A method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller

Abstract

This invention discloses an experimental method for judging the stability of the internal flow field of a centrifugal pump impeller, including the following steps: Judgment condition one: After modal decomposition of the internal flow field of the centrifugal pump impeller, the standard velocity V of the flow field from the impeller inlet to the middle of the flow channel in the first and second order modes is satisfied, and large-scale structures only appear in the region near the pressure surface at the outlet, where X max X represents the maximum measured speed. min X is the minimum measured speed. i The measured velocity value is shown at the test point. Beneficial effects: Using the above method to detect the stability of the internal flow field of a centrifugal pump impeller provides a basis for guiding the actual operation of the pump in engineering, thereby enabling in-depth analysis of the performance and fault diagnosis of the centrifugal pump. It largely determines whether the pump is operating stably, not only improving the pump's efficiency but also providing excellent protection.

Description

Technical Field

[0001] This invention relates to the fields of fluid machinery and centrifugal pump technology, and more specifically, to a method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller. Background Technology

[0002] Centrifugal pumps, as general-purpose machinery, are widely used in various sectors of the national economy, especially in water conservancy, aerospace, and petrochemical industries, where they play a vital role. Therefore, improving the efficiency of centrifugal pumps, expanding their stable operating range, and enhancing their safety and reliability are crucial for the national economy, energy conservation, and environmental protection. Currently, many scholars have conducted numerical simulations of the three-dimensional flow in centrifugal pumps, and using numerical simulation methods to study the internal flow field of the centrifugal pump impeller has become one of the important means of improving and optimizing centrifugal pumps.

[0003] The stability of the internal flow field of a centrifugal pump impeller has a significant impact on pump performance. Instability can lead to adverse effects such as decreased cavitation resistance, head hump, increased pressure pulsation, and backflow. Therefore, a simple and effective method is needed to quickly determine whether the internal flow field of a centrifugal pump impeller is stable, thereby reducing the performance degradation caused by instability in the impeller's internal flow field.

[0004] No effective solutions have yet been proposed to address the problems in the relevant technologies. Summary of the Invention

[0005] To address the problems in related technologies, this invention proposes an experimental method for judging the stability of the internal flow field of a centrifugal pump impeller, thereby overcoming the aforementioned technical problems existing in the existing related technologies.

[0006] Therefore, the specific technical solution adopted by the present invention is as follows:

[0007] A method for experimentally determining the stability of the internal flow field of a centrifugal pump impeller includes the following steps;

[0008] Judgment Condition 1: After modal decomposition of the internal flow field of the centrifugal pump impeller, the standard velocity V of the flow field from the impeller inlet to the middle of the flow channel in the first and second order modes satisfies... Furthermore, large-scale structures only appear in the region near the pressure surface at the outlet, where X max X represents the maximum measured speed. min X is the minimum measured speed. i The speed value measured at the test point;

[0009] Judgment condition two: The largest eigenvalue λ among the eigenvalues ​​of the flow field modal decomposition. max and the minimum eigenvalue λ min The ratio, i.e. It is a response to the sensitivity to flow field errors. Meanwhile, after the time coefficient is Fourier transformed, no obvious peak values ​​appear in the amplitude values ​​of the first-order mode and second-order mode spectra within a specific frequency range;

[0010] Judgment Condition 3: The turbulence intensity coefficient K from the impeller inlet to the middle of the flow channel satisfies 0.0001 < K < 0.0004, and the turbulence intensity increases sharply in the region near the pressure surface at the impeller outlet. It is the horizontal velocity component of the flow field in the impeller channel. U is the velocity component in the vertical direction of the impeller flow field. tip The tip velocity of the blade;

[0011] If the internal flow field of the centrifugal pump to be tested simultaneously meets the above three judgment conditions under different operating conditions, then the internal flow field of the centrifugal pump is in a stable flow state; if any one of the judgment conditions is not met, then it is in an unstable flow state.

[0012] Preferably, the following steps are also included;

[0013] S1: Construct an experimental platform for testing the internal flow field stability of a centrifugal pump;

[0014] S2: The experiment uses centrifugal pump impellers of different sizes and specifications. The pump cover and impeller are made of transparent plexiglass. The liquid used in the experiment is water.

[0015] S3: Use a high-speed camera to photograph the flow field of the centrifugal pump impeller channel to obtain its internal velocity field;

[0016] S4: After performing modal decomposition on the obtained velocity field, we obtain the mode diagrams and eigenvalues ​​of the internal flow field of the impeller;

[0017] S5: Use MATLAB software to obtain the turbulence intensity coefficient distribution map of the obtained velocity field;

[0018] S6: Obtain the spectrum using the Fast Fourier Transform algorithm in MATLAB;

[0019] By using the first and second mode diagrams of the internal flow field of the impeller, the distribution diagram of the turbulence intensity coefficient, the condition index, and the spectrum diagram, and based on the above judgment conditions, it is possible to quickly determine whether the internal flow field of the pump is in a stable flow state.

[0020] Preferably, the modal decomposition method is used to remove noise information from the flow field, including the following steps;

[0021] Flow field x at any time i It can be represented as average flow and pulsation quantity x iThe superposition of ', that is

[0022] The core of representing the flow field using mode decomposition is to represent the fluctuating quantity x. i It is represented by the linear superposition of low-order mode decomposition bases, that is:

[0023] Where N is the number of flow field snapshots, u j (x) is a mode decomposition basis, a j (i) represents the mode coefficients of the j-th basis at time i. To obtain the mode decomposition basis, the correlation matrix C = P should be calculated first. T P;

[0024] P = [x1', x'2, ... x'] N C is a matrix composed of snapshots of the flow field fluctuations over time. C is a symmetric matrix, therefore its eigenvalues ​​are non-negative, as shown by the formula CA. j =λ j A j Implement the eigenvalue calculation for C

[0025] λ j and A j For the j-th eigenvalue and eigenvector respectively, the mode decomposition basis is defined as:

[0026] The modal coefficients corresponding to each mode are:

[0027] The solutions are sorted according to the magnitude of the eigenvalues ​​in the equation, λ1 > λ2 > ... > λ N ≥0.

[0028] As a preferred embodiment, the method also includes relating the turbulence intensity coefficient and time coefficient to the flow field. The specific method for calculating the turbulence intensity coefficient K is as follows:

[0029] The Fast Fourier Transform method is k = 0, 1, ..., N-1.

[0030] Preferably, the centrifugal pump internal flow field stability testing test bench includes a computer, a laser, a torque meter, a shaft encoder, a motor, a test pump, a high-speed camera, a pressure sensor, a water tank, an electronic flow meter, and a test pump test bench. The computer is connected to the laser, high-speed camera, pressure sensor, and electronic flow meter respectively. The synchronizer is connected to the laser. The motor is connected to the test pump through the torque meter. The motor, torque meter, and test pump are fixed on the test bench. The water tank is connected to the test pump to form a loop.

[0031] The beneficial effects of this invention are as follows:

[0032] I. The velocity field of the impeller flow channel was obtained using the Particle Image Method (PIV), and the internal flow field of the centrifugal pump impeller was reduced in order using mode decomposition. First-order and second-order mode diagrams of the internal flow field, as well as the turbulence intensity coefficient distribution, were plotted using MATLAB software. Simultaneously, a Fast Fourier Transform (FFT) algorithm was performed using MATLAB to obtain the frequency spectrum. The mode diagrams, turbulence intensity coefficient distribution, conditional exponent, and frequency distribution were used to quickly determine whether the internal flow field of the centrifugal pump impeller was in a stable state. Using this method to detect the stability of the internal flow field of the centrifugal pump impeller provides a basis for guiding the actual operation of the pump in engineering, enabling in-depth analysis of the centrifugal pump's performance and fault diagnosis. This method significantly improves the pump's efficiency and provides excellent protection.

[0033] Second, this method can more intuitively judge the stability of the internal flow field of a centrifugal pump impeller. The method is simple and clear, eliminating the need for tedious operations such as drawing grids and numerical flow simulation, saving time, and the judgment results are relatively accurate. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic flowchart illustrating the experimental method for determining the stability of the internal flow field of a centrifugal pump according to an embodiment of the present invention.

[0036] Figure 2 This is a diagram of an experimental setup for determining the stability of the internal flow field of a centrifugal pump according to an embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of a centrifugal pump test impeller according to an embodiment of the present invention;

[0038] Figure 4 This is a specific application scenario according to an embodiment of the present invention in 1.0Q. BEP First and second order mode diagrams of the internal flow field of a centrifugal pump impeller under steady-state conditions obtained by mode decomposition at different flow rates;

[0039] Figure 5 This is a specific application scenario according to an embodiment of the present invention in 1.0Q. BEP Distribution of turbulence intensity coefficient in the steady-state flow field inside the centrifugal pump impeller at a given flow rate;

[0040] Figure 6 In a specific application scenario according to an embodiment of the present invention, at 0.6QBEP First and second order mode diagrams of the centrifugal pump impeller under unstable flow field conditions obtained by mode decomposition at different flow rates;

[0041] Figure 7 In a specific application scenario according to an embodiment of the present invention, at 0.6Q BEP Distribution of turbulence intensity coefficient under unstable flow field conditions inside the centrifugal pump impeller at a given flow rate;

[0042] Figure 8 This is a specific application scenario according to the embodiments of the present invention. A graph showing the changing patterns of traffic flow;

[0043] Figure 9 In a specific application scenario according to an embodiment of the present invention, at 0.6Q BEP Spectrum diagrams of the first and second modes of the centrifugal pump impeller under unstable flow conditions; the left side shows the time coefficients of the first and second modes; the right side shows the fast Fourier transforms of the first and second modes. Detailed Implementation

[0044] To further illustrate the various embodiments, the present invention provides accompanying drawings, which are part of the disclosure of the present invention. These drawings are mainly used to illustrate the embodiments and can be used in conjunction with the relevant descriptions in the specification to explain the operating principles of the embodiments. With reference to these drawings, those skilled in the art should be able to understand other possible implementation methods and the advantages of the present invention. The components in the drawings are not drawn to scale, and similar component symbols are generally used to represent similar components.

[0045] According to an embodiment of the present invention, a method for experimentally determining the stability of the internal flow field of a centrifugal pump impeller is provided.

[0046] Example 1;

[0047] like Figure 1-9 As shown, the experimental method for determining the stability of the internal flow field of a centrifugal pump impeller according to an embodiment of the present invention includes the following steps;

[0048] Step S1: Construct an experimental platform for testing the internal flow field stability of a centrifugal pump;

[0049] Step S2: The experiment uses centrifugal pump impellers of different sizes and specifications. Both the pump cover and the impeller are made of transparent plexiglass. The liquid used in the experiment is water.

[0050] Step S3: Use a high-speed camera to photograph the flow field of the centrifugal pump impeller channel to obtain its internal velocity field;

[0051] Step S4: After performing modal decomposition on the obtained velocity field, the modal diagrams and eigenvalues ​​of each order of the internal flow field of the impeller are obtained;

[0052] Step S5: Use MATLAB software to obtain the turbulence intensity coefficient distribution map of the obtained velocity field;

[0053] Step S6: Use the MATLAB algorithm to perform a fast Fourier transform to obtain the spectrum;

[0054] Judgment Condition 1: After modal decomposition of the internal flow field of the centrifugal pump impeller, the standard velocity V of the flow field from the impeller inlet to the middle of the flow channel in the first and second order modes satisfies... Furthermore, large-scale structures only appear in the region near the pressure surface at the outlet, where X max X represents the maximum measured speed. min X is the minimum measured speed. i The speed value measured at the test point;

[0055] Judgment condition two: The largest eigenvalue λ among the eigenvalues ​​of the flow field modal decomposition. max and the minimum eigenvalue λ min The ratio, i.e. It is a response to the sensitivity to flow field errors. Meanwhile, after the time coefficient is Fourier transformed, no obvious peak values ​​appear in the amplitude values ​​of the first-order mode and second-order mode spectra within a specific frequency range;

[0056] Judgment Condition 3: The turbulence intensity coefficient K from the impeller inlet to the middle of the flow channel satisfies 0.0001 < K < 0.0004, and the turbulence intensity increases sharply in the region near the pressure surface at the impeller outlet. It is the horizontal velocity component of the flow field in the impeller channel. U is the velocity component in the vertical direction of the impeller flow field. tip The tip velocity of the blade;

[0057] If the internal flow field of the centrifugal pump to be tested simultaneously meets the above three judgment conditions under different operating conditions, then the internal flow field of the centrifugal pump is in a stable flow state; if any one of the judgment conditions is not met, then it is in an unstable flow state.

[0058] Example 2;

[0059] like Figure 2 As shown, the centrifugal pump internal flow field stability testing test bench includes a computer, a laser, a torque meter, a shaft encoder, a motor, a test pump, a high-speed camera, a pressure sensor, a water tank, an electronic flow meter, and a test pump test bench. The computer is connected to the laser, high-speed camera, pressure sensor, and electronic flow meter respectively. The synchronizer is connected to the laser. The motor is connected to the test pump through the torque meter. The motor, torque meter, and test pump are fixed on the test bench. The water tank is connected to the test pump to form a loop.

[0060] The impeller's geometric parameters are as follows: 5 blades, blade width of 7mm, blade thickness of 4mm, blade inlet diameter of 56mm, and impeller blade outlet diameter of 142mm.

[0061] Example 3;

[0062] like Figure 4 As shown, in specific application scenarios in 1.0Q BEP After performing modal decomposition on the obtained velocity field under the flow rate, the first and second order mode diagrams of the internal flow field of the impeller were obtained. Under the first and second order modes, the standard velocity of the flow field from the impeller inlet to the middle of the flow channel is between 0.001 and 0.004, and the large-scale structure only appears in the region near the pressure surface at the outlet.

[0063] like Figure 5 As shown, in specific application scenarios in 1.0Q BEP The turbulence intensity coefficient distribution map was obtained by using MATLAB software on the obtained velocity field under the flow rate. The turbulence intensity coefficient K from the impeller inlet to the middle of the flow channel is between 0.0001 and 0.0004, and the turbulence intensity coefficient increases sharply in the region near the pressure surface at the impeller outlet.

[0064] like Figure 6 As shown, in specific application scenarios, at 0.6Q BEP After performing modal analysis on the obtained velocity field under the flow rate, the first and second mode diagrams of the internal flow field of the impeller were obtained. It can be clearly observed that the large-scale structure has a wide distribution range and mainly appears at the inlet and middle of the impeller flow channel. This does not meet the first judgment condition, so it is in an unstable flow state.

[0065] like Figure 7 As shown, in specific application scenarios, at 0.6Q BEP Using MATLAB software, the distribution map of the turbulence intensity coefficient K was obtained from the velocity field at the given flow rate. It can be observed that the turbulence is mainly concentrated in the inlet and outlet regions of the impeller channel.

[0066] like Figure 8 As shown in the curves of the condition index under various traffic conditions in specific application scenarios, it is clear that at 1.0Q... BEP The condition index is less than 500, while all other conditions are greater than 500.

[0067] like Figure 9 As shown, in the application scenario at 0.6Q BEP The obtained velocity field was subjected to a fast Fourier transform using the MATLAB algorithm to obtain a spectrum. It can be clearly observed that the amplitude values ​​of the first-order mode and the second-order mode spectrum both have peak values, indicating that the flow is in an unstable state.

[0068] It is obvious that 0.6QBEP The condition does not meet the above three criteria, therefore the internal flow field of the centrifugal pump impeller is in an unstable flow state, 1.0Q BEP Since the above criteria are met, the flow is in a stable state.

[0069] The above method is used to detect the stability of the internal flow field of a centrifugal pump impeller, providing a basis for guiding the actual operation of the pump in engineering. This allows for in-depth analysis of the centrifugal pump's performance and fault diagnosis, significantly improving pump stability and enhancing its efficiency while providing excellent protection. Furthermore, it allows for a more intuitive assessment of the internal flow field stability of the centrifugal pump impeller. The method is simple and straightforward, eliminating the need for tedious operations such as mesh drawing and flow numerical simulation, saving time, and providing relatively accurate results.

[0070] In summary, by employing the above-mentioned technical solution of this invention, the velocity field of the impeller flow channel is obtained using the Particle Image Method (PIV), and the internal flow field of the centrifugal pump impeller is reduced in order using mode decomposition. Combined with MATLAB software, the first and second-order mode diagrams of the internal flow field and the turbulence intensity coefficient distribution diagram are plotted. Simultaneously, a fast Fourier transform is performed using the MATLAB algorithm to obtain the spectrum diagram. The mode diagrams, turbulence intensity coefficient distribution, conditional exponent, and frequency distribution are used to quickly determine whether the internal flow field of the centrifugal pump impeller is in a stable state. Using this method to detect the stability of the internal flow field of the centrifugal pump impeller provides a basis for guiding the actual operation of the pump in engineering, thereby enabling in-depth analysis of the performance and fault diagnosis of the centrifugal pump. It largely detects whether the pump is operating stably, not only improving the pump's efficiency but also providing excellent protection. This method can more intuitively determine the stability of the internal flow field of the centrifugal pump impeller. The method is simple and clear, eliminating tedious operations such as grid drawing and flow numerical simulation, saving time, and the judgment results are relatively accurate.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller, characterized in that, Includes the following steps; Judgment Condition 1: After modal decomposition of the internal flow field of the centrifugal pump impeller, the standard velocity V of the flow field from the impeller inlet to the middle of the flow channel in the first and second order modes satisfies... Furthermore, large-scale structures only appear in the region near the pressure surface at the outlet, where X max X represents the maximum measured speed. min X is the minimum measured speed. i The measured speed value at the test point; Judgment condition two: The largest eigenvalue λ among the eigenvalues ​​of the flow field modal decomposition. max and the minimum eigenvalue λ min The ratio, i.e. It is a response to the sensitivity to flow field errors. Meanwhile, after the time coefficient is Fourier transformed, no obvious peak values ​​appear in the amplitude values ​​of the first-order mode and second-order mode spectra within a specific frequency range; Judgment Condition 3: The turbulence intensity coefficient K from the impeller inlet to the middle of the flow channel satisfies 0.0001 < K < 0.0004, and the turbulence intensity increases sharply in the region near the pressure surface at the impeller outlet. It is the horizontal velocity component of the flow field in the impeller channel. U is the velocity component in the vertical direction of the impeller flow field. tip The tip velocity of the blade; If the internal flow field of the centrifugal pump to be tested simultaneously meets the above three judgment conditions under different operating conditions, then the internal flow field of the centrifugal pump is in a stable flow state; if any one of the judgment conditions is not met, then it is in an unstable flow state.

2. The method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller according to claim 1, characterized in that, It also includes the following steps; S1: Construct an experimental platform for testing the internal flow field stability of a centrifugal pump; S2: The experiment uses centrifugal pump impellers of different sizes and specifications. The pump cover and impeller are made of transparent plexiglass. The liquid used in the experiment is water. S3: Use a high-speed camera to photograph the flow field of the centrifugal pump impeller channel to obtain its internal velocity field; S4: After performing modal decomposition on the obtained velocity field, we obtain the mode diagrams and eigenvalues ​​of the internal flow field of the impeller; S5: Use MATLAB software to obtain the turbulence intensity coefficient distribution map of the obtained velocity field; S6: Obtain the spectrum using the Fast Fourier Transform algorithm in MATLAB; By using the first and second mode diagrams of the internal flow field of the impeller, the distribution diagram of the turbulence intensity coefficient, the condition index, and the spectrum diagram, and based on the above judgment conditions, it is possible to quickly determine whether the internal flow field of the pump is in a stable flow state.

3. The method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller according to claim 2, characterized in that, The application of modal decomposition to eliminate noise interference in the flow field includes the following steps; Flow field x at any time i It can be represented as average flow and pulsation x' i The superposition, that is The core of representing the flow field using modal decomposition is to represent the fluctuating quantity x' i It is represented by the linear superposition of low-order mode decomposition bases, i.e. Where N is the number of flow field snapshots, u j (x) is a mode decomposition basis, a j (i) represents the mode coefficients of the j-th basis at time i. To obtain the mode decomposition basis, the correlation matrix C = P should be calculated first. T P; P = [x'1, x'2, ... x' N C is a matrix composed of snapshots of the flow field fluctuations over time. C is a symmetric matrix, therefore its eigenvalues ​​are non-negative, as shown by the formula CA. j =λ j A j To solve for the eigenvalues ​​of C; λ j and A j For the j-th eigenvalue and eigenvector respectively, the mode decomposition basis is defined as: The modal coefficients corresponding to each mode are: The solutions are sorted according to the magnitude of the eigenvalues ​​in the equation, λ1 > λ2 > ... > λ N ≥0.

4. The method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller according to claim 2, characterized in that, This also includes associating the turbulence intensity coefficient and time coefficient with the flow field. The specific method for calculating the turbulence intensity coefficient K is as follows: The Fast Fourier Transform method is 5. The method for experimentally judging the stability of the internal flow field of a centrifugal pump impeller according to claim 2, characterized in that, The centrifugal pump internal flow field stability testing test bench includes a computer, a laser, a torque meter, a shaft encoder, a motor, a test pump, a high-speed camera, a pressure sensor, a water tank, an electronic flow meter, and a test pump test bench. The computer is connected to the laser, high-speed camera, pressure sensor, and electronic flow meter respectively. The synchronizer is connected to the laser. The motor is connected to the test pump through the torque meter. The motor, torque meter, and test pump are fixed on the test bench. The water tank is connected to the test pump to form a loop.

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