JP3124517B2 - High specific speed mixed flow pump - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a high-performance engine in which surging does not occur and remarkable fluctuations and increases in shaft power are suppressed even in an operation range in which the discharge rate is smaller than a specified discharge rate. It relates to a mixed flow pump having a specific speed.

[0002]

2. Description of the Related Art In general, a high-head pump has a low specific speed, and a low-head pump has a high specific speed, and a pump of an optimum type is adopted according to use conditions such as a flow rate and a total head. However, in recent years, in order to reduce the cost of pump equipment, it has been demanded to use a pump having a large specific speed at a high head and to reduce the size of the pump. Therefore, researches on using a mixed flow pump having a high specific velocity Ns of 1000 or more at a high head have been actively conducted.

FIG. 6 shows an example of a conventional mixed flow pump having a high specific speed.
This will be described with reference to FIG. FIG. 6 is a sectional view of a main part of a conventional high specific speed mixed flow pump. FIG. 7 is an external perspective view of the impeller of the conventional high specific speed mixed flow pump shown in FIG. FIG. 8 is a pump characteristic diagram of the mixed flow pump having the high specific speed shown in FIG. FIG. 9 is a diagram showing the shape of the impeller blades of the conventional high specific speed mixed flow pump on a meridional section and explaining the possibility that surging or the like may occur in an operation region where the discharge amount is small.

First, the structure of a conventional high specific speed mixed flow pump will be described with reference to FIG. A main shaft 14 is supported on the inner casing 10 via a bearing 12 so as to be rotatable around the axis. A hub 16 is fixed to the tip of the main shaft 14, and a plurality of impeller blades 18 are provided on the outer peripheral wall of the hub 16. The hub 16 and the impeller blades 18 form an impeller. An outer casing 20 is disposed coaxially with the inner casing 10.
And a plurality of guide vanes 22, 22
Are provided, and both are integrated. Further, a suction casing 24 is connected to the tip of the outer casing 20 around the outer periphery of the rotation trajectory of the outer peripheral edge of the impeller blades 18.

In an example of a mixed flow pump having a specific speed Ns of 1250, the hub ratio D1 / D2 is about 0.54,
On the meridional section, the angle θ formed between the main shaft 14 and a straight line passing through the tip-side outlet end and the hub-side outlet end of the impeller blades 18, 18,... Is about 48 degrees, and the hub-side inlet of the impeller blades 18, 18,. Angle δ between the straight line passing through the end and the outlet end on the hub side and the spindle 14
(In other words, the angle between the outer peripheral wall of the hub 16 and the main shaft 14) is about 30 degrees. Here, D1 is the impeller blade 1
8, 18... Are the outer diameters of the outlet ends on the hub side, and D2 is the outer diameter of the outlet end on the chip side.

Therefore, as shown in FIG. 7, the shape of the conventional impeller of the mixed flow pump having a relatively large specific speed Ns is such that the hub 16 has a sharp conical shape with a relatively small apex angle. The impeller blades 18, 18 projecting from the outer peripheral wall are provided.
Is provided so that the petals open widely as a whole. Conventionally, it is considered that the loss increases when the direction of the flow of the meridian at the exit of the impeller is greatly changed with respect to the flow in the axial direction at the suction side of the impeller, and the hub of the impeller blades 18, 18,. The angle δ between a straight line passing through the side entrance end and the hub side exit end and the main shaft 14 was set to 30 degrees or less.

[0007]

When such a conventional mixed flow pump having a high specific speed is operated with the discharge amount reduced from the specified discharge amount, first, as shown in FIG. , And may exceed the limit of the driving machine and damage the driving machine. It is to be noted that providing a margin for the shaft power of the drive unit is inevitably expensive for the drive unit, and is not a practical improvement measure. Further, when the discharge amount is reduced, the characteristics of the entire head partially rise rightward, so-called surging occurs, and stable operation cannot be obtained. And further, near the deadline,
Shaft power is greatly increased.

In operation at the specified discharge rate, the fluid flows uniformly in the Meridian direction as shown by the solid arrow in FIG. This creates a radial pressure gradient commensurate with the centrifugal force due to the circumferential velocity that the fluid receives within the impeller, and the fluid flows in the Meridian direction and does not move in the radial direction in particular because the pressure gradient and the centrifugal force are balanced. . However, when the discharge amount decreases, this balance is lost, and the centrifugal force becomes larger than the radial pressure gradient, so that the fluid moves to the tip side, and the pressure near the tip of the impeller outlet side is increased. And Meridian speed increases. As a result, the pressure gradient of the flow from the impeller suction side to the discharge side increases along with the suction casing 24 outside the impeller, and the flow is separated on the casing close to the impeller outlet end, thereby increasing the loss. I do. Further, when the discharge amount is reduced, a flow is generated such that the fluid moves obliquely from the hub side to the tip side in the impeller in the meridian direction, as shown by a broken arrow in FIG. Backflow occurs at the end, and further backflow occurs near the impeller suction side tip. As a result, the loss increases and the shaft power also increases.

As described above, in the conventional mixed flow pump having a high specific speed, it is difficult to operate with a discharge amount smaller than a specified discharge amount. Was inappropriate.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional high specific speed mixed flow pump as described above, and suppresses the occurrence of surging by suppressing the flow in the radial direction of the impeller. It is an object of the present invention to provide a mixed flow pump having a high specific speed.

[0011]

In order to achieve the above object, a high specific speed mixed flow pump according to the present invention has a straight line passing through a tip end end and a hub end end of an impeller blade on a meridional section. The angle between the main shaft of the impeller and the main shaft is 40 degrees or less, the angle between the straight line passing through the hub-side inlet end and the hub-side outlet end of the impeller blade and the main shaft is 30 degrees or more, and the hub ratio of the impeller outlet is It is configured as 0.6 or more.

It is also possible to configure the specific speed Ns to be 1150 or more.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a sectional view of a main portion of an embodiment of a high specific speed mixed flow pump according to the present invention. FIG.
FIG. 2 is an external perspective view of an impeller of the high specific speed mixed flow pump of the present invention shown in FIG. 1. FIG. 3 is a diagram showing the shape of the impeller blades of the high specific velocity mixed flow pump shown in FIG. 1 on a meridional section. FIG. 4 is a pump characteristic diagram of the high specific speed mixed flow pump shown in FIG. FIG. 5 fixes the dimensions of the impeller outlet side,
It is a figure which shows the ratio of the required effective suction head when the angle which the straight line which passes through the hub-side entrance end and the hub-side exit end of an impeller blade makes with the main shaft is reduced based on 52 degrees. 1 and 2, the same members as those in FIGS. 6 and 7 are denoted by the same reference numerals, and redundant description will be omitted.

1 and 2, FIG. 6 and FIG.
Are basically the same as the configuration of the mixed flow pump having the high specific speed shown in FIG. 1, but the shapes of the hub 16 and the impeller blades 18, 18,... First, in a mixed flow pump having a high specific speed Ns of 1365, the hub ratio D1 / D2 is set to 0.63, and the impeller blade 1
The angle θ between the main shaft 14 and a straight line passing through the tip-side outlet end and the hub-side outlet end of 8, 18... Is 35 degrees, and the impeller blade 1
The angle δ between the main shaft 14 and a straight line passing through the hub-side inlet end and the hub-side outlet end of 8, 18,... (In other words, the angle between the outer peripheral wall of the hub 16 and the main shaft 14) is 52 degrees. Here, D1 is the outer diameter of the hub-side outlet end of the impeller blades 18, 18,.... In the description of the embodiment of the present invention, the specific speed Ns is represented by Expression 1.

(Equation 1)

Therefore, as shown in FIG. 2, the shape of the impeller of the mixed flow pump having a high specific speed according to the present invention is such that the hub 16 has a flat and low conical shape having a relatively large apex angle, and has an outer peripheral wall. The protruding impeller blades 18, 18,... Are provided so that the petals as a whole are narrowed toward the upstream side and closed. By comparing FIG. 2 showing the impeller of the present invention with FIG. 7 showing the conventional impeller, the difference in the shape will be apparent. And
The shape of the hub 16 of the present invention greatly changes the flow in the meridian direction on the exit side of the impeller with respect to the flow in the axial direction on the suction side of the impeller, which is contrary to conventional common sense. .

The hub 16 and the impeller blades 18, 18,...
The reason why the above-described shape is adopted will be described below. In the conventional high specific speed mixed flow pump, when the discharge amount is smaller than the specified discharge amount, the centrifugal force and the head acting on the fluid at the tip-side outlet end and the hub-side outlet end of the impeller blades 18, 18,... Due to the large difference, surging or the like occurs. Therefore, in order to improve this, it is desirable to reduce the difference between the centrifugal force and the lift acting on the fluid at the tip-side outlet end and the hub-side outlet end of the impeller blades 18, 18,. For this purpose, first, the impeller blades 18,
18, the diameter D2 of the outlet end on the tip side and the diameter D of the outlet end on the hub side
1 and the hub ratio D1 / D2 is increased. And if the hub ratio is simply increased, the impeller blades 18,
And the required discharge amount cannot be secured. Therefore, the angle θ between the straight line passing through the tip-side outlet end and the hub-side outlet end of the impeller blades 18 on the meridional section and the main shaft 14 may be reduced. Is smaller, the angle φ between the straight line passing through the tip-side outlet end and the hub-side outlet end of the impeller blades 18 on the meridional section and the outer peripheral wall of the hub 16 becomes smaller. It is known that, when the angle φ becomes small, the flow becomes uneven and unstable near the outlet end of the impeller blades 18, 18. Therefore, in order to increase the angle φ, the angle δ between the main shaft 14 and a straight line passing through the hub-side entrance end and the hub-side exit end of the impeller blades 18 on the meridional section (that is, the outer peripheral wall of the hub 16) (The angle between the main shaft 14 and the main shaft 14) needs to be increased.

From this viewpoint, the specific speed Ns is 1365
Using an impeller set so that the angle θ is 35 degrees, the hub ratio D1 / D2 is 0.63, and the angle δ is 52 degrees,
When the performance test of the high specific speed mixed flow pump of the present invention was performed with the rotation speed of the main shaft 14 set to 1420 rpm, FIG.
The pump performance as shown in the figure was obtained. As is clear from FIG. 4, even in the operation region where the discharge amount is smaller than the specified discharge amount, there is no portion that rises partially to the right in the entire head, and there is no possibility of surging. Also, it was confirmed that the change in the shaft power due to the change in the discharge amount was smaller than that of the conventional high specific speed. The specific speed Ns of the conventional high specific speed mixed flow pump to be compared is 1250, whereas the specific speed Ns of the high specific speed mixed flow pump of the present invention is 1365. Significant improvements in pump characteristics have been made under more severe conditions.

Further, assuming that the specific speed Ns is 1150, the positions of the arithmetic mean diameter Dm on the outlet side of the impeller blades 18, 18,...
, And an impeller blade 18 as an example of an average mixed flow pump having exit angles of 25 degrees and 52 degrees and five blades, respectively.
The flow pattern at the position of the arithmetic mean diameter Dm on the outlet side and the outer peripheral diameter D1 at the outlet end on the hub side of the hub ratio D1
/ D2 and the angle θ are variously changed, and the flow is calculated using the energy equation and the force balance equation.
The effects of 1 / D2 and the angle θ were examined. As a result, the hub ratio D1
/ D2 is 0.6 and the angle θ is 40 degrees, the meridian speed ratio and the total head ratio at the position of the hub-side exit end D1 and the arithmetic average diameter Dm are 0.8: 1 and 0.9: 1. became.
The greater the Meridian speed ratio and the total head ratio, the less surging occurs. Therefore, in order to make the Meridian speed ratio and the total head ratio equal to or larger than the above, the angle θ is equal to or less than 40 degrees and the hub ratio D1 / D2 is set to 0.
Must be at least 6.

Further, in order to make the flow at the outlet of the impeller uniform and stable, the impeller blade 1
The angle δ between the straight line passing through the hub-side inlet end and the hub-side outlet end and the main shaft 14 (ie, the angle formed between the outer peripheral wall of the hub 16 and the main shaft 14) is examined from the viewpoint of cavitation performance. added. In the high specific speed mixed flow pump of the present invention used in the pump performance experiment, the angle δ between the outer peripheral wall of the hub 16 and the main shaft 14 was maintained while D1 was kept constant without changing the shape of the impeller other than the hub 16. The required effective suction head (NPSH) was calculated by changing the value to 52 degrees or smaller. Then, when the ratio to the required effective suction head at another angle δ was determined based on the required effective suction head having an angle δ of 52 degrees, the relationship shown in FIG. 5 was found. FIG.
As shown in the above, when the angle δ is 30 degrees and 25 degrees, they are 1.11 and 1.16, respectively. In the high specific speed operation region, the cavitation performance becomes more severe and the required effective suction head increase by 10% is considered to be the limit of the cavitation performance reduction. It is necessary to be at least degree.
When the angle δ was 25 degrees, it became clear that the flow at the exit of the impeller might not be stable.

In the above embodiment, the impeller blades 18,
The number of 18 ... is 4 as is clear from FIG.
The present invention is not limited to this, and may be three or more as in the conventional example.

[0021]

As described above, since the high specific speed mixed flow pump according to the present invention is constituted, the following special effects can be obtained.

In the mixed flow pump having a high specific speed according to the present invention, even in an operation region where the discharge amount is smaller than the specified discharge amount, there is no surging and a remarkable fluctuation of the shaft power, and the pump is stable in a wide region. Can be operated.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main portion of an embodiment of a high specific speed mixed flow pump according to the present invention.

FIG. 2 is an external perspective view of the impeller of the high specific speed mixed flow pump of the present invention shown in FIG.

FIG. 3 is a view showing the shape of the impeller blade of the high specific velocity mixed flow pump shown in FIG. 1 on a meridional section.

FIG. 4 is a pump characteristic diagram of the high specific speed mixed flow pump shown in FIG. 1;

FIG. 5 is a view showing a necessary effect when an angle between a main shaft and a straight line passing through a hub-side inlet end and a hub-side outlet end of an impeller blade is fixed with respect to 52 degrees while fixing an impeller outlet side dimension. It is a figure which shows the ratio of a suction head.

FIG. 6 is a sectional view of a main portion of a conventional mixed flow pump having a high specific speed.

FIG. 7 is an external perspective view of an impeller of the conventional high specific speed mixed flow pump shown in FIG.

FIG. 8 is a pump characteristic diagram of the mixed flow pump having a high specific speed shown in FIG. 6;

FIG. 9 is a view showing the shape of the impeller blade of the conventional mixed flow pump having a high specific speed on a meridional section and explaining the possibility that surging or the like may occur in an operation region where the discharge amount is small.

[Explanation of symbols]

14 Main shaft 16 Hub 18 Impeller blade θ In the meridional section, the angle between the straight line passing through the tip-side outlet end and the hub-side outlet end of the impeller blade and the main shaft δ On the meridional section, the hub-side inlet end of the impeller blade Angle between the straight line passing through the hub-side exit end and the main shaft D1 Outer diameter of the hub-side exit end of the impeller blade D2 Outer diameter of the tip-side exit end of the impeller blade φ With the tip-side exit end of the impeller blade in meridional section Angle between the straight line passing through the hub end and the outer peripheral wall of the hub

Claims (2)

(57) [Claims] 1. An angle between a straight line passing through the tip-side outlet end and the hub-side outlet end of the impeller blade and the main shaft of the impeller on a meridional section is 40 degrees or less, and the impeller blade has a hub-side inlet end. The angle between the straight line passing through the outlet end on the hub side and the main shaft is 30
And a hub ratio at the impeller outlet is set to 0.6 or more. 2. The mixed flow pump according to claim 1, wherein the specific speed Ns is 1150 or more.