Numerical simulation of the rise of two parallel unequal bubbles in a viscoelastic fluid

The interaction of two parallel unequal bubbles in a viscoelastic fluid was investigated numerically using OpenFoam, the volume of fluid method (VOF) combined with a surface tension model to trace the gas-liquid interface, and the Giesekus model to characterise the rheological properties of the fluid. The numerical results are in good agreement with experimental results from the literature. The effects of bubble diameter, initial spacing between bubbles and rheological properties of the fluid on the rise, separation and convergence of the two bubbles were investigated. The flow field properties and viscoelastic stress distribution around the bubbles were explored. As the bubble spacing increases, the maximum and terminal velocities of the two bubbles increase, and the relative positions of the bubbles change when they come into contact. As the relaxation time λ increases, the contact time of the bubbles decreases, the small bubbles tend to have an inverted teardrop shape and the large bubbles have less deformation and no sharp tail; the relaxation time directly affects the accumulation of viscoelastic stress, leading to changes in the velocity of the bubbles at contact, and their maximum and terminal velocities increase. Bubbles in highly elastic fluids are more prone to negative wake phenomena.