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 tw o-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 chose n for validation of the simulation models. Long-time-averaged liquid veloci ty profiles and time series at specific points are compared with experiment al data. The main focus lays on the influence of turbulence modelling. Lami nar and turbulent simulations are carried out. A standard k-epsilon model i s used to describe turbulence occurring in the continuous fluid. Additional ly turbulent dispersion of the gas bubbles can be taken into consideration. The results show that a turbulent model has to be considered to gain corre ct results. The laminar model shows a chaotic behaviour and not the harmoni c oscillations observed in experiments. In contrast good agreement of the r esults can be obtained for three-dimensional calculations including turbule nce. Distinct modelling of turbulent dispersion seems not to be necessary f or the chosen test case. Furthermore, it can be concluded that a three-dime nsional simulation with a sufficient fine resolution is necessary for accur ate results. The test column depth, which is the determining length scale, must be resolved meticulously to receive accurate turbulence intensity in t he bubble column. The conclusion concerning grid refinement and independenc e still needs further evaluations but fails up to now due to the limited co mputational power. Finally, two-phase bubbly flow calculations are carried out successfully wi th commercial CFD software in a transient way with the two-fluid model. The computational calculations still need very high resources. Further develop ments and model discussions are strongly recommended. (C) 1999 Elsevier Sci ence Ltd. All rights reserved.