Research On Mechanism Of Infrasound Source Induced By Separated Push-pull Flow

In this thesis, a new method to generate infrasound is developed.A round piston is used for acoustic model of infrasound generator. According towave theory, the relations among the sound level, the working frequency, the dimensionof the projectors and the vibrating velocity are analyzed. These works will offerreferences for aeroacoustic analysis and design.A recently developed alternative technology which is referred to as the rotaryspeaker is analyzed. The rotary speaker generates infrasound with fluctuating signalpressure pulses created by the dynamically controlled blade pitch. According toquasi-steady hypothesis and the effective particle velocity model, the rotary speaker isconsidered as a planar radiator. The sound field of the rotary speaker is analyzed byutilizing theoretical model for the source and a boundary element method. How theparameters of the rotary speaker may influence the sound field is studied. Measuring ofsound field is done and the measured results are compared to model and numericalsimulation results.A new method to generate infrasound which is referred to as separated push-pullflow modulation is developed. This mechanism of infrasound keeps the advantages ofrotary speaker in radiating low-frequency sound: to produce infrasound through theprovision of the air flow rate oscillation rather than the actual displacement of the pistonsurface oscillations. It doesn’t need to be installed on baffle or closed box to achieve ahigher radiation power. Avoid its disadvantages of difficulties in controlling blade pitch,complicated structure and requiring of special installation. Compared to the currentunipolarity air source, separated push-pull flow modulation infrasound generator usesboth positive and negative air chambers in the modulation, in conditions of positive andnegative air chamber pressures matching, greatly improves the gas utilization ratio andeffectiveness.