For this summer, I will do some projects related to fluid surface reconstruction. And it is very important to have some flexible solvers for partial derivative equations, like Navier Stokes equations. I searched on-line, and it took me some time to find this. http://www.innovative-cfd.com/cfd-solver.html. Some good non-commercial solvers for computational fluid dynamics are as followings, Wind-US, OpenFOAM, CFL3D, OVERFLOW, USM3D, Gerris and etc.