CN110009746B - Automatic generation method of hexahedral mesh with boundary layer for reactor fuel assembly - Google Patents

Abstract

The invention discloses a hexahedron grid automatic generation method with a boundary layer of a reactor fuel assembly, which comprises the following steps of 1, carrying out geometric pretreatment, and reserving thickness space of a grid of the boundary layer on the surface of a fuel rod; 2. the fluid area is divided into a complex geometric area and a simple geometric area with mixing wings; 3. finishing the meshing of the complex geometric area with the mixing wings obtained in the step 2 by utilizing a tetrahedral meshing method; 4. converting the tetrahedral mesh generated in the step 3 into a HEX8 hexahedral mesh; 5. converting the HEX8 hexahedral mesh generated in the step 4 into a HEX20 hexahedral mesh; 6. generating a simple geometric area grid; 7. generating boundary layer grids near the surface of the fuel rod; the invention solves the problems that computational fluid dynamics calculation software based on a spectral element method is difficult to establish a complex geometric model, a hexahedral mesh with complex geometry of a boundary layer cannot be generated, and the like.

Description

Automatic generation method of hexahedral mesh with boundary layer for reactor fuel assembly

technical field

The invention belongs to the technical field of geometric hexahedral grid generation methods, in particular to a method for automatically generating hexahedral grids with boundary layers of a reactor fuel assembly.

Background technique

At present, computational fluid dynamics analysis, as an important analysis method, occupies an important position in the field of engineering calculation and scientific research. At present, there are many types of CFD analysis tools, and the numerical discrete methods used are not the same. At present, the commonly used calculation methods are mostly those with good geometric applicability and low calculation accuracy: they are relatively tolerant in terms of mesh division, and can use tetrahedral mesh to complete spatial discretization and complete the simulation calculation of fluid domains enclosed by complex geometry. However, due to the inherent properties of the calculation method, the calculation accuracy is low, and the flow field details cannot be effectively identified, and it is difficult to improve the calculation accuracy through secondary development. Therefore, it is quite difficult to complete high-precision computing tasks.

The spectral element method is a spatially discrete method. When solving partial differential equations discretely, this method uses high-order polynomials as basis functions, which can greatly improve the accuracy of calculation results. When using a high-precision model for computational fluid flow and heat transfer analysis, the spectral element method can ensure the accuracy of the results as much as possible, accurately capture the flow details of the fluid, and provide reliable and effective data support for design analysis. . The CFD software based on the spectral element method, as the second generation of fluid dynamics analysis software, has high calculation accuracy and convergence speed, and can solve the problem of inaccurate analysis and prediction results of the current CFD software at the calculation method level.

However, it is difficult to popularize the spectral element method at present. One of the more prominent contradictions is that the spectral element method can only use hexahedral mesh to support calculation, and the current hexahedral mesh division process is generally done manually, that is, using geometric block-geometric association- Set Mesh Parameters - Process implementation for generating meshes. This process not only requires technicians to have quite high mesh division experience, but also has a large workload and low mesh generation efficiency. The most important thing is that this scheme cannot be used to complete geometric division for complex structures. Therefore, the invention of an automatic generation method of hexahedral mesh is of great significance for the application of spectral element method.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for automatically generating a hexahedral mesh with boundary layer of a reactor fuel assembly, which solves the problem that a suitable geometric model cannot be used when the thermal hydraulic analysis of the reactor fuel assembly is performed due to the complexity of the geometric model. The problem of generating a hexahedral mesh with a boundary layer by the method makes it possible to use the computational fluid dynamics software based on the spectral element method to complete the thermal-hydraulic analysis of the reactor fuel assembly.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for automatically generating a hexahedral mesh with a boundary layer of a reactor fuel assembly, comprising the following steps:

Step 1: Geometric preprocessing process: According to the actual reactor fuel assembly structure, use UG 10.0 3D modeling software to conduct 3D modeling of the fuel assembly. The structure diagram of the actual reactor fuel assembly completes the two-dimensional sketch drawing of the stirring wing structure; then use the stretching function of the UG 10.0 software to obtain a thick three-dimensional stirring wing model, and use the known bending function to bend the stirring wing model to complete. The establishment of the mixing wing model; then, the three-dimensional fuel rod model is established by the method of stretching; when establishing the three-dimensional fuel rod model, the thickness space of the boundary layer mesh on the surface of the fuel rod is reserved; then the Boolean logic function of the UG 10.0 software is used. Establishment of fluid areas outside the reactor fuel assemblies;

Step 2: Partitioning process of the fluid region: The computational fluid region of the reactor fuel assembly is divided into a simple geometric region and a complex geometric region with a stirring vane. Specifically, the normal line and the fuel rod axis are respectively established 1 cm upstream and 1 cm downstream of the stirring vane Consistent plane, with the above two planes as the interface, the computational fluid region is divided into three parts, which is convenient for subsequent processing;

Step 3: Tetrahedral meshing process of complex geometric regions with scrambled wings: Use ANSYS-ICEM software to complete the meshing task of complex geometric regions obtained in Step 2 using its well-known automatic tetrahedral meshing function : It is only necessary to set the macro size of the tetrahedral mesh, and use the well-known automatic calculation function of the ANSYS-ICEM software to complete the tetrahedral meshing process of complex geometric regions with mixing wings;

Step 4: The process of converting the tetrahedral mesh to the HEX8 hexahedral mesh: In the ANSYS-ICEM software, using its well-known function of converting the tetrahedral mesh to the HEX8 hexahedral mesh, the obtained in step 3 is mixed with All tetrahedral meshes in the complex geometry region of the wing are split, and each tetrahedral mesh is split into four HEX8 hexahedral meshes, and the HEX8 hexahedral mesh division result is obtained in the complex geometry region with the mixing wing;

Step 5: The process of converting the HEX8 hexahedral mesh to the HEX20 hexahedral mesh: In the ANSYS-ICEM software, using its well-known function of increasing the midpoint of the mesh edge, for all the HEX8 hexahedral mesh edges obtained in step 4. Mark the midpoint to complete the conversion process from HEX8 hexahedral meshes in complex geometric regions with mixing wings to HEX20 hexahedral meshes. At this time, the surface meshes on the interface between the complex geometry area with the mixing wing and the simple geometry area are all quadrilateral meshes;

Step 6: Simple geometric region mesh generation process: In the ANSYS-ICEM software, using its mesh stretching function, the surface mesh on the interface between the complex geometric region with the mixing wing and the simple geometric region in step 5 is Stretch in the simple geometry area, and get the HEX20 hexahedral mesh in the simple geometry area;

Step 7: The generation process of the boundary layer mesh near the surface of the fuel rod: the specific method is as follows:

Step 7-1: In the ANSYS-ICEM software, merge the surface meshes of the fuel rod surface in the complex geometric region and the simple geometric region, and place the above surface meshes in the same part;

Step 7-2: Using the mesh stretching function of the ANSYS-ICEM software, the surface mesh of the fuel rod surface is stretched along the inner normal direction of the fuel rod surface to obtain a hexahedral mesh. The generated hexahedral mesh requires the step The positions reserved in 1 are filled and act as boundary layer meshes near the surface of the fuel rods.

Compared with the prior art, the present invention has the following advantages:

1. With the help of UG10.0 3D modeling software and ANSYS ICEM meshing software, this mesh generation method realizes the complex geometry hexahedral mesh generation process, which provides convenience for the popularization of computational fluid dynamics software based on spectral element method;

2. The grid generation method adopts a highly automated grid generation method, which can greatly reduce the operation steps and workload of technicians and improve work efficiency compared with the traditional manual grid generation method.

Description of drawings

Fig. 1 is the flow chart of the method of the present invention.

Figure 2 is a schematic diagram of the 3D geometrical model of the 5×5 bundle of the advanced pressurized water reactor fuel assembly.

Figure 3 is a schematic diagram of the flow field area.

FIG. 4 is a schematic diagram of the partition of a simple geometry region and a complex geometry region with mixing wings.

Fig. 5 is a schematic diagram of a tetrahedral mesh in a complex geometric region with scrambled wings.

Figure 6 is a schematic diagram of HEX20 hexahedral meshing in a complex geometric region with a stirring wing.

Figure 7 is a schematic diagram of the HEX20 hexahedral mesh of simple geometry regions and complex geometry regions with mixing wings.

FIG. 8 is a schematic diagram of the boundary layer grid near the surface of the fuel rod.

Detailed ways

The present invention will be further described in detail below with reference to the flow chart shown in FIG.

Step 1: Use the UG 10.0 3D modeling software to establish a 3D geometric model of the 5×5 bundles of the advanced pressurized water reactor fuel assembly. The modeling content includes the modeling of the stirring wing and the modeling of the fuel rods: first, the two-dimensional sketch of the stirring wing structure is completed by using the structure diagram of the 5×5 rod bundle of the advanced pressurized water reactor fuel assembly; Using the stretching function to obtain a thick 3D mixing wing model, and using the bending function to bend the mixing wing model, the establishment of the mixing wing model is completed; then, a 3D fuel rod model is established by stretching. When establishing the geometric model, pay attention to the need to increase the diameter of the fuel rod, the increment is the thickness of the boundary layer at the surface of the reserved fuel rod, which is used for the generation of the boundary layer mesh in step 7. The three-dimensional geometric model of the 5 × 5 bundles of the advanced PWR fuel assembly is shown in Fig. 2. Then, the Boolean logic function of the UG 10.0 software was used to establish the fluid region outside the 5×5 rod bundle of the advanced pressurized water reactor fuel assembly. The obtained fluid region is shown in Figure 3.

Step 2: Partitioning process of the fluid region: The computational fluid region of the 5×5 rod bundle of the advanced PWR fuel assembly is divided into a simple geometric region and a complex geometric region with mixing wings. Specifically, a plane with the normal line consistent with the axis of the fuel rod is established at 1 cm upstream and 1 cm downstream of the stirring blade, and the above two planes are used as the interface to divide the fluid region into three parts, which is convenient for subsequent processing. The results of the partition in this example As shown in Figure 4.

Step 3: Tetrahedral meshing process for complex geometric regions with scrambled wings: Using ANSYS-ICEM software, use its tetrahedral meshing function to complete the meshing task of complex geometric regions obtained in Step 2: only The macro size of the tetrahedral mesh needs to be set, and the automatic calculation function of the ANSYS-ICEM software is used to complete the tetrahedral meshing process of complex geometric regions with mixing wings. The automatically divided tetrahedral mesh is shown in Figure 5. .

Step 4: The process of converting tetrahedral meshes to HEX8 hexahedral meshes: In the ANSYS-ICEM software, using the function of converting tetrahedral meshes to HEX8 hexahedral meshes, the mesh with stirring wings obtained in step 3 All tetrahedral meshes in the complex geometry area are split, and each tetrahedral mesh is split into four HEX8 hexahedral meshes, and the HEX8 hexahedral mesh division results are obtained in the complex geometry area with mixing wings, and the final generated mesh The grid is shown in Figure 6.

Step 5: The process of converting the HEX8 hexahedral mesh to the HEX20 hexahedral mesh: In the ANSYS-ICEM software, use the function of adding the midpoint of the mesh edge to the midpoint of all the HEX8 hexahedral mesh edges obtained in step 4. Mark and complete the conversion process of converting the HEX8 hexahedral mesh in the complex geometric region with the mixing wing to the HEX20 hexahedral mesh; at this time, the surface mesh on the interface between the complex geometric region and the simple geometric region with the mixing wing All are quadrilateral grids.

Step 6: Simple geometric region mesh generation process: In the ANSYS-ICEM software, using its mesh stretching function, the surface mesh on the interface between the complex geometric region with the mixing wing and the simple geometric region in step 5 is Stretch in the simple geometric region to obtain the HEX20 hexahedral mesh in the simple geometric region, and the final mesh result is shown in Figure 7;

Step 7: The generation process of the boundary layer mesh near the surface of the fuel rod: the specific method is as follows:

Step 7-1: In the ANSYS-ICEM software, merge the surface meshes of the fuel rod surface in the complex geometric region and the simple geometric region, and place the above surface meshes in the same part;

Step 7-2: Using the mesh stretching function of the ANSYS-ICEM software, the surface mesh of the fuel rod surface is stretched along the inner normal direction of the fuel rod surface to obtain a hexahedral mesh. The generated hexahedral mesh requires the step The positions reserved in 1 are filled and act as boundary layer meshes near the surface of the fuel rods. The final boundary layer mesh is the ring mesh in Figure 8.

The parts not described in detail in the present invention belong to the common knowledge of those skilled in the art.

Claims (1)

1. A method for automatically generating a hexahedral mesh with boundary layer of a reactor fuel assembly, characterized in that, comprising the steps: Step 1: Geometric preprocessing process: According to the actual reactor fuel assembly structure, use UG10.0 3D modeling software to carry out 3D modeling of the fuel assembly. The modeling content includes the modeling of the stirring wing and the modeling of the fuel rod: First, Use the structure diagram of the actual reactor fuel assembly to complete the two-dimensional sketch of the stirring wing structure; then use the stretching function of the UG10.0 software to obtain a thick three-dimensional stirring wing model, and use the bending function to bend the stirring wing model. The establishment of the mixing wing model; then, the three-dimensional fuel rod model is established by the method of stretching; when the three-dimensional fuel rod model is established, the thickness space of the boundary layer mesh on the surface of the fuel rod is reserved; then the Boolean logic of the UG10.0 software is used Function to establish the fluid region outside the reactor fuel assembly; Step 2: Partitioning process of the fluid region: The computational fluid region of the reactor fuel assembly is divided into a simple geometric region and a complex geometric region with a stirring vane. Specifically, a plane is established 1 cm upstream and 1 cm downstream of the stirring vane, respectively. The normal line needs to be parallel to the axis of the fuel rod, and the above two planes are used as the interface to divide the fluid area into three parts, which is convenient for subsequent processing; Step 3: Tetrahedral meshing process for complex geometric regions with scrambled wings: Using ANSYS-ICEM software, use its tetrahedral meshing function to complete the meshing task of complex geometric regions obtained in Step 2: only The macro size of the tetrahedral mesh needs to be set, and the automatic calculation function of the ANSYS-ICEM software is used to complete the tetrahedral meshing process of complex geometric regions with mixing wings; Step 4: The process of converting tetrahedral meshes to HEX8 hexahedral meshes: In the ANSYS-ICEM software, using the function of converting tetrahedral meshes to HEX8 hexahedral meshes, the mesh with stirring wings obtained in step 3 All tetrahedral meshes in the complex geometry area are split, each tetrahedral mesh is split into four HEX8 hexahedral meshes, and the HEX8 hexahedral mesh division results are obtained in the complex geometry area with mixing wings; Step 5: The process of converting the HEX8 hexahedral mesh to the HEX20 hexahedral mesh: In the ANSYS-ICEM software, use the function of adding the midpoint of the mesh edge to the midpoint of all the HEX8 hexahedral mesh edges obtained in step 4. Mark and complete the conversion process of converting the HEX8 hexahedral mesh in the complex geometric region with the mixing wing to the HEX20 hexahedral mesh; at this time, the surface mesh on the interface between the complex geometric region and the simple geometric region with the mixing wing All are quadrilateral grids; Step 6: Simple geometric region mesh generation process: In the ANSYS-ICEM software, using its mesh stretching function, the surface mesh on the interface between the complex geometric region with the mixing wing and the simple geometric region in step 5 is Stretch in the simple geometric region to obtain the HEX20 hexahedral mesh in the simple geometric region; Step 7: The generation process of the boundary layer mesh near the surface of the fuel rod: the specific method is as follows: Step 7-1: In the ANSYS-ICEM software, merge the surface meshes of the fuel rod surface in the complex geometric region and the simple geometric region, and place the above surface meshes in the same part; Step 7-2: Using the mesh stretching function of the ANSYS-ICEM software, the surface mesh of the fuel rod surface is stretched along the inner normal direction of the fuel rod surface to obtain a hexahedral mesh. The generated hexahedral mesh requires the step The positions reserved in 1 are filled and act as boundary layer meshes near the surface of the fuel rods.

Images