Best practices

Recommended settings for GeometryAI meshing, followed by how to define the fluid domain for the common simulation scenarios. The parameters themselves are described in How GeometryAI works.

Recommended settings

Start from the defaults, generate a first mesh, and adjust locally from there. The table gives a sensible starting point for each of the main parameters and when to change it.

Parameter	Recommended starting point	When to adjust
Geometry accuracy WebUI · geometry_accuracy · details	Default global value	Refine locally with a geometry refinement rather than lowering it globally. If the process log reports early termination, coarsen the global value or move the fine accuracy into a local refinement.
Surface max edge length WebUI · surface_max_edge_length · details	Generous (large) global value	Keep it generous so it does not silently dominate the node-count target; tighten it locally with a surface refinement only where finer elements are needed.
Target surface node count WebUI · target_surface_node_count · details	The primary lever for overall mesh size	For a refinement study, scale it by x and Surface max edge length by 1 / sqrt(x) together (see Running a mesh refinement study).
Preserve thin geometry WebUI · preserve_thin_geometry · details	Off; enable only where needed	Turn on, ideally through a local geometry refinement, for thin parts such as trailing edges and fins, keeping the rest of the mesh coarse.
Sealing size and Remove hidden geometry WebUI · sealing_size · remove_hidden_geometry · details	Use for dirty or non-watertight CAD	Prefer these cleanup options over manual CAD repair; together they handle most production geometries.
Symmetry plane (half-model) WebUI · details	Use for symmetric, zero-yaw cases	Roughly halves the mesh size.

For general meshing guidance that applies across all workflows, see the meshing knowledge base.

Running a mesh refinement study

To study mesh convergence, scale the whole surface mesh up or down consistently rather than changing one parameter in isolation. The recommended approach uses Target surface node count (WebUI, target_surface_node_count) as the single driver:

• Multiply Target surface node count by a refinement factor x (for example 2 for a finer level, 0.5 for a coarser one).

• Scale Surface max edge length (WebUI, surface_max_edge_length) by 1 / sqrt(x) at the same time. Node density on a surface scales with the inverse square of the edge length, so this keeps the edge-length cap consistent with the requested node count and prevents it from binding unexpectedly between levels.

Keeping the two in step means the curvature scaling continues to drive the mesh at every level, so successive meshes differ by a controlled, roughly uniform factor. If Surface max edge length is left fixed while only the node count changes, it will eventually become the binding constraint and the meshes will stop refining as expected (see Target surface node count under Controlling the surface mesh).

Defining the fluid domain

When the GeometryAI (GAI) workflow meshes an assembly, it has to decide which surfaces bound the fluid and which sit outside it. Three controls drive that decision, and they are independent of one another:

• Mesh exterior (WebUI), set per body group, declares which side of a body the fluid is on (outside or inside).

• Remove hidden geometry (WebUI, remove_hidden_geometry), a single global toggle, decides whether occluded interior faces are discarded.

• Seed point volumes (WebUI, SeedpointVolume) select which connected region is the fluid; the flood starts from them.

This section explains what each control does, how they combine, and which combination to use for the common simulation scenarios. The mechanics of generating the zones themselves (custom volumes, custom zones, the flood-fill workflow) are covered in Volume Mesher; this section is about choosing the settings that delimit the domain.

Note

These controls apply to the GAI surface mesher workflow. See Meshing for how the beta mesher and GAI toggles select each workflow.

Mesh exterior

Mesh exterior (WebUI), written mesh_exterior in the body-group settings, is a per-body-group flag (true by default) that declares which side of a body the fluid is on:

• true (the default): the fluid is outside the body. The body is a solid the flow passes around, such as the object of study (a car, an aircraft, a building).

• false: the fluid is inside the body. The body is an enclosure whose interior is meshed and whose faces bound the domain from the outside, such as a wind tunnel or a user-defined farfield.

The fluid domain is the region that is outside every mesh_exterior=true body and inside every mesh_exterior=false body. For a car inside a wind tunnel, that is exactly the gap between them: outside the car and inside the tunnel.

Because it defaults to true, most cases never set it explicitly: an external-aerodynamics model, and the walls that bound an internal-flow cavity, all keep the default. You only set false on a body that should contain the fluid, such as an enclosing wind tunnel or user-defined farfield. Setting such an enclosing body to true instead would tell the mesher the fluid is outside it, which is not what you want, and a seed point cannot make up for it (see the seed does not replace the flag below).

Set mesh_exterior on each body group from the geometry browser; see GUI Guide: Geometry for the control.

Note

mesh_exterior is a beta feature and its interface may change.

Remove hidden geometry

Remove hidden geometry (WebUI, remove_hidden_geometry) is a single global toggle (off by default, GAI surface mesher only). When it is on, face classification runs on the mesh_exterior=true bodies and drops the faces that the flow can never reach, for example the seats inside a closed car body or the components inside an engine bay. Bodies set to mesh_exterior=false are not classified and are therefore unaffected.

With the toggle off you still obtain a valid mesh, but the occluded interior surfaces are retained, which adds elements that do not contribute to the external solution. Turn it on when the geometry carries interior parts that are hidden from the flow.

The parameter itself, together with Min passage size (min_passage_size) and Remove baffle faces (remove_baffle_faces), is described under Cleaning up the geometry.

Seed points and flooding

Within the fluid side defined by mesh_exterior, the mesher picks the connected region to mesh by flooding it from one or more seed points. When no seed point is supplied, the default seeds are the corners of the geometry bounding box, which is what makes ordinary external-aerodynamics cases work without any explicit seeding.

The seed selects and orients the fluid region; it does not change which side of a body is fluid. Place the seed outside the object for external aerodynamics, inside the enclosed region for internal flow (for example the cabin of an HVAC model), and in the gap between the model and an enclosing wind tunnel.

Important

A seed point is not a substitute for mesh_exterior. Seeding inside a body that is left at mesh_exterior=true does not turn its interior into the fluid domain; the flag, not the seed, decides which side of each body is fluid. An enclosing wind tunnel must therefore be mesh_exterior=false regardless of where the seed is placed.

Defining a Seed point volume explicitly (WebUI, point_in_mesh) is covered on the seed point volume page of the WebUI guide and, on the Python side, in Volume Mesher.

Choosing settings per scenario

The table below summarises the typical combination for each common scenario. Default seeding means the bounding-box corner seeds, with no explicit seed point.

Scenario	Mesh exterior	Remove hidden geometry	Seeding
External aerodynamics (car, aircraft) with an automated farfield	true on the model	On if the model has hidden interior parts; otherwise off	Default seeding (outside the model)
Internal flow (HVAC, duct, manifold)	true on the bodies bounding the cavity	Usually on, to discard surfaces outside the cavity	Seed point inside the cavity
Wind tunnel or user-defined farfield enclosing a model	false on the tunnel/farfield body, true on the model inside it	As needed on the model	Seed point in the gap between the model and the enclosure
Porous media	true on the model	As needed	Seed so the porous medium lies inside the meshed domain

Fluid-domain classification for the common scenarios. mesh_exterior sets which side of each body is fluid (outside a true body, inside a false body), and the seed selects the connected region to mesh.

See also

• Body-group setup: GUI Guide: Geometry

• Hidden-geometry and mesh defaults: mesh parameters

• Farfield types: farfield

• Seed-point volumes: seed point volume

• Zone generation and the flood-fill workflow: Volume Mesher

• Python API: meshing reference

Comparison with a standard wrapper

The comparisons below show the input geometry, the result of a standard wrapper, and the GeometryAI surface for the same detailed regions. The red arrows highlight regions where the standard wrapper produces defects (intersections or non-manifold elements) that GeometryAI avoids.

Wing mirror and A-pillar: input geometry, a standard wrapper, and GeometryAI.

Input geometry	Standard wrapper	GeometryAI

Engine bay: input geometry, a standard wrapper, and GeometryAI.

Input geometry	Standard wrapper	GeometryAI