Comparison between RANS and 3D-PTV measurements of Newtonian and non-Newtonian fluid flows in a stirred vessel in the transitional regime

Newtonian and non-Newtonian fluid flows in a vessel (T=H=180 mm) stirred with a Rushton turbine (C=D=T/3) have been simulated in CFD using steady RANS in the transitional regime (183≤Re≤1,086). The numerical results have been compared against 3D-PTV measurements. For Newtonian fluids, the different turbulence models predicted the same mean flow, which matched well the experimental velocity data. The standard k-ε model predicted the power numbers closest to expected values and resolved 80 % (at Re=943) and 89 % (Re=86) of the total energy dissipation. Simulations of the non-Newtonian flows presented challenges. For shear thinning rheology, the simulated mean flow patterns did not correspond to the measured ones. CFD also predicted a higher mean velocity, compared to PTV. For yield stress fluids, the numerical predictions of the cavern boundaries were in reasonably good agreement with the experimental observations.