Sample Surfaces

Sample Surfaces#

Sample surfaces are imported surface geometries used for extracting and analyzing flow field data at specific locations within the simulation domain.

Overview#

Sample surfaces allow you to use arbitrary surface geometries in the flow field to capture detailed flow properties. Unlike slices (which are planar and created in the GUI), sample surfaces can conform to complex shapes imported from external files, providing flexibility for flow analysis in regions of interest.

Sample surfaces are accessed through the Resource panel (see Top Bar), alongside geometry resources.

Note

A sample surface is a monitoring entity: a non-manifold surface used to measure quantities at internal locations. It is distinct from a baffle face, which is a non-manifold input face that the GeometryAI mesher removes or thickens during meshing preprocessing (see Baffle face treatment). The key difference: a baffle face is part of the input geometry processed by the mesher, whereas a sample surface is not represented in the mesh (the flow solution is sampled onto it).

Importing Sample Surfaces#

To import a sample surface:

  1. Open the Resource panel

  2. Select the Sample surface tab

  3. Click the Import button

  4. Select a surface geometry file to import

  5. The imported sample surface will appear in the Sample surfaces section of the Entities browser

Supported Formats#

Sample surfaces can be imported from STL, CGNS or UGRID files. These three formats are the complete set.

Points to observe when preparing the file:

  • A UGRID file must be uploaded together with its .mapbc file.

  • Volume mesh files in UGRID or CGNS format are also accepted; their boundary faces become the sample surface.

  • The file must be uncompressed. An archived file (for example .gz) is rejected when the case runs.

  • All patches and zones in the file are merged into one sample surface. Named boundaries inside a CGNS or UGRID file do not appear as separate output surfaces.

  • Coordinates are read exactly as stored, in the coordinate frame and length unit of the volume mesh. No unit conversion is applied, so convert the file before importing it if it was authored in different units.

To reposition an imported surface without editing the file, assign it to a coordinate system; the system’s translation, rotation and scaling are applied to the surface.

Using Sample Surfaces#

A sample surface can be assigned to a Surface Output, a Time-averaging Surface Output (mean values only) and a Surface Integral Output. It is not available for boundary conditions, mesh refinement or the other output types.

Because the solution is interpolated onto the surface from the volume mesh rather than computed on it, the surface-specific wall fields (Cf, yPlus, heatFlux and similar) cannot be requested on a sample surface. Only volume fields and the surface’s own solution.node_unit_normal are available.

A single Surface Integral Output cannot mix sample surfaces with simulation surfaces; create separate outputs if you need both.

Warning

A sample surface is never trimmed to fit the geometry. Nodes lying inside a solid body or outside the mesh are written as NaN in a surface output and dropped from a surface integral, so an integral can silently cover only part of the surface. The solver log lists every skipped node.

See also