Abstract
The phenomena described in this paper are concerned with air-column oscillation induced by acoustic standing wave in a closed duct driven by a sound source. When the driving frequency is in the vicinity of the resonance frequency of the air-column, a large amplitude oscillatory flow is produced in the duct. According as an increase of the amplitude, steady pressure distribution, steady streaming and thermoacoustic effect appear in addition to the oscillatory fluid motion in the duct. The steady streaming, which is called Rayleigh's acoustic streaming caused by frictional dissipation in the Stokes layer, results in circulating flows within each segment of 1/4 wave-length of the standing wave. When a strong acoustic standing wave is superimposed on the field of unstable convection generating in a horizontal duct by heating of duct floor, the coupling of acoustic streaming on the convection is capable of transforming it.
This paper describes experimental investigations on the coupling of the acoustic streaming with the natural convection developed in a rectangular duct. The results obtained show that the coupling of the sound field on the unstable convection not only transforms it into a stable convection with cellular structure characterized by the wave length of the sound, but also the velocity of convection current increases.
