APPLICATION OF SOUND INTENSITY TECHNIQUE IN HELICOPTER ACOUSTICS

Applications of the sound intensity technique to characterize helicopter interior and exterior acoustic fields are considered. Based on inflight sound intensity measurements, it is observed that reliable intensity measurements can be made in the highly reactive and diffuse interior sound field of a helicopter. These measurements proved successful in identifying "acoustically hot" areas on the helicopter interior surfaces. Near-field sound intensity measurements of a sound source on a rotating arm, simulating a rotor exterior acoustic field, allow sound radiation directivity and sound power to be quantified. The sound power level so determined is shown to be insensitive to background noise. Azimuthal and radial localization of sound sources on the rotating arm is also shown to be possible by sound intensity measurements triggered by a once per revolution signal. Some practical limitations in applying such measurements are identified and discussed.