Pycnoclinic acoustic force

Abstract

The interaction of high amplitude sound with density gradients in the background gas through which the sound propagates gives rise to the pycnoclinic acoustic force (PAF). This force is a generalization of acoustic radiation pressure for non-isentropic systems and is large compared to the known second-order pressure associated with sound when there is a large density change over a distance that is shorter than a wavelength. The PAF can squeeze pockets of low density gas or pull dense gas into regions of lower density. It is needed for a full understanding of Rijke and Sondhauss tubes, combustion in the presence of sound, and acoustic mixing of different density gases. A mathematical derivation is given and photographs in the literature provide evidence for its existence. The authors demonstrate an acoustic plasma trap based on these principles.The interaction of high amplitude sound with density gradients in the background gas through which the sound propagates gives rise to the pycnoclinic acoustic force (PAF). This force is a generalization of acoustic radiation pressure for non-isentropic systems and is large compared to the known second-order pressure associated with sound when there is a large density change over a distance that is shorter than a wavelength. The PAF can squeeze pockets of low density gas or pull dense gas into regions of lower density. It is needed for a full understanding of Rijke and Sondhauss tubes, combustion in the presence of sound, and acoustic mixing of different density gases. A mathematical derivation is given and photographs in the literature provide evidence for its existence. The authors demonstrate an acoustic plasma trap based on these principles.