THERMAL EFFECTS OF INTERNAL GAS ON THE OSCILLATIONS OF A CLUSTER OF BUBBLES

The governing equations of a cluster of bubbles are derived by taking account of the thermal effects of the internal gas and the three-dimen sional translational motion and deformation of each bubble. The equati ons are applied to the nonlinear oscillations of multiple interacting bubbles. The frequency response curves are obtained for two typical ar rangements of bubbles with the same radii, The present results are com pared with the results of polytropic analysis in which the thermal eff ects are evaluated using the effective polytropic index and the effect ive viscosity. It is shown that the heat transfer inside the bubble is important in investigating the nonlinear bubble oscillations. The pol ytropic relation for the internal gas does not hold when the nonlinear ity of the radial oscillation becomes strong. Both radial and surface oscillations are affected by the translational motion of each bubble. It is also shown that the subharmonic oscillation of interacting bubbl es occurs more easily than that of an isolated bubble due to the bubbl e-bubble interaction.