What characterizes supersonic flow?

Supersonic flow is characterized by a Mach number that is greater than 1. The Mach number, defined as the ratio of the flow velocity to the speed of sound in the medium, indicates whether the flow is subsonic, sonic, or supersonic. When the Mach number exceeds 1, it signifies that the flow velocity is greater than the speed of sound, resulting in characteristics such as shock waves and changes in pressure and temperature. This distinction is fundamental in fluid dynamics and aerodynamics, affecting the design and analysis of systems like aircraft and nozzles.

In contrast, a Mach number equal to 1 indicates sonic flow, where the flow speed matches the speed of sound, while a Mach number less than 1 indicates subsonic flow, where the speed of the flow is below the speed of sound. The concept of a Mach number not being defined does not apply as there is always a defined speed of sound relative to the medium. Thus, identifying supersonic flow requires recognizing that the Mach number must be greater than 1.