What is nozzle choking?

Nozzle choking occurs in fluid dynamics when the flow velocity at the nozzle's exit reaches the speed of sound, resulting in the flow becoming sonic. This phenomenon typically happens in converging nozzles when the pressure ratio between the upstream and downstream conditions is sufficiently high. Once choking occurs, any further decrease in downstream pressure does not increase the mass flow rate, as the flow becomes limited by the sonic speed at the nozzle's throat. Choking is a critical concept in the design and operation of rocket engines and gas turbines, as it influences performance and efficiency.