Nonlinear oscillation of a spherical gas bubble in acoustic fields

Radial motion of a spherical air bubble in acoustic fields is observed experimentally. The radius-time curves and frequency responses are obtained from the experiment for comparison with a numerical calculation. The calculation is based on a mathematical model in which the thermo-fluid mechanics of the gas in the bubble is precisely described. An oscillatory pressure field is generated in a cylindrical cell, which consists of two piezoceramic transducers and a glass cylinder. A new bubble generator is developed. It is able to generate a bubble filled with an arbitrary kind of gas. The bubble motion is observed by high-speed photography. The time history of the bubble radius is measured from the pictures. The pressure field has a frequency of 19.2 kHz and its amplitude is up to 40 kPa. The bubble has an initial radius within the range from 0.1 mm to 0.25 mm. A highly viscous silicone oil, whose kinematic viscosity is 100 mm2/s, is used for the liquid to keep the spherical shape of the bubble. A quantitatively good agreement between the experimental and numerical results is obtained. The difference between experiment and theory based on the polytropic approximation for the gas is briefly discussed.