Rotary kinetic fluid motors or pumps – Working fluid passage or distributing means associated with... – Casing with axial flow runner
Reexamination Certificate
2001-03-20
2003-04-01
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Working fluid passage or distributing means associated with...
Casing with axial flow runner
C415S119000, C415S173100, C415S914000
Reexamination Certificate
active
06540482
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a turbo-machine, and in particular to a turbo-type hydro machine being able to prevent flow instability from occurring within fluid (in particular, a water including freshwater and seawater), which flows in an inside thereof, by suppressing rotation of an impeller and stalls in rotation thereof due to re-circulation flow at an inlet of the impeller, irrespective of the types and fluid thereof.
In more detail, the turbo-type machine according to the present invention has an impeller of non-voluminous type, and in particular, it relates to a pump or a pump turbine (a turbo-type pump turbine), in which the fluid flowing therein is a liquid (such as, a water including fresh water and seawater). Namely, according to the present invention, it is possible to prevent the flow instability from occurring within the fluid, by suppressing pre-swirl in main flow of the re-circulation at an inlet of the impeller and/or stalls in rotation of the impeller, and further to reduce generation of cavitations in the impeller, which accompanies increases in vibrations and noises therewith, therefore being suitable for a mixed-flow pump, in particular, which is applicable to a re-circulation water pump, etc., to be used as a drainage pump in a city, or used in a thermal power plant or a nuclear power plant, etc.
FIG. 13
shows a typical characteristic curve between head and flow rate in the turbo-machine of the conventional art, including the mixed-flow pump shown in
FIG. 14
therein, where the horizontal axis is a parameter indicative of a flow rate, while the vertical axis a parameter indicative of the head. Namely, the head falls down in a 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., the characteristic of uprising at the right-hand side). And, when the flow rate rises up further, exceeding over the region of uprising at the right-hand side, then the head falls down again. In a case where the turbo-machine is operated at the flow rate with 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, uprising at the right-hand side on the head-flow rate curve in the conventional turbo-machine mentioned above, is caused since, although the re-circulation comes out at an outer edge on the inlet of the impeller when the flow rate comes to be low in the fluid flowing through the turbo-machine, but at this instance, a flow passage or a channel for the liquid flowing within the turbo-machine is narrowed, thereby generating a swirl in the liquid (see FIG.
14
).
For improving the characteristic of such uprising at the right-hand side in the conventional turbo-machine, as is disclosed in, for example “A New Passive Device to Suppress Several Instabilities in Turbomachines by Use of J-Groove” (Turbomachine Association, published Nov. 1, 1998) presented in a Japan-US Science Cooperation Business Seminar held on Nov. 1 to 6, 1998, it is already proposed by Mr. Junichi KUROKAWA, who is an inventor of the resent invention, and is already known, to provide a plural number of grooves in an axial direction of the pump (i.e., the direction of pressure gradient in fluid) on an inner surface of a casing of the mixed-flow pump.
In the turbo-machine according to the conventional art mentioned above, an idea of providing the grooves in the axial direction of the pump (i.e., the direction of pressure gradient in fluid) on the inner surface of the casing is adopted, for improving the characteristic of uprising at the right-hand side in the turbo-machine, however according to the present inventors, it is acknowledged there sometimes occurs a case where the following problems are caused due to the cavitations generated in the casing with such the idea of providing the grooves formed on the inner surface of the casing.
Namely, the cavitations that comes up to the problem is a phenomenon, where a large number of bubbles occur due to evaporation within the liquid when the pressure of the liquid flowing within the pump is decreased down in the vicinity of the saturated vapor pressure, for example, and those bubbles generated flow within the pump, and/or are collapsed accompanying with recovery of the pressure within the pump. And, such the generation of the cavitations gives damages upon wall surfaces of the impeller, as well as the casing, and it may also cause harmful effects, such as, increase in the vibrations and/or noises, and decrease in the performance thereof, as well.
Also,
FIG. 15
shows an experimental result of vibration acceleration, as one representative example of the vibrations and/or noises due to influences of the cavitations, wherein the horizontal axis indicates the flow rate without dimension while the vertical axis the vibration acceleration without dimension thereof. In particular, black circles (&Circlesolid;) in the figure show a flow rate-vibration acceleration curve in a condition where the pump is high in NPSH, in which no groove is formed on the casing thereof, white circles (◯) in a condition where the pump is low in NPSH, in which no groove is formed on the casing thereof, black triangles (▴) in a condition where the pump is high in NPSH, in which the grooves are formed on the casing in the direction of pressure gradient, and white triangles (&Dgr;) in a condition where the pump is low in NPSH, in which the grooves are formed on the casing in the direction of pressure gradient, respectively. Herein, the NPSH means an effective suction head, and it indicates how much higher a total pressure, which the liquid upon a standard surface of the impeller has, than the saturated vapor pressure of that liquid at that temperature. Namely, the lower the NPSH, the nearer to the saturated vapor pressure, i.e., it comes to the condition where the cavitations can easily occur therein.
As shown in the
FIG. 15
, in the pump in which no groove is formed on the casing thereof, comparing the black circles (&Circlesolid;) of high NPSH to the white circles (◯) of low NPSH, the white circles are as about 1.3 times large as the black ones, at the maximum in the vibrations thereof between &phgr;=0.6-1.0, but it does not matter in particular. However, with the black triangles (▴) and white triangles (&Dgr;) indicating the characteristic curves of the pumps, in which the grooves are formed on the inner surface of the casing in the direction of pressure gradient (i.e., the axial direction), as is apparent from the figure, when comparing the black triangles of high NPSH to the white triangles of low NPSH, the white triangles of low in the NPSH of the pump comes to be about as 2.1 times large as the black ones, at the maximum in the vibration thereof between &phgr;=0.6-1.0, and there can be sometimes found cases where the vibrations and/or noises are increased extraordinarily.
A reason of this can be explained as below, upon the basis of an observation of the condition in generating the cavitations within the pump, and an analysis of turbulences in the flow within the pump in a case where no such the cavitations occurs.
Namely, with the impeller of a small outer diameter for aiming at small-sizing of the pump, a load upon a blade is large, therefore a pressure difference between a negative pressure surface and a pressure surface of the blade comes to be large, and in a case where the NPSH is low, the cavitations
4
occurs in an aperture or gap
3
between the blades
122
of the impeller and the casing, as shown in
FIGS. 16 and 17
. However, the
FIG. 16
shows a view of the inner surface of the casing, on which the grooves
124
are formed, being expanded schematically, and the
FIG. 17
a cross-section view of the blade of the impeller, being cut by a horizontal cross-section perpendicular to a pump axis thereof. The cavitations
4
occurring in this gap
3
Irie Kouichi
Kurokawa Junichi
Okamura Tomoyoshi
Sudo Sumio
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