Analysis of the bubble size distribution in a breaking wave using a VOF method and an identification algorithm

A numerical simulation of a three-dimensional breaking wave is conducted using a VOF (volume-of-fluid) method to investigate the wave breaking dynamics and the bubble size distribution. The wave is initialized using the third-order Stokes wave solution. The initial wave slope and velocity fields generate turbulent wave breaking. Various interfacial phenomena are observed including a jet forming, a jet impacting to the free-surface, ejecting spray, entraining air pocket, and breakup. Bubbles with various sizes are formed from turbulent breakup of the air pocket during active breaking time. To obtain the bubble size distribution, an identification algorithm is proposed to accurately count independent bubbles. The proposed algorithm successfully identified independent bubble structures. A joining algorithm is also introduced to consider bubble structures spanning multiple blocks for parallel computations. The obtained bubble size distribution averaged during active breaking time is proportional to r^-10/3 for radii larger than the Hinze scale and shows good agreement with previous experiment and simulation results as well as the theoretical model.22Ykc