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11.7.6 Using the 2.5D Model

For 3D simulations only, you can select the 2.5D model under Models in the Dynamic Mesh Parameters panel. This model allows for a specific subset of smoothing and remeshing techniques.

The 2.5D mesh essentially is a 2D triangular mesh which is expanded, or extruded, along the normal axis of the specific dynamic zone that you are interested in modeling. The triangular surface mesh is remeshed and smoothed on one side, and the changes are then extruded to the opposite side. Rigid body motion is applied to the moving face zones, while the triangular extrusion surface is assigned to a deforming zone with remeshing and smoothing enabled. The opposite side of the triangular mesh is assigned to be a deforming zone as well, with only smoothing enabled, as in Figure  11.7.39.

Note that in the Smoothing tab of the Dynamic Mesh Parameters panel (Figure  11.7.38), the 2.5D model allows you to change only the Boundary Node Relaxation value and the Number of Iterations. Also note that the Remeshing tab of the Dynamic Mesh Parameters panel automatically has Face Remeshing enabled.

Figure 11.7.38: The Smoothing Tab for the 2.5D Model
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For more information on setting smoothing and remeshing parameters, see Section  11.7.1.

The 2.5D model only applies to mapable (i.e., extrudable) mesh geometries such as pumps, as in Figure  11.7.39. Only the aspects of the geometry that represent the "moving parts" need to be extruded in the mesh.

Figure 11.7.39: 2.5D Extruded Gear Pump Geometry
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You must only apply smoothing to the opposite side of the extruded mesh, since FLUENT requires the geometry information for the dynamic zone. FLUENT projects the nodes back to its geometry after the extrusion. Without this geometry information, the dynamic zones tends to lose its integrity.

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In parallel, a partition method that partitions perpendicular to the extrusion surface should be used. For example, if the normal of the extrusion surface points in the x-direction then Cartesian-Y or Cartesian-Z would be the perfect partition methods.

The 2.5D model is used in combination with a DEFINE_GRID_MOTION UDF. (See here of the separate UDF Manual for information about hooking this UDF.) This UDF is associated with the extrusion surface that is adjacent to the cell zone, in turn applying the same deformation to the entire cell zone. This approach is particularly useful when modeling gear pumps that are predominantly extruded hexahedral meshes. For more information about this UDF, contact your support engineer.


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