Numerical modeling of a OK rotor-stator mixing device

Abstract

The flow field induced in an Outokumpu TankCell and by a OK rotor-stator mixing device in a process size flotation cell was simulated by cfd using two main grid types. The effects of different grid types were investigated with structured and unstructured grids. The geometry used was axisymmetric and a sector of 60 degrees of the tank with periodic boundaries was modeled. Finally, validation measurements and calculations with a laboratory size flotation cell were done. A “hybrid” grid for a laboratory size OK flotation cell with unstructured cells in the rotor domain and structured cells in the stator and tank domain was generated. Preprocessing and computational mesh generation process of complicated geometries like the OK rotor-stator mixing device can take considerably long time with regular structure type grids. This type of geometry is where meshes with irregular structure can be used much easier and with less processing time. Preprosessing and grid generation was done with the commercial Fluent Gambit 1.3. The CFD code Fluent 5.5 was used in the simulation. Standard k-e turbulence model and standard wall functions were used. Multiple reference frame method was used in all simulations instead of the computationally slower sliding mesh method. Simulations were done in one phase ( l ). Calculated velocity fields on horizontal and vertical planes, pressure distributions on rotor and stator surfaces and turbulent magnitudes were compared with structured and unstructured grid types. No grid dependency was found. Comparisons between velocity and turbulence results measured using the LDV (Laser Doppler Velocimetry) technique and CFD modeling were done. The predicted velocity components agreed well with the values obtained from LDV. The standard k-e model underpredicts the k level in the flotation cell compared to measured values. It was shown that a CFD model with periodicity, hybrid grid and MRF approach can be used for detailed studies on the design and operation of the Outokumpu flotation cell.