Numerical modelling of an acoustically-driven bubble : the growth and collapse near a wall.
Thesis DisciplineMechanical Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
The acoustically-driven collapse of a bubble results from the oscillating position of an ultrasound transducer face in a liquid medium. Existing fully-compressible models of bubble collapse have been applied to represent the Rayleigh collapse and the shock-induced collapse. These applications may not adequately represent the conditions associated with the acoustically-driven collapse. The current work presents a fully-compressible model that is the first to capture the collapse of a bubble set in a liquid medium subjected to an ultrasound transducer. The oscillating transducer face is represented by an immersed moving reflective boundary. The flow is simulated using a conservative interface capturing method, which includes the use of a high-order WENO reconstruction, a maximum-principle-satisfying and positivity-preserving limiter, and the HLLC approximate Riemann flux. The numerical method is verified by quantitative comparison to the benchmark shock-bubble problem.
The bubble growth, before the bubble collapse, is considered using a Rayleigh-Plesset (RP) approximation. The RP growth initialised collapse (RPGI) model is used to investigate the collapse of a near-wall cavitation bubble. The RPGI model is also used to investigate the influence of common growth assumptions, like neglecting surface tension, on the subsequent collapse of the bubble.
The direct simulation of both the growth and collapse, which we refer to as the acoustically-driven growth and collapse (ADGC) model, is used to investigate the dynamics of the bubble growth and the subsequent collapse with varying standoff distance from the near-wall. The ADGC model is also modified to capture the influence of nearby bubbles on the growth and collapse of the single bubble, providing insight into bubble cloud dynamics.