Nitsche Constraints
Some boundary conditions are implemented using Nitsche constraints. These boundary conditions include
•
Wall
— Slip, sliding walls, and moving walls (that is, walls with nonzero translational velocity).
•
Periodic Flow Condition
•
Flow Continuity
The formulation used in the Fluid Flow interfaces in single-phase flow interfaces corresponds to the Symmetric Interior Penalty Galerkin method (SIPG). The SIPG method can be regarded to satisfy the boundary conditions in an integral sense rather than pointwise. More information on SIPG can be found in
Ref. 15
.
In particular, the SIPG formulation includes a penalty parameter that must be large enough for the formulation to be coercive. The higher the value, the better the boundary condition is fulfilled, but a too high value results in an ill-conditioned equation system. The penalty parameter is implemented according to
Ref. 16
.