3D finite volume simulations of dense granular flow inside rotating cylinders

Granular materials are widely diffused in industry as well as in nature, but a reliable and effective description of their motion is still at a rather early stage of development. Among the benchmark problems of granular dense flow, the rotating drum is one of the most challenging, yet intriguing and technologically relevant. In proper ranges of operating conditions, granular materials inside rotating drums display a continuum motion near their free surface. The motion of those discrete systems has been studied both experimentally and through Discrete Element Method (DEM) numerical simulations; however, it can also be regarded as the flow of a continuum medium, thus allowing a continuum mechanics approach. In this thesis, we solve the continuum dynamic equations by adopting the visco-plastic JFP constitutive model (Jop et al., Nature 441, 727-730, 2006) for the stress tensor, and study the continuous flow of dry grains inside axially rotating cylinders through 3D Finite Volume simulations (FVM). We investigate the effect of the ratio D/dp between the diameters of cylinder and particles, of the aspect ratio of the cylinder AR=width/diameter, of the angular velocity omega, and of the slip between drum wall and particles. Numerical results are found to quantitatively agree with experimental results from different authors, and also catches some distinctive features of the drum flow of granular materials, such as, e.g., the existence of axial components of the surface velocity, or the differences of the flow fields near the lateral wall and at the center plane, ect. Our simulations demonstrate that the basic physics of the dense granular flow is captured by the simple JFP model, and that continuum mechanics can be used to get a physical insight in granular dense state phenomenology. CFD simulations may then be of help to rationalize the broad wealth of experimental results with these materials.