Hi

Although I've had quite a lot of experience modelling single phase flows using CFD, I would like to know how easy it would be to set up a multi-phase flow problem in CFX-5.7.

My problem is:

1) A simple square tank with an outlet pipe on the top.

2) A inlet water pipe on one of the side walls above the mud layer, i.e. only sucking water in.

3) A mud layer on the bottom of the tank.

4) Water filling the rest of the tank above the mud.

Basically (this might be a bit of an understatement!) would like see under what conditions the mud might get sucked up and out of the outlet.

My questions are:

1) Which multi-phase model should I use?

2) Are there specific grid generation issue's I need to consider above making the grid refined enough in the water/mud interface region.

3) Do you need to initialise the flow domain i.e. set the mud water level before the simulation takes place?

4) What are the major problems and pitfalls of solving such problems?

Regards James

I'd recommend the following general approach: - use an inhomogeneous multiphase calculation - water as continuous phase - mud as dispersed phase - set maximum packing for the mud - activate the solids pressure force for mud as well as a drag law appropriate for high packing (eg, Gidaspow or Wen Yu) - There's probably some physics not accounted for in these settings (eg, how to keep mud 'sticky') but it might be a good start - you do need to initialize the flow domain because the initial conditions will set the amount of mud in the domain - you'll probably need to set your initial pressure field to be consistent with the initial volume fraction field and the buoyancy reference density. See the free surface bump tutorial and the buoyancy documentation for an example and further details. - it probably wouldn't hurt to have a nice grid where you expect the interface to be