Ansys DesignModeler – Boolean

Boolean operations combine bodies: Unite merges them into one, Subtract removes one from another, Intersect keeps only the shared volume, and Imprint Faces transfers the contact footprint without changing the shapes.

For CFD the important one is Subtract. The fluid domain is rarely drawn directly; you build an enclosure around the model and subtract the solid from it, so what remains is exactly the volume the fluid occupies. Selecting whether the tool body is kept or consumed is what lets you reuse the same solid for later operations.

Imprint Faces earns its place in multi body models. It splits the faces where two bodies touch so the contact region becomes a face of its own, which gives you a clean surface to assign boundary conditions or a local mesh sizing to.