I am trying to find a paper that I saw about a year ago. I am not sure of the actual date of the paper.
I believe it was a finite difference CFD paper. The interesting part of the paper was the addition of a single degree of freedom variable to all of the mass conservation equations. This residual mass conservation variable was included to stabilize the iteration of their scheme.
Alternatively, I would be interested in suggestions on handling convergence issues that may be caused by replacing one of the mass conservation equations with a pressure average along the outlet of the fluid domain.
I am also considering switching to the pressure Poisson equations with a projection method to be selected later.