Bubble migration in a viscoelastic duct flow*

Interface-resolved direct numerical simulations have been performed to study the bubble migration in a viscoelastic pressure-driven duct flow using the Giesekus model. Flow parameters are varied to reveal the effects of bubble deformability, fluid elasticity, shear thinning and inertia on the bubble migration. The rate of bubble migration is found to be much higher than a solid particle mainly due to the slip condition. The bubble-induced secondary flow velocity is also found to be an order of magnitude higher than the one induced by a solid particle under similar flow conditions. At a higher Weissenberg number, the flow becomes elastically unstable due to the curvature of streamlines across the bubble. It is found that at the lower values of β (polymeric to solvent viscosity ratio), shear thinning effect suppresses this path instability whereas at the higher value of β, shear thinning effect reverses its role and promotes path instability. During the flow build up, the fluctuations are only observed in the migration velocity of the bubble when the dominant lift force is due to elasticity. Simulations are also performed to investigate onset of a chaotic flow by injecting multiple bubbles into the viscoelastic duct flow.