Non-Newtonian effects on solid particles settling in sharp stratification

Abstract

Gravitational settling of solid particles through density interfaces is studied numerically when at least one of the fluids is non-Newtonian. The Carreau–Yasuda model is used to model the shear-thinning behavior of the non-Newtonian fluid. The coupled level-set and volume-of-fluid method is used to track the interface between the two fluids. It is found that the presence of shear-thinning fluids significantly affects the settling dynamics of solid spheres. For lower power index, the lighter fluid is more entrained by the sphere into the denser fluid. It is revealed that the sphere velocity after impacting the interface increases with the power index, density ratio and buoyancy jump. The shear-thinning effect of the upper and lower non-Newtonian fluids is quite noticeable and the motion of the solid sphere before crossing the interface is different to the case of Newtonian fluids. For the case of upper Newtonian fluid, there is a smaller resistance force at the interface, which causes the sphere to fall in the lower non-Newtonian fluid with about 90% of its terminal velocity.