Joining fluid meshes

The flow solver can automatically join separately-created fluid meshes that share a common boundary. This can reduce modeling effort and model sizes.

The solver automatically joins separately-created fluid meshes when the following conditions are met:

• Two polygon bodies meshed with 3D fluid elements share a boundary.

• At the boundary, the free faces of elements in one body are co-planar with the free faces of the elements in the other body.

• The common boundary is not meshed with thermal elements (elements with thermal material properties).

• For the serial flow solver, the Connect Disjoint Fluid Meshes check box is selected on the 3D Flow page of the Solution dialog box.

• For the parallel flow solver, the Disjoint Fluid Mesh Pairing simulation object is defined at the boundary between the two bodies.

There is no need for nodes to match, but mesh density on the matching polygon faces should be similar. Large differences in mesh density between the two polygon faces will cause degradation of accuracy and performance.

If your model is large or complex, with many disjoint fluid mesh faces to join, the memory demands on your system will be high. To avoid memory overruns, test a simpler version of the model before proceeding.

The Mesh Mating Condition is an alternative to joining fluid meshes that sometimes delivers better performance and accuracy at the cost of additional model preparation time. For more information, see Mesh mating conditions.

Assembly meshing technique

A more specific application of this basic method is of particular interest for modeling assemblies such as electronics boxes and similar constructions:

• Build and mesh a main assembly part, including its air mesh. Leave voids in the air mesh where you want to add variable sub-assemblies, such as heat sinks, PCBs, power supplies, and so on.

• Build and mesh two or more variable sub-assemblies.

• Mesh an air polygon body around and slightly larger than each variable sub-assembly. Call this the pre-meshed module.

• Position the pre-meshed module in one void so that it shares common fluid mesh boundaries wherever fluid must flow from one domain to the other. Repeat as required.

• Indicate to the flow solver to automatically connect disjoint fluid meshes:If you use the serial flow solver, make sure the Connect Disjoint Fluid Meshes check box is selected.If you use the parallel flow solver, define one Disjoint Fluid Mesh Pairing simulation object at each common fluid mesh boundary.

• Solve your coupled thermal-flow solution.

Once a sub-assembly is meshed, there is no need to ever mesh it again. You can build a library of these sub-assemblies and develop standardized modular sizes and shapes for common types of sub-assembly. Creating multiple configurations of a product then becomes much easier.

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