Viscous resuspension of non-Brownian particles: determination of the concentration profiles and particle normal stresses

We perform local measurements of both the velocity and the particle volume fraction to study viscous resuspension in non-Brownian suspensions for Shields numbers ranging from to . With this aim, a suspension of polymethacrylate spherical particles dispersed in a lighter Newtonian fluid (Triton X100) is sheared in a vertical Couette cell where both velocity and particle density mappings are performed. We show that the radial profiles of the velocity and of the particle volume fraction are inconsistent in the framework of local rheology of a Newtonian material and that these discrepancies disappear for a neutrally buoyant suspension. The vertical concentration profiles are used to deduce the third particle normal stress, Sigma(p)(33), by solving the Cauchy equation. The value of Sigma(p)(33) is shown not to vary linearly with shear rate but rather through a power law with an exponent close to 0.7, irrespective of the value of the particle volume fraction, in accordance with the recent results of Saint-Michel et al. (Phys. Fluids, vol. 31, 2019, 103301). Finally, we compare our results with the results of previous studies where alpha(3) = Sigma(p)(33)/eta 0(gamma) over dot (with eta(0) the viscosity of the suspending liquid and (gamma) over dot the shear rate) was deduced from the macroscopic measurement of the height of the resuspended layer. The agreement is satisfactory.

Automated summary

This study investigates the viscous resuspension in non-Brownian suspensions through local measurements of both velocity and particle volume fraction. The radial profiles of velocity and particle volume fraction are found to be inconsistent within the framework of local rheology of a Newtonian material, but discrepancies disappear for neutrally buoyant suspensions. The third particle normal stress is derived from vertical concentration profiles, showing a power law relationship with shear rate and an exponent close to 0.7, consistent with recent research.