Definition
A duct or passage whose internal cross-sectional area decreases from inlet to outlet, causing subsonic gas flowing through it to accelerate and its static pressure to drop.
Plain English
A pipe or channel that gets narrower along its length. As air or exhaust gas moves through it, the gas speeds up and its pressure falls.
Context Anchor
Seen in aircraft engine airflow discussions, especially gas turbine inlet, compressor, diffuser, and exhaust nozzle sections.
Derivation
From the Latin convergere, meaning 'to incline together' or 'to come together.' The walls of the duct converge toward each other, narrowing the passage.
Why Pilots Care
It increases exhaust velocity to help produce thrust in turbojet and turbofan engines.
Analogy
Like putting your thumb partly over a garden hose: the same amount of water has less room to pass, so it speeds up as it leaves.
Intuition Check
Do not read “convergent” as simply meaning two things point toward each other. Here it means the passage area gets smaller in the direction the air or gas is moving.
Example Sentence 1
The exhaust section of the turbojet uses a convergent duct to accelerate the gases as they leave the engine.
Example Sentence 2
Mechanics inspected the convergent duct section of the compressor for wear that could affect airflow speed.