I have to solve a simulation of fluid flow on Ansys, but my prof wants me to run a parallel simulation using the Volume of Fluid method in something with more visible guts than Ansys? Any recommendations, or should I try doing it in Matlab?
I would advise against using MATLAB - you will be spending too much time reinventing the wheel. OpenFOAM has a VoF implementation readily available (interFoam), and you can find hints on adding solidification phase change code here. There are other, more sophisticated, open source codes such as Gerris and Paris, but you may find it more difficult to add phase change. If you're into finite elements, also have a look at Elmer.