Three-dimensional numerical simulation of air exhausted from submerged nozzles

Underwater exhaust produces an intricate unsteady two-phase flow field. For exploring the methods to predict the structure of air-water flow field and revealing the interaction of gas and water, three-dimensional underwater gas jet model with the VOF multiphase flow tracking method was adopted to simulate the transient flow field of gas jet into water. The air-water two-phase flow and its acoustic characteristic of turbulent gas exhausted from underwater nozzles were experimentally investigated in the early stages. Process of bubbles formation, detachment, fragmentation and coalescence were recorded clearly. The simulated results which were compared with the prior experimental results proved that the model almost accurately catches the behaviour of underwater bubbles. A few points were set in the two phase flow field to monitor pressure fluctuation. It had shown that higher air flow rate causes intense gas-column contraction and consequent bubble fragmentation, leading to higher amplitude and frequency of pressure fluctuation.