Coupling of midaudio frequency thermoacoustic prime movers.

Abstract

Multiple unit midaudio frequency thermoacoustic engine arrays have been studied in terms of synchronized self-sustaining oscillators. Thermoacoustic engines can be acoustically coupled through shared gas when attached to a common cavity. The coupling between devices was studied by varying the cavity volume, and by varying the separation distance between devices in an array. Frequency and phase measurements for two-engine arrays have suggested that the engines entrain at a common frequency with approximately zero phase difference implying the onset of synchronization. Amplitude measurements of synchronized arrays suggest that the acoustic amplitude is equal to the sum of the amplitudes of each uncoupled engine, and agree with predictions. Synchronization of four or more units in an array implies that the coupling between engines is global and depends on the volume of the cavity and the density of the gas within the cavity. The detuning between two engines was increased until synchronization no longer occurred. The threshold for this was found to be for a frequency difference of between 80 and 98 Hz for the given coupling strength when operating near 2.5 kHz. [Research supported by the U.S. Army Space and Missile Defense Command/U.S. Army Forces Strategic Command.]