POLYFLOW - Conflict of velocity boundary conditions

Some flow situations may require to impose velocity boundary conditions that are not necessarily compatible. A typical example occurs when boundaries A and B are perpendicular to each other, and when a vanishing velocity is imposed along boundary A while a non-zero normal velocity component is imposed on boundary B. The conflict appears at the intersection between these boundaries, where a decision is made by te program.
This concerns all versions of POLYFLOW.
In order to circumvent this trouble, the user may proceed as follows.
- Impose the zero velocity boundary condition on the first wall
- Select vanishing forces on the second wall
- Impose the required velocity conditions on the second wall by means of a sub-model. Another way consists of replacing the vanishing velocity condition by a slipping condition with a high coefficient in the slipping law (this will guarantee that a nearly vanishing velocity is obtained).
This solution can also be applied when a non-vanishing tangential velocity is imposed; there the definition of the slipping boundary condition must involve the definition of the required non-vanishing wall velocity.

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