On spherical vapor bubble collapse in viscoelastic fluids

Cavitating vapor bubbles, occur in variety of engineering applications, employing complex fluids as operating medium. Especially in biomechanics, biomedical applications as well as in polymer processing, fluids exhibit viscoelastic properties and fundamentally different behavior than Newtonian fluids. To explain the influence of viscoelasticity on cavitation a detailed understanding of the viscoelastic influence on bubble dynamics and of the underlying mechanisms is essential. With this study we provide in-depth numerical investigations of the spherical vapor bubble collapse in viscoelastic fluids. A compressible, density-based, 3D finite-volume solver with explicit time integration is used together with a conservative, compressible formulation for the constitutive equations of three different viscoelastic models, namely the upper convected Maxwell model, the Oldroyd-B model and the simplified linear Phan-Thien Tanner model. 3D simulations of the collapse dynamics are carried out to show the viscous and viscoelastic stress development during the collapse, and its relation to the occurring deformations. Collapse behavior is investigated for various elasticity, viscosity and constitutive models. It is demonstrated that viscoelasticity fundamentally alters the collapse behavior and evolution of stresses. It is observed that viscoelastic stresses develop with a time delay proportional to elasticity and show different spatial distributions as opposed to Newtonian stresses. Viscoelasticity introduces isotropic stress components even though the spherical collapse leads to purely deviatoric (elongational) deformation. Furthermore, the distinct influence of constitutive models is illustrated and the influence of viscoelastic models with solvent contribution is explained. For the upper convected Maxwell model, we show that for increased elasticity shock wave emission can be observed depending on the applied grid resolution.