hydrodynamics is the field of water (and other liquid) dynamics and thermodynamics has some role in it, even if constrained by the incompressible assumption of a liquid.

Dear Ma, the combustion process including air flow rate, liquid or gaseous fuel, flame, combustion products is one of the more important processes where fluid(hydro)dynamics and thermodynamics are related by Navier-Stokes equations and Energy equation: velocity, pressure and temperature fields influence each other.

Gianluca

Hydrodynamic is the field where the interest of flow behavior, velocity, pressure, mass flow rate .... thermodynamic is the field where the interest is energy, heat, entropy exergy and thermal-diffusion in resume the heat state of the system. the relation between two fields is, that in thermodynamic system is in its dynamic state, where we using its mass flow or it's pressure drop or another hydrodynamic parameter for defining the state energetic or thermal for an system.