Hydrodynamics is a special part of theoretical physics or applied mathematics which investigates the equation of flow of fluids. This equation is very nonlinear, and therefore it is very difficult to study hydrodynamics both theoretically and numerically. Complex Hydrodynamics studies dynamics of complex fluids or fluids in complex geometries. Nanohydrodynamics studies dynamics of fluids inside of various nanopores and nano channels. The field is very fascinating, as resulting dynamics can be absolutely non trivial, which is not possible to guess.
Example of research
Zatovsky A.V.†, Zvelindovsky, A.V. “Hydrodynamic fluctuations of a liquid with anisotropic molecules” Physica A 298 (2001) 237-254.