A double-suction centrifugal pump for suppressing impeller pressure pulsation and its design method

Abstract

The present invention relates to a double-suction centrifugal pump for suppressing impeller pressure pulsation and its design method. The double-suction centrifugal pump includes: a suction chamber, an impeller, a fixed guide vane, a volute, long blades, and short blades; the suction chamber has a structure of two axially symmetric suction chambers on both sides, the impeller is a double-suction closed impeller with axially symmetric blades back to back, the suction chamber is part of the volute, the fixed guide vane is installed in the volute cavity, the blades in the double-suction centrifugal pump include the long blades and the short blades, and the long and short blades are staggered on the impeller. A fixed guide vane is installed at the outlet of the runner. The fixed guide vane is required not to have too large a diameter, and the diameter range does not exceed 115% of the impeller diameter. The width of the guide vane is 1.15 - 1.2 times the width of the blade outlet. The installation angle of the inlet of the guide vane blade is 0 - 5°, and the installation angle of the outlet of the guide vane blade is 5 - 15°. The present invention can, on the basis of maintaining the basic requirements of efficiency and head, greatly reduce the intensity of the pressure pulsation inside the volute caused by the dynamic and static interference between the impeller and the guide vane.

Description

Technical Field

[0001] The present invention relates to a double-suction centrifugal pump and its design method, specifically to a double-suction centrifugal pump for suppressing impeller pressure pulsation that can significantly reduce the internal pressure pulsation intensity in the volute caused by the dynamic and static interference between the impeller and the guide vane while maintaining the basic requirements of efficiency and head, and its design method. Background Art

[0002] Double-suction centrifugal pumps are mainly used in water transfer projects with large flow rates and high heads. At present, in most cases, its main body consists of a spiral suction chamber, two back-to-back arranged impellers, and a volute. However, due to the uneven flow at the outlets of the two impellers and their interaction, high-amplitude and high-intensity pressure pulsations are generated at the impeller outlets due to the dynamic and static interference of the blades. The area between the impeller and the guide vane is an area where dynamic and static interference is likely to occur in a centrifugal pump, and the most significant area is from the impeller outlet edge to the guide vane inlet edge. Due to the influence of the limited number of blades at the impeller outlet, there are differences in velocity between the pressure side and the suction side at the outlet edge, which will cause a large velocity change at the guide vane inlet edge in a short time, and then have a large impact on the guide vane body. This effect may also be transmitted upstream or downstream.

[0003] High-amplitude and high-intensity pressure pulsations will cause problems such as unit vibration and cavitation, seriously threatening the operation stability and safety of the pump station. At present, the commonly used methods for suppressing pressure pulsations mainly start from the impeller design, but the effect is not good, and it is difficult to control the superiority of hydraulic performance. Summary of the Invention

[0004] Aiming at the above problems, the main purpose of the present invention is to provide a double-suction centrifugal pump for suppressing impeller pressure pulsation and its design method that can significantly reduce the internal pressure pulsation intensity in the volute caused by the dynamic and static interference between the impeller and the guide vane while maintaining the basic requirements of efficiency and head.

[0005] The present invention solves the above technical problems through the following technical solutions: A double-suction centrifugal pump for suppressing impeller pressure pulsation, the double-suction centrifugal pump for suppressing impeller pressure pulsation includes: a suction chamber, an impeller, a fixed guide vane, a volute, long blades, and short blades; the suction chamber is a structure of an axisymmetric two-sided suction chamber, the impeller is an axisymmetric double-suction closed impeller with blades back-to-back, the suction chamber is a part of the volute, the fixed guide vane is installed in the volute cavity, the blades in the double-suction centrifugal pump include the long blades and the short blades, and the long blades and the short blades are staggered on the impeller.

[0006] In a specific embodiment of the present invention, the corresponding dimensions of the contact surface between the fixed guide vane and the volute are the same, and the fixed guide vane is directly clamped and installed in the volute cavity.

[0007] In a specific embodiment of the present invention, the number of long blades and short blades is equal, and the stagger angle at which the long blades and short blades are staggeredly distributed on the impeller is 360 / n / 2, where n is the number of long blades and short blades.

[0008] In a specific embodiment of the present invention, for the stationary guide vane of the double-suction centrifugal pump, the stationary guide vane has the characteristics that the guide vane diameter range does not exceed 115% of the impeller outlet diameter, the inlet blade setting angle of the guide vane blades is 0 to 5°, the outlet blade setting angle of the guide vane blades is 5° to 15°, the wrap angle is greater than 50°, and the guide vane inlet width is 1.15 to 1.2 times the impeller outlet width.

[0009] In a specific embodiment of the present invention, the number of guide vane blades provided on the stationary guide vane ranges from 5 to 12.

[0010] In a specific embodiment of the present invention, the number of blades on the impeller is 8, among which there are 4 long blades and 4 short blades.

[0011] In a specific embodiment of the present invention, the length of the short blades is 70% - 75% of the length of the long blades.

[0012] In a specific embodiment of the present invention, the double-suction centrifugal pump is a low-specific-speed centrifugal pump, which is a centrifugal pump with a specific speed lower than 40.

[0013] A design method for a double-suction centrifugal pump to suppress impeller pressure pulsation, the design method comprising the following steps:

[0014] (1), According to the original pump type design requirements, conduct a preliminary design of the impeller. The impeller blades are designed in the form of long and short blades. Design 4 long blades and 4 short blades for the impeller, and the ratio of the angle between the short blade and the adjacent two long blades is 0.5;

[0015] (2), Based on the head requirement, considering the incidence angle, design the inlet blade setting angle, outlet blade setting angle and wrap angle of the impeller blades;

[0016] (3), To reduce pressure pulsation, design the two impellers to be staggeredly arranged;

[0017] (4) To control the size as much as possible, first design the guide vane diameter range not to exceed 1.15 times the impeller diameter range;

[0018] (5), According to the outlet flow velocity angle, design the guide vane inlet blade setting angle;

[0019] (6), To avoid dynamic-static interference, the number of guide vane blades and the number of impeller blades need to be relatively prime, and determine the number of guide vane blades;

[0020] (7) Consider the smooth transition of flow and reduction of flow resistance, and design the outlet angle and wrap angle of the guide vane;

[0021] (8) Design the spiral shape and cross-sectional shape of the volute according to the outlet diameter of the guide vane and the pump outlet;

[0022] (9) Obtain the designed hydraulic performance parameters and pressure pulsation results through CFD numerical simulation;

[0023] (10) Complete the design.

[0024] In a specific embodiment of the present invention, in step (2), the inlet setting angle is between 16.5° and 21°, the outlet setting angle is between 21° and 23°, and the wrap angle is 180 - 200°.

[0025] The positive and progressive effects of the present invention are as follows: The design method of a double-suction centrifugal pump for suppressing impeller pressure pulsation provided by the present invention, for a double-suction centrifugal pump with a specific speed lower than 40, two back-to-back impellers are arranged staggeredly, and the stagger angle is 360 / n / 2, and long and short blades are used, and the short blades are 70% - 75% of the length of the long blades; a fixed guide vane is installed at the outlet of the runner. The fixed guide vane is required not to have too large a diameter, and the diameter range does not exceed 115% of the impeller diameter. The width of the guide vane is 1.15 - 1.2 times the outlet width of the blade. The inlet setting angle of the guide vane blade is 0 - 5°, the outlet setting angle of the guide vane blade is 5 - 15°, and the wrap angle is greater than 50°. The present invention can significantly reduce the internal pressure pulsation intensity of the volute caused by the dynamic and static interference between the impeller and the guide vane while maintaining the basic requirements of efficiency and head. Description of the Drawings

[0026] Figure 1 is a schematic structural diagram of the outside of a double-suction centrifugal pump of the present invention.

[0027] Figure 2 is a schematic structural diagram of the inside of a double-suction centrifugal pump of the present invention.

[0028] Figure 3-1 is a schematic structural diagram of the fixed guide vane of an example of the present invention.

[0029] Figure 3-2 is Figure 3-1 the A-A sectional view of

[0030] Figure 4 is a schematic diagram of the arrangement of long and short blades.

[0031] Figure 5 is a schematic diagram of the impeller structure at different positions of long and short blades.

[0032] Figure 6 is a comparison chart of the head before and after improvement of an example of the present invention.

[0033] Figure 7 This is a comparison chart of efficiency before and after improvement for an example of the present invention.

[0034] Figure 8-1 This is the result of pressure pulsation before and after improvement for an example of the present invention.

[0035] Figure 8-2 This is the result of pressure pulsation before and after improvement for an example of the present invention.

[0036] The following are the names corresponding to the reference numerals in the present invention:

[0037] In the figure: suction chamber 1, impeller 2, stationary guide vane 3, volute 4, long blade 5, short blade 6, impeller blade outlet width 7, guide vane inlet width 8, guide vane blade inlet setting angle 9, guide vane blade outlet setting angle 10, impeller outlet diameter 11, guide vane diameter range 12, guide vane blade wrap angle 13. Detailed implementation manners

[0038] The following provides a preferred embodiment of the present invention in conjunction with the attached drawings to elaborate in detail on the technical solution of the present invention.

[0039] Figure 1 This is a structural example diagram of a double-suction centrifugal pump of the present invention. As shown in the above figure: A double-suction centrifugal pump for suppressing impeller pressure pulsation provided by the present invention includes a suction chamber 1, an impeller 2, a stationary guide vane 3, a volute 4, long blades 5, and short blades 6; the suction chamber 1 has a structure of two axially symmetric suction chambers on both sides, the impeller 2 is an axially symmetric double-suction closed impeller with blades back to back, the suction chamber is a part of the volute 4, the stationary guide vane 3 is installed in the cavity of the volute 4, the blades in the double-suction centrifugal pump include long blades 5 and short blades 6, and the long blades 5 and short blades 6 are staggered on the impeller.

[0040] The stationary guide vane 3 is provided with guide vane blades, the corresponding dimensions of the contact surface between the stationary guide vane 3 and the volute 4 are the same, and the stationary guide vane 3 is directly stuck in the cavity of the volute 4 installed.

[0041] The number of long blades 5 and short blades 6 is equal, and the staggered angle of the staggered distribution of the long blades 5 and short blades 6 on the impeller is 360 / n / 2, where n is the number of long blades and short blades.

[0042] For the stationary guide vane 3 of the double-suction centrifugal pump, the stationary guide vane 3 has a feature that the guide vane diameter range 12 does not exceed 115% of the impeller outlet diameter 11, the degree of the guide vane blade inlet setting angle 9 on the stationary guide vane 3 is 0 to 5°, the degree of the guide vane blade outlet setting angle 10 is 5° to 15°, the wrap angle 13 is greater than 50°, and the guide vane inlet width 8 is 1.15 to 1.2 times the impeller outlet width 7.

[0043] The number of guide vane blades provided on the stationary guide vane 3 in the present invention ranges from 5 to 12, preferably 9.

[0044] The number of blades on the impeller 2 in the present invention can be 8, among which there are 4 long blades 5 and 4 short blades 6. The length of the short blade 6 is 70% - 75% of the length of the long blade 5.

[0045] The double - suction centrifugal pump in the present invention is a centrifugal pump with a low specific speed, that is, a centrifugal pump with a specific speed lower than 40.

[0046] The present invention also provides a design method for a double - suction centrifugal pump to suppress impeller pressure pulsation. This design method includes the following steps:

[0047] (1), According to the original pump type design requirements, for example, a double - suction centrifugal pump with a pump inlet diameter of 300 mm and a specific speed of 33, conduct a preliminary design of the impeller. The impeller blades are designed in the form of long and short blades. Design 4 long blades and 4 short blades for the impeller, and the ratio of the angle between the short blade and the adjacent two long blades is 0.5.

[0048] (2), Based on the head requirements, according to Euler's equation, etc., under the condition of considering the incidence angle, design the inlet setting angle, outlet setting angle and wrap angle of the impeller blades (for example, the inlet setting angle is between 16.5° and 21°, the outlet setting angle is between 21° and 23°, and the wrap angle is about 190°).

[0049] (3), To reduce pressure pulsation, design the two impellers to be stagger - arranged (for example, the stagger angle arrangement is 22.5°).

[0050] (3) To control the size as much as possible, first design the guide vane diameter range not exceeding 1.15 times the impeller diameter range.

[0051] (4), According to the outlet flow velocity angle, design the guide vane inlet setting angle (for example, the angle between the absolute flow velocity and the circumferential velocity is about 1°, considering the incidence angle, it is approximately designed as 3.5°).

[0052] (5), To avoid dynamic - static interference, the number of guide vane blades and the number of impeller blades need to be relatively prime, and determine the number of guide vane blades (for example, the number of impeller blades is 8, to avoid dynamic - static interference, design the number of guide vane blades as 9).

[0053] (6), Considering smooth flow transition and reducing flow resistance, design the guide vane outlet angle and guide vane wrap angle (for example, design the guide vane outlet angle as 9° and the wrap angle as about 55°).

[0054] (7), According to the guide vane outlet diameter and the pump outlet, design the volute spiral shape and cross - section shape.

[0055] (8) Through CFD numerical simulation, the designed hydraulic performance parameters and pressure pulsation results are obtained (for example: after design, compared with the original scheme, the efficiency is increased by 10%, the head curve becomes flatter, the peak-to-peak value of pressure pulsation is reduced to 10% - 14% of the original, the peak value of the main frequency is significantly suppressed, and the effect is obvious.

[0056] (9) Complete the design.

[0057] In order to overcome the deficiencies of the existing methods for suppressing pressure pulsation and maintain the high-efficiency operation of double-suction centrifugal pumps. In the present invention, by installing fixed guide vanes and arranging long and short blades alternately, while suppressing pressure pulsation, the original operating efficiency is maintained.

[0058] Long and short blades are an impeller form in centrifugal pumps that can effectively suppress the dynamic-static interference inside the pump. By setting short blades in the original impeller flow channel, the secondary flow in the flow channel can be eliminated, the influence relationship between the impeller and downstream components can be improved, and the pressure pulsation characteristics of the pump can be improved. For the impeller with the form of long and short blades, the short blades can be arranged in the middle of two adjacent blades, or relatively close to one of the adjacent blades. The position of the short blades is defined as ε:

[0059]

[0060] In the formula: ε is the ratio of the angle between the short blade and two adjacent long blades; ε t is the angle between the short blade and the long blade adjacent to its suction surface; ε d is the angle between the long blade and the adjacent long blade.

[0061] The following is a specific implementation example: Taking a double-suction centrifugal pump with a pump inlet diameter of 300 mm as an example. The specifications and data of the main components, as well as the pressure pulsation suppression effect, are listed. The specific speed of this pump is 33, the number of long blades of the designed impeller is 4, its inlet setting angle is 16.5 - 21°, the outlet setting angle is 22.5°, the wrap angle is 190°, the number of short blades is 4, located in the middle of the long blades, and the length is 72% of the short blades. The number of guide vane blades is 9, the inlet setting angle of the blades is 3.5°, the outlet setting angle is 9°, and the wrap angle is 54.81°. After improvement, both the efficiency and head are increased. The peak-to-peak value of pressure pulsation is reduced to 10% - 14% of the original, and the effect of suppressing pressure pulsation is obvious.

[0062] Figure 6 is the comparison diagram of the head before and after improvement of an example of the present invention. From Figure 6 it can be concluded that after improvement, within the operating range, the head of the pump is higher than that of the original pump, especially at the large flow rate position; the head curve becomes flatter and has a better adaptation range.

[0063] Figure 7 is the comparison diagram of the efficiency before and after improvement of an example of the present invention. FromFigure 7 It can be concluded that after the improvement, within the operating range, the efficiency of the pump has also increased compared to the original pump; the point of maximum efficiency is located at a flow rate of 1000 m 3 / h.

[0064] Figure 8-1 is the result of pressure pulsation before and after the improvement of an example of the present invention. Figure 8-2 is the result of pressure pulsation before and after the improvement of an example of the present invention. From Figure 8-1 it can be concluded that after the improvement, the maximum amplitude of the pressure pulsation has been significantly weakened, and the maximum amplitude of the pressure pulsation has been reduced to about 14% of that of the original pump.

[0065] From Figure 8-2 it can be concluded that after the improvement, the characteristic frequency of the pressure pulsation has changed, and the main frequency has become 100 Hz; and the amplitude value of the highest main frequency (100 Hz) is about 12.5% of the highest main frequency (240 Hz) of the original pump. The pressure pulsation has been significantly suppressed and improved.

[0066] The present invention can play a role in significantly reducing the intensity of pressure pulsation inside the volute caused by the dynamic and static interference between the impeller and the guide vane on the basis of maintaining the basic requirements of efficiency and head.

[0067] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will have various changes and improvements, and these changes and improvements all fall within the scope of the present invention claimed. The scope of the present invention claimed is defined by the appended claims and their equivalents.

Claims

1. A double-suction centrifugal pump for suppressing impeller pressure pulsation, characterized in that: The double-suction centrifugal pump for suppressing impeller pressure pulsation includes: a suction chamber, an impeller, a fixed guide vane, a volute, long blades, and short blades; the suction chamber has a structure of two axially symmetric suction chambers on both sides, the impeller is a double-suction closed impeller with axially symmetric blades back to back, the suction chamber is a part of the volute, the fixed guide vane is installed in the volute cavity, the blades in the double-suction centrifugal pump include the long blades and the short blades, and the long blades and the short blades are staggered on the impeller; The corresponding dimensions of the contact surface between the fixed guide vane and the volute are the same, and the fixed guide vane is directly clamped and installed in the volute cavity; The number of long blades and short blades is equal, and the staggered angle of the staggered distribution of the long blades and the short blades on the impeller is 360 / n / 2, where n is the number of long blades and short blades; For the fixed guide vane of the double-suction centrifugal pump, the diameter range of the guide vane does not exceed 115% of the impeller outlet diameter. The inlet setting angle of the guide vane blades on the fixed guide vane is 0-5°, the outlet setting angle of the guide vane blades is 5°-15°, the included angle is greater than 50°, and the inlet width of the guide vane is 1.15-1.2 times the impeller outlet width; The number of guide vane blades provided on the fixed guide vane ranges from 5 to 12; The length of the short blade is 70%-75% of the length of the long blade; The double-suction centrifugal pump is a low-specific-speed centrifugal pump, which is a centrifugal pump with a specific speed lower than 40.

2. The double-suction centrifugal pump for suppressing impeller pressure pulsation according to claim 1, characterized in that: The number of blades on the impeller is 8, including 4 long blades and 4 short blades.

3. The design method of a double-suction centrifugal pump for suppressing impeller pressure pulsation according to any one of claims 1-2, characterized in that: The design method includes the following steps: (1), According to the original pump type design requirements, conduct a preliminary design of the impeller. The impeller blades are designed in the form of long and short blades. The long blades of the impeller are designed to be 4, the short blades are designed to be 4, and the ratio of the angle between the short blade and the adjacent two long blades is 0.5; (2), According to the head requirement, under the condition of considering the incidence angle, design the inlet setting angle, outlet setting angle and included angle of the impeller blades; (3), To reduce pressure pulsation, design the two impellers to be staggered; (4), To control the size as much as possible, first design the diameter range of the guide vane not to exceed 1.15 times the impeller diameter range; (5), According to the outlet flow velocity angle, design the inlet setting angle of the guide vane; (6), To avoid dynamic and static interference, the number of guide vane blades and the number of impeller blades need to be relatively prime, and determine the number of guide vane blades; (7), Considering smooth flow transition and reducing flow resistance, design the outlet angle and included angle of the guide vane; (8), According to the guide vane outlet diameter and the pump outlet, design the spiral shape and cross-sectional shape of the volute; (9), Through CFD numerical simulation, obtain the designed hydraulic performance parameters and pressure pulsation results; (10), Complete the design.

4. The design method of a double-suction centrifugal pump for suppressing impeller pressure pulsation according to claim 3, characterized in that: In step (2), the inlet setting angle is between 16.5° and 21°, the outlet setting angle is between 21° and 23°, and the included angle is 180-200°.

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