Numerical and experimental investigations of an air bubble rising in a Carreau-Yasuda shear-thinning liquid

The dynamics of an air bubble rising in a quiescent shear-thinning fluid modelled using a simplified Carreau-Yasuda rheological model is investigated numerically and experimentally. For the parameter values considered in the present study, a rising bubble in a shear-thinning fluid exhibits three-dimensional behaviour. Both path instabilities (zigzagging/spiralling motion) and topological changes are observed for an air bubble rising in a shear-thinning fluid. However, for a Newtonian surrounding fluid, a bubble maintains azimuthal symmetry and rises in a straight path for the same set of parameters. The mechanism of this three-dimensional behaviour is investigated by inspecting the variation of vertical vorticity component and viscosity. Experiments have also been conducted using a high speed camera to visualise the bubble rise behaviour in both Newtonian and shear-thinning fluids as surrounding media. The shapes and trajectories of the bubble obtained from experiments show qualitative agreement with those obtained from numerical simulations.