The Sedimentation of Particulate Suspensions Under Orthogonal Shear: Mechanisms at Finite Weissenberg Number

Predicting the settling rates of non-Brownian particles suspended in complex fluids is critical to a number of engineering applications, including oil and gas recovery. A topic of specific importance involves particle suspensions in viscoelastic fluids experiencing an applied shear force in a direction perpendicular to gravity (referred to as orthogonal shear). In viscoelastic fluids, a nonlinear coupling between the orthogonal shear flow and the settling of particles has been observed [1]. Describing the underlying mechanisms and quantifying the effect of this coupling drag, which results from orthogonal shear on a sphere settling in a viscoelastic fluid, is the focus of this talk.

This talk looks at the role of fluid elasticity on single particles settling in orthogonal shear using experiments and numerical simulations. Previously, it has been shown that fluid elasticity with orthogonal shear can significantly reduce the settling rate of rigid spheres [2, 3]. New experiments were performed to study this enhanced coupling drag as a function of shear Weissenberg number, sedimentation Weissenberg number, and particle confinement in Boger fluids. This elastic effect was also studied using fully 3D simulations of flow past a rigid sphere, with the FENE-P constitutive model used to describe the polymeric fluid rheology. These simulations show good agreement with the experiments and allow for further insight into the mechanism of elasticity-enhanced drag. Results suggest the coupling drag, as well as the mechanism itself, are dependent on the shear Weissenberg number, sedimentation Weissenberg number, and particle confinement. In the low Weissenberg number regime (<1), these results are compared to existing results and theory. New results at high shear and sedimentation Weissenberg numbers (>1) provide novel insights into the elasticity-induced coupling drag enhancement for particles settling in orthogonal shear.

[1] Van den Brule, B.H.A.A., and Gheissary, G. J. Non-Newton. Fluid Mech., 49 (1993): 123-132.

[2] Padhy, S.et al. J. Non-Newton. Fluid Mech., 197 (2013): 48-60.

[3] Housiadas, K.D., and Tanner, R.I. J. Non-Newton. Fluid Mech., 183-184 (2012): 52-56