Large eddy simulation of a bubble column using dynamic sub-grid scale model

Euler-Euler simulations of the gas-liquid flow in a square cross-sectioned bubble column with LES (two sub-grid scale models) and the k-epsilon model are presented. The sub-grid scale modeling is based on the Smagorinsky kernel in both its original form and the dynamic procedure of Germano. The attempt has been made to assess the performance of these two sub-grid scale models. The Smagorinsky model with model constant C-s = 0. 12 performs quite well, and gives results almost identical to those given by the dynamic procedure of Germano. The SGS models are modified to account for bubble induced turbulence (Sato model) and it is observed that it does not change the results much. Predictions are also compared with the available experimental data. All the non-drag forces (turbulent dispersion force (only for RANS), virtual mass force, lift force) and drag force were incorporated in the model. An extended k-epsilon turbulence model has been used with extra source terms introduced to account for the interaction between the bubbles and the liquid. Though both LES models showed agreement in predictions, the Germano model still can be used to have estimates of C-s value which are not known a priori. Moreover, if objective is to understand the steady and time averaged features, RANS can also perform well. (C) 2007 Elsevier B.V. All rights reserved.