Hydrodynamics

Perhaps compressibility for one.

Your instructor should be able to answer this question for you, in the proper context for your level of knowledge.

Hydrodynamics (incompressible fluids) is much easier than aerodynamics. I would swat up on hydro first and when you're thoroughly at home with that move on to aero. If you already know something about aero you should have no problem with hydro.

This is a well understood question for those who are versed in the subject.

Its thirty years since I did any of this but as I recall the lower velocity aerodynamic stuff is essential incompressible (as for hydrodynamics), and "science" can be (and is) substituted for the other once the model sizes and velocities are correctly scaled. Part of this scaling also involves the proper recognition of differences in viscosity and density etc. which include Reynolds number and the like.

Why don't you get yourself access to a good book on the subject and start reading. It will take more than a couple of posts from here to know enough to not be "dangerous".

Cavitation applies to liquids but not to gases. Apart from that...

But there are things that apply to gases but not to liquids, compressibilty for one.

The other replies are correct....hydrodynamics is easier than aerodynamics in most applications. But why wouold you use aerodynamic formulae when there are so many texts with al the hydrodynamics equations you need?

I would suggest finding a copy of Crane Technical Paper 410; it is practically a bible for hydrodynamics and contains a wealth of information. Another good resource is Cameron Hydraulic Data from Flow Serve Corp. Lastly, the Mechanical Engineering Review Manual for the PE exam is also good and covers both topics.

The fundamental formulas (for lift and drag) are the same, provided compressiblity is not an issue (in things the size of an airplane, at speeds that are significantly subsonic). Mass density of the fluids are of course different.

However, hydrodynamics can include what happens at the interface between air and water, (as in planing behavior vs displacement behavior in boats) and as a result hydrodynamics (as it applies to boats) is more complicated than most aerodynamics. For instance, in about 15 seconds you can calculate the basic lift and drag of an airplane wing. The classic paper on calculating planing resistance for boats is by Savitsky, and goes on for 20-some pages.

As someone else mentioned, cavitation and ventilation are phenomena that must be considered in hydrodynamics but not aerodynamics.