Multiphase VoF Problem
 

I'm trying to simulate a 2D gravity driven flow in a V funnel (image attached). I’m using multiphase explicit VOF with courant number = 1. Phase 1 is air and phase 2 is a Bingham fluid. The flow is transient with gravity ON.


The outlet BC is pressure outlet (0 Pa) with backflow vol. fraction of phase 2 = 1
The inlet BC is pressure inlet (rho * g * h) with vol. fraction of phase 2 = 0


In this case the fluid flows unrealistically fast. The flow expected at ~2s is reached at ~0.2s.


I tried an inlet BC of pressure outlet (0 Pa) with backflow vol. fraction of phase 2 = 0. This was based on a tank drainage tutorial from YouTube. This BC works accurately for water but not for non-Newtonian laminar case.


Is there some pressure setting or solution method that I’m missing here. Any help would be appreciated.