Periodic boundary conditions are used when the physical geometry of interest and the expected flow pattern have a periodically repeating nature. This means that the flows across two opposite planes in your computational model are identical. Periodic boundary conditions can be applied to a pair of boundary sections, which are referred to as the inlet and outlet of the periodic condition. The velocity profile for the inlet and outlet will be the same, but a difference of normal force or pressure will be allowed between them.
To define periodic boundary conditions on a pair of boundary sections, select one of them (the order is not significant) and follow these steps:
Select the Inlet of periodic condition menu item in the list of boundary condition choices.
Inlet of periodic condition
In the resulting Inlet of periodic cond. panel, select the corresponding periodic boundary section (the outlet of the periodic condition) and click Select.
Specify the transformation of coordinates and velocity field on the inlet to those along the outlet. There are two ways to do this:
Specify a rotation matrix and/or translation vector explicitly. For rotational periodicity, specify the rotation matrix.
Direct modification of rotation matrix
For translational periodicity, specify the translation vector.
Direct modification of translation vector
The rotation matrix and/or translation vector, once applied to the coordinates of a node along the inlet, will produce the coordinates of the corresponding node along the outlet.
Specify a pair of corresponding points, one on the inlet and one on the outlet.
Definition by source-target points
Ansys Polyflow will determine the proper rotation matrix and translation vector based on these two points, and then apply it to the rest of the points on the inlet to obtain the points on the outlet.
Check the transformation to be sure it is consistent with the mesh.
Test of the transformation
When you are satisfied with the inputs, accept the settings.
Accept current parameters
Specify either the flow rate
Flow rate imposed
or the difference in normal force
Normal force imposed
between the inlet and the outlet.
Note that there are no inputs for the outlet of the periodic condition.