Add a refinement region around a body

Put cells where the flow is interesting — a wake, a separation region, a gap — without refining the whole domain.

Runs on the free tier, subject to the cell cap.

Refine the surface

Select Refinements. The Surface refinement section applies to the geometry itself:

Level min — every cell touching the surface reaches this level.
Level max — reached only where the surface curves more sharply than the feature angle.
Cells between — buffer cells between levels. Higher is smoother and gives better quality, at more cells.
Max cells — a hard budget. Refinement stops when it is reached, so the mesh may not achieve the levels above.

The read-out under them gives the resulting base and surface cell sizes and an estimated cell count. It turns amber when the estimate exceeds Max cells.

Add a volumetric region

Press + Add refinement region.
Set Shape — box or sphere.
Set Mode:
- inside — refine cells within the shape.
- outside — refine cells beyond it.
- distance — refine within a Distance of the shape.
Set Level — the refinement level applied inside the region.
For a box, size it with Ahead, Wake, Sides, Above and Below. These are in body lengths (L) off the geometry bounding box, so a wake box is a large Wake and modest values elsewhere.

Each region card has an enable/disable link and a ✕ to remove it. Disabled regions stay in the case and are not meshed.

Then re-mesh

Press Generate mesh. Refinement regions have no effect until the mesh is regenerated — the viewport preview follows the settings live, the mesh on disk does not, and Mesh says so when the two have diverged.

Check it worked

The cell-count estimate on Refinements rose by roughly the factor you expected.
After meshing, Quality still passes: refinement that pushes non-orthogonality or skewness up has cost you more than it bought.
In the viewport, set the Display Mode to Mesh or Slice under Geometry and confirm the small cells are where you put the region.

Why the levels matter rather than a target size: Concepts.