A collaborative control method for transition process of large-scale inclined axial flow pump station

Abstract

The present invention discloses a method for coordinated control of the transition process of a large-scale inclined axial flow pump station. The present invention establishes a high-precision numerical calculation grid model of a large-scale inclined pump station, and can derive the performance characteristics of the shutdown transition process of the inclined axial flow pump station based on the coordinated control of the impeller and the gate. At the same time, based on three-dimensional numerical calculation, the influence of different impeller and gate coordinated control schemes on the shutdown transition process performance of the inclined axial flow pump station can be analyzed, thereby better realizing the screening of impeller and gate coordinated control schemes, ensuring the structural safety of the pump during the shutdown transition process of the inclined axial flow pump station, and improving the life of the pump.

Description

Technical Field

[0001] The invention belongs to the technical field of pump station optimization, and in particular relates to a transition process coordinated control method for a large-scale inclined axial flow pump station. Background Art

[0002] In recent years, global warming has led to a significant increase in extreme weather. The lack of drainage capacity in urban sewer systems and the rapid rise in water levels often put cities at risk of flooding and waterlogging. In order to quickly alleviate flood disasters, large cities widely build large pumping stations. In urban drainage pumping stations, axial flow pumps are widely used because of their relatively simple structure and good performance in low head sections. Among vertical axial flow pumps, horizontal axial flow pumps and inclined axial flow pumps, the inclined axial flow pump has broad application prospects due to its simple and compact structure, low construction cost, convenient maintenance, and superior operating performance. It is increasingly being adopted by urban drainage pumping stations. The inclined structure of the inclined axial flow pump will lead to some specific motion characteristics that affect the safety of the pump, but this has been ignored in current research on the inclined axial flow pump. The transition process of the pump, such as startup, shutdown, and flow adjustment, will cause the pump system to be accompanied by the greatest instability during operation, so the transition process is very important for the pump. If not handled properly, severe vibration, noise, and cavitation may occur, leading to damage to the pump and pipeline system, and ultimately to pump station failure. In addition, the surge in extreme weather in recent years has also brought more uncertainty to the transition process of water pumps. Therefore, special attention should be paid to the safety of the transition process of large pumping stations.

[0003] Among all the transition processes of the oblique axial flow pump, the shutdown transition process requires special attention because the impeller is not controlled by the motor and is only affected by hydraulic force. It is easy to reverse under the action of a large reverse water flow, so the shutdown transition process requires special attention. The gate is a very important component of the axial flow pump station. It controls the flow rate by controlling the lifting speed during the startup and shutdown process. Appropriate gate speed control can ensure the safety of the pump station transition process. If the design is improper, the gate will suffer huge impact and pulsation, resulting in friction and wear between the gate and the wall, reducing the service life of the gate. Therefore, it is very necessary to study the impact of the coordinated control scheme of the impeller and the gate on the performance of the pump station.

[0004] The research methods of the transition process include experimental methods and numerical calculation methods. Compared with the experimental method, the numerical calculation method of large units can avoid the damage of the unit caused by the test and is being adopted more and more. Numerical calculation includes one-dimensional calculation and three-dimensional calculation. One-dimensional calculation is very fast, but the credibility of one-dimensional calculation is not as good as three-dimensional calculation. With the development of computer technology, it has become possible to use CFD to perform three-dimensional precise calculations of large pump station units. In the past decade, a series of studies on the transition process of large pump stations have been carried out at home and abroad based on the CFD method. However, in these studies, there is no mention of the shutdown transition process of the inclined axial flow pump with gate movement, which makes the analysis of the transition process characteristics of the inclined axial flow pump lack of reference. At the same time, previous three-dimensional studies have ignored the influence of different impeller and gate coordinated control schemes, and cannot provide a reasonable impeller and gate adjustment reference for the pump station unit. Summary of the invention

[0005] The purpose of the present invention is to solve the problems existing in the prior art and to provide a method for coordinated control of the transition process of a large-scale inclined axial flow pump station.

[0006] The specific technical solutions adopted by the present invention are as follows:

[0007] A method for coordinated control of a transition process of a large-scale inclined axial flow pump station, comprising:

[0008] S1. Extract the water body model of the pump station from the three-dimensional model of the inclined axial flow pump station as the calculation domain, and divide the calculation domain into grids;

[0009] S2. In the inclined axial flow pump station, multiple gate closing speed values ​​are sampled within the gate closing speed control range, thereby obtaining multiple sets of coordinated control schemes for the impeller and the gate during the shutdown process; in each set of coordinated control schemes, the gate starts to descend and close from the fully open state according to the corresponding sampled gate closing speed value, and the impeller stops power output when the gate starts to descend and close;

[0010] S3, taking each set of cooperative control schemes in S2 as the target cooperative control scheme, numerical simulation is performed in the fluid simulation software respectively, and the simulation data corresponding to each set of cooperative control scheme is obtained; wherein the numerical simulation process for the target cooperative control scheme is as follows:

[0011] First, in the fluid simulation software, the first UDF program for determining the inlet and outlet pressure gradient boundary conditions is set according to the water head conditions of the upstream and downstream pools in the water body model. The second UDF program for calculating the impeller speed in each time step is set according to the impeller torque balance equation. The third UDF program for calculating the gate opening through the gate descent speed control function during the transient simulation process is set according to the gate closing speed value in the target collaborative control scheme.

[0012] Then, the characteristic parameters of the oblique axial flow pump that need to be monitored in real time in the calculation domain are set in the fluid simulation software, where the characteristic parameters include: the axial force of the impeller, the forces in two radial directions, the axial torque and the torque in two radial directions, as well as the pressure pulsation signals at three positions: in front of the impeller, between the impeller and the guide vane, and behind the guide vane, as well as the impeller speed and the flow rate at the pump outlet;

[0013] Finally, on the basis of setting the characteristic parameters for monitoring, the steady-state calculation of the pump is continuously performed when the gate is fully open and the impeller speed is unchanged, until the characteristic parameters are calculated to be stable, and then the first UDF program, the second UDF program and the third UDF program are loaded to start simulating the shutdown transition process. When the shutdown transition process starts to be simulated, the pump impeller is only subjected to hydraulic force, and the gate begins to decrease at a uniform speed according to the set gate closing speed value. During the gate descent process, the entire calculation domain is gradually increased according to the preset time step and total calculation time. The closing simulation of the gate is realized by the dynamic grid technology, and the motion simulation of the impeller is realized by the multiple reference system (MRF); after calculating all the time steps, the time series data of the characteristic parameters in the entire shutdown transition process are obtained;

[0014] S4. For all collaborative control schemes, extract the forces and torques of the impeller in three directions from the time series data corresponding to each set of collaborative control schemes, so as to analyze the mechanical characteristics of the oblique axial flow pump, select the collaborative control scheme that meets the preset mechanical characteristic standards as the alternative collaborative control scheme, and eliminate the collaborative control scheme that does not meet the preset mechanical characteristic standards;

[0015] S5. For the alternative collaborative control schemes, extract the pressure pulsation signals at three positions, namely, in front of the impeller, between the impeller and guide vane, and behind the guide vane, from the time series data corresponding to each set of collaborative control schemes, and perform short-time Fourier transform (STFT) processing on the time series data of the pressure pulsation signals, so as to analyze the pressure pulsation situation inside the inclined axial flow pump during the shutdown transition process, and select the alternative collaborative control scheme that meets the preset pump pressure pulsation standard as the final collaborative control scheme, which is used for collaborative control of the impeller and gate during the transition process of the large-scale inclined axial flow pump station.

[0016] Preferably, in S1, UG software is used to extract a water model of the pumping station from the three-dimensional model of the inclined axial flow pumping station, thereby establishing a numerical calculation grid model of the pumping station.

[0017] Preferably, in S1, the entire computational domain is divided into a hexahedral structured grid using ICEM meshing software.

[0018] Preferably, in S2, a plurality of gate closing speed values ​​are sampled within the closing speed control range by uniform sampling.

[0019] Furthermore, in S2, the number of samples of the gate closing speed values ​​is 5 to 10.

[0020] Preferably, the fluid simulation software is Fluent fluid simulation software.

[0021] Preferably, in S3, the first UDF program and the second UDF program used by all cooperative control schemes during the numerical simulation process are the same, and the third UDF program is different.

[0022] Preferably, the preset mechanical property standards include an axial force standard and a radial torque standard; the axial force standard is that the peak value of the reverse axial force in the axial force time domain curve of the impeller does not exceed the axial component of gravity, or the amount by which the peak value of the reverse axial force exceeds the axial component of gravity is lower than a first threshold; the radial torque standard is that the peak average value of the pulsation segment in the horizontal radial torque time domain curve of the impeller does not exceed a second threshold.

[0023] Preferably, the preset pump pressure pulsation standard is: for the pressure pulsation signal at a point between the impeller and the guide vane, the maximum intensity of the pressure pulsation extracted from the short-time Fourier transform (STFT) processing result thereof does not exceed a third threshold value.

[0024] Preferably, the first threshold, the second threshold and the third threshold are optimally determined by actual operating condition tests of the inclined axial flow pump station.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] The present invention can ensure the accuracy of calculation by establishing a high-precision numerical calculation grid model of a large-scale inclined pump station. Moreover, the present invention can derive the performance characteristics of the shutdown transition process of the inclined axial flow pump station based on the coordinated control of the impeller and the gate. At the same time, based on three-dimensional numerical calculation, the influence of different impeller and gate coordinated control schemes on the shutdown transition process performance of the inclined axial flow pump station can be analyzed, thereby better realizing the screening of impeller and gate coordinated control schemes, ensuring the structural safety of the pump during the shutdown transition process of the inclined axial flow pump station, and improving the life of the pump. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic diagram of the inclined axial flow pump station model;

[0028] Figure 2 Provides high-precision numerical calculation grid models for pumping stations;

[0029] Figure 3 Pressure gradient boundary conditions for upstream and downstream pools written based on UDF;

[0030] Figure 4Three locations for pressure monitoring;

[0031] Figure 5 This is the numerical calculation flow chart of the shutdown transition process of the oblique axial flow pump;

[0032] Figure 6 It is a mechanical characteristic curve analysis diagram, including (a) the change of axial force with time, (b) the change of axial torque with time, and (c) the change of torque in two radial directions with time;

[0033] Figure 7 STFT of the pressure pulsation signal at three monitoring points under five schemes. DETAILED DESCRIPTION

[0034] The present invention is further described and illustrated below in conjunction with the accompanying drawings and specific embodiments. The technical features of each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0035] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with the accompanying drawings. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below. The technical features in each embodiment of the present invention can be combined accordingly without conflicting with each other.

[0036] In the description of the present invention, it should be understood that the terms "first" and "second" are only used for the purpose of distinguishing descriptions, and should not be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features.

[0037] In the present invention, numerical calculation of the transition process of the inclined axial flow pump station based on the coordinated control of the gate and the rotor can obtain some unique properties of the pump station during the transition process, and can predict the stability and safety of the pump station during the transition process. Common transition process analysis includes external characteristic analysis, pressure pulsation analysis, and flow field characteristic analysis. For ease of understanding, before the present invention introduces the technical solution in detail, some technical terms related to the coordinated control of the gate and the rotor are explained:

[0038] 1.CFD numerical calculation technology.

[0039] CFD, or computational fluid dynamics, is a branch of fluid mechanics. CFD is the product of the combination of modern fluid mechanics, numerical mathematics and computer science. It is an interdisciplinary science with strong vitality. It uses electronic computers as tools and applies various discrete mathematical methods to conduct numerical experiments, computer simulations and analytical research on various problems in fluid mechanics to solve various practical problems. In this project, it is used to calculate the shutdown transition process of the inclined axial flow pump station.

[0040] 2. Dynamic mesh technology and MRF technology.

[0041] Dynamic mesh technology has a wide range of applications in the field of simulation. It can effectively solve the simulation calculation problem when the computational domain is deformed and moving. In this project, it is used to simulate the descent process of the gate. MRF, or multiple reference system, can ensure that the movement of objects is simulated without deforming the mesh. In this project, it is used to simulate the rotation of the impeller. These two technologies are important prerequisites for realizing the coordinated control of the impeller and the gate.

[0042] 3.STFT signal processing technology.

[0043] STFT, short-time Fourier transform, is a pulsation signal processing technology. Short-time Fourier uses a sliding window mechanism, sets the window size and step size, allows the window to slide on the time domain signal, and calculates the Fourier transform of each window separately, forming frequency domain signals corresponding to different time windows, which are spliced ​​together to form data (time-frequency signal) with frequency varying over time. Since STFT can obtain the frequency and amplitude of the signal over time, it is used in this project to analyze pressure pulsation signals.

[0044] 4.UDF technology.

[0045] UDF, or user-defined function, is a C function that can be dynamically loaded by the simulation software solver to enhance its standard functions. UDF is used to write programs for secondary development of simulation software and customize some complex situations in simulation. In this project, it is used for the coordinated control of gates and rotors in simulation.

[0046] In addition, if Figure 1 As shown, the typical structure of the oblique axial flow pump station in the present invention mainly includes the following structures: downstream water tank, upstream water tank, inlet flow channel, pump section, outlet flow channel and gate, among which the gate and impeller are important components in the transient process calculation process and are also the control objects in the present invention. The key point of the simulation process in the present invention is the impeller, which is the core component of the pump and its force will directly affect the life of the pump.

[0047] In a preferred embodiment of the present invention, a method for coordinated control of transition process of a large-scale inclined axial flow pump station is provided, and the specific steps are as follows:

[0048] S1. Extract the water model of the pump station from the three-dimensional model of the inclined axial flow pump station as the calculation domain, and divide the calculation domain into grids.

[0049] In the present invention, UG software can be used to extract the water body model of the pumping station from the three-dimensional model of the inclined axial flow pumping station, thereby establishing a numerical calculation grid model of the pumping station.

[0050] In the present invention, the ICEM meshing software can be used to divide the entire computational domain into hexahedral structured grids.

[0051] S2. In the inclined axial flow pump station, multiple gate closing speed values ​​are sampled within the closing speed control range of the gate, thereby obtaining multiple sets of coordinated control schemes for the impeller and the gate during the shutdown process; in each set of coordinated control schemes, the gate starts to descend and close from the fully open state according to the corresponding sampled gate closing speed value, and the impeller stops power output when the gate starts to descend and close.

[0052] In the present invention, a plurality of gate closing speed values ​​may be sampled within the closing speed control range in a uniform sampling manner.

[0053] In the present invention, having more sampling points for the gate closing speed value will make the simulation more representative, but considering the efficiency problem, the number of sampling points for the gate closing speed value within the range can be set to 5 to 10.

[0054] S3, taking each set of cooperative control schemes in S2 as the target cooperative control scheme, numerical simulation is performed in the fluid simulation software respectively, and the simulation data corresponding to each set of cooperative control scheme is obtained; wherein the numerical simulation process for the target cooperative control scheme is as follows:

[0055] First, in the fluid simulation software, the first UDF program for determining the inlet and outlet pressure gradient boundary conditions is set according to the water head conditions of the upstream and downstream pools in the water body model. The second UDF program for calculating the impeller speed in each time step is set according to the impeller torque balance equation. The third UDF program for calculating the gate opening through the gate descent speed control function during the transient simulation process is set according to the gate closing speed value in the target collaborative control scheme.

[0056] Then, the characteristic parameters of the oblique axial flow pump that need to be monitored in real time in the calculation domain are set in the fluid simulation software, where the characteristic parameters include: the axial force of the impeller, the forces in two radial directions, the axial torque and the torque in two radial directions, as well as the pressure pulsation signals at three positions: in front of the impeller, between the impeller and the guide vane, and behind the guide vane, as well as the impeller speed and the flow rate at the pump outlet;

[0057] Finally, on the basis of setting the monitoring characteristic parameters, the pump is first continuously calculated in a steady state when the gate is fully open and the impeller speed is unchanged, until the characteristic parameters are calculated to be stable, and then the first UDF program, the second UDF program and the third UDF program are loaded to start simulating the shutdown transition process. When the shutdown transition process starts to be simulated, the pump impeller is only subjected to hydraulic force, and the gate begins to decrease at a uniform speed according to the set gate closing speed value. During the gate descent process, the entire calculation domain is gradually increased according to the preset time step and total calculation time. Transient numerical calculations are performed, where the gate closing simulation is realized by the dynamic mesh technology, and the impeller motion simulation is realized by the multiple reference system (MRF); after calculating all time steps, the time series data of the characteristic parameters in the entire shutdown transition process are obtained, that is, the aforementioned simulation data.

[0058] In the present invention, the fluid simulation software that can be used is Fluent fluid simulation software.

[0059] In the present invention, the first UDF program and the second UDF program used in the numerical simulation process of all cooperative control schemes may be the same, and the third UDF program may be different.

[0060] S4. For all collaborative control schemes, extract the forces and torques of the impeller in three directions from the time series data corresponding to each set of collaborative control schemes, so as to analyze the mechanical characteristics of the oblique axial flow pump, select the collaborative control scheme that meets the preset mechanical characteristic standards as the alternative collaborative control scheme, and eliminate the collaborative control scheme that does not meet the preset mechanical characteristic standards.

[0061] S5. For the alternative collaborative control schemes, extract the pressure pulsation signals at three positions, namely, in front of the impeller, between the impeller and guide vane, and behind the guide vane, from the time series data corresponding to each set of collaborative control schemes, and perform short-time Fourier transform (STFT) processing on the time series data of the pressure pulsation signals, so as to analyze the pressure pulsation situation inside the inclined axial flow pump during the shutdown transition process, and select the alternative collaborative control scheme that meets the preset pump pressure pulsation standard as the final collaborative control scheme, which is used for collaborative control of the impeller and gate during the transition process of the large-scale inclined axial flow pump station.

[0062] In the present invention, the above-mentioned preset mechanical property standards and preset pump pressure pulsation standards need to be determined based on the inclined axial flow pump's own tolerance to mechanical properties and pump pressure pulsation in the inclined axial flow pump station, so as to ensure that the pump structure will not suffer fatigue loss and delay the service life of the pump.

[0063] As a preferred implementation of the present invention, the preset pressure pulsation standard in the pump includes an axial force standard and a radial torque standard; the axial force standard is that the peak value of the reverse axial force in the axial force time domain curve of the impeller does not exceed the axial component of gravity, or the amount by which the peak value of the reverse axial force exceeds the axial component of gravity is lower than a first threshold; the radial torque standard is that the peak average value of the pulsation segment in the horizontal radial torque time domain curve of the impeller does not exceed a second threshold.

[0064] As a preferred implementation of the present invention, the preset pressure pulsation standard in the pump is: for the pressure pulsation signal at the position point between the impeller and the guide vane, the maximum intensity of the pressure pulsation extracted from the short-time Fourier transform (STFT) processing result does not exceed the third threshold.

[0065] It should be noted that the above-mentioned first threshold, second threshold and third threshold need to be determined through the actual operating condition test of the inclined axial flow pump station to determine the optimal value. The three thresholds of different inclined axial flow pump stations may be different and need to be determined according to the pump's own structure and material characteristics.

[0066] The transition process collaborative control method of a large inclined axial flow pump station shown in S1 to S5 above is applied to a specific example to demonstrate the technical effect that can be achieved.

[0067] Example

[0068] like Figure 1 As shown, the structure of the inclined axial flow pump station in this example is shown, which mainly includes the following structures: downstream water tank, upstream water tank, inlet flow channel, pump section, outlet flow channel and gate, among which the gate and impeller are important components in the transition process calculation process. The shaft of the impeller in this example is a 20-degree inclined structure. The gate is a double gate. Before the shutdown transition process calculation begins, the pump is first calculated in a steady state. During the steady-state calculation, the impeller speed remains unchanged and the gate is fully open. After calculating that the characteristic parameters of the pump are basically unchanged, the shutdown transition process is calculated on this basis. Let the pump impeller be only subjected to hydraulic force, and at the same time, the gate begins to descend at a uniform speed.

[0069] The specific process of the transition process collaborative control method of a large inclined axial flow pump station in this embodiment is described in detail below. The process is as follows:

[0070] Step 1: According to Figure 1 The three-dimensional model of the inclined axial flow pump station shown in the figure is used to extract the water body model of the pump station using UG software. Then, the ICEM meshing software is used to divide the entire calculation domain into hexahedral structured grids to establish a high-precision numerical calculation grid model (computational domain) of the pump station. The completed numerical calculation grid model is shown in Figure 2 As shown in Figure 2, the computational domain includes the impeller domain and the guide vane domain.

[0071] Step 2. In order to simulate the influence of the gate descent speed on the shutdown transition process of the inclined axial flow pump station, according to the upper and lower limit requirements of the pump station for the gate speed, 5 gate closing speed values ​​are selected by uniform sampling within the gate closing speed control range, and the coordinated control scheme of the impeller and the gate during the shutdown process is designed for each gate closing speed value. From the slowest gate speed to the fastest, they are named Scheme 1, Scheme 2, Scheme 3, Scheme 4, and Scheme 5, and numerical calculations are performed on the five schemes respectively. In each set of coordinated control schemes, the gate starts to descend and close from the fully open state according to the corresponding sampled gate closing speed value, and the impeller stops power output when the gate begins to descend and close, that is, there is no driving force provided by the shaft, and it is only affected by hydraulic force.

[0072] Step 3: Take each set of collaborative control schemes in step 2 as the target collaborative control scheme, perform numerical simulation in the fluid simulation software Fluent, and obtain the simulation data corresponding to each set of collaborative control schemes. The numerical simulation process for the target collaborative control scheme is as follows:

[0073] Step 3.1: Write the inlet and outlet pressure gradient boundary condition UDF (i.e. the first UDF program) and load it on the inlet and outlet boundaries. According to the water depth of the inlet and outlet pools, write the pressure gradient function in the UDF to calculate the inlet and outlet pressures. In Fluent, assign pressure gradient boundary conditions to the inlet and outlet boundaries, and the pressure value is determined by the loaded UDF. The inlet and outlet boundary conditions of the five schemes are the same.

[0074] Step 3.2: Based on UDF, write the gate descent speed control function in the transient calculation process, and combine it with the dynamic grid to perform deformation control of the gate descent, that is, to form the third UDF program. When the gate opening is less than or equal to 0, it means that the gate is completely closed, and the movement of the gate is considered to have stopped. The formula for calculating the gate opening according to the gate descent speed control function is shown in formula (1):

[0075] Δ h =G h -v×t (1)

[0076] Among them, t, v, Δ h , and G h They respectively represent the total calculation time, the speed of the gate, the opening of the gate, and the total height of the gate.

[0077] Step 3.3: Write a UDF program (i.e., the second UDF program) for calculating the impeller speed at each time step based on the torque balance equation. The derivation process of the torque balance equation is shown in equations (2) to (3):

[0078]

[0079]

[0080] Among them, w i , w i+1 , ΔT, M h , M f , and J represent the speed of the previous time step, the speed of the next time step, the time step, the water torque on the impeller, the friction torque at the bearing, and the moment of inertia of the impeller. i , ΔT, M h , M f It can be obtained from the simulation results of the previous time step, where ΔT and J are known quantities.

[0081] After the three UDF programs are written, they can be loaded and assigned to the impeller speed control and the gate descent speed control.

[0082] Step 3.4: Set the characteristic parameters of the oblique axial flow pump that need to be monitored in real time in the calculation domain in Fluent, including: the pressure and velocity parameters of the cross section before the inlet flow channel and after the outlet flow channel, the axial force of the impeller ( Figure 1 in the x direction) and in the two radial directions ( Figure 1 y and z directions), axial torque ( Figure 1 x direction) and two radial directions ( Figure 1 The torque in the y and z directions) is measured at three locations (such as the front of the impeller, the middle of the impeller and the guide vane, and the back of the guide vane). Figure 4 The pressure pulsation signal at the three positions (point 1, point 2, and point 3) shown in the figure, the speed of the impeller, and the flow rate at the pump outlet. After all the characteristic parameters are set, before the shutdown transition process starts to be calculated, the pump is first calculated in a steady state. During the steady-state calculation, the impeller speed remains unchanged and the gate is fully open. After calculating that the characteristic parameters of the pump are basically unchanged, the first UDF program, the second UDF program, and the third UDF program are loaded on this basis to start simulating the shutdown transition process. When the shutdown transition process starts to be simulated, the pump impeller is only affected by hydraulic force. At the same time, the gate begins to drop at a uniform speed according to the set gate closing speed value. During the gate descent process, the entire calculation domain begins to be gradually lengthened according to the pre-set time step and total calculation time. Transient numerical calculations are performed, in which the gate closing simulation is realized by dynamic mesh technology, and the impeller motion simulation is realized by multiple reference frames (MRF). The entire process of numerical calculation during the entire shutdown transition process simulation is as follows. Figure 5 After calculating all time steps, the time series data of the characteristic parameters in the entire shutdown transition process are obtained.

[0083] Step 4: For all collaborative control schemes, extract the force and torque of the impeller in three directions from the time series data corresponding to each set of collaborative control schemes, so as to perform a mechanical property analysis on the oblique axial flow pump, select the collaborative control scheme that meets the preset mechanical property standards as the alternative collaborative control scheme, and eliminate the collaborative control scheme that does not meet the preset mechanical property standards.

[0084] In this embodiment, the mechanical characteristics of the inclined axial flow pump during shutdown transition are analyzed as follows:

[0085] Step 4.1: Draw the corresponding curve based on the obtained mechanical data and torque data of the impeller.

[0086] Step 4.2: Analysis of mechanical characteristics of the shutdown transition process of the inclined axial flow pump. First, analyze Scheme 1 alone to obtain the characteristics of the shutdown transition process of the inclined axial flow pump. Figure 6 In (a) and (b), when the pump is powered off and the gate begins to drop, the direction of the flow velocity and the impeller speed have not changed, so the direction of the pump's axial force and axial torque remains unchanged. However, as time goes by, the impeller does not exert an active torque and is mainly affected by water force. When the water begins to flow backwards due to gravity, the axial force and torque begin to gradually decrease and reverse in direction after a certain period of time, reaching a maximum value in the reverse direction after a period of time. As the gate gradually closes, the reverse water flow decreases, and the axial force and axial torque gradually decrease again until the impeller stops. Figure 6 In (c), it can be found that the torque of Scheme 1 in the y and z directions has a certain offset, and the torque in the z direction is translated upward as a whole. Figure 1 It can be found that this is because the pump is affected by gravity. Under the combined force of downward gravity and axial hydraulic force, the impeller will fluctuate in a downward trend. The external force in the y direction is balanced, and the torque gradually converges to 0. Therefore, it can be found that the inclined axis structure has a significant impact on the performance of the pump. If the downward offset movement is carried out for a long time, the degree of wear on the bearing may be greater than that of the vertical shaft pump.

[0087] Step 4.3: Compare and analyze the five gate descent speed schemes to obtain the influence of gate descent speed on the mechanical properties of the inclined axial flow pump during the shutdown transition process. Figure 6 It can be seen from (a), (b) and (c) that the gate speed has a significant effect on the mechanical properties of the pump. When the descent speed is faster, the impeller is subjected to force and torque for a shorter time, but there will be greater reverse axial force and axial torque. If the axial force is too large, it may cause damage to the motor. Figure 6 (a) Middle G xis the axial component of gravity. It can be found that when the gate descends faster than the speed of Scheme 3, the reverse axial force is significantly greater than the axial component of gravity, which is the lifting phenomenon. The lifting phenomenon is very harmful to the pump and motor. It can be seen that the gate speed has a significant impact on the performance of the pump shutdown transition process.

[0088] Therefore, in this example, the preset mechanical property standards include an axial force standard and a radial torque standard.

[0089] The axial force standard is that the peak value of the reverse axial force in the impeller's axial force time domain curve does not exceed the axial force component of gravity, or the amount by which the peak value of the reverse axial force exceeds the axial force component of gravity is lower than the first threshold. Figure 6 The highest peak value of the axial force time domain curve of each solution in (a) cannot exceed G x The horizontal line has a certain amount, which can be determined based on the structural performance of the actual pump.

[0090] The radial torque standard is that the peak value average value of the pulsation section in the horizontal radial torque time domain curve of the impeller does not exceed the second threshold value. Figure 6 M of each solution in (c) z The peak value average value in the pulsation section of the oscillation does not exceed a threshold value, and this threshold value can also be determined according to the structural performance of the actual pump.

[0091] For example, in this example, after screening by the axial force standard, only Scheme 2 and Scheme 1 meet the requirements. After further screening by the radial torque standard, only Scheme 2 meets the requirements, and Scheme 2 is selected as an alternative collaborative control scheme.

[0092] Step 5. For the alternative collaborative control schemes, extract the pressure pulsation signals at three positions, namely, in front of the impeller, between the impeller and the guide vane, and behind the guide vane, from the pattern time series data corresponding to each set of collaborative control schemes, and perform short-time Fourier transform (STFT) processing on the time series data of the pressure pulsation signal to analyze the pressure pulsation situation inside the inclined axial flow pump during the shutdown transition process, and select the alternative collaborative control scheme that meets the preset pump pressure pulsation standard as the final collaborative control scheme, which is used to collaboratively control the impeller and gate during the transition process of the large-scale inclined axial flow pump station.

[0093] In this example, the analysis process of the pressure pulsation characteristics of the inclined axial flow pump during shutdown transition is as follows:

[0094] Step 5.1: Based on the pressure signals at the three monitoring points of the impeller, draw STFT graphs.

[0095] Step 5.2: Analysis of pressure pulsation characteristics during the shutdown transition process of the inclined axial flow pump. First, analyze Scheme 1 alone to obtain the pressure pulsation characteristics of the shutdown transition process of the inclined axial flow pump. Figure 7 It can be found in (a), (b) and (c) that the pulsation conditions at different positions of the pump are similar, and there are frequency bands for blades to pass through. This shows that the fluctuations in the pump are the result of the interaction between movement and stillness. As the turbulence intensity of the fluid flow in the pump increases first and then decreases, the intensity of the fluctuations in the pump also increases first and then decreases. The number of high-frequency bands at point 2 is the largest, and the color is darker, and point 2 is closest to the impeller. This shows that the intensity of the fluctuations near the impeller is greater than the intensity of the fluctuations in the inlet and outlet flow channels.

[0096] In this example, the preset pump pressure pulsation standard is: for the pressure pulsation signal at the position point between the impeller and the guide vane, the maximum intensity of the pressure pulsation extracted from the short-time Fourier transform (STFT) processing result does not exceed the third threshold. Figure 7 The maximum intensity of the pressure pulsation extracted from the results does not exceed a threshold, which can also be determined based on the structural performance of the actual pump.

[0097] For example, in this example, after screening by the preset pump pressure pulsation standard, Scheme 2 still meets the requirements, then this Scheme 2 can be used to coordinate the transition process of the inclined axial flow pump station to ensure that the performance of the pump is not affected by the destructive axial force and pulsation in the transition process.

[0098] The above-described embodiment is only a preferred solution of the present invention, but it is not intended to limit the present invention. A person skilled in the relevant technical field may make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, any technical solution obtained by equivalent replacement or equivalent transformation falls within the protection scope of the present invention.

Claims

1. A method for coordinated control of transition process of a large-scale inclined axial flow pump station, characterized in that: include: S1. Extract the water body model of the pump station from the three-dimensional model of the inclined axial flow pump station as the calculation domain, and divide the calculation domain into grids; S2. In the inclined axial flow pump station, multiple gate closing speed values ​​are sampled within the gate closing speed control range, thereby obtaining multiple sets of coordinated control schemes for the impeller and the gate during the shutdown process; in each set of coordinated control schemes, the gate starts to descend and close from the fully open state according to the corresponding sampled gate closing speed value, and the impeller stops power output when the gate starts to descend and close; S3, taking each set of cooperative control schemes in S2 as the target cooperative control scheme, numerical simulation is performed in the fluid simulation software respectively, and the simulation data corresponding to each set of cooperative control scheme is obtained; wherein the numerical simulation process for the target cooperative control scheme is as follows: First, in the fluid simulation software, the first UDF program for determining the inlet and outlet pressure gradient boundary conditions is set according to the water head conditions of the upstream and downstream pools in the water body model. The second UDF program for calculating the impeller speed in each time step is set according to the impeller torque balance equation. The third UDF program for calculating the gate opening through the gate descent speed control function during the transient simulation process is set according to the gate closing speed value in the target collaborative control scheme. Then, the characteristic parameters of the oblique axial flow pump that need to be monitored in real time in the calculation domain are set in the fluid simulation software, where the characteristic parameters include: the axial force of the impeller, the forces in two radial directions, the axial torque and the torque in two radial directions, as well as the pressure pulsation signals at three positions: in front of the impeller, between the impeller and the guide vane, and behind the guide vane, as well as the impeller speed and the flow rate at the pump outlet; Finally, on the basis of setting the characteristic parameters for monitoring, the steady-state calculation of the pump is continuously performed when the gate is fully open and the impeller speed is unchanged, until the characteristic parameters are calculated to be stable, and then the first UDF program, the second UDF program and the third UDF program are loaded to start simulating the shutdown transition process. When the shutdown transition process starts to be simulated, the pump impeller is only subjected to hydraulic force, and the gate begins to drop at a uniform speed according to the set gate closing speed value. During the gate descent process, the entire calculation domain is gradually increased according to the preset time step and total calculation time. The closing simulation of the gate is realized by the dynamic grid technology, and the motion simulation of the impeller is realized by the multiple reference system MRF; after calculating all the time steps, the time series data of the characteristic parameters in the entire shutdown transition process are obtained; S4. For all collaborative control schemes, extract the forces and torques of the impeller in three directions from the time series data corresponding to each set of collaborative control schemes, so as to analyze the mechanical characteristics of the oblique axial flow pump, select the collaborative control scheme that meets the preset mechanical characteristic standards as the alternative collaborative control scheme, and eliminate the collaborative control scheme that does not meet the preset mechanical characteristic standards; S5. For the alternative collaborative control schemes, extract the pressure pulsation signals at three positions, namely, in front of the impeller, between the impeller and guide vane, and behind the guide vane, from the time series data corresponding to each set of collaborative control schemes, and perform short-time Fourier transform (STFT) processing on the time series data of the pressure pulsation signals, so as to analyze the pressure pulsation situation inside the inclined axial flow pump during the shutdown transition process, and select the alternative collaborative control scheme that meets the preset pump pressure pulsation standard as the final collaborative control scheme, which is used for collaborative control of the impeller and gate during the transition process of the large-scale inclined axial flow pump station.

2. The method for coordinated control of transition process of a large-scale inclined axial flow pump station according to claim 1, characterized in that: In S1, the water body model of the pumping station is extracted from the three-dimensional model of the inclined axial flow pumping station using UG software, thereby establishing a numerical calculation grid model of the pumping station.

3. The transition process coordinated control method of a large-scale inclined axial flow pump station according to claim 1 is characterized in that: In S1, the entire computational domain is divided into hexahedral structured grids using ICEM grid division software.

4. The method for coordinated control of transition process of a large-scale inclined axial flow pump station according to claim 1, characterized in that: In S2, a plurality of gate closing speed values ​​are sampled within the closing speed control range by uniform sampling.

5. The transition process coordinated control method of a large-scale inclined axial flow pump station according to claim 4 is characterized in that: In S2, the number of sampling of gate closing speed values ​​is 5 to 10.

6. The method for coordinated control of transition process of large-scale inclined axial flow pump station according to claim 1, characterized in that: The fluid simulation software is Fluent fluid simulation software.

7. The method for coordinated control of transition process of a large-scale inclined axial flow pump station according to claim 1, characterized in that: In S3, the first UDF program and the second UDF program used by all cooperative control schemes during the numerical simulation process are the same, and the third UDF program is different.

8. The transition process coordinated control method of a large-scale inclined axial flow pump station according to claim 1 is characterized in that: The preset mechanical property standards include an axial force standard and a radial torque standard; the axial force standard is that the peak value of the reverse axial force in the axial force time domain curve of the impeller does not exceed the axial component of gravity, or the amount by which the peak value of the reverse axial force exceeds the axial component of gravity is lower than a first threshold; the radial torque standard is that the peak average value of the pulsation segment in the horizontal radial torque time domain curve of the impeller does not exceed a second threshold.

9. The method for coordinated control of transition process of a large-scale inclined axial flow pump station according to claim 7, characterized in that: The preset pump pressure pulsation standard is: for the pressure pulsation signal at a point between the impeller and the guide vane, the maximum intensity of the pressure pulsation extracted from the short-time Fourier transform (STFT) processing result thereof does not exceed a third threshold value.

10. The method for coordinated control of transition process of a large-scale inclined axial flow pump station according to claim 1, characterized in that: The first threshold, the second threshold and the third threshold are optimally determined through actual operating condition tests of the inclined axial flow pump station.

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