LES and URANS modelling of turbulent liquid-liquid flow in a static mixer: Turbulent kinetic energy and turbulence dissipation rate

The present study deals with numerical simulations of turbulent flow of a liquid-liquid system in a Kenics static mixer with ten inserts. CFD approach was used in two modes: large eddy simulation (LES) and unsteady Reynolds averaged Navier-Stokes (URANS). Large eddy simulation in the static mixer was carried out using the dynamic kinetic energy subgrid-scale model with standard wall functions whereas in URANS approach the standard k-ɛ turbulent model and standard wall functions were applied. Two-phase flow was modelled employing the “mixture model” of the Eulerian type. The simulations were performed mainly for the Reynolds number of 10000 with the volumetric ratio of 99 % of water to 1 % of oil. The investigations revealed that due to distinct distributions of the turbulence measures, the drop breakup process occurs with varying intensity in different locations within the mixer inserts. Significantly higher local values of the dissipation rate, ɛ, were predicted in URANS than in LES. However, both modelling methods indicated high values of ɛ at the beginning and the end of the mixer inserts, which implies the maximum shearing action exerted on the drops. Consequently, the inflow and outflow zone of each insert are the regions of the highest breakup intensity.