if anyone has time to play with it (I do not right now) this might be something worthwile. take a look at the example I linked to... http://gfs.sourceforge.net/wiki/index.php/Main_Page http://gfs.sourceforge.net/examples...tml#htoc10
If you're looking into free CFD codes I've heard good things about OpenFOAM. I've never used it but it sounds like a pretty decent code if you're into that sort of thing. Personally I like STAR-CCM+ but thats a little pricy for most people here.