WAVE-PROPAGATION IN POROUS-MEDIA CONTAINING A DILUTE GAS-LIQUID MIXTURE - THEORY AND EXPERIMENTS

The influence of a small amount of gas within the saturating liquid of a porous medium on acoustic wave propagation is investigated. It is a ssumed that the gas volumes are spherical, homogeneously distributed, and that they are within a very narrow range of bubble sizes. It is sh own that the compressibility of the saturating fluid is determined by viscous, thermal, and a newly introduced Blot-type damping of the osci llating gas bubbles, with mean gas bubble size and concentration as im portant parameters. Using a super-saturation technique, a homogeneous gas-liquid mixture within a porous test column is obtained. Gas bubble size and concentration are measured by means of compressibility exper iments. Wave reflection and propagation experiments carried out in a v ertical shock tube show pore pressure oscillations, which can be expla ined by incorporating a dynamic gas bubble behaviour in the linear Blo t theory for plane wave propagation.