Elastoviscoplastic effects on liquid plug propagation and rupture in an airway model

Non-Newtonian effects on liquid plug propagation and rupture occurring in distal airways are studied computationally using the volume-of-fluid solver Basilisk. The plug is driven by an applied constant pressure in a rigid axisymmetric tube whose inner surface is coated by a thin non-Newtonian liquid film. Extensive simulations are performed to investigate the effects of viscoelasticity on the plug and film dynamics, revealing an elastic instability for sufficiently large Weissenberg numbers. Under unstable conditions, we also identify a resonance that amplifies the stresses created by the elastic instability. A corresponding mechanical analog is proposed to explain the occurrence of the resonance in terms of the ratio between the Laplace number and the Weissenberg number. The robustness of our analysis to viscoplastic effects is finally tested using the Saramito-Herschel-Bulkley rheological model.