Rotor of a siren
Rotor (of a siren)
The moving part of the modulator containing apertures or "ports" corresponding to those of the stator. The relative displacement between the two sets of ports interrupts the flow of compressed air thereby producing a modulated output.
Please note that this is the term as it stands in the original IALA Dictionary edition (1970-1989)
International Association of Marine Aids to Navigation and Lighthouse Authorities - AISM