Treat connectivity as an engineering model. Parts describe geometry; regions carry continua; boundaries define exposed region surfaces; contacts capture geometric adjacency; interfaces communicate between selected boundaries or regions.
Separate geometry topology from simulation topology
Imported parts and part surfaces are not the same objects as regions and boundaries. A clean workflow deliberately decides which volumes should become separate regions, which surfaces need boundary identity and where information must pass between regions.
Use contacts to preserve geometric relationships
Part contacts describe where geometry parts touch or correspond. They are useful for automating downstream connectivity, but a geometric contact alone does not guarantee that the final physics coupling is correct. Always inspect the resulting region/boundary/interface structure.
Use interfaces when two simulation regions must communicate
Interfaces are appropriate when adjacent regions need flux or solution transfer across a shared or mapped connection. Examples include fluid-fluid connectivity, rotating interfaces and fluid-solid coupling. The exact interface model depends on the physics and mesh relationship.
Keep physical boundaries distinct from internal connectivity
Inlets, outlets, walls, symmetry planes and other external conditions should remain clearly identifiable. Avoid accidentally leaving an internal face as a wall or merging surfaces that need different thermal or flow conditions.
Run connectivity QA before solving
Check region volumes, boundary areas, interface pairs, normals, contact coverage and expected mass/heat paths. A five-minute topology audit is cheaper than diagnosing a converged solution with an unintended wall blocking the flow.
Run the engineering check
Use the linked Abecator calculator or workflow to turn the setup decision into a quantitative check.
Continue the Abecator path
- Technical Case: CHT Contact Resistance
- Technical Case: Rotating Interfaces
- STAR-CCM+ Professional Workflow Training
- CFD Troubleshooting & Model Review
Primary Siemens reference
STAR-CCM+ is a Siemens product name. Abecator is independent and this article is original engineering guidance; it does not reproduce Siemens documentation or third-party tutorial text.