Hydrodynamic simulations of laboratory scale bubble columns fundamental studies of the Eulerian-Eulerian modelling approach

The Eulerian-Eulerian model is used for the hydrodynamic simulation of a two-phase gas-liquid flow in a laboratory scale bubble column. The behaviour of the air-water system characterises a test case for bubbly flow with low gas void fractions. A dynamic lest case with a centred gas sparger is chosen for validation of the simulation models. Long-time-averaged liquid velocity profiles and time series at specific points are compared with experimental data. The main focus lays on the influence of turbulence modelling. Laminar and turbulent simulations are carried out. A standard k-epsilon model is used to describe turbulence occurring in the continuous fluid. Additionally turbulent dispersion of the gas bubbles can be taken into consideration. The results show that a turbulent model has to be considered to gain correct results. The laminar model shows a chaotic behaviour and not the harmonic oscillations observed in experiments. In contrast good agreement of the results can be obtained for three-dimensional calculations including turbulence. Distinct modelling of turbulent dispersion seems not to be necessary for the chosen test case. Furthermore, it can be concluded that a three-dimensional simulation with a sufficient fine resolution is necessary for accurate results. The test column depth, which is the determining length scale, must be resolved meticulously to receive accurate turbulence intensity in the bubble column. The conclusion concerning grid refinement and independence still needs further evaluations but fails up to now due to the limited computational power. Finally, two-phase bubbly flow calculations are carried out successfully with commercial CFD software in a transient way with the two-fluid model. The computational calculations still need very high resources. Further developments and model discussions are strongly recommended. (C) 1999 Elsevier Science Ltd. All rights reserved.