In the world of aerodynamics, there are several branches and sub-branches of different types of aerodynamics. In the big picture the field of aerodynamics can be broken down into external and internal aerodynamics. External aerodynamics is thought of external flow around an isolated body, with the typical example being flow around an aircraft wing section, or perhaps around an automobile. There is typically a far field ambient condition, with an isolated body moving through the field (or you can view it as the fluid moving over the body). Internal aerodynamics is thought of as a flow moving through some confined space or passage, with a prime example being flow through turbomachinery, such as a compressor or turbine. There are other ways to classify aerodynamic flow, such as subsonic flow (Mach No. <0.8, including low Mach No. incompressible flow, say Mach No. <0.3), transonic flow (around Mach No. = 1, say 0.8 to 1.2), supersonic flow (Mach No. > 1.2), and even hypersonic flow (Mach No. >5). Turbomachinery design encompasses the first three types of flow regimes, subsonic through supersonic. So in general, turbomachinery aerodynamics is predominately internal flow, over a range of Mach Numbers.