Development of a pneumatic infrasound generator

This thesis details the experimental development of a pneumatic infrasound generator, the purpose of which is for calibration, testing, and research. The source was an assembly of an air reservoir, a motor, and a rotor/stator pair, in the context of a siren. A rotating ball valve acted as the rotor/stator and modulated the compressed air from the reservoir as it vented into the atmosphere. The ball valve cross sectional area as a function of time varied as a triangular waveform, which in practice caused the infrasonic waveforms to be effectively sinusoidal. This thesis opens with a brief motivation for the creation of the source, in addition to previously developed infrasound generators and an overview of wind noise. The apparatus construction is then described. A theory is developed that describes the acoustic radiation from the infrasound generator as the superposition of a monopole and a dipole. Flow visualization, propagation, frequency response, reservoir volume, directivity, and jet velocity experimental setups and results are described next. The outcomes of the research are subsequently discussed, including a brief overview of a scaled up model of the infrasound generator.