What happens to the velocity of subsonic air as it passes through a convergent nozzle?

As subsonic air passes through a convergent nozzle, its velocity increases due to the principle of conservation of mass, often referred to as the continuity equation. In a convergent nozzle, the cross-sectional area decreases, and for the mass flow rate to remain constant, the air must move faster as it exits the nozzle. This is an application of Bernoulli's principle, which dictates that as the velocity of a fluid increases, its pressure decreases.

In subsonic flow, as air accelerates through the narrowing passage of the nozzle, kinetic energy increases while pressure energy decreases, leading to an increase in speed until the exit. The transition through a convergent nozzle effectively converts the potential energy associated with pressure into kinetic energy in the form of velocity, resulting in a higher velocity at the nozzle's exit compared to its entry.

This phenomenon is fundamental in aerodynamics and gas dynamics, emphasizing how the design of a nozzle influences airflow characteristics and plays a crucial role in turbine engine performance.