If you pack too much matter into a small space, you are likely to get some undesirable consequences as anyone vacationing with small kids will be all too aware. If you have to sit on your suitcase to get it closed, you are likely to be greeted by the sight of your holiday clothes circling on the carousel at your destination. Similar consequences befall the engineer simulating two-way coupled fluid-particle systems when they overload cells in the CFD mesh with too much DEM matter.
I refer, of course, to the previous requirement that a DEM particle must be smaller than the flow cell it occupies for two-way coupled simulations. This limitation is due to the way the effects of the DEM particle are applied purely to the flow cell in which the particle centroid lies, and not to adjacent cells that are also overlapped by the particle. When DEM particles are larger than the cell, this results in large sources of momentum and energy being applied to individual cells causing instability and divergence. However, it is not just stability that can be compromised, but also accuracy, with the void fraction of the particle not being fully accounted for if the volume of the cell is smaller than the particle.
In practice, this rendered some applications impossible to simulate as geometrical features forced the mesh size to be smaller than particles.
The recent release of STAR-CCM+® v11.06 changes all that with DEM source smoothing…Read more