A novel two-grid formulation for fluid–particle systems using the discrete element method

Discrete element modeling (DEM) coupled with computational fluid dynamics (CFD) provides an excellent platform to analyze fluid–particle systems. In all previous work, the fluid and particle systems are solved on a single grid. Contradictory requirements posed by resolution of fine scale fluid features such as turbulence, friction and heat transfer coefficient at immersed surfaces, and the resolution of important geometrical features, versus the necessity to maintain smoothness in particle solid fraction distribution on the chosen grid, often make single grid calculations untenable. To overcome this challenge, we have developed a novel two-grid technique in which a coarser particle grid is mapped on to a fine fluid grid. The technique uses suitable mappings to transfer fluid field variables from fluid-to-particle grid, and interphase transfer terms and void fractions from particle-to-fluid grid. The method is applied to a jetting fluidized bed of 750 μm particles with a characteristic jet width of 1.6 mm. Results in the form of time-averaged void fractions and solid-velocity for two inlet jet velocities with single and multiple jets are compared to experiments. The results agree reasonably well with the experiments validating the two-grid approach for cases where single grid DEM–CFD would have been difficult to apply.