Cases

Any field can be overridden by its dotted path — on the command line (--set flow.mach=0.6), in a job request ("overrides": {"flow.mach": 0.6}) or in a pipeline stage. Unknown paths are rejected (by the service with a hint); values are validated against the schema.

A --set value is read as JSON (numbers, true/false, null, lists); anything else is text. A number or true/false given for a field that holds text stays text, so --set mesh.params.code=2412 is the string "2412"; a quoted JSON string ('"2412"') is always a string.

file reads an external mesh; mesh.geometry_order then has no effect, because the file carries its own degree. Formats, the Gmsh recipe, the checks and the service’s mesh store are described under Mesh files.

coordinates replaces the NACA section by a spline fit of arbitrary aerofoil data (trailing edge → upper surface → leading edge → lower surface → trailing edge). nz > 0 extrudes an aerofoil, cylinder or flat-plate section into a spanwise-periodic 3-D mesh of hexahedra (at least three elements across the span). first_cell is the height of the first cell at the wall in chords, measured along the grid line; wall_blend scales the tangent with which the grid lines leave the wall, in units of the line length.

An extruded mesh has the boundary groups of its section and no boundary across the span, and its force coefficients are per unit span (the default reference.area is span). With nz and span the turbulent preset flat_plate_sa becomes a 3-D case with six conserved variables; the wall distance of the turbulence model is that of the section in every spanwise plane. An extruded case with viscous terms or with shock capturing is not the same discrete problem as its section, though. The default penalty of the viscous scheme, which the artificial viscosity of shock capturing uses as well, is the number of faces of an element, 6 for hexahedra and 4 for quadrilaterals (penalty parameter), so the two solutions differ as two discretizations of one flow do, not by round-off. And at any penalty the scheme leaves a viscous extruded solution with a small spanwise velocity that changes sign across the mid-plane of every element. It is driven by the jumps of the in-plane velocity between elements: inside an element the viscous stress is built from the gradient lifted from all faces, on a spanwise face from the local gradient alone.

What the parameters without a description above mean:

params are validated against the generator: an unknown, missing or mistyped parameter is a validation error (422 from the service). pg is not a parameter (set mesh.geometry_order), code must be a quoted 4-digit string, nz is 0 or at least 3, and span is positive.

Defaults follow the generator and the flow model: walls are slip_wall for inviscid and noslip_adiabatic for viscous cases; outer boundaries are farfield; the bump channel and the flat plate use total_inlet / pressure_outlet (the plate also symmetry ahead of its leading edge and farfield on top). A box and a mesh file have no defaults: give a condition for every non-periodic side of the box, and for every boundary group of the file. A missing one is reported when the case is built, not by validation of the specification alone; the service does report it for a mesh file, at POST /cases/validate and on submission, because it reads the stored mesh. A condition for a group the mesh does not have is an error. Override per group:

discretization:
  boundaries: {wall: noslip_isothermal}
flow:
  reynolds: 500
  extra: {t_wall: 1.2}

Available: farfield, slip_wall, symmetry, slip_wall_mirror, noslip_adiabatic, noslip_isothermal, pressure_outlet, total_inlet (formulation).

flow.extra holds boundary data and one model switch, all as plain numbers: t_wall, p_back, pt_in, tt_in (ratios to the free-stream static values) and suth, the non-dimensional Sutherland temperature $S/T_\infty$ — when present, the viscosity follows Sutherland’s law instead of being constant (governing equations).

Three conditions read data from flow.extra: noslip_isothermal needs t_wall, pressure_outlet needs p_back, and total_inlet needs pt_in and tt_in. The bump channel and the flat plate supply defaults: the isentropic total conditions of flow.mach for pt_in and tt_in, and p_back = 1. Elsewhere a missing entry is a validation error that names the boundary group, the condition and the key.

With turbulence: sa two more entries of flow.extra are read: chi_inf, the free-stream ratio $\tilde\nu/\nu$ (default 3), and prt, the turbulent Prandtl number (default 0.9). Mach number, angles, Reynolds number and these model data are differentiable inputs of the discipline.

The reference section sets what the force and moment coefficients are normalised with. The defaults suit the generators (unit chord, quarter-chord moment point); a mesh file usually needs its own.

A wall group is a boundary group with a wall condition (slip_wall, symmetry, slip_wall_mirror, noslip_adiabatic, noslip_isothermal). Without groups the coefficients are integrated over all of them; groups restricts them to the named ones. The coefficients of a component cover the groups of that component in either case.

Which of these to change when a solve does not converge: Troubleshooting.

POST /api/v1/cases/validate (or the agent tool validate_case) resolves a case without solving it and returns the element count, degrees of freedom, block size and the device the service would choose. The digest in the response identifies the exact specification; a job with the same specification and the same requests is served from the result cache as long as the code is unchanged. For a case on a mesh file the digest and the cache key cover the contents of the file, not its name.