December 1, 2020
Whereas non-conformal interfaces connect cell zones along matching face zones, overset interfaces connect cell zones by interpolating cell data in the overlapping regions. For overset meshing to be successful, the cell zones must overlap sufficiently. An advantage of overset meshing is that the individual parts of an overset mesh can be generated independently and with fewer constraints than if the parts had to fit together conformally or along non-conformal interfaces. This can make it easier to replace parts of a mesh without having to remesh large parts or even the complete mesh.
Figure 6.49: Overset Component and Background Mesh
Figure 6.49: Overset Component and Background Mesh shows a simplified mesh for a simulation of flow over a cylinder in a duct. The mesh consists of two parts—a background mesh representing the duct and a separate component mesh around the cylinder. The case is set up in Fluent as an overset case by specifying the outer boundary of the cylinder mesh as overset (boundary type), and by creating an overset interface containing the two cell zones. With these two steps complete, Fluent automatically establishes the necessary connectivity between the meshes when the flow is initialized. In this process, cells that fall outside the computational domain are classified as dead cells. The cells where the flow equations are solved are referred to as solve cells. Receptor cells receive data interpolated from another mesh. The donor cells—the cells where the receptors get their data—are a subset of the solve cells. For the above case, Figure 6.50: Solve Cells After Initialization shows the solve cells of the mesh after the flow is initialized. Note that in parallel, you can print partition statistics to get information about some of the cell classifications, as described in Interpreting Partition Statistics.
Figure 6.50: Solve Cells After Initialization
- Background zones are the cell zones that make up the background mesh of the computational domain. Background zones cannot have overset boundaries.
- Component zones overlay background zones and have overset boundaries near where they connect to the background and other component zones. If multiple component zones are connected, at least one of these zones needs to have an overset boundary.
All cell types generally supported in Fluent are supported with overset meshing, including polyhedral cells in 3D. The different zones paired in an overset interface can have different element types or can have mixed element types.
Overset meshing in Fluent is compatible with mesh adaption. The mesh zones of an overset interface can be locally adapted using all available adaption tools.
Overset meshing can be used for steady-state or transient solutions. Note that for steady-state cases in parallel that use the default Metis partitioning, ANSYS Fluent will automatically repartition overset meshes when the solution is initialized or data is read; a model-weighted partitioning that is designed for optimal performance is used.
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