Experimental and numerical investigation of free surface formation in an unbaffled stirred tank

Abstract

The aim of this study was to conduct an experimental and numerical analysis of the hydrodynamics of twophase flow in an unbaffled mixer equipped with a Rushton turbine. The analysis revealed clear limitations of RANS-based turbulence models under strong, axially symmetric swirling flow conditions. All analyzed models in this group (k-", SST k-!, RSM) significantly overestimated the power number, with relative errors ranging from 95% to over 119%, which limits their utility as predictive tools in engineering practice. Furthermore, they failed to correctly represent velocity field structures, and predictions of vortex shape and depth showed poor correlation with experimental results. In contrast, the LES model demonstrated clear superiority: it predicted mixing power with a minimal error of 3:4% and velocity distributions with high precision. Additionally, it accurately reproduced the geometry of the vortex funnel, confirming its suitability for modeling flows with strong turbulence anisotropy and a dynamic free surface.