Some Notes on Boundary Conditions

Some Notes on Boundary Conditions

An effect of dividing the momentum equations with

respectively is that for example ud obtains a value even if

. In many cases ud will tend to uc in lack of a dispersed phase. So on inlets where

, it is appropriate to set ud=uc.

A fixed value for

should only be prescribed if there is no transport of

toward the inlet. If, for example, a cloud of dispersed phase with higher

than the prescribed value somehow reaches the inlet,

will actually be “consumed”.

When specifying a dispersed phase flux, make sure to specify an appropriate velocity to go with the flux to avoid nonphysical concentrations of

close to the boundary.

At walls, where it is possible to prescribe a wall leakage, the continuous phase normal velocity is set to

For a dispersed phase leakage:

Wall leakage for one phase works best if combined with slip condition for the other phase so that the mixture is given maximum freedom to react to the leakage.