OpenFOAM

OpenFOAM is a suete of software tools designed to address finite volume problems, similar to Ansys FLuent/CFX. It has seen widespread usage in industry and acadamia at institutions such as Boeing, Volkswagen, and MIT. Like all open source software, OpenFOAM may be freely modified to create custom solutions to challenging problems. Since it is amenable to automation, it is a good choice for parametric studies or as a component of a systems simulation.

Read more about OpenFOAM here