U.S. patent number 3,771,925 [Application Number 05/315,961] was granted by the patent office on 1973-11-13 for supersonic centrifugal compressor.
This patent grant is currently assigned to Societe Alsacienne De Constructions Atomiques-De Telecommunications Et. Invention is credited to Jean-Marie Eugene Friberg, Jean-Marie Merigoux.
United States Patent |
3,771,925 |
Friberg , et al. |
November 13, 1973 |
**Please see images for:
( Certificate of Correction ) ** |
SUPERSONIC CENTRIFUGAL COMPRESSOR
Abstract
The fixed portion of the rotor casing defines with the disc
extension or a rotary disc carrying radially extending blades an
annular deceleration space leading into a diffuser whose fixed
vanes define passages inclined to the radial direction.
Inventors: |
Friberg; Jean-Marie Eugene
(Bourg-La-Reine, FR), Merigoux; Jean-Marie
(Palaiseau, FR) |
Assignee: |
Societe Alsacienne De Constructions
Atomiques-De Telecommunications Et (Paris, FR)
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Family
ID: |
9049034 |
Appl.
No.: |
05/315,961 |
Filed: |
December 18, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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104876 |
Jan 8, 1971 |
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Foreign Application Priority Data
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Jan 14, 1970 [JA] |
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45/7001293 |
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Current U.S.
Class: |
415/181; 416/185;
416/188; 415/208.3; 415/224.5 |
Current CPC
Class: |
F04D
21/00 (20130101); F04D 29/284 (20130101) |
Current International
Class: |
F04D
29/28 (20060101); F04D 21/00 (20060101); F04d
021/00 (); F04d 029/44 () |
Field of
Search: |
;415/119,219A,213,181,211,204,206,207 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Raduazo; Henry F.
Parent Case Text
This is a Continuation, of application Ser. No. 104,876, filed Jan.
8, 1971, now abandoned.
Claims
We claim:
1. A supersonic centrifugal compressor comprising:
a rotor casing,
a rotor mounted for rotation about its axis within said casing,
said casing and said rotor having spaced opposed, similarly curved
surfaces defining therebetween a gas flow path which changes from
axial to radial,
a plurality of circumferentially spaced blades carried by said
rotor and extending outwardly of said rotor surface from the
vicinity of the compressor axis throughout that portion of the flow
path which changes from axial to radial,
said rotor surface being formed at its radially outboard end by a
single radial disc whose periphery extends radially beyond the
outboard edges of said blades to form a disc extension,
said rotor casing surface extending in a radial direction
substantially parallel to said disc extension to form a gas
deceleration chamber with said disc extension,
a diffuser chamber having fixed vanes defining passages leading
from said deceleration chamber and inclined to the radial
direction, and
said fixed vanes of said diffuser chamber extending outwardly from
a point on said casing generally adjacent the periphery of said
disc extension.
2. The compressor as claimed in claim 1, wherein said casing
includes axially spaced fixed walls to define said diffuser chamber
and to support said fixed diffuser vanes therebetween.
3. The compressor as claimed in claim 1, wherein the diffuser
passages are divergent.
4. The compressor as claimed in claim 2, wherein the diffuser
passages are divergent.
5. The compressor as claimed in claim 1, wherein the leading edges
of the diffuser vanes have sharp edges for supersonic operation
with low losses.
6. The compressor as claimed in claim 2, wherein the leading edges
of the diffuser vanes have sharp edges for supersonic operation
with low losses.
7. The compressor as claimed in claim 3, wherein the leading edges
of the diffuser vanes have sharp edges for supersonic operation
with los losses.
8. The compressor as claimed in claim 4, wherein the leading edges
of the diffuser vanes have sharp edges for supersonic operation
with low losses.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention concerns a supersonic centrifugal compressor
providing a high compression ratio and increased output.
2. Description of the Prior Art
It has long been known that a fairly high compression ratio may be
obtained in a centrifugal compressor by giving to the fluid under
compression a high rotational speed and then transforming the thus
obtained kinetic energy into pressure.
It has already been proposed to transform this kinetic energy into
pressure, very simply, by using a rotating diffuser whose profile
is obtained by extending the radii of the rotating blade support
disc beyond the blades. The expansion of the fluid between two
walls both moving at speeds close to that of the fluid then takes
place with a fairly high efficiency.
Such devices, however, cannot be used when a high compression
ratio, about 5 for example, is required with a single compressor
stage. For this, the peripheral speed of rotation of the rotor
blades must be as high as 400 or 500 meters per second, requiring
even higher speeds at the periphery of the rotating diffuser.
Centrifugal stresses then become high enough to deform the blade
support discs. To these mechanical stresses are added others
particularly brought about by thermal expansion of the compressor
elements.
It has subsequently been proposed to replace the rotary diffuser
with a fixed diffuser with two walls prolonging the rotating blade
support discs and whose radii are limited in this case to those of
the blades. The supersonic movement of the fluid over the fixed
walls, particularly the downstream wall on which the pressure is
generally higher because of the curved path followed by the fluid,
leads to losses in efficiency significantly reducing the available
increase in pressure ratio.
It has also been proposed to mount a diffuser arranged to receive
the fluid at supersonic speeds and having a convergent or
convergentdivergent profile downstream of the rotor.
These various proposals have not, however, provided a significant
increase in the available compression ratio in a single compressor
stage, and certain of them bring about output instabilities or
mechanical difficulties.
SUMMARY OF THE INVENTION
The invention is intended to provide an imrpoved supersonic
centrifugal compressor.
In accordance with the invention, a supersonic centrifugal
compressor has a rotor with substantially radially extending blades
mounted on the face of a profiled support disc, the external
diameter of the disc exceeding that of the blades to form a disc
extension. A fixed portion of the rotor casing has an internal
surface so arranged that an annular deceleration space is formed
between that surface and the disc extension, this deceleration
space leading into a diffuser with fixed vanes defining passages
inclined to the radial direction.
Using the invention, it is possible to reduce the disadvantages of
the previously proposed compressors and to provide a high
compression ratio with a high and stable output.
The invention exploits the discovery that in providing a higher
deceleration than that obtained with an equivalent rotary diffuser
in a space situated beyond the periphery of the rotor, it is
possible not only to eliminate the mechanical difficulties of
providing a rotor with two mobile blade support discs, but also to
combine the compressor with a supersonic diffuser at whose entry
the fluid is moving at a speed only slightly supersonic such that a
system of weak shock waves is obtained. Thus, in the diffuser, the
efficiency of the transformation of kinetic energy into pressure is
increased, thereby increasing the overall efficiency.
According to the invention, this deceleration is obtained between
the fixed wall of the disc casing and the extension of the blade
support disc.
The rotor casing is suitably adapted to define a fluid inlet, a
rotor shroud conforming to the blade profile, said fixed portion of
the rotor casing, and opposite walls of the diffuser supporting
fixed vanes thereof.
The diffuser preferably provides divergent passages generating
substantially plane re-compression waves.
The leading edges of the fixed vanes of the diffuser are suitably
thin to be better adapted to supersonic operation.
The faces between which is defined the annular deceleration space,
namely that of the fixed portion of the rotor casing and that of
the blade disc extension, are preferably substantially parallel and
provide a significant deceleration of the supersonic flow between
their inside and outside diameters.
It should be noted that this deceleration, as opposed to the case
with previously proposed techniques, is obtained with friction
losses reduced to a minimum and with lowered mechanical stresses.
Because of the form of the passage within which the fluid is
accelerated by the rotor, the fluid in the rotary diffuser exerts a
higher pressure on the moving blade support disc which is moving at
a relatively slow speed than on the upstream wall which is fixed
and with respect to which the fluid is moving at high speed. It
appears that this property of the compressor significantly
increases the output and is an important contribution to the very
high pressure ratios obtained.
Moreover, it is known that the upstream wall when rotating at high
speeds undergoes important deformations because of its shape.
In the compressor provided by the invention, this wall is fixed and
only experiences thermal stresses which are easily mastered by one
skilled in the art.
The diffuser thus receives a flow which is sufficiently decelerated
that its speed is only slightly supersonic and it then becomes
possible to set up a system of weak shockwaves and to obgain in the
fixed diffuser and efficiency approaching unity.
The combination of the compressor rotor and diffuser is such that
the increase in output obtained compensates the friction losses in
the space between the moving blades of the rotor and the fixed
blades of the diffuser. The stability of the flow is increased and
the rotor comprises only a single disc of increased radius so that
better mechanical strength is obtained.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described in more detail, by way of
example only, with reference to the accompanying diagrammatic
drawing, in which:
FIG. 1 is an axial section through the single stage supersonic
centrifugal compressor of the present invention, showing only that
part of the compressor above its rotor axis.
FIG. 2 is a section through the compressor of FIG. 1 taken
perpendicularly to its axis of rotation.
DESCRIPTION OF THE PREFERRED EMBODIMENT
In the present example, the compressor serves for compressing air
and has a compression ratio of the order of 9.
Referring to the Figures, the compressor has a single rotor 1 with
radially extending blades 2 mounted on the face of a profiled
support disc 3. The external diameter of the disc 3 exceeds that of
the blades 2 to form a disc extension 3'.
The rotor shroud 5 is shaped to define a fluid inlet 11 and a rotor
shroud 5" conforming to the profile of the blades 2. The internal
surface 5.sub.1 of this rotor shroud 5" lies very close to the
forward faces of the blades 2, as is clearly seen in FIG. 1. This
profile is that of a cone with curved generatrix.
The rotor casing continues to define a fixed wall portion facing
the disc extension 3', an annular deceleration space 4 being
defined between this fixed wall and the forward face of the
extension 3' which, in use of the compressor, moves at a speed
approaching that of the air under compression. This deceleration
space 4 leads into a diffuser 6 with fixed blades 9 supported
between parallel annular walls formed by sections of the rotor
casing.
As is seen clearly in FIG. 2, th diffuser 6 has six diverging
passages 7 defined by the fixed vanes 9 and arranged at an angle to
the radial direction. At the diffuser entry, the air under
compression is travelling at supersonic speed.
The distance between the rim of the profiled support disc 3 and the
leading edges 9' of the fixed blades 9 of the diffuser 6 is made
very small, and is chosen to take into account the radial expansion
of the disc when turning at supersonic speed.
The rotor is keyed to a shaft shown schematically by its axis
10.
The internal face 5.sub.1 of the rotor shroud 5 is made as small as
practicable so as to avoid loss of speed by the air. Where this
face extends beyond the blades 2, to define the disc extension 3'
the annular deceleration space 4, it runs substantially parallel to
the front face of the extension 3'.
Where a particularly high output is required, any suitable form of
flow distributor may be mounted upstream of the rotor so as to
reduce the relative speed of the air at the fluid entry 11. When
the rotor is turning at 33,000 r.p.m., the rotary speed of the
blade periphery corresponds to a Mach number in the region of 1.3.
The airspeed at the outlet from the blades 2 is then of the order
of Mach 1.2.
In the deceleration space 4 the airspeed decreases to a value less
than Mach 1.1 by the time it reaches the leading edge 9' of the
fixed vanes 9 of the diffuser 6. The entry losses are
negligible.
The air enters the diffuser 6 at a speed which is only slightly
supersonic and accelerates gradually to provide a recompression
wave, when it decelerates inside the diffuser because of its now
subsonic speed.
The overall efficiency of a compressor stage such as just described
may reach some 80 per cent.
It will be appreciated that a number of compressor stages such as
just described may be combined to provide a multi-stage
compressor.
In the compressor just described, because of the incurving form of
the internal surface 5.sub.1 of the rotor shroud, the air exerts on
the extension 3' a greater pressure than on the fixed wall of the
rotor casing. It appears that this property of the compressor
provides a significant increase in the output and has an important
effect on the provision of a high compression ratio.
In the previously proposed rotary diffusers, the upstream diffuser
wall suffers significant deformations because of its form, in the
compressor just described this wall is fixed and so is subject only
to thermal deformations which are more readily compensated.
In the compressor just described, the diffuser receives a fluid
flow which is sufficiently decelerated that its speed is only
slightly supersonic so that it is possible to obtain a system of
weak shockwaves and consequently a diffuser efficiency approaching
unity. Using the invention, the increased efficiency obtained
largely compensates the friction losses encountered in the space
between the moving blades of the rotor and the fixed blades of the
diffuser. The stability of flow is improved Moreover, since the
rotor features only a single profiled support disc, it presents a
better mechanical resistance.
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