High-fidelity simulations of viscoelastic filament dynamics undergoing airflow-induced thinning and breakup

Flow resulting from a cough or sneeze is inherently multi-phase and multi-scale, as it involves the dispersion of small liquid droplets in a gaseous fluid. Understanding the multi-phase nature of expiratory flow and its potential to suspend small droplets for longer durations than would have otherwise occurred in single-phase jets can be crucial for accurate predictions of respiratory disease infections. To this end, it is also critical to develop sophisticated models capable of capturing the non-Newtonian flow behavior in these settings. Here, we consider axisymmetric simulations of impulsively started viscoelastic jets, identifying the effects of the injection flowrate, the fluid elasticity, and the extensibility of the polymer chains on the rate-of-thinning and the pinch-off singularities. In addition, we perform three-dimensional simulations of viscoelastic jets, using Adaptive Mesh Refinement (AMR) to investigate the role of non-axisymmetric perturbations in the jet profile. Specifically, we study numerically the thinning and breakup process of a viscoelastic ligament induced by a transverse airflow. In this configuration, we simulate a viscoelastic filament of saliva attached to human lips undergoing deformation due to air flow generated by the corresponding vocalization. We examine the role of viscoelastic effects in controlling morphology and the dynamic response to the imposed deformation compared to the Newtonian case. Sub-grid scale modelling strategies to accelerate the computations, which make use of high-fidelity simulation data, are also discussed.