Turbo machines

Details Turbo machines Turbo machines

1999-09-20

2001-10-16

Look, Edward K. (Department: 3745)

Rotary kinetic fluid motors or pumps

With sound or vibratory wave absorbing or preventing means...

Reexamination Certificate

active

06302643

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to turbo machines, and in particular relates to a turbo machine able to prevent instability in flow, by suppressing swirl due to recirculation flow at an inlet of an impeller and by suppressing rotation stalls of the impeller, irrespective of the types and the fluid thereof.
In more details, the present invention relates to the turbo machines, such as for a pump, a compressor, a blower, etc., having non-volume type impeller therewith, and in particular, relates to the turbo machine being able to prevent from the instability in flow, by suppressing a swirl or pre-whirl which is generated due to a main flow or component of the recirculation occurring at an inlet of an impeller and by suppressing rotation stalls thereof, thereby being suitable to be applied into a mixed-flow pump, which is used widely as water circulating pumps in a thermal power plant or in a nuclear power plant, a drainage pump, as well as, relates to a pump station into which is applied the turbo machine according to the present invention.
2. Description of Prior Art
Rotary machines being called by a name of “turbo machine” can be classified as below, depending upon the fluids by which the machines are operated and in types thereof.
1. With fluids by which the machine is operated:
Liquid, and Gas.
2. In Types:
An axial flow type, a mixed-flow type, and a centrifugal type.
In
FIG. 22
showing a cross-section view of a mixed-flow pump which is now mainly or widely used due to ease of operation. It comprises a suction casing
11
, a pump
12
and a diffuser
13
, in a sequence from upper stream to down stream thereof.
A blade (of an impeller)
122
rotating within a casing
121
of the pump
12
is rotationally driven on a rotary shaft
123
, thereby supplying energy to the liquid which is suctioned from the suction casing
11
. The diffuser
13
has a function of converting a portion of velocity (or kinetic) energy of the liquid into static pressure.
FIG. 23
shows a typical characteristic curve between head and flow rate of the turbo machine including the mixed flow pump shown in
FIG. 22
, where the horizontal axis shows a parameter indicating the flow rate, while the vertical axis a parameter indicating the head.
Namely, the head decreases in reverse relation to increase of the flow rate in a region of low flow rate, however it rises up following the increase of the flow rate during the time when the flow rate lies within a S region (i.e., a portion uprising or jumping up at the right-hand side in the characteristic curve). And, when the flow rate rises up further, exceeding the right-hand uprising portion of the characteristic curve, the head begins to again, following the increase in the flow rate.
Then, in a case where the turbo machine is operated with the flow rate of such the characteristic curve of uprising at the right-hand side, a mass of the liquid vibrates by itself, i.e., generating a surging phenomenon.
Such the characteristic curve of uprising at the right-hand side is caused, since the recirculation comes out at an outer edge of the inlet of the impeller when the flow rate flowing through the turbo machine is low, and at that instance, a flow passage or a channel for the liquid flowing into the turbo machine is narrowed, thereby generating a swirl in the liquid (see FIG.
22
).
Since the surging gives damages not only upon the turbo machine, but also upon conduits or pipes which are connected to upper stream and down stream sides thereof, it is inhibited to be practiced in a region of low flow rate. Further, there were already proposed various methods for suppressing the surging as below, other than an improvement made in the shape (i.e., profile) of the blade, for the purpose of expanding or enlarging the operation region of the turbo machine.
1. Casing treatment:
Thin or narrow grooves or drains, being from 10% to 20% of a chordal length of the blade, are formed in a casing region where the impeller lies, so as to improve a stall margin.
FIGS.
24
(
a
) and (
b
) show explanatory views of the casing treatment which were already proposed, in particular, FIG.
24
(
a
) shows a positional relationship between the casing treatment and the blades, and FIG.
24
(
b
) shows the cross section views of the casing treatment.
Namely, with the casing treatment which were already proposed, the grooves being sufficient in the depth are formed in an inner wall (i.e., flow surface) of the casing on the region where the blades lie, in an axial direction, in a peripheral direction, or in an oblique direction, alternatively, in a radial direction or an oblique direction, respectively.
Though is not yet investigated clearly the mechanism on how the casing treatment enables the improvement in the stall margin theoretically, it can be considered that because the fluid of high pressure is spouted out or injected into a low energy region and inhibits occurrence of the installing cells.
2. Separator:
A separator is provided for dividing the recirculation flow occurring at the outer edge of the inlet of the impeller into a reverse flow portion and a forward flow portion (i.e., in a main flow direction), in the region of low flow rate, thereby prohibiting the expansion of the recirculation.
FIGS.
25
(
a
)-(
c
) are explanatory views for the separators, each of which is applied to the turbo machine of the axial flow type, in particular, there are proposed a suction ring type (in FIG.
25
(
a
)), a blade separator type (in FIG.
25
(
b
)), and an air separator type (in FIG.
25
(
c
)), respectively.
In the suction ring type (in FIG.
25
(
a
)), the reverse flow is enclosed within an outside of the suction ring, and in the blade separator type (in FIG.
25
(
b
)) is provided a fin between the casing and the ring. Further, with the air separator type (in FIG.
25
(
c
)), a front end or a tip of the moving wing (i.e., the blade) is opened so as to introduce the reverse flows into the outside of the casing, thereby prohibiting the swirl from being generated due to the reverse flows by means of the fin. Thus, it is more effective, comparing with the former two types mentioned, however, comes to be large-scaled in the devices thereof.
3. Active control:
This is to suppress the generation of the swirl due to the recirculation by injecting or spouting out the high pressure fluid from an outside into a spot where the recirculation occurs.
Furthermore, as an example of the conventional turbo machines, a mixed-flow pump will be described hereinafter. To a mixed-flow pump, it is required to show a head-flow rate characteristic curve (hereinafter, called by “head curve”) having no behavior uprising at the right-hand side for enabling a stable operation, in a case where the pump is operated over the whole flow range thereof. However, ordinarily in a pump, it is common that the characteristics, such as an efficiency representing performance of the pump, a stability of the head curve, a cavitation performance, and an axial motive power for closure, etc., are in reversed relationships to one another. Namely, if trying to improve one of those characteristics, the other one(s) is is decreased down, therefore there is a problem that it is difficult to obtain improvements in at least two or more characteristics at the same time. For example, with a pump in which consideration was made primarily onto the efficiency thereof, the head curve shows a remarkable behavior uprising at the right-hand side in a portion thereof, thereby it has a tendency to be unstable.
For obtaining a head curve continuously falling down at the right-hand side for enabling the stable operation, in the conventional arts, as is mentioned in the above, it is already known that the casing treatment or the separator is provided or treated therein. Such the structure is already described, for example in U.S. Pat. No. 4,212,585.
SUMMARY OF THE INVENTION
However, in accordance with the casing treatment and the separators of the prior arts mentioned above, although it is possible to shift th

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