Editing Compressible flow (section)

{{Short description|Branch of fluid mechanics}}
'''Compressible flow''' (or '''gas dynamics''') is the branch of [[fluid mechanics]] that deals with flows having significant changes in fluid [[density]]. While all flows are [[compressibility|compressible]], flows are usually treated as being [[incompressible flow|incompressible]] when the [[Mach number]] (the ratio of the speed of the flow to the speed of sound) is smaller than 0.3 (since the density change due to velocity is about 5% in that case).<ref name="J.D. Anderson 2007">Anderson, J.D., ''Fundamentals of Aerodynamics'', 4th Ed., McGraw–Hill, 2007.</ref> The study of compressible flow is relevant to high-speed aircraft, jet engines, rocket motors, high-speed entry into a planetary atmosphere, gas pipelines, commercial applications such as abrasive blasting, and many other fields.