Note: Descriptions are shown in the official language in which they were submitted.
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CENTRIFUGAL ROTOR
The present invention relates to a centrifugal rotor.
The technical field of this invention is that of the fluid, liquid or gaseous
compression. The invention therefore relates to both pumps as well as
compressors
which make a supply of liquid or gas respectively possible, from a given
pressure to a
higher pressure.
There are many techniques to increase the pressure of a fluid. A common
technique consists in centrifuging the fluid upon which stress is exerted
which in turn
causes an increase in its pressure. For the implementation of this technique,
there are
many different structures of pumps and compressors depending upon many
parameters
including the related fluid, the environment (size, etc.) and desired
performance
(compression rate, etc.). Subsequently, we will focus on pumps and compressors
comprising at least one centrifugal rotor associated with an axial diffuser.
A centrifugal rotor is a rotor having an axis of rotation. It is designed to
compress a fluid flowing in a direction parallel to its axis of rotation, the
compressed fluid
leaving the rotor in a radial direction outwardly. When the compressed fluid
must flow
axially, one solution is to direct the fluid exiting the rotor so that it
changes the direction of
flow. The element used for this purpose is a fixed part called an axial
diffuser and it has
at least one duct to direct the compressed fluid. The downstream end of the
duct, that is
to say the end which is remote from the centrifugal rotor, is axially oriented
in
accordance with the direction that one wishes to direct the compressed fluid.
The
purpose of the axial diffuser is to then take a turn at about 900 to the
outgoing fluid from
the centrifugal rotor so as to guide it axially.
Document FR-2874241 discloses a high-efficiency centrifugal rotor which uses
truncated blades with a radial diffuser. The wake of the blade recloses in the
diffuser and
by working with the wakes of the other adjacent blades creates a stratified
flow that
gradually expands within the diffuser. We thus find in this document a rotor
incorporating
a diffuser. The very thick blades are located in the lower part of the rotor.
US-1,447,916 illustrates another embodiment of a rotor incorporating a
diffuser.
The latter may be a single piece with the rotor portion comprising blades or
it may be a
separate piece secured to the rotor portion comprising the blades. Although it
is noted
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that in all the figures illustrating the vanes, they only extend over one part
of the device
(corresponding to the centrifugal rotor) and not to the peripheral output of
the device and
that the portion corresponding to the centrifugal rotor has a perfectly radial
outlet
upstream from the diffuser.
One technical problem encountered with such a structure is that it is the
source
of pressure loss in the compressed fluid. It is indeed known that when a fluid
flows, it
undergoes pressure losses that depend on the conduit in which it is found,
induding any
changes in direction undergone.
It is not possible to eliminate the pressure drop that are particularly
related to
the nature of the fluid itself (particularly its viscosity) but this invention
is to provide the
means to minimize as much as possible these losses.
An object of this invention is thus, for a given compression stage, comprising
a
centrifugal rotor and an axial diffuser, to increase the performance of this
stage, i.e., for
example, obtaining a higher compression ratio for a given power or for a given
compression reducing the mechanical power needed to be exerted on the rotor to
make
it turn.
To this end, this invention proposes a centrifugal rotor comprising:
- a hub having a longitudinal axis,
- a fluid inlet,
- a first flange, upstream and having an opening around the hub,
- a second flange, separated downstream from said first flange by the vanes
thereby forming channels each delimited by the first flange, the second flange
and two
vanes extending from the fluid inlet to a peripheral outlet.
According to this invention, in the proximity of the peripheral outlet, the
first
flange has a concave area oriented towards the channels while the second
flange has a
convex area oriented towards the channels.
Due to the form thus given to the outlet channels, the passage of a radial
flow
within the centrifugal rotor to an axial flow in the diffuser upstream from
the rotor is
performed less brusquely making it possible to limit the losses in pressure
when the fluid
changes direction.
To have a rotor that is simple to produce, the first flange and the second
flange
advantageously have a circular shape around the longitudinal axis.
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For example it is anticipated that the surface tangent to the concave region
of
the first flange exiting the channel, forms an angle of between 10 and 450,
preferably
between 10 and 30 , with a radial plane perpendicular to the longitudinal
axis. Likewise,
it is anticipated that the surface tangent to the convex region of the second
flange exiting
the channel, forms an angle of between 10 and 45 , preferably between 10 and
30 ,
with a radial plane perpendicular to the longitudinal axis.
To better guide the fluid in a centrifugal rotor according to the invention,
it is
advantageously provided that the vanes extend to the outer peripheral exterior
edge of
the first flange and/or of the second flange.
To easily create an acceleration of the fluid exiting the centrifugal rotor,
the first
flange advantageously has an outer peripheral edge adjacent to the channels
which
have a greater diameter than an outer peripheral edge adjacent to the channels
of the
second flange. At the edge with the greater diameter, which corresponds to the
outside
of the curved shape given to the outlet of the centrifugal rotor, the speed is
therefore
higher. This is preferable because the path to be traveled along the outside
of a turn is
greater than that of the inside of a turn. In this way, a more uniform
distribution of the
velodty is promoted when the fluid then moves in a substantially longitudinal
direction.
This invention further relates to a centrifugal compressor and/or a
centrifugal
pump comprising a centrifugal rotor as described above.
Details and advantages of this invention will become more apparent from the
following description with reference to the accompanying drawings in which:
Figure 1 illustrates a centrifugal rotor of the prior art with a cross
sectional view
of a half rotor mounted in a compressor,
Figure 2 is a view similar to that of Figure 1 for a centrifugal rotor
according to a
first embodiment of this invention,
Figure 3 is a view similar to the preceding views according to a second
embodiment of this invention, and
Figure 4 is a cross-section view in perspective along the cut line IV-IV of
Figure
2.
Those skilled in the art will recognize a centrifugal rotor 2 in Figure 1
mounted
inside a housing 4, for example a compressor housing, and a shaft 6 having a
longitudinal axis 8. The following description will be made with reference to
a working air
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compressor (or more generally a gaseous fluid compressor), but this invention
may also
be applied to pumps for liquids.
When the centrifugal rotor 2 is rotated by the shaft 6, the air (or other
gaseous
fluid) is drawn into the centrifugal rotor 2 in a longitudinal direction
relative to the
longitudinal axis 8, and is driven in a mixed flow motion in the centrifugal
rotor 2 while
rotating and appear radially with respect to the longitudinal axis 8.
The centrifugal rotor 2 is built in one piece and comprises a hub 10, a first
flange or upstream flange 12, a second flange or downstream flange 14 and
vanes 16.
The hub 10 enables a connection between the shaft 6 and the centrifugal rotor
2. It has an overall circular, cylindrical, tubular shape and is provided with
a means to
fasten it to the shaft 6. For example, a longitudinal groove is typically
provided in the hub
and the shaft 6 to receive a longitudinal spline or even grooves, or any other
type of
connection.
The downstream flange 14 is connected directly to the hub 10 and extends
radially relative to the longitudinal axis 8. The upstream/downstream
direction is defined
relative to the direction of the air flow in the centrifugal rotor 2. Indeed,
in Figure 1 (as
well as in the other figures) air is drawn to the right of the rotor and then
moves
longitudinally to the left before being driven in a radial direction to be
oriented finally, after
leaving the centrifugal rotor 2 in a longitudinal direction back towards the
left of the figure.
Thus the upstream elements are arranged to the right of the downstream
elements in
the figures.
The upstream flange 12 faces the downstream flange 14 and is connected
thereto by the vanes 16 thereby defining the channels for the air between the
two
flanges. The air is thus introduced between the inner surfaces of the flanges
and vanes
in a centrifugal radial manner.
The upstream flange 12 does not extend to the hub 10 but remains at a
distance therefrom. A sealing bearing 18 faces the hub 10 in front. Towards
the inside of
the centrifugal rotor 2, the front sealing bearing 18 with the hub 10 defines
an inlet
chamber 20 with an annular opening 22 upstream of the inlet chamber 20.
Towards the
exterior, the front sealing bearing 18 is machined to enable it to create a
seal of the
centrifugal rotor 2 in rotation within the housing 4. For example, a seal may
be used,
such as for example a labyrinth ring 24, as an interface between the
centrifugal rotor 2
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and the housing 4. As can be seen in the figures, the centrifugal rotor 2 also
includes a
further sealing bearing 18 on the downstream side, or a rear sealing bearing,
which
extends from the downstream flange 14 and receives another labyrinth ring 24 .
The channels driving air between the upstream flange 12 and downstream
flange 14, each have an outlet 26 (Figure 1) radially oriented at the largest
diameter of
the flanges. The air then enters a diffuser 28 in which it is guided so that
the air flow is
more longitudinal than radial. The channels 30 in the diffuser 28 also make it
possible to
convert the helical movement of the air flow to a substantially straight
movement.
Figures 2 and 4 illustrate a first embodiment of a centrifugal rotor according
to
this invention. As shown in the drawing, the overall structure is
substantially the same in
Figure 1 and in Figures 2 to 4. Thus, the references in Figure 1 are used in
Figures 2 to
4 to designate similar elements. A centrifugal rotor is thus found 2 rotatably
mounted in a
housing 4 around a shaft 6 having a longitudinal axis 8. The centrifugal rotor
2 is sealed
off relative to the housing 4 thusly ensured in particular through the sealing
bearings 18
working together with the labyrinth rings 24 (or other type of seal). A hub 10
enables a
connection between the rotor and the shaft 6, for example by means of a spline
that is
not shown. The centrifugal rotor 2 further comprises an upstream flange 12 and
downstream flange 14 interconnected by vanes 16. The upstream flange 12 has a
sealing bearing 18 which with the hub 10 defines an inlet chamber 20 of the
annular
opening 22. Again, when the centrifugal rotor 2 rotates around the
longitudinal axis 8 of
the air (or other fluid) is being drawn through the opening 22 (longitudinal
suction) to be
compressed in a helico-centrifugal motion and then again become longitudinally
oriented within a diffuser 28 optionally provided with channels.
The differences between a rotor of the prior art and a centrifugal rotor 2
according to this invention are essentially located at the outputs 26, that is
to say at the
area having the greatest diameter of the upstream flange 12, of the downstream
flange
14 and the vanes 16.
Compared with centrifugal rotors of a compressor (or pump) known in the prior
art, this invention proposes to provide an outlet for air flow in a
centrifugal rotor (or other
fluid) having an improved velocity vector to enter into the longitudinal
diffuser. For this
purpose, it is expected that the air channels will be slightly bent (defined
by the flanges
and the vanes) in the centrifugal rotor 2 close to the outlets 26. A curvature
is thus
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produced at the output of the centrifugal rotor which makes it possible to
increase the
speed of the air towards the outside of the curvature.
While in the embodiment of Figure 1, it is noted that the inner face of the
upstream flange 12 and the surface of the downstream flange 14 are
substantially plane
(and slightly converging), the inner surface of the upstream flange 12 has,
near the
output 26, a concave area 32 and the inner surface of the downstream flange 14
has,
near the outlet 26, opposite the concave area 32, a convex area 34.
If we then consider a surface 36 tangent to the inner surface of the
downstream flange 14 at the outlet 26, this surface is substantially conical
(cone axis of
the longitudinal axis 8) and forms, with a radial plane illustrated by a
dotted line, angle a.
In the embodiment of Figure 2, this angle is about 15 and it is about 30 in
the
embodiment of Figure 3. Preferably, this angle will be comprised between 100
and 45 .
In the centrifugal rotors of the prior art, as illustrated by Figure 1, this
angle is
substantially zero.
To avoid overloading the Figures, the surface tangent to the inner surface of
the upstream flange 12 was not illustrated. A substantially conical surface is
also found
here, around the longitudinal axis 8, which forms, with the radial plane
illustrated, an
angle which is preferably less than 45 , for example between 10 and 45
Figure 4 illustrates that the vanes 16 extend into the convex area 34 of the
downstream flange 14. Of course, they extend in a similar manner into the
concave
zone 32 of the upstream flange 12. Preferably, as illustrated in this Figure
4, the vanes
16 extend to the peripheral edge of the upstream flange 12 and the downstream
flange
14, that is to say, up to the output 26 of the rotor.
In Figure 3, H is referenced by the line having the greatest diameter of the
inner surface of the downstream flange 14 and by S for the line having the
greatest
diameter of the inner surface of the upstream flange 12. S and H are circles
the center of
which lies on the longitudinal axis 8, Rs and RH radius respectively. As is
apparent from
Figure 3 (this is also visible in Figure 2 but slightly less pronounced), R8>
R. Thus, for a
same average speed over the air outlet surface outside the centrifugal rotor
2, the
peripheral speed of the air in the vicinity of point S is greater than that of
the air near the
point H. This also applies to the absolute tangential velocity. The air is
accelerated from
the upstream side (exterior to the exiting "turn" of the rotor), thereby
making it possible to
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have a more uniform speed at the input of a substantially longitudinal section
of the
diffuser. Therefore, the losses in pressure, if only within the diffuser, are
reduced and
therefore make it possible to increase the yield of the device.
The shape of the centrifugal rotor according to this invention thus allows a
more gradual transition from a radial air flow to a longitudinal flow. The
distribution of fluid
velocities through a passage section of the diffuser is more uniform and
regular. The
pressure drops are thus limited and a gain in terms of yield is obtained at a
time when
the fluid passes from an essentially radial flow to an axial flow as it flows
into the axial
diffuser.
Note that the channels in the centrifugal rotor 2 have a passage in which the
flow is substantially radial. The inner surfaces of the upstream flange and
the
downstream flange each have an inversion of curvature. And the inner surface
of the
upstream flange 12 has a convex area near the inlet chamber 20 and then it
extends
from the hub 10 after a curved area, said inner surface has a concave area as
described
above. And the inner surface of the upstream flange 14 has a convex area near
the inlet
chamber 20 and then it extends from the hub 10 after a curved area, said inner
surface
has a concave area as described above. The trajectory of the fluid in the
channels
defined by the flanges and the vanes in the centrifugal rotor 2 and thus has a
curve.
To better guide the fluid in the curved rotor, the vanes 16 extend into the
curved region (that is to say up to the concave area of the inner surface of
the upstream
flange and to the convex area of the inner surface of the downstream flange)
and guide
the fluid preferably to the outlet 26. The blades 16 thus are also curved.
They preferably
extend from the inlet chamber 20 to the line H and the line S, or for example
up to the
vicinity of these lines (to least 10 mm in these lines).
Of course, this invention is not limited to the preferred embodiments
described
above as non-limiting examples, but it also relates to the variants within the
reach of
those skilled in the art.
8
It also concerns variations on the embodiment that will be found within the
scope of
professionals in the field within the framework of the Claims below.
Date Recue/Date Received 2021-04-06
