JPS6332959Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a vortex generation prevention device that prevents the generation of air suction vortices and underwater vortices generated in a pump suction water tank, and does not reduce pump performance.

FIG. 1 shows a conventional pump suction tank that is generally used. If the distance Y from the center line of the suction pipe 5 to the rear wall 1 of the tank is large, the air suction vortex "A
is likely to occur. Therefore, in order to prevent the generation of air suction vortices and reduce the amount of excavation of the pump suction water tank, the distance Y should be made small, and the critical submersion depth, which is the suction pipe immersion depth when air suction vortices start to occur, should be reduced. Sc
needs to be made smaller.

However, if the distance Y is too small,
As shown in Figure 2, the outer edge of the bell mouth and the rear wall of the tank 1
The pump performance decreases as the gap between
is generated, causing vibration and noise.

Further, depending on the pumping station, the distance Y may have to be increased due to civil engineering structure or water intake conditions. In such cases, conventionally the third
As shown in Figures a and b, a method is sometimes adopted in which a vertical plate 7 is installed across the width of the water channel on the upstream side of the suction pipe 5, but when this method is used, the flow channel is rapidly narrowed down. This causes a drop in pump performance due to fluid loss and uneven flow near the suction port.
Furthermore, depending on the conditions, an air suction vortex "A" may be generated on the upstream side of the suction pipe 5 due to the flow A shown in FIG. 3b.

In addition, as another measure when the distance Y is large, the fourth
As shown in the figure, a vertical plate 8 may be provided close to the suction pipe 5 and behind it, extending across the width direction of the water channel and reaching the bottom surface 2 of the water tank. However, in this case, if the vertical plate 8 is brought too close to the suction pipe 5, the second
Similar to the case shown in the figure, there are problems such as a decrease in pump performance and the generation of underwater vortices.

Furthermore, in order to prevent the generation of air suction vortices without degrading pump performance as much as possible, a method has been proposed in which the rear wall of the water tank near the free surface protrudes toward the suction pipe to narrow the space behind the suction pipe. (Refer to Utility Model Publication No. 39-36893).

In this method, air suction vortices do not occur directly behind the suction pipe because the gap is small, but it is not sufficient to prevent suction vortices from occurring diagonally behind and to the sides of the suction pipe. Furthermore, this method has little effect on preventing sidewall vortices. In other words, the sidewall vortex is
This occurs due to the flow near the free surface crossing the suction pipe, being reversed by the rear wall of the tank, and then heading upstream near the bottom of the tank, and the shear flow at the confluence of that flow and the flow near the suction port. Yes, but
If the rear wall of the water tank near the free surface is made to protrude toward the suction pipe side, the flow near the free surface will be reversed and it will not be possible to suppress the wraparound flow toward the upstream side.
There is almost no effect in preventing sidewall vortices. Furthermore, if the rear wall of the water tank near the free surface is made to protrude toward the suction pipe side, there is no effect of suppressing the swirling flow around the suction pipe.

In addition, in order to reduce civil engineering costs and prevent air suction vortices, it has been proposed to attach a vertical plate that reaches the side wall of the water tank or a ring-shaped member to the suction pipe itself. (See Publication No. 4590). However, with this method,
Because the flow near the free surface is blocked by a vertical plate or ring-like member before crossing the suction pipe,
The amount of flow that goes around from behind the suction pipe becomes extremely small, and the condition of the flow into the pump deteriorates. Also,
As shown in Figure 3, an upward flow occurs behind the pump, and an air suction vortex "A" may occur.Also, when using this method, the suction pipe is installed and the area of the water channel is the smallest. , Therefore, when the waterway flow velocity is high, the flow is blocked by the vertical plate or ring-shaped member, which increases the turbulence of the flow and makes it unstable.For these reasons, the pump performance may be adversely affected. Furthermore, in cases where the suction pipe is made of cast metal, such as in a mixed-flow pump, and the external shape changes greatly, it is problematic to attach a vertical plate or ring-shaped member to the suction pipe itself, and in large-diameter pumps, Normally, the pump is suspended from the floor, but if a vertical plate or ring-shaped member is attached to the suction pipe, the pump cannot be easily pulled up, making maintenance management difficult.

Furthermore, in order to prevent swirling flow and air suction vortices, we have proposed a system in which a horizontal wall is provided between the suction pipe and the rear wall of the tank near the free surface, and a vertical wall is provided between the horizontal wall and the bottom of the tank. (Refer to Utility Model Publication No. 44-6930 and Utility Model Publication No. 50-42401). However, with this method, even if swirling flow and air suction vortices can be prevented, the back of the suction pipe is completely covered by a horizontal wall and there is no free surface. Due to the vertical movement of the water level in that part due to the free surface, it is no longer possible to absorb fluctuations in the flow approaching the suction pipe. In other words, by making the back of the suction pipe a free surface, the space behind the suction pipe serves as a kind of accumulator.
If the back of the suction pipe is completely covered by a horizontal wall, it will not be able to fulfill its role, and the pulsation will become large, especially when the approaching flow velocity is high and the waves are large. In addition, the flow near the free surface that wraps around the back of the pump is completely blocked, making the flow near the suction port non-uniform and reducing pump performance.

The present invention has been made to solve the above-mentioned drawbacks of the conventional pump suction water tank vortex generation prevention device, and its purpose is to prevent not only air suction vortices but also underwater vortices and side wall vortices. It is an object of the present invention to provide a vortex generation prevention device for a pump suction tank that does not cause a decrease in pump performance, is structurally simple, and is economical.

As a result of various studies and experiments, the present inventors installed a vertical wall 9 across the width direction of the water channel between the suction pipe 5 and the rear wall 1 of the aquarium, and the lower end of the vertical wall 9 was connected to the suction pipe 5. It has been found that the above object can be well achieved by having a gap C above the lower end of the aquarium and the aquarium bottom surface 2, and forming a free surface between the aquarium and the rear wall 1 of the aquarium. This is the heading that led to this invention.

Further, in the embodiment of the present invention, if the distance between the lower end of the vertical wall 9 and the aquarium bottom surface 2 is C, and the distance between the lower end of the suction pipe 5 and the aquarium bottom surface 2 is Z, then C=1.5Z.
It is preferable to set the relationship to be 3Z.

The flow across the suction pipe 5 of the near-channel flow is separated by the vertical wall 9 into a flow near the free surface and a flow near the tank bottom. Since the flow near the free surface becomes a downward flow due to the vertical wall 9 as it approaches the suction pipe 5, the air suction vortex "A" caused by the wake vortex behind the suction pipe 5 is less likely to occur.
In addition, there is no vertical wall 9 in the suction port 6 portion of the suction pipe 5, and even if a vertical wall 9 is provided, underwater vortices "S" connecting the vertical wall 9 and the suction port 6 will be less likely to occur, and the flow near the suction port 6 will be reduced. Since it is not restricted by the vertical wall 9, the flow velocity distribution will not be uneven, and the pump performance will not deteriorate.Furthermore, the flow near the free surface crosses the suction pipe 5 and flows after the water tank. After being reversed by the wall 1, the vertical wall 9 prevents the flow from moving upstream near the tank bottom 2. Therefore, the shear flow at the confluence of the reversed flow and the flow near the suction port is weak, and a side wall vortex "L" is also generated. In addition, there is a free surface between the vertical wall 9 and the rear wall 1 of the aquarium, and the water level in the space between the vertical wall 9 and the rear wall 1 of the aquarium can freely move up and down. It plays the role of an accumulator and can absorb fluctuations in the flow approaching the suction pipe 5 to obtain a stable flow.
Furthermore, the vertical wall 9 also serves the function of preventing swirling flow.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

Figures 5a and 5b show an embodiment of the present invention, in which a vertical wall 9 is provided between the suction pipe 5 and the rear wall 1 of the tank, extending in the width direction of the waterway. The lower end is located above the lower end of the suction pipe 5, has a gap C between it and the bottom surface 2 of the aquarium, and forms a free surface between it and the rear wall 1 of the aquarium. It is appropriate to set the gap C so that the relationship C=1.5Z to 3Z is established, where Z is the distance from the bottom surface 2 of the water tank to the lower end of the suction pipe 5. Further, if the distance between the vertical wall 9 and the center of the suction pipe 5 is e, the distance between the vertical wall 9 and the rear wall 1 of the water tank is f, and D is the bell mouth diameter of the suction pipe 5, the mutual dimensions are e = approx. It is appropriate to set the relationship such that 0.5D and f>1D.

In FIG. 6, the approaching flow A between the lower end of the suction pipe 5 and the free surface 4 is separated by a vertical wall 9 into a flow A and a flow C, with the flow B being neutral. The flow A is a flow near the free surface, and this flow A becomes a downward flow due to the vertical wall 9 as it approaches the suction pipe 5, so the air suction vortex caused by the wake vortex behind the suction pipe 5 In other words, the vertical wall 9 has the function of suppressing the air suction vortex "A" by reducing the distance Y shown in FIG. Since there is a gap C between the water tank bottom 2 and the water tank bottom 2, the flow near the suction port 6 is not restricted by the vertical wall 9, so the flow velocity distribution is not uneven, and the vertical wall 9 is not restricted. Even if the vertical wall 9 is provided, there will be no deterioration in pump performance.Also, since the vertical wall 9 does not exist near the suction port 6 of the suction pipe 5, even if the vertical wall 9 is provided, the vertical plate 8 and the suction port 6 shown in FIG. Underwater vortex "S" that connects the free surface is also difficult to generate. Also, the side wall vortex "L" is the flow A near the free surface, as shown in Figure 7 a, b, and c.
The flow crosses the suction pipe 5, is reversed by the tank rear wall 1, and then heads upstream near the tank bottom 2, and is caused by the shear flow at the confluence point P of that flow and the flow B near the suction port. do. However, vertical wall 9
By providing , the flow A near the free surface is prevented from reversing and heading upstream, and therefore, the shear flow at the confluence point P of the upstream reversed flow A near the free surface and the flow B near the suction port is weak,
Sidewall vortices "L" are less likely to occur.

In addition, the vertical wall 9 is provided so as to form a free surface between it and the rear wall 1 of the water tank, so that the water level between them can freely rise and fall, acting as a kind of accumulator, and absorbing fluctuations in the flow approaching the suction pipe 5, thereby obtaining a stable flow. Providing a free surface between the vertical wall 9 and the rear wall 1 in this way is effective especially when the flow velocity of the approaching flow is high and the waves are large. Furthermore, since the water tank behind the suction pipe 5 is partitioned by the vertical wall 9, the swirling flow around the suction pipe 5 is also suppressed.

[Brief explanation of the drawing]

Figures 1 and 2 are side views showing how air suction vortices and underwater vortices are generated in a conventional pump suction water tank, and Figures 3a and b are side views of a conventional pump suction water tank equipped with means for preventing vortex generation. A plan view and a side view showing the state of generation of air suction vortices,
FIG. 4 is a side view showing how underwater vortices are generated in a conventional pump suction tank provided with a means for preventing vortex generation according to another embodiment, and FIGS. A plan view and a side view of a pump suction water tank equipped with a vortex generation prevention device; FIG. 6 is a side view showing the state of flow near a waterway in a pump suction water tank equipped with a vortex generation prevention device according to an embodiment of the present invention; FIGS. 7a, b, and c are a side view and a front view showing how sidewall vortices are generated. 1...Rear wall, 2...Bottom surface, 3...Side wall, 4...
Free surface, 5... Suction pipe, 6... Suction port, 9...
vertical wall.

Claims (1)

[Scope of Claim for Utility Model Registration] (1) A vertical wall provided across the width of the waterway between the suction pipe and the rear wall of the water tank, and the vertical wall is used to prevent the flow of water that crosses the suction pipe of the flow near the waterway. has a lower end above the lower end of the suction pipe and has a gap between it and the bottom of the tank so that the flow is separated behind the suction pipe into a flow near the free surface and a flow near the bottom of the tank, and 1. A vortex generation prevention device for a pump suction water tank, characterized in that the device is installed in the water tank so that a free surface is formed between the water tank and the rear wall of the water tank. (2) If the distance between the bottom of the vertical wall and the bottom of the tank is C, and the distance between the bottom of the suction pipe and the bottom of the tank is Z, then C
The first claim for utility model registration is characterized in that the relationship is set so that = 1.5Z to 3Z.
A vortex generation prevention device for a pump suction water tank as described in .