Pressure and Velocity Fluctuation in the Numerical Simulation of Bubble Detachment in a Venturi-Type Bubble Generator

The Venturi-type bubble generator proposed by Oak Ridge National Laboratory is used to produce micro-sized bubbles. In this paper, a numerical simulation is carried out to study the process of the bubble formation and detachment from a wall orifice of a Venturi-type bubble generator in a cross-flowing liquid. The Volume-of-Fluid (VOF) method is applied to track the two-phase interface and study the evolution of the bubble formation. The result of the computation provides a visual three-dimensional bubble and shows the process of bubble formation and detachment. Three stages are identified during bubble formation (the expansion stage, the rising stage, and the collapse stage). Because of the compressibility of the gas, a fluctuation of the pressure and the mass flow rate in the gas chamber is observed, which is considered a significant effect on the bubble formation and detachment. The mechanism of the bubble detachment is clarified with the help of the mass flow rate fluctuation. The equivalent diameter is compared with that predicted by a previous model. A Coupled Level Set Volume-of-Fluid (CLSVOF) simulation is compared with the VOF simulation; the three stages and the fluctuation are also observed in the CLSVOF simulation.