Definition
A duct shaped like a ring, formed by the space between two concentric cylinders. In turbine engines and engine cooling systems, an annular duct channels airflow through the ring-shaped passage between an inner and outer wall.
Plain English
A donut-shaped passage. Air flows through the open ring between an inner tube and an outer tube that surrounds it.
Context Anchor
Seen in turbine-engine maintenance when describing airflow passages around the center section of an engine.
Derivation
From the Latin 'annulus,' meaning 'small ring.' The shape of the duct is literally a ring, so the name describes the cross-section the air flows through.
Why Pilots Care
Understanding annular ducts helps in recognising how air is routed through turbine engines for combustion, cooling, and bypass flow — all critical to how the engine produces thrust and stays within temperature limits.
Analogy
Picture two cans, one inside the other with a gap between them. Air flowing through that gap is flowing through an annular duct.
Intuition Check
Do not picture a straight tube. An annular duct is a passage shaped like a ring around something.
Example Sentence 1
Cooling air is directed through the annular duct surrounding the combustion chamber to keep the outer casing within temperature limits.
Example Sentence 2
Air flows through the annular duct surrounding the turbine core to maintain efficient engine operation.