Simulation of granular jets: Is granular flow really a perfect fluid?

Abstract

We perform three-dimensional simulations of the impact of a granular jet for both frictional and frictionless grains. Small shear stress observed in the experiment [X. Cheng et al., Phys. Rev. Lett. 99, 188001 (2007)] is reproduced through our simulation. However, the fluid state after the impact is far from a perfect fluid, and thus the similarity between granular jets and quark gluon plasma is superficial because the observed viscosity is finite and its value is consistent with the prediction of the kinetic theory.

Numerical analysis of impact processes of granular jets

“…Here, we report that the shear viscosity consistent with our previous results, except its density dependence, and the assumption of the zero yield stress would be natural, by performing threedimensional simulation [9].…”

“…Thus, the correspondence between granular flow and QGP would be superficial [9]. However, through this analysis, zero yield stress, which is the residual stress without deformation, is assumed, though we presented three indirect evidences to support the assumption.…”

“…The solid lines represent the corresponding fitting lines. Judging from the fitting, the assumption of zero yield stress in our setup [9] would be natural.…”

Drag Law of Two-Dimensional Granular Fluids

“…The viscosity of the granular fluid, however, obtained from the Couette flow is much larger than that obtained from the drag experiment. Indeed, an experiment for a granular jet (Cheng et al 2007) as well as simulations (Ellowitz et al 2013;Müller et al 2014) suggested that the granular fluid can be approximately represented by a perfect fluid, though there exist counter arguments (Sano and Hayakawa 2012;Sano and Hayakawa 2013). Therefore, another purpose of this paper is to resolve the current confusing situation on the rheology of granular fluids.…”

Impact dynamics of granular jets with noncircular cross sections

“…In spite of 16 orders of magnitude difference in their energy scales, the two examples share one common feature: they both illustrate emergent hydrodynamic flows out of strongly interacting discrete particles. Thus, granular jet impact has been studied in part as a macroscopic analog of the RHIC experiment [5,10,11] or as a fluid with a finite viscosity [12,13]. Indeed, similar to the anisotropic ejecta pattern of the quark-gluon plasma, an asymmetric granular sheet was produced in an experiment using a granular jet with a rectangular cross-section [5].…”