Simplified stirrer modelling for the prediction of time averaged hydrodynamics in stirred vessels

In the vicinity of the outlet of a six-bladed Rushton turbine detailed LDV-measurements were performed to obtain equations for the radial and tangential velocities and the turbulent kinetic energy as function of the height co-ordinate. The equations were used as impeller boundary conditions in CFD-calculations with CFDS-Flow3D for two different grids, 48,000 and 66,000 grid cells, and with k-ε and AS turbulence models. Comparison with measured data of velocities and turbulent kinetic energy showed that the calculations with the coarser grid with k- ε-modelling gave good results in fairly short CPU-times. Calculated values of the relative local energy dissipation rates, which are a key parameter in mixing models, showed good agreement with dissipation rates derived from measured velocities by using the inviscid estimate. Absolute local energy dissipation rates can be obtained by multiplying the calculated relative results by the actual mean energy dissipation rate.