1 概述 Overview
2.5D 网格重构是一种快速网格重构方法，主要应用于涡旋压缩机等存在复杂平面运动且无法简化为二维计算的问题。
2.5D remeshing is a fast remeshing method, mainly used for problems with complex planar motion that cannot be simplified to two-dimensional, such as centrifugal compressors.
涡旋压缩机工作原理（视频源：维基百科）Working principle of scroll compressor (video source: Wikipedia)
适用于 2.5D 动网格的问题特点：
- 计算域几何形状为柱体类形状，两个端面平行且形状相同，端面和侧面垂直
- 计算域的网格类型为三棱柱单元（虽然 Fluent 界面上显示支持六面体和多面体单元重构，实际上会由于网格无法重构导致单元负体积）
- 两个端面网格均为三角形单元，且单元分布完全相同
- 侧面垂直于端面，其网格为四边形单元
- 运动部分为侧面，运动规律为速度方向始终平行于端面的刚体运动
Characteristics of problems suitable for 2.5D dynamic mesh:
- The geometric shape of the computational domain is cylinder-like, with two parallel end faces of the same shape, and the end faces are perpendicular to the side faces
- The mesh type in the computational domain is prism cells (although Fluent interface shows support for hexahedral and polyhedral cell remeshing, but it will actually lead to negative cell volumes due to inability to remeshing)
- The meshes on both end faces are triangular cells, with completely identical cell distributions
- The side faces are perpendicular to the end faces, with quadrilaterial cell meshes The moving part is the side face, with rigid body motion of velocity always parallel to the end face
2 设置过程 Setup process
以如下模型，讲述 2.5D 动网格设置过程。
The 2.5D dynamic mesh setup process is described using the following model.
上述模型中：
- 蓝色为端面，分别命名为“symmetry_1”和“symmetry_2”
- 黄色为运动的侧面，命名为“wall_moving”
- 红色为固定的侧面，命名为“wall_fixed”
In the above model:
- Blue represents the end faces, named "symmetry_1" and "symmetry_2" respectively
- Yellow represents the moving side face, named "wall_moving"
- Red represents the fixed side face, named "wall_fixed"
2.1 设置动网格方法 Set dynamic mesh method
在动网格设置页面，勾选“smoothing”和“remeshing”选项。
In the dynamic mesh setup page, check the "smoothing" and "remeshing" options
网格光顺方法中，2.5D 仅支持拉普拉斯方法，必须选择如图所示选项。
In the mesh smoothing methods, 2.5D only supports Laplace method, the options must be set as shown.
网格重构方法设置如图所示。
The remeshing settings are set as shown.
参数设置部分：
- 结合初始网格分布合理设置单元尺寸范围
- 建议网格重构频率设置为 1
Parameters:
- Set cell size range appropriately based on initial mesh distribution S
- suggest remeshing interval to be 1
2.2 网格区域设置 Mesh zone settings
2.2.1 运动侧面 Moving side face
运动边界设置如图所示，必须使用“rigid body”类型。
The moving boundary is set as shown, must use "rigid body" type.
运动规律定义采用UDF方式，代码如图所示。
The motion is defined by UDF, code as shown
2.2.2 端面 End faces
端面的“symmetry_1”类型为“deforming”，形状设置为平面，相关参数参考几何模型。
The end face "symmetry_1" type is set to "deforming", geometry definition set as plane, parameters refer to geometric model.
在网格设置部分，勾选“smoothing”和“remeshing”选项。
In "meshing options", check "smoothing" and "remeshing".
端面的“symmetry_2”设置类似，网格设置部分只勾选“smoothing”，不勾选“remeshing”。
The setup for "symmetry_2" is similar, in "meshing options", only check "smoothing" but uncheck "remeshing".
2.2.3 固定侧面 Fixed side face
未设置部分，Fluent 默认为固定边界，无运动。为谨慎起见，可对固定侧面创建“stationary”类型的动网格区域。
Unset parts are fixed boundaries by default in Fluent. For caution, can create "stationary" type dynamic mesh zone for fixed side face.
3 动网格结果 Dynamic mesh results
动网格变化如动画所示。
Mesh changes are shown in animations.
端面网格更新 End face mesh update
侧面运动效果Side face motion
4 注意事项 Notes
网格重构涉及较复杂的单元质量维持，重点注意事项包括：文章来源：https://www.toymoban.com/news/detail-805753.html
- 涉及网格重构的动网格问题需要时间步长足够小，大时间步长下很容易出现单元负体积
- 建议时间步长设置：单个步长下，运动距离不超过单元尺寸的一半，即节点运动的库朗特数小于 0.5
- 建议在开启计算之前，在动网格设置页面先预览运动形式和网格重构过程，避免因为运动定义等原因导致计算出错
Remeshing involves relatively complex cell quality conservation, key points include:文章来源地址https://www.toymoban.com/news/detail-805753.html
- Problems involving remeshing require sufficiently small time steps, large time steps can easily lead to negative cell volumes
- Suggested time step settings: motion distance within one step should not exceed half of cell size, i.e. Courant number of node motion is less than 0.5
- Suggest previewing motion and remeshing process in dynamic mesh setup page before starting calculation, to avoid errors due to motion definitions etc.
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