Hydrodynamic approach to multibubble sonoluminescence

• Bubble clusters containing several thousand micro bubbles were investigated numerically.
• We obtained velocity profile and radiation pressure field in a bubble cluster.
• The radiation pressure field affects to increase the effective mass of individual bubble.
• Calculated pulse width from MBSL is approximately 210 ps, longer than that from SBSL.
• Spectral peak shifts to higher wavelength as the number of bubble in the cluster increases.

The velocity profile and radiation pressure field of a bubble cluster containing several thousand micro bubbles were obtained by solving the continuity and momentum equations for the bubbly mixture. In this study, the bubbles in the cluster are assumed to be generated and collapsed synchronously with an applied ultrasound. Numerical calculations describing the behavior of a micro bubble in a cluster included the effect of the radiation pressure field from the synchronizing motion of bubbles in the cluster. The radiation pressure generated from surrounding bubbles affects the bubble’s behavior by increasing the effective mass of the bubble so that the bubble expands slowly to a smaller maximum size. The light pulse width and spectral radiance from a bubble in a cluster subjected to ultrasound were calculated by adding a radiation pressure term to the Keller–Miksis equation, and the values were compared to experimental values of the multibubble sonoluminescence condition. There was close agreement between the calculated and observed values.