Boundary placement and defaults

Boundary conditions can be defined on:

• outer domain faces, using domain.boundary_conditions; or
• faces of insulating cuboids, using cuboid_components[].boundary_conditions.

Each condition selects a rectangle, circle, annulus, or full patch on an axis-aligned face. Use Select a boundary region to configure one.

Default behavior

Vanellus assigns unconfigured interfaces automatically:

• A fluid–solid interface is a wall to the fluid.
• A fluid–insulating or conducting–insulating interface is adiabatic.
• A fluid–conducting or conducting–conducting interface has no thermal boundary condition. Both regions belong to the thermal domain, so temperature and heat transfer are solved together. See Conducting and insulating domains.
• Unconfigured outer domain faces are walls to fluid and adiabatic to the thermal domain.

Explicit overrides

An explicit condition replaces the default on its selected patch—for example, turning part of a wall into an inlet, outlet, heated patch, or fixed-temperature patch. It selects existing boundary cells; it does not create an opening or change the geometry.

The selected cells must support the condition:

• Fluid conditions, such as inlets and outlets, must lie entirely beside fluid. They cannot be placed on a solid–solid interface.
• Thermal conditions cannot be applied at fluid–conducting or conducting–conducting interfaces: these lie inside the thermal domain, where heat transfer is solved between neighboring cells. An insulating–insulating interface cannot carry a thermal condition either, because temperature is not solved on either side.

CTM and CAD components

Compact thermal models do not accept explicit boundary_conditions. Their resistor network defines the thermal behavior of their faces.

CAD components also do not accept explicit boundary_conditions. Their fluid interfaces are always walls. An insulating CAD component creates adiabatic thermal interfaces; a conducting CAD component joins the thermal domain without an interface condition.

See also

• CAD voxelization explains the stepped cell faces that form CAD interfaces.
• Flow boundary conditions explains what each inlet and outlet imposes.
• Thermal boundary conditions explains fixed temperature, heat flux, radiation, and adiabatic behavior.
• Fan and linked-fan boundaries explains fan-curve coupling.
• Compact thermal models explains the resistor networks that control CTM faces.
• API reference lists the available condition fields and values.