(162c) A Cartesian Cut Cell Method for Gas/Solids Flow

The implementation of a Cartesian cut cell method into the multiphase flow solver MFIX (Multiphase Flow with Interphase Exchange) is presented. The solids phase is treated as an interpenetrating phase, and mass and momentum balance equation are solved for gas and solids phases. Momentum transfer between the solids and gas phase is achieved through an empirical drag law. The cut cell method described by Kirkpatrick et al. to represent curved boundaries for the solution of the Navier-Stokes equations on a staggered three-dimensional Cartesian grid is extended to gas/solids flows.

The background Cartesian grid is intersected with curved or sloping surfaces describing the boundaries, resulting in the generation of cut cells. A special treatment is required to compute fluxes through cut cell faces, and the contribution to the wall shear stress must be included. The same treatment applies for both gas and solids phases.

The accuracy of the method is first tested for simple single phase benchmark cases such as the flow in a channel skewed with respect to the background grid, and the flow past a cylinder. Results show a clear improvement with the cut cell method compared to the traditional staircase step representation of boundaries. The method is subsequently applied to several gas/solids flows.