In the field of astrophysics, the term hydrodynamics is commonly
used for fluid dynamics, the study of forces and motion in bodies
of liquids or gases. In some scientific/engineering fields, the
term is used more specifically to refer to the dynamics of
non-compressible fluids, i.e., liquids, reserving the term
aerodynamics for the dynamics of gases. (In astrophysics, there
do exist circumstances where the formulae for non-compressible fluids are
useful approximations of the dynamics of gases.)
A simulation of fluid flows (hydrodynamic model
or hydrodynamical model) can be used for modeling Earth
oceans or atmosphere, or the same for atmospheres of
astronomical bodies.
Magnetohydrodynamics (MHD) is the study of electrically conducting fluids (either
liquid or gas) in motion and their interaction with coincident
electric and magnetic fields. Other subclasses of hydrodynamics: