Improve mesh quality

Change the mesh when instability follows highly stretched cells, abrupt size transitions, or unnecessary geometric detail.

Reduce cell aspect ratio

Lower mesh_settings.max_aspect_ratio to restrict the ratio between cell widths on different axes. This can make pressure, energy, and other diffusion-dominated systems easier to solve, but it adds mesh planes and can increase the total cell count substantially.

Run a dry run after each change and compare the cell count and narrowest cells before committing to a full solve.

Smooth cell-size transitions

Lower max_growth_rate when adjacent cell widths change too abruptly. If the problem starts in a wall-normal region, also review boundary_layer_growth_rate. These limits spread fine resolution farther from its source, increasing cell count in exchange for smoother transitions.

Remove unintended mesh complexity

Closely spaced component faces, tiny cuboids, and preserved CAD vertices can create sliver cells or propagate fine planes through the rectilinear mesh.

• Increase fuse_threshold only enough to merge near-coincident planes that do not represent required geometry.
• Increase bbox_cull_threshold only for cuboids that are safe to remove completely.
• Disable preserve_cad_vertices when detailed or curved CAD creates unnecessary fixed planes.

Fusing can move faces, close gaps, or collapse components; culling removes components rather than coarsening them. Inspect the dry-run geometry after either change and confirm that required passages, thicknesses, and contacts remain.

After improving the mesh, rerun with the same physical model and numerics. This separates the effect of mesh conditioning from later preset, relaxation, or preconditioner changes.

See also

• Mesh resolution and controls explains aspect ratio, growth, fusing, and culling.
• Rectilinear meshing explains why local detail can affect a complete axis.
• Configure the mesh shows how to adjust cell sizes and growth limits.