A simulation method for multi-valve constant pressure opening and closing

Abstract

The application discloses a simulation method for multi-valve constant-pressure opening and closing, and belongs to the technical field of computational fluid mechanics. The application provides a simple and high-precision processing method for complex working conditions such as a multi-valve opening and closing hydraulic system, multi-valve opening and closing in cylinder compression and the like, and multi-valve constant-pressure opening and closing, can be used for solving computational fluid dynamics of multi-valve constant-pressure opening and closing, and provides a general solution method. Compared with a traditional method for solving valve constant-pressure opening and closing, the method is simple to implement, and can more timely and accurately open the valve at constant pressure.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of computational fluid dynamics, and particularly relates to a simulation method for multi-valve constant pressure opening and closing. BACKGROUND

[0002] Computational fluid dynamics is one of the important ways to carry out fluid mechanics research, and plays an increasingly important role in studying the flow characteristics of fluid in the process of valve opening and closing, including flow velocity, pressure distribution, turbulent kinetic energy, etc. In the multi-valve hydraulic system and the multi-valve cylinder compression problem, the valve is often opened when reaching a certain pressure. When computational fluid dynamics is used to simulate the constant pressure opening and closing of the valve, the conventional boundary condition setting method is difficult to be used for the research of such problems.

[0003] In order to be able to realize the timely conversion of the wall boundary condition of the multi-valve surface to the pressure outlet / inlet boundary condition after the multi-valve surface reaches the preset pressure, and keep the outlet / inlet pressure at the preset value, and not affect the internal pressure of the fluid domain, researchers propose a simulation method for multi-valve constant pressure opening and closing. In the fluid calculation process, the program is read at the initial stage of each time step, and the valve is opened and closed when the area-weighted pressure of the valve surface reaches the preset value, realizing the conversion of the boundary condition and the setting of the outlet / inlet pressure. For such problems, there is a traditional processing method, which uses the EVENT monitoring time step in the dynamic mesh module. When the calculation time reaches the preset time step, the boundary condition is converted, and the outlet / inlet pressure is set at the preset time step.

[0004] For most valve opening and closing problems that reach a preset pressure, such as the opening and closing of the overflow valve and the pressure relief valve, there are currently two methods to solve them, as follows:

[0005] Method one: constant time opening and closing valve. The EVENT function in the dynamic mesh module is used to monitor the time step, and when the time step reaches the preset value, the wall boundary condition of the valve surface is converted to the pressure outlet / inlet boundary condition, and the outlet / inlet pressure value is set. Using this method, the pressure outlet / inlet boundary condition needs to be set as the wall boundary condition first, and the fluid mechanics calculation simulation is carried out, and the area-weighted pressure value at the wall boundary condition is monitored. The time step when the area-weighted pressure reaches the preset value is recorded, and the time step is used as the time step preset value for boundary condition conversion. This method has good effect for the opening and closing of a single valve, but when there are multiple constant pressure opening and closing valves in the system, because the opening and closing pressures of different valves are not the same, it is difficult to accurately obtain the time step when each valve reaches the preset pressure, so this method is no longer applicable to the system with multiple constant pressure opening and closing valves.

[0006] Method two: directly set the boundary condition of the valve face as a pressure outlet / inlet boundary condition. Set the valve face as a pressure outlet / inlet boundary condition, and set the opening and closing pressure as a predetermined value. In general hydraulic systems, the set pressure value of the valve face has little effect on the pressure of the internal region, and can achieve a relatively ideal effect. However, when simulating in-cylinder compression, the pressure preset value of the valve face will directly affect the average pressure value of the compressible fluid in the closed space. Therefore, this method cannot solve the problem of constant pressure opening and closing of the valve during adiabatic compression.

[0007] The above problems need to be solved, and therefore a simulation method for constant pressure opening and closing of multiple valves is proposed. SUMMARY

[0008] The technical problem to be solved by the present application is how to solve the above-mentioned problems existing in the prior art, and a simulation method for constant pressure opening and closing of multiple valves is provided.

[0009] The present application solves the above technical problems by the following technical solutions, and the present application comprises the following steps:

[0010] Step S1: simplify multiple constant pressure valves into one face during CFD simulation flow calculation and name them, which are used for valve constant pressure opening and closing algorithm identification, and perform grid division on the valve face and the fluid domain where the valve face is located to obtain the parameters of the calculation domain grid division;

[0011] Step S2: set the grid type as FLUENT type, and set the boundary condition of the valve face as a wall boundary condition according to the actual working state of the valve at the initial calculation time step;

[0012] Step S3: set the area weighted average pressure curve to monitor the area weighted average pressure of each valve face;

[0013] Step S4: set the following contents in the valve constant pressure opening and closing algorithm: read the area weighted average pressure value of each valve face at the beginning of each time step of CFD simulation flow calculation; set the area weighted average pressure of each valve face when opening as P maxi , and set the judgment conditions, including the area weighted average pressure of each valve face and P maxi , and the size relationship judgment of the current calculation time and the preset time; at the beginning of each calculation time step, compare the area weighted average pressure value of each valve face with P maxi , and compare the current calculation time with the preset time; when the area weighted average pressure of each valve face is less than P maxithe size relationship and the current calculation time and the preset time meet the judgment condition, the valve surface boundary condition is converted into the pressure outlet / inlet boundary condition, and the outlet / inlet pressure is set to P maxi If not, the boundary condition conversion is not performed, and the condition judgment is continued when the next calculation time step starts; wherein, i represents the i-th valve surface;

[0014] Step S5: setting a command to execute the valve constant pressure opening and closing algorithm at the start of each calculation time step;

[0015] Step S6: setting the physical problem solving parameters;

[0016] Step S7: performing numerical solution;

[0017] Step S8: repeating steps S4-S5 at the start of each time step until the simulation stops.

[0018] Further, in the step S1, the parameters include the grid precision and density of the valve surface and the fluid domain where the valve surface is located, and each valve surface is named.

[0019] Further, in the step S3, the area weighted average pressure curve is set to monitor the area weighted average pressure of each valve surface.

[0020] Further, in the step S5, the valve constant pressure opening and closing algorithm is used to control the valve constant pressure opening and closing, and the specific control logic of the valve constant pressure opening and closing algorithm is as follows:

[0021] Step S51: defining a variable name, initializing the area weighted average pressure of each valve surface to 0, and assigning the initialized pressure value to the variable;

[0022] Step S52: defining a function name;

[0023] Step S53: defining the current value of the area weighted average pressure curve of each valve surface at the start of each time step, and assigning the value to the variable name in step S51;

[0024] Step S54: defining a judgment condition to judge whether the current calculation time and the preset time meet the judgment condition;

[0025] Step S55: defining a judgment condition to judge whether the current value of the area weighted average pressure curve of each valve surface meets the judgment condition; maxi

[0026] Step S56: executing a command stream when the area weighted average pressure of each valve surface and P maxi ​When the size relationship and the current calculation time and the preset time meet the judgment condition, the boundary condition of each valve surface is converted into the pressure outlet / inlet boundary condition;

[0027] Step S57: execute the command flow to set the outlet pressure of the corresponding valve surface as P maxi ;

[0028] Step S58: if both step S54 and step S55 are correct, execute step S56 and step S57; if one of S54 and S55 is incorrect, do not execute the command flow and wait for the next calculation time step to start to continue reading the program to make a judgment until the condition is met.

[0029] Further, in the step S51, the defined variable name means the area-weighted average pressure value of each valve surface, which is used to store the area-weighted average pressure value of each valve surface at the start of each calculation time step.

[0030] Further, in the step S52, the function name corresponding to the defined function content is step S53 to step S58.

[0031] Compared with the prior art, the simulation method for multiple valve opening and closing at a constant pressure has the following advantages: the simulation method for multiple valve opening and closing at a constant pressure gives a simple and high-precision method for multiple valve opening and closing of a hydraulic system, in-cylinder compression, and other complex working conditions requiring multiple valve opening and closing at a constant pressure, which can provide a general solution for computational fluid dynamics with multiple valve opening and closing at a constant pressure. Compared with the traditional method for solving valve opening and closing at a constant pressure, the method is simple to implement and can open the valve at a constant pressure more timely and accurately. BRIEF DESCRIPTION OF DRAWINGS

[0032] Fig. 1 The structure of the research object in the embodiment of the application is shown in the figure;

[0033] Fig. 2 The fluid calculation domain after filling of the original calculation domain in the embodiment of the application is shown in the figure;

[0034] Fig. 3 The simulation flowchart of the simulation method for multiple valve opening and closing at a constant pressure in the embodiment of the application is shown in the figure;

[0035] In the figure, 1 is an oil distribution plate, 2 is a diaphragm, 3 is an exhaust valve, 4 is an intake valve, 5 is a cylinder head, 6 is an oil inlet valve / oil outlet valve, 7 is a piston, 8 is a cylinder body, 9 is an exhaust valve surface, 10 is nitrogen, 11 is an intake valve surface, 12 is an oil inlet valve / oil outlet valve surface, and 13 is hydraulic oil. DETAILED DESCRIPTION

[0036] The following will be described in detail the embodiments of the present application, the embodiments in the technical solutions of the present application as the premise, gives the detailed implementation and specific operation process, but the protection scope of the present application is not limited to the following examples.

[0037] As Figs. 1-3 shown, in this embodiment, the multi-valve pressure opening and closing simulation method of the present application is applied to the two-way fluid-structure coupling simulation of the diaphragm compressor.

[0038] The opening and closing of each valve during the operation of the piston in the diaphragm compressor is as follows:

[0039] When the piston 7 is at the bottom dead center, the intake valve 4 stops inhaling nitrogen 10, and the oil inlet valve / oil outlet valve 6 stops oiling. At this time, the intake valve 4 and the oil inlet valve / oil outlet valve 6 are in a closed state, and the valve in the closed state is regarded as a wall boundary condition in the CFD simulation flow simulation calculation. When the piston 7 moves upward from the bottom dead center, the diaphragm 2 is driven upward due to the pressure difference, and the pressure of the hydraulic oil 13 and the nitrogen 10 is increased. When the pressure of the oil inlet valve / oil outlet valve surface 12 reaches 0.7 MPa, the oil inlet valve / oil outlet valve 6 starts to discharge oil. When the pressure of the exhaust valve surface 9 reaches 0.5 MPa, the exhaust valve 3 starts to discharge gas until the piston 7 reaches the top dead center. When the piston 7 moves downward from the top dead center, the diaphragm 2 is driven downward due to the pressure difference, and at this time the nitrogen 10 starts to expand. When the pressure of the intake valve surface 11 is reduced to 0 MPa, the intake valve 4 starts to inhale nitrogen. The specific implementation steps are as follows:

[0040] Step 1: The grid division is carried out for the fluid calculation domain filled in the diaphragm compressor, and the local encryption is carried out for the simplified valve surface grid. The valve surfaces are named, the intake valve surface 11 is named as inlet, the exhaust valve surface 9 is named as outlet, and the oil inlet valve / oil outlet valve surface 12 is named as wall_change.

[0041] It should be noted that all the pressures in this embodiment are relative pressures, and 0 MPa corresponds to the standard atmospheric pressure 101325 Pa.

[0042] Step 2: According to the operation of the diaphragm compressor, when the piston 7 is at the bottom dead center, the boundary conditions of the intake valve surface 11, the exhaust valve surface 9 and the oil inlet valve / oil outlet valve surface 12 are all wall boundary conditions.

[0043] Step 3: Set the area weighted average pressure curve to monitor the area weighted average pressure of the exhaust valve surface 9, the intake valve surface 11 and the oil inlet valve / oil outlet valve surface 12.

[0044] Step 4: Write a program to achieve the following functions (i.e. the valve constant pressure opening and closing algorithm described below): At the beginning of each time step of the CFD simulation flow simulation calculation, read the area-weighted average pressure curve of the exhaust valve face 9, the intake valve face 11, and the oil inlet valve / oil outlet valve face 12, and extract the current pressure value of the area-weighted average pressure curve of the exhaust valve face 9, the intake valve face 11, and the oil inlet valve / oil outlet valve face 12, and compare it with the preset pressure of the outlet / inlet of each valve, and compare the current calculation time with the preset time.

[0045] Step 5: Write a program to achieve the following functions: When the piston 7 moves upwards from the bottom dead center, the piston 7 compresses the hydraulic oil 13 in the cylinder, and the hydraulic oil 13, after being divided by the oil distribution plate 1, acts on the diaphragm 2 to push the diaphragm 2 upwards. In the process of the piston 7 compressing the hydraulic oil 13 to push the diaphragm 2 to compress the nitrogen 10, when the oil outlet pressure of the oil inlet valve / oil outlet valve 6 reaches 0.7 MPa, the oil inlet valve / oil outlet valve face 12 is converted from a wall boundary condition to a pressure outlet boundary condition, and the outlet preset pressure is 0.7 MPa. At the same time, when the pressure of the exhaust valve face 9 reaches 0.5 MPa, the exhaust valve face 9 is converted from a wall boundary condition to a pressure outlet boundary condition, and the outlet preset pressure is 0.5 MPa. After the piston 7 reaches the top dead center and moves downward, the pressure difference drives the diaphragm 2 to move downward. When the nitrogen pressure in the diaphragm compressor expands from 0.5 MPa to 0 MPa, the intake valve face 11 is converted from a wall boundary condition to a pressure inlet boundary condition, and the inlet preset pressure is 0 MPa.

[0046] Step 6: At the beginning of each time step of the CFD simulation flow simulation calculation, read the program, and when the area-weighted average pressure of each valve face reaches the preset pressure and the time step is within the defined range, execute the program content, otherwise continue to read.

[0047] Step 7: Set the physical problem solving parameters;

[0048] Step 8: Numerical solution;

[0049] In this example, the control logic of the valve constant pressure opening and closing algorithm is as follows:

[0050] 1、For the exhaust valve surface: (1) define variable name, initialize the area-weighted average pressure of the exhaust valve surface to 0 MPa, and assign the initialized pressure value to the variable; (2) define function name, which is convenient for identifying, reading and executing functions in the algorithm during CFD calculation; (3) define the current value of the area-weighted average pressure curve of the exhaust valve surface at the start of each time step, and assign the value to the variable name in (1); (4) define the judgment condition: whether the current calculation time is less than the preset time 0.14s; (5) define the judgment condition: whether the current value of the area-weighted average pressure curve of the exhaust valve surface is greater than 0.5 MPa; (6) if (4) and (5) are both correct, execute the command stream to convert the boundary condition of the exhaust valve surface to pressure outlet, and the outlet pressure of the exhaust valve surface is 0.5 MPa; if one of (4) and (5) is incorrect, do not execute the command stream and wait for the next calculation time step to start to continue reading the program to make judgments;

[0051] 2、For the inlet valve / oil outlet valve surface: (1) define variable name, initialize the area-weighted average pressure of the oil outlet valve surface to 0 MPa, and assign the initialized pressure value to the variable; (2) define function name, which is convenient for identifying, reading and executing functions in the algorithm during CFD calculation; (3) define the current value of the area-weighted average pressure curve of the inlet valve / oil outlet valve surface at the start of each time step, and assign the value to the variable name in (1); (4) define the judgment condition: whether the current calculation time is less than the preset time 0.06s; (5) define the judgment condition: whether the current value of the area-weighted average pressure curve of the inlet valve / oil outlet valve surface is greater than 0.7 MPa; (6) if (4) and (5) are both correct, execute the command stream to convert the boundary condition of the inlet valve / oil outlet valve surface to pressure outlet, and the outlet pressure of the inlet valve / oil outlet valve surface is 0.7 MPa; if one of (4) and (5) is incorrect, do not execute the command stream and wait for the next calculation time step to start to continue reading the program to make judgments;

[0052] 3. For the inlet valve surface: (1) define variable name, initialize the area-weighted average pressure of the inlet valve surface to 0 MPa, and assign the initialized pressure value to the variable; (2) define function name, which is convenient for identifying, reading and executing functions in the algorithm during CFD calculation; (3) define the current value of the area-weighted average pressure curve of the inlet valve surface at the start of each time step, and assign the value to the variable name in (1); (4) define the judgment condition: whether the current calculation time is greater than the preset time 0.147s; (5) define the judgment condition: whether the current value of the area-weighted average pressure curve of the inlet valve surface is less than 0 MPa; (6) if (4) and (5) are both correct, execute the command stream to convert the boundary condition of the inlet valve surface to a pressure inlet, and the inlet pressure of the inlet valve surface is 0 MPa; if one of (4) and (5) is incorrect, do not execute the command stream and wait for the next calculation time step to start to continue reading the program to make judgments;

[0053] The program language of the valve constant pressure opening and closing algorithm in this example is as follows:

[0054] (rp-var-define 'pressure_monitor 0.0'real#f) Note: (1) define variable name 1: pressure_monitor (rp-var-define 'pressure_moniter 0.0'real#f) Note: (1) define variable name 2: pressure_moniter (rp-var-define 'pressure_monitinr 0.0'real#f) Note: (1) define variable name 3: pressure_monitinr (define (change_boundary) Note: (2) (change_boundary) is the name of function 1, which is convenient for identifying, reading and executing functions during CFD calculation (let ((pressure_monitor (pick-a-real " / / report / surface-integrals / area-weighted-avg outlet () pressure no" 1))) Note: (3) extract the current value of the area-weighted average pressure curve of the valve surface, and assign the value to the variable name

[0055] (if (<= (rp getvar 'flow-time) 0.14) Note: (4) judgment condition (if (>= pressure_monitor 500000) Note: (5) judgment condition (begin

[0056] (ti-menu-load-string "define / boundary-conditions / zone-type wall_change pressure-outlet") Note: (6) command stream to convert wall to pressure outlet

[0057] (ti-menu-load-string "define / boundary-conditions / pressure-outlet wall_change pressure,, 500000") Note: (6) command stream to set outlet pressure to 500,000 Pa )))))

[0059] (define (change_boundary1) Note: (change_boundary1) is the name of function 2 (let ((pressure_moniter (pick-a-real " / / report / surface-integrals / area-weighted-avg wall_change pressure no" 1))) Note: (3) extract current value of area weighted average pressure curve for the wall and assign it to the variable name in

[0060] (if (<= (rpgetvar 'flow-time) 0.06) Note: (4) conditional (if (>= pressure_moniter 700000) Note: (5) conditional (begin

[0061] (ti-menu-load-string "define / boundary-conditions / zone-type wall_change pressure-outlet") Note: (6) command stream to convert wall to pressure outlet (ti-menu-load-string "define / boundary-conditions / pressure-outlet wall_change pressure,, 700000")))) Note: (6) command stream to set outlet pressure to 700,000 Pa

[0062] (define (change_boundary2) ; comment: (change_boundary2) is the name of function 3 (let ((pressure_monitor (pick-a-real " / / report / surface-integrals / area-weighted-avg inlet() pressure no" 1))) ; comment: (3) extracts the current value of the area-weighted average pressure curve of the valve face and assigns it to the variable name

[0063] (if (>= (rpgetvar 'flow-time) 0.147) ; comment: (4) test condition (if (<= pressure_monitor 0) ; comment: (5) test condition (begin

[0064] (ti-menu-load-string "define / boundary-conditions / zone-type inlet pressure-inlet") ; comment: (6) command stream to convert the wall to a pressure inlet (ti-menu-load-string "define / boundary-conditions / pressure-inlet inlet pressure,,0")

[0065] ))))) ; comment: (6) command stream to set the outlet pressure to 0 Pa

[0066] In summary, the simulation method of the multi-valve constant pressure opening and closing of the above-mentioned embodiment gives a simple and high-precision method for the multi-valve opening and closing of the hydraulic system, the multi-valve opening and closing in the cylinder compression, and other complex working conditions, which needs to process the multi-valve constant pressure opening and closing. It can provide a general solution method for the computational fluid dynamics of the multi-valve constant pressure opening and closing. Compared with the traditional method of solving the valve constant pressure opening and closing, the implementation is simple, and the valve can be opened more timely and accurately.

[0067] Although the embodiments of the present application have been shown and described above, it should be understood by those skilled in the art that the above-mentioned embodiments are exemplary and cannot be understood as limiting the present application, and those skilled in the art can make changes, modifications, replacements and variations to the above-mentioned embodiments within the scope of the present application.

Claims

1. A multi-valve pressure maintaining opening and closing simulation method, characterized by, The method comprises the following steps: Step S1: simplifying the multiple constant pressure valves into a plane and naming them respectively in the CFD simulation flow simulation calculation, for valve constant pressure opening and closing algorithm identification, carrying out grid division on the valve plane and the fluid domain where the valve plane is located, to obtain the grid division parameters of the calculation domain; Step S2: setting the grid type as FLUENT type, setting the boundary condition of the valve plane as a wall boundary condition according to the actual working state of the valve at the initial calculation time step; Step S3: setting an area weighted average pressure curve to monitor the area weighted average pressure of each valve plane; Step S4: In the valve constant pressure opening and closing algorithm, the following is set: at the beginning of each time step of the CFD simulation flow simulation calculation, the area-weighted average pressure value of each valve surface is read; the area-weighted average pressure when each valve surface is opened is set as P maxi , and the judgment conditions are set, including the size relationship between the area-weighted average pressure of each valve surface and P maxi , and the size relationship between the current calculation time and the preset time; at the beginning of each calculation time step, the area-weighted average pressure value of each valve surface is compared with P maxi , and the current calculation time is compared with the preset time; when the size relationship between the area-weighted average pressure of each valve surface and P maxi , and the relationship between the current calculation time and the preset time meet the judgment conditions, each valve surface is converted from the wall boundary condition to the pressure outlet / inlet boundary condition; and the outlet / inlet pressure is set as P maxi ; if not, no boundary condition conversion is performed, and the condition judgment is continued at the beginning of the next calculation time step; wherein i represents the i-th valve surface; Step S5: setting a command to execute the valve constant pressure opening and closing algorithm at the beginning of each calculation time step; Step S6: setting the physical problem solving parameters; Step S7: performing numerical solution; Step S8: repeating steps S4-S5 at the beginning of each time step until the simulation stops.

2. The method according to claim 1, wherein, In the step S1, the parameters include the grid precision and density of the valve plane and the fluid domain where the valve plane is located, and each valve plane is named.

3. The method of claim 1, wherein the method further comprises: In the step S3, the area weighted average pressure curve is set to monitor the area weighted average pressure of each valve plane.

4. The method of claim 1, wherein, In the step S5, the valve constant pressure opening and closing algorithm is used to control the valve constant pressure opening and closing, and the specific control logic of the valve constant pressure opening and closing algorithm is as follows: Step S51: defining a variable name, initializing the area weighted average pressure of each valve plane to 0, and assigning the initialized pressure value to the variable; Step S52: defining a function name; Step S53: defining the current value of the area weighted average pressure curve of each valve plane at the beginning of each time step, and assigning the value to the variable name in step S51; Step S54: defining a judgment condition to judge whether the relationship between the current calculation time and the preset time meets the judgment condition; Step S55: defining a judgment condition, judging whether the relationship between the current value of the area-weighted average pressure curve of each valve face extracted and P maxi satisfies the judgment condition; Step S56: execute the command flow, when the size relationship between the area-weighted average pressure of each valve surface and P maxi and the relationship between the current calculation time and the preset time meets the judgment condition, convert the boundary condition of each valve surface into the pressure outlet / inlet boundary condition; Step S57: execute the command stream to set the outlet pressure of the corresponding valve face to P maxi ; Step S58: if steps S54 and S55 are both correct, steps S56 and S57 are executed; if one of S54 and S55 is incorrect, the command flow is not executed and the program is continued to be read at the beginning of the next calculation time step until the condition is met.

5. The method of claim 4, wherein, In the step S51, the defined variable name means the area weighted average pressure value of each valve plane, which is used to store the area weighted average pressure value of each valve plane at the beginning of each calculation time step.

6. The method of claim 4, wherein, In the step S52, the function content corresponding to the defined function name is steps S53-S58.

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