What is the relationship between fluid dynamics, hydrodynamics, and aerodynamics?
Answers
Answer:
Hydrodynamics = mechanics of liquid (incompressible fluids), inside ducts and also in open channels and shallow flows. They are essentially isothermal, only friction must be considered in very special cases.
Aerodynamics = mechanics of air flows, normally in extensive domains over solid obstacles (i.e., for application to atmospheric flight and re-entry), wherein ideal and boundary layer flow are important. (However, general air or gas dynamics can be studied also inside ducts.) For low speeds (Mach number squared much less than unity) without heat transfer, it is equivalent to the flow of a liquid. For high speeds, heating by compression and friction become relevant. In supersonic flows, mechanics is very complex because shock waves appear. (Curiously, this is analogous to hydraulic jumps and flow of a liquid in an open channel.)
Fluid mechanics (or dynamics) = all above, plus some additional questions not normally covered, such as capillary flows, fluid dynamic lubrication, and some others.