8. Radiated airborne noise

8.1 Fluctuating flows

Fluctuating flow noise concerns duct outlets and cavities excited by wind. The phenomenology is the same as that already described for water. There are many cavities with no average flow (surface cracks) to be monitored on a ship. The most worrying sources are chimneys and air vents.

• Heat engine chimneys

  In fact, these are large mufflers placed in the chimney flue. They differ from car exhausts in their frequency range (a few tens of herz) and in the fact that they excite relatively flimsy superstructures. Fluctuating flow noise is reduced by the...