Fully-resolved simulation of a gas-fluidized bed : a critical test of DEM models

We performed Direct Numerical Simulation (DNS) of a gas-fluidized bed using the Immersed Boundary method combined with traditional Computational Fluid Dynamics. We have compared the individual fluid-particle force with the force as evaluated in an unresolved Discrete Element Model (DEM) simulation using closures for the gas-solid force for one fluidisation condition. We find that the average DEM gas-solid force is about 33 % smaller than the "true" value which follows from the DNS model. For more realistic DEM simulations, a modification of the gas-solid force calculation is required, for instance by adding fluctuations or including the effect of the granular temperature.