 3A, 3B, 4A and 4B above.

In some embodiments, transverse cross sections 86 of wheel tunnels 60 are oval. In some embodiments transverse cross sections 86 of wheel tunnels 60 diverge along the flow path from periphery openings 62 to face openings 66, so that transverse cross sections 86 (Figure 4B) proximal to face openings 66 are larger than transverse cross sections 86 proximal to periphery openings 62.

In some embodiments angles φ₆&, (fho and ψη (in Figure 4B) are, independently, at least about 20°, at least about 25°, at least about 30°, at least about 40°, at least about 50°, and even at least about 60° with respect to the radial direction. In some embodiments angles <7¼8, ψιο and φη, are, independently not more than about 80°, not more than about 75° and even not more than about 70° with respect to the radial direction. In some embodiments angles φ₆&, (fho and φ_Ίι, are between about 20 and about 80°. In some embodiments angles φ₆&, qho and ψη, are between about 30 and about 70°.

In some embodiments, centerlines 88 of wheel tunnels 60 have the shape of an ideal spiral, a helix, as is depicted in Figures 2A and 2B. In some embodiments centerlines 88 deviate from the shape of a helix but retain a general shape of a spiral, namely winding around a given direction essentially in a same course, clockwise or anticlockwise, while progressing along that direction, thus having curvature and torsion of unchanging sign. In some embodiments centerlines 88 have curvature K=2/DS (where Ds is the spiral diameter) and pitch Is so that 0<7s<3*Ds.

Figure 6 is a schematic depiction of periphery 45 of an embodiment of a working wheel such as 40. The spatial arrangement of wheel tunnels 60 inside working wheel 40 is such that periphery openings 62 of wheel tunnels 60 are not located at a constant distance from edge 47 between periphery 45 and tunnel face 42. Rather, periphery openings 62 of each group 68, 70 and 72 of wheel tunnels are located at a different specific distance from edge 47, C₆&, C₁₀ and C₇₂, respectively.

Figure 7A is a schematic depiction of a working wheel 100 in accordance with the teachings herein. Working wheel 100 comprises a tunnel face 42, a back face 44, a periphery 45 and an axis of rotation 46. Tunnel face 42 is substantially planar and perpendicular to axis 46. Back face 44 has a cross sectional dip 102 to reduce wheel 100 mass and mechanical stress when operated. Periphery 45 is a surface of rotation generated by a substantially rectilinear generatrix, generating a periphery including an edge 103 separating between two surfaces of truncated cones.

Working wheel 100 further comprises a single rotationally- symmetrical disk 50 and a plurality of hollow wheel tunnels 60 passing through disk 50. Disk 50 is arranged concentrically around axis of rotation 46, substantially between tunnel face 42 and back face 44 and substantially constituting working wheel 100.

Each wheel tunnel 60 passes from a respective periphery opening 62 in periphery 45 of working wheel 100, to a respective face opening 66 in tunnel face 42, in a substantially continuous smooth curved shape throughout working wheel 100.

Wheel tunnels 60 have substantially spiral shapes and are divided into three groups, 68, 70 and 72, where tunnels in each group are characterized by geometric parameters identical to the respective geometrical parameters of other tunnels in the same group, but may be different from the respective geometrical parameters of tunnels in the other two groups. Specifically, wheel tunnels in the different groups have different path length, different curvature, different radial distance of the face opening 66 from axis 46, and different direction proximal to a respective face opening 66.

Line 104 depicts the projection of centerline 88 (not depicted) of one wheel tunnel 60 from group 68 on a radial plane (a plane containing axis 46 and a radial direction) passing through the center of transverse cross section 86 (not shown) proximal to periphery opening 62 of the one wheel tunnel 60. Similarly, line 106 depicts the projection of centerline 88 of one wheel tunnel 60 from group 70 on a radial plane passing through the center of transverse cross section 86 (not shown) proximal to periphery opening 62 of that one wheel tunnel 60 5 from group 70. Lastly, line 108 depicts the projection of centerline 88 of one wheel tunnel 60 from group 72 on a radial plane passing through the center of transverse cross section 86 (not shown) proximal to periphery opening 62 of that one wheel tunnel 60 from group 72. The projection lines 104, 106, and 108 show that wheel tunnels 60 in working wheel 100 have different geometric parameters according to the group each wheel tunnel 60 belongs to, and

10 specifically have a different total length, a different curvature and a different total deflection.

As a result centerlines 88 of wheel tunnels 60 in groups 68, 70 and 72, have radial distances rl, r2 and r3, respectively, from axis of rotation 46 at the respective points 110, 112 and 114 of centerlines 88 crossing cross-section I-I line.

The separation of wheel tunnels 60 into three groups having such different curved

15 shapes, and the spatial arrangement of wheel tunnels 60 inside working wheel 100, allows a relatively dense packing of wheel tunnels inside working wheel 100, introducing a relatively large number of tunnels and a relatively high proportion of void in a given working wheel volume, thus potentially providing a higher efficiency of the working wheel. Further, wheel tunnels 60 are spatially arranged inside working wheel 100 so that proximal to periphery 45,

20 wheel tunnels 60 are directed in a plane roughly perpendicular to axis of rotation 46.

Proximal to tunnel face 42, wheel tunnels 60 are directed in a plane roughly parallel to axis of rotation 46. Projection lines 104, 106 and 108 show that the spiral shapes of wheel tunnels 60 provide smooth and continuous flow path, having an even distribution of the required total curvature along the flow path, thus improving the flow regime inside the tunnel and reducing

25 mechanical and thermal stress on the tunnel walls. Lines 116 and 118 mark the radial distances between which wheel tunnels 60 are located.

Working wheel 100 further comprises hollows in the form of cavities 120, located at designated areas inside working wheel 100 and proximal to periphery 45, substantially between wheel tunnels 60 of group 72 and consequently between any two triplets 84. Cavities

30 120 reduce the total mass near periphery 45 and moment of inertia of working wheel 100, and consequently reduce the stress on working wheel 100 during operation. Holes 122 allow the substantially unobstructed flow of fluid into an out of cavities 120, to prevent over or under pressure in cavities 120 resulting from changes in pressure during working wheel operation. In Figure 7B, working wheel 100 is schematically depicted in front cross section. It is seen that wheel tunnels 60 are arranged inside working wheel 100 in three groups 68, 70 and 72. Centerlines 88 of wheel tunnels 60 belonging to the three groups have different radial distances from axis of rotation 46, thus centerlines 88 cross the plane of cross section I-I at three different radii, rl, r2 and r3, respectively. As discussed above, wheel tunnels 60 are grouped into triplets 84, each triplet consists of one wheel tunnel 60 from each group 68, 70 and 72 so that the three wheel tunnels 60 in a triplet 84 have neighboring periphery openings 62 in periphery 45 of working wheel 100.

Similarly to the discussed above regarding working wheel 40, Figures 7A and 7B provide a non- limiting example of an embodiment of a working wheel 100. Some embodiments of a working wheel 100 comprise wheel tunnels 60 having different geometrical parameters, different shape or different structure from wheel tunnels 60 in Figures 7A and 7B above. In some embodiments, wheel tunnels 60 of a working wheel 100 are divergent from periphery openings 62 to face openings 66.

In some embodiments wheel tunnels 60 may have a general spiral shape namely winding around a given direction essentially in a same course, clockwise or anticlockwise, while progressing along that direction, thus having curvature and torsion of unchanging sign.

In Figure 8, an additional embodiment of a working wheel in accordance with the teachings herein, working wheel 130, is schematically depicted in side cross section. Working wheel 130 comprises a tunnel face 42, a back face 44, a periphery 45 and an axis of rotation 46. Tunnel face 42 is substantially planar and perpendicular to axis 46. Similarly to working wheel 100, periphery 45 is a surface of rotation generated by a substantially rectilinear generatrix, generating a periphery including an edge 103 separating between two surfaces of truncated cones.

Working wheel 130 further comprises two rotationally- symmetrical disks 132 and

134, fixedly joined concentrically at joining surface 136 with bolts 138 and arranged concentrically around axis of rotation 46 and between tunnel face 42 and back face 44 of working wheel 130.

A plurality of hollow wheel tunnels 60 of working wheel 130 passes through disks 132 and 134, each wheel tunnel 60 passing from a respective periphery opening 62 in periphery 45 to a respective face opening 66 in tunnel face 42. As discussed above, wheel tunnels 60 of working wheel 130 have substantially spiral shapes and are divided into three groups, 68, 70 and 72. In Figure 8, lines 104, 106 and 108 indicate the projection of centerlines 88 (not shown) of one wheel tunnel 60 from each group 68, 70 and 72, respectively, on radial planes (planes containing axis 46 and the radial direction) passing through the centers of transverse cross sections 86 (not shown) of each the three wheel tunnels, proximal to periphery openings 62 of the three wheel tunnels 60. Projection lines 104, 106, and 108 show that wheel tunnels 60 in working wheel 130 have different geometric parameters according to the group 68, 70 or 72 to which a wheel tunnel 60 belongs, and specifically have different total length, different curvature, different radial direction from axis of rotation 46, and different direction proximal to a respective face opening 66..

Further, wheel tunnels 60 are spatially arranged inside working wheel 130 so that proximal to periphery 45, wheel tunnels 60 are directed in a plane roughly perpendicular to axis of rotation 46 and proximal to tunnel face 42 wheel tunnels 60 are directed in a plane roughly parallel to axis of rotation 46. Moreover, projection lines 104, 106 and 108 show that the spiral shape of wheel tunnels 60 provides a smooth and continuous flow path, having an even distribution of the required total curvature along the flow path and no corners or elbows, thus improving the flow regime inside the tunnel and reducing mechanical and thermal stress on the tunnel walls.

As in the discussion above regarding working wheels 40 and 100, in some embodiments, wheel tunnels 60 diverge along flow path from periphery openings 62 to face openings 66. Accordingly, transverse cross sectional area of at least some wheel tunnels 60 proximal to face openings 66 is larger than transverse cross sectional area of the same wheel tunnels proximal to periphery opening 62, to obtain a desired gas pressure ratio between periphery openings 62 and face openings 66.

In some embodiments working wheel 130 comprises hollows in the form of depressions 120 at designated areas on periphery 45 of working wheel 130 and substantially between wheel tunnels 60 from group 72. Hollows 120 reduce the total mass and moment of inertia of working wheel 130, and consequently reduce the stress on working wheel 130 during operation.

In Figure 9 an embodiment of a nozzle ring 148 and a working wheel 150 of a turbomachine, in accordance with the teachings herein, are schematically depicted in side cross section. Working wheel 150 comprises a periphery 45, a tunnel face 42, a back face 44 and an axis of rotation 46. Both tunnel face 42 and back face 44 are substantially planar and perpendicular to axis 46. Similarly to working wheels 100 and 130 (Figures 7A and 8) periphery 45 is a surface of rotation generated by a substantially rectilinear generatrix, generating a periphery having an edge 103 separating between two surfaces of truncated cones. Working wheel 150 further comprises three disks 152, 154 and 156, respectively, fixedly joined together concentrically with bolts 138, and arranged concentrically around axis of rotation 46 and between tunnel face 42 and back face 44 of working wheel 150. Disks 152 and 154 are joined along joining surfaces 158, and disks 154 and 156 are joined along joining surfaces 160. Joining surfaces 158 and 160 each have a substantially planar section, 162 and 164, respectively, and a conical section 166 and 168, respectively. An angle 170 between conical section 166 of joining surface 158 and axis of rotation 46 is θ\, and an angle 172 between conical section 168 of joining surface 160 and axis of rotation 46 is θ₂. Mechanical load and stress on each of disks 152, 154 and 156 during operation of working wheel 150 are higher as a disk has a larger radius. Consequently, angle 170 is larger than angle 172 (ft <£¾) so that the mass of disk 152 is reduced near periphery 45.

A plurality of hollow wheel tunnels 60 pass through disks 152, 154 and 156, each tunnel passing from a respective periphery opening 62 in periphery 45 of working wheel 150 (disk 152), to a respective face opening 66 in tunnel face 42 of working wheel 150 (disk 156). Line 106 is the projection of centerline 88 of a wheel tunnel 60 on a radial plane passing through the wheel tunnel as discussed above in Figure 7A. As discussed above for wheel tunnels in working wheels 40, 100 and 130, wheel tunnels 60 in working wheel 150, have a substantially spiral shape. Lines 116 and 118 mark the radial distances from axis 46 between which wheel tunnels 60 are located. In some embodiments wheel tunnels 60 diverge along flow path from periphery openings 62 to face openings 66, as is indicated by lines 116 and 118.

As working wheel 150 is a turbine working wheel, working wheel 150 is generally used in conjunction with a nozzle ring 148. A suitable nozzle ring such as 148 is described in "Novel blade-free turbomachine concept for microgasturbine engine applications^'" A.Soudarev, A.Souryaninov, V.Tikhoplav, A.Molchanov, P.Avran, L.Lelait, TS-041, Proceedings of the International Gas Turbine Congress Tokyo, 2003, and in "Pioneer concept of blade-free turbomachines for micro gas turbine engines" A.Soudarev, A.Souryaninov, V.Tikhoplav, A.Molchanov, P.Avran, L.Lelait TS-019, Proceedings of the International Gas Turbine Congress Tokyo 2007.

Working wheels such as 40, 100, 130 or 150 may be made of any suitable material or combination of materials. A person having ordinary skill in the art is able, upon perusal of the description herein as well as of the references cited herein, of selecting the suitable materials and methods of manufacture to implement the teachings herein, based on factors including: the usage of the working wheel (e.g., as a turbine working wheel of a turbine, as an impeller of a compressor); size (physical dimensions) of the working wheel; working pressures and temperatures of the turbomachine comprising the working wheel; and rotation speed. Specifically the at least one disk of the working wheel (disk 50 in working wheels 40 and 100, disks 132 and 134 in working wheel 130 and disks 152, 154 and 156 in working wheel 5 150) is made of any suitable material, as discussed above.

In some embodiments, a working wheel or a disk of a working wheel as described herein is made of a metal, especially metals such as known in the art of gas-turbine manufacture. A person having ordinary skill in the art is able, upon perusal of the description herein, of making a working wheel and/or the disk thereof from a metal including curved, and0 particular spiral shaped, wheel tunnels in accordance with the teachings herein. In some such embodiments, a disk of a working wheel as described herein comprises hollow ceramic liners 94 (as depicted in Figures 3B and 6), lining at least part of the walls of the wheel tunnels 60 of the disk, for example to provide the wheel tunnel walls with greater resistance to high temperature fluids flowing therethrough. In some embodiments where such a working wheel5 is used as turbine working wheel of a gas turbine, the use of such protective liners allows a higher operating temperature. In some embodiments, e.g. embodiments employed in gas turbines, ceramic materials are typically sustainable at higher temperature than metal, therefore using hollow ceramic liners inside wheel tunnels 60 protect tunnels 60 and allow employing higher gas temperatures, thus in some embodiments allowing the gas turbine to0 operate with a higher thermal efficiency.

In some embodiments a disk or disks of a working wheel as described herein is made of a ceramic material. Ceramic materials are advantageous in working wheels of gas turbines due to light weight, stiffness and ability to withstand high temperatures. A person having ordinary skill in the art is able, upon perusal of the description herein, of making a working5 wheel and/or the disk thereof from a ceramic material including spiral shaped wheel tunnels. For example, in some embodiments, a disk of a working wheel as described herein may be fashioned from a ceramic material using a lost wax technique. One such possible method for manufacturing a ceramic disk with curved tunnels may comprise pressing a ceramic disk incorporating a plurality of dummies made of appropriate material, e.g., a metal such as0 aluminum, having the desired shape, and situated in the appropriate location, of the tunnels inside the disk; and after the pressing eliminating the dummies using a lost wax technique, for example by heating the disk to a temperature sufficient to eliminate the dummies (e.g., leads to melting, sublimation or decomposition of the dummies). In some embodiments, a disk of a working wheel as described herein may be fashioned from a ceramic material using a free- forming technique as described, for example, in PCT patent publication WO 2003/053102. In some embodiments, employing such methods for manufacturing a working wheel comprising spiral wheel tunnels has a further advantage of providing a working wheel made up of a single disk having a high total deflection of flow direction with respect to the axial direction, allowing high turbomachine efficiency with a small number of parts.

A working wheel as described herein may be of any suitable size for a desired implementation. That said, the teachings herein are exceptionally useful for small- sized working wheels, for example, a turbine working wheel or a compressor impeller in a micro gas-turbine. Thus, in some embodiments, a working wheel as described herein, especially when implemented as a component of a gas-turbine, has an outer diameter of not more than about 50 mm, not more than about 30mm, not more than about 20 and even not more than about 10 mm. Such a small working wheel is advantageously fashioned of a ceramic material as the small size leads to a relatively low mass of the working wheel with concomitant relatively low tensile stress.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the scope of the appended claims.

Citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the invention.

Section headings are used herein to ease understanding of the specification and should not be construed as necessarily limiting.

Claims

CLAIMS:

1. A working wheel comprising:

a tunnel face, a back face, a periphery and an axis of rotation;

at least one rotationally- symmetrical disk, arranged concentrically around said axis of rotation and substantially between said tunnel face and said back face; and

a plurality of hollow wheel tunnels, each said wheel tunnel passing through said disk from a periphery opening in said periphery of said working wheel to a face opening in said tunnel face of the working wheel

wherein each said wheel tunnel has a substantially continuous smooth curved shape throughout the working wheel.

2. The working wheel of claim 1, wherein said continuous smooth curved shape is substantially a spiral.

3. The working wheel of any of claims 1 to 2, wherein proximal to said periphery, at least some said wheel tunnels are directed in a direction in a plane roughly perpendicular to said axis of rotation.

4. The working wheel of any of claims 1 to 3 wherein proximal to said tunnel face, at least some said wheel tunnels are directed in a direction in a plane roughly parallel to said axis of rotation.

5. The working wheel of any of claims 1 to 4, including at least two different types of wheel tunnels, each type having a different substantially smooth curved shape.

6. The working wheel of any of claims 1 to 5, including two different types of wheel tunnels, each type having a different substantially smooth curved shape.

7. The working wheel of any of claims 1 to 6, including three different types of wheel tunnels, each type having a different substantially smooth curved shape.

8. The working wheel of any of claims 1 to 7, wherein said periphery openings in said periphery are at a distance from an edge between said tunnel face and periphery of the working wheel and from an edge between said back face and periphery of the working wheel.

9. The working wheel of any of claims 5 to 8, wherein said periphery openings of each said different type of wheel tunnels are at a different distance from an edge between said periphery and said tunnel face of the working wheel.

10. The working wheel of any of claims 5 to 9, wherein said face openings of each said different type of wheel tunnels are at different distances from said axis of rotation in said tunnel face of the working wheel.

11. The working wheel of any of claims 1 to 10, wherein at least one said periphery openings is substantially an ellipsoid.

12. The working wheel of any of claims 1 to 11, wherein at least one said face opening is substantially an ellipsoid.

13. The working wheel of any of claims 1 to 12, wherein at least one said wheel tunnel has a respective said face opening with a transverse cross-sectional area greater than a transverse cross-sectional area of a respective said periphery opening.

14. The working wheel of any of claims 1 to 13, comprising two said rotationally- symmetrical disks, both arranged concentrically around said axis of rotation substantially between said tunnel face and said back face, said two disks fixedly joined together.

15. The working wheel of any of claims 1 to 14, comprising three said rotationally- symmetrical disks, all three arranged concentrically around said axis of rotation substantially between said tunnel face and said back face, said three disks fixedly joined together.

16. The working wheel of any of claims 1 to 15, wherein said at least one said disk is made of a ceramic material.

17. The working wheel of any of claims 1 to 16, wherein said at least one said disk is made of a metal.

18. The working wheel of claim 17, further comprising a hollow ceramic liners held inside said wheel tunnels

19. The working wheel of any of claims 1 to 18, wherein said back face is a fluid bearing surface operable as part of a hydrostatic gas thrust bearing.

20. The working wheel of any of claims 1 to 19, wherein said working wheel further comprise hollows proximal to said periphery.

21. The working wheel of any of claims 1 to 20, wherein a proportion of the working wheel that is tunnel void is at least about 30%.

22. A turbomachine, comprising a working wheel of any of claims 1 to 21.

23. The turbomachine of claim 22, being a centripetal turbine and said working wheel is a turbine working wheel.

24. The turbomachine of claim 22, being a centrifugal compressor and said working wheel is an impeller

25. A gas turbine, comprising:

a turbine including a turbine working wheel; and

a compressor including an impeller;

wherein at least one of said turbine working wheel and said impeller is a working wheel of any of claims 1 to 21.

26. The gas turbine of claim 25, wherein said turbine working wheel is a said working wheel of any of claims 1 to 21.

27. The gas turbine of any of claims 25 to 26, wherein said impeller is a said working wheel of any of claims 1 to 21.