Centrifugal pump impeller cutting method

Abstract

The invention discloses a centrifugal pump impeller cutting method. The method comprises the steps that a relational expression among the cutting amount, the cutting angle, the specific speed and the performance of a double suction pump is established; according to the actual required lift, the established cutting correction formula is used for determining cutting parameters including the cutting angle and the cutting amount; constructing a three-dimensional modeling model of the optimal scheme based on the determined cutting amount and cutting angle; performing grid division on the three-dimensional modeling model to obtain three-dimensional model data; analyzing the three-dimensional model data to obtain external characteristics of the three-dimensional modeling model so as to determine that the cutting parameters meet the external characteristics; and comparing the result of the optimal scheme with the result obtained by the traditional theoretical formula, and verifying the accuracy and the stability. By the adoption of the technical scheme, the performance prediction accuracy and the operation stability after the centrifugal pump impeller is cut are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of pump manufacturing, and in particular relates to a centrifugal pump impeller cutting method. Background Art

[0002] Double-suction centrifugal pumps are widely used in water conservancy and irrigation projects, urban water supply and drainage, industrial circulating water, and inter-basin water transfer due to their large flow and high head, good anti-cavitation performance, easy maintenance, and long service life. With the development of science and technology and the improvement of environmental protection requirements, the application scope of double-suction pumps will be further expanded. Double-suction pumps often encounter problems such as low efficiency and unstable operation due to unreasonable impeller design during operation. As one of the core components of double-suction pumps, the design and improvement of the impeller has a vital impact on the performance of the pump.

[0003] In order to expand the application scope of centrifugal pumps, when there is a deviation between the performance of the water pump and the actual demand in the project, the impeller is usually cut to change the outer diameter of the impeller to make the pump performance meet the requirements. However, the cutting formula currently used in cutting impellers is mainly applicable to single-stage single-suction centrifugal pumps, and mainly corrects the cutting amount. At present, most of the research on the correction of the cutting formula is aimed at single-stage single-suction pumps. Due to the complex structure of double-suction pumps, the error between the calculated value and the actual value of the existing empirical formula will become larger, and impeller cutting will cause unstable flow inside the double-suction pump, thereby affecting the operational reliability. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a centrifugal pump impeller cutting method.

[0005] To achieve the above object, the present invention adopts the following technical solution:

[0006] A centrifugal pump impeller cutting method, comprising:

[0007] S1. Establish the cutting formula of full-speed double-suction pump to determine the relationship between cutting volume and performance;

[0008] S2. Establish the cutting formula of cutting amount, specific speed and pump performance;

[0009] S3, determining the relationship between the specific speed cutting angle and the performance;

[0010] S4. According to the relationship between the cutting angles at different specific speeds, a correction formula for the cutting amount and the cutting angle based on the specific speed is obtained;

[0011] S5. Determine the cutting amount and cutting angle according to the proposed cutting correction formula, and select the cutting parameters of the impeller outer diameter, the impeller front cover plate, and the impeller rear cover plate under the current cutting amount;

[0012] S6. Cut the impeller based on the determined cutting amount and cutting angle, and construct a three-dimensional model of the design solution.

[0013] Preferably, in S1, it is assumed that the impeller outlet areas and outlet angles are equal before and after cutting, that is, D2b2=D'2b'2, β2=β'2, then:

[0014]

[0015]

[0016] D2”=0.75D2'+0.25D2

[0017] Where H is the lift before cutting, H' is the lift after cutting, D2 is the outer diameter of the impeller before cutting, D'2 and D"2 are both the outer diameters of the impeller after cutting, u2 is the circumferential velocity of the blade outlet before cutting, u'2 is the circumferential velocity of the blade outlet after cutting, and v m2 is the axial velocity of the blade outlet before cutting, v' m2 is the axial velocity of the blade outlet after cutting.

[0018] Preferably, in S2, the specific speed is limited to establish a functional relationship between the cutting amount, the specific speed and the double-suction pump performance, and the formula is:

[0019] D2”'=δD2'+(1-δ)D2”

[0020] ΔD=D2-D2”'

[0021] Where D”’2 is the outer diameter of the impeller after final cutting, ΔD is the cutting amount, and δ is the correction coefficient, which ranges from 0.43 to 0.6.

[0022] Preferably, in S3, the best cutting angle is selected with the highest efficiency as the goal, and regression analysis is used to fit curves of the relationship between the cutting angle and the cutting amount of the three double-suction pumps with low, medium and high specific speeds, respectively, and the specific functional relationship is determined by a polynomial, and the relationship is:

[0023]

[0024] Where θ is the cutting angle and b2 is the impeller outlet width.

[0025] Preferably, in S4, the correction formula of the cutting amount and cutting angle based on the specific speed is:

[0026] θ=a(ΔD%) 3 -b(ΔD%) 2 +c(ΔD%)-d.

[0027] Preferably, in S6, based on the determined cutting amount and cutting angle, the original model is cut by UG NX 3D modeling software, and the impeller is beveled in a positive direction, that is, cut from the front cover plate outlet toward the rear cover plate, to complete the 3D modeling.

[0028] Preferably, the method further includes: S7, meshing the three-dimensional model of the design solution to obtain three-dimensional model data; analyzing the three-dimensional model data to obtain external characteristics of the three-dimensional model to determine whether the cutting parameters meet the external characteristics.

[0029] The present invention can effectively reduce the turbulence of the fluid at the impeller outlet while more accurately meeting the use requirements, making the fluid flow smoother and reducing energy loss, thereby improving the operating efficiency of the pump, reducing energy consumption, and reducing operating costs; reducing vibration, ensuring the stability of the impeller at high-speed rotation, and greatly improving the operating state of the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0031] Figure 1 This is a flow chart of a centrifugal pump impeller cutting method according to an embodiment of the present invention;

[0032] Figure 2 Schematic diagram of the two-dimensional structure of the centrifugal pump impeller cutting method according to an embodiment of the present invention; wherein D 21 —Front cover diameter; D 22 —rear cover plate diameter; D2—impeller outer diameter before cutting; D2'—average outer diameter of the impeller after cutting; θ—cutting angle;

[0033] Figure 3 This is a schematic diagram comparing the standard deviations of different cutting formulas;

[0034] Figure 4 Schematic diagram of the internal flow comparison of different cutting formulas. DETAILED DESCRIPTION

[0035] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0036] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0037] Embodiment 1:

[0038] like Figure 1 As shown, an embodiment of the invention provides a centrifugal pump impeller cutting method, comprising:

[0039] S1. Establish the cutting formula of full-speed double-suction pump to determine the relationship between cutting volume and performance;

[0040] S2. Limit the specific speed of the double-suction pump and establish a cutting formula for the cutting amount, specific speed and pump performance;

[0041] S3. Determination of the relationship between the specific speed cutting angle and performance;

[0042] S4. Establish the relationship between the cutting angles at different specific speeds, and propose correction formulas for the cutting amount and cutting angle based on the specific speed;

[0043] S5. Determine the cutting amount and cutting angle according to the proposed cutting correction formula, and select the cutting parameters of the impeller outer diameter, the impeller front cover, and the impeller rear cover under the cutting amount at this time;

[0044] S6. Cut the impeller based on the determined cutting amount and cutting angle, and construct a three-dimensional model of the design scheme;

[0045] S7. Meshing the three-dimensional model of the design solution to obtain three-dimensional model data; analyzing the three-dimensional model data to obtain external characteristics of the three-dimensional model to determine whether cutting parameters meet external characteristics.

[0046] As an implementation of the embodiment of the present invention, in S1, it is assumed that the impeller outlet areas and outlet angles are equal before and after cutting, that is, D2b2=D'2b'2, β2=β'2, then:

[0047]

[0048]

[0049] D2”=0.75D2'+0.25D2

[0050] Where H is the lift before cutting, H' is the lift after cutting, D2 is the outer diameter of the impeller before cutting, D'2 and D"2 are both the outer diameters of the impeller after cutting, u2 is the circumferential velocity of the blade outlet before cutting, u'2 is the circumferential velocity of the blade outlet after cutting, and v m2 is the axial velocity of the blade outlet before cutting, v'm2 is the axial velocity of the blade outlet after cutting.

[0051] As an implementation method of the embodiment of the present invention, in S2, since the application scope of the full specific speed cutting formula is too large, the calculated result has a large error with the actual calculation, and the performance prediction accuracy is low, the specific speed is limited to establish a functional relationship between the cutting amount, the specific speed and the double-suction pump performance, and the formula is:

[0052] D2”'=δD2'+(1-δ)D2”

[0053] ΔD=D2-D2”'

[0054] Where D”’2 is the outer diameter of the impeller after final cutting, ΔD is the cutting amount, and δ is the correction coefficient, which ranges from 0.43 to 0.6.

[0055] As an implementation method of the present invention, in S3, the best cutting angle is selected with the highest efficiency as the goal, and regression analysis is used to fit the relationship between the cutting angle and the cutting amount of the three double-suction pumps with low, medium and high specific speeds, respectively, and the specific functional relationship is determined by polynomials. The impeller is beveled within a certain range, and its cutting angle range is based on the right-angle triangle relationship between the cutting amount, the cutting angle, and the impeller outlet width, and the relationship is:

[0056]

[0057] Where θ is the cutting angle and b2 is the impeller outlet width.

[0058] As an implementation method of an embodiment of the present invention, in S4, according to the determined functional relationship, a general form is set, the coefficients are fitted, and the value ranges of the correction coefficients a, b, c, and d are obtained respectively, and a correction formula for the cutting amount and cutting angle based on the specific speed is proposed, and the formula is generalized to be applicable to each type of specific speed pump, and the relationship is:

[0059] θ=a(ΔD%) 3 -b(ΔD%) 2 +c(ΔD%)-d

[0060] As an implementation of the embodiment of the present invention, in S5, according to the proposed correction formula, a correction coefficient is selected based on the specific speed to determine the final cutting amount and cutting angle.

[0061] As an implementation of the embodiment of the present invention, in S6, based on the determined cutting amount and cutting angle, the following steps are performed: Figure 2As shown, the original model is cut by UG NX 3D modeling software, and the impeller is beveled in a positive direction, that is, cut from the front cover outlet toward the rear cover to complete the 3D modeling.

[0062] As an implementation of an embodiment of the present invention, the generated three-dimensional model is imported into the ANSYS WorkBench platform in S8, meshing is completed based on ANSYS Meshing, and numerical analysis of the model is completed using ANSYS CFX, and the three-dimensional model data is analyzed including solving the RANS coupled SST model, setting the convergence accuracy target and the maximum number of iterations. The external characteristics of the corresponding model are obtained to determine whether the cutting parameters meet the external performance.

[0063] Embodiment 2:

[0064] The following is a specific speed n s =235 double suction pump and a specific speed n s =90 double suction pump is the research object, specific speed n s =235 double suction pump design flow Q d 4000m 3 / h, head H is 35m, impeller outer diameter D2 = 554mm, specific speed n s =90 double suction pump design flow Q d 500m 3 / h, the lift H is 40m, and the impeller outer diameter D2 is 365mm. The present invention is further described in detail in conjunction with the accompanying drawings and specific implementation methods.

[0065] The present invention provides a centrifugal pump impeller cutting method for improving performance prediction accuracy and operation stability, comprising the following steps:

[0066] 1.n s =235 double suction pump

[0067] (1) According to the relationship between cutting amount, cutting angle, specific speed and pump performance, a cutting correction formula is established, because the specific speed n s =235, so the values ​​of δ, a, b, c, and d are 0.43, 0.5, 9.6, 59.7, and 107, respectively, as shown in Table 1. The following relationship is established:

[0068]

[0069] D2”=0.75D2'+0.25D2

[0070] D2”'=0.43D2’+0.57D2”

[0071] ΔD=D2-D2”'

[0072]

[0073] θ=0.5(ΔD%) 3 -9.6(ΔD%) 2 +59.7(ΔD%)-107

[0074] Table 1

[0075] Specific speed n≤90 90<n≤170 170<n≤240 δ 0.6 0.56 0.43 a 0.2～0.5 0.5～0.75 0.3～0.5 b 9.0～9.5 10～13 9.5～10.0 c 55～56 14～15 59.0～60.0 d 95～100 140～145 105～107

[0076] (2) According to the actual use requirements of the double-suction pump, assuming that the actual required head is 30 meters, determine the cutting amount and cutting angle, and solve:

[0077]

[0078] D2”=0.75×515.2+0.25×554=524.9(mm)

[0079] D2”'=0.43×515.2+0.57×524.9=520.7(mm)

[0080] ΔD=554-520.7=33.3(mm)

[0081]

[0082] θ=0.5(6) 3 -9.64(6) 2 +59.7×6-107=10(°)

[0083] Therefore, the cutting amount is determined to be 33.3 mm, the diameter after cutting is 520.7 mm, the cutting rate is 6%, and the optimal bevel angle is 10°.

[0084] (3) According to the determined cutting amount and cutting angle, the impeller outlet is beveled forward, such as Figure 2 As shown, it is cut obliquely from the front cover outlet toward the rear cover, and the UG NX 3D software is used to complete the 3D modeling of the optimal design solution.

[0085] (4) Import the three-dimensional model generated in step 3 into the ANSYS WorkBench platform, complete meshing based on ANSYS Meshing, and use ANSYS CFX to complete the numerical analysis of the model and obtain the external characteristics of the corresponding model.

[0086] (5) Based on the standard deviation, the internal flow characteristics and stability of the design are analyzed.

[0087] Furthermore, the cutting diameter obtained in step 2 is the average diameter of the impeller after cutting, and its formula is:

[0088]

[0089] Where D 21 —Front cover diameter, D 22 —Rear cover diameter.

[0090] Furthermore, the design model of step 3 is 3D modeled by UG NX 3D software, and finally converted into a standard 3D model format (Parasolid) for output.

[0091] Furthermore, the process of dividing the impeller and pump chamber using ANSYS Meshing in step 4 uses a component identification and parameter setting plug-in developed in Python to complete the identification, naming and meshing of each surface of the impeller and pump chamber.

[0092] Furthermore, the numerical analysis method described in step 4 is based on the commercial CFD software ANSYS CFX, and the RANS coupled SST k-ω model is used for solution; specifically, the discrete format of the convection term is set to the second-order upwind double-suction pump inlet condition as the total pressure inlet, the reference pressure as 0Pa, and the outlet as the mass flow outlet. In the unsteady calculation, the total calculation time is 0.606061s, and the time step is 3.38×10 -4 s, that is, a total of 14 cycles are calculated, and the time step is the time required for the impeller to rotate 3°. The head, efficiency, pressure and other parameters are monitored, and the overall calculation domain is divided into a rotating domain and a stationary domain. The impeller is the rotating domain, and the wall rotation speed is the impeller speed. The rest of the components are stationary domains, and the walls are all no-slip boundaries. The convergence accuracy is taken as 10 -5 The obtained external characteristic data of the design scheme are compared with other cutting formulas. The correction formula proposed by the present invention has the smallest error of 4.5%, which is 10.7% and 7.7% lower than the relative errors of the other two cutting formulas, respectively, which improves the accuracy of performance prediction. The correction formula proposed by the present invention has the highest efficiency and the strongest working capacity, as shown in Table 2.

[0093] Table 2

[0094]

[0095] Furthermore, the lift and efficiency data of the last cycle in the calculation are taken for standard deviation σ value analysis, and the formula is:

[0096]

[0097] Where: σ represents the standard deviation, Σ represents the sum, Xi represents the value of each data point, μ represents the mean of the data set, and N represents the total number of data points.

[0098] The larger the standard deviation, the more dispersed the data is and the worse the stability is; the smaller the standard deviation, the more concentrated the data is and the better the stability is. Figure 3 As shown, Formula 1 is the data of the general formula, Formula 2 is the data of the Sulzer formula, and Formula 3 is the data obtained by the modified formula proposed by the present invention. When the modified formula is cut according to the present invention, that is, when the bevel angle θ=10°, the standard deviation of the head and efficiency are both the smallest, indicating that the external characteristics of the pump are relatively stable during unsteady flow under the design condition, and the water pressure changes less with time.

[0099] Furthermore, for example Figure 4 As shown, it can be seen that the flow condition of the double-suction pump impeller is significantly improved after positive bevel cutting within a certain range, and the vortex structure is reduced first. For this double-suction pump, θ=10° is a relatively suitable cutting angle.

[0100] 2.n s =90 double suction pump

[0101] (1) According to the relationship between cutting amount, cutting angle, specific speed and pump performance, a cutting correction formula is established, because the specific speed n s =90, so the values ​​of δ, a, b, c, and d are 0.6, 0.5, 9.5, 56, and 98, respectively, as shown in Table 3. The following relationship is established:

[0102]

[0103] D2”=0.75D2'+0.25D2

[0104] D2”'=0.6D2’+0.4D2”

[0105] ΔD=D2-D2”'

[0106]

[0107] θ=0.5(ΔD%) 3 -9.5(ΔD%) 2 +56(ΔD%)-98

[0108] Table 3

[0109] Specific speed n≤90 90<n≤170 170<n≤240 δ 0.6 0.56 0.43 a 0.2～0.5 0.5～0.75 0.3～0.5 b 9.0～9.5 10～13 9.5～10.0 c 55～56 14～15 59.0～60.0 d 95～100 140～145 105～107

[0110] (2) According to the actual use requirements of the double-suction pump, assuming that the actual required head is 36 meters, determine the cutting amount and cutting angle, and solve:

[0111]

[0112] D2”=0.75×346.3+0.25×365=351(mm)

[0113] D2”'=0.6×346.3+0.4×351=348.2(mm)

[0114] ΔD=365-348.2=16.8(mm)

[0115]

[0116] θ=0.5(4.5) 3 -9.5(4.5) 2 +56×4.5-98=7(°)

[0117] Therefore, the cutting amount is determined to be 16.5 mm, the diameter after cutting is 348.5 mm, the cutting rate is 4.5%, and the optimal bevel angle is 7°.

[0118] (3) According to the determined cutting amount and cutting angle, the impeller outlet is beveled forward, such as Figure 2 As shown, it is cut obliquely from the front cover outlet toward the rear cover, and the UG NX 3D software is used to complete the 3D modeling of the optimal design solution.

[0119] (4) Import the three-dimensional model generated in step 3 into the ANSYS WorkBench platform, complete meshing based on ANSYS Meshing, and use ANSYS CFX to complete the numerical analysis of the model and obtain the external characteristics of the corresponding model.

[0120] Furthermore, the cutting diameter obtained in step 2 is the average diameter of the impeller after cutting, and its formula is:

[0121]

[0122] Where D 21 —Front cover diameter, D 22 —Rear cover diameter.

[0123] Furthermore, the design model of step 3 is 3D modeled by UG NX 3D software, and finally converted into a standard 3D model format (Parasolid) for output.

[0124] Furthermore, the process of dividing the impeller and pump chamber using ANSYS Meshing in step 4 uses a component identification and parameter setting plug-in developed in Python to complete the identification, naming and meshing of each surface of the impeller and pump chamber.

[0125] Furthermore, the numerical analysis method described in step 4 is based on the commercial CFD software ANSYS CFX, and the RANS coupled SST k-ω model is used for solution; specifically, the discrete format of the convection term is set as the inlet condition of the second-order upwind double-suction pump is the total pressure inlet, the reference pressure is 0Pa, and the outlet is the mass flow outlet. The overall calculation domain is divided into a rotating domain and a stationary domain, in which the impeller is the rotating domain, the wall rotation speed is the impeller speed, and the other parts are all stationary domains, the walls are all no-slip boundaries, and the convergence accuracy is taken as 10 -5 .

[0126] The external characteristic data of the design scheme obtained has a head of 36.93 meters and a relative error of about 2.6%. The error is well controlled and the accuracy of performance prediction is improved. When the bevel angle is 7°, the efficiency can reach 88.13 meters and the working capacity is also strong.

[0127] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A centrifugal pump impeller cutting method, characterized in that: include: S1. Establish the cutting formula of full-speed double-suction pump to determine the relationship between cutting volume and performance; S2. Establish the cutting formula of cutting amount, specific speed and pump performance; S3, determining the relationship between the specific speed cutting angle and the performance; S4. According to the relationship between the cutting angles at different specific speeds, a correction formula for the cutting amount and the cutting angle based on the specific speed is obtained; S5. Determine the cutting amount and cutting angle according to the proposed cutting correction formula, and select the cutting parameters of the impeller outer diameter, the impeller front cover plate, and the impeller rear cover plate under the current cutting amount; S6. Cut the impeller based on the determined cutting amount and cutting angle, and construct a three-dimensional model of the design solution.

2. The centrifugal pump impeller cutting method according to claim 1, characterized in that: In S1, it is assumed that the impeller outlet areas and outlet angles are equal before and after cutting, that is, D2b2 = D'2b'2, β2 = β'2, then: D2”=0.75D2'+0.25D2 Where H is the lift before cutting, H' is the lift after cutting, D2 is the outer diameter of the impeller before cutting, D'2 and D"2 are both the outer diameters of the impeller after cutting, u2 is the circumferential velocity of the blade outlet before cutting, u'2 is the circumferential velocity of the blade outlet after cutting, and v m2 is the axial velocity of the blade outlet before cutting, v' m2 is the axial velocity of the blade outlet after cutting.

3. The centrifugal pump impeller cutting method according to claim 2, characterized in that: In S2, the specific speed is limited to establish a functional relationship between the cutting amount, the specific speed and the double-suction pump performance, and the formula is: D2”'=δD2'+(1-δ)D2” ΔD=D2-D2”' Where D”’2 is the outer diameter of the impeller after final cutting, ΔD is the cutting amount, and δ is the correction coefficient, which ranges from 0.43 to 0.

6.

4. The centrifugal pump impeller cutting method according to claim 3, characterized in that: In S3, the best cutting angle is selected with the highest efficiency as the goal, and regression analysis is used to fit the relationship between the cutting angle and the cutting amount of the three double-suction pumps with low, medium and high specific speeds. The specific functional relationship is determined by a polynomial, and the relationship is: Where θ is the cutting angle and b2 is the impeller outlet width.

5. The centrifugal pump impeller cutting method according to claim 4, characterized in that: In S4, the correction formula of the cutting amount and cutting angle based on the specific speed is: θ=a(ΔD%) 3 -b(ΔD%) 2 +c(ΔD%)-d。 6. The centrifugal pump impeller cutting method according to claim 5, characterized in that: In S6, based on the determined cutting amount and cutting angle, the original model is cut by UG NX 3D modeling software, and the impeller is cut in a positive bevel direction, that is, cut from the front cover plate outlet toward the rear cover plate direction, to complete the 3D modeling.

7. The centrifugal pump impeller cutting method according to claim 6, characterized in that: Also includes: S7, meshing the three-dimensional model of the design solution to obtain three-dimensional model data; The three-dimensional model data is analyzed to obtain the external characteristics of the three-dimensional model to determine whether the cutting parameters meet the external characteristics.

Images