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(11) | EP 0 090 891 A1 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Turbine |
| (57) A dual pressure turbine has radial impulse stages (73,74,75) driven by higher pressure
working fluid, and axial flow stages (76) driven by lower pressure working fluid,
which may be the fluid exhausted from the last radial impulse stage. The rotors of
all the stages are coupled coaxially into a unitary rotary unit. |
[0001] The invention relates to turbines, which are arranged to be driven by a working fluid such as steam.
[0002] The aim of the invention is to provide a high efficient turbine and, in accordance with the present invention, this is achieved by a dual pressure turbine comprising a high pressure section having at least one radial impulse turbine stage; a low pressure section having at least one axial flow turbine stage; means for introducing working fluid at one pressure into the high pressure section to drive the radial impulse stage; and means for introducing working fluid at a lower pressure into the low pressure section to drive the axial flow stage.
[0003] This novel combination of radial impulse and axial flow staging is significantly more efficient than conventional turbine designs.
[0004] The turbine may have means for mixing working fluid exhausted from the high pressure section with further working fluid to provide the lower pressure working fluid to be introduced into the low pressure section. In this case for example steam discharged from the high pressure section may be combined with steam supplied to the turbine at low pressure, the mixture being delivered to the low pressure turbine stage. Maximum utilization of available energy is promoted by this arrangement.
[0005] Alternatively, the turbine may have a single inlet, this inlet communicating with the or the first of the radial impulse stages; whereby the working fluid discharged from the or the last of the radial impulse stages is transferred to the or the first axial flow stage to provide the whole of the working fluid which is supplied to the low pressure section.
[0006] A turbine of this construction is of the "once- through" type. Thus all of the working fluid is supplied to the turbine at one pressure, and the working fluid is discharged directly from the radial impulse staging into the first of the axial flow stages. At some sacrifice in efficiency, this design reduces complexity, lowers maintenance costs, and increases reliability; and it has a faster response time. Consequently this one-through arrangement may prove superior in applications, such as naval shipboard use, where the advantages identified above take precedence over efficiency.
[0007] The rotors of each of the radial impulse and axial flow stages may be connected coaxially as a single rotary unit. This eliminates the need for gearing between the high and low pressure sections along with the associated expense and power loss. In this case there will usually be a common casing containing both the high and low pressure sections.
[0008] Radial impulse turbines have been well developed for decades. In their most recent form, such turbines have included a rotor with buckets oriented transversely to the direction of wheel rotation and opening at the periphery of the wheel. The elastic working fluid is supplied to the buckets via, e.g., a nozzle ring surrounding the rotor. The, or at least one, radial impulse stage in the high pressure section may be of this construction and preferably certain valuable features are incorporated, particularly to accommodate higher than conventional working fluid velocities.
[0009] According to one of these features, the radial impulse stage comprises a rotor having buckets spaced around the opening at the periphery thereof; and means for introducing the higher pressure working fluid into the buckets to turn the rotor; each of the buckets having an entrance at one side of the rotor and an exit at the other side of the rotor, and the buckets being so shaped that the flow vectors of the fluid entering and exiting from each bucket in use are substantially parallel to one another and to planes perpendicular to the axis of the rotor. This leads to significantly greater efficiency than in conventional flow designs.
[0010] According to a second of the features, the radial impulse stage comprises a rotor having buckets spaced around and opening at the periphery thereof; and an annular array of nozzles for introducing the higher pressure working fluid into the buckets to turn the rotor; the outlets of the nozzles communicating with the entrance of the buckets substantially completely around the circumference of the rotor. The working fluid is then admitted to the buckets from a locus which encircles the wheel and is essentially uninterrupted. Efficiency is also promoted if the cross sections of the buckets and of the nozzle outlets, perpendicular to the flow of working fluid,have substantially right angular corners. This arrangement effectively reduces unwanted power-wasting shock and turbulance.
[0011] According to a third of the features, the radial impulse stage comprises a rotor having buckets spaced around and opening at the periphery thereof; and a nozzle ring for introducing the higher pressure working fluid into the buckets to turn the rotor; the rotor being completely shrouded between entrances and exits of the buckets by a surrounding shroud to maximize the work available from the working fluid; and the nozzle ring abutting an upstream face of the shroud whereby the shroud provides the downstream walls of the nozzles. The shrouding keeps the character of the flow, the circulation of which is otherwise of generally unspecified character, constant, adjacent to the buckets. This eliminates the windage loss that occurs in conventional, unshrouded or partially shrouded radial impulse turbines.
[0012] According to a fourth of the features, the radial impulse stages comprises a rotor having buckets spaced around and opening at the periphery thereof; and a nozzle ring containing an annular array of nozzles for introducing the higher pressure working fluid into the buckets to turn the rotor; the nozzle ring also comprising vanes which separate and partly define the contours of adjacent nozzles, the vanes having surfaces which face the axis of the respective rotor and which are continuously curved from their edges at the nozzle outlets to their portions lying radially outwardly of the edges of the adjacent vanes.
[0013] The edge of each vane at the nozzle outlet preferably presents an included wedge angle of not more than 3°. An 11° or greater wedge angle is typical in prior art designs. We have found, however, that markedly increased efficiency can be obtained by decreasing this angle to a maximum of 3°. This also reduces wakes and comparable flow disturbances. The decrease in wedge angle, in addition, reduces stresses imposed on the rotor by working fluid distributed to it from the turbine nozzles.
[0014] The high pressure section may include first and second radial impulse stages each comprising a rotor with buckets spaced around and opening at the periphery. thereof, and a nozzle ring containing an annular array of working fluid distribution nozzles surrounding the rotor, each of the nozzles having an inlet opening at the outer periphery of the ring and an outlet opening at the inner periphery of the ring; and flow directing means for turning working fluid discharged radially outwardly from the buckets of the first stage rotor axially towards the second stage rotor and then radially inwardly into the inlets of the nozzles of the second stage nozzle ring.
[0015] In a further useful arrangement the high pressure section includes first and second radial impulse stages each comprising a rotor with buckets spaced around and opening at the periphery thereof, and a nozzle ring containing an annular array of working fluid-distribution nozzles surrounding the rotor; and the high pressure section also includes means for conducting working fluid discharged from the buckets of the first stage rotor into the nozzles surrounding the second stage rotor after that fluid has passed once through the buckets of the first stage rotor, and a discharge plenum on the downstream side of the second stage rotor, the buckets in the second stage rotor being so shaped as to dump the working fluid into the discharge plenum after that fluid has passed once through the buckets of the second rotor.
[0016] Two examples of turbines constructed in accordance with the invention are illustrated in the accompanying drawings, in which:-
Figure 1 is a partial side view of a first turbine;
Figure 2 is a partial axial section through the high pressure section of the first turbine;
Figure 3 is a similar section through the low pressure section of the first turbine;
Figure 4 is a fragmentary section in a radial plane through part of a rotor and nozzle ring of a radial impulse stage in the high-pressure section of the first turbine; and,
Figure 5 is a partial side view with some parts in axial section of a second turbine.
[0017] The turbine 6 of Figures 1 to 4, includes an elongate, external casing 7 which has a generally circular cross-section and is made up of a number of bolted-together casing components.
[0018] The interior of the casing 7 is divided into a high pressure section 8 and a low pressure section 9 (see Figures 2 and 3).
[0019] The high pressure section 8 has two impulse turbine stages 10 and 11; the low pressure section 9 has six conventional, axial flow turbine stages 12, 13, 14, 15, 16 and 17.
[0020] Each of the high and low pressure turbine stages includes a rotor which is identified by the same reference character as the stage but followed by the letter R.
[0021] The eight rotors 10R...17R are coupled together with Curvic splines (assembled Curvic fittings are shown diagrammatically in Figure 3 and identified by reference character 18). The components of the resulting assembly are held together by a single tension bolt 19. and the assembly is rotatably supported in the casing 8 by appropriate bearings (not shown). The upstream (or front) end of the assembly is splined to accept a drive coupling (the splines are not shown), and provide a power take-off upstream of the high pressure section.
[0022] Referring now specifically to Figure 2, the first and second stage rotors 10R and 11R in the high pressure section 8 of the turbine 6 are cast from 17-4PH stainless steel or a comparable material for steam service.
[0023] The first stage rotor 10R is surrounded by an annular nozzle ring 20-of which nozzles 21 are of the convergent configuration illustrated in Figure 4. The nozzles are defined between vanes 21A formed by metal left in the process of milling the ring 22 to form the nozzles. The vanes have sharp edges 21C, presenting a wedge angle of up to 3°, and curved surfaces 21B which face radially inwardly towards the axis of the rotor and extend from the edges 21C to positions overlying the edges 21C of the next vane. The curvature of the surfaces 21B is similar to, i.e. within ± 10% of, that of the outer periphery of the rotor. The nozzles each has an inlet 22 opening onto the outer periphery of the nozzle ring and an outlet 23 opening onto its inner periphery, and they are of square cross section perpendicular to the fluid flow at their discharge ends. The outlets of the nozzles 21 are radially aligned with entrances 24 to buckets 25 in a peripheral flange 26 of the first stage rotor 10R as shown in Figure 2.
[0024] These buckets are equiangularly spaced and they are typically formed by milling with the cutter inclined at an angle of 18° to the radial.
[0025] The buckets 25 have a section perpendicular to the fluid flow with substantially right_angular corners 27 (see Figure 4), an entrance 24 adjacent to the upstream side of the rotor, an exit 28 adjacent to the downstream side of the rotor and a part circular impulse surface 29 between the entrance and the exit.
[0026] Maximum efficiency can be obtained by so milling the buckets as to produce transition curves on their entrance and exit sides. This minimizes losses attributable to the working fluid impinging on the rotor as it changes direction in flowing through the buckets.
[0027] High efficiency can be obtained by making the profile of the trailing edge surface 30 of each bucket as a smooth curve terminating in a sharp edge as shown in Figure 4. Appropriate curves can be readily generated by casting. Alternatively, these curves could be milled off to provide flats which produce a sharp wedge, with an included angle of about 3°, with the adjacent surface of the next bucket. This removes excess metal from the rotor and also produces a good match to the relative spouting velocity of the working fluid discharged from the nozzle ring. That, together with the sharp leading edges produced by milling the flats, minimizes flow irregularities and contributes to efficiency.
[0028] A groove is milled in the rotor before the buckets 25 are milled. This groove extends continuously around, and opens into, the periphery of the rotor and generates slots in the eventual leading edges of the buckets. The groove is primarily provided to accommodate the shank of a cutter used to form the buckets, but also eliminates excess metal from the rotor and lowers rotor and bucket stresses.
[0029] The outlets 23 of the nozzles 21 form an almost continuous circle around the rotor 10R. This, together with the sharp edge between adjacent buckets provides essentially full arc admission of working fluid to the buckets and ensures that the buckets are smoothly filled. That contributes significantly to the efficiency of the turbine.
[0030] The nozzle ring 20 is coupled by an antirotation pin 31 to a radial flange 32 at the downstream end of an annular, high pressure inlet manifold 33. The manifold is bolted between casing components 34 and 35 on the upstream side of high pressure section first stage rotor 10R.
[0031] The nozzle ring 20 is clamped against the flange 32, and the downstream walls of the nozzles 21 are formed, by a plate-like inner shroud 36 of the casing component 35. The latter is bolted between the manifold 33 and an outer casing component 37.
[0032] Working fluid is supplied to the first stage 10 of the turbine 6 through an inlet 38 which communicates with the interior of the high pressure inlet manifold 33. The working fluid flows axially from the manifold through an annular inlet 39 between the outer periphery of the nozzle ring 20 and the inner wall of the manifold 33. It then flows radially inwards into,the nozzles 21 in the nozzle ring 20 as shown by arrow 40 in Figure 2.
[0033] The working fluid is discharged from the nozzles into the buckets 25 of the rotor 10R, flowing through the latter to drive the rotor. It then flows radially outwards as indicated by arrow 41. The entrance and exit flow vectors of the working fluid are parallel.
[0034] Efficiency is also promoted by completely shrouding the buckets 25 between their entrances 24 and exits 28 by the shroud 36, which completely surrounds the rotor 10R. This complete shrouding minimizes power- robbing turbulence. It also promotes efficiency by maintaining a free surface on the exit side of reach bucket. Furthermore, because the exiting working fluid does not impinge on the shroud 36, its exit momentum is preserved. This is an attribute of particular importance in multi-stage turbines.
[0035] The outwardly flowing working fluid discharged from the buckets of the rotor 10R is turned first axially and then radially inwards (see arrow 42) by the cooperation between the casing component 37 and an annular, disc-like flow director 43: The latter is fixed to the upstream side of a radially and inwardly extending annular flange 44 on the casing component 37 by screw threaded fasteners 45.
[0036] Leakage between flow director 43 and the assembly of turbine rotors 10R ... 17R is inhibited by cooperating seals 46 and 47. These seals are supported by the flow director at its inner periphery and by high pressure section first and second stage rotors 10R and 11R.
[0037] The working fluid discharged from the first stage 10 flows into nozzles 48 formed in a nozzle ring 49 surrounding the second stage rotor 11R. Again, the nozzle outlets are aligned with entrances 50 to buckets 51 which are similar to the buckets 25.
[0038] The nozzle ring 49 is seated in a recess 52 in'the flow director 43 and is clamped against the upstream side of the flange 44 by the flow director and the fasteners 45. The upstream face of the flange forms the rear or downstream walls of the nozzles.
[0039] The nozzles 48, not shown in detail herein, will preferably be of a convergent configuration like that shown in Figure 4.
[0040] The second stage rotor 11R is, like that discussed previously, completely shrouded. In this case, the shrouding is effected by the circular, radially oriented flange 44 on the casing component 37.
[0041] After passing through the buckets 51 of the second stage turbine rotor 10R, the working fluid is discharged radially outwards from the buckets through exits 53 into an annular plenum 54 located between the high and low pressure turbine sections 8 and 9. Here, the working fluid discharged from the high pressure section of the turbine is combined with working fluid introduced to the turbine through an inlet 55 and an annular low pressure inlet manifold 56 surrounding the plenum 54.
[0042] Communication between the manifold and the plenum 54 is effected by an inwardly directed, circular opening 57. The nozzle is defined by axially extending, circular bosses 58 and 59, which are integral parts of the casing component 37, and by the manifold 56 and the inlet 55.
[0043] - The working fluid mixture flows axially as indicated by arrow 60 in Figures 2 and 3 into the low pressure section 9 of the turbine 6. That section of the turbine 6 (which is of conventional axial flow design) is best shown in Figure 3.
[0044] Each turbine stage in the low pressure section includes one of the previously mentioned rotors, composed of a disc 61 to which an annular array of blades 62 is attached. Upstream from each rotor is a conventional annular array of stationary nozzles 63. The nozzles of each stage are attached to an annular nozzle support 64 which is fixed to the casing component 37.
[0045] Leakage past the nozzles in each stage is inhibited by a circular diaphragm 65, a seal 66 at the inner circumference of the diaphragm, and a cooperating seal 67 supported by the discs of adjacent rotors.
[0046] An axially extending, circular flange 68 is fixed to the diaphragm 65 of the first axial flow stage 12 to guide the working fluid mixture from the annular exhaust plenum 54 into the nozzles 63 of the first axial turbine stage.
[0047] As is also shown in Figure 3, each of the low pressure, axial flow stages preferably includes an annular, abradable rub ring 69 which is part of the nozzle support of that stage and surrounds its rotor. These rub rings allow minimum tip clearance for the working fluid to be employed, lowering leakage of the working fluid past the blade tips.
[0048] Flow of the working fluid through the low pressure section is conventional with the working fluid being discharged from the blades 62 of the sixth stage rotor 17R into an annular exhaust manifold (not shown). The working fluid is discharged from this manifold and the turbine casing through an exhaust duct 70 (see Figure 1).
[0049] One turbine of the character just described, designed to produce 1800 shaft horsepower (136872 m Kg/s) [600 shaft horsepower (45624 m Kg/s) of that in the high pressure impulse section], is shown in Figures 2 and 3.
[0050] Typically, this turbine will be supplied with high pressure steam at 200 psia (14 Kg/cm2) and 720oF (382°C) at a rate of 3.23 lbs/second (1.47 kg/s) and with low pressure steam at 40 psia (2.8 Kg/cm2) and 790°F (4210C) at 0.76 lbs/second (0.35 Kg/s).
[0051] The design pressure of the steam exhausted from the last stage of the low pressure, axial flow section of the turbine is 0.65 psia (0.046 Kg/cm2).
[0052] The rotors of the two impulse stages 10 and 11 in the high pressure section 8 of the turbine 6 are, respectively, 11.75 and 13.875 inches (0.30 and 0.35m) in diameter; and the mid-chord lengths of the blades 62 in the low pressure axial flow section of the turbine range from 0.6 inch (0.015m) in the first stage 12 to 5.16 inches (0.13m) in the sixth stage 17. The discs on which the blades are mounted are all 13.5 inches (0.34m) in diameter.
[0053] The invention may also be applied to a once- through turbine having a combination of radial impulse and axial flow stages. A turbine of this type, which also includes a more efficient arrangement for transferring working fluid from one radial impulse stage to the next and which demonstrates that more than two radial impulse stages can be employed, is shown at 71 in Figure 5.
[0054] In many respects, the turbine 71 is similar to the previously described example. Consequently, and for the sake of clarity and conciseness, the turbine 71 will be described primarily in reference to those features which distinguish it from the previously described turbine.
[0055] The turbine 71 includes an elongate, external casing 72 housing three radial impulse stages 73, 74, and.75 and seven axial flow stages 76 ... (only one of which is shown).
[0056] Each of the axial flow stages (which can be of the character described above in conjunction with the turbine 6) and each of the impulse turbine stages includes a rotor which is identified by the same reference character as the stage but followed by the letter R.
[0057] The ten rotors 73R ... 76R are coupled together by Curvic fittings 77 and held in assembled relationship by a tension bolt 78. Appropriate bearings (not shown) rotatably support the resulting assembly in the casing 72.
[0058] The rotors 73R, 74R, and 75R of the radial impulse stages may be like those employed in the turbine 6; and they are surrounded by shrouds 79, 80, and 81 to obtain those above discussed benefits which complete shrouding is capable of providing.
[0059] The first stage rotor 73R is surrounded by an annular nozzle ring 82 with nozzles of the type illustrated in Figure 4.
[0061] Working fluid is supplied to the first stage 73 of the turbine 71 through a working fluid inlet 84 which communicates with the interior of inlet manifold 83. The working fluid flows from the manifold through an annular inlet 85 into the nozzles in the nozzle ring.
[0062] The working fluid is discharged from the nozzles into the buckets of the rotor 73R, flowing through the latter to drive the rotor.
[0063] The outwardly flowing working fluid discharged from the buckets of the rotor 73R is turned first axially and then radially inward by the cooperation between the turbine casing 72 and a flow director 86. The latter is similar to the flow directors employed in the turbine 6 shown in Figure 2..This keeps the stream of working fluid exiting from the buckets from spreading as it is directed from the first stage rotor 73R to a nozzle ring 87 in the second radial impulse stage 74. That is important in that it minimizes energy losses as the transfer of fluid is affected.
[0064] The operation of the second and third radial impulse stages 74 and 75 and the transfer of the working fluid between the latter are both essentially as just described and as discussed in conjunction with the previous embodiment.
[0065] From the rotor of the third radial impulse stage 75 the working fluid flows against the surface of the shroud 81, turning into the first of the axial flow stages 76.
[0066] Flow of the working fluid through the axial flow stages is conventional with the working fluid being discharged from the last stage rotor into an annular exhaust manifold (not shown). The working fluid is discharged from this manifold and the turbine casing through an exhaust duct similar to that shown in Figure 1.
[0067] It will be apparent to those skilled in the relevant arts that three is not a limit on the number of .radial impulse stages that can be employed in the radial impulse turbine sections and that efficiency can be increased by increasing the number of stages. However three stages is considered a practical limit for the most part, simply because subsequent stages tend to become too massive.
1. A dual pressure turbine (6) comprising a high pressure section (8) having at least
one radial impulse turbine stage (10); a low pressure section (9) having at least
one axial flow turbine stage (12); means (38) for introducing working fluid at one
pressure into the high pressure section to drive the radial impulse stage; and means
(56) for introducing working fluid at a lower pressure into the low pressure section
to drive the axial flow stage.
2. A turbine according to claim 1, which has means (54)for mixing working fluid exhausted
from the high pressure section with further working fluid to provide the lower pressure
working fluid to be introduced into the low pressure section.
3. A turbine according to claim 2, in which the mixing means comprises an annular
plenum (54) between the high and low pressure sections (8,9); an annular inlet manifold
(56) surrounding the plenum; an annular flow passage (57) interconnecting the inlet
manifold and plenum; and means (55) through which working fluid can be introduced
into the inlet manifold.
4. A turbine according to claim 1, which has a single inlet (84), this inlet communicating
with the or the first of the radial impulse stages (73); whereby the working fluid
discharged from the or the last of the radial impulse stages (75) is transferred to
the or the first axial flow stage (76) to provide the whole of the working fluid which
is supplied to the low pressure section.
5.. A turbine according to any one of the preceding claims, which comprises a casing
(7) containing both the high and low pressure sections; each of the radial impulse
and axial flow stages having a rotor (10R,17R), and all the rotors being connected
coaxially as a single rotary unit.
6. A turbine according to claim 5, in which the rotary unit provides power take-off
means upstream of the high pressure section.
7. A turbine according to any one of the preceding claims, in which the radial impulse
stage (10) comprises a rotor (10R) having buckets (25) spaced around and opening at
the periphery thereof; and means (20) for introducing the higher pressure working
fluid into the buckets to turn the rotor; each of the buckets having an entrance (24)
at one side of the rotor and an exit (28) at the other side of the rotor, and the
buckets being so shaped that the flow vectors of the fluid entering and exiting from
each bucket in use are substantially parallel to one another and to planes perpendicular
to the axis of the rotor.
8. A turbine according to any one of the preceding claims, in which the radial impulse
stage (10) comprises a rotor (10R) having buckets (25) spaced around and opening at
the periphery thereof; and an annular array of nozzles (21) for introducing the higher
pressure working fluid into the buckets to turn the rotor; the outlets (23) of the
nozzle communicating with the entrances (24) of the buckets substantially completely
around the circumference of the rotor.
9. A turbine according to claim 8, in which the cross sections of the buckets (25)
and of the nozzle outlets (23), perpendicular to the flow of working fluid, have substantially
right angular corners.
10. A turbine according to any one of the preceding claims, in which the radial impulse
stage (10) comprises a rotor (10R) having buckets (25) spaced around and opening at
the periphery thereof; and a nozzle ring (20) for introducing the higher pressure
working fluid into the buckets to turn the rotor; the rotor being completely shrouded
between entrances (24) and exits (28) of the buckets by a surrounding shroud (36)
to maximize the work available from the working fluid; and the nozzle ring (20) abutting
an upstream face of the shroud whereby the shroud provides the downstream walls of
the nozzles.
11. A turbine according to any one of the preceding claims, in which the radial impulse
stage (10) comprises a rotor (10R) having buckets (25) spaced around and opening at
the periphery thereof; and a nozzle ring (20) containing an annular array of nozzles
(21) for introducing the higher pressure working fluid into the buckets to turn the
rotor; the nozzle ring also comprising vanes (21A) which separate and partly define
the contours of adjacent nozzles, the vanes having surfaces (21B) which face the axis
of the respective rotor and which are continuously curved from their edges (21C) at
the nozzle outlets (23) to their portions lying radially outwardly of the edges of
the adjacent vanes.
12. A turbine according to claim 11, in which the edge (21C) of each vanes presents
an included wedge angle of not more than 3°.
13. A turbine according to claim 11 or claim 12, in which the curvature of the vane
surfaces (21B) is similar to that of the outer periphery of the rotor.
14. A turbine according to any one of the preceding claims, in which the high pressure
section (8) includes first and second radial impulse stages (10,11) each comprising
a rotor (10R,11R) with buckets (25) spaced around and opening at the periphery thereof,
and a nozzle ring (20) containing an annular array of working fluid distribution nozzles
(21) surrounding the rotor, each of the nozzles having an inlet (22) opening at the
outer periphery of the ring (20) and an outlet (23) opening at the inner periphery
of the ring; and flow directing means (37,43) for turning working fluid discharged
radially outwardly from the buckets of the first stage rotor (10R) axially towards
the second stage rotor (11R) and then radially inwardly into the inlets of the nozzles
(48) of the second stage nozzle ring (49).
15. A turbine according to claim 14, in which the flow directing means comprises a
radially oriented annular member (43) disposed between the first and second stage
rotors (10R,11R) in abutting relationship with the upstream side of the second stage
nozzle ring (49), the outer periphery of the member (43) being spaced inwardly from
a casing (37) to provide a flow passage therebetween; and seal means (46,47) being
provided at the inner periphery of the member for keeping working fluid discharged
from the first stage rotor (10R) from leaking around the member to the second radial
impulse stage (11).
16. A turbine according to any one of claims 1 to 13, in which the high pressure section
(8) includes first and second radial impulse stages (10,11) each comprising a rotor
(10R,11R) with buckets (25) spaced around and opening at the periphery thereof, and
a nozzle ring (20) containing an annular array of working fluid distribution nozzles
(21) surrounding the rotor; and in which the high pressure section also includes means
(43) for conducting working fluid discharged from the buckets of the first stage rotor
into the nozzles surrounding the second stage rotor (11R) after that fluid has passed
once through the buckets of the first stage rotor, and a discharge plenum (54) on
the downstream side of the second stage rotor, the buckets in the second stage rotor
being so shaped as to dump the working fluid into the discharge plenum after that
fluid has passed once through the buckets of the second rotor.