A Fluid Simulation Method for Rotating Machinery

Abstract

The present invention discloses a fluid simulation method for a rotary machine, and the steps include: 1) extracting a computational fluid domain from a three-dimensional model file of a rotary machine to be analyzed; 2) selecting a solution type; 3) using a grid generation module to process the three-dimensional model file to generate a CFD computational grid; 4) determining a fluid medium and all its flow parameters; 5) initially configuring a solver and initializing the solver according to the initial configuration information; 6) according to the selected solution type, using the initialized solver to simulate the flow field value of the selected fluid medium on the grid under the condition of setting flow parameters, and obtaining the target distribution of the fluid. The present invention greatly accelerates the convergence speed of CFD fluid simulation calculation.

Description

Technical Field

[0001] The invention belongs to the technical field of computer software, and in particular relates to a fluid simulation method for a rotating machinery. Background Art

[0002] Computational Fluid Dynamics (CFD) is an analysis of systems involving fluid flow, heat conduction and other related physical phenomena through computer numerical calculations and image display. Numerical simulation has unique advantages over experimental research, such as low cost, short cycle, complete data acquisition, and simulation of various measured data states during actual motion. It plays an important guiding role in commercial or laboratory applications such as design and transformation. Therefore, CFD technology has been increasingly used and promoted the development of commercial CFD software.

[0003] Rotating machinery is widely used in aviation, electricity, machinery, chemical industry and other fields. As the core component of rotating machinery, the impeller works under high speed and heavy load for a long time. Its performance directly determines the performance and working efficiency of the whole machine, so it is necessary to use computational fluid dynamics (CFD) simulation method to simulate the actual operation of the impeller. Summary of the invention

[0004] In view of the problems existing in the prior art, an object of the present invention is to provide a fluid simulation method for a rotating machinery.

[0005] The technical solution of the present invention is:

[0006] A fluid simulation method for a rotating machine, comprising the steps of:

[0007] 1) Extract the computational fluid domain from the three-dimensional model file of the rotating machinery to be analyzed;

[0008] 2) Select the solution type;

[0009] 3) Using a grid generation module to process the three-dimensional model file to generate a CFD calculation grid;

[0010] 4) Determine the fluid working medium and all its flow parameters;

[0011] 5) Initialize the solver and initialize the solver according to the initial configuration information;

[0012] 6) According to the selected solution type, the initialized solver is used to simulate the flow field value of the selected fluid on the grid under the set flow parameters to obtain the target distribution of the fluid.

[0013] Furthermore, the initial configuration of the solver includes boundary condition setting, initialization setting, option setting, solver option setting, convergence condition setting, multi-block setting, and CFD startup setting;

[0014] The boundary condition setting is used to set the calculation type and specific condition parameters of the inlet and outlet of the calculation fluid domain according to the actual working conditions of the impeller; the actual working condition setting includes the radial distribution value of the inlet total pressure, the radial distribution value of the inlet total temperature, the radial distribution value of the inlet pre-swirl angle, the radial distribution value of the outlet static pressure, and the mass flow rate; and only two of the inlet total pressure, outlet static pressure, and mass flow rate can be arbitrarily selected as boundary conditions;

[0015] The initialization setting is used to estimate the initial value of the iterative calculation in the entire CFD numerical simulation process according to the set boundary conditions;

[0016] The option setting is used to set the inlet boundary condition model and the outlet boundary condition model of the computational fluid domain;

[0017] The solver option settings are used to set the adopted turbulence model, wall treatment method, time advancement format, and decomposition matrix free parameters;

[0018] The convergence condition setting is used to set the calculation termination condition of the solver;

[0019] The multi-block settings are used to select compressibility or incompressibility, spatial discrete format, Merkle preprocessing, global residual smoothing, solution accuracy, and storage of intermediate results;

[0020] The CFD startup settings are used to set operating parameters.

[0021] Furthermore, the method for initializing the solver according to the initial configuration information is: first initialize the CPU parallel environment and divide the CPU parallel into blocks; then generate and initialize the grid, and set the initial boundary conditions according to the boundary conditions; then set the inlet boundary of the turbulent flow, and initialize the initial value or read the existing solution as the initial value; then calculate the mass flow at the boundary, and use the boundary conditions and the selected boundary condition model to update the boundary values ​​in the grid; then initialize the frozen rotor method or the circumferential averaging method for data interaction at the interface between the dynamic and static grids; then set the inflow value to the virtual grid.

[0022] Further, in step 6), the flow field value is simulated through iterative loop steps 61) to 65): 61) updating the interface of the grid; 62) performing inner iterative loop correction on the initial value through steps 621) to 628) so that it continuously approaches the convergence result; 63) updating the physical time of the current time step; 64) processing and displaying the convergence curve in real time; 65) if the maximum number of iterations is reached or the iteration converges or an immediate end instruction is received, the iterative loop ends; wherein the inner iterative loop includes the following steps: 621) starting the inner iteration, checking whether the user has issued an immediate end command, if the end command is issued, stopping the iteration, otherwise proceeding to step 622); 622) checking whether the currently calculated enthalpy and entropy values ​​are within the value range of the quick table , if the check fails, the quick table is updated, if it passes, step 623) is performed; 623) the grid interface data is updated and exchanged; 624) the flow field values ​​on each grid are calculated to obtain the corrected flow field values, and the residual is calculated using the flow field values ​​before and after the correction; 625) the residual is smoothed, and then the turbulence and Y+ are calculated according to the selected turbulence model; wherein Y+ = (Vt*Y) / mu, Y is the thickness of the first layer of grid on the wall, Vt is the shear velocity, and mu is the kinematic viscosity; 626) the Courant number is adjusted according to the result obtained in step 625); 627) the pressure is adjusted according to the adjusted Courant number to satisfy the normalization condition, and the initial value is corrected according to the adjusted pressure; 628) the inner iteration is terminated if the maximum number of iterations or the iteration convergence condition is reached.

[0023] Furthermore, by adjusting the speed operating point and boundary type operating point, you can choose to run multiple calculation conditions at one time; CPU parallel settings can also be performed during CFD startup settings. There are three CPU parallel modes: pure MPI mode, pure OpenMP mode, and MPI and OpenMP mixed mode.

[0024] Furthermore, the initial configuration of the solver also includes the setting of multiple grid methods. When multiple grid methods are selected, interpolation and reconstruction are performed between coarse and fine grids at different levels during CFD calculations, and cyclic iterations are performed so that the calculation results approach the convergence conditions more quickly, reducing the number of internal iterations and time iterations, thereby accelerating CFD calculations.

[0025] Furthermore, the initial configuration of the solver also includes multi-operating condition settings, which is used to run multiple calculation conditions at one time by adjusting the speed operating point and the boundary type operating point; the solution types include cross-blade mode, flow mode and full three-dimensional mode; when the flow mode is selected, when the solver configuration is initialized, it is necessary to configure the flow-related parameters and calculate the blade angle in the flow area.

[0026] Furthermore, the target distribution of the fluid is static pressure distribution, velocity distribution, temperature distribution or density distribution of the fluid.

[0027] A server, characterized in that it comprises a memory and a processor, wherein the memory stores a computer program, the computer program is configured to be executed by the processor, and the computer program comprises instructions for executing each step in the above method.

[0028] A computer-readable storage medium stores a computer program, wherein the computer program implements the steps of the above method when executed by a processor.

[0029] The advantages of the present invention are as follows:

[0030] The present invention provides a fluid simulation method for a rotating machinery, which adopts a cylindrical coordinate system internally, and the processing of the interaction surface between the rotor and the stator supports the frozen rotor method and the circumferential average method; the loss model function is integrated in the through-flow solver; implicit Gauss-Seidel iteration or explicit dual time step method (inner and outer double-layer iteration), multi-grid method, residual smoothing processing and other methods are adopted, which greatly accelerates the convergence speed of CFD fluid simulation calculation. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic diagram of the overall process of the present invention.

[0032] Figure 2 It is a schematic diagram of the solver configuration initialization process in the present invention.

[0033] Figure 3 It is a schematic diagram of CFD solution calculation in the present invention.

[0034] Figure 4 It is a schematic diagram of the inner iterative loop in the present invention.

[0035] Figure 5 is the static pressure distribution of the fluid. DETAILED DESCRIPTION

[0036] The present invention is further described in detail below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention but not to limit the scope of the present invention.

[0037] The present invention provides a fluid simulation method for a rotating machine. Figure 1 As shown, it includes the following steps:

[0038] S1. Obtain the three-dimensional model file of the rotating machinery to be analyzed and extract the computational fluid domain;

[0039] S2. Select the solution type, cross-blade mode, through-flow mode or full 3D mode; cross-blade mode and through-flow mode are used for the preliminary design of rotating machinery, while full 3D can be used for any required stage;

[0040] S3. Use the mesh generation module to process the 3D model file and generate a CFD calculation mesh;

[0041] S4. Determine the fluid working medium and all its flow parameters;

[0042] S5. Initially configure the solver; the solver is a CFD solver;

[0043] S6. Initializing the solver configuration according to the initial configuration of the solver;

[0044] S7.CFD solution calculation: according to the selected solution type, the solver is used to simulate the flow field value of the selected fluid working medium on the grid under the set flow parameters to obtain the target distribution of the fluid, such as the static pressure distribution, velocity distribution, temperature distribution or density distribution of the fluid;

[0045] S8. Post-process the solution results and draw data charts;

[0046] S9. Save the solution calculation results or export the results.

[0047] The initial configuration of the solver includes boundary condition settings, initialization settings, option settings, solver option settings, convergence condition settings, multi-block settings, CFD startup settings, etc.

[0048] Boundary condition setting: used to set the calculation type and specific condition parameters of the inlet and outlet of the computational fluid domain according to the actual working conditions of the impeller. The actual working conditions that the user needs to set include: the radial distribution value of the inlet total pressure, the radial distribution value of the inlet total temperature, the radial distribution value of the inlet pre-swirl angle, the radial distribution value of the outlet static pressure, and the mass flow rate. Among the three inlet total pressure, outlet static pressure, and mass flow rate, the user can only arbitrarily select and specify two of them as boundary conditions.

[0049] Initialization settings: Estimate the initial values ​​of the iterative calculations during the entire CFD numerical simulation process according to the set boundary conditions (i.e. the initial values ​​of the static pressure, density, and velocity at each grid point; the initial values ​​of the inlet and outlet positions are directly specified by the boundary conditions). The static pressure and density values ​​change linearly from the inlet to the outlet, the velocity direction is completely along the geometric flow direction, and the relative velocity magnitude reduces friction in the stationary blade section and increases work in the moving blade section.

[0050] Option settings: You can further set the boundary condition model for the inlet and outlet of the computational fluid domain in detail, select the data transfer method for the dynamic and static interaction surface, and set whether the inlet, outlet, and dynamic and static interaction surface has reflection.

[0051] Solver option settings: used to select the turbulence model, wall treatment method, time advancement format, and decomposition matrix free parameters used in the analysis and calculation.

[0052] Convergence condition setting: Set the critical value of the root mean square residual or mass flow residual. When the residual value during the iteration process reaches the set value, the iteration ends.

[0053] Multi-block settings: used to select compressible or incompressible, spatial discretization format, Merkle preprocessing, global residual smoothing, solution accuracy, and saving of intermediate results. Among them, the spatial discretization formats that can be selected are: central difference, third-order upwind (AUSM) format, and first-order upwind (AUSM) format.

[0054] CFD startup settings: used to set operating parameters: steady or unsteady, and whether to draw residual curves during solution.

[0055] like Figure 2 As shown, the solver configuration initialization includes the following steps:

[0056] S6.1, initialize the CPU parallel environment;

[0057] S6.2.CPU parallel block;

[0058] S6.3, generate and initialize the grid;

[0059] S6.4, initializing boundary conditions;

[0060] S6.5, set the inlet boundary of turbulence;

[0061] S6.6. Initialize the initial value or read the existing solution (i.e., if the calculation has been performed before, the calculation can be continued based on the previous calculation result) as the initial value;

[0062] S6.7. Calculate the mass flow rate at the boundary;

[0063] S6.8, updating boundary values ​​in the grid using the boundary conditions and the selected boundary condition model;

[0064] S6.9, initialize the frozen rotor method or circumferential averaging method for data interaction at the interface between the dynamic and static grids;

[0065] S6.10, set the inflow value to the virtual grid. The virtual grid is a method of processing boundary conditions by extending the "CFD calculation grid" to the outside of the boundary by two layers of grids.

[0066] like Figure 3 As shown, the CFD solution calculation includes the following steps:

[0067] S7.1 starts a time iteration loop;

[0068] S7.2 Update the mesh interface;

[0069] S7.3 performs an inner iterative loop correction on the initial value so that it continuously approaches the convergence result;

[0070] S7.4 updates the physical time of the current time step;

[0071] S7.5 processes and displays the convergence curve (in several forms) in real time;

[0072] S7.6 If the maximum number of iterations is reached or the iterations converge or an immediate termination instruction is received, the time iteration loop ends;

[0073] S7.7 ends the CFD solution calculation.

[0074] like Figure 4 As shown, the inner iteration loop contains the following steps:

[0075] S7.3.1 Start inner iteration;

[0076] S7.3.2 Check whether the user has issued an immediate termination command;

[0077] S7.3.3 checks whether the currently calculated enthalpy and entropy values ​​are within the value range of the quick table. If they pass, proceed to S7.3.4; if they fail, update the quick table; the quick table uses enthalpy and entropy to calculate pressure, temperature, density, etc., including the minimum value, maximum value, number of sampling points of enthalpy, the minimum value, maximum value, number of sampling points of entropy, and the pressure, temperature, density, etc. of all sampling positions. Updating the quick table includes: updating the value range of the table, and using the fluid working medium library to calculate the pressure, temperature, density, etc. of the new sampling position.

[0078] S7.3.4 Update and exchange grid interface data using the method set forth in S6.9;

[0079] S7.3.5 iteratively calculate the flow field value to obtain a corrected flow field value, and calculate the residual using the flow field values ​​before and after correction;

[0080] S7.3.6 Residual smoothing;

[0081] S7.3.7 Calculate turbulence and Y+ based on the selected turbulence model; where Y+ is calculated by the formula: Y+ = (Vt*Y) / mu, where Y is the thickness of the first layer of wall mesh, Vt is the shear velocity, and mu is the kinematic viscosity;

[0082] S7.3.8 Use the CFL adaptive update algorithm to automatically adjust the CFL (Courant number) value;

[0083] S7.3.9 adjust the pressure according to the adjusted Courant number so that it satisfies the normalization condition and save the output data;

[0084] S7.3.10 If the maximum number of iterations is reached or the iteration converges (residual or mass flow), or an instruction to end immediately is received, the inner iteration is terminated.

[0085] Furthermore, you can also select multiple grid methods when initially configuring the solver. When multiple grid methods are selected, interpolation and reconstruction are performed between coarse and fine grids at different levels during CFD calculations, and cyclic iterations are performed to make the calculation results approach the convergence conditions faster, reduce the number of internal iterations and time iterations, and thus accelerate CFD calculations. The optional cyclic strategies include V-type cycle, W-type cycle, and FMV type.

[0086] Furthermore, multiple operating conditions can be set up during the initial configuration of the solver: multiple calculation conditions can be run at one time by adjusting the speed operating point and boundary type operating point. Different boundary conditions can be configured according to different operating conditions to calculate the mechanical properties under non-design operating points (different pressures, temperatures, flows, speeds, etc.).

[0087] Furthermore, you can also set CPU parallelism when starting CFD. There are three CPU parallel modes: pure MPI mode, pure OpenMP mode, and MPI and OpenMP mixed mode.

[0088] Furthermore, when S4 determines the fluid working medium and all its flow parameters, you can use a self-built fluid library or load an external fluid library to select the required working medium; the fluid medium library contains attribute parameters of a variety of real media, including but not limited to refrigerants, alkanes, fuels, common gases, water and other common fluid media.

[0089] Furthermore, when S2 selects the flow mode, the flow-related parameters need to be configured when the S6 solver configuration is initialized, and the blade angle in the flow area needs to be calculated.

[0090] Taking the static pressure distribution simulation of fluid as an example, the results are as follows: Figure 5 shown.

[0091] Although the specific embodiments of the present invention are disclosed for the purpose of illustration, the purpose is to help understand the content of the present invention and implement it accordingly, those skilled in the art will understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the best embodiment, and the scope of the present invention is subject to the scope defined in the claims.

Claims

1. A fluid simulation method for a rotating machine, comprising the steps of: 1) Extract the computational fluid domain from the 3D model file of the rotating machinery to be analyzed; 2) Select the solution type; 3) Using a mesh generation module to process the three-dimensional model file to generate a CFD calculation mesh; 4) Determine the fluid working medium and all its flow parameters; 5) Initially configuring the solver and initializing the solver according to the initial configuration information, wherein the initial configuration includes initialization settings for estimating initial values ​​of iterative calculations in the entire CFD numerical simulation process according to set boundary conditions; 6) According to the selected solution type, the initialized solver is used to simulate the flow field value of the selected fluid on the grid under the set flow parameters to obtain the target distribution of the fluid; Among them, in step 6), the flow field value is simulated through iterative loop steps 61)~65): 61) update the interface of the grid; 62) through steps 621)~628), the initial value is corrected in an inner iterative loop so that it continuously approaches the convergence result; 63) update the physical time of the current time step; 64) the convergence curve is processed and displayed in real time; 65) if the maximum number of iterations is reached or the iteration converges or an immediate end instruction is received, the iterative loop ends; wherein the inner iterative loop includes the following steps: 621) start the inner iteration, check whether the user If an immediate end command is issued, the iteration is stopped if an end command is issued, otherwise step 622 is performed); 622) Check whether the currently calculated enthalpy and entropy values ​​are within the value range of the quick table. If the check fails, the quick table is updated. If it passes, step 623 is performed); 623) Update and exchange grid interface data; 624) Calculate the flow field values ​​on each grid to obtain the corrected flow field values, and use the flow field values ​​before and after correction to calculate the residual; 625) Smooth the obtained residual, and then calculate the turbulence and Y+ according to the selected turbulence model; where Y+ = (Vt*Y) / mu, Y is the thickness of the first layer of wall grid, Vt is the shear velocity, and mu is the kinematic viscosity; 626) Adjust the Courant number according to the result obtained in step 625); 627) Adjust the pressure according to the adjusted Courant number so that it meets the normalization condition, and correct the initial value according to the adjusted pressure; 628) If the maximum number of iterations or the iteration convergence condition is reached, the inner iteration is terminated.

2. The method according to claim 1, characterized in that: Initial configuration of the solver includes boundary condition setting, option setting, solver option setting, convergence condition setting, multi-block setting, and CFD startup setting; The boundary condition setting is used to set the calculation type and specific condition parameters of the inlet and outlet of the calculation fluid domain according to the actual working conditions of the impeller; the actual working condition setting includes the radial distribution value of the inlet total pressure, the radial distribution value of the inlet total temperature, the radial distribution value of the inlet pre-swirl angle, the radial distribution value of the outlet static pressure, and the mass flow rate; and only two of the inlet total pressure, outlet static pressure, and mass flow rate can be arbitrarily selected as boundary conditions; The option setting is used to set the inlet boundary condition model and the outlet boundary condition model of the computational fluid domain; The solver option settings are used to set the adopted turbulence model, wall treatment method, time advancement format, and decomposition matrix free parameters; The convergence condition setting is used to set the calculation termination condition of the solver; The multi-block settings are used to select compressibility or incompressibility, spatial discrete format, Merkle preprocessing, global residual smoothing, solution accuracy, and storage of intermediate results; The CFD startup settings are used to set operating parameters.

3. The method according to claim 2, characterized in that The method for initializing the solver according to the initial configuration information is as follows: first, the CPU parallel environment is initialized and the CPU parallel is divided into blocks; then, a grid is generated and initialized, and an initial boundary condition is set according to the boundary condition; then, an inlet boundary of the turbulent flow is set, and the initial value is initialized or an existing solution is read as an initial value; then, the mass flow at the boundary is calculated, and the boundary value in the grid is updated using the boundary condition and the selected boundary condition model; Then the frozen rotor method or circumferential averaging method is initialized for data interaction at the interface between the dynamic and static grids; Then set the inflow value to the virtual grid.

4. The method according to claim 2, characterized in that: By adjusting the speed operating point and boundary type operating point, you can choose to run multiple calculation conditions at one time; CPU parallel settings are also performed during CFD startup settings. There are three CPU parallel modes: pure MPI mode, pure OpenMP mode, and MPI and OpenMP mixed mode.

5. The method according to claim 1, characterized in that The initial configuration of the solver also includes the setting of multiple grid methods. When multiple grid methods are selected, interpolation and reconstruction are performed between coarse and fine grids at different levels during CFD calculations, and cyclic iterations are performed so that the calculation results approach the convergence conditions more quickly, reducing the number of internal iterations and time iterations, thereby accelerating CFD calculations.

6. The method according to claim 1, characterized in that The initial configuration of the solver also includes multi-condition settings, which are used to run multiple calculation conditions at one time by adjusting the speed operating point and the boundary type operating point; the solution types include cross-blade mode, flow mode and full three-dimensional mode; when the flow mode is selected, when the solver configuration is initialized, the flow-related parameters need to be configured and the blade angle in the flow area needs to be calculated.

7. The method according to claim 1, characterized in that The target distribution of the fluid is the static pressure distribution, velocity distribution, temperature distribution or density distribution of the fluid.

8. A server, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, the computer program is configured to be executed by the processor, and the computer program comprises instructions for executing each step in the method according to any one of claims 1 to 7.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the steps of the method according to any one of claims 1 to 7 are implemented.

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