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Pre-Processing
Simcenter STAR-CCM+ solves physics problems on a computational mesh. To provide this mesh, you first define geometry using internal or external tools, and then create a mesh pipeline whose operations generate the mesh in repeatable steps.
Meshing
A mesh is a discretized representation of a geometric domain. This domain can include real-world geometry, its content, and its surrounding environment.
Mesh Refinement
Simcenter STAR-CCM+ can refine the mesh by approximating the wake region or using solution-based approach. These features allow you to achieve efficient refinement by reducing the cell size in areas of interest.
Field Function Mesh Refinement
To achieve successively more accurate solutions, you can refine the mesh with respect to a solution quantity (such as turbulent kinetic energy). In Simcenter STAR-CCM+, you achieve successive refinement using mesh refinement tables or field functions.
Creating a Field Function for Mesh Refinement
The first step in field function mesh refinement is to create a field function that returns the mesh size with respect to an appropriate solution quantity.

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Pre-Processing
Simcenter STAR-CCM+ solves physics problems on a computational mesh. To provide this mesh, you first define geometry using internal or external tools, and then create a mesh pipeline whose operations generate the mesh in repeatable steps.
- 3D-CAD
  3D-CAD is a feature-based parametric modeler within Simcenter STAR-CCM+ that allows you to build geometries from scratch. The geometries that you create with 3D-CAD are stored as 3D-CAD models, which you can then convert to geometry parts for integration with the meshing and simulation process.
- Modeling Geometry
  This part of the User Guide describes how to use 3D-CAD, the parametric solid modeler available within Simcenter STAR-CCM+. It also describes the features and tools available for further preparation of the geometry model and its surfaces.
- The Surface Repair Tool
  The Surface Repair tool diagnoses errors in, and provides repair tools for, tessellated surfaces and part curves. The same tool allows you to reorganize discretized geometry by searching for face-based features and attributes then assigning the results to new or existing part surfaces or curves.
- Defining the Regions Layout
  An essential part of the process in setting up your simulation is to define the relationship between geometry parts and regions, boundaries, and interfaces.
- Meshing
  A mesh is a discretized representation of a geometric domain. This domain can include real-world geometry, its content, and its surrounding environment.
  - Mesh Construction
    Within a bounding volume defined by geometrical surfaces, Simcenter STAR-CCM+ can construct meshes for finite volume and finite element solvers.
  - Meshers in Simcenter STAR-CCM+
    The meshers in Simcenter STAR-CCM+ generate surface and volume meshes for geometry parts that are assigned to regions and make them ready for analysis.
  - Parts-Based Meshing
    Parts-based meshing (PBM) is a meshing strategy in which you create one or more mesh operations that define workflows for preparing, fixing, and processing geometry. A major benefit of PBM is that every mesh operation you create forms part of a linear and repeatable process.
  - The Meshing Workflow
    This section contains the recommended workflow for setting up and generating the volume mesh at the parts level.
  - Mesh Operations
    Mesh operations perform actions on geometry parts that you can easily repeat whenever their input parts or properties are changed.
  - Mesh Descriptions
    A mesh description is a version of a surface or volume mesh belonging to a geometry part. Geometry parts can have more than one surface mesh description associated with them. You create and change descriptions by importing surfaces or executing operations.
  - Custom Mesh Controls
    Custom controls override any default controls for the surface and volume meshers. This facility allows you to refine or coarsen the mesh for part curves, part surfaces, geometry parts, and specified volumes.
  - Surface Meshers
    Simcenter STAR-CCM+ contains meshing tools which can be used to help prepare a high-quality surface mesh before a volume mesh can be generated.
  - Volume Meshers
    Simcenter STAR-CCM+ contains different types of meshers that can be used to generate a volume mesh starting from a suitably prepared surface mesh.
  - Mesh Refinement
    Simcenter STAR-CCM+ can refine the mesh by approximating the wake region or using solution-based approach. These features allow you to achieve efficient refinement by reducing the cell size in areas of interest.
    - Mesh Refinement in a Specified Volume
    - Wake Refinement
      Wake refinement using the Parts-Based meshing approach allows you to define the direction, distance, and spread angle of the wake relative to a part surface or part curve from which the wake grows.
    - Field Function Mesh Refinement
      To achieve successively more accurate solutions, you can refine the mesh with respect to a solution quantity (such as turbulent kinetic energy). In Simcenter STAR-CCM+, you achieve successive refinement using mesh refinement tables or field functions.
      - Creating a Field Function for Mesh Refinement
        The first step in field function mesh refinement is to create a field function that returns the mesh size with respect to an appropriate solution quantity.
      - Creating an XYZ Internal Table for Mesh Refinement
        You use the mesh refinement field function to populate an XYZ internal table of mesh sizes, with respect to each cell, face, or parcel centroid. Populating the table applies the field function to the existing volume mesh and its solution data.
      - Applying the Field Function or Table of Mesh Sizes
        The final stage is to apply the field function or table of mesh sizes to the meshing model properties.
  - Directed Meshing
    Directed meshing is a method for generating high quality swept meshes on geometries in Simcenter STAR-CCM+. The method operates by sweeping a mesh from the surfaces of a geometry through its volume onto a facing target surface.
  - Two Dimensional and Axisymmetric Meshes
    The use of a one-cell-thick three-dimensional mesh is much less efficient than using a real two-dimensional mesh for two-dimensional and axisymmetric simulations. When circumstances allow, use real two-dimensional meshes.
  - Turbomachinery Mesh
    Turbomachinery applications with axial blades typically require a flow-aligned, structured mesh. This type of mesh has implicit connectivity and a fixed number of vertex or face neighbors, leading to a more accurate solution.
  - Mesh Visualization
    You can visualize any mesh representation in Simcenter STAR-CCM+. After you have imported or generated a mesh, you visualize it to check the cell quality and mesh validity.
  - Checking the Surface Mesh
    The volume mesh quality is directly dependent on the surface mesh quality. Therefore, it is crucial to make sure that all surface meshes are of good quality.
  - Checking the Volume Mesh
    This section describes the tools available for checking the validity and quality of the volume mesh, and for diagnosing problem areas. Such problems can then be fixed, either inside Simcenter STAR-CCM+ or in the originating mesh generator.
  - Meshing Field Functions Reference
    This section contains a list of field functions that are related to meshing.
  - Working With Representations
    This section provides information on representations as a useful part of the meshing process.
  - Scaling the Entire Mesh
    Scaling the mesh is important as the units of the model must be in meters before running an analysis.
  - Working with Baffles
  - Exporting Mesh and Solution Data
    This section outlines the steps for exporting Simcenter STAR-CCM+ mesh and solution data to formats that can be used in other CAE packages.
  - Multi-Region Meshing
    This section outlines the surface requirements for performing multi-region meshing, as well as step-by-step instructions when starting from surface imports that result in single region and multiple regions definitions. Additionally, guidelines are provided on what the best approaches are for exporting surface data from CAD packages when multiple regions are required.

Creating a Field Function for Mesh Refinement

The first step in field function mesh refinement is to create a field function that returns the mesh size with respect to an appropriate solution quantity.

In this example, if the turbulent kinetic energy is greater than 4 J/kg, the mesh size is 0.1 m; otherwise it is 5 m.

Note

It is important to consider your initial mesh resolution when creating a mesh refinement field function. If your initial mesh is coarse, define a field function that ensures you get a smooth variation in cell sizes. A refinement field function that defines an abrupt change in cell sizes results in poor mesh grading and quality.

To create a field function:

Right-click the Automation > Field Function manager and select New > Scalar.
Select the Field Function node and click the ellipsis next to the Definition property.
- In this example, the field function name is Mesh Size.
You are recommended to apply the following conditions when creating and using a field function:
- A field function must be cell-based and return a scalar value
- To minimize the time taken to iterate a step, consider a cell size based on the initial mesh resolution
- Specify a field function that does not over refine the mesh
- To achieve an optimal mesh, run the solution for at least 100 to 200 iterations per step to partially converge it
In the Field Function - Definition dialog, enter a conditional expression that returns the mesh size with respect to a solution characteristic.
Click OK to save the field function definition.

Note The mesh size units are always meters; regardless of the preferred length unit.
Next, you can assign this field function directly to the mesher or use it to create an internal table for mesh refinement.

There are a number of differences between field function and mesh refinement table. The most notable difference is that field function refinement is a significantly faster method and uses less memory. Using the field function refinement directly is more precise than the mesh refinement table and generates fewer mesh cells. Creating a table from a field function before using the table for mesh refinement does not produce the same mesh as using the field function directly.

In order to achieve an optimal mesh in minimum time, you should carry out multiple refinement and solution iterations.