Device for transferring fluid between two successive stages...

Details Device for transferring fluid between two successive stages... Device for transferring fluid between two successive stages...

1998-12-18

2001-04-24

Lopez, F. Daniel (Department: 3745)

Rotary kinetic fluid motors or pumps

Working fluid passage or distributing means associated with...

Plural rigidly related blade sets

C415S208200

Reexamination Certificate

active

06220816

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a device for transferring fluid between two successive stages of a multistage centrifugal turbomachine, the device comprising a stator assembly incorporating a plurality of return channels which pick up the high speed fluid flow leaving a centrifugal impeller of one stage of the turbomachine for the purpose of rectifying, slowing down, and conveying said flow to the inlet of another centrifugal impeller of an adjacent stage of the turbomachine.
PRIOR ART
FIG. 3
shows an example of a known multistage turbopump as fitted to the cryogenic rocket engines known under the name Vulcain, and it serves to feed those engines with liquid hydrogen. The turbopump of
FIG. 3
comprises, inside a case
301
,
302
: a two-stage centrifugal pump, each stage comprising a respective impeller
305
,
355
fitted with respective blades
306
,
356
and secured to a common central rotary shaft
322
. An inducer
331
conferring good suction characteristics and making possible a high speed of rotation, of about 35,000 revolutions per minute (rpm), is placed at the inlet of the pump on the working fluid feed duct. Turbine elements
332
,
333
fed with a flow of hot gases admitted via a torus
334
are secured to the central shaft
322
to drive it together with the impellers
305
,
355
, and are disposed behind the second stage of the pump.
The central shaft
322
is supported by ball bearings
323
and
324
disposed respectively at the front and at the rear of the assembly constituted by the two-stage pump and the turbine. References
310
and
304
designate respective link ducts between the outlet of the first stage of the pump and the inlet to the second stage of the pump, and the duct for delivering the working fluid from the outlet of the second stage of the pump, a diffuser
307
being disposed at the inlet of the toroidal delivery duct
304
.
The link ducts
310
are formed through the body of an inter-stage stator and are made up in three portions: a radial diffuser
308
having thick blades, a return bend
309
without blades, and a centripetal rectifier
311
having return blades. That solution provides good hydraulic performance providing the radial diffuser
308
is large enough, thereby giving rise to considerable radial bulk. The losses caused by the sudden change in section at the outlet from the radial diffuser
308
and by incidence at the inlet to the centripetal rectifier
311
are difficult to control. To obtain sufficient efficiency, the diffuser
308
must therefore be long in the radial direction of the machine. The non-bladed bend
309
contributes neither to reducing the tangential speed nor to mechanical strength. The rectifier
311
needs to be properly set in terms of incidence. As a result it is relatively complex to make the link ducts for the embodiment shown in FIG.
3
and it is not possible to obtain good compactness.
The inter-stage stator which picks up the flow leaving a first centrifugal impeller at high speed and which rectifies it, slows it down, and feeds it to the inlet of a second impeller thus constitutes one of the main elements in the architecture of a multistage turbomachine (centrifugal pump or centrifugal compressor) and determines the radial and axial size of the turbomachine.
OBJECT AND BRIEF DESCRIPTION OF THE INVENTION
The present invention seeks to remedy the above-specified drawbacks and to enable an inter-stage fluid transfer device to be made that provides good control of the flow all along its path, that is of limited size, particularly in the radial direction, and that simplifies manufacture while also reducing mechanical stresses.
These objects are achieved by a device for transferring fluid between two successive stages of a multistage centrifugal turbomachine, the device comprising a stator assembly incorporating a plurality of return channels which pick up the high speed fluid flow leaving a centrifugal impeller of one stage of the turbomachine for the purpose of rectifying, slowing down, and conveying said flow to the inlet of another centrifugal impeller of an adjacent stage of the turbomachine,
wherein each of the return channels is constituted by a continuous shaped individual tubular element, wherein a first continuous return channel is defined by a set of varying sections defined by parameters and normal to a mean line situated in a predefined plane (P
1
P
2
P
3
) containing the axis of the turbomachine, the mean line having a rectilinear first portion, a curved second portion in the form of a circular arc of radius R
CO2
and a rectilinear third portion, and wherein the various return channels are identical and derived from one another by rotation about the axis of the turbomachine.
Preferably, the mean line of the first return channel further comprises a fourth portion having a large radius of curvature R
CO1
oriented in the opposite direction to the curved second portion to bring the orientation of the mean line parallel to the axis of the turbomachine.
A continuous return channel of the invention makes it possible to control the flow all along its path.
By identifying a mean line contained in a plane, it is possible to simplify the design and the manufacture of a channel by making it possible in relatively simple and analytic manner to describe channel shapes which guarantee minimum bulk and optimized channel operation, in particular by avoiding any sudden changes of direction and by ensuring that flow diffusion takes place for the most part in rectilinear portions situated on either side of the deflector bend.
More particularly, the mean line of the first continuous return channel is contained in a plane (P
1
P
2
P
3
) predefined by a first point P
1
, a second point P
2
, and a third point P
3
such that the first and second points P
1
, P
2
are contained in a plane normal to the axis of the turbomachine, the second and third points P
2
, P
3
are contained in a plane containing the axis of the turbomachine, the position of the first point P
1
is determined to correspond to the imposed distance between the inlet of the first channel and the outlet of the centrifugal impeller situated facing it, and the orientations of the vector P
1
P
2
defined by the first and second points P
1
, P
2
and of the vector P
2
P
3
defined by the second and third points P
2
, P
3
correspond respectively to the orientation of the rectilinear first portion and to the orientation of the rectilinear third portion of the mean line of the first continuous return channel.
In a fluid transfer device of the invention, the axially terminating end portions of the continuous return channels do not have blades.
This avoids peripheral secondary flows forming which would otherwise generate distortion in the flow at the inlet to the second impeller.
In a particular aspect of the invention, the sections normal to the mean line of the first continuous return channel are defined by their areas, by form factors A, B, and m, and by their angles of orientation &agr; between the local axis of each section and the normal {overscore (b)} to the predefined plane (P
1
P
2
P
3
).
By way of example, the shapes of the sections normal to the mean line of the first continuous return channel are defined by the formula:
x
m
A
m
+
y
m
B
m
=
1
where A, B, and m are parameters representing form factors.
The continuous return channels of the invention lend themselves well to parametric description.
Thus, in a particular embodiment, the mean line of a continuous return channel contained in the predefined plane (P
1
P
2
P
3
) is defined by the following parameters:
R
0
=mean radius of the fluid transfer device at the inlet of the continuous return channel;
&bgr;
0
=the angle of the mean line of the channel at said inlet relative to the tangent to the circle defined by the mean radius R
0
;
b
0
=the width of the continuous return channel at said inlet;
R
2
h=the radius of the hub at the inlet to the other impeller situated in register with the outlet of the continuous return channel;
R
2
t&eq

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