Numerical simulation of bubble dynamics in a Phan-Thien-Tanner liquid: non-linear shape and size oscillatory response under periodic pressure.

We study non-linear bubble oscillations driven by an acoustic pressure with the bubble being immersed in a viscoelastic, Phan-Thien-Tanner liquid. Solution is provided numerically through a method which is based on a finite element discretization of the Navier-Stokes flow equations. The proposed computational approach does not rely on the solution of the simplified Rayleigh-Plesset equation, is not limited in studying only spherically symmetric bubbles and provides coupled solutions for the velocity, stress fields and bubble interface. We present solutions for non-spherical bubbles, with asphericity being addressed by means of Legendre polynomials or associated Legendre functions. A parametric investigation of the bubble dynamical oscillatory response as a function of the fluid rheological properties shows that the amplitude of bubble oscillations drastically increases as liquid elasticity (quantified by the Deborah number) increases or as liquid viscosity decreases (quantified by the Reynolds number). Extensive numerical calculations demonstrate that increasing elasticity and/or viscosity of the surrounding liquid tend to stabilize the shape anisotropy of an initially non-spherical bubble. Results are shown for pressure amplitudes 0.2-2MPa and Deborah, Reynolds numbers in the intervals of 1-8 and 0.094-1.256, respectively.