JP4277328B2 - Device for preventing vortex generation in pump suction tank - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a vortex generation prevention device for a pump suction water tank, and more particularly to a vortex generation prevention device for a pump suction water tank suitable for preventing the generation of a submerged vortex.
[0002]
[Prior art]
First, the prior art will be described with reference to FIGS.
6 is a schematic cross-sectional view illustrating a problem of a conventional pump suction water tank, FIG. 7 is a schematic cross-sectional view illustrating one shape of a pump suction water tank having a conventional ceiling, and FIG. 8 is a conventional water shielding wall. It is a figure which shows one shape of the pump suction water tank which has this, (a) is a schematic plan view, (b) is a schematic sectional drawing, FIG. 9 is a figure explaining the subject of the pump suction water tank which has the conventional dividing wall. (A) is a schematic plan view, (b) is a schematic cross-sectional view, FIG. 10 is a diagram for explaining the problems of a conventional pump suction tank, (a) is a schematic plan view, and (b) is a schematic plan view. It is a schematic sectional drawing.
[0003]
In FIG. 6, 1A is a pump suction water tank without a ceiling having an open channel 7 upstream, and 2 is a pump installed by opening a bell mouth 3 (suction port) in the pump suction water tank 1A. Is a vertical shaft pump in which the pump suction pipe 4 stands upright in the pump suction water tank 1A.
When the pump 2 installed with the bell mouth 3 (suction port) opened in the pump suction water tank 1A shown in FIG. 6 is operated, a vortex may be generated in the vicinity of the bell mouth 3. When a cavity is generated at the center of this vortex, it becomes a vortex called an air suction vortex 15, a submerged vortex 16, etc., and this has an adverse effect on the pump 2 such as vibration and noise.
[0004]
In addition, these vortices are more likely to occur as the flow velocity Vb in the bell mouth 3 of the pump 2 and the flow velocity Vs in the water channel or the pump suction water tank 1A increase, which hinders space saving of the pump suction water tank.
In order to prevent such vortices, conventionally, for example, various vortex prevention devices such as those shown in “Explanation Table 3.1” on page 25 of “Japan Society of Mechanical Engineers Standard JSME004-1984” published by the Japan Society of Mechanical Engineers have been used. Have been used.
[0005]
The pump suction water tank 1 shown in FIG. 7 has a structure having a ceiling 10 and a water channel that moves from the open water channel 7 to the closed water channel 6 on the upstream side. A vortex generation preventing plate 18 is provided from the bottom of the water tank to the end wall of the water tank against the vortex generated at the lower part of the pump suction pipe 4 to suppress the generation of the vortex.
In addition, when there is a bent portion in the upstream portion of the pump suction water tank 1 such as a transition from the open water passage 7 to the closed water passage 6, as shown in, for example, Japanese Utility Model Publication No. 1-30640, the closed water passage shown in FIG. 6 is provided with a water-impervious wall 19 orthogonal to the water channel at the frontmost part of the inlet side, and the ratio of the diameter of the bell mouth 3 of the pump 2 to the distance from the bell mouth 3 to the impermeable wall 19 is 1.1 to 2.9 There have been means for preventing the generation of underwater vortices caused by the drift in the width direction of the water channel caused by the bent portion.
[0006]
[Problems to be solved by the invention]
In the equipment shown in FIG. 7, when a strong flow bias occurs in the width direction of the water channel upstream of the pump 2, the swirl of the flow in the lower part of the pump suction pipe 4 becomes very strong, and thus a vortex is locally generated. In some cases, the vortex generation preventing plate 18 cannot obtain the expected vortex prevention effect.
[0007]
Originally, the shapes of the pump suction water tank and the suction water channel are greatly influenced by the location conditions of the drainage station and the plant, for example, and it is rare that the shape can be determined so that the flow of the water channel becomes ideal. In the prior art shown in FIG. 8, when the closed channel 6 of the channel for introducing water into the pump suction tank 1 is long, that is, the transition from the open channel 7 to the closed channel 6 and the bell mouth 3 (pump suction port). ) Is more than 2.9 times the diameter of the bell mouth 3, the effect of the vortex generation preventing plate 18 cannot be expected. Needless to say, there is no effect when there is a bent portion in the closed channel 6.
[0008]
Furthermore, as in the prior art shown in FIG. 9, the water channel for introducing water into the pump suction tank 1 is divided into two or more by the dividing wall 9 or the like, and the average flow velocity of each water channel varies depending on the upstream conditions. In this case, even if the water shielding wall 19 is provided, the average flow velocity of each water channel hardly changes and flows into the pump suction water tank 1 while maintaining the flow velocity difference. As a result, strong swirling in the vicinity of the pump suction pipe 4 The air suction vortex and the underwater vortex 16 are generated from the flow, and the vortex prevention effect cannot be expected.
[0009]
Furthermore, when the cross-sectional shape seen from the side surface of the impermeable wall 19 is simply rectangular and the distance between the pump 2 and the impermeable wall 19 is short, the impermeable flow from the upstream open channel 7 as shown in FIG. A part of the flow stagnates in the vicinity of the wall 19, and a swirling flow 17 based on a shear flow due to a difference in flow velocity is generated between the stagnation slow flow velocity and the fast flow velocity, which becomes an air suction vortex and enters the pump 2. May be inhaled. These things hindered further pump-suction water tanks, space savings in waterways, and higher flow rates.
[0010]
The present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is to prevent the generation of vortices in the vicinity of the pump in a pump suction water tank with a ceiling, and to operate the pump stably. An object of the present invention is to provide an apparatus for preventing vortex generation of a pump suction water tank that can be maintained and can further reduce the size and speed of the pump suction water tank and reduce the construction cost of the entire facility.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the first means of the vortex generation prevention device for a pump suction water tank according to the present invention is a pump suction water tank having a ceiling, and a suction port is installed in the pump suction water tank. A pump, a water channel for introducing water into the pump suction water tank after the transition from the open water channel to the closed water channel upstream of the pump suction water tank, and a transition from the upstream of the open water channel to the closed water channel In the pump suction water tank facility provided with a dividing wall that divides the closed water channel into two or more, supporting the ceiling of the closed water channel existing in the vicinity of the pump suction water tank, and on the upstream side of the pump , A structure that closes a part of the water channel is provided in the width direction of the water channel from the ceiling of the pump suction water tank in the section from the pump to the rear edge of the dividing wall .
[0012]
In order to achieve the above object, the second means of the vortex generation preventing device for a pump suction water tank according to the present invention is characterized in that, in the first means, the structure that blocks a part of the water channel is upstream of the structure. The shape is inclined to the upstream side from the lower end point of the structure.
[0013]
A third means for achieving the above object is characterized in that, in the second means, the structure that blocks a part of the water channel has an inclination angle of 25 ° to 60 ° on the upstream side of the structure. .
[0014]
The fourth means for achieving the above object is that, in any one of the second and third means, the structure for blocking a part of the water channel is such that the upstream shape of the structure is based on the lower end point of the structure. In addition, the upper surface of the water channel is squeezed from the upstream of the water tank to the structure by forming a tapered surface at the joint with the side wall of the pump suction water tank.
[0015]
A fifth means for achieving the above object is that, in the fourth means, the taper shape of the joint portion between the structure blocking a part of the water channel and the side wall of the pump suction water tank is the taper shape and the side wall of the pump suction water tank. And the angle between the top and the bottom of the water channel is 15 ° to 45 °.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to FIGS.
[Embodiment 1]
1A and 1B are views of a vortex generation preventing device for a pump suction water tank according to a first embodiment of the present invention, wherein FIG. 1A is a schematic plan view and FIG. 1B is a schematic cross-sectional view. In the figure, the same reference numerals as those in FIG.
[0017]
In FIG. 1, 1 is a pump suction water tank having a ceiling 10, and 2 is a pump installed by opening a bell mouth 3 (suction port) in the pump suction water tank 1. The pump 2 is, for example, a pump suction pipe Reference numeral 4 denotes a vertical shaft pump which stands upright in the pump suction water tank 1. Reference numeral 5 denotes an impeller provided in the pump suction pipe 4. 6 is a closed channel having a ceiling 10, and 7 is an open channel having an open top.
[0018]
8 is a ceiling-side protruding structure, and this ceiling-side protruding structure 8 is a structure that closes the upper part of the water channel from the pump suction water tank 1 near the pump upstream of the pump 2 or the ceiling 10 of the closed channel 6. , Provided in the width direction of the water channel. The ceiling-side protruding structure 8 shown in FIG. 1 has a rectangular cross section protruding from the ceiling 10.
[0019]
By providing the ceiling-side protruding structure 8 in this way, even if a drift occurs in the water channel due to the shape of the water channel upstream of the pump suction water tank 1 or other factors, the water channel rapidly contracts at the portion of the ceiling-side protruding structure 8. The drift is rectified immediately before the pump 2 by the contraction effect. As a result, the swirling flow in the lower part of the pump suction pipe 4 is suppressed, and the generation of vortices can be prevented even if the average flow velocity of the water channel increases more than before.
In addition, when the distance of the closed water channel 6 upstream of the pump suction water tank 1 is long, the ceiling-side protruding structure 8 is provided in the vicinity of the upstream side of the pump 2 even if there is a factor causing a drift such as a bent portion in the closed water channel 6. By providing, the vortex prevention effect can be exhibited.
[0020]
[Embodiment 2]
FIGS. 2A and 2B are views of a vortex generation preventing device for a pump suction water tank according to a second embodiment of the present invention, wherein FIG. 2A is a schematic plan view and FIG. 2B is a schematic cross-sectional view. In the figure, the same reference numerals as those in FIG. 9 denote the same parts as in the prior art.
In the facility shown in FIG. 2, a dividing wall 9 is provided upstream of the pump 2. This dividing wall 9 exists from the transition part from the open water channel 7 to the closed water channel 6 to the pump suction water tank 1 vicinity, and divides the said closed water channel 6 into two or more.
[0021]
In such a pump suction water tank 1, in this embodiment, in the pump suction water tank 1 or the closed channel 6, the section from the pump suction pipe 4 to the terminal portion of the dividing wall 9 partially closes the water channel from the ceiling 10. The protruding structure 8 was provided in the width direction of the water channel. In many cases, the dividing wall 9 is provided for the purpose of supporting the ceiling 10 of the closed channel 6, and a sluice is provided on the upstream side of the two divided channels to control the flow rate of the channel or for the purpose of inspection or the like. There may be cases where one of the sluices is closed while the pump is running.
[0022]
In that case, there is a difference in the flow rates of the divided two water channels, and the average flow velocity of the two water channels is different from V ₁ and V _2, and as a result, the confluence of the two water channels immediately before the pump 2 is large in the water channel width direction. A drift occurs, and the presence of a strong swirling flow is promoted at the lower part of the pump suction pipe 4 so that a vortex is easily generated. However, even in such a case, by providing the ceiling side protruding structure 8 as shown in FIG. 2, the uneven flow caused by the flow rate difference between the two water channels is caused immediately before the pump 2 by the contraction effect by the water channel rapid contraction. Rectified. As a result, the strength of the swirling flow in the lower part of the pump suction pipe 4 is suppressed, and the occurrence of vortices can be prevented even if the average flow velocities V ₁ and V _{2 of} the two water channels increase more than before.
[0023]
[Embodiment 3]
Drawing 3 is a figure of the eddy generation prevention device of the pump suction cistern showing the 3rd embodiment of the present invention, (a) is a schematic plan view and (b) is a schematic sectional view. In the figure, the same reference numerals as those in FIG. 2 denote the same parts as in the previous embodiment.
The installation shown in FIG. 3 differs from the embodiment shown in FIG. 2 in that the ceiling-side protruding structure 8 in FIG. 2 has a rectangular cross-section protruding from the ceiling 10, whereas the ceiling side shown in FIG. The protruding structure 21 has an inclined surface 21a that is inclined upstream from the lower end point of the structure.
[0024]
By doing so, the cross-sectional change of the water channel from the upstream of the water channel to the lower end point of the ceiling-side protruding structure 21 becomes continuous, and the stagnation of the flow in the vicinity of the upstream of the ceiling-side protruding structure 21 is reduced. Even when there is a drift, vortices such as the swirl flow 17 shown in FIG. 10 can be prevented. Moreover, since the channel cross-sectional change is continuous, the resistance of the water channel is reduced, and the load required for the operation of the pump 2 can be reduced. Here, the inclination angle θ1 of the inclined surface 21a can be maximized by setting the inclination angle θ1 to 25 ° to 60 °. When θ1 is less than 25 °, the inclination is steep and the effect of forming the inclined surface 21a is poor. In addition, when the inclination of θ1 exceeds 25 °, the effect of making the flow uniform with respect to the drift is lost.
[0025]
FIG. 4 is a diagram of the vortex generation limit channel flow velocity for explaining the effect in each embodiment of the present invention.
The diagram of FIG. 4 shows the results of an experiment conducted on the vortex generation preventing effect of the ceiling-side protruding structure in the case where a drift occurs upstream in the channel width direction in order to support the above vortex generation preventing effect. The positional relationship between the ceiling-side protruding structure and the pump is all the same. A vortex generation preventing plate 18 is provided at the lower part of the pump suction pipe 4.
[0026]
In the diagram of FIG. 4, the horizontal axis represents the ratio V1: V2 of the drift of the two channels in the width direction of the channel, the vertical axis represents the critical channel flow velocity Vs at which the vortex is generated, and the solid line represents the ceiling-side protruding structure. In the case where there is not, the large broken line indicates the limit channel flow velocity Vs when the ceiling-side protruding structure (with a rectangular cross section) is present, and the alternate long and short dash line indicates the limit channel flow velocity Vs when there is the ceiling-side protruding structure (with inclination).
The diagram of FIG. 4 shows that underwater vortices are generated when the flow velocity is larger than each line.
[0027]
As the ratio V1: V2 of the drift in the width direction of the upstream water channel increases, the critical water channel flow velocity Vs tends to decrease, and a submerged vortex tends to occur. As apparent from FIG. 4, when there is no ceiling-side protruding structure, when a rectangular ceiling-side protruding structure is provided, and when an inclined surface is provided on the upstream side of the ceiling-side protruding structure, The vortex generation limit water channel flow velocity Vs is improved, and it can be seen that vortices are hardly generated due to the presence of the ceiling-side protruding structure. In addition, the inclination angle θ1 of the ceiling-side protruding structure was not significantly different in the range of 25 ° to 60 °.
[0028]
From the above experimental results, it becomes possible to increase the flow velocity of the pump suction water tank and water channel and to save space more than before, and the construction cost can be reduced as a whole pump system.
[0029]
[Embodiment 4]
5A and 5B are diagrams of a vortex generation preventing device for a pump suction water tank according to a fourth embodiment of the present invention. FIG. 5A is a schematic plan view, and FIG. 5B is a schematic cross-sectional view. In the figure, the same reference numerals as those in FIG. 3 denote the same parts as in the previous embodiment.
In the embodiment shown in FIG. 5, the ceiling-side protruding structure 22 has an inclined surface 22 a that is inclined upstream from the lower end point of the structure, and the joint with the side wall of the pump suction water tank 1 is a tapered surface. 23 is formed, and the upper channel of the water channel is narrowed from the upstream of the water channel to the ceiling-side protruding structure 22.
[0030]
It is known that vortices generated near the upstream side of the ceiling-side protruding structure 22 are mostly generated near the side wall of the pump suction water tank 1 regardless of the presence or absence of drift. This is because the stagnation of the flow is likely to occur at the corner between the ceiling-side protruding structure 22 and the side wall, and the vortex is generated by the shear flow due to the flow velocity difference. Therefore, by forming the corner portion with the side wall of the ceiling-side protruding structure 22 as a tapered surface 23, it is possible to suppress the occurrence of stagnation of the flow generated in the vicinity of the water channel side wall near the upstream side of the ceiling-side protruding structure 22. The generation of vortices can be prevented.
[0031]
The taper shape of the corner portion between the ceiling-side protruding structure 22 and the side wall is the same in that the vortex suppressing effect is improved regardless of whether the cross-sectional shape of the ceiling-side protruding structure is rectangular or an inclination angle is provided. . Furthermore, when the taper angle θ2 of the taper-shaped surface 23 of the joint with the side wall of the ceiling-side protruding structure 22 is 15 ° to 45 ° when viewed from the upper part of the water channel, an optimal vortex generation preventing effect is obtained. If θ2 is less than 15 °, the inclination is gentle and the effect of forming the tapered surface 23 is poor. In addition, if the angle of inclination θ2 exceeds 45 °, a stagnation of the flow tends to occur at the corner between the ceiling-side protruding structure 22 and the side wall, and the effect of suppressing vortex generation is lost.
[0032]
【The invention's effect】
As described above in detail, according to the present invention, in a pump suction water tank with a ceiling, the generation of vortex in the vicinity of the pump is prevented, stable operation of the pump is maintained, and the pump suction water tank is further miniaturized. In addition, it is possible to provide a vortex generation prevention device for a pump suction water tank that can increase the flow velocity and reduce the construction cost of the entire facility.
[Brief description of the drawings]
1A and 1B are diagrams of a vortex generation preventing device for a pump suction water tank according to a first embodiment of the present invention, wherein FIG. 1A is a schematic plan view and FIG. 1B is a schematic cross-sectional view.
FIGS. 2A and 2B are diagrams of a vortex generation preventing device for a pump suction water tank according to a second embodiment of the present invention, in which FIG. 2A is a schematic plan view and FIG. 2B is a schematic cross-sectional view.
FIGS. 3A and 3B are diagrams of a vortex generation preventing device for a pump suction water tank according to a third embodiment of the present invention, wherein FIG. 3A is a schematic plan view, and FIG. 3B is a schematic cross-sectional view.
FIG. 4 is a diagram of the vortex generation limit channel flow velocity for explaining the effect in each embodiment of the present invention.
FIGS. 5A and 5B are views of a vortex generation preventing device for a pump suction water tank according to a fourth embodiment of the present invention, wherein FIG. 5A is a schematic plan view and FIG. 5B is a schematic cross-sectional view.
FIG. 6 is a schematic cross-sectional view for explaining a problem of a conventional pump suction water tank.
FIG. 7 is a schematic cross-sectional view showing one shape of a conventional pump suction water tank having a ceiling.
8A and 8B are views showing a shape of a conventional pump suction water tank having a water-impervious wall, wherein FIG. 8A is a schematic plan view and FIG. 8B is a schematic cross-sectional view.
FIGS. 9A and 9B are diagrams for explaining a problem of a pump suction water tank having a conventional dividing wall, where FIG. 9A is a schematic plan view and FIG. 9B is a schematic cross-sectional view.
10A and 10B are diagrams for explaining the problems of a conventional pump suction water tank, in which FIG. 10A is a schematic plan view, and FIG. 10B is a schematic cross-sectional view.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Pump suction water tank, 2 ... Pump, 3 ... Bell mouth, 4 ... Pump suction pipe, 6 ... Closed channel, 7 ... Open channel, 8, 21, 22 ... Ceiling side protruding structure, 9 ... Dividing wall, 10 ... Ceiling, 21a, 22a ... inclined surface, 23 ... tapered surface.

Claims (5)

A pump suction water tank having a ceiling, a pump installed with a suction port opened in the pump suction water tank, and the pump suction water tank after moving from an open channel to a closed water channel having a ceiling upstream of the pump suction water tank A water channel that introduces water into the water channel, a transition portion from the upstream of the open water channel to the closed water channel having a ceiling and the vicinity of the pump suction water tank to support the ceiling of the closed water channel, the closed water channel In the pump suction water tank equipment provided with a dividing wall that divides the
A structure for closing a part of the water channel is provided in the width direction of the water channel from the ceiling of the pump suction water tank in a section from the pump to the rear edge of the dividing wall on the upstream side of the pump. The vortex generation prevention device for the pump suction water tank. The pump suction water tank vortex according to claim 1, wherein the structure that blocks a part of the water channel has an upstream shape of the structure that is inclined upstream from a lower end point of the structure. Occurrence prevention device. The apparatus for preventing vortex generation in a pump suction water tank according to claim 2 , wherein the structure that blocks a part of the water channel has an inclination angle of 25 to 60 degrees on the upstream side of the structure. The structure that closes a part of the water channel has an inclined surface in which the upstream shape of the structure is inclined upstream from the lower end point of the structure, and the junction with the side wall of the pump suction tank is tapered The vortex generation preventing device for a pump suction water tank according to claim 2 or 3, wherein a surface is formed and the upper part of the water channel is narrowed from the upstream of the water tank to the structure . The taper shape of the joint part between the structure that closes a part of the water channel and the side wall of the pump suction water tank is such that the angle between the taper shape and the side wall of the pump suction water tank is 15 ° to 45 ° when viewed from the upper part of the water channel. The vortex generation preventing apparatus for a pump suction water tank according to claim 4 .

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