Ansys Meshing – Body of Influence

A Body of Influence is a dummy body used only to tell the mesher where to refine. It never becomes part of the simulation: it is frozen and suppressed for physics, so the solver never sees it, but any cell falling inside it takes the size you assigned.

This is how you refine a region rather than a surface. A wake behind a car, the shear layer of a jet, the path a free surface will follow, the volume around a rotating impeller: none of these coincide with a face of the geometry, so a face sizing cannot capture them.

The usual mistake is making the body too large, which inflates the cell count without improving the result. Draw it around the region where the gradients actually are, and keep the size ratio with the surrounding mesh gentle so the transition stays smooth.