Studying the sedimentation and shearing of macroscopic suspensions

Camilla Voeltz , Eberhard Bodenschatz

Cornell University, LASSP

The temporal evolution of an interface between glycerin and a glycerin-sand suspension of small packing fraction (obtained using the hindered settling phenomenon) driven by gravity is experimentally investigated. The growth rates for the different wave numbers characterizing the developing front are defined by means of a Fourier analysis. To model the observed behavior, we apply the idea of the Rayleigh-Taylor instability for a homogeneous fluid with vertically varying density and viscosity. A good agreement between the experimental and theoretical results is obtained. A brief second part will cover an experimental study of the viscosity of a macroscopic suspension under steady shear, which demonstrates that macroscopic suspensions show thixotropic behavior. The temporal decrease of the viscosity under shear coincides with the formation of a hexagonal pattern.