Numerical Simulation of the Bubble Cloud Dynamics in an Ultrasound Field
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We use a coupled Eulerian-Lagrangian method to simulate the dynamics of a spherical bubble cloud with various void fractions excited by high-amplitude ultrasound pulses. We consider two cases: a single cycle of a sinusoidal waveform whose wavelength is large compared to the cloud diameter, and multiple cycles with a short wavelength. For the long wavelength, bubble cloud dynamics are nearly spherically symmetric. Bubbles near the periphery grow more than the those close to the center, and the collapse of bubbles propagates inward from the periphery of the cloud. The structure and the dynamics of the cloud are scaled with the cloud interaction parameter introduce by d’Agostino and Brennen. It is shown that polydispersity does not significantly alter the cloud dynamics. In the short wavelength case, the clouds develop an anisotropic structure in the direction of the incident wave propagation. Over a wide range of the void fraction, the distal side of the cloud is shielded from the incident wave and bubbles grow less. As characterized by the center of volume of the cloud, the anisotropy is similar over the range of volume fractions considered. The results of the study can be used to characterize the acoustic cavitation in ultrasound therapies.