Aerodynamics problems have been divided into two main branches: external and internal. The external aerodynamics studies how the air flows around the solid objects, while the internal aerodynamics studies how the air flows through the interior components of these objects, such as the jet engine or the air conditioning pipe.
A second classification is divided into below, near or above the speed of sound. Subsonic is the nomenclature for problems below the speed of sound, transonic for speed below and above the speed of sound, supersonic for speeds higher than the speed of sound and hypersonic for speeds exceeding much the sound barrier, roughly over Mach 5 and above.
- Subsonic aerodynamics. When the fluids flowing a certain object have the properties of inviscid, incompressible and irrotational, it has rached a potential flow and can be called subsonic flight aerodynamics.
- Transonic aerodynamics. It refers to speeds between Mach 0.8 and 1.2. Some flight from this category might become supersonic just in some parts of the aircraft airflow, while other might remain subsonic.
- Supersonic aerodynamics. The supersonic aerodynamics involve speeds greater than the speed of sound, thus Mach 1. In supersonic flow, fluids react differently than in the subsonic flight. At the speed of sounds, fluids build a stagnation pressure over the body of the flight object. The most visual demonstration is when the fluid strike an object. The disturbance changes the flow pattern, and gives the impression that the air or the fluid knows that the flight object is there and is avoiding it on purpose. Also, at these speeds, when the fluid touches the body of the flight object it makes it change its properties: pressure, density, temperature, causing an irreversible shock wave. The shock wave is the main clue that the supersonic flight is achieved.
- Hypersonic aerodynamics. Since 1970, scientists agreed that only the flight above Mach 5 can be considered hypersonic flights. It is characterised by the temperature flow behind the shock wave, chemical presence of the gas, present in the rocket flight.