Valve two-phase critical flow coupling simulation method and system

Abstract

The invention provides a valve two-phase critical flow coupling simulation method and system.The valve two-phase critical flow coupling simulation method comprises the steps that valve upstream and downstream boundary conditions needed by three-dimensional CFD analysis are calculated through a target two-phase critical flow model, and then assumed parameters in a two-phase flow model are corrected in reverse according to the three-dimensional CFD analysis result; through mutual iterative correction between the two phases, the difficulty that upstream and downstream boundary condition parameters of the valve cannot be determined can be ingeniously avoided, the efficiency and accuracy of two-phase critical flow calculation can be effectively improved, and rapid analysis of the valve process design and the inventive flowing property is facilitated.

Description

Technical Field

[0001] The present invention relates to the technical field of the design of the reactor coolant system and the dedicated safety system of a nuclear power plant, and particularly relates to a method and system for coupling simulation of two-phase critical flow of a valve. Background Art

[0002] The phenomenon of two-phase critical flow generally exists in the reactor coolant system and the dedicated safety system of a nuclear power plant. When the rate at which the fluid flows out of the system is no longer affected by the downstream pressure drop, this kind of flow is called critical flow.

[0003] Specifically, critical flow occurs in both single-phase flow and two-phase flow, and their flow characteristics are as follows:

[0004] For single-phase critical flow, the fluid medium reaches the speed of sound, and the upstream flow is no longer affected by the downstream pressure drop; and because the relaxation time of its molecules is short enough, single-phase critical flow is approximately in a thermodynamic equilibrium state.

[0005] For two-phase critical flow, while the pressure of the fluid medium (saturated liquid or liquid with a certain degree of subcooling) drops sharply along the flow channel, there is also a strong mass, momentum, and energy exchange between phases. Because the vaporization due to the expansion of the liquid phase leads to a continuous change in the vapor quality, there must be various two-phase flow patterns and flow pattern transitions between adjacent flow states in the flow channel. In addition, obvious interphase imbalance characteristics (such as flashing) will occur when the fluid expands rapidly, which is more complex than single-phase critical flow.

[0006] When the reactor coolant system of a nuclear power plant is depressurized in a step-by-step controlled manner, the high-temperature and high-pressure saturated liquid (or liquid with a certain degree of subcooling) enters the downstream pipe system through the valve or orifice plate on the pressure relief pipe and is finally discharged to the environment. During the fluid discharge process, the flow area after the valve throttling suddenly decreases, resulting in a sharp drop in the downstream pressure and reaching the minimum value. Subsequently, the downstream pressure gradually recovers along the flow channel and cannot recover above the saturated pressure, thereby causing continuous flashing of the liquid. In addition, when the discharge flow rate no longer increases with the decrease of the downstream pressure, two-phase critical flow is formed.

[0007] It should be noted that the phenomenon of two-phase critical flow is of great significance to the safety of nuclear reactors, the safety-related systems of nuclear power plants, and the design of their equipment, which is mainly reflected in the following two aspects:

[0008] First, the two-phase critical flow rate is an important parameter for measuring the flow capacity of the valve, which not only determines the pressure relief speed of the reactor coolant system but also is closely related to the start-up time of the dedicated safety system. If the dedicated safety system cannot provide timely and effective cooling for the reactor core, then even if the reactor can be shut down in time, the possibility of an accident cannot be excluded.

[0009] Second, the two-phase critical flow pressure drop is a parameter closely related to the two-phase critical flow rate, which determines whether the valve can perform specific functions under operating conditions (e.g., whether the valve can be opened and closed normally, and whether the discharge flow rate meets the system design requirements). In addition, the liquid flashing phenomenon caused by the two-phase critical flow has potential destructiveness to pipelines and valves, which not only causes pipeline vibration and noise, but also leads to severe wear of the valve sealing surface, reducing the equipment performance.

[0010] For important valves such as the isolation relief valve of the reactor coolant system in nuclear power plants, the two-phase critical flow rate and pressure drop are important inputs for valve process design, and detailed analysis is required through experiments combined with computational fluid dynamics (CFD) technology. Therefore, high-fidelity numerical simulation is a very important means in valve process design.

[0011] In actual engineering, important valves such as the isolation relief valve of the reactor coolant system are usually large-diameter valves with very complex flow channel structures, and need to operate under high temperature and pressure, steam-water two-phase, large flow rate and large pressure difference conditions.

[0012] For the numerical simulation of such special valves, the conventional technique is to use CFD software to establish a computational domain and generate grids by taking the valve with a complex structure and the local upstream and downstream pipelines as a whole, and then directly simulate the two-phase critical flow through the valve using multiphase flow models and phase change models. The difficulty of this technique is very high, and its deficiencies are mainly reflected in the following two aspects:

[0013] First, the valve structure is complex, the modeling calculation amount is large, the simulation calculation takes a long time, and the calculation efficiency is low.

[0014] Second, the boundary condition parameters (such as velocity, pressure, dryness, etc.) of the upstream and downstream pipelines of the valve are affected by factors such as the upstream system pressure and the ambient back pressure, and are difficult to directly determine. If the boundary condition parameters are set unreasonably, incorrect flow field calculation results may be obtained, which may even cause numerical instability and calculation divergence, and the accuracy is low.

[0015] Based on this, the inventors of the present application propose a method and system for coupling simulation of two-phase critical flow in valves in order to solve at least one of the above technical problems. Summary of the Invention

[0016] The technical problem to be solved by the present invention is to overcome the defects of low calculation efficiency and low accuracy in the numerical simulation of valves in the prior art, and to provide a method and system for coupling simulation of two-phase critical flow in valves.

[0017] The present invention solves the above technical problems through the following technical solutions:

[0018] The first aspect of the present invention provides a method for coupling simulation of two-phase critical flow in a valve, characterized by comprising:

[0019] Step 1: Determine the effective flow area according to the geometric dimensions of the valve, and establish an equivalent single-stage orifice geometric model based on the effective flow area;

[0020] Step 2: Determine the computational fluid domain, mesh division, numerical solver, and physical model according to the single-stage orifice geometric model;

[0021] Step 3: Select a target two-phase critical flow model to calculate and determine the two-phase critical flow rate and the upstream and downstream boundary condition parameters for CFD analysis according to the upstream saturated water stagnation pressure of the valve and the set two-phase critical flow pressure drop; wherein, the upstream boundary condition parameters include the pressure at the inlet of the first upstream connecting pipe;

[0022] Step 4: Generate a numerical model using the numerical solver parameters and the physical model parameters, then complete the boundary condition setting using the upstream and downstream boundary condition parameters obtained in Step 3, run the CFD solver for iterative calculation, and output the pressure at the inlet of the second upstream connecting pipe and the two-phase critical flow pressure drop;

[0023] Step 5: Compare the pressure at the inlet of the first upstream connecting pipe with the pressure at the inlet of the second upstream connecting pipe; if the relative error is less than the preset limit value, output the CFD analysis results, and the CFD analysis results include the two-phase critical flow rate and the two-phase critical flow pressure drop; if the relative error is greater than or equal to the preset limit value, reset the two-phase critical flow pressure drop in Step 2, and repeat Steps 3 to 5 for iterative correction to obtain the CFD analysis results;

[0024] Step 6: According to the CFD analysis results obtained in Step 5, establish a numerical model of the actual valve corresponding to the equivalent single-stage orifice geometric model, and obtain the two-phase critical flow rate and pressure drop of the actual valve through CFD analysis.

[0025] According to an embodiment of the present invention, Step 2 includes:

[0026] Step 21: Import the single-stage orifice geometric model into a computer program for mesh division;

[0027] Step 22: Establish the computational fluid domain;

[0028] Step 23: Set the surface mesh, volume mesh, and boundary layer mesh parameters;

[0029] Step 24: Generate structured and unstructured meshes;

[0030] Step 25: If the mesh quality meets the requirements, save the simulation file and record the computational fluid domain and mesh generation parameters; if the mesh quality does not meet the requirements, go back to Step 23 to readjust the surface mesh, volume mesh, and boundary layer mesh parameters until the mesh quality meets the requirements;

[0031] Step 26: Select a physical model and a numerical solver;

[0032] Step 27: Set the parameters of the numerical solver and the physical model;

[0033] Step 28: Save the simulation file obtained in Step 25 and record the parameters of the numerical solver and the physical model in Step 27.

[0034] According to an embodiment of the present invention, Step 3 includes:

[0035] Step 31: Calculate the pressure at the outlet of the downstream connecting pipe according to the upstream saturated water stagnation pressure of the valve and the critical pressure ratio;

[0036] Step 32: Calculate the physical property parameters of the corresponding saturated water and saturated steam using the physical property parameter calculation formula for saturated water and steam according to the pressure at the outlet of the downstream connecting pipe;

[0037] Step 33: Calculate the dryness and void fraction at the outlet of the downstream connecting pipe using the adiabatic throttling model and critical flow conditions according to the determined physical property parameters of saturated water and saturated steam, and calculate the two-phase critical flow mass flow rate using the thermodynamic equation in the target two-phase critical flow model; wherein, the target two-phase critical flow model is the classical two-phase critical flow model;

[0038] Step 34: Determine the outlet boundary condition parameters for three-dimensional CFD analysis according to the pressure, dryness, and void fraction at the outlet of the downstream connecting pipe;

[0039] Step 35: Set the two-phase critical flow pressure drop through the orifice according to the physical property parameters of saturated water and saturated steam, and calculate the pressure and specific volume at the inlet of the upstream connecting pipe using the pressure drop equation in the target two-phase critical flow model;

[0040] Step 36: Calculate the velocity at the inlet of the upstream connecting pipe according to the two-phase critical flow mass flow rate, the pressure, and specific volume at the inlet of the upstream connecting pipe, and determine the inlet boundary condition parameters for three-dimensional CFD analysis;

[0041] Step 37: Record the inlet boundary condition parameters in Step 36 and the outlet boundary condition parameters in Step 34 for three-dimensional CFD analysis.

[0042] According to an embodiment of the present invention, step 4 includes:

[0043] Step 41, import the grid generated in step 25;

[0044] Step 42, input the numerical solver parameters and physical model parameters obtained in step 28, and generate a numerical model;

[0045] Step 43, complete the boundary condition setting according to the inlet boundary condition parameters and outlet boundary condition parameters obtained in step 37;

[0046] Step 44, use the grid in step 41, the numerical model in step 42, and the inlet boundary condition parameters and outlet boundary condition parameters in step 43 as the input of the CFD solver, run the CFD solver for numerical solution, conduct two-phase critical flow CFD analysis and output the calculation results;

[0047] Step 45, determine whether the CFD calculation results obtained in step 44 converge; if not, go to step 42 to readjust the numerical solver parameters and physical model parameters. If they converge, output the CFD calculation results.

[0048] According to an embodiment of the present invention, step 5 includes:

[0049] Step 51, extract the pressure at the inlet of the upstream connecting pipe and the two-phase critical flow pressure drop from the CFD calculation results in step 44;

[0050] Step 52, compare the pressure at the inlet of the upstream connecting pipe obtained in step 51 with the pressure at the inlet of the upstream connecting pipe obtained in step 35, calculate the relative error between the two and determine whether it is less than the preset error limit; if not, go to step 35 to reset the two-phase flow pressure drop; if it is satisfied, stop the calculation and output the CFD calculation results;

[0051] Step 53, confirm whether all two-phase critical flow conditions have been completed for CFD analysis; if not, go to step 42 to start the CFD analysis for the next condition; if it has been completed, output the CFD calculation results for all conditions.

[0052] According to an embodiment of the present invention, step 6 includes:

[0053] Step 61, establish a geometric model according to the actual geometric dimensions of the valve;

[0054] Step 62, determine the computational fluid domain, mesh division, numerical solver, and physical model according to the geometric model;

[0055] Step 63: Determine the pressure at the inlet of the upstream connecting pipe and the pressure at the outlet of the downstream connecting pipe corresponding to each working condition according to the CFD calculation results of all working conditions in Step 53;

[0056] Step 64: Generate a numerical model with the parameter settings in Step 62 and Step 63, conduct CFD analysis of the actual two-phase critical flow of the valve and output the calculation results;

[0057] Step 65: Confirm whether the CFD analysis of all two-phase critical flow conditions of the valve is completed; if not, enter Step 64 to start the CFD analysis of the next working condition; if completed, save the CFD calculation results of all working conditions, and record the two-phase critical flow rate and the two-phase critical flow pressure drop of the valve.

[0058] According to an embodiment of the present invention, Step 62 further includes:

[0059] Step 621: Import the geometric model established in Step 61 into a computer program for mesh generation;

[0060] Step 622: Establish a computational fluid domain;

[0061] Step 623: Set the parameters of surface mesh, volume mesh and boundary layer mesh;

[0062] Step 624: Generate structured and unstructured meshes;

[0063] Step 625: Check whether the mesh quality meets the requirements. If not, enter Step 623 to re-adjust the parameters of surface mesh, volume mesh and boundary layer mesh until the required mesh quality is obtained; if satisfied, save the simulation file and record the computational fluid domain and mesh generation parameters;

[0064] Step 626: Select a physical model and a numerical solver;

[0065] Step 627: Set the parameters of the numerical solver and the physical model;

[0066] Step 628: Save the simulation file and record the parameters of the numerical solver and the physical model.

[0067] According to an embodiment of the present invention, Step 64 includes:

[0068] Step 641: Import the mesh generated in Step 625;

[0069] Step 642: Input the parameters of the numerical solver and the physical model recorded in Step 628 to generate a numerical model;

[0070] Step 643: Complete the boundary condition setting according to the pressure at the inlet of the upstream connection pipeline and the pressure at the outlet of the downstream connection pipeline recorded in Step 63;

[0071] Step 644: Run the CFD numerical solution, conduct the CFD analysis of the two-phase critical flow of the valve, and output the calculation results;

[0072] Step 645: Determine whether the CFD calculation results converge; if not, go to Step 642 to readjust the numerical solver and physical model parameters; if they converge, output the CFD calculation results.

[0073] The second aspect of the present invention also provides a computer program product, including a computer program, which when executed by a processor implements the steps executed by a computer in the method described above.

[0074] The third aspect of the present invention also provides a computer-readable storage medium having a computer program, which when executed by a processor implements the steps executed by a computer in the method described above.

[0075] The fourth aspect of the present invention also provides a simulation system, including:

[0076] A memory capable of storing instructions executable by a processor;

[0077] A processor capable of executing the instructions to implement the steps executed by a computer in the method described above.

[0078] The positive and progressive effects of the present invention are as follows:

[0079] In the two-phase critical flow coupling simulation method of the valve of the present invention, the target two-phase critical flow model is used to calculate the boundary conditions of the upstream and downstream of the valve required for three-dimensional CFD analysis, and then the parameters assumed in the two-phase flow model are corrected based on the three-dimensional CFD analysis results. Through mutual iterative correction between the two, it can not only skillfully avoid the difficulty of determining the boundary condition parameters of the upstream and downstream of the valve, but also effectively improve the efficiency and accuracy of the two-phase critical flow calculation, which is beneficial to the rapid analysis of the valve process design and the flow performance of the invention. Description of the Drawings

[0080] The above and other features, properties, and advantages of the present invention will become more obvious through the following description in conjunction with the drawings and embodiments, where:

[0081] Figure 1 is a flowchart of the two-phase critical flow coupling simulation method of the valve of the present invention;

[0082] Figure 2 is a schematic diagram of the actual valve model of the present invention being equivalent to a single-stage orifice geometric model;

[0083] Figure 3 It is a flow chart of the method for setting the geometric model, computational fluid domain, mesh division and model parameters of the two-phase critical flow of the present invention;

[0084] Figure 4 It is a flow chart of the calculation method for the upstream and downstream boundary condition parameters applicable to the three-dimensional CFD analysis of the two-phase critical flow of the present invention;

[0085] Figure 5 It is a flow chart of the iterative CFD calculation method according to an embodiment of the present invention;

[0086] Figure 6 It is a flow chart of the two-phase critical flow pressure drop coupling iterative calculation method according to an embodiment of the present invention;

[0087] Figure 7 It is a flow chart of the CFD calculation method for the two-phase critical flow of the valve according to an embodiment of the present invention;

[0088] Figure 8 It is a structural schematic diagram of the simulation system of the present invention. Specific embodiments

[0089] The present invention will be further described below in conjunction with specific embodiments and the accompanying drawings. More details are set forth in the following description to facilitate a full understanding of the present invention. However, the present invention is obviously capable of being implemented in many different ways other than as described herein. Those skilled in the art can make similar generalizations and deductions according to the actual application situation without departing from the connotation of the present invention. Therefore, the scope of protection of the present invention should not be limited by the content of this specific embodiment.

[0090] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification and claims of this application and the above drawings are intended to cover non-exclusive inclusion.

[0091] Refer to Figure 1 , the present invention proposes a two-phase critical flow coupling simulation method for valves, including the following steps:

[0092] S1. Determine the effective flow area according to the valve geometric dimensions, and establish an equivalent single-stage orifice geometric model based on the effective flow area.

[0093] Refer to Figure 2 , for simplifying the geometric modeling of the actual valve, the present invention uses a single-stage orifice to equivalent the actual valve, and the orifice opening area is the same as the effective flow area of the valve.

[0094] Furthermore, the length of the upstream and downstream connecting pipes of the orifice plate should be at least greater than 10 times the nominal diameter of the valve to ensure the full development of turbulent flow.

[0095] S2. Determine the computational fluid domain, mesh generation, numerical solver, and physical model according to the single-stage orifice plate geometric model.

[0096] Specifically, please refer to Figure 3 , and step 2 includes:

[0097] Step 21. Import the single-stage orifice plate geometric model into the computer program for mesh generation. Among them, the computer program for mesh generation is mesh generation software, and the mesh generation software uses existing software, which will not be elaborated here.

[0098] Step 22. Establish the computational fluid domain.

[0099] Step 23. Set the surface mesh, volume mesh, and boundary layer mesh parameters.

[0100] Step 24. Generate structured and unstructured meshes.

[0101] Step 25. Check whether the mesh quality meets the requirements; if the mesh quality meets the requirements, save the simulation file and record the computational fluid domain and mesh generation parameters; if the mesh quality does not meet the requirements, enter step 23 to re-adjust the surface mesh, volume mesh, and boundary layer mesh parameters until the mesh quality meets the requirements.

[0102] Step 26. Select the physical model and numerical solver.

[0103] Step 27. Set the numerical solver parameters and physical model parameters.

[0104] Step 28. Save the simulation file obtained in step 25 and record the numerical solver parameters and physical model parameters in step 27.

[0105] S3. Select the target two-phase critical flow model to calculate and determine the two-phase critical flow rate and the upstream and downstream boundary condition parameters for CFD analysis according to the upstream saturated water stagnation pressure of the valve and the set two-phase critical flow pressure drop; among them, the upstream boundary condition parameters include the pressure at the inlet of the first upstream connecting pipe.

[0106] Refer to Figure 4 , and step 3 specifically includes:

[0107] Step 31. Calculate the pressure at the outlet of the downstream connecting pipe according to the upstream saturated water stagnation pressure of the valve and the critical pressure ratio.

[0108] It should be noted that the stagnation pressure refers to the pressure when the moving fluid is isentropically stagnated and its velocity becomes zero. The stagnation pressure characterizes the pressure at which all the kinetic energy of the fluid is converted into pressure energy, and numerically it is equal to the sum of the static pressure and the dynamic pressure.

[0109] The critical pressure ratio is the ratio of the pressure at the outlet of the downstream connecting pipe to the stagnation pressure of the upstream saturated water when the flow reaches the critical state. At this time, the flow rate is the maximum value, that is, the critical flow rate.

[0110] According to the test results of the open literature, for the two-phase critical flow in a pipe with an equal-length channel, the critical pressure ratio approaches a certain constant, and its value is about 0.55. Therefore, the pressure at the outlet of the downstream connecting pipe can be directly calculated by the following formula:

[0111] p2 = 0.55 × p0;

[0112] where p2 is the pressure at the outlet of the downstream connecting pipe, and p0 is the stagnation pressure of the upstream saturated water of the orifice plate.

[0113] Step 32: According to the pressure at the outlet of the downstream connecting pipe, use the physical property parameter calculation formula of saturated water and steam to calculate the physical property parameters of the corresponding saturated water and saturated steam.

[0114] Specifically, the corresponding expressions of the physical property parameter calculation formula of saturated water and steam are:

[0115] v 2fs = F1(p2), v 2gs = G1(p2);

[0116] h 2fs = F2(p2), h 2gs = G2(p2);

[0117] s 2fs = F3(p2), s 2fs = G3(p2);

[0118] where p2 is the pressure at the outlet of the downstream connecting pipe, v 2fs is the corresponding specific volume of saturated water, v 2gs is the corresponding specific volume of saturated steam, h 2fs is the corresponding enthalpy of saturated water, h 2gs is the corresponding enthalpy of saturated steam, s 2fs is the corresponding entropy of saturated water, s 2gs is the corresponding entropy of saturated steam, and F1(p2), F2(p2), F3(p2), G1(p2), G2(p2), G3(p2) are functions related to the pressure at the outlet of the downstream connecting pipe. These functions are well-known functions in this field and will not be elaborated here.

[0119] Step 33: Calculate the dryness and void fraction at the outlet of the downstream connecting pipe using the adiabatic throttling model and critical flow conditions based on the determined physical properties of saturated water and saturated steam, and calculate the two-phase critical flow mass flow rate using the thermodynamic equation in the target two-phase critical flow model; where the target two-phase critical flow model is the classical two-phase critical flow model.

[0120] Among them, the expression corresponding to the adiabatic throttling model is:

[0121] s0 = (1 - x2)s 2fs + x2s 2gs ;

[0122] Among them, s0 is the upstream saturated water stagnation entropy, and x2 is the dryness at the outlet of the downstream connecting pipe.

[0123] Among them, the expression corresponding to the critical flow condition is:

[0124]

[0125]

[0126] S = S c ;

[0127] Among them, S is the slip ratio, α2 is the void fraction at the outlet of the downstream connecting pipe, and S c is the critical slip ratio.

[0128] Among them, the expression corresponding to the thermodynamic equation in the classical two-phase critical flow model is:

[0129]

[0130] h2 = (1 - x2)h 2fs + x2h 2gs ;

[0131]

[0132] Among them, h0 is the upstream saturated water stagnation enthalpy, h2 is the downstream static enthalpy, G is the two-phase critical mass flow rate, and v″′2 is the specific volume of the steam-water mixture at the outlet of the downstream connecting pipe.

[0133] Step 34: Determine the outlet boundary condition parameters for 3D CFD analysis based on the pressure, dryness, and void fraction at the outlet of the downstream connecting pipe.

[0134] Step 35: Set the two-phase critical flow pressure drop through the orifice according to the physical properties of saturated water and saturated steam, and calculate the pressure and specific volume at the inlet of the upstream connecting pipe using the pressure drop equation in the target two-phase critical flow model.

[0135] Among them, the expression corresponding to the pressure drop equation in the classical two-phase critical flow model is as follows:

[0136] p1 - p2 = G 2 (v′2 - v1) + Δp f ;

[0137] v1 = F(p1);

[0138]

[0139] Among them, p1 is the saturated water pressure at the inlet of the upstream connecting pipe, p2 is the pressure at the outlet of the downstream connecting pipe, v1 is the specific volume of saturated water at the inlet of the upstream connecting pipe, F(p1) is a function related to the pressure at the inlet of the upstream connecting pipe, v′2 is the specific volume of the steam-water mixture at the outlet of the downstream connecting pipe, and Δp f is the two-phase critical flow pressure drop through the orifice plate.

[0140] It should be noted that for the assumed two-phase critical flow pressure drop, its initial value can be calculated and determined according to the single-phase flow pressure drop through the orifice plate, and the corresponding expression is:

[0141]

[0142] Among them, K is the orifice plate resistance coefficient under single-phase flow conditions, which can be obtained from the hydraulic calculation manual.

[0143] Step 36: Calculate the flow velocity at the inlet of the upstream connecting pipe according to the two-phase critical flow mass flow rate, the pressure and specific volume at the inlet of the upstream connecting pipe, and determine the inlet boundary condition parameters for three-dimensional CFD analysis.

[0144] Among them, the expression for calculating the flow velocity at the inlet of the upstream connecting pipe is:

[0145] u1 = G·v1;

[0146] Among them, u1 is the flow velocity at the inlet of the upstream connecting pipe.

[0147] Step 37: Record the inlet boundary condition parameters in Step 36 and the outlet boundary condition parameters in Step 34 for three-dimensional CFD analysis.

[0148] The inlet boundary condition parameters include at least the saturated water flow velocity; the outlet boundary condition parameters include at least the pressure, dryness, and void fraction.

[0149] S4: Use the numerical solver parameters and the physical model parameters to generate a numerical model, then complete the boundary condition setting using the upstream and downstream boundary condition parameters obtained in Step 3, run the CFD solver for iterative calculation, and output the second upstream connecting pipe inlet pressure and the two-phase critical flow pressure drop.

[0150] Refer to Figure 5 , Step 4 specifically includes:

[0151] Step 41: Import the grid generated in Step 25.

[0152] Step 42: Input the numerical solver parameters and physical model parameters obtained in Step 28, and generate a numerical model.

[0153] Step 43: Complete the boundary condition setting according to the inlet boundary condition parameters and outlet boundary condition parameters obtained in Step 37.

[0154] Step 44: Use the grid in Step 41, the numerical model in Step 42, and the inlet boundary condition parameters and outlet boundary condition parameters in Step 43 as the input of the CFD solver, run the CFD solver for numerical solution, conduct two-phase critical flow CFD analysis and output the calculation results.

[0155] Step 45: Determine whether the CFD calculation results obtained in Step 44 converge; if not, go to Step 42 to readjust the numerical solver parameters and physical model parameters. If they converge, output the CFD calculation results.

[0156] Among them, determining whether the CFD calculation results converge further includes:

[0157] The CFD calculation results should at least meet the following convergence evaluation criteria to be considered convergent.

[0158] Among them, the convergence evaluation criteria include:

[0159] The root mean square residual is less than or equal to 10 -5 ;

[0160] The mass flow rate at the inlet of the upstream connecting pipe and the mass flow rate at the outlet of the downstream connecting pipe reach equilibrium.

[0161] S5: Compare the pressure at the inlet of the first upstream connecting pipe and the pressure at the inlet of the second upstream connecting pipe; if the relative error is less than the preset limit, output the CFD analysis results, and the CFD analysis results include two-phase critical flow rate and two-phase critical flow pressure drop; if the relative error is greater than or equal to the preset limit, reset the two-phase critical flow pressure drop in Step 2 and repeat Steps 3 to 5 for iterative correction to obtain the CFD analysis results.

[0162] Refer to Figure 6 , Step 5 specifically includes:

[0163] Step 51: Extract the pressure at the inlet of the upstream connecting pipe and the two-phase critical flow pressure drop from the CFD calculation results in Step 44.

[0164] Step 52: Compare the pressure at the inlet of the upstream connecting pipe obtained in Step 51 with the pressure at the inlet of the upstream connecting pipe obtained in Step 35, calculate the relative error between the two, and determine whether it is less than the preset error limit value; if not satisfied, go to Step 35 to reset the two-phase flow pressure drop; if satisfied, stop the calculation and output the CFD calculation results.

[0165] Among them, the expression for determining whether the relative error is less than the preset error limit value is:

[0166]

[0167] Among them, p″1 is the pressure at the inlet of the upstream connecting pipe calculated using CFD software, p′1 is the pressure at the inlet of the upstream connecting pipe calculated using the classical two-phase critical flow model, and ε is the preset error limit value.

[0168] Among them, the preset error limit value includes:

[0169] The relative error of the processing pressure at the inlet of the upstream connecting pipe is 5%.

[0170] Step 53: Confirm whether the CFD analysis of all two-phase critical flow conditions has been completed; if not completed, go to Step 42 to start the CFD analysis of the next condition; if completed, output the CFD calculation results of all conditions.

[0171] S6. According to the CFD analysis results obtained in Step 5, establish a numerical model of the actual valve corresponding to the equivalent single-stage orifice plate geometric model, and obtain the two-phase critical flow rate and pressure drop of the actual valve through CFD analysis.

[0172] Refer to Figure 7 , Step 6 specifically includes:

[0173] Step 61: Establish a geometric model according to the actual geometric dimensions of the valve.

[0174] Step 62: Determine the computational fluid domain, mesh division, numerical solver, and physical model according to the geometric model.

[0175] It should be noted that Step 62 specifically includes the following steps:

[0176] Step 621: Import the geometric model established in Step 61 into the computer program for mesh division;

[0177] Step 622: Establish the computational fluid domain;

[0178] Step 623: Set the parameters of surface mesh, volume mesh, and boundary layer mesh;

[0179] Step 624: Generate structured and unstructured meshes;

[0180] Step 625: Check whether the mesh quality meets the requirements. If not, go back to Step 623 to readjust the parameters of surface mesh, volume mesh, and boundary layer mesh until the mesh quality meets the requirements. If it meets the requirements, save the simulation file and record the computational fluid domain and mesh generation parameters;

[0181] Step 626: Select the physical model and numerical solver;

[0182] Step 627: Set the parameters of the numerical solver and physical model;

[0183] Step 628: Save the simulation file and record the parameters of the numerical solver and physical model.

[0184] Step 63: Determine the pressure at the inlet of the upstream connecting pipe and the pressure at the outlet of the downstream connecting pipe corresponding to each working condition according to the CFD calculation results of all working conditions in Step 53.

[0185] Step 64: Generate a numerical model with the parameter settings in Steps 62 and 63, conduct a CFD analysis of the two-phase critical flow of the actual valve, and output the calculation results.

[0186] Step 64 specifically includes the following steps:

[0187] Step 641: Import the mesh generated in Step 625;

[0188] Step 642: Input the parameters of the numerical solver and physical model recorded in Step 628 to generate a numerical model;

[0189] Step 643: Complete the boundary condition setting according to the pressure at the inlet of the upstream connecting pipe and the pressure at the outlet of the downstream connecting pipe recorded in Step 63;

[0190] Step 644: Run the CFD numerical solver, conduct a CFD analysis of the two-phase critical flow of the valve, and output the calculation results;

[0191] Step 645: Judge whether the CFD calculation results converge. If not, go back to Step 642 to readjust the numerical solver and physical model parameters. If they converge, output the CFD calculation results.

[0192] Among them, judging whether the CFD calculation results converge further includes:

[0193] The CFD calculation results are considered to converge if they meet at least the following convergence evaluation criteria.

[0194] The convergence evaluation criteria include:

[0195] The RMS residual is less than or equal to 10 -5 ;

[0196] The mass flow rate at the inlet of the upstream connecting pipe and the mass flow rate at the outlet of the downstream connecting pipe are balanced.

[0197] Step 65, confirm whether the CFD analysis of all two-phase critical flow conditions of the valve is completed; if not, proceed to step 64 to start the CFD analysis of the next condition; if completed, save the CFD calculation results of all conditions, and record the valve two-phase critical flow and two-phase critical flow pressure drop.

[0198] In summary, the valve two-phase critical flow coupling simulation method of the present invention uses the classic two-phase critical flow model to calculate the valve upstream and downstream boundary conditions required for three-dimensional CFD analysis, and then corrects the assumed pressure drop parameters in the two-phase critical flow model according to the three-dimensional CFD analysis results. Through mutual iterative correction, it can cleverly avoid the difficulty of determining the valve upstream and downstream boundary condition parameters, and effectively improve the efficiency and accuracy of the two-phase critical flow calculation, which is conducive to rapid optimization and iteration of designers.

[0199] refer to Figure 8 As shown, the present application also provides a simulation system 1000, including a memory 1001 and a processor 1002, the memory can store instructions that can be executed by the processor 1002; the processor 1002 can execute instructions to implement the steps performed by the computer in the valve two-phase critical flow coupling simulation method introduced in the above embodiment.

[0200] It is understood that it should be noted that the above-mentioned memory and processor are not limited to a specific memory and processor. Furthermore, in the embodiment adopting the distributed structure, each step can adjust the specific execution terminal according to the actual situation, and the specific scheme of each step implemented in a specific terminal should not limit the protection scope of this application.

[0201] According to another aspect of the present application, the present application also provides a computer-readable medium.

[0202] The computer-readable medium provided in the present application has computer instructions thereon. When the computer instructions are executed by a processor, the program can be executed by the processor to implement the steps executed by the program in the method described in the above embodiment.

[0203] According to yet another aspect of the present application, the present application also provides a computer program product.

[0204] The above computer-readable medium provided by the present application includes a computer program, and when the computer program is executed by a processor, the steps executed by the program can be implemented as the steps executed by the program in the method introduced in the above embodiments.

[0205] The various illustrative logical modules and circuits described in connection with the embodiments disclosed herein can be implemented or executed using a general-purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof designed to perform the functions described herein. A general-purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The processor may also be implemented as a combination of computing devices, such as a combination of a DSP and a microprocessor, multiple microprocessors, one or more microprocessors cooperating with a DSP core, or any other such configuration.

[0206] The steps of the methods or algorithms described in connection with the embodiments disclosed herein may be embodied directly in hardware, in a software module executed by a processor, or in a combination of both. The software module may reside in RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, registers, a hard disk, a removable disk, a CD-ROM, or any other form of storage medium known in the art. An exemplary storage medium is coupled to the processor such that the processor can read from, and write to, the storage medium. In the alternative, the storage medium may be integrated into the processor. The processor and the storage medium may reside in an ASIC. The ASIC may reside in a user terminal. In the alternative, the processor and the storage medium may reside as discrete components in a user terminal.

[0207] In one or more exemplary embodiments, the described functionality may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software as a computer program product, the functions may be stored on or transmitted via a computer-readable medium as one or more instructions or code. The computer-readable medium includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. The storage media may be any available media that can be accessed by a computer. By way of example and not limitation, such computer-readable media can include RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a web site, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. As used herein, disk and disc include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks typically reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media.

[0208] Although this application is disclosed above in preferred embodiments, it is not intended to limit this application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of this application. Therefore, any modifications, equivalent changes, and embellishments made to the above embodiments based on the technical essence of this application without departing from the technical solutions of this application shall fall within the protection scope defined by the claims of this application.

Claims

1. A valve two-phase critical flow coupling simulation method, characterized in that: include: Step 1, determining the effective flow area according to the valve geometric dimensions, and establishing an equivalent single-stage orifice plate geometric model based on the effective flow area; Step 2, determining the computational fluid domain, meshing, numerical solver and physical model according to the single-stage orifice plate geometric model; Step 3: According to the upstream saturated water stagnation pressure of the valve and the set two-phase critical flow pressure drop, a target two-phase critical flow model is selected to calculate and determine the two-phase critical flow rate and upstream and downstream boundary condition parameters for CFD analysis; wherein the upstream boundary condition parameters include the pressure at the inlet of the first upstream connecting pipeline; Step 4: Generate a numerical model using the numerical solver parameters and the physical model parameters, then use the upstream and downstream boundary condition parameters obtained in step 3 to complete boundary condition setting, run the CFD solver for iterative calculation, and output the inlet pressure of the second upstream connecting pipeline and the two-phase critical flow pressure drop; Step 5, comparing the pressure at the inlet of the first upstream connecting pipeline with the pressure at the inlet of the second upstream connecting pipeline; if the relative error is less than a preset limit, outputting a CFD analysis result, the CFD analysis result including a two-phase critical flow rate and a two-phase critical flow pressure drop; if the relative error is greater than or equal to the preset limit, resetting the two-phase critical flow pressure drop in step 2, and repeating steps 3 to 5 for iterative correction to obtain a CFD analysis result; Step 6: Based on the CFD analysis results obtained in step 5, a numerical model of an actual valve is established corresponding to the equivalent single-stage orifice plate geometric model, and the two-phase critical flow and pressure drop of the actual valve are obtained through CFD analysis.

2. The valve two-phase critical flow coupling simulation method according to claim 1 is characterized in that: The step 2 comprises: Step 21, importing the single-stage orifice plate geometric model into a computer program for meshing; Step 22, establishing a computational fluid domain; Step 23, setting the surface mesh, volume mesh and boundary layer mesh parameters; Step 24, generating structured and unstructured grids; Step 25, if the mesh quality meets the requirements, save the simulation file and record the computational fluid domain and meshing parameters; if the mesh quality does not meet the requirements, enter the step 23 to readjust the surface mesh, volume mesh and boundary layer mesh parameters until the mesh quality meets the requirements; Step 26: Select the physical model and numerical solver; Step 27: setting the numerical solver parameters and the physical model parameters; Step 28, saving the simulation file obtained in step 25 and recording the numerical solver parameters and the physical model parameters in step 27.

3. The valve two-phase critical flow coupling simulation method according to claim 2 is characterized in that: The step 3 comprises: Step 31, calculating the pressure at the outlet of the downstream connecting pipeline according to the saturated water stagnation pressure upstream of the valve and the critical pressure ratio; Step 32, according to the pressure at the outlet of the downstream connecting pipeline, the physical property parameters of the corresponding saturated water and saturated water vapor are calculated using the calculation formula of the physical property parameters of saturated water and water vapor; Step 33, according to the determined physical parameters of saturated water and saturated water vapor, the dryness and cavitation fraction at the outlet of the downstream connecting pipe are calculated using the adiabatic throttling model and the critical flow condition, and the two-phase critical flow mass flow rate is calculated using the thermodynamic equation in the target two-phase critical flow model; wherein the target two-phase critical flow model is a classical two-phase critical flow model; Step 34, determining the outlet boundary condition parameters for three-dimensional CFD analysis according to the pressure, dryness and cavitation fraction at the outlet of the downstream connecting pipe; Step 35, according to the physical properties of the saturated water and saturated water vapor, set the two-phase critical flow pressure drop through the orifice plate, and use the pressure drop equation in the target two-phase critical flow model to calculate the pressure and specific volume at the inlet of the upstream connecting pipeline; Step 36, calculating the flow velocity at the inlet of the upstream connecting pipe according to the two-phase critical flow mass flow rate, the pressure at the inlet of the upstream connecting pipe and the specific volume, and determining the inlet boundary condition parameters for three-dimensional CFD analysis; Step 37: Record the inlet boundary condition parameters in step 36 and the outlet boundary condition parameters in step 34 for three-dimensional CFD analysis.

4. The valve two-phase critical flow coupling simulation method according to claim 3 is characterized in that: The step 4 comprises: Step 41, importing the mesh generated in step 25; Step 42: input the numerical solver parameters and physical model parameters obtained in step 28, and generate a numerical model; Step 43, completing the boundary condition setting according to the inlet boundary condition parameters and the outlet boundary condition parameters obtained in step 37; Step 44, using the grid in step 41, the numerical model in step 42, and the inlet boundary condition parameters and the outlet boundary condition parameters in step 43 as inputs of a CFD solver, running the CFD solver for numerical solution, performing two-phase critical flow CFD analysis and outputting calculation results; Step 45, determine whether the CFD calculation result obtained in step 44 converges; if not, enter step 42, readjust the numerical solver parameters and physical model parameters, and if converged, output the CFD calculation result.

5. The valve two-phase critical flow coupling simulation method according to claim 4 is characterized in that: The step 5 comprises: Step 51, extracting the pressure at the inlet of the upstream connecting pipeline and the two-phase critical flow pressure drop from the CFD calculation results in step 44; Step 52: Compare the pressure at the inlet of the upstream connecting pipe obtained in step 51 with the pressure at the inlet of the upstream connecting pipe obtained in step 35, calculate the relative error between the two and determine whether it is less than a preset error limit; if not, enter step 35 to reset the two-phase flow pressure drop; if satisfied, stop the calculation and output the CFD calculation result; Step 53, confirm whether the CFD analysis of all two-phase critical flow conditions is completed; if not, enter the step 42 to start the CFD analysis of the next condition; if completed, output the CFD calculation results of all conditions.

6. The valve two-phase critical flow coupling simulation method according to claim 5, characterized in that: The step 6 comprises: Step 61, establishing a geometric model according to the actual geometric dimensions of the valve; Step 62, determining the computational fluid domain, network partitioning, numerical solver and physical model according to the geometric model; Step 63, according to the CFD calculation results of all working conditions in step 53, determine the pressure at the inlet of the upstream connecting pipeline and the pressure at the outlet of the downstream connecting pipeline corresponding to each working condition; Step 64, using the parameter settings of step 62 and step 63 to generate a numerical model, conduct CFD analysis of the actual valve two-phase critical flow and output the calculation results; Step 65, confirm whether the CFD analysis of all two-phase critical flow conditions of the valve is completed; if not, enter the step 64 to start the CFD analysis of the next condition; if completed, save the CFD calculation results of all conditions, and record the valve two-phase critical flow and two-phase critical flow pressure drop.

7. The valve two-phase critical flow coupling simulation method according to claim 6, characterized in that: The step 62 further comprises: Step 621, importing the geometric model established in step 61 into a computer program for meshing; Step 622, establishing a computational fluid domain; Step 623, setting surface mesh, volume mesh and boundary layer mesh parameters; Step 624, generating structured and unstructured grids; Step 625, check whether the mesh quality meets the requirements. If not, proceed to step 623 to readjust the surface mesh, volume mesh and boundary layer mesh parameters until the mesh quality meets the requirements. If it meets the requirements, save the simulation file and record the computational fluid domain and mesh partitioning parameters. Step 626, selecting a physical model and a numerical solver; Step 627, setting numerical solver parameters and physical model parameters; Step 628: Save the simulation file and record the numerical solver parameters and physical model parameters.

8. The valve two-phase critical flow coupling simulation method according to claim 7 is characterized in that: The step 64 comprises: Step 641, importing the mesh generated in step 625; Step 642, inputting the numerical solver parameters and physical model parameters recorded in step 628 to generate a numerical model; Step 643, completing the boundary condition setting according to the pressure at the inlet of the upstream connecting pipe and the pressure at the outlet of the downstream connecting pipe recorded in step 63; Step 644, run CFD numerical solution, carry out valve two-phase critical flow CFD analysis and output calculation results; Step 645, determine whether the CFD calculation results converge; if not, enter the step 642, readjust the numerical solver and physical model parameters; if converged, output the CFD calculation results.

9. A computer program product, characterized in that The method comprises a computer program, which, when executed by a processor, implements the steps performed by a computer in the method according to any one of claims 1 to 8.

10. A computer-readable storage medium, characterized in that: A computer program is provided, which, when executed by a processor, implements the steps performed by a computer in the method according to any one of claims 1 to 8.

11. A simulation system, characterized in that: include: a memory capable of storing instructions executable by a processor; A processor capable of executing the instructions to implement the steps performed by a computer in the method according to any one of claims 1 to 8.

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