A flow past a mouth of a deep cavity can result in an exciation of high - amplitude acoustic pulsations. such pulsations are often encounterd in gas-transport systems, heat exchangers and other industrial processes involving transport of a fluid through a pipleline.
I really don't know how noise occurs.
one said "swirls induced by separation interact between each other and generating noise."
when rotating flow contract with other rotating flow, noise occurs? how??
Cavitation is accompanied by noise due to the formation and collapse of bubbles. Cavitation can be quite damaging, even to tough materials.
Cavity noise is a commonly found in air crafts and air conditioning ducts. This tend to be characterised by three main phenomenon: (Separation from the leading edge generates a shear flow that ends up creating (1) and (2))
1) A feedback loop inside the cavity due to recirculation.
2) An edge tone like phenomenon at the trailing edge.
3) Feedback pressure waves.
Such tones are now called the Rossiter modes,
naca.central.cranfield.ac.uk/reports/arc/rm/3438.pdf
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