CN115659727A

CN115659727A - Grid division method with spiral complex structure

Info

Publication number: CN115659727A
Application number: CN202211246258.0A
Authority: CN
Inventors: 步珊珊; 祁伟; 李振中; 陈德奇
Original assignee: Chongqing University
Current assignee: Chongqing University
Priority date: 2022-10-12
Filing date: 2022-10-12
Publication date: 2023-01-31

Abstract

The invention provides a grid division method with a spiral complex structure. The grid dividing method with spiral complex structure includes arranging multiple fuel rods inside the rod bundle assembly with spiral winding wires, and fixing adjacent fuel rods with winding wires wound in certain pitch. The grid division method with the spiral complex structure adopts step contact to replace line contact, reduces the narrow slit geometric area and effectively improves the grid quality of the area. The method for rotationally stretching the two-dimensional grid into the three-dimensional grid effectively avoids the difficulty that the three-dimensional spiral geometric model is difficult to directly generate the high-quality grid. The method of structured grids and unstructured grids is adopted to carry out structured grid division on local complex areas, and grid quality and quantity are guaranteed. And other simple areas are subjected to unstructured gridding, so that the gridding process is simpler. The number of meshes in each direction can be effectively controlled by using structured mesh division in complex areas such as a solid-liquid contact area and a spiral and rod contact area.

Description

Grid division method with spiral complex structure

Technical Field

The invention relates to the technical field of reactor thermal hydraulic power, in particular to a grid dividing method with a spiral complex structure.

Background

CFD simulation analysis is an important method of obtaining flow field information within a bundle assembly. Before the CFD numerical simulation is performed, a geometric model is first built and meshes are divided according to a study object. CFD analysis on bundle channels tends to be computationally expensive. A certain number of meshes and a high quality mesh are essential for the subsequent CFD calculation. However, the prior art meshing of the helical bundle geometry model has a big problem: (1) the line contact between the helical structure and the rods forms a narrow slit structure, which results in a large mesh aspect ratio, resulting in poor mesh quality. (2) The spiral structure is a three-dimensional special structure, if the structure directly generates a grid, the distortion rate of the grid is large, and the grid is difficult to be attached to an actual geometric model, so that the actual flowing heat transfer condition cannot be correctly reflected.

At present, the grid can be divided into a structured grid and an unstructured grid according to the form and combination arrangement of the grid, and when the grid is divided by a geometric model with a spiral rod bundle, both grid methods can be adopted, but certain defects exist.

When the structured grid is adopted to divide the grid for the spiral rod bundle, ICEM software is taken as an example, a plurality of hexahedral blocks need to be divided for the geometric model, the sizes of the blocks are between the size of the geometric model and the size of the actual grid, the hexahedral and regularly arranged grid forms the blocks, a plurality of different blocks fit the actual geometric model, and finally the division of the whole geometric model into the structured grid is realized. However, due to the three-dimensional complexity of the helical bundle geometry model, if a structured grid is to be implemented, many blocks are required, which are particularly difficult to fit the actual geometry, complicated to operate, and require a particularly large amount of time and effort, and in addition, in the geometric model with helical bundles, there are narrow slit regions formed by the contact of the helix with the lines on the rod surface, and when hexahedral grids are used for these regions, the grid aspect ratio or twist rate becomes large, resulting in particularly poor grid quality. For these problems, the current solution is to divide the entire computation domain into a plurality of regions from the axial direction, and when the helical deflection angle of each region is small, the division into blocks and then the grid division can be performed.

When the unstructured grid is adopted to divide the grid for the spiral rod bundle, taking Meshing software as an example, the geometric model is directly composed of the tetrahedral grid or the tetrahedral grid plus the hexahedral grid, the grid divided by the method can better fit the actual geometric model, but the grid quantity cannot be effectively controlled, especially in the narrow slit area of the surfaces of the spiral and the rod, the grid quantity can be rapidly increased, and the grid quality is poor. The current solution to these problems is to grid the whole rod solid and fluid domains, and use surface contact or no contact for the narrow slits of local line contact, but the biggest problem with this approach is the huge number of grids, which has to use more CFD computing resources, i.e. consume more computer cache and more computing time.

Therefore, the development of a grid division method with a spiral complex structure is of great significance.

Disclosure of Invention

The invention aims to provide a grid division method with a spiral complex structure so as to solve the problems in the prior art.

The technical solution adopted for the purpose of the present invention is a lattice division method with a spiral complex structure, wherein a rod bundle assembly with spiral filament winding comprises a plurality of rod bundles arranged in a flow channel. There is a gap between adjacent bundles. The single bundle includes fuel rods and a wire wrap. The wire wrap is wound around the outer wall of the fuel rod at a fixed pitch. The grid division method with the spiral complex structure comprises the following steps:

1) And establishing a three-dimensional geometric model of the spirally wound wire rod bundle component. The three-dimensional geometric model comprises a solid region, a fluid region A and a fluid region B. Wherein solid regions are formed within the fuel rods and the wire windings. The fluid region a is a rod-proximal fluid region that includes filament winding features. The cross section of the fluid area A is circular. The fluid area A is in a torsional structure around the axial direction. The fluid region B is a mainstream region fluid region that does not contain filament winding features. The fluid region B is a portion of the flow channel excluding the solid region and the fluid region a. The fluid area B is provided with a plurality of hollow areas.

2) Any cross section of the three-dimensional geometric model is obtained. The boundary line formed by the area of the single fuel rod and the corresponding wire winding in the cross section is identified. The line contact of the wire wrap and the fuel rod in the boundary line is simplified to be step contact, forming a solid region boundary line. The area within the solid area boundary line is taken as the two-dimensional solid area of a single bundle.

And constructing a solid region circumcircle according to the solid region boundary line. A separation circle is constructed outside the solid area tangent circle. The separation circle is concentric with the circumscribed circle. The diameter of the separating circle is larger than the diameter of the circumscribed circle by at least two boundary layer grid heights. The area between the solid area boundary line and the separating circle is taken as the two-dimensional fluid area a of the single bundle.

The two-dimensional solid area and the two-dimensional fluid area a of all the bundles in the cross-section are removed to obtain a two-dimensional fluid area B.

3) And (3) constructing a two-dimensional structured grid of the single rod bundle two-dimensional solid area by using fluid dynamics software to obtain the solid area two-dimensional grid. And rotationally stretching the two-dimensional grid to form a solid domain three-dimensional grid.

4) And (3) constructing a two-dimensional structured grid of the two-dimensional fluid area A of the single rod bundle by using fluid dynamics software to obtain a two-dimensional grid of the fluid area. And rotationally stretching the two-dimensional grid of the fluid domain to form a structured grid of the fluid domain A.

5) And splicing the solid domain three-dimensional grid of the generated single rod bundle and the structured grid of the fluid domain A to form Part A.

6) A geometric model of the fluid region B is constructed using three-dimensional modeling software. And performing mesh division on the geometric model of the fluid region B, and performing three-dimensional unstructured mesh on the fluid region B.

7) And after array replication is carried out on the Part A, the Part A is spliced with the three-dimensional unstructured grid of the fluid area B to form an integral computational domain grid.

Further, in step 3) and step 4), the ansys cem cfd software is used to construct a two-dimensional structured grid of solid domains and fluid domains a.

Further, in the step 4), the two-dimensional mesh of the fluid domain is rotationally stretched along the axis of the fuel rod during the rotational stretching.

Further, in step 6), mesh division is performed on the geometric model of the fluid region B by using the Meshing software.

Further, the total height of the ribbon spiral wound bundle assembly was 600mm. The gap between adjacent fuel rods was 10.5mm. The diameter of the wire wrap is 1.2mm. The pitch of the wire wrap is 200mm.

The technical effects of the invention are undoubted:

A. step contact is adopted to replace line contact, so that the narrow slit geometric area is reduced, and the grid quality of the area is effectively improved;

B. the method of rotationally stretching the two-dimensional grid into the three-dimensional grid is adopted, so that the difficulty that the high-quality grid is difficult to directly generate by a three-dimensional spiral geometric model is effectively avoided;

C. the method of structured grids and unstructured grids is adopted to carry out structured grid division on local complex areas, and the quality and the quantity of the grids are guaranteed; unstructured gridding is carried out on other simple areas, so that the gridding process is simpler;

D. the number of meshes in each direction can be effectively controlled by using structured mesh division in complex areas such as a solid-liquid contact area and a spiral and rod contact area.

Drawings

FIG. 1 is a ribbon spiral wound bundle geometry;

FIG. 2 shows two cases with helically wound bundles;

FIG. 3 is a simplified process of contacting the helix with the bundle;

FIG. 4 is a re-decomposition of the geometric model;

FIG. 5 is solid domain structured meshing;

FIG. 6 is a fluid domain structured meshing;

FIG. 7 is a fluid domain unstructured meshing;

fig. 8 is a merged view of all meshes.

Detailed Description

The present invention will be further described with reference to the following examples, but it should be understood that the scope of the subject matter described above is not limited to the following examples. Various substitutions and alterations can be made without departing from the technical idea of the invention and the scope of the invention is covered by the present invention according to the common technical knowledge and the conventional means in the field.

Example 1:

the present embodiment provides a grid partitioning method with a spiral complex structure. The spiral wound bundle assembly includes a plurality of bundles arranged in a flow channel. There are gaps between adjacent bundles. The single bundle comprises fuel rods 1 and a wire winding 2. The wire 2 is wound around the outer wall of the fuel rod 1 at a fixed pitch. The grid division method with the spiral complex structure comprises the following steps:

1) And establishing a three-dimensional geometric model of the rod bundle assembly with the spiral wire winding. The three-dimensional geometric model includes a solid region 3, a fluid region A4, and a fluid region B5. Wherein the fuel rods 1 and the wire windings 2 form a solid area 3. The fluid region A4 is a rod-proximal fluid region that contains filament winding features. The cross-section of the fluid region A4 is circular. The fluid region A4 is in a twisted configuration about the axial direction. The fluid region B5 is a mainstream region fluid region that does not contain filament winding features. The fluid region B5 is a portion of the flow channel excluding the solid region 3 and the fluid region A4. The fluid region B5 has a plurality of hollow-out regions therein.

2) Any cross section of the three-dimensional geometric model is obtained. The boundary line formed by the area of the single fuel rod 1 and the corresponding wire winding 2 in the cross section is identified. The line contact of the wire winding 2 and the fuel rod 1 in the boundary is simplified to be the step contact, forming the solid region boundary line. The area within the solid area boundary line is taken as the two-dimensional solid area of a single bundle.

And constructing a solid region circumcircle according to the solid region boundary line. A separating circle is constructed outside the solid area tangent circle. The separation circle is concentric with the circumscribed circle. The diameter of the separating circle is larger than the diameter of the circumscribed circle by at least two boundary layer grid heights. The area between the solid area boundary line and the separating circle is taken as the two-dimensional fluid area a of the single bundle.

3) And (3) constructing a two-dimensional structured grid of the single rod bundle two-dimensional solid area by using fluid dynamics software to obtain a solid area two-dimensional grid 6. And (3) performing rotary stretching on the two-dimensional grid 6 to form a solid domain three-dimensional grid 7.

4) And (3) constructing a two-dimensional structured grid of the two-dimensional fluid area A of the single rod bundle by using fluid dynamics software to obtain a two-dimensional grid 8 of the fluid area. The two-dimensional grid of fluid domains 8 is rotationally stretched along the central axis of the fuel rod 1 to form a structured grid 9 of fluid domains a.

Referring to fig. 2, fig. 2a shows the case of no interference in the axial helix, with no contact between the projections of the wire windings 2 of adjacent bundles. Fig. 2b shows the case of interference of the axial spirals with contact between the projections of the windings 2 of adjacent bundles. The two-dimensional grid eccentric stretching method can be suitable for two structures in the drawing. In step 4), the fluid field two-dimensional grid 8 is rotationally stretched along the axis of the fuel rod 1. The center of the separating circle in the cross section does not coincide with the center of the fuel rod but is at a distance. The rotational stretching according to the axis is eccentric rotational stretching, and the structured grid 9 of the fluid domain a is in a torsion structure around the axial direction.

5) And splicing the solid domain three-dimensional grid 7 and the structured grid 9 of the fluid domain A of the generated single rod bundle to form Part A.

6) A geometric model of the fluid region B5 is constructed using three-dimensional modeling software. The geometric model of the fluid region B5 is gridded, the fluid region B being a three-dimensional unstructured grid 11.

7) After array replication is carried out on Part A, the Part A is spliced with the three-dimensional unstructured grid 11 of the fluid area B to form an integral calculation domain grid.

It is worth noting that the narrow gaps in the solid region 3 and the fluid region 4 result in poor mesh quality and large number of meshes if the unstructured mesh is used, so that the structured mesh is used to control the shape and number of the meshes at the narrow gaps, thereby controlling the quality and number of the whole mesh, and the method of adopting the rotary stretching mesh for the spiral structure is less in workload. The fluid domain 5 adopts an unstructured grid, and as the fluid domain 5 cannot be formed by axial stretching, if the three-dimensional structured grid is adopted for direct division, the method is more complicated, so that the unstructured grid division method is adopted.

Example 2:

the main steps of this example are the same as example 1, wherein, in step 3) and step 4), the ansys cem cfd software is used to construct a two-dimensional structured grid of solid domains 3 and fluid domains A4.

Example 3:

the main steps of this embodiment are the same as those of embodiment 1, wherein, in step 6), mesh division is performed on the geometric model of the fluid region B5 by using Meshing software.

Example 4:

the main steps of this embodiment are the same as those of embodiment 1, wherein, referring to fig. 1 to 8, the embodiment takes a 2 × 2 ribbon spiral filament-wound rod bundle assembly as an example, and further details of embodiment 1 are described. In this embodiment, the total height of the assembly of helically wound tow bars is 600mm. The gap between adjacent fuel rods 1 is 10.5mm. The diameter of the winding 2 is 1.2mm. The pitch of the wire wrap is 200mm. To meet the geometric topological requirements and to ensure the quality of the grid, the line contact of the wire winding 2 and the fuel rod 1 is simplified to be step contact, see fig. 3. Such geometric treatments have negligible effect on the flow heat transfer characteristics. Referring to fig. 5, the two-dimensional grid 6 is subjected to rotational stretching to form a solid domain three-dimensional grid 7. Referring to fig. 6, the two-dimensional grid 8 is subjected to rotational stretching to form a solid domain three-dimensional grid 9. For the axial helical interference-free model, direct rotational stretching was performed. For the axial spiral interference model, the rotational stretching is performed eccentrically. Referring to fig. 7, a geometric model of the fluid region B5 is constructed using three-dimensional modeling software, and then the geometric model is directly gridded using Fluent Meshing software to form a three-dimensional unstructured grid 11 of the fluid region B5. Referring to fig. 8, a solid domain three-dimensional structured grid 7, a structured grid 9 of fluid domains a, and an unstructured grid 11 of fluid domains B are merged together to form an overall computational domain grid.

The embodiment solves the problem of meshing with the spiral rod bundle geometric model, so that the meshing is more efficient, the number of meshes obtained by the meshing can be controlled, and the quality is better.

Claims

1. The grid division method with the spiral complex structure is characterized in that the rod bundle assembly with the spiral filament winding comprises a plurality of rod bundles which are distributed in a flow channel; gaps exist between adjacent rod bundles; the single rod bundle comprises a fuel rod (1) and a wire winding (2); the wire winding (2) is wound on the outer wall of the fuel rod (1) at a fixed pitch; the grid division method with the spiral complex structure comprises the following steps:

1) Establishing a three-dimensional geometric model with a spirally wound wire rod bundle component; the three-dimensional geometric model comprises a solid region (3), a fluid region A (4) and a fluid region B (5); wherein a solid region (3) is formed in the fuel rod (1) and the wire winding (2); the fluid region A (4) is a rod-proximal fluid region containing filament winding characteristics; the cross section of the fluid area A (4) is circular; the fluid area A (4) is in a torsional structure around the axial direction; the fluid region B (5) is a main flow region fluid region which does not contain filament winding characteristics; the fluid area B (5) is a part of the flow channel except the solid area (3) and the fluid area A (4); a plurality of hollow areas are arranged in the fluid area B (5);

2) Obtaining any cross section of the three-dimensional geometric model; identifying a boundary line formed by an area where a single fuel rod (1) and a corresponding wire winding (2) are located in the cross section; simplifying the line contact between the wire winding (2) and the fuel rod (1) in the boundary line into step contact to form a solid region boundary line; taking the area within the boundary line of the solid area as a two-dimensional solid area of a single rod bundle;

constructing a solid region circum-tangent circle according to the solid region boundary line; constructing a separating circle outside the solid area tangent circle; the separating circle is concentric with the circumscribed circle; the diameter of the separating circle is larger than that of the circumscribed circle by at least two boundary layer grid heights; taking the area between the boundary line of the solid area and the separating circle as a two-dimensional fluid area A of a single rod bundle;

removing the two-dimensional solid area and the two-dimensional fluid area A of all the rod bundles in the cross section to obtain a two-dimensional fluid area B;

3) Constructing a two-dimensional structured grid of a single rod bundle two-dimensional solid area by using fluid dynamics software to obtain a solid area two-dimensional grid (6); rotationally stretching the two-dimensional grid (6) to form a solid domain three-dimensional grid (7);

4) Constructing a two-dimensional structured grid of a two-dimensional fluid area A of a single rod bundle by using fluid dynamics software to obtain a fluid area two-dimensional grid (8); rotationally stretching the fluid domain two-dimensional grid (8) to form a structured grid (9) of fluid domains A;

5) Splicing the generated solid domain three-dimensional grid (7) of the single rod bundle and the structured grid (9) of the fluid domain A to form Part A;

6) Constructing a geometric model of the fluid region B (5) using three-dimensional modeling software; meshing a geometric model of a fluid region B (5), wherein the fluid region B is a three-dimensional unstructured mesh (11);

7) After array replication is carried out on Part A, the Part A is spliced with a three-dimensional unstructured grid (11) of a fluid area B to form an integral calculation domain grid.

2. A method of meshing with a helical complex structure according to claim 1, wherein: in steps 3) and 4), the ansys icem cfd software is used to construct a two-dimensional structured grid of solid domains (3) and fluid domains a (4).

3. A method of meshing with a helical complex structure according to claim 1, wherein: in the step 4), during rotary stretching, the fluid domain two-dimensional grid (8) is subjected to rotary stretching along the axis of the fuel rod (1).

4. A method of meshing with a helical complex structure according to claim 1, wherein: in step 6), mesh division is performed on the geometric model of the fluid region B (5) by using Meshing software.

5. A method of meshing with a helical complex structure according to claim 1, wherein: the total height of the spirally wound wire rod bundle component is 600mm; the clearance between the adjacent fuel rods (1) is 10.5mm; the diameter of the winding wire (2) is 1.2mm; the pitch of the wire wrap is 200mm.