Assessment of standard k-ε, RSM and LES turbulence models in a baffled stirred vessel agitated by various impeller designs

In the present work, laser-doppler anemometry measurements as well as CFD simulations have been performed for the flow generated by various impellers, namely disc turbine (DT), a variety of pitched blade down flow turbine impellers varying in blade angle (Standard PBTD60, 45 and 30) and hydrofoil (HF) impeller. The tank was fully baffled, and the flow regime was turbulent. The objective of the present work was to carry out a detailed investigation of the predictive capabilities of the various turbulence models, i.e. the standard k-ε model, Reynolds-stress transport model (RSTM) and large eddy simulations (LES). In case of LES, effect of subgrid scales on the resolved scales has been modeled by dynamic one equation subgrid-scale model. The simulated values of the mean axial, radial and tangential velocities along with the turbulent kinetic energy have been compared with the measured LDA data. It has been identified that the present SGS LES model performs well for predicting all the flow variables. Whereas, RSM and standard k-ε model underpredict the turbulent kinetic energy profiles significantly in the impeller region. RSM can capture well all the mean flow characteristics and the standard k-ε model fails to simulate the mean flow associated with the strong swirl. Energy content of the precessional vortex has been quantified for all the five impeller designs. Intermediate frequencies inbetween the mean circulation and the precession instability have been identified having a non-dimensional frequency of 0.04 to 0.07 for all the impeller designs under consideration