Assessment of scale-adaptive turbulence modeling in coupled CFD-PBM 3D flow simulations of disperse liquid-liquid flow in a baffled stirred tank with particular emphasis on the dissipation rate

Abstract

The effect of scale-adaptive simulations (SAS) on the droplet size distribution (DSD) is assessed in a baffled stirred tank and compared with a classical statistical turbulence model in terms of the widely used shear-stress transport (SST) eddy-viscosity model. DSD predictions are obtained by 3D multiphase flow simulations coupled with a population balance model. Inclusion of a turbulent dispersion model in the SST model simulations leads to a more homogeneous volume fraction field but has no visible effect on the DSD. On the one hand, enhanced mixing by the SAS shows a broader and more homogeneous DSD throughout the tank than predicted by the SST model, corresponding to experimental trends. On the other hand, turbulence energy dissipation rate ε is considerably underestimated by the SAS, leading to less breakup activity, while coalescence is essentially unaffected. It is suggested that SAS should be improved with regard to a sounder ε prediction in future studies.