Simulation of granular jet: Is granular flow really a "perfect fluid?"
  We perform three-dimensional simulations of a granular jet impact 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, 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. 
Tomohiko G. Sano and Hisao Hayakawa
cond-mat.soft cond-mat.stat-mech physics.flu-dyn