Geometry preparation should make the CFD topology explicit. Decide which bodies become solids, which volumes become fluid, where interfaces and boundaries must exist, and which small features are physically irrelevant before meshing begins.
Start with the engineering question
A fillet can be irrelevant in one simulation and essential in another. A small hole can be cosmetic for external aerodynamics but dominate leakage flow in thermal management. Before simplifying anything, list the outputs you need: pressure drop, cooling flow, drag, wall heat flux, forces, mixing or temperature uniformity.
Remove detail only when it does not change the physics
- Suppress logos, tiny fastener details and decorative features that do not affect the flow.
- Keep gaps, seals, slots and sharp edges when they control leakage, separation or jets.
- Replace unnecessarily complex components with simpler bounding geometry when only blockage matters.
- Exploit repeated/instanced geometry when the software workflow supports it efficiently.
Recent STAR-CCM+ releases have continued to improve 3D-CAD and geometry-handling workflows, including operations for repeated bodies and faster preparation of complex assemblies.
Create boundaries intentionally
Face splits, imprinted edges and part surfaces are not cosmetic organization: they determine where you can apply boundary conditions, mesh controls and reports. Preserve an edge when it separates two surfaces that need different physics or resolution. Remove it when it only creates unnecessary surface fragmentation.
Finish the important geometry topology before investing heavily in regions, boundary assignments, interfaces and reports. Late geometry edits can invalidate downstream selections.
Fluid-domain creation needs clean closure
For internal flow, the key object is often the negative volume occupied by fluid rather than the original solids. For external flow, you may create an enclosure and subtract the body. In either case, leaks or unintended openings can create the wrong fluid region even when the CAD looks visually correct.
Use booleans, volume extraction or wrapping according to geometry quality and the level of fidelity required. If direct operations fail because of topology defects, switch to Surface Repair or Surface Wrapper rather than repeatedly forcing a broken boolean.
Recommended CFD geometry workflow
- Import using a robust CAD representation.
Use native or neutral CAD according to the source and translation quality.
- Verify scale, body count and orientation.
Catch unit and assembly errors before any modelling work.
- Simplify irrelevant features.
Remove detail based on physics and mesh scale.
- Create meaningful face topology.
Prepare surfaces needed for boundaries, interfaces and local controls.
- Build or extract the fluid domain.
Check closure and component contacts.
- Run geometry diagnostics.
Repair only the defects that matter to the next stage.
- Freeze the topology before setup expansion.
Then create regions, boundaries, interfaces, mesh operations and reports.
Continue from geometry to mesh
Use the Mesh Advisor to translate curvature, gaps, walls and wakes into targeted controls.