Method and device for simulating fault shutdown transition process of centrifugal pump under cavitation condition

Abstract

The invention discloses a method and a device for simulating a fault shutdown transition process of a centrifugal pump under a cavitation condition, and relates to the technical field of numerical simulation of fluid machinery, the method comprises the following steps: establishing a water body model of the centrifugal pump; performing boundary naming and grid division on the water body model to obtain a grid model; performing single-phase flow steady-state simulation calculation based on the grid model to obtain a single-phase flow steady-state simulation result; a multi-phase flow model is constructed, a single-phase flow steady-state simulation result is used as a cavitation calculation initial flow field, cavitation steady-state simulation calculation is carried out, inlet pressure boundary conditions are dynamically adjusted, and a cavitation steady-state simulation result is obtained; constructing an impeller angular velocity time-varying function, and performing shutdown transition process simulation transient calculation by taking the cavitation steady-state simulation result as an initial flow field to obtain a shutdown transition process simulation transient calculation result; and repeating the simulation iteration process to obtain a final shutdown transition process simulation result. According to the invention, the simulation precision of the fault shutdown transition process of the centrifugal pump is improved.

Description

Technical Field

[0001] The present application relates to the technical field of numerical simulation of fluid machinery, and particularly to a simulation method and device for the transition process of a centrifugal pump during fault shutdown under cavitation conditions. Background Art

[0002] Due to their unique advantages of high efficiency and stability, large vertical centrifugal pumps have been widely used in many large-scale water diversion projects, and the market demand is extremely strong. However, the hydraulic structure of such pump devices is more complex than that of conventional centrifugal pumps. Especially at critical moments such as fault shutdown and startup, there are often high-risk and unstable transient transition processes. The coupled action of cavitation effects and flow separation will trigger a double instability mechanism, which poses a severe challenge to the safe and stable operation of water diversion projects and limits the further promotion of large vertical centrifugal pumps in the fields of water diversion and irrigation.

[0003] In the case of the unit encountering a fault shutdown, the large vertical centrifugal pump will undergo a series of complex state conversions, including pump conditions, braking conditions, turbine conditions, and even runaway conditions. Due to the frequent and rapid conversion of these conditions, the flow pattern inside the pump is extremely complex and changeable, and the induced unsteady cavitation flow can induce intense pressure pulsations. The violent fluctuations in the flow field will cause the axial force borne by the unit to increase sharply. When entering the runaway state, if the vibration caused by excessive speed exceeds the bearing limit of the unit, it may cause serious damage to the unit structure, thereby triggering production safety accidents, posing a major threat to the lives of operators, and bringing incalculable losses. Therefore, in-depth and detailed research on the transient characteristics during the fault shutdown process of large vertical centrifugal pumps is of great significance for ensuring their safe and stable operation. However, the simulation results of traditional methods deviate greatly from the actual situation, and the simulation accuracy is low. Summary of the Invention

[0004] The purpose of the present application is to provide a simulation method and device for the transition process of a centrifugal pump during fault shutdown under cavitation conditions, which can more realistically reflect the complex flow field changes and dynamic characteristics during the fault shutdown transition process, and improve the simulation accuracy of the centrifugal pump fault shutdown transition process.

[0005] To achieve the above object, the present application provides the following solutions.

[0006] In the first aspect, the present application provides a simulation method for the transition process of a centrifugal pump during fault shutdown under cavitation conditions, including the following steps.

[0007] Establish a water body model of the centrifugal pump.

[0008] Name the boundaries and divide the grid of the water body model to obtain a grid model.

[0009] Based on the grid model, perform steady-state simulation calculations for single-phase flow to obtain the steady-state simulation results of single-phase flow.

[0010] Construct a multiphase flow model, use the steady-state simulation results of single-phase flow as the initial flow field for cavitation calculation, perform steady-state cavitation simulation calculations, and dynamically adjust the inlet pressure boundary conditions to obtain the steady-state cavitation simulation results; the multiphase flow model introduces the Zwart-Gerber-Belamri cavitation model.

[0011] Construct a time-varying function of the impeller angular velocity, and use the steady-state cavitation simulation results as the initial flow field to perform transient calculations for the shutdown transition process simulation to obtain the transient calculation results of the shutdown transition process simulation.

[0012] Determine whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final simulation results of the shutdown transition process.

[0013] In a second aspect, the present application provides a simulation device for the shutdown transition process of a centrifugal pump under cavitation conditions, including the following modules.

[0014] A water body model establishment module for establishing a water body model of the centrifugal pump.

[0015] A grid model construction module for naming the boundaries and dividing the grid of the water body model to obtain a grid model.

[0016] A single-phase flow steady-state simulation calculation module for performing single-phase flow steady-state simulation calculations based on the grid model to obtain the steady-state simulation results of single-phase flow.

[0017] A steady-state cavitation simulation calculation module for constructing a multiphase flow model, using the steady-state simulation results of single-phase flow as the initial flow field for cavitation calculation, performing steady-state cavitation simulation calculations, and dynamically adjusting the inlet pressure boundary conditions to obtain the steady-state cavitation simulation results; the multiphase flow model introduces the Zwart-Gerber-Belamri cavitation model.

[0018] A transient calculation module for the shutdown transition process simulation for constructing a time-varying function of the impeller angular velocity, and using the steady-state cavitation simulation results as the initial flow field to perform transient calculations for the shutdown transition process simulation to obtain the transient calculation results of the shutdown transition process simulation.

[0019] A simulation iteration module for determining whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final simulation results of the shutdown transition process.

[0020] In a third aspect, the present application provides a computer device, including: a memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor executes the computer program to implement the above-mentioned simulation method for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions.

[0021] In a fourth aspect, the present application provides a computer-readable storage medium, on which a computer program is stored, and when the computer program is executed by a processor, it implements the above-mentioned simulation method for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions.

[0022] According to the specific embodiments provided by the present application, the following technical effects are disclosed:

[0023] The present application provides a simulation method and device for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions. After obtaining the steady-state simulation results of single-phase flow, a multiphase flow model is constructed, and the steady-state simulation results of single-phase flow are used as the initial flow field for cavitation calculation. Cavitation steady-state simulation calculation is carried out, and the inlet pressure boundary condition is dynamically adjusted to obtain the steady-state simulation results of cavitation. The cavitation effect is fully considered, and the generation, development, and collapse processes of cavitation bubbles, as well as the resulting pressure pulsation, vibration noise, and other phenomena, can be more accurately simulated, so as to more realistically reflect the complex flow field changes and dynamic characteristics during the transition process of a fault shutdown. By constructing a time-varying function of the impeller angular velocity to perform transient calculation for the simulation of the shutdown transition process, the transient changes in the flow field structure during the change of the impeller speed can be accurately captured, further improving the simulation accuracy, and solving the problem that traditional methods often ignore the cavitation effect or adopt a simplified model, resulting in a large deviation between the simulation results and the actual situation. Description of the Drawings

[0024] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0025] Figure 1 It is an application environment diagram of a simulation method for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions in an embodiment of the present application;

[0026] Figure 2 It is a flow diagram of a simulation method for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions provided by an embodiment of the present application;

[0027] Figure 3 It is a specific process diagram of a simulation method for the transition process of a centrifugal pump during a fault shutdown under cavitation conditions provided by an embodiment of the present application;

[0028] Figure 4 It is a field diagram of the model pump test provided by an embodiment of the present application;

[0029] Figure 5 It is a schematic structural diagram of a centrifugal pump provided by an embodiment of the present application;

[0030] Figure 6 It is a computational grid diagram of a centrifugal pump provided by an embodiment of the present application;

[0031] Figure 7 It is a curve diagram of the change of external characteristics during the shutdown process provided by an embodiment of the present application;

[0032] Figure 8 It is a curve diagram of the axial and radial forces received by the impeller during the shutdown process provided by an embodiment of the present application;

[0033] Figure 9 It is a schematic diagram of the change curve of the pressure in the vane - less area near the cut - off tongue over time during the shutdown process provided by an embodiment of the present application;

[0034] Figure 10 It is a schematic diagram of the functional modules of a simulation device for the transition process of a centrifugal pump during fault shutdown under cavitation conditions provided by an embodiment of the present application;

[0035] Figure 11 It is a schematic structural diagram of a computer device provided by an embodiment of the present application. Detailed implementation manners

[0036] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0037] Aiming at the problems existing in the related technologies, the present application provides a full - flow - field simulation calculation method for the transition process of a large - scale vertical centrifugal pump during fault shutdown under cavitation conditions. By monitoring the change of the torque received by the impeller and writing the formula of the impeller speed change with torque into a UDF program, the change law of cavitation characteristics during the shutdown process is effectively simulated, thereby providing scientific guidance for the shutdown process.

[0038] To make the above - mentioned objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0039] The simulation method for the transition process of a centrifugal pump during fault shutdown under cavitation conditions provided by the embodiments of the present application can be applied to, for example Figure 1In the application environment shown. Among them, the terminal 102 communicates with the server 104 through the network. The data storage system can store the data that the server 104 needs to process. The data storage system can be set separately, integrated on the server 104, placed on the cloud or other servers. The terminal 102 can send the simulation request to be processed to the server 104. After receiving the simulation request to be processed, the server 104 establishes a water body model of the centrifugal pump; names the boundaries and divides the grids of the water body model to obtain a grid model, performs single-phase flow steady-state simulation calculations based on the grid model to obtain single-phase flow steady-state simulation results, constructs a multiphase flow model, uses the single-phase flow steady-state simulation results as the initial flow field for cavitation calculation, performs cavitation steady-state simulation calculations, and dynamically adjusts the inlet pressure boundary conditions to obtain cavitation steady-state simulation results, constructs a time-varying function of the impeller angular velocity, and uses the cavitation steady-state simulation results as the initial flow field to perform transient calculation of the shutdown transition process simulation to obtain the transient calculation results of the shutdown transition process simulation, repeats the simulation iteration process, and obtains the final transient calculation results of the shutdown transition process simulation. The server 104 can feedback the final transient calculation results of the shutdown transition process simulation for the simulation request to be processed to the terminal 102. In addition, in some embodiments, the simulation method for the shutdown transition process of a centrifugal pump under cavitation conditions can also be implemented separately by the server 104 or the terminal 102.

[0040] Among them, the terminal 102 can be, but is not limited to, various desktop computers, laptop computers, smart phones, tablet computers, Internet of Things devices, and portable wearable devices. The Internet of Things devices can be smart speakers, smart TVs, smart air conditioners, smart in-vehicle devices, etc. The portable wearable devices can be smart watches, smart bracelets, head-mounted devices, etc. The server 104 can be implemented by an independent server or a server cluster composed of multiple servers, and can also be a cloud server.

[0041] In an exemplary embodiment, as Figure 2 and Figure 3 shown, a simulation method for the shutdown transition process of a centrifugal pump under cavitation conditions is provided. This method is executed by a computer device, and can be specifically executed separately by a computer device such as a terminal or a server, or jointly executed by a terminal and a server. In the embodiments of the present application, taking this method applied to Figure 1 the server 104 in

[0042] Step 201, establish a water body model of the centrifugal pump.

[0043] Step 202, name the boundaries and divide the grids of the water body model to obtain a grid model.

[0044] Step 203: Perform steady-state simulation calculations for single-phase flow based on the grid model to obtain the steady-state simulation results of single-phase flow.

[0045] Step 204: Construct a multiphase flow model, use the steady-state simulation results of single-phase flow as the initial flow field for cavitation calculation, perform steady-state cavitation simulation calculations, and dynamically adjust the inlet pressure boundary conditions to obtain the steady-state cavitation simulation results; the Zwart-Gerber-Belamri cavitation model is introduced into the multiphase flow model.

[0046] Step 205: Construct a time-varying function of the impeller angular velocity, and use the steady-state cavitation simulation results as the initial flow field to perform transient calculations for the shutdown transition process simulation to obtain the transient calculation results of the shutdown transition process simulation.

[0047] Step 206: Determine whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final shutdown transition process simulation results.

[0048] Implement the above Steps 201 to 206, construct a multiphase flow model, use the steady-state simulation results of single-phase flow as the initial flow field for cavitation calculation, perform steady-state cavitation simulation calculations, and dynamically adjust the inlet pressure boundary conditions to obtain the steady-state cavitation simulation results, fully considering the cavitation effect. Utilizing the powerful multiphase flow simulation ability of Fluent software, it can more accurately simulate the generation, development, and collapse process of cavitation bubbles, as well as the phenomena such as pressure pulsation and vibration noise caused thereby, thus more realistically reflecting the complex flow field changes and dynamic characteristics during the fault shutdown transition process. By using the method of writing the impeller speed control equation (i.e., the time-varying function of the impeller angular velocity) with UDF and performing transient calculations for the shutdown transition process simulation by constructing the time-varying function of the impeller angular velocity, it can accurately capture the transient changes in the flow field structure during the impeller speed change process, further improving the simulation accuracy. This application specifically relates to a high-precision simulation method for the transient process of a large vertical centrifugal pump during fault shutdown considering inertial deceleration and cavitation dynamic evolution. By establishing a multi-physical field coupling model of speed time-varying - cavitation phase change - turbulent pulsation, it realizes the reconstruction of the transient cavitation flow field and the prediction of hydraulic excitation force during the fault shutdown process.

[0049] In experimental research, the unstable flow during the shutdown process seriously affects the operation safety and stability of the test bench. The development and application of CFD simulation technology effectively reduce the high costs required for experiments and make up for some limitations of experimental observations and theoretical analyses. Fluent has been widely used in the field of flow simulation based on the finite volume method. After processing the calculation results, multiple data such as entropy production, vorticity, pressure, and velocity, as well as visualization cloud maps, can be obtained to verify the practicality of the calculation results and their consistency with the actual situation.

[0050] In order to explore the instability of the transient flow during the shutdown transition process under cavitation conditions, based on the multiphase flow field by Fluent software and compiling the UDF program, the dynamic variation law of the vapor volume fraction with the pressure field is accurately described, reducing the research cost and time.

[0051] In another exemplary embodiment of the present application, step 201 specifically includes: establishing a water body model of the centrifugal pump using 3D modeling software such as UG, AutoCAD, Solidworks, or Creo; the water body model is a water body model including an inlet and outlet extension section, an impeller domain, and a diffuser domain.

[0052] Based on parametric modeling technology, a water body model including an inlet and outlet extension section, an impeller domain, and a diffuser domain is constructed to ensure that the deviation of the geometric characteristics from the hydraulic profile of the prototype pump is less than 0.5%; that is, a simulation analysis water body model of the model pump of the large vertical centrifugal pump is created using 3D modeling software. Taking the UG software as an example below, the establishment process of the water body model is introduced in detail.

[0053] The field test diagram of the model pump is as Figure 4 shown, which includes a vacuum tank, a high-pressure water tank, a motor, a torque meter, a low-pressure water tank, a test pump, a vacuum pump, a booster pump, a globe valve, and an electromagnetic flowmeter. The large vertical centrifugal pump model pump is modeled using UG software and a *.igs format file is output. As Figure 5 shown in the schematic diagram of the centrifugal pump structure, it includes a volute, an impeller, a stationary guide vane, front and rear cavities, an inlet pipe, and an outlet pipe. The diameter of the impeller inlet section of the geometric model is 312.21 mm, the diameter of the outlet section is 456 mm, the number of blades is 7, the impeller speed is 1000 r / min, the number of guide vanes is 11, and the guide vanes are arranged between the outlet of the centrifugal impeller and the inlet of the spiral volute.

[0054] In step 202 above, the water body model is imported into CFD ICEM, the boundary naming and mesh generation of the water body model are performed, and the boundary layer mesh is encrypted in the dynamic and static interference area to control the y+ value in the range of 5 - 30 and import the completed mesh into Fluent. The y+ value is a dimensionless number used to describe the ratio of the distance from the mesh node to the wall surface to the flow characteristic scale. The mesh is divided into unstructured mesh and structured mesh. In this embodiment, hexahedral structured mesh can be used.

[0055] The boundary naming and mesh generation in Step 202 are as follows: Import the *.igs geometry file established in Step 201 into ANSYS CFD ICEM. Name each boundary and component such as the impeller, volute, inlet and outlet pipes in the water body model file. At the same time, set the mesh size. The mesh is divided into high-quality hexahedral structured meshes. Use the O-block topology around the impeller and guide vane blades, and perform boundary layer encryption to obtain more accurate flow details and improve the simulation accuracy. The material is set as the water phase. To evaluate the influence of mesh nodes on the simulation accuracy, the GCI (Grid Convergence Index) grid uncertainty estimation method based on Richardson extrapolation is used to estimate the discretization error of the computational grid to determine the number of grids. The final determined number of grids is 8.3 million. As Figure 6 shown, save the mesh file as the *.msh format.

[0056] In another exemplary embodiment of the present application, Step 203 may include the following steps: Set a pressure boundary at the inlet of the mesh model and a flow rate boundary at the outlet. The single-phase flow is the water phase. The fixed wall surface adopts a no-slip boundary. The interface between the rotating domain and the stationary domain in the steady simulation is set as a frozen rotor; Use the SST k-ω turbulence model to close the N-S equations, establish an initial flow field of the steady single-phase flow through the multiple reference frame method, and perform the steady-state simulation calculation of the single-phase flow to obtain the steady-state simulation result of the single-phase flow.

[0057] Import the *.msh mesh file established in Step 202 into Fluent. Perform preprocessing settings in Fluent, set the pressure-velocity coupling algorithm and the second-order upwind scheme, set the cell region, boundary conditions, solution method, fluid motion control equations and turbulence model, and perform the steady-state simulation calculation of the single-phase flow. Among them, set a pressure boundary at the inlet and a flow rate boundary at the outlet. The single-phase flow is the water phase. The fixed wall surface adopts a no-slip boundary. The interface between the rotating domain and the stationary domain in the steady simulation is set as a frozen rotor. Establish an initial flow field of the steady single-phase flow through the multiple reference frame method. To ensure the calculation accuracy of the near-wall surface and the mainstream area, the SST k-ω model is selected as the turbulence model. Use the SST k-ω turbulence model to close the N-S equations, and complete the steady calculation of the single-phase flow with the above settings.

[0058] Set the multiphase flow model and introduce the Zwart-Gerber-Belamri cavitation equation. Use the steady-state calculation result of the single-phase flow completed in Step 203 as the initial flow field for the cavitation calculation, and perform the steady-state simulation calculation of the cavitation. Use the pressure gradient method to dynamically adjust the inlet pressure boundary condition until the critical cavitation number is reached, that is, continuously reduce the inlet pressure until the cavitation critical point.

[0059] Set up a multiphase flow model, set the inlet liquid volume fraction to 1, set the material to the water phase and the gas phase. For the vapor phase and the liquid phase in this embodiment, they are water vapor and water respectively. The vaporization pressure is the saturated vapor pressure at 20 °C, and the remaining settings are the same as those in step 203. By continuously reducing the inlet pressure until the head drops by 3%, the cavitation critical point is reached, and the cavitation steady-state calculation is completed.

[0060] The multiphase flow model (the centrifugal pump cavitation flow computational fluid dynamics (CFD) model) includes the continuity equation and momentum equation of multiphase flow (the continuity equation and momentum equation of multiphase flow are collectively referred to as the cavitation flow control equation), the cavitation model, and the turbulence model.

[0061] The continuity equation and momentum equation of multiphase flow are expressed as follows:

[0062]

[0063] In the formula: ρ m is the mixture density, determined by the liquid density and the gas density; t is the time; u i , u j , u k respectively represent the transient velocity components in the x, y, and z directions (m / s); x i , x j , x k respectively represent the coordinate components in the x, y, and z directions; f i is the body force; p is the instantaneous pressure vector; t is the time; μ is the laminar viscosity; μ t is the turbulent eddy viscosity; δ ij represents the Kronecker symbol (when i = j, δ ij = 1; when i ≠ j, δ ij = 0).

[0064] The calculation formula for the mixture density ρ m is shown in the following formula:

[0065] ρ m = α v ρ v + (1 - α v )ρ l (3).

[0066] In the formula: ρ l and ρ v are the liquid density and the gas density respectively, kg / m 3 ; α v is the volume fraction of the gas phase.

[0067] Using the Zwart-Gerber-Belamri cavitation model simplified based on the Rayleigh-Plesset equation, the mass transfer rate between phases of the Zwart-Gerber-Belamri cavitation model is expressed as:

[0068]

[0069] Where: m is the mass transfer rate between phases; F e is the empirical coefficient of the evaporation term, F e = 50; r g is the volume fraction of gas nuclei contained in the unit liquid, r g = 5×10 -4 ; α v is the volume fraction of the gas phase; p v is the saturated vapor pressure of the gas phase, Pa; R b is the average radius of the cavitation bubble, R b = 10 -6 m; p is the instantaneous pressure vector; p l is the saturated vapor pressure of the liquid phase, Pa; F c is the empirical coefficient of the condensation term, F c = 0.01.

[0070] In the above step 205, a time-varying function of the impeller angular velocity is constructed. By compiling the UDF program in Fluent, the dynamic coupling of the inertial deceleration process and the transient flow field is realized. Using the cavitation steady-state simulation calculation results as the initial flow field, the inlet and outlet boundary conditions are modified so that both the inlet and outlet boundary conditions are set as pressure boundaries. The interface between the rotating domain and the stationary domain is set as a transient rotor motion, and the transient calculation of the shutdown transition process simulation is carried out. The transient calculation results of the shutdown transition process simulation include the spatio-temporal distribution information of key parameters such as pressure, velocity, and cavitation volume fraction.

[0071] The impeller speed change formula is written as a UDF program. The speed change formula, that is, the time-varying function of the impeller angular velocity, is shown as follows.

[0072]

[0073] Where: J is the moment of inertia of the centrifugal pump rotor component (impeller and its rotating shaft), kg·m 2 ; dt is the change in unit time, s; is the change in angular velocity per unit time, rad / s; M i is the torque received by the rotor component, N·m, including the torque M t of the liquid flow on the impeller and the frictional resistance torque M f of the bearing on the rotor component. Usually, M f is ignored in the calculation.

[0074] Set the inlet and outlet pressure boundary conditions to make them more suitable for the actual application scenario to ensure the accuracy of the simulation calculation, that is, set the corresponding boundary conditions for different working conditions. When simulating the cavitation number working condition, set different cavitation numbers, that is, different inlet pressure boundary values.

[0075] In another exemplary embodiment of the present application, step 206 includes the following steps 301 to 302.

[0076] Step 301: Perform post-processing analysis on the simulation transient calculation results of the shutdown transition process to obtain the post-processing analysis results; the post-processing analysis includes cloud maps of the internal flow field pressure, velocity, and vorticity at different shutdown times.

[0077] Use post-processing software to perform post-processing analysis on the simulation transient calculation results of the shutdown transition process. The post-processing software such as CFD-POST or Tecplot is used to generate cloud maps of the internal flow field pressure, velocity, vorticity, etc. at different shutdown times to display the simulation results.

[0078] Step 302: Determine whether the simulation transient calculation results of the shutdown transition process meet the data requirements of the actual shutdown transition process. If not, repeat the simulation iteration process to obtain the final simulation results of the shutdown transition process.

[0079] According to the calculation results of the fault shutdown transition process of the large vertical centrifugal pump under cavitation conditions obtained by simulation calculation, determine whether the simulation transient calculation results of the shutdown transition process are in line with the actual situation. Specifically, compare the curves of the rotational speed and flow rate varying with time obtained by simulation with the actual rotational speed and flow rate change curves. If the simulation transient calculation results of the shutdown transition process are in line with the actual situation, the simulation ends; if not, the mesh or pre-processing settings need to be corrected, and the above calculation steps are repeated.

[0080] Figure 7 It is a curve graph of the external characteristic changes during the shutdown process. The external characteristics during the shutdown process include the pump working condition, the pump deceleration working condition, the turbine working condition, the turbine deceleration working condition, and the runaway condition; M rel represents the relative torque value, that is, the ratio of the torque at a certain instantaneous moment to the torque at the initial shutdown moment; Q rel represents the relative flow rate value, that is, the ratio of the flow rate at a certain instantaneous moment to the flow rate at the initial shutdown moment; n rel represents the relative rotational speed value, that is, the ratio of the rotational speed at a certain instantaneous moment to the rotational speed at the initial shutdown moment. Figure 8 It is a curve graph of the axial and radial forces on the impeller during the shutdown process. The axial and radial forces on the impeller include the radial force F X , the radial force F Y and the axial force F Z ; Figure 9It is a schematic diagram of the variation curve of the pressure P1 in the blade - less area near the cut - off tongue with time during the shutdown process.

[0081] This application can not only intuitively obtain the internal flow characteristic distribution of a large vertical centrifugal pump under cavitation conditions, reduce the experimental cost of related research, but also ensure the accuracy of the simulation calculation method, providing an important reference for studying the shutdown characteristics of large vertical centrifugal pumps.

[0082] This application has the following beneficial effects:

[0083] First, a three - dimensional full - flow - path parametric model of the model pump including inlet and outlet extension sections is constructed, and a hexahedral structured grid system that meets the cavitation flow solution accuracy is established in the CFD ICEM software; it is imported into Fluent for pre - processing settings; by defining dynamic boundary conditions and multiphase flow medium parameters, a staged progressive solution strategy is adopted: first, the initial flow field calculation of steady - state single - phase flow is carried out, then the cavitation model is introduced for two - phase cavitation flow field iteration, and grid independence verification is implemented; further, by establishing a dynamic coupling mechanism between the time - varying function of the impeller speed and the flow field parameters, the collaborative solution of the inertial shutdown process and the cavitation transient effect under the power - off condition is realized; finally, the calculation results are post - processed and analyzed. This application uses a simulation calculation method verified by experiments, can obtain data closer to the transition process of fault shutdown, and can provide important guidance for the study of the transient characteristics of unstable flow in the shutdown transition process of large vertical centrifugal pumps under cavitation conditions.

[0084] Relying on the excellent three - dimensional modeling and design functions of UG software, this application has successfully constructed a complete large vertical centrifugal pump model. On this basis, using the advanced numerical simulation technology and complex flow field simulation ability of Fluent, the shutdown process of the centrifugal pump under cavitation conditions is calculated and analyzed, the variation characteristics of the external characteristic parameters during the shutdown process are obtained, and the internal flow field is deeply analyzed, providing a theoretical basis for revealing the unstable flow characteristics of the fault shutdown transition process of large vertical centrifugal pumps under cavitation conditions.

[0085] This application can simulate the fault shutdown transition process under different working conditions (such as different cavitation numbers), obtain the spatio - temporal distribution information of key parameters such as pressure, velocity, and cavitation volume fraction, so as to comprehensively analyze the influence mechanism of cavitation on the fault shutdown process and reveal the internal laws of the occurrence and development of cavitation and eddy currents in the internal flow field.

[0086] Aiming at the problem of insufficient data reliability in current simulation research, this application conducts experimental verification. By comparing with actual experimental data, the simulation model is further optimized and adjusted to form a systematic and reliable high - precision simulation technology.

[0087] The method of this application can greatly reduce the R & D cost and shorten the R & D cycle. The traditional method relies on physical experiments, which requires building complex experimental benches, with high costs, long cycles, and it is difficult to obtain comprehensive flow field information. The method of this application uses numerical simulation technology, which can easily simulate various working conditions, obtain rich flow field data, intuitively obtain the internal flow characteristics distribution of a large vertical centrifugal pump under cavitation conditions, reduce the test costs of related research, ensure the accuracy of the simulation calculation method, and provide an important reference for studying the shutdown characteristics of large vertical centrifugal pumps.

[0088] This application also provides an application scenario that applies the above-mentioned simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions. Specifically: The simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions provided in this embodiment can be applied in the simulation scenario of the transition process of a centrifugal pump failure shutdown. The simulation scenario of the transition process of a centrifugal pump failure shutdown includes a request receiving link and a simulation link for the transition process of a centrifugal pump failure shutdown; the simulation request to be processed enters the simulation link for the transition process of a centrifugal pump failure shutdown from the request receiving link to obtain the corresponding final simulation result of the shutdown transition process. The simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions provided in this embodiment belongs to the simulation link for the transition process of a centrifugal pump failure shutdown. Specifically, in the process of the simulation link for the transition process of a centrifugal pump failure shutdown for a video, a water body model of the centrifugal pump can be established; boundary naming and mesh division are performed on the water body model to obtain a mesh model, a single-phase flow steady-state simulation calculation is performed based on the mesh model to obtain a single-phase flow steady-state simulation result, a multiphase flow model is constructed, the single-phase flow steady-state simulation result is used as the initial flow field for cavitation calculation, a cavitation steady-state simulation calculation is performed, and the inlet pressure boundary condition is dynamically adjusted to obtain a cavitation steady-state simulation result, a time-varying function of the impeller angular velocity is constructed, and the cavitation steady-state simulation result is used as the initial flow field to perform a transient calculation of the shutdown transition process simulation to obtain a transient calculation result of the shutdown transition process simulation. The simulation iteration process is repeated to obtain the final simulation result of the shutdown transition process.

[0089] Based on the same inventive concept, an embodiment of this application also provides a simulation device for the transition process of a centrifugal pump failure shutdown under cavitation conditions for implementing the above-mentioned simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions. The solution provided by this device to solve the problem is similar to the solution described in the above method. Therefore, the specific limitations in one or more embodiments of the following simulation device for the transition process of a centrifugal pump failure shutdown under cavitation conditions can refer to the limitations for the simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions in the above text, and will not be repeated here.

[0090] In an exemplary embodiment, as Figure 10 shown, a simulation device for the transition process of a centrifugal pump failure shutdown under cavitation conditions includes the following modules.

[0091] A water body model establishment module T1 for establishing a water body model of a centrifugal pump.

[0092] A grid model construction module T2 for naming boundaries and dividing grids of the water body model to obtain a grid model.

[0093] A single-phase flow steady-state simulation calculation module T3 for performing single-phase flow steady-state simulation calculations based on the grid model to obtain single-phase flow steady-state simulation results.

[0094] A cavitation steady-state simulation calculation module T4 for constructing a multiphase flow model, using the single-phase flow steady-state simulation results as the initial flow field for cavitation calculation, performing cavitation steady-state simulation calculations, and dynamically adjusting the inlet pressure boundary conditions to obtain cavitation steady-state simulation results; the multiphase flow model introduces the Zwart-Gerber-Belamri cavitation model.

[0095] A shutdown transition process simulation transient calculation module T5 for constructing a time-varying function of the impeller angular velocity and using the cavitation steady-state simulation results as the initial flow field to perform shutdown transition process simulation transient calculations to obtain shutdown transition process simulation transient calculation results.

[0096] A simulation iteration module T6 for determining whether the shutdown transition process simulation transient calculation results meet the requirements of the actual shutdown transition process data. If not, the simulation iteration process is repeated to obtain the final shutdown transition process simulation results.

[0097] In an exemplary embodiment, a computer device is provided. The computer device can be a server or a terminal, and its internal structure diagram can be as Figure 11 shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, abbreviated as I / O), and a communication interface. Among them, the processor, the memory, and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store centrifugal pump failure shutdown transition process simulation data. The input / output interface of the computer device is used for the processor to exchange information with external devices. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, it realizes a method for simulating the failure shutdown transition process of a centrifugal pump under cavitation conditions.

[0098] Those skilled in the art can understand, Figure 11The structure shown is only a block diagram of some structures related to the solution of this application, and does not constitute a limitation on the computer device to which the solution of this application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine some components, or have different component arrangements.

[0099] In an exemplary embodiment, a computer device is provided, including a memory and a processor. A computer program is stored in the memory, and when the processor executes the computer program, the steps in the above method embodiments are implemented.

[0100] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0101] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use, and processing of relevant data need to comply with relevant regulations.

[0102] Those of ordinary skill in the art can understand that all or part of the processes of implementing the methods in the above embodiments can be completed by instructing relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above methods. Among them, any reference to a memory, database, or other medium used in the embodiments provided in the present application can include at least one of non-volatile and volatile memories. Non-volatile memories can include read-only memory (ROM), magnetic tapes, floppy disks, flash memories, optical memories, high-density embedded non-volatile memories, resistive random access memories (ReRAM), magnetoresistive random access memories (MRAM), ferroelectric random access memories (FRAM), phase change memories (PCM), graphene memories, etc. Volatile memories can include random access memory (RAM) or external cache memories, etc. By way of illustration and not limitation, RAM can be in various forms, such as static random access memory (SRAM) or dynamic random access memory (DRAM), etc.

[0103] The databases involved in the embodiments provided in the present application can include at least one of relational databases and non-relational databases. Non-relational databases can include distributed databases based on blockchain, etc., without limitation. The processors involved in the embodiments provided in the present application can be general-purpose processors, central processors, graphics processors, digital signal processors, programmable logics, data processing logics based on quantum computing, etc., without limitation.

[0104] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0105] Specific examples are used in this article to elaborate on the principles and implementation manners of the present application. The descriptions of the above embodiments are only used to help understand the methods and core ideas of the present application; at the same time, for those of ordinary skill in the art, according to the ideas of the present application, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A simulation method for the transition process of a centrifugal pump during failure shutdown under cavitation conditions, characterized in that, The simulation method for the transition process of a centrifugal pump failure shutdown under cavitation conditions includes: Establishing a water body model of the centrifugal pump; Naming the boundaries and meshing the water body model to obtain a mesh model; Performing single-phase flow steady-state simulation calculations based on the mesh model to obtain single-phase flow steady-state simulation results; Constructing a multiphase flow model, using the single-phase flow steady-state simulation results as the initial flow field for cavitation calculation, performing cavitation steady-state simulation calculations, and dynamically adjusting the inlet pressure boundary conditions to obtain cavitation steady-state simulation results; The multiphase flow model introduces the Zwart-Gerber-Belamri cavitation model; Constructing a time-varying function of the impeller angular velocity, and using the cavitation steady-state simulation results as the initial flow field to perform transient calculations for the shutdown transition process simulation to obtain transient calculation results for the shutdown transition process simulation; Judging whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final simulation results for the shutdown transition process.

2. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, wherein Establishing a water body model of the centrifugal pump specifically includes: Using 3D modeling software such as UG, AutoCAD, Solidworks, or Creo to establish a water body model of the centrifugal pump; The water body model is a water body model including inlet and outlet extension sections, an impeller domain, and a diffuser domain.

3. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, wherein, Performing single-phase flow steady-state simulation calculations based on the mesh model to obtain single-phase flow steady-state simulation results, specifically including: Setting a pressure boundary at the inlet of the mesh model, setting a flow rate boundary at the outlet, the single-phase flow being the water phase, using a no-slip boundary for the fixed wall, and setting the interface between the rotating domain and the stationary domain as a frozen rotor for steady-state simulation; Using the SST k-ω turbulence model to close the N-S equations, establishing an initial flow field for steady-state single-phase flow through the multiple reference frame method, and performing single-phase flow steady-state simulation calculations to obtain single-phase flow steady-state simulation results.

4. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, characterized in that The multiphase flow model includes the continuity equation and momentum equation of multiphase flow. The continuity equation and momentum equation of multiphase flow are expressed as follows: Where: ρ m is the mixed density, determined by the liquid-phase density and the gas-phase density; t is time; u i , u j , u k respectively represent the transient velocity components in the x, y, and z directions; x i , x j , x k respectively represent the coordinate components in the x, y, and z directions; f i is the body force; p is the instantaneous pressure vector; t is time; μ is the laminar viscosity; μ t is the turbulent eddy viscosity; δ ij represents the Kronecker symbol.

5. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, characterized in that The interphase mass transfer rate of the Zwart-Gerber-Belamri cavitation model is expressed as: Where: m is the interphase mass transfer rate; F e is the empirical coefficient of the evaporation term; r g is the volume fraction of gas nuclei contained in the unit liquid; α v is the volume fraction of the gas phase; p v is the saturation vapor pressure of the gas phase; R b is the average radius of the cavitation bubble; p is the instantaneous pressure vector; p l is the saturation vapor pressure of the liquid phase; F c is the empirical coefficient of the condensation term.

6. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, characterized in that, The time-varying function of the impeller angular velocity is: Where: J is the moment of inertia of the centrifugal pump rotor component; dt is the change per unit time; is the change in angular velocity per unit time; M i is the torque acting on the rotor component.

7. The simulation method for the transition process of the centrifugal pump failure shutdown under cavitation conditions according to claim 1, wherein, Judging whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final simulation results for the shutdown transition process, specifically including: Performing post-processing analysis on the transient calculation results of the shutdown transition process simulation to obtain post-processing analysis results; The post-processing analysis includes cloud maps of the internal flow field pressure, velocity, and vorticity at different shutdown times; Judging whether the transient calculation results of the shutdown transition process simulation meet the requirements of the actual shutdown transition process data. If not, repeat the simulation iteration process to obtain the final simulation results for the shutdown transition process.

8. A cavitation condition centrifugal pump fault shutdown transition process simulation device based on the cavitation condition centrifugal pump fault shutdown transition process simulation method according to any one of claims 1-7, characterized in that, The simulation device for the transition process of a centrifugal pump failure shutdown under cavitation conditions includes: A water body model establishment module for establishing a water body model of the centrifugal pump; A mesh model construction module for naming the boundaries and meshing the water body model to obtain a mesh model; A single-phase flow steady-state simulation calculation module for performing single-phase flow steady-state simulation calculations based on the mesh model to obtain single-phase flow steady-state simulation results; The cavitation steady-state simulation calculation module is used to construct a multiphase flow model, use the single-phase flow steady-state simulation result as the initial flow field for cavitation calculation, perform cavitation steady-state simulation calculation, and dynamically adjust the inlet pressure boundary condition to obtain the cavitation steady-state simulation result; the multiphase flow model introduces the Zwart-Gerber-Belamri cavitation model; The shutdown transition process simulation transient calculation module is used to construct a time-varying function of the impeller angular velocity, and use the cavitation steady-state simulation result as the initial flow field to perform shutdown transition process simulation transient calculation to obtain the shutdown transition process simulation transient calculation result; The simulation iteration module is used to determine whether the shutdown transition process simulation transient calculation result meets the requirements of the actual shutdown transition process data. If not, the simulation iteration process is repeated to obtain the final shutdown transition process simulation result.

9. A computer device, comprising: A memory, a processor, and a computer program stored on the memory and executable on the processor, wherein the processor executes the computer program to implement the centrifugal pump fault shutdown transition process simulation method under cavitation conditions according to any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by the processor, it implements the centrifugal pump fault shutdown transition process simulation method under cavitation conditions according to any one of claims 1-7.

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