The subsonic inlet section is characterized by a subsonic speed (Mach<1) and a narrowing (convergent) cross-section
The critical section of the nozzle is characterized by flow at the speed of sound (Mach=1)
The expansion part of the nozzle is characterized by a supersonic flow (Mach>1) and a gradually expanding (divergent) cross-section
Efficiency, or nozzle losses, i.e. energy losses of converting pressure energy into kinetic energy, depend on achieving the ideal shape of the nozzle.
A nozzle, slang for a nozzle, is a device for controlling the direction or characteristics of a fluid flow. The nozzle is often formed only by a pipe or an extension with a variable cross-section. The main purpose of a nozzle is to control the speed, direction, weight, shape and/or pressure of the jet coming out of it. In the nozzle, the velocity of the fluid increases at the expense of its pressure energy. A nozzle has the opposite characteristics of a diffuser, the main purpose of which is to reduce velocity and increase pressure