Releasing Bubbles: Direct Numerical Simulations of Oscillating Bubbles in Elastoviscoplastic Fluids

We employ direct numerical simulations (DNS) to investigate the dynamics of bubbles in elastoviscoplastic (EVP) materials. EVP materials are a broad class of complex fluids. When the stress applied to the material is below the yield stress, it behaves like a viscoelastic solid, whereas when the stress exceeds the yield stress, it behaves like a viscoelastic liquid. Crucially, the yield stress property allows EVP materials to entrap air bubbles. The entrapped bubbles, however, can be released from the materials when the suspension is subjected to acoustic excitations. To investigate this further, we use DNS to obtain detailed insights into the flow structure of the surrounding medium as well as the shapes of the deformed bubble interface as a function of the rheological properties. We then develop a simple theoretical model to account for specific features of the time evolution of the radius and the displacement of the bubble.