US3869220A

US3869220A - Rotary machines

Info

Publication number: US3869220A
Application number: US335162A
Authority: US
Inventors: Colin Andrew Miller Tayler
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1972-02-23
Filing date: 1973-02-23
Publication date: 1975-03-04
Anticipated expiration: 1992-03-04
Also published as: GB1420600A

Abstract

A rotary machine comprising at least one row of rotor blades circumferentially distributed on a rotor and disposed in a rotor blade passage between at least one row of upstream stator blades and at least one row of downstream rotor blades is provided with partitions in the upstream and downstream stator blades to provide a plurality of arcuate segmented flowpaths through the rotor blading. A confined flowpath between a machine inlet and a machine outlet intersects the rotor blading at each arcuate segmented flowpath in turn from the upstream side to the downstream side. This invention when applied to a compressor provides a machine in which several stages of compression of a fluid may be achieved using a single row of rotor blades.

Description

Q United States Patent 1191 1111 3,869,220

Tayler- 1 Mar. 4, 1975 [54] ROTARY MACHINES 1,137,590 4/1915 Ehrhart 415/56 3,070,349 12 1962 St t l 5 5 Inventor: g gg i Tayler Bnstol, 3,292,899 12/1966 n [73] Assignee: The Secretary of State for Defence in P i E i -C, J, Husar Her Bl'li M testy S Attorney, Agent, or FirmCameron, Kerkam, Sutton. Government of the United Kingdom St & Stowell of Great Britain and Northern Ireland, London, England 57 [22] Filed: Feb. 23, 1973 1 ABSTRACT A rotary machine comprising at least one row of rotor [2]] Appl- 3351162 blades circumferentially distributed on a rotor and disposed in a rotor blade passage between at least one [30] Foreign Application priority Data row of upstream stator blades and at least one row of Feb. 23, 1972 Great Britain IIIIIIIIIIIIIII H 8278/72 downstream rotor blades is provided with partitions in Jan. 5, 1973 Great Britain ..'726/73 the upstream and downstream stator blades to provide a pluralityof arcuate segmented flowpaths through the 52 us. c1. 41s 56 l bladmg' A P f between a machine isli 1m. (:1. F01d 1/12 and a machme (met ntersects the blading 58 Field 61 Search 415/5256 at each arcuate Segmented flOWPah in mm mm the upstream side to the downstream side. This invention [56] References Cited when applied to a compressor provides a machine in which several stages of compression of a fluid may be 1 099 970 D ZZI PATENTS 415/56 achieved using a single row of rotor blades.

o 1,118,557 11/1914 Kubiak 415/56 10 Claims, 6 Drawing Figures c 4 8 9 fl "J htu'"*"' .20 I I llama 26 27 IIIA'IIIIIAMII PATENTEU 41975 3, 869 22 0 sum 1 95 5 ROTARY MACHINES This invention relates to rotary machines, more particularly to compressors requiring a high pressure ratio and/or low mass flows for refrigeration and cryogenic pumping.

In cryogenies, pneumatics for instrumentation or control, and refrigeration, in which high pressure ratios and very low flows are required, pumping is usually carried out by a reciprocating compressor; however, because of its size, weight, and the problem of oil contamination, other solutions to the pumping problem have been sought.

Thus more recently a multistage centrifugal compressor for cryogenic duties in the production of liquid helium has been developed. Because of the low flows involved, the size of each unit is very small and a very high rotational speed (up to 200,000 rpm) is required. No suitable prime mover for industrial use is widely available, and such prime movers have proved difficult to develop.

It is therefore an object of the present invention to provide a machine for coping with low flows and/or high pressure ratios of compact size and capable of being driven by commonly available prime movers.

A subsidiary object is to provide a machine for coping with low flows and/or high pressure ratios in which oil contamination is avoided.

A compressor constructed in accordance with the present invention takes advantage of the high efficiency and pressure rise obtainable with a single stage axial machine, regenerating this a controlled number of times. To obtain the same pressure rise with low flows with conventional multistage axial flow compressors, would theoretically require such small blades in the later stages as to be virtually microscopic.

It has been found that a compressor according to the present invention designed for the same cryogenic duties as the known centrifugal compressor requires a rotational velocity of less than a quarter of that of the centrifugal compressor.

In order that the invention might be more fully understood and further features appreciated the following description will refer to the accompanying drawings, in which:

FIG. I is an axial view of a first compressor according to the invention adapted to operate upon compressible fluid sectioned on the line CC of FIG. 2.

FIG. 2 is a section on the line EE of FIG. 1,

FIG. 3 is a developed view of the confined flowpath of the compressor of FIG. 1,

FIG. 4 is a longitudinal section of a second compressor according to the invention sectioned on the line ZZ of FIG. 6,

FIG. 5 is a transverse section of the second compressor sectioned on the line XX of FIG. 4, and

FIG. 6 is a further transverse section of the second compressor sectioned on the line YY of FIG. 4.

In FIGS. 1' to 3 the illustrated compressor comprises a rotor I mounted on a shaft 2 provided with a flange for connection to a prime mover (not shown). The shaft 2 is journalled at bearing 11 into the case 8; bearing 11 would be a gas bearing particularly when it is desired to eliminate the risk of oil contamination. A plurality of radially directed aerofoil sectioned rotor blades 3 are circumferentially distributed around the periphery of rotor 1 and operate in a space 4, known as the rotor blade passage, between a row of upstream stator blades 5 and a row of downstream stator blades 6, both of the rows of stator blades being circumferentially disposed in an annular aperture 44 around rotor 1. The rows of

stator blades

5 and 6 extend from the inner surface of an annulus 7 disposed outside the blade tips of the row of rotor blades 3. A toroidal space 9 outside annulus 7 is formed between the case 8 and annulus 7, into which toroidal space 9 the annular aperture 44 around the rotor opens at both ends.

The annular aperture 44 the rotor 1 intersecting the row of rotor blades 3 is divided by a plurality of radially directed circumferentially distributed partitions 12 (in upstream stator blade row 5) and 24 (in downstream blade row 6) the

partitions

12 and 24 each occupying at least one stator blade pitch. The partitions 24 are slightly displaced in the direction of rotation of the rotor the partitions 12 (the arrangement being most clearly shown in FIG. 3). The

partitions

12 and 24 divide the annular aperture around rotor 1 into a plurality of successively arranged arcuate segmented flowpaths 13-19 each intersecting a portion of the rotor blade row. As the illustrated compressor is specifically adapted for compressing a compressible fluid (e.g. helium gas), the arcuate segmented flowpaths are of decreasing aperture from the first, 13, to the last, 19. Entry to the first arcuate segmented flowpath 13 is provided by a convergent inlet channel 20 extending outside case 8, and whose wall 21 terminates at a flange 22 to which a low pressure fluid source may be connected. Each partition 24 extends from the stator blade row 6 into the toroidal space 9 and is continued to join the next following partition 12 which is similarly extended from the stator blade row 5 into the toroidal space 9, the

extended partitions

12 and 24 occupy the whole height between the case 8 and annulus 7 thereby defining a plurality of return flowpaths 32 to 37 within the casing 8 angled to the axis of the shaft 2, each leading from downstream of one arcuate segmented flowpath to upstream of the next following arcuate segmented flowpath; thus return flowpath 32 leads from the downstream side of arcuate segmented flowpath 13 to the upstream side of the next following arcuate segmented flowpath l4, and return flowpath 33 leads from the downstream side of arcuate segmented flowpath 14 to the upstream side of arcuate segmented flowpath 15 around the rotor blade tips. Downstream of the last arcuate segmented flowpath 19 a divergent diffuser passage extends through case 8 forming an outlet 25 whose walls 26 have a flange 27 for connection to a high pressure fluid sink (not shown). It will be seen that the com bination of arcuate segmented flowpaths and

return flowpaths

13, 32,14, 33, 15, 34,16, 35, 17, 36, 18, 37, I9, taken in turn provides a confined flowpath from inlet 20 to outlet 25 intersecting the row of rotor blades seven times.

Conveniently the annulus 7 is flared outwards toward its

edges

38 and 39 so that feed back channels 32 37 take a convergent form on their approach to the arcu' ate segmented flowpaths 14 19 and a divergent diffuser form 23 downstream of segmented flowpaths 13 In use the row of rotor blades 3 is normally driven from intersection with a lower pressure arcuate segmented flowpath to intersection with a higher pressure arcuate segmented flowpath, eg from arcuate flowpath 16 to arcuate segmented flowpath 17. To prevent high losses due to compressed fluid being passed from the high pressure final stage of compression in arcuate segmented flowpath 19 back to the low pressure first stage of compression in arcuate flowpath 13, the partition particularly designated 42 in the upstream row of stator blades 5 between arcuate segmented flowpath l9 and arcuate segmented flowpath 13 is considerably thicker than the other partitions l2 and 24.

Rotor 1 and rotor blades 3 are formed from a single disc forging with the row of rotor blades 3 being machined to an aerofoil section integrally from the forged disc. To prevent leakage along the face of the rotor, seals 28 are provided between the face of the rotor and a fixed annular hub 29 which has a central orifice 30 through which shaft 2 passes and a circumferential flange 31 forming part of the wall of feedback flowpaths 32 37.

A lateral frusto-conical hub 40 fitted to an internal flange 41 of case 8 covers the remaining exposed portion of rotor 1.

Flow of compressible fluid, for which this particular compressor is adapted, can most easily be followed by reference to FIG. 3.

Compressible fluid (e.g. helium gas) from low pressure source enters the machine through convergent entry inlet and passes through arcuate segmented flowpath l3 intersecting parts of the rows of stator blades 5, rotor blades 3, and stator blades 6 in turn, so entering the diffuser 23 forming part of feedback flowpath 32, the flow returns around the outside of annulus 7 before entering the following arcuate segmented flowpath 14 to intersect the row of rotor blades again. This process is repeated on five further occasions until the flow passes through the last arcuate segmented flowpath l9 and leaves the machine through outlet 25, having intersected the row of rotor blades on seven occasions.

The isothermal efficiency of the machine can be improved by providing intercooling between stages of compression. This is most easily arranged by providing that the feedback flowpaths are formed in ducts around the outside of the case as illustrated in FIGS. 4 to 6.

ln FIGS. 4 to 6 those items common to FIGS. 1 to 3 are given the same reference numerals. The compressor of FIGS. 4 to 6 comprises a rotor I mounted on a shaft 2 journalled into case 8 at one end and lateral hub 45 bolted to the case 8 at the other. A row of radially directed aerofoil sectioned rotor blades 3 are circumferentially distributed around the rotor 1 and operate in a space 4, the rotor blade passage, between a row of upstream stator blades 5 and a row of downstream stator blades 6, both of said rows of stator blades comprising a plurality of radially directed blades disposed in an annular aperture 44 around the periphery of rotor 1. The blades of rows of

stator blades

5 and 6 occupy the full height of annular aperture 44.

Aperture 44 is divided by radially directed partitions 24 in the row of stator blades 6 not less than one rotor blade pitch in width, and similar opposed partitions (not shown) in the row ofstator blades 5. These partitions provided a plurality of discreet arcuate segmented flowpaths through the row of rotor blades 3; in the compressor illustrated there are four arcuate segmented flowpaths l3 16. As this compressor is adapted to compress a compressible fluid, eg helium gas, the arcuate segmented flowpaths are of decreasing aperture from the first 13 to the last 16.

A convergent passage passes through the lateral hub 45 and forms an inlet 20 to the first arcuate segmented pass 13. The wall 21 of inlet 20 is provided with a flange at its outer end which may be used to connect the compressor to a low pressure source of compressible fluid. At its inner end the wall 21 is formed integrally with the partitions in the row of stator blades 5 defining the arcuate segmented flowpath l3.

Downstream of arcuate segmented flowpath 13 is provided a feedback flowpath 46 around the outside of the rotor to the next arcuate segmented flowpath 14 through a further portion of the row of rotor blades 3.

Subsequent feedback flowpaths

47, 48 from downstream of arcuate segmented flowpath 14 to upstream of arcuate segmented flowpath l5, and from downstream of arcuate segmented flowpath 15 to upstream of arcuate segmented flowpath 16 provide a confined flowpath from the inlet 20 to an outlet 25 downstream of arcuate segmented flowpath 16. The wall 26 of outlet 25 has a flange 27 which may be connected to a high pressure sink for the compressed fluid.

Feedback flowpaths

46, 47, 48 each comprise a confined path through a divergent diffuser 23, and offset 180 bend 49, return duct 50, offset 180 bend 51, and convergent channel 52 from the downstream side of one arcuate flowpath to the upstream side of the next following arcuate flowpath. The side walls of the divergent diffusers 23 are integrally fromed with the partitions 24. Divergent diffusers 23 are each connected through an offset l bends 49 to a return duct 50 around the outside of rotor 1. The return duct 50 is provided with intercooling comprising, in this instance. a honeycomb of piping 53 through which coolant fluid may pass between an inlet 54 and outlet 55. The flowpath on leaving return duct 50 enters another offset bend 51 to a convergent passage 52 on the upstream side of the next following arcuate segmented flowpath through the row of rotor blades 3.

The provision of intercooling in the return ducts 50 greatly improves the isothermal efficiency of machines of this type.

When the machine is to be used in compressing compressible fluids, such as helium gas, the arcuate segmented flowpaths through the row of rotor blades are of decreasing aperture from the first 13, to the last 16'. furthermore the cross-sectional areas of equivalent parts of the

feedback flowpaths

46, 47, 48 also decrease from the first 46 to the last 48.

The rotor blades 3 are normally driven from a lower pressure arcuate segmented flowpath to a higher pressure arcuate segmented flowpath, that is in such a direction as to drive any fluid carried over in the rotor blades from a lower pressure to a higher pressure, eg from arcuate segmented flowpath 14 to arcuate segmented flowpath 15.

In this embodiment the partitions are several stator blade pitches in thickness, and leakage between passes is minimised.

Rotor 1 and its blades 3 are formed from a single disc forging, the baldes 3 being machined to an aerofoil section integrally from the forged disc. In order to prevent leakage from the blade tips and between arcuate flowpaths, the row of rotor blades 3 are manufactured to have close tolerance with the rows of

stator blades

5 and 6. Furthermore to prevent leakage along the face of the rotor, seals 28 are provided between both faces of the rotor and the body of the machine.

In operation, compressible fluid from a low pressure source enters the compressor through convergent entry channel 20 to arcuate segmented flowpath 13 through a portion of the tow of rotor blades 3. The inlet flow makes its first pass through a portion of the upstream row of stator blades 5 separated from flows in the adjoining arcuate

segmented flowpaths

14 and 16 by the partitions. After passing through the upstream stator blades where the flow is directed towards the rotating rotor blades at the required angle, energy is imparted to the fluid. Some of the energy is converted to pressure rise in the diffusing rotor blade passages, and some in the following stationary row of downstream stator blades 6. Further conversion of fluid velocity to pressure rise is carried out in the following diffuser 23 forming part of feedback flowpath 46. The fluid then turns through 180 in bend 49.

The fluid passes back through duct 50 making contact with the cooling surface on intercooling piping 53 before executing another 180 turn in bend 51 from which convergent channel 52 takes the fluid into the stator blades in arcuate segmented flowpath 14. The fluid on leaving arcuate segmented flowpath 14 repeats the process in feedback flowpath 47. The fluid flowpath is therefore of a controlled pattern, the width of each successive arcuate flowpath being designed to match the reduced area required for the increase in fluid density. The fluid passes through each of the arcuate segmented

flowpaths

13, 14, 15, 16 in turn being directed from the downstream side of one arcuate segmented flowpath to the upstream side of the

next feedback flowpaths

46, 47, 48 in turn. The fluid leaves the last arcuate segmented flowpath l6 and enters the diffusing outlet 25 by which it leaves the compressor at a high pressure, having passed through portions of the row of rotor blades four times.

The invention has been particularly described in its simplest form with the rotor having blades 21 single row of rotor blades and one row each of upstream and downstream stator blades. The invention is not limited to this configuration, for the rotor may have a plurality of rows of rotor blades operating between a plurality of rows of stator blades, so that when fluid passes through a arcuate flowpath it undergoes multistage compression before being fed back to the next following arcuate segmented flowpath.

Furthermore the described method of intercooling in FIGS. 4 to 6 with a honeycomb of longitudinal water cooling pipes along the return duct is intended as merely being illustrative of the intercooling. Many methods of providing intercooling will occur to those versed in the art and any such method could be used in the present invention.

It may be found advantageous in the compressor of F108. 4 to 6 to replace the 180 offset right angle bends by plenum chambers.

The partitions in this second embodiment are considerably thicker (at least three stator blade pitches) than those illustrated in the first embodiment in FIGS. 1 to 3. Thus in this second embodiment there is no particular need to construct the partition between the last and the first arcuate flowpath more thickly than the others.

The number of arcuate flowpaths provided around the rotor is a matter of design, the embodiments described with reference to the figures are merely illustrative in showing seven and four arcuate flowpaths respectively, any convenient number of such arcuate flowpaths may be provided to suit the particular application for the machine.

Again the illustrated embodiments were of machines adapted for use with compressible fluids, however where the fluid to be operated on is incompressible the arcuate flowpaths would be of equal aperture.

It is not necessary for the direction of rotation of the rotor to be as described, this invention would not preclude the rotation of the rotor generally from a high pressure environment to a lower pressure environment, stepping, of course, back to a high pressure environment between the first and the last arcuate segmented pass.

1 claim:

1. A compressor comprising a case and mounted within said case:

a. a rotor,

b. an annular aperture coaxial with said rotor and surrounding the periphery of said rotor,

c. at least one row of rotor blades circumferentially distributed on the periphery of the rotor and projecting into said annular aperture dividing the annular aperture into an upstream side and a downstream side,

d. a row of upstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture and disposed upstream of said row of rotor blades,

e. a row of downstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed downstream of said row of rotor blades,

. a rotor blade passage formed between said row of upstream stator blades and said row of downstream rotor blades wherein said row of rotor blades operates,

g. partitions provided in each row of stator blades, each partition occupying at least one stator blade pitch, each partition in the downstream row of stator blades being substantially opposed by a corresponding partition in the upstream row of stator blades,

h. a plurality of arcuate segmented flowpaths arranged around the periphery of the rotor intersecting said row of rotor blades in a direction substantially normal to the direction of travel of the rotor blades, each of said arcuate segmented flowpaths being formed between pairs of corresponding partitions in said upstream and said downstream rows of stator blades, the arcuate segmented flowpaths being arranged successively from a first arcuate segmented flowpath to a last arcuate segmented flowpath,

. a plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmented flowpath, wherein each of the return flowpaths runs from the downstream side of its associated arcuate segmented flowpath to the upstream side of the next following arcuate seg mented flowpath,

j. an inlet from without the case to the first arcuate segmented flowpath, and

k. an outlet from the last arcuate segmented flowpath to without the case.

2. A compressor according to claim 1 additionally including: an annulus around said annular aperture and coaxial with the rotor, a toroidal chamber provided within the case, and said plurality of return flowpaths being within said toroidal chamber.

3. A compressor according to claim 2 wherein said confined return flowpaths each comprises an enclosed pipe from downstream of its associated arcuate segmented flowpath to upstream of the next following segmented flowpath.

4. A compressor according to claim 3 including two 180 off-set bends in each of said enclosed pipes.

5. A compressor according to claim 3 including two plenum chambers in each of said enclosed pipes.

6. A compressor according to claim 3 including a convergent passage immediately upstream of each arcuate segmented flowpath and a divergent passage immediately downstream of each arcuate segmented flowpath.

7. A compressor according to claim 2 including extensions of said partitions into said toroidal chamber each extension occupying the whole height of said toroidal chamber and wherein the extension of a partition in the row of downstream stator blades is integrally formed with the extension of the next following partition from its corresponding opposed partition in the row of upstream stator blades, and said confined return flowpath formed between the integrally formed partition extensions.

8. A compressor according to claim 7 additionally comprising a thicker partition between the last arcuate segmented flowpath and the first arcuate segmented flowpath in the upstream row of stator blades than the other partitions.

9. A compressor comprising a case and mounted within said case:

a. a rotor,

d. at least one row of upstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed upstream of said row of rotor blades,

e. at least one row of downstream stator blades radially distributed around the interior of said annular aperture, occupying the height of said annular aperture, and disposed downstream of said row of rotor blades,

f. a rotor blade passage formed between said row of upstream stator blades and said row of downstream stator blades wherein said row of rotor blades operates,

g. partitions provided in each row of stator blades, each partition occupying at least one stator blade pitch, each partition in the downstream row of stator blades being substantially opposed by a corresponding partition in the upstream row of stator blades.

. a plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmented flowpath, wherein each of the return flow paths runs from the downstream side of its associated arcuate segmented flowpath to the upstream side of the next following arcuate segmented flowpath,

j. an inlet from without the case to the first arcuate segmented flowpath,

R. an outlet from the last arcuate segmented flowpath to without the case,

1. an annulus around said annular aperture and coaxial with the rotor,

m. a toroidal chamber provided within the case, and said plurality of return flowpaths being within said toroidal chamber, n. said confined return flowpaths each comprising an enclosed pipe from downstream of its associated arcuate segmented flowpath to upstream of the next following segmented flowpath,

0. two off-set bends in each of said enclosed pipes,

p. a convergent passage immediately upstream of each arcuate segmented flowpath and a divergent passage immediately downstream of each arcuate segmented flowpath.

10. A compressor comprising a case and mounted within said case:

a. a rotor,

e. at least one row of downstream stator blades radially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed downstream of said row of rotor blades,

h. a plurality of arcuate segmented flowpaths arranged around the periphery of the rotor intersecta plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmented flowpath, wherein each of the return flowpaths runs from the downstream side of its associated arcuate segmented flowpath t the upstream side of the next following arcuate segmented flowpath,

an inlet from without the case to the first arcuate segmented flowpath,

k, an outlet from the last arcuate segmented fiowpath to without the case,

1. an annulus around said annular aperture and coaxial with the rotor,

m. a toroidal chamber provided within the case. and

said plurality of return flowpaths being within said toroidal chamber,

n. extensions of said partitions into said toroidal chamber each extension occupying the whole height of said toroidal chamber and wherein the extension ofa partition in the row of downstream stator blades is integrally formed with the extension of the next following partition from its corresponding opposed partition in the row of upstream stator blades, and said confined return fiowpath formed between the integrally formed partition extension, 0. a thicker partition between the last arcuate segmented flowpath and the first arcuate segmented flowpath in the upstream row of stator blades wider

Claims

1. A compressor comprising a case and mounted within said case: a. a rotor, b. an annular aperture coaxial with said rotor and surrounding the periphery of said rotor, c. at least one row of rotor blades circumferentially distributed on the periphery of the rotor and projecting into said annular aperture dividing the annular aperture into an upstream side and a downstream side, d. a row of upstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture and disposed upstream of said row of rotor blades, e. a row of downstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aPerture, and disposed downstream of said row of rotor blades, f. a rotor blade passage formed between said row of upstream stator blades and said row of downstream rotor blades wherein said row of rotor blades operates, g. partitions provided in each row of stator blades, each partition occupying at least one stator blade pitch, each partition in the downstream row of stator blades being substantially opposed by a corresponding partition in the upstream row of stator blades, h. a plurality of arcuate segmented flowpaths arranged around the periphery of the rotor intersecting said row of rotor blades in a direction substantially normal to the direction of travel of the rotor blades, each of said arcuate segmented flowpaths being formed between pairs of corresponding partitions in said upstream and said downstream rows of stator blades, the arcuate segmented flowpaths being arranged successively from a first arcuate segmented flowpath to a last arcuate segmented flowpath, i. a plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmented flowpath, wherein each of the return flowpaths runs from the downstream side of its associated arcuate segmented flowpath to the upstream side of the next following arcuate segmented flowpath, j. an inlet from without the case to the first arcuate segmented flowpath, and k. an outlet from the last arcuate segmented flowpath to without the case.

4. A compressor according to claim 3 including two 180* off-set bends in each of said enclosed pipes.

9. A compressor comprising a case and mounted within said case: a. a rotor, b. an annular aperture coaxial with said rotor and surrounding the periphery of said rotor, c. at least one row of rotor blades circumferentially distributed on the periphery of the rotor and projecting into said annular aperture dividing the annular aperture into an upstream side and a downstream side, d. at least one row of upstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed upstream of said row of rotor blades, e. at least one row of downstream stator blades radially distributed around the interior of said annular aperture, occupying the height of said annular aperture, and disposed downstream of said row of rotor blades, f. a rotor bLade passage formed between said row of upstream stator blades and said row of downstream stator blades wherein said row of rotor blades operates, g. partitions provided in each row of stator blades, each partition occupying at least one stator blade pitch, each partition in the downstream row of stator blades being substantially opposed by a corresponding partition in the upstream row of stator blades. h. a plurality of arcuate segmented flowpaths arranged around the periphery of the rotor intersecting said row of rotor blades in a direction substantially normal to the direction of travel of the rotor blades, each of said arcuate segmented flowpaths being formed between pairs of corresponding partitions in said upstream and said downstream rows of stator blades, the arcuate segmented flowpaths being arranged successively from a first arcuate segmented flowpath to a last arcuate segmented flowpath, i. a plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmented flowpath, wherein each of the return flow paths runs from the downstream side of its associated arcuate segmented flowpath to the upstream side of the next following arcuate segmented flowpath, j. an inlet from without the case to the first arcuate segmented flowpath, k. an outlet from the last arcuate segmented flowpath to without the case, l. an annulus around said annular aperture and coaxial with the rotor, m. a toroidal chamber provided within the case, and said plurality of return flowpaths being within said toroidal chamber, n. said confined return flowpaths each comprising an enclosed pipe from downstream of its associated arcuate segmented flowpath to upstream of the next following segmented flowpath, o. two 180* off-set bends in each of said enclosed pipes, p. a convergent passage immediately upstream of each arcuate segmented flowpath and a divergent passage immediately downstream of each arcuate segmented flowpath.

10. A compressor comprising a case and mounted within said case: a. a rotor, b. an annular aperture coaxial with said rotor and surrounding the periphery of said rotor, c. at least one row of rotor blades circumferentially distributed on the periphery of the rotor and projecting into said annular aperture dividing the annular aperture into an upstream side and a downstream side, d. at least one row of upstream stator blades radially directed and circumferentially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed upstream of said row of rotor blades, e. at least one row of downstream stator blades radially distributed around the interior of said annular aperture, occupying the whole height of said annular aperture, and disposed downstream of said row of rotor blades, f. a rotor blade passage formed between said row of upstream stator blades and said row of downstream stator blades wherein said row of rotor blades operates, g. partitions provided in each row of stator blades, each partition occupying at least one stator blade pitch, each partition in the downstream row of stator blades being substantially opposed by a corresponding partition in the upstream row of stator blades, h. a plurality of arcuate segmented flowpaths arranged around the periphery of the rotor intersecting said row of rotor blades in a direction substantially normal to the direction of travel of the rotor blades, each of said arcuate segmented flowpaths being formed between pairs of corresponding partitions in said upstream and said downstream rows of stator blades, the arcuate segmented flowpaths being arranged successively from a first arcuate segmented flowpath to a last arcuate segmented flowpath, i. a plurality of confined return flowpaths, each of said return flowpaths being associated with an arcuate segmented flowpath except the last arcuate segmeNted flowpath, wherein each of the return flowpaths runs from the downstream side of its associated arcuate segmented flowpath to the upstream side of the next following arcuate segmented flowpath, j. an inlet from without the case to the first arcuate segmented flowpath, k. an outlet from the last arcuate segmented flowpath to without the case, l. an annulus around said annular aperture and coaxial with the rotor, m. a toroidal chamber provided within the case, and said plurality of return flowpaths being within said toroidal chamber, n. extensions of said partitions into said toroidal chamber each extension occupying the whole height of said toroidal chamber and wherein the extension of a partition in the row of downstream stator blades is integrally formed with the extension of the next following partition from its corresponding opposed partition in the row of upstream stator blades, and said confined return flowpath formed between the integrally formed partition extension, o. a thicker partition between the last arcuate segmented flowpath and the first arcuate segmented flowpath in the upstream row of stator blades wider than the other partitions.