Numerical simulation of a bubble rising in shear-thinning fluids

Abstract

a b s t r a c tThe motion of a single bubble rising freely in quiescent non-Newtonian viscous fluids was investigated experimentally and computationally. The non-Newtonian effects in the flow of viscous inelastic fluids are modeled by the Carreau rheological model. An improved level set approach for computing the incompressible two-phase flow with deformable free interface is used. The control volume formulation with the SIMPLEC algorithm incorporated is used to solve the governing equations on a staggered Eulerian grid. The simulation results demonstrate that the algorithm is robust for shear-thinning liquids with large density ( 1 / g up to 103 ) and high viscosity (Á 1 /Á g up to 10 4 ). The comparison of the experimental measurements of terminal bubble shape and velocity with the computational results is satisfactory. It is shown that the local change in viscosity around a bubble greatly depends on the bubble shape and the zero-shear viscosity of non-Newtonian shear-thinning liquids. The shear-rate distribution and velocity fields are used to elucidate the formation of a region of large viscosity at the rear of a bubble as a result of the rather stagnant flow behind the bubble. The numerical results provide the basis for further investigations, such as the numerical simulation of viscoelastic fluids.

Hydrodynamic interaction between a pair of bubbles ascending in shear-thinning inelastic fluids

“…The results shown in Fig. 19 are similar to the ones obtained by [53] for similar Re numbers (Re ∼ 10). The maximum viscosity values agree well with the values given by the rheological data fitted with the Carreau model.…”

“…Zhang et al [53] made a similar comparison of their numerical terminal bubble velocities obtained with thinning and Newtonian fluids. In order to make the comparison they changed the value of the flow index (similar to what was done here) but considering a constant zero-shear viscosity value (we considered a shear-rate dependent viscosity).…”

The viscosity distribution around a rising bubble in shear-thinning non-newtonian fluids

“…Therefore, information on the local viscosity distribution around rising bubbles is necessary for the better understanding of the bubble moving behavior in non-Newtonian fluids. Unfortunately, although Zhang et al (2010) numerically explored the local viscosity distribution around bubbles in shear-thinning non-Newtonian fluids using the level set approach, so far there is little experimental information about the local viscosity distribution around bubbles rising in non-Newtonian fluids.…”

suLDA Characterization of the Velocity Field around a Growing and Rising Bubble in Shear-thinning Fluid

“…Fan et al 28 focused on the interaction between two parallel rising bubbles by analyzing the velocity field around bubbles using PIV. Zhang et al 29 applied an improved level set method to simulate the motion of deformable bubble in shear-thinning fluids, and found that two separated zones in the vortex-shedding regime formed as a region of wake with high viscosity appeared. Li et al 30 explored experimentally a hollow cylindrical low viscosity region around the bubble wake and a high viscosity region in the central bubble wake around a rising bubble in CMC fluids.…”