What is the sonic category of inlet ducts that is not subsonic?

Inlet ducts are designed to manage the airflow into a gas turbine engine effectively. When discussing the sonic categories of inlet ducts, they are categorized based on the Mach number, which is the ratio of the speed of the object to the speed of sound in the surrounding medium.

The correct answer refers to the category of flow where the speed exceeds the speed of sound, which is characterized as supersonic flow. In supersonic flows, the airflow velocity is greater than Mach 1. This type of flow can present unique challenges and design considerations in the construction of inlet ducts, such as shockwave management and flow separation.

Other categories such as hypersonic, transonic, and sonic represent different flow regimes. Hypersonic flow typically refers to speeds greater than Mach 5 and involves even more extreme aerodynamic effects. Transonic flow encompasses speeds around Mach 1, where both subsonic and supersonic flows coexist. Sonic flow, on the other hand, refers to conditions precisely at Mach 1, where the speed of the flow matches the speed of sound.

Thus, supersonic is the appropriate descriptor for inlet ducts that do not operate at subsonic speeds, as it indicates that the flow speed exceeds that threshold.