I am trying to model a hull as it passes through the water. What I am interested in is the bow wave that is caused by a bluff object passing through a viscous fluid. I understand how to setup the solution in Fluent, but I do not know how to model a free surface problem (i.e. set the boundary conditions) for Fluent 5.0. I can model my volumes, but how do I define and/or mesh what is air & what is water?

I am using Gambit for the modelling.

Any help would be appreciated.

Thank you.

You have to use the VOF approach of FLUENT. In order to resolve the air water interface adequatly, You should start with a moderate grid resolution of the flow field and then refine the mesh near the interface using grid adaption.

But how do I define what is water & what is air? Basically, here is my practice setup. I have a large box (my overall volume) and in the center I have a sphere (my bluff body). I want the sphere to be half submerged at a speed/time of zero. How do I tell Gambit/Fluent that all fluid below the sphere equator is water and all fluid above the sphere equator is air?

Initialize under "SOLVE/Initialize" all cells as "air". Mark all the cells which should contain water using "ADAPT/Region". Then return to "SOLVE/Initialize/Patch" and patch these cells as "water".

Ohhhhhhhhh! So nothing is done in the modeller to specifiy fluid type. Got it, Thank you very much!

I do not know what results you have obtained since August, but I'm involved in the same problem. I'm trying to model a simple ship hull, using an hybrid mesh (tet, wed, hexa) and steady solver

Using only hexa, the results (modelling a cylinder)seem to be good, but using hybrid mesh (and therefore a different setup) the free surface goes down near pressure outlet. There are a lot of problems, if you want we could collaborate.

Best regards