Surfaces and Named Selections

Surfaces and Named Selections#

Surfaces (also called named selections or boundary patches) are named regions of the mesh boundary. Properly named surfaces are essential for applying boundary conditions in simulation and for organizing mesh exports.

What Are Named Selections?#

When the mesher generates a mesh, every face on the domain boundary is assigned to a named selection. These names carry through to the simulation setup — boundary conditions (inlet velocity, outlet pressure, wall type) are applied to named selections by name. The solver never sees raw face indices; it sees patch names.

Named selections are created from three sources:

Domain boundaries — Studio automatically names the bounding box faces (inlet, outlet, sides, top, ground) based on domain type and flow direction
CAD surface names — Face or body names from STEP/IGES files are preserved and become named selections automatically
User-defined selections — Any additional groupings you create manually in the Surfaces tab

Auto-Created Named Selections#

When you generate a mesh, Studio creates these named selections automatically:

External Flow#

Named Selection	Description
`inlet`	Upstream face of the domain box
`outlet`	Downstream face of the domain box
`top`	Top face of the domain box
`side_left`, `side_right`	Lateral faces
`ground`	Bottom face (when ground plane is enabled)
`symmetry`	Symmetry cut plane (when enabled)
(geometry face names)	Faces from your CAD file (e.g., `car_body`, `windshield`)

Internal Flow#

Named Selection	Description
`inlet`	Open inlet face(s) detected on the geometry
`outlet`	Open outlet face(s) detected on the geometry
(geometry face names)	Interior wall surfaces from the CAD file

Rotating Machinery#

Named Selection	Description
`inlet`, `outlet`	Domain inlet/outlet
`rotating_wall`	Rotating geometry surfaces
`stationary_wall`	Stationary housing surfaces
`mrf_interface`	Rotating/stationary zone interface

Managing Named Selections#

Viewing and Editing#

Navigate to the Surfaces tab in your workspace
All named selections are listed with their face count and current type
Click a selection to highlight it in the 3D viewer
Rename any selection by clicking the name field

Creating New Selections#

To group multiple CAD faces into a single named selection:

Select multiple faces in the 3D viewer (Shift + click, or drag to box-select)
Click Create Selection in the Surfaces panel
Enter a name for the new selection
All selected faces are merged into this patch

This is useful when a CAD file has many individual face IDs for what should logically be one surface (e.g., a car body split into dozens of separate STEP faces).

Splitting Selections#

To separate faces from an existing selection:

Select the faces you want to split out in the 3D viewer
Click Extract in the Surfaces panel
Assign the extracted faces to a new or existing selection

Recommended Naming Conventions#

Use lowercase names that describe the physical role:

Name	Description
`inlet`	Flow entry surface
`outlet`	Flow exit surface
`wall`	Generic solid wall
`car_body`	Vehicle body
`ground`	Ground plane
`symmetry`	Symmetry plane
`top`, `side_left`, `side_right`	Far-field boundaries
`wheel_front_left`	Specific component surfaces

Tip

Studio’s AI Assistant and boundary condition auto-detection use surface names to assign BCs automatically. Using standard names like inlet, outlet, and wall enables full automation of the simulation setup step.

How Named Selections Are Processed#

When you click Generate Mesh, the following happens on the backend:

The domain geometry and all named selection assignments are serialized and sent to the cloud GPU job
During meshing, the block AMR grid is classified — each block is tagged as fluid, solid, or cut-cell
All boundary faces of the fluid region are assigned to their named selections based on the geometry input
CAD face names from STEP files are matched to faces in the cut-cell mesh using spatial proximity and normal direction
Domain boundary faces (inlet, outlet, sides) are assigned automatically based on their position
The final named selection map is stored with the mesh and used directly in the simulation setup

After meshing, you can view the named selection assignments in the 3D viewer and make any corrections before running a simulation.

Per-Selection Mesh Controls#

For STEP/IGES files with preserved face topology, you can set mesh parameters on individual named selections:

Surface Mesh Size Override#

Override the global cell size for specific surfaces. Useful for:

Finer resolution on aerodynamically important surfaces (leading edges, spoilers)
Coarser resolution on less important surfaces (far-field, housing)

Feature Angle#

Controls how the mesher handles sharp edges. Faces meeting at angles greater than the feature angle threshold are treated as separate geometric features and receive refined AMR at the edge.

Low angle (15–30°) — Captures more edges, finer mesh along features
High angle (45–60°) — Only captures sharp edges, fewer refinement cells

Named Selection Types#

Each named selection has a boundary type that the solver uses to apply the correct physics:

Selection Type	Description
Wall	No-slip solid boundary
Inlet	Flow entry
Outlet	Flow exit
Symmetry	Mirror plane
Far-field	Distant boundary

Types are assigned automatically from surface names and domain type. You can override any assignment in the Surfaces tab.

Auto-Detection#

Studio can automatically identify and name common boundary types:

Domain boundaries — Inlet, outlet, top, sides, ground are named based on position and domain configuration
Geometry surfaces — CAD face names from STEP files are preserved automatically
Open faces — For internal flow, open faces (inlets, outlets) are detected by their exposure to the domain boundary

Use the AI Assistant to trigger auto-detection: “Detect and name the surfaces on my geometry”