VOF PLEASE HELP!!!!!

Matthew Roberts

HELP!

I wish to model 3D turbulent flow and water surface superelevation in open channel meandering rivers. My channel geometry consists of three 180 degree constant radius of

curvature bends, rectangular in cross-section. I have split the inlet face in gambit along the air/water interface and in fluent given a vol. fraction 1.0 to phase 2(water) for the

water inlet and a vol. fraction 0.0 to phase 2(water) for the air inlet.

Q1: Do I need to patch the initial volume of water/air into the channel(as this is complex) or can I simply let the VOF model determine the liquid/gas interface as the fluid

flows through the geometry, since I'm using an unsteady solver?

Q2: When I initialise the entire flow field the options available to provide flow velocities are in the cartesian x,y,z coordinate directions, however this is not applicable when

providing an initial guess for the flow around a bend! At present I am simply leaving the velocities as the default zero. Is there a way of specifying a downstream velocity

parallel to the channel walls to reduce the convergence time?

Q3: Finally, I have specified the air and water inlets as velocity inlets, is OUTFLOW the best BC for the outlet or should I use PRESSURE OUTLET? Also what about the

BC along the upper surface ABOVE the air as I want to ensure its an "open channel", do I specify SYMMETRY of PRESSURE INLET (as detailed in the tutorial guide)?

Any advice would be gratefully appreciated, Cheers Mat