JP3964535B2 - Pump head turbine pipe for high head and high indentation depth - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention includes a runner chamber drain pipe that connects between a runner chamber that houses the runner and a suction pipe, etc., and high-pressure air is injected into the runner chamber so that water in the runner chamber is connected below the runner chamber. The present invention relates to a pump turbine for a high head and a high indentation depth in which a runner is idled by being pushed down into a suction pipe.
[0002]
[Prior art]
Recently, hydraulic machines such as pump turbines have become high-headed for economic efficiency, and the suction height or pushing depth of such high-headed hydraulic machines is relatively high from the viewpoint of preventing cavitation. As a result, the water pressure in the suction pipe is high.
[0003]
By the way, in such a pump turbine, a phased operation is often performed in which the runner of the pump turbine is idled for a long period of time in order to quickly respond to stabilization of the power system and changes in power demand.
[0004]
FIG. 13 is a longitudinal sectional view schematically showing a pump turbine for explaining the phase adjustment operation.
[0005]
In FIG. 13, reference numeral 1 denotes a pump turbine, and a runner 3 is attached to the lower end of the drive shaft 2, and the runner 3 is disposed in the runner chamber 4. The outer periphery of the runner chamber 4 is provided with cable shea ring 5, a plurality of guide vanes 6 is disposed on the runner 3 and concentrically between its casing 5 and runner chamber 4. A suction pipe 7 is connected to the lower end portion of the runner chamber 4, and a first runner chamber drain pipe 8 that communicates between the side pressure chamber 4 a and the suction pipe 7 of the runner chamber 4. A second runner chamber drain pipe 9 is provided between the runner outer peripheral flow path 4b between the runner 3 and the guide vane 6 and the suction pipe 7.
[0006]
In such a pump turbine 1, in order to reduce the power load during phased operation, after the guide vane 6 is fully closed, high-pressure air is supplied into the suction pipe 7 to drain the water in the runner chamber 4. The water is drained into the suction pipe 7 and the water surface L is pushed down by a predetermined distance from the lower end portion 3a of the runner 3, and the runner 3 is idled to reduce the driving torque. In addition, the first and second runner chamber drain pipes 8 and 9 communicate between the runner chamber 4 and the suction pipe 7 to promote drainage of water in the runner chamber 4, and stable phase adjustment operation over a long period of time. Can be implemented.
[0007]
By the way, in the phase adjustment operation, the air in the space 10 between the runner 3 and the water surface L is swirled in the rotation direction by the action of the runner centrifugal wind pressure by the rotation of the runner 3, and the water surface L as shown in FIG. Large undulations and swaying occur, particularly when the pressure in the suction pipe 7 is high.
[0008]
Accordingly, the water in the suction pipe 7 is scattered and adheres to the runner 3, and the rotation of the runner 3 is unbalanced, the input of the drive shaft 2 is rapidly increased, and a part of the high-pressure air is caused by the fluctuation of the water surface L. May leak toward the downstream side 7b of the suction pipe 7 through the elbow portion 7a of the suction pipe 7, and the supply of high-pressure air into the runner chamber 4 may not be able to catch up.
[0009]
[Problems to be solved by the invention]
Therefore, in order to solve the above-mentioned problems, Japanese Patent Application Laid-Open No. 6-260375 and Japanese Patent Application Laid-Open No. 3-260375 that define the height of the suction pipe are defined as the shape of the suction pipe for suppressing air leakage. No. 260375, etc., but handling when the density ratio correction fluid number is large is not clear. To suppress leakage to the downstream side of the suction pipe, it is possible to obtain a certain effect by making the height of the suction pipe considerably large, but considering the economics of civil engineering work, the height of the suction pipe is more than necessary. There is no merit in making it high. Accordingly, there is a need for a method for setting an appropriate shape or height of the suction pipe in a region where the density ratio correction fluid number is large, but no proposal for such a method has been found at present.
[0010]
The present invention has been made in view of the circumstances as described above. When the runner is idling, the shaft input does not increase, and high-pressure air is not leaked in a large amount downstream of the suction pipe. The primary purpose is to perform the phased operation, and by appropriately determining the shape of the suction pipe and the height of the suction pipe, it is possible to improve the economics of civil engineering work without increasing the height of the suction pipe more than necessary. The purpose is to obtain a high-head and high-push-in depth pump turbine with the second objective of sufficiently achieving.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1
High-pressure-head high-pump-depth pump-turbine suction pipe in which high-pressure air is injected into a suction pipe connected to a runner chamber for storing the runner to push down the water surface in the suction pipe and cause the runner to idle in the air. In
The runner outlet diameter is D (m), the runner outlet peripheral speed is Ue (m / s), the air density is ρa (kg / m ³ ), the water density is ρw (kg / m ³ ), and the gravity When the acceleration is g (m / s ² ), the density ratio correction fluid number Fd is
Fd = {ρa / (ρw−ρa)} ^1/2 Ue / (g · D)
And define
Corresponding to this density ratio correction fluid number Fd in the range of 1.2 ≦ Fd ≦ 1.8
F d-c = F d (0.24F d +0.88)
The critical density ratio corrected fluid number Fd-c obtained based on the relational expression
And a combination diagram of the suction height F and draft tube elbow offset dimension R of the draft tube relative to the limit density ratio correction Froude number Fd-c that has been obtained through experiments in advance,
The combination of the suction pipe height F and the suction pipe elbow offset dimension R of the suction pipe is determined .
[0012]
The invention according to claim 4
High-pressure-head high-pump-depth pump-turbine suction pipe in which high-pressure air is injected into a suction pipe connected to a runner chamber for storing the runner to push down the water surface in the suction pipe and cause the runner to idle in the air. In
The runner outlet diameter is D (m), the runner outlet peripheral speed is Ue (m / s), the air density is ρa (kg / m ³ ), the water density is ρw (kg / m ³ ), and the gravity When the acceleration is g (m / s ² ), the density ratio correction fluid number Fd is
Fd = {ρa / (ρw−ρa)} ^1/2 Ue / (g · D)
And define
Corresponding to this density ratio correction fluid number Fd in the range of 1.2 ≦ Fd ≦ 1.8
F d-c = F d (0.24F d +0.88)
Based on the relational expression, the limit density ratio corrected fluid number Fd-c is obtained,
For this critical density ratio corrected fluid number Fd-c,
F / D = 3.34F dc ² −9.95F d−c +11.02
as well as,
R / D = −1.15F dc ² + 5.71Fd-c −4.35
The suction pipe height F and the suction pipe elbow offset dimension R are determined so as to satisfy the following relationship.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to FIGS. In the figure, the same parts as those in FIG.
[0014]
In FIG. 1, reference numeral 1 denotes a pump turbine, and a runner 3 is attached to the lower end of the drive shaft 2, and the runner 3 is disposed in the runner chamber 4. A caging 5 is provided on the outer periphery of the runner chamber 4, and a plurality of guide vanes 6 are disposed concentrically with the runner 3 between the casing 5 and the runner chamber 4. A suction pipe 7 is connected to the lower end portion of the runner chamber 4, and a first runner chamber drain pipe 8 that communicates between the side pressure chamber 4 a and the suction pipe 7 of the runner chamber 4. A second runner chamber drain pipe 9 is provided between the runner outer peripheral flow path 4b between the runner 3 and the guide vane 6 and the suction pipe 7.
[0015]
Therefore, when performing so-called phased operation in which the runner 3 is idling in the air in such a high head / high indentation pump turbine, the guide vane 6 is fully closed and then connected to the upper portion of the suction pipe. High-pressure air is supplied from a high-pressure air injection pipe (not shown), water in the runner chamber 4 is replaced with air, and the water level is lowered below the lower end of the runner 3. In this case, normally, in order to efficiently supply high-pressure air, the upper limit L1 of the specified push-down water level and the lower limit L2 of the specified push-down water level are set in the suction pipe 7.
[0016]
In other words, when the water surface is first pushed down, and after entering the phased operation, the supply air is supplied by air leakage, and the lower limit L2 of the specified water surface level is set as the water surface level at which air supply is stopped. As a water surface level for replenishing air so as not to get too close to the runner, a specified depressing water surface level L1 is set.
[0017]
Moreover, the drainage of the water in the runner chamber 4 is promoted by the first runner chamber drain pipe 8 and the second runner chamber drain pipe 9 to enable stable phase adjustment operation.
[0018]
FIG. 2 shows a procedure for determining the suction pipe elbow offset dimension R and the suction pipe height F for suppressing air leakage for a power generation requirement with a density ratio corrected fluid number of 1.2 to 1.8. Is.
[0019]
First, when the essential points of the power plant are given, the runner outlet diameter, the main engine speed, and the indentation depth are determined from these, and the density ratio corrected fluid number Fd is calculated. In other words, the runner outlet diameter D (m), the runner outlet peripheral velocity Ue (m / s), the density of the air ρa (kg / m ^3), the density of water ρw (kg / m ³⁾ and gravity acceleration Is g (m / s ² ), and the density ratio corrected fluid number Fd is Fd = {ρa / (ρw−ρa)} ^1/2 Ue / (g · D)
Calculate as In this case, the density of air and the density of water are determined from the indentation depth.
[0020]
Next, the limit density ratio corrected fluid number Fd-c is obtained from the density ratio corrected fluid number Fd using a conventional relational expression in consideration of the actual value. This relational expression gives a margin when the suction pipe is determined by the method of the present invention. When the air is supplied to the suction pipe, the lowering of the pushed down water level due to the supercharging due to the operation delay of the air supply valve and the downstream of the suction pipe Taking into account the increase in shaft input due to water drop entrainment due to the rise of the water level pushed down due to air leakage after a certain period of time and the leakage of water after a certain period of time, etc. It has become a formula. In particular,
As shown in FIG. 3, Fd-c = Fd (0.24Fd + 0.88) (1)
The following relational expression.
[0021]
If the limit density ratio corrected fluid number Fd-c is obtained, the relationship between the limit density ratio corrected fluid number Fd-c obtained from the experiment, the suction pipe elbow offset dimension, and the suction pipe height is shown, and the suction pipe elbow offset dimension R and A combination of suction pipe heights F is obtained. An appropriate suction pipe is determined from this combination.
[0022]
Here, in the pump turbine for a high head and high indentation depth according to the present invention, in determining the suction pipe determination policy, the limit density ratio correction fluid number Fd-c, the suction pipe elbow offset dimension and the suction pipe are determined by the verification test performed. The method for obtaining the relationship diagram of the height and the method for determining the suction pipe elbow offset dimension and the suction pipe height will be specifically described.
[0023]
First, in the combination of a specific suction pipe elbow offset dimension R and suction pipe height F, the push-down water level is changed under several density ratio correction fluid numbers to change the shaft input and the amount of leakage. It detects and obtains the limit water level Zt (FIG. 4) of the shaft input and the limit water level Z1 (FIG. 4) of the air leakage characteristics.
[0024]
Next, as shown in FIG. 5, the horizontal axis represents the density ratio corrected fluid number, and the vertical axis represents the ratio of the axial input limit water level Zt and the amount of air leakage to the runner outlet diameter D of the limit water level Z1. The density ratio correction fluid number at the intersection of the straight line plotting Zt / D and the straight line plotting Z1 / D at each density ratio correction fluid number is a combination of the suction pipe elbow offset dimension and the suction pipe height. The limit density ratio corrected fluid number is Fd-c.
[0025]
The critical density ratio corrected fluid number Fd-c is also obtained for combinations of many other suction pipe elbow offset dimensions R and suction pipe heights F in this way.
[0026]
From these results, the relationship between the limit density ratio corrected fluid number Fd-c, the ratio R / D of the suction pipe elbow offset size to the runner outlet diameter D, and the ratio F / D of the suction pipe height to the runner outlet diameter D FIG. 6 shows an example of a diagram arranged as follows. Note that only three types of curves in FIG. 6 are displayed for explanation.
[0027]
Next, a method for obtaining a combination of the suction pipe elbow offset dimension and the suction pipe height from the diagram of FIG. 6 and the aforementioned limit density ratio corrected fluid number Fd-c will be described with reference to FIG.
[0028]
When the limit density ratio corrected fluid number Fd-c obtained by the above-described method is, for example, a value a, the R / D range corresponding to the value a is b1 or more in FIG. The possible range is c3 or less and c2 or more. This indicates that increasing R / D decreases F / D, and decreasing R / D increases F / D. In this case, as R / D approaches from b1 to b2, F / D decreases from c3 to c2, but the rate of decrease decreases, and when R / D is greater than or equal to b2, F / D remains c2. It should be noted that it is hardly reduced. Therefore, the R / D considered to be appropriate is determined in consideration of this. For explanation, it is assumed that R / D = b in FIG. Of course, when it is intended to make the suction pipe height as low as possible, it is conceivable to adopt b2 for R / D as an option.
[0029]
When R / D is determined, the limit density ratio corrected fluid number Fd-c on each F / D curve at R / D = b is read. These values are a1, a2 and a3 as shown in FIG. From these, a diagram as shown in FIG. 8 is created. Then, an interpolation equation is obtained from the data of these three points, and the value a is substituted into this to calculate F / D = c.
[0030]
As described above, it is possible to determine an appropriate suction pipe according to the essential points of the power plant.
[0031]
As described above, in the above embodiment of the present invention, the density ratio correction fluid number Fd is 1.2 to 1.8 or less, and is calculated from the essential points of the power plant in the region including the unprecedented high region. The limit density ratio corrected fluid number Fd-c is obtained from the density ratio corrected fluid number Fd, and the relationship between the experimentally determined suction pipe elbow offset dimension R and suction pipe height F and the limit density ratio corrected fluid number Fd-c If the suction pipe is determined from the figure, the suction pipe height is not increased more than necessary, that is, economical and stable phase adjustment operation can be performed even in civil engineering work.
[0032]
By the way, in the above embodiment, when the combination of the suction pipe elbow offset dimension R and the suction pipe height F is determined from the limit density ratio correction fluid number Fd-c, there are considerable degrees of freedom in the options. There is. However, for each type of suction pipe height, if the suction pipe elbow offset dimension exceeds a certain value, the limit density ratio corrected fluid number Fd-c tends not to be so large even if the suction pipe elbow offset dimension is increased. And when the suction pipe elbow offset dimension is increased more than necessary, the range of the non-circular cross-section of the suction pipe becomes longer, so there is a possibility that measures for strength may be required. Therefore, when determining the shape of the suction pipe, there is a proper combination of the suction pipe elbow offset dimension and the suction pipe height if reasonably considered. This is shown in FIG.
[0033]
The appropriate offset dimension curve shown in FIG. 9 is the suction pipe elbow offset dimension on the relationship curve between the suction pipe elbow offset dimension R / D and the limit density ratio corrected fluid number Fd-c for each suction pipe height. This is a smooth connection between points where the increasing tendency of the limit density ratio correction fluid number Fd-c weakens with increasing R / D. Next, limit density ratio correction fluid number Fd-c at each point is obtained, limit density ratio correction fluid number Fd-c is plotted on the horizontal axis, and suction pipe elbow offset dimension R / D and suction pipe height are plotted on the vertical axis. FIG. 10 shows the arrangement of the F / D. From the experimental detailed data, these two curves, the suction pipe elbow offset dimension R / D curve for the critical density ratio corrected fluid number Fd-c, and the suction pipe height F / D for the critical density ratio corrected fluid number Fd-c. The formula defining the curve is as follows.
(R / D) = − 1.15F dc ² + 5.71Fd−c −4.35 (2)
And (F / D) = 3.34F dc ² −9.95Fd−c + 11.02 (3)
[0034]
As described above, the limit density ratio corrected fluid number Fd-c is obtained from the density ratio corrected fluid number Fd calculated from the power plant requirements, and is calculated by using the equations (2) and (3), thereby calculating the suction pipe. The appropriate suction pipe elbow offset R and suction pipe height F can be uniquely determined.
[0035]
As described above, in this embodiment, the density ratio corrected fluid number calculated from the essential points of the power plant in the area including the unprecedented high area where the density ratio corrected fluid number Fd is 1.2 to 1.8 or less. If the limit density ratio correction fluid number Fd-c is obtained from Fd and the suction pipe is determined from the calculation formula that gives the appropriate suction pipe elbow offset dimension R and the suction pipe height F obtained experimentally, the suction will be more than necessary. It is possible to perform an economical and stable phase adjustment operation without increasing the pipe height, that is, in civil engineering work.
[0036]
On the other hand, FIG. 11 shows the second runner chamber drain pipe 9 communicating with the suction pipe 7 and the outer peripheral flow path 4b between the runner 3 and the guide vanes 6 arranged on the outer periphery thereof. It is an example which shows the model test result of the pump air leakage characteristic at the time of providing in the said suction pipe cross section of the position below less than 1.3D by the vertical distance upwards from the elbow part upper surface lower end part of a path | route. 11 (a) to 11 (c), the positions of the second runner chamber drain pipe 9 and the bottom end of the upper surface of the elbow part of the suction pipe flow path are the same, and only the suction pipe height is changed. R / D is about 2.8.
[0037]
If the suction pipe elbow offset dimension is larger than the conventional suction pipe as in this example, the amount of air leakage will be reduced overall at the same suction pipe height, and the change in the amount of air leakage will be After the peak value is once shown at a certain level of the pushed-down water level, it decreases as the pushed-down water level becomes lower, and reaches the lowermost end of the upper surface of the elbow part of the suction pipe flow path and leaks at once. Here, in the air leakage characteristics when the suction pipe height F / D shown in (a) and (b) is 3.7 or 4, the peak portion has two peaks. As a result of detailed observation by experiment, the first peak of this cap peak was sucked out by the bubbles flowing out from the suction pipe opening of the second runner chamber drain pipe being caught in the underwater vortex generated by the water surface fluctuation. It was found to be caused by a direct discharge downstream of the tube. If this effect is removed, the air leakage characteristics can be improved.
[0038]
Therefore, the suction pipe opening position of the second runner chamber drain pipe 9 was tested by changing several vertical distances from the lowermost end of the upper surface of the elbow part of the suction pipe flow path. As a result, when the suction pipe is provided in the cross section of the suction pipe at a vertical distance of 1.3D or more upward from the lowermost end of the upper surface of the elbow part of the suction pipe flow path, the change in the amount of leakage is shown by the solid line in FIG. Thus, the hatched portion disappeared, and it was verified that bubbles flowing out from the suction pipe opening of the second runner chamber drain pipe were not caught in the underwater vortex generated by the water surface fluctuation.
[0039]
In this way, the opening of the second runner chamber drain pipe 9 to the suction pipe flow path is located at a position that is 1.3D or more away from the bottom end of the upper surface of the elbow part of the suction pipe flow path by a vertical distance of 1.3D or more. In this case, the air bubbles flowing out from the second runner chamber drain pipe 9 are caught in the vortex in the water generated by the fluctuation of the water surface and directly flow out to the downstream of the suction pipe, which causes an increase in the amount of air leakage. Never do. Further, in this case, since the second runner chamber drain pipe can be connected in an arbitrary direction of the same cross section, the degree of freedom in piping design is improved.
[0040]
【The invention's effect】
As described above, according to the present invention, it is possible to calculate the appropriate suction pipe of the pump turbine for the high head and high indentation depth from the essential points of the power plant, so that the degree of freedom in selection in the power plant design is greatly increased. Thus, it is possible to obtain a high drop and high indentation depth pump turbine equipped with an economically advantageous suction pipe. In addition, when the runner is idling, it is possible to obtain a high-head and high-push-depth pump turbine capable of stable idling for a long time with a small amount of air leakage.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view schematically showing a pump turbine for high head and high indentation depth according to the present invention.
FIG. 2 is a diagram for explaining a method in a case where an appropriate suction pipe is determined from a power generation requirement.
FIG. 3 is a diagram for obtaining a limit density ratio corrected fluid number Fd-c using a density ratio corrected fluid number Fd calculated from a power generation requirement.
FIG. 4 is a diagram showing a relationship between a pushed-down water level, shaft input, and air leakage amount during idling operation in an experiment.
FIG. 5 is an auxiliary diagram for obtaining a limit density ratio corrected fluid number Fd-c from a shaft input with respect to a plurality of density ratio corrected fluid numbers Fd and a limit water level of an air leakage amount for a specific suction pipe in an experiment.
FIG. 6 is a diagram showing the relationship between the suction pipe elbow offset dimension and the suction pipe height and the limit density ratio corrected fluid number Fd-c obtained experimentally.
FIG. 7 is a diagram illustrating a method for determining a suction pipe elbow offset dimension.
FIG. 8 is a diagram showing a method for determining a suction pipe height.
FIG. 9 is a diagram showing an appropriate offset dimension curve.
FIG. 10 is a graph showing a relationship between a development density ratio correction fluid number Fd-c, a suction pipe elbow offset dimension, and a suction pipe height based on an appropriate offset dimension curve.
FIG. 11 shows the model leakage characteristics when the second runner chamber drain pipe is provided on the cross section of the suction pipe at a vertical distance of less than 1.3D from the lowermost part of the upper surface of the elbow part of the suction pipe flow path. The figure which shows a result.
FIG. 12 shows the model leakage characteristics when the second runner chamber drain pipe is provided on the cross section of the suction pipe at a vertical distance of 1.3D or more upward from the bottom end of the upper surface of the elbow section of the suction pipe flow path. The figure which shows a result.
FIG. 13 is a longitudinal sectional view schematically showing a conventional high drop / high indentation depth pump turbine.
[Explanation of symbols]
1 pump turbine 3 runner 4 runner chamber 4a side pressure chamber 4b runner outer peripheral flow path 5 casing 6 guide vane 7 suction pipe 7a suction pipe elbow part 7b suction pipe downstream side 8 first runner chamber drain pipe 9 second runner chamber drain pipe L1 specified lowering water level upper limit L2 specified lowering water level lower limit

Claims (4)

High-pressure-head high-pump-depth pump-turbine suction pipe in which high-pressure air is injected into a suction pipe connected to a runner chamber for storing the runner to push down the water surface in the suction pipe and cause the runner to idle in the air. In
The runner outlet diameter is D (m), the runner outlet peripheral speed is Ue (m / s), the air density is ρa (kg / m ³ ), the water density is ρw (kg / m ³ ), and the gravity When the acceleration is g (m / s ² ), the density ratio correction fluid number Fd is
Fd = {ρa / (ρw−ρa)} ^1/2 Ue / (g · D)
And define
Corresponding to this density ratio correction fluid number Fd in the range of 1.2 ≦ Fd ≦ 1.8
F d-c = F d (0.24F d +0.88)
The critical density ratio corrected fluid number Fd-c obtained based on the relational expression
And a combination diagram of the suction height F and draft tube elbow offset dimension R of the draft tube relative to the limit density ratio correction Froude number Fd-c that has been obtained through experiments in advance,
A suction pipe of a pump turbine for a high drop / high indentation depth, wherein a combination of a suction pipe height F of the suction pipe and a suction pipe elbow offset dimension R is determined .   For a specific combination of suction pipe elbow offset size and suction pipe height, the push-down water level is changed under several types of density ratio corrected fluid numbers to determine the limit water level Zt for shaft input and the limit water level Z1 for air leakage characteristics. The density ratio correction fluid number at the intersection of the straight line plotting Zt / D and the straight line plotting Z1 / D for each density ratio correction fluid number is a combination of the above specified suction pipe elbow offset dimension and suction pipe height. The suction pipe of a high drop and high indentation pump turbine according to claim 1, wherein the limit density ratio correction fluid number is Fd-c.   Obtain a relationship diagram of the limit density ratio correction fluid number Fd-c and the combination of R / D and F / D, and use the R / D value corresponding to the desired limit density ratio correction fluid number from the diagram. In this R / D value, the limit density ratio corrected fluid number on each F / D curve is read, and the value of F / D is determined from the relationship between the limit density ratio corrected fluid number and F / D. The suction pipe of a pump turbine for high head and high indentation depth according to claim 2, characterized in that High-pressure-head high-pump-depth pump-turbine suction pipe in which high-pressure air is injected into a suction pipe connected to a runner chamber that houses the runner to push down the water surface in the suction pipe and cause the runner to idle in the air. In
The runner outlet diameter is D (m), the runner outlet peripheral speed is Ue (m / s), the air density is ρa (kg / m ³ ), the water density is ρw (kg / m ³ ), and the gravity When the acceleration is g (m / s ² ), the density ratio correction fluid number Fd is
Fd = {ρa / (ρw−ρa)} ^1/2 Ue / (g · D)
And define
Corresponding to this density ratio correction fluid number Fd in the range of 1.2 ≦ Fd ≦ 1.8
F d-c = F d (0.24F d +0.88)
Based on the relational expression, the limit density ratio corrected fluid number Fd-c is obtained,
For this critical density ratio corrected fluid number Fd-c,
F / D = 3.34F dc ² −9.95F d−c +11.02
as well as,
R / D = −1.15F dc ² + 5.71Fd-c −4.35
A suction pipe of a pump head for a high drop and high indentation depth, wherein a suction pipe height F and a suction pipe elbow offset dimension R are determined so as to satisfy the relationship.

Images