Multi-scale modeling of dispersed gas-liquid two-phase flows

In this work the status of computational modeling of bubbly flows is reviewed. The theory of four different models is introduced and typical examples are given illustrating the capabilities of these models. The volume of fluid model and the front tracking model are used to investigate the behavior of individual bubbles. It is found that both models are well suited to investigate the shape and transient behavior of individual bubbles. An Euler-Lagrange model is used to simulate the flow in a lab-scale bubble column, accounting for coalescence and break-up. The predicted bubble size distributions show reasonable agreement with experiments. However, better break-up models are necessary for further improvement. Finally an Euler-Euler model is used to simulate the flow in a lab-scale bubble column. It is shown that the use of a proper drag model is vital for accurate prediction of the bubble column dynamic

Numerical investigation of closures for interface forces acting on single air-bubbles in water using volume and fluid and front tracking models

Closures for the drag and virtual mass forces acting on a single air bubble rising in initially quiescent pure water have been numerically investigated using direct numerical simulation techniques. A 3D Front Tracking model was used and the results were compared with simulation results obtained with a 2D Volume of Fluid model to assess the influence of the third dimension. In the simulations realistic values were taken for the physical properties, i.e., a density ratio of 800. The computed time-averaged terminal rise velocity and mean aspect ratio for individual air bubbles ranging in equivalent diameter from 1 to 10 mm rising in pure water compare well with available experimental data