What is Sonic number?

The Sonic number is a concept in fluid dynamics that characterizes the flow of fluid around a body, particularly in relation to the speed of sound in the medium. It is defined as the ratio of the flow velocity to the speed of sound in that fluid. This number is crucial in applications involving compressible flows, such as aerodynamics and aerospace engineering, as it helps determine whether a flow is subsonic, transonic, supersonic, or hypersonic. The Sonic number can influence the design and performance of vehicles and structures interacting with high-speed flows.