Definition
A duct whose internal cross-sectional area increases in the direction of airflow, causing subsonic air passing through it to slow down and rise in static pressure.
Plain English
A passage that gets wider as the air moves through it. As the space opens up, the air slows down and its pressure goes up.
Context Anchor
Seen in aircraft air ducts, engine air passages, ventilation systems, and discussions of airflow through aircraft structures.
Derivation
From the Latin divergere, meaning 'to bend away' or 'to spread apart.' A diverging duct literally spreads apart along its length, which matches what the walls of the duct are doing.
Why Pilots Care
Diverging ducts are how engines and systems trade air speed for pressure. In a turbine engine diffuser, for example, fast-moving air from the compressor is slowed in a diverging duct so it enters the combustion section at higher pressure and a usable speed.
Analogy
Think of air moving through a hallway that gradually gets wider. The passage is still guiding the air, but the space available to the air is increasing.
Grounding Statement
Picture a cone-shaped tube with the narrow end at the inlet and the wide end at the outlet. Air enters fast and tightly packed in the narrow end, then spreads out and slows as the tube opens up, leaving the wide end at higher pressure but lower speed.
Intuition Check
Do not read diverging as meaning the duct splits into two paths. Here it means the duct’s passage gets larger in the direction of airflow.
Example Sentence 1
The diffuser section behind the compressor is a diverging duct that slows the airflow before it enters the combustion chamber.
Example Sentence 2
Air pressure rose inside the diverging duct as velocity dropped, confirming normal operation of the inlet system.