FORMATION OF SHOCK-WAVES IN GAS-LIQUID FOAMS

The purpose of the present investigation is to analyze the phenomenon of shock wave formation in gas-liquid foams and to explain the qualita tive differences which are found when comparing results from shock tub e experiments performed with foams and bubbly liquids. It is well know n that oscillatory pressure waves in bubbly liquids may reach an ampli tude twice as large as that of the original pressure impulse. However, experiments showed that pressure disturbances in foams always attenua te without significant change in the wave pressure profile. In the pre sent study this behavior is explained by analyzing shock wave formatio n using the Burgers equation which is derived from the conservation la ws for a bubbly liquid. It is shown that the parameter of non linearit y in the Burgers equation describing wave propagation in bubbly liquid s is about 40 times higher than in foams. At the same time coefficient of bulk viscosity of a foam is about 10(3) times greater than that of a bubbly liquid. This explains why in shock tube experiments with foa ms shock waves are not detected while they are easily observed when bu bbly liquids are used under similar conditions.