### Speaker

Prof.
Namiko Mitarai
(Niels Bohr Institute)

### Description

Wet granular materials shows behavior very different from
that of dry granular materials, and the behavior depends
strongly on the amount of the liquid. When grains are
partially wet, the liquid bridges and clusters exert the
cohesive force among grains [1]. For larger amount of
liquid, the pores among grains are filled and the system
becomes dense slurry, where both grain-liquid interaction
and grain-grain interaction play important roles [2-4].
In this talk, we introduce simple models to describe the
behavior of wet granular materials [1-3]. We especially
focus on a model for a dense mixture of granules and liquid,
that shows a severe shear thickening and is called a
dilatant fluid. We construct a fluid dynamics model for the
dilatant fluid by introducing a phenomenological state
variable for a local state of dispersed particles [2,3]. We
demonstrate that the model can describe basic features of
the dilatant fluid, and predicts an instability in a shear
flow for some regime to exhibit the shear thickening
oscillation, i.e., the oscillatory shear flow alternating
between the thickened and the relaxed states [2,3]. We also
report the first experimental observation of the shear
thickening oscillation with starch-water mixture in the
Tayler-Couette flow geometry [4].
REFERENCES
[1] N. Mitarai and H. Nakanishi, "Simple model for wet
granular materials with liquid clusters", Eur. Phys. Lett.
88 64001 (2009).
[2] H. Nakanishi and N. Mitarai, “Shear Thickening
Oscillation in a Dilatant Fluid”, J. Phys. Soc. Jpn, 80,
033801 (2011).
[3] H. Nakanishi, S. Nagahiro, and N. Mitarai, “Fluid
dynamics of dilatant fluids”, Phys. Rev. E, 85, 011401 (2012).
[4] S. Nagahiro, H. Nakanishi, and N. Mitarai, “Experimental
observation of shear thickening oscillation”,
arXiv:1211.2886 (2012).