Periodic Flow Condition
The Periodic Flow Condition splits its selection into a source group and a destination group. Fluid that leaves the domain through one of the destination boundaries enters the domain through the corresponding source boundary. This corresponds to a situation where the geometry is a periodic part of a larger geometry. If the boundaries are not parallel to each other, the velocity vector is automatically transformed.
If the boundaries are curved, it is recommended to only include two boundaries.
No input is required when Compressible flow (Ma<0.3) is selected for Compressibility under the Physical Model section for the physics interface. Typically when a periodic boundary condition is used with a compressible flow, the pressure is the same at both boundaries and the flow is driven by a volume force.
PRESSURE DIFFERENCE
This section is available when Incompressible flow is selected for Compressibility under the Physical Model section for the physics interface.
A value or expression should be specified for the Pressure difference, psrc − pdst. This pressure difference can, for example, drive the fully developed flow in a channel.
To set up a periodic boundary condition, both boundaries must be selected in the Periodic Flow Condition node. COMSOL Multiphysics automatically assigns one boundary as the source and the other as the destination. To manually set the destination selection, a Destination Selection subnode is available from the context menu (by right-clicking the parent node) or from the Physics toolbar, Attributes menu. All destination sides must be connected.
Constraint Settings
This section is displayed by clicking the Show button () and selecting Advanced Physics Options.
Orientation of Source
For information about the Orientation of Source section, see Orientation of Source and Destination in the COMSOL Multiphysics Reference Manual.
This boundary condition is not compatible with the projection method equation form.