Disclosure of Invention
The invention aims to solve the problems in the prior art and provide a method for designing the cutting of a centrifugal pump impeller with multiple low specific speeds, wherein a series of different cutting schemes are arranged by adopting a test design method (Design of Experiment, DOE); and carrying out CFX calculation on each scheme, establishing a functional relation between impeller parameters and external characteristic performance, and adopting regression analysis to establish a functional model so as to obtain optimal design parameters, and cutting the impeller outer diameter, the front cover plate and the rear cover plate on the premise of meeting the basic external characteristic performance of the centrifugal pump so as to reduce the friction loss of the impeller disc, thereby reducing the shaft power and realizing the purpose of no overload of the centrifugal pump with low specific speed.
The technical aim of the invention is mainly solved by the following technical scheme: the low specific speed centrifugal pump impeller cutting design method is characterized by comprising the following steps:
s1, selecting initial geometric parameters: selecting cutting parameters of the impeller outer diameter, the impeller front cover plate and the impeller rear cover plate, and determining a value range of the cutting parameters;
s2, scheme design is carried out: designing a plurality of groups of cutting schemes by adopting a test design method;
s3, determining the external characteristics of the impeller of each parameter scheme: calculating impellers of each group of schemes to obtain the external characteristics of each scheme;
s4, performing three-dimensional modeling: adopting regression analysis to establish a functional relation between each parameter and external characteristics, and carrying out calculation and prediction of the external characteristics on function assignment to obtain an impeller model of optimal solution parameters;
and S5, performing test verification on the optimal solution parameters obtained by the function assignment optimization of the S4 to determine that the cutting parameters meet the external characteristic performance.
A series of different cutting schemes are arranged by adopting a test design method (Design of Experiment, DOE), and 12 groups or so are usually preferable schemes; in the step S2, CFX calculation is carried out on each scheme (ANSYS CFX software is adopted), a function model is established by adopting regression analysis, and experimental verification is carried out on optimal solution parameters obtained by function assignment optimizing in the step S4, so that cutting parameters (the parameters are the outer diameter of an impeller, the outer diameter of a front cover plate and the outer diameter of a rear cover plate) are determined to meet the outer characteristic performance, and the impeller of the optimal scheme is determined, so that the shaft power is greatly reduced on the basis of not influencing the outer characteristic performance of the centrifugal pump, and the purpose of no overload of the centrifugal pump with low specific speed is realized.
As a further improvement and supplement to the technical scheme, the invention adopts the following technical measures:
and S4, carrying out grid division on the three-dimensional modeling, and then carrying out function assignment calculation.
Determining the outer diameter of an outlet of the impeller as D2, and cutting the impeller according to cutting parameters to ensure that the blade diameter of the impeller is D1, d1= [0, D2-3]; the diameter of a front cover plate of the impeller is D2, d2= [0, D2-3]; the diameter of the rear cover plate of the impeller is D3, d3= [0, D2-3].
The cutting amount of the blades, the front cover plate and the rear cover plate of the impeller is not more than 3mm.
And adopting regression analysis to establish functional relations between all parameters and external characteristics of all schemes, wherein the established functional model is as follows:
+204.0752×d 3 。
and carrying out assignment optimization on the function model to obtain optimal solution parameters d1=135, d2=132 and d3=132.
The invention has the beneficial effects that: a series of different cutting schemes are arranged by adopting a test design method (Design of Experiment, DOE) to carry out multi-objective optimization design. Carrying out CFX calculation on each scheme by adopting ANSYS CFX software, establishing a functional relation between impeller parameters and external characteristic performance, establishing a functional model by adopting regression analysis, predicting and optimizing the most functional model, thereby obtaining optimal design parameters, and reducing friction loss of an impeller disc by cutting the impeller outer diameter, a front cover plate and a rear cover plate on the premise of meeting basic external characteristic performance of the centrifugal pump, thereby reducing shaft power and realizing the purpose of no overload of the centrifugal pump with low specific rotation speed.
Detailed Description
The technical scheme of the invention is further specifically described below through examples and with reference to the accompanying drawings.
Examples: as shown in fig. 1. The low specific speed centrifugal pump impeller cutting design method is characterized by comprising the following steps:
s1, selecting initial geometric parameters (initial geometric parameters obtained based on a traditional hydraulic design method): selecting cutting parameters of the impeller outer diameter, the impeller front cover plate and the impeller rear cover plate, and determining a value range of the cutting parameters;
s2, scheme design is carried out: designing a plurality of groups of cutting schemes by adopting a test design method;
s3, determining the external characteristics of the impeller of each parameter scheme: calculating impellers of each group of schemes to obtain the external characteristics of each scheme;
s4, adopting CREO to carry out three-dimensional modeling on the impeller: adopting regression analysis to establish a functional relation between each parameter and external characteristics, and carrying out calculation and prediction of the external characteristics on function assignment to obtain an impeller model of optimal solution parameters;
and S5, performing test verification on the optimal solution parameters obtained by the function assignment optimization of the S4 to determine that the cutting parameters meet the external characteristic performance.
A series of different cutting schemes are arranged by adopting a test design method (Design of Experiment, DOE), and 12 groups or so are usually preferable schemes; in the step S2, CFX calculation is carried out on each scheme (ANSYS CFX software is adopted), a function model is established by adopting regression analysis, and experimental verification is carried out on optimal solution parameters obtained by function assignment optimizing in the step S4, so that cutting parameters (the parameters are the outer diameter of an impeller, the outer diameter of a front cover plate and the outer diameter of a rear cover plate) are determined to meet the outer characteristic performance, and the impeller of the optimal scheme is determined, so that the shaft power is greatly reduced on the basis of not influencing the outer characteristic performance of the centrifugal pump, and the purpose of no overload of the centrifugal pump with low specific speed is realized.
And S4, carrying out grid division on the three-dimensional model (carrying out unstructured grid division on the impeller by adopting ICED), and then leading in CFX (computational fluid dynamics) to carry out function assignment calculation.
As shown in fig. 2, determining the outer diameter of an outlet of the impeller as D2, and cutting the impeller according to cutting parameters to ensure that the blade diameter of the impeller is D1, d1= [0, D2-3]; the diameter of a front cover plate of the impeller is D2, d2= [0, D2-3]; the diameter of the rear cover plate of the impeller is D3, d3= [0, D2-3].
The cutting amount of the blades, the front cover plate and the rear cover plate of the impeller is not more than 3mm.
And adopting regression analysis to establish functional relations between all parameters and external characteristics of all schemes, wherein the established functional model is as follows:
and carrying out assignment optimization on the function model to obtain optimal solution parameters d1=135, d2=132 and d3=132.
Taking a centrifugal pump IS3-28-0.75 with low specific rotation speed as an example, the flow rate of the design working condition of the pump IS 3m3/h, the lift IS 28m, the efficiency IS 21%, the matched power of the motor IS 0.75Kw, and the external diameter D2 = 138mm. The maximum shaft power of the pump is 1330w when the pump is in large flow, and is larger than pmax=1285w specified by the national standard motor, so the design method related to the technical scheme is adopted for improvement, and the specific steps are as follows:
step 1, the diameter d1 after impeller blade cutting, the diameter d2 after impeller front cover plate cutting and the diameter d3 after impeller rear cover plate cutting are adopted, the design ranges of cutting parameters are respectively d1= {132, 135 and 138}, d2= {132, 134, 136 and 138}, and d3= {132, 134, 136 and 138}, and a DOE test design method is adopted to obtain 12 groups of design schemes;
and carrying out fluid domain modeling on impellers of each group of schemes, dividing grids, assembling the fluid domain grids with the original pump body, guiding the grids into CFX, and carrying out constant and unsteady numerical simulation calculation to obtain the data of the lift, the efficiency and the shaft power of the external characteristics of the centrifugal pump.
And carrying out regression analysis on the calculated lift, efficiency, shaft power and flow and carrying out function fitting to obtain a function model.
Table 1 below shows the external characteristic data obtained by numerical simulation for each set of design parameters.
d 1 |
d 2 |
d 3 |
Q(m 3 /h)
|
H(m)
|
η(%)
|
P(w)
|
132
|
132
|
132
|
3
|
30.16
|
34.31
|
377.82
|
132
|
138
|
138
|
3
|
29.72
|
34.83
|
366.05
|
132
|
136
|
134
|
3
|
29.82
|
35.62
|
358.98
|
138
|
136
|
138
|
3
|
31.67
|
37.9
|
357.01
|
138
|
132
|
136
|
3
|
31.43
|
37.6
|
357.38
|
135
|
132
|
138
|
3
|
31.6
|
36.48
|
370.42
|
135
|
138
|
132
|
3
|
30.67
|
35.11
|
375.2
|
138
|
138
|
134
|
3
|
31.85
|
35.93
|
378.6
|
138
|
134
|
132
|
3
|
31.54
|
36.28
|
371.5
|
132
|
134
|
136
|
3
|
30.29
|
36.64
|
354.25
|
135
|
136
|
136
|
3
|
30.97
|
37.96
|
349.13
|
135
|
134
|
134
|
3
|
30.94
|
35.71
|
370.95 |
TABLE 1
Regression analysis was performed on the data from Table 1 above to obtain a fitted function model
And carrying out assignment optimization on the function model to obtain optimal solution parameters d1=135, d2=132 and d3=132.
Cutting the impeller according to the optimal parameters, and performing a prototype test to test performance, the following table 2 is test data:
TABLE 2
As can be seen from table 2 above, the maximum shaft power is reduced by 101w compared with the design requirement, and the other external characteristic lifts and efficiencies also meet the design requirement.
The efficiency simulated in table 1 is only hydraulic efficiency, power is water power; while the efficiency tested in table 2 is the unit efficiency (i.e., the product of motor efficiency and pump efficiency), and the power is the motor input power. So CFX simulated head data can truly reflect the head of the pump, while the values of efficiency and power are merely used as references, but the trend of its efficiency (i.e. power) can also be predicted.
The foregoing description is only of the preferred embodiments of the invention and is not intended to limit the invention. In the above-described embodiments, the present invention is susceptible to various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.