Fluid internal particle motion simulation method based on CFD-DEM coupling

Abstract

The invention discloses a fluid internal particle motion simulation method based on CFD-DEM coupling. Comprising the following steps: constructing a three-dimensional model, and exporting the three-dimensional model as a. Step file; grid division is carried out on the solid and the grid between the solid and the drainage basin, and a. Msh file is generated; a dynamic grid motion control file is generated, and a. Model file is reserved; the. Msh file is imported into DEM simulation software, and a. Case file with the initial time being 0 is exported; and performing fluid mechanics and discrete phase calculation on the. Model file in CFD simulation software, and exporting a particle motion track and a variable change curve. According to the method, control over the moving part is more accurate, the movement trend of particles in the three-dimensional model can be accurately simulated, and particle movement simulation animation and variable data of more real points are output; the obtained simulation coupling result not only can judge the movement condition of the abrasive particles, but also can improve the structure according to a fluid mechanics (CFD) calculation result, optimize work and design parameters, reduce power loss and improve transmission performance.

Description

Technical Field

[0001] The present invention relates to the field of computer simulation of fluid lubrication, in particular to particle motion simulation of bidirectional coupling between fluid and discrete phase elements, specifically a method for simulating particle motion inside a fluid based on CFD-DEM coupling. Background Art

[0002] During the running-in process and normal service of variable-angle bevel gears, manufacturing and installation errors, tooth meshing, and bearing rotation generate solid abrasive particles of various shapes. If these particles enter the gear meshing area, they are more likely to cause wear on the tooth surfaces, reducing gear life and transmission accuracy. Furthermore, the particle movement process cannot be observed manually; the size, quantity, and shape of the abrasive particles generated within the gearbox can only be detected through oil flow, which increases labor costs and manufacturing time.

[0003] At present, domestic research on the movement of particles inside gearboxes is mostly focused on two-dimensional planes, and cannot fully simulate the movement trajectory and laws of abrasive particles. At the same time, for the special structure of helicopter intermediate reducers with large angles and high speeds, the traditional use of a single software to study the system's lubrication characteristics and internal particle movement cannot meet the simulation requirements, and it is difficult to simulate real working conditions.

[0004] The application of multi-software coupling method for simulation can give full play to the advantages of each software and solve the complex problems of coupling difficulties and inaccurate results in existing simulation schemes. In many fields, there are already schemes for simulating the motion laws of objects through multiple software. For example, the document with the announcement number "CN111324994B" discloses "Simulation calculation method for simulating the surface distribution of hard phase particles based on FLUENT", which simulates the particle motion by using the discrete phase function in Fluent alone. However, the problem with this scheme is that it does not fully consider the interaction between the discrete phase and the fluid, nor does it consider the influence of factors such as particle shape on its motion law. The simulation is inaccurate, so it cannot be used for the simulation of particle motion inside the fluid during the running-in process of variable angle bevel gears. The simulation results cannot truly reflect the particle motion inside the fluid, and it is difficult to provide effective theoretical support. In addition, Fluent's calculation method for non-spherical particles is difficult. At the same time, it is necessary to calculate the volume of particles generated per unit area, so the operation is complicated. Summary of the Invention

[0005] The present invention provides a method for simulating particle motion inside a fluid based on CFD-DEM coupling, so as to solve the technical problems existing in the prior art such as low calculation efficiency, inaccurate simulation and complex operation.

[0006] In order to achieve the above object, the technical solution of the present invention is: a method for simulating particle motion inside a fluid based on CFD-DEM coupling, comprising the following steps:

[0007] Step 1: Build a 3D model and export it as a .step file.

[0008] Step 2: Mesh the solid and the grid between the solid and the flow field to generate the .msh file;

[0009] Step 3: Generate a dynamic mesh motion control file: For non-orthogonal gear reducers with an angle between the rotating shaft and the coordinate axis, write a UDF file in the .x_t format. Use the UDF file to control the motion of the model with such a large angle structure, and retain the .model file.

[0010] Step 4: Generate particle information: Import the .msh file generated in step 2 into the DEM simulation software, build a particle factory, and export a .case file with an initial time of 0;

[0011] Step 5. Perform simulation: Perform multi-physics field coupling on the CFD model and DEM model through the coupling interface file. Perform fluid mechanics and discrete phase calculations on the .model file in step 3 in the CFD simulation software. If the calculation does not converge, redefine the boundary conditions or solve the time step until the calculation converges. Then, derive the particle motion trajectory and variable change curve.

[0012] Furthermore, in the above step 1, the model parts constructed are entities assembled according to assembly relationships, and the gaps between moving parts are adjusted during modeling.

[0013] Furthermore, in the above step 2, in the meshing, the flow domain and the solid component are divided into two regions, and only the flow domain is meshed, while the mesh in contact with the solid component uses a dynamic mesh model.

[0014] Furthermore, in the above step 3, the UDF file is written in C++ language.

[0015] Furthermore, in the above step 4, the .case file with the initial time of 0 includes the particle geometry, material, and quantity.

[0016] Compared with the prior art, the advantages of the present invention are:

[0017] 1. The model parts constructed in the present invention are all entities and are assembled according to the actual assembly relationship, which facilitates the subsequent Boolean operation of the entity and the watershed part, easily distinguishes the watershed entity model, and facilitates subsequent mesh division; when exporting the three-dimensional model, the format is set to the .step format that can retain all information such as the product's geometry, properties, and materials. The constructed three-dimensional model is exported as a .step file that can ensure the accuracy and consistency of the data between different software, so that it can be used for the next step of mesh division to generate a .msh file.

[0018] 2. In the meshing method described in the present invention, the watershed and solid components are divided into two regions. Only the watershed is meshed, while the mesh in contact with the solid component uses a dynamic mesh model. This allows the position or topology of the mesh nodes to be dynamically adjusted, directly simulating a moving object. The generated .msh file is imported into the DEM simulation software to generate particle information, and the .case file is exported as the initial state for discrete phase calculation. This effectively reduces the amount of calculation and compensates for the disadvantage that CFD simulation software cannot calculate the motion of non-spherical particles.

[0019] 3. In step three, the UDF file is written in C++. This code is highly portable and allows for more precise control of moving parts that are not parallel or aligned with coordinate axes. This breaks through the limitations of traditional motion control and allows for arbitrary rotation and translation of moving parts, providing even more precise control. Using a UDF file to control the moving mesh provides a convenient way to maintain the .model file without modifying other environment variables for subsequent changes to the working conditions.

[0020] 4. The interface file of the present invention includes a UDF interface file. When performing multi-physics field coupling, the particle trajectory obtained by the CFD-DEM software coupling simulation can accurately simulate the movement trend of particles within the three-dimensional model. It can more accurately analyze the effect of the flow field on the particles, making up for the deficiency that workers cannot directly observe the movement of particles. It outputs more realistic particle motion simulation animation and variable data. The obtained simulation coupling results can not only judge the movement of abrasive particles, but also improve the structure based on the fluid dynamics (CFD) calculation results, optimize working and design parameters, reduce power loss and improve transmission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a flow chart of a method for simulating particle motion inside a fluid based on CFD-DEM coupling;

[0022] Figure 2 It is a three-dimensional model diagram;

[0023] Figure 3 is the grid cross-section;

[0024] Figure 4 To generate particle information graph;

[0025] Figure 5 This is the DEM simulation particle trajectory diagram. DETAILED DESCRIPTION

[0026] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only used to explain the present invention and are not used to limit the scope of the present invention.

[0027] The present invention provides a method for simulating particle motion inside a fluid based on CFD-DEM coupling, comprising the following steps:

[0028] Step 1: Construction and export of 3D model:

[0029] When constructing a 3D model, all components are created as solids to facilitate subsequent meshing, suppress moving parts, and delineate the fluid region. During modeling, the gaps between moving parts should be enlarged. This can be achieved by using methods such as translation, ensuring that the gap size is at least 3 to 5 times the mesh size. This is to prevent excessive deformation of the dynamic mesh during simulation. The 3D model is then exported as a .step file.

[0030] The 3D model is exported in .step format which can retain all the information of the product such as geometry, properties, materials, etc. Figure 2 As shown, the .step file ensures the accuracy and consistency of data between different software, ensures compatibility, and is used to generate the .msh file for grid partitioning.

[0031] Step 2: Grid division: Figure 3 As shown, meshing is performed on the solid and between the solid and flow domains. This meshing requires dividing the flow domain and solid components into two regions. Only the flow domain is meshed, while the mesh near the movement gap is refined. An .msh file is generated for the CFD-DEM simulation model.

[0032] The specific steps of this embodiment are as follows: based on the fact that the interior of the modeled parts are all solid, the moving parts are suppressed after Boolean operations to prevent component redundancy, the flow domain and solid components are divided into two areas, only the flow domain part is meshed, the number of gap meshes is increased, the meshes intersecting with the moving parts are named as walls, and the model is exported as an .msh file.

[0033] Step 3: Dynamic mesh motion control:

[0034] For moving parts with an angle between the rotating shaft and the coordinate axis, write a UDF file in the .x_t file format to control the motion of the model of this large-angle structure, and retain the CFD simulation model .model file.

[0035] Use C++ language to write UDF files.

[0036] Step 4: Figure 4 As shown, generate particle information: import the generated .msh file into the DEM simulation software, use the DEM simulation software to generate particle information, control the particle geometry, material, quantity and other parameters to build a particle factory, and export the .case file with the initial time being 0.

[0037] The specific operations of this embodiment are: importing the .msh file into the DEM simulation software, generating a discrete phase of solid particles with different materials, shapes and other parameters based on requirements, setting collision parameters and virtual planes, and then exporting a .case file with an initial time of 0 containing particle information as the initial state of the discrete phase in the CFD simulation model.

[0038] Step 5: Perform simulation:

[0039] Through the coupling interface file CFD model and DEM model to carry out multi-physics field coupling, customize the function in CFD simulation software, use the built-in coupling compiler to load, and keep the DEM simulation model consistent with the CFD simulation model working conditions, and check whether the coupling interface in the DEM simulation software is in working state. Finally, set the step size and number of steps to calculate the .model file in the CFD simulation software. If the calculation does not converge, redefine the boundary conditions or solve the time step until the calculation converges, and output the particle motion simulation animation, as shown in the attached figure. Figure 5 As shown, the particle motion trajectory is derived.

[0040] The following CFD-DEM coupled method for simulating particle motion within a fluid is specifically targeted at aviation intermediate reducers. Its implementation steps include:

[0041] Step 1: Construction and export of 3D model: Figure 1 The figure shows a flow chart of a method for simulating particle motion inside a fluid based on CFD-DEM coupling. First, an aviation intermediate reducer model is established. The model parts are the established box model and assembled entities. At the same time, the gaps between moving parts need to be adjusted during modeling. Figure 2 As shown in the figure, the generated .step file retains all the information of the product, such as the geometric shape, properties, and materials, and is used for subsequent meshing of the model.

[0042] Step 2: Perform Boolean operations on the 3D model in step 1) to separate the fluid area and the solid area. The rigid body is suppressed or deleted after the Boolean operation. In order to prevent the mesh from being distorted during movement, a translation method is used to translate along the axis of the moving part and appropriately expand the gap between the moving parts. Figure 3As shown, in addition, in order to ensure calculation accuracy, it is necessary to encrypt the number of grids through which the fluid can flow, name the grid geometry walls, and facilitate subsequent UDF file control, and retain the .msh file.

[0043] Step 3: Use UDF file for dynamic mesh motion control and compile it using the compiler provided by the CFD simulation software.

[0044] UDF is mainly controlled by the DIFINE_CG_MOTION(name,dt,vel,omega,time,dtime) command, where name is the name of the dynamic mesh wall to be controlled in the .msh file, omega[0]=-v*sin(alph) means movement at the angle alph in the negative direction of the x-axis with a velocity v, and 1 and 2 can also be used to represent the y and z axes. This method is more accurate for controlling moving parts.

[0045] Step 4: Import the .msh file with the node coordinates into the DEM simulation software, as shown in the attached Figure 4 As shown in the figure, the motion properties and collision parameters of the discrete phase are defined, its virtual plane is generated, and the DEM calculation time step and total number of steps are defined. It is important to note that the DEM time step t2 must be 0.1 to 1 times the CFD simulation software time step t1. Finally, coupling is performed.

[0046] Step 5: Figure 5 As shown, the coupled CFD-DEM standardized simulation model is calculated. If the calculation does not converge, the boundary conditions are redefined or the time step is solved until the calculation converges, and the output data and simulation animation are obtained.

[0047] The scope of protection of the present invention is not limited to the above-mentioned embodiments. All technical solutions based on this concept fall within the scope of protection of the present invention. It should be noted that for those skilled in the art, several improvements and variations without departing from the principles of the present invention should also be considered as the scope of protection of the present invention.

Claims

1. A method for simulating particle motion inside a fluid based on CFD-DEM coupling, characterized by: The following steps are involved: Step 1: Build a 3D model and export it as a .step file. Step 2: Mesh the solid and the grid between the solid and the flow field to generate the .msh file; Step 3: Generate a dynamic mesh motion control file: For non-orthogonal gear reducers with an angle between the rotating shaft and the coordinate axis, write a UDF file in the .x_t format. Use the UDF file to control the motion of the model with such a large angle structure, and retain the .model file. Step 4: Generate particle information: Import the .msh file generated in step 2 into the DEM simulation software, build a particle factory, and export a .case file with an initial time of 0; Step 5. Perform simulation: Perform multi-physics field coupling on the CFD model and DEM model through the coupling interface file. Perform fluid mechanics and discrete phase calculations on the .model file in step 3 in the CFD simulation software to derive the particle motion trajectory and variable change curve.

2. The method for simulating particle motion in a fluid based on CFD-DEM coupling according to claim 1, characterized in that: In the step 1, the model parts constructed are entities assembled according to assembly relationships, and the gaps between moving parts are adjusted during modeling.

3. The method for simulating particle motion in a fluid based on CFD-DEM coupling according to claim 2, characterized in that: In the step 2, in the meshing, the flow domain and the solid component are divided into two regions, and only the flow domain is meshed, while the mesh in contact with the solid component uses a dynamic mesh model.

4. The method for simulating particle motion in a fluid based on CFD-DEM coupling according to claim 3, characterized in that: In the step 3, the UDF file is written in C++ language.

5. The method for simulating particle motion in a fluid based on CFD-DEM coupling according to claim 4, characterized in that: In step 4, the .case file with an initial time of 0 includes the particle geometry, material, and quantity.

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