Disclosure of Invention
The invention aims to solve the problems in the prior art and provide a Design method for cutting an impeller of a centrifugal pump at multiple low specific speeds, wherein a series of different cutting schemes are arranged by adopting a Design of Experiment (DOE) Design method; and on the premise of meeting the basic external characteristic performance of the centrifugal pump, the friction loss of an impeller disc is reduced by cutting the outer diameter of the impeller, the front cover plate and the rear cover plate, so that the shaft power is reduced, and the aim of no overload of the centrifugal pump with low specific speed is fulfilled.
The technical purpose of the invention is mainly solved by the following technical scheme: the design method for cutting the impeller of the centrifugal pump with the low specific speed is characterized by comprising the following steps of:
s1, selecting initial geometric parameters: selecting cutting parameters of the outer diameter of the impeller, the front cover plate of the impeller and the rear cover plate of the impeller, and determining the value range of the cutting parameters;
s2, carrying out scheme design: 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 the impellers of each group of schemes to obtain the external characteristics of each scheme;
s4, three-dimensional modeling: establishing a functional relation between each parameter and the external characteristic by adopting regression analysis, and carrying out calculation and prediction on the external characteristic on function assignment to obtain an impeller model of the optimal solution parameter;
s5, carrying out test verification on the optimal solution parameters obtained by assigning and optimizing the function of S4 to determine that the cutting parameters meet the external characteristic performance.
A series of different cutting schemes are arranged by adopting a Design of experience (DOE), and about 12 groups of cutting schemes are generally preferred; in the step of S2, CFX calculation is carried out on each scheme (ANSYS CFX software is adopted), a function model is established by regression analysis, optimal solution parameters obtained by assigning and optimizing the function of S4 are verified by experiments, so that the cutting parameters (the parameters are the outer diameter of the impeller, the outer diameter of the front cover plate and the outer diameter of the rear cover plate) meet the external characteristic performance, the impeller of the optimal scheme is determined, the shaft power is greatly reduced on the basis of not influencing the external characteristic performance of the centrifugal pump, and the purpose that the low-specific-speed centrifugal pump is not overloaded is achieved.
As a further improvement and supplement to the above technical solution, the present invention adopts the following technical measures:
in the step S4, mesh division is performed on the three-dimensional model, and then function assignment calculation is performed.
Determining the outer diameter of an outlet of the impeller to be D2, and cutting the impeller according to cutting parameters, so that the diameter of a blade of the impeller is D1, and D1 is [0, D2-3 ]; the diameter of a front cover plate of the impeller is D2, D2 is [0, D2-3 ]; the diameter of the back cover plate of the impeller is D3, D3 ═ 0, D2-3.
The cutting amount of the blade, the front cover plate and the rear cover plate of the impeller is not larger than 3 mm.
And establishing a functional relation between each parameter and the external characteristics of each scheme by adopting regression analysis, wherein the established functional model is as follows:
+204.0752×d3。
and (3) carrying out assignment optimization on the function model to obtain the optimal solution parameters of d 1-135, d 2-132 and d 3-132.
The invention has the following beneficial effects: a series of different cutting schemes are arranged by adopting a Design of experience (DOE) method to carry out multi-objective optimization Design. The method comprises the steps of 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 function model by adopting regression analysis, predicting and optimizing the most function model to obtain optimal design parameters, and reducing friction loss of an impeller disc by cutting the outer diameter of the impeller, a front cover plate and a rear cover plate on the premise of meeting the basic external characteristic performance of the centrifugal pump, thereby reducing shaft power and achieving the purpose that the centrifugal pump with low specific speed is not overloaded.
Example (b): as shown in fig. 1. The design method for cutting the impeller of the centrifugal pump with the low specific speed is characterized by comprising the following steps of:
s1, selecting initial geometric parameters (based on the initial geometric parameters obtained by the traditional hydraulic design method): selecting cutting parameters of the outer diameter of the impeller, the front cover plate of the impeller and the rear cover plate of the impeller, and determining the value range of the cutting parameters;
s2, carrying out scheme design: 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 the impellers of each group of schemes to obtain the external characteristics of each scheme;
s4, three-dimensional modeling is carried out on the impeller by adopting CREO: establishing a functional relation between each parameter and the external characteristic by adopting regression analysis, and carrying out calculation and prediction on the external characteristic on function assignment to obtain an impeller model of the optimal solution parameter;
s5, carrying out test verification on the optimal solution parameters obtained by assigning and optimizing the function of S4 to determine that the cutting parameters meet the external characteristic performance.
A series of different cutting schemes are arranged by adopting a Design of experience (DOE), and about 12 groups of cutting schemes are generally preferred; in the step of S2, CFX calculation is carried out on each scheme (ANSYS CFX software is adopted), a function model is established by regression analysis, optimal solution parameters obtained by assigning and optimizing the function of S4 are verified by experiments, so that the cutting parameters (the parameters are the outer diameter of the impeller, the outer diameter of the front cover plate and the outer diameter of the rear cover plate) meet the external characteristic performance, the impeller of the optimal scheme is determined, the shaft power is greatly reduced on the basis of not influencing the external characteristic performance of the centrifugal pump, and the purpose that the low-specific-speed centrifugal pump is not overloaded is achieved.
In step S4, mesh division (unstructured mesh division is performed on the impeller by using the ICED) is performed on the three-dimensional model, and then CFX is introduced to perform function assignment calculation.
As shown in fig. 2, determining the outlet outer diameter of the impeller to be D2, and cutting the impeller according to cutting parameters so that the blade diameter of the impeller is D1, and D1 is [0, D2-3 ]; the diameter of a front cover plate of the impeller is D2, D2 is [0, D2-3 ]; the diameter of the back cover plate of the impeller is D3, D3 ═ 0, D2-3.
The cutting amount of the blade, the front cover plate and the rear cover plate of the impeller is not larger than 3 mm.
And establishing a functional relation between each parameter and the external characteristics of each scheme by adopting regression analysis, wherein the established functional model is as follows:
and (3) carrying out assignment optimization on the function model to obtain the optimal solution parameters of d 1-135, d 2-132 and d 3-132.
Taking a low specific speed centrifugal pump IS3-28-0.75 as an example, the designed working condition flow of the pump IS 3m3/h, the lift IS 28m, the efficiency IS 21%, the matching power of the motor IS 0.75Kw, and the outer diameter D2 of the impeller IS 138 mm. The maximum shaft power of the pump is 1330w when the pump is in large flow, and is more than the Pmax (maximum power) 1285w specified by a national standard motor, so the pump is improved by adopting the design method related to the technical scheme, and the pump comprises the following specific steps:
step 1, cutting back diameter d1 of an impeller blade, cutting back diameter d2 of an impeller front cover plate and cutting back diameter d3 of the impeller rear cover plate, determining the design ranges of cutting parameters, namely d1 ═ 132, 135 and 138, d2 ═ 132, 134, 136 and 138, and d3 ═ 132, 134, 136 and 138, and obtaining 12 sets of design schemes by adopting a DOE test design method;
and carrying out fluid domain modeling on the impellers of each group of schemes, dividing grids, assembling the grids with the original pump body fluid domain grids, introducing the grids into a CFX (computational fluid dynamics) to carry out steady-state and unsteady-state numerical simulation calculation, and obtaining the head, efficiency and shaft power data 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 simulating the design parameters and values of each set of schemes.
d1 |
d2 |
d3 |
Q(m3/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 is performed on the data in the table 1 to obtain a fitting function model of
And (3) carrying out assignment optimization on the function model to obtain the optimal solution parameters of d 1-135, d 2-132 and d 3-132.
Cutting the impeller according to the optimal parameters, and testing the performance of a prototype test, wherein 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 to the design requirement, and other external characteristic lifts and efficiencies also meet the design requirement.
The efficiency simulated in table 1 is only hydraulic efficiency, and the power is water power; while the efficiency tested in table 2 is the unit efficiency (i.e., the product of the motor efficiency and the pump efficiency) and the power is the motor input power. Therefore, the CFX simulation head data can truly reflect the head of the electric pump, and the values of the efficiency and the power are only used as reference, but the trend of the efficiency (namely the power) can also be predicted.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. In the above embodiments, the present invention may be variously modified and changed. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.