No one has mentioned OpenFOAM?
I know nothing about CFD (except that I see a huge amount of amateur stuff on the web that is obviously quite wrong eg in calculated Cd figures) but I know of an aerodynamicist using a professional(?) version of OpenFOAM.
Maybe I'm just dumb, but no one has quite explained how you develop the shape of
your car to model in CFD - 3D scanning?
OpenFoam is
here.