Theoretical and numerical study of air entrainment and bubble size distribution in strong free-surface turbulent flow at large Froude and Weber number

Abstract

Strong turbulence near an air-water interface, characterized by large Froude (Fr) and Weber number (We), leads to significant interactions and exchanges between gas and liquid, resulting in measurable air entrainment. Air entrainment influences a number of physical processes in the nature, including air-sea gas transfer, production of the sea-salt aerosol and scavenging of biological surfactant. The key factor in controlling these processes is the size distribution of entrained bubbles. However, the underlying mechanisms/physics of air entrainment driven by free-surface turbulence (FST) and the resulted bubble size distribution still remain unclear. Therefore, detailed studies on air entrainment in strong free-surface turbulence (SFST) are of fundamental scientific interest. With recent interest in modeling the white bubbly water in ship wakes, these studies are also of practical importance to the design and analysis of modern surface vessels. In this thesis, we perform both theoretical and numerical studies on air entrainment and bubble size distribution in SFST at large Fr and We. The thesis work 1) characterizes the unique turbulence characteristics of SFST; 2) quantifies the entrainment volume and the corresponding size distribution of SFST air entrainment; 3) elucidates the mechanisms/physics of the bubble size distribution of SFST entrainment; 4) provides useful insight and guidance to the development of sub-grid air entrainment models ...