Definition
A duct whose internal cross-sectional area increases in the direction of airflow. In subsonic flow, this shape causes the air to slow down, which raises its static pressure and increases its temperature. Divergent ducts are used in turbine engine inlets and diffuser sections to convert the kinetic energy of fast-moving air into pressure before the air enters the compressor or combustion section.
Plain English
A pipe or passage that gets wider as the air flows through it. Because the space opens up, the air slows down and its pressure rises.
Context Anchor
Seen in aircraft powerplant airflow discussions, especially where a duct is shaped to slow air and raise pressure before it reaches another engine section.
Derivation
From Latin divergere, meaning 'to bend apart' or 'spread out.' A divergent duct literally spreads outward along its length, which is exactly what gives it its pressure-raising effect.
Why Pilots Care
The pressure rise produced by divergent ducting is part of how a turbine engine prepares incoming air for efficient combustion. Understanding this helps explain why inlet design and condition matter to engine performance.
Analogy
Think of water flowing from a narrow hose into a wider pipe. As the path opens up, the flow spreads out and slows down.
Grounding Statement
Picture a hallway that gets wider as you walk down it. A crowd moving through has to spread out and slow down — the same thing happens to air in a divergent duct.
Intuition Check
Divergent does not mean the air is uncontrolled or random here. It means the duct walls spread farther apart in the direction the air is moving.
Example Sentence 1
The engine inlet acts as a divergent duct, slowing the incoming air and raising its pressure before it reaches the compressor.
Example Sentence 2
The widening shape of the divergent duct helps convert exhaust velocity into additional thrust.