Troubled CFD Simulation

Chuck Leakeas

I have a unconfined circular impinging jet problem that has variable fluid properties and buoyancy effects present in the flow field. The jet is facing vertically upward along the axial direction. I have much trouble with this simulation when I add in the effects of buoyancy and variable fluid properties. The b.c. on the vertical stationary free surface is found from the continuity eqn. to be du/dr = -u/r in axisymmetric form. The hortzontal boundary is also a stationary free surface whose b.c. becomes dv/dz = 0, again from continuity eqn. The code is a collocated form of the SIMPLE method using the Power Law method for the convection terms. The flow is steady and laminar with a Re number through the jet of about 100. When I have no buoyancy and variable fluid properties the solution looks very good. When the other effects are added this problem turns into a nightmare! If the solution converges it does not look physically realistic. The program has already solved this problem with a coarser grid so I don't think there's a bug in the code, but now that I refine the mesh I have this problem. Even before I had much trouble solving this with the coarser grid but I managed to get to the solution. If anyone has any insight into this problem could you please contact me or response in this discussion group.