Viskoelastik iki-fazlı sistemlerin hesaplamalı yöntemlerle modellenmesi

A front-tracking method is developed for direct numerical simulations of viscoelastic two-phase systems in which one or both phases could be viscoelastic. One set of governing equations is written for the whole computational domain and different phases are treated as a single fluid with variable material and rheological properties. The method has been validated for various benchmark single-phase and two-phase viscoelastic flow problems. The method has been demonstrated to be grid convergent with a second-order spatial accuracy for all the cases considered in this paper. Then, the method is applied to study two-phase viscoelastic systems in a pressure-driven flow in a capillary tube with a sudden contraction and expansion. The effects of viscoelasticity in drop and bulk fluids are investigated including high Weissenberg and Reynolds number cases up to Wi = 100 and Re = 100. The FENE-CR model is used to account for the fluid viscoelasticity. Extensive computations are performed to examine drop dynamics for a wide range of parameters. It is found that viscoelasticity strongly interacts with drop interface in a non-monotonic and complicated way. Finally, the method is employed to investigate the effects of viscoelasticity on dynamics of a droplet impacting and spreading on flat solid surfaces. The contact angle is determined dynamically based on the empirical correlation proposed by Kistler (1993). The emphasis is placed on the influence of viscoelasticity and extensive simulations are performed for a wide range of parameters. It has been found that the viscoelasticity favors drop rebound in contrast with the well-known anti-rebound effects of polymer additives. Some recent experimental studies have suggested that the anti-rebound effects of polymeric additives are not due to the change in the bulk properties of the drop, but rather due to the modification of wetting properties of the substrate. A simple model is developed to test this hypothesis. The computational results are found to support this hypothesis and show that the anti-rebound behavior can be captured by the modification of the surface wetting properties in the receding phase.