(79f) Plunging of Solid Surfaces Into the Viscoelastic Fluid: An Experimental/Numerical Study

Viscoelastic free surface flows have practical applications in coating technology, polymer processing, and enhanced oil recovery. Numerous researchers in the past have focused their effort on understanding of the coating dynamics of Newtonian and viscoelastic fluids in a wide variety of coating geometries such as blade coaters, extrusion slot coaters, forward-roll coaters (co- and counter-rotating), and roll-plate coaters. Most of these studies have had as their focus flow instabilities at the air-fluid interface in the front of the coater in an effort to understand the dependence of onset conditions on various flow and fluid parameters to prevent interfacial instabilities in industrial processes. In this study however, we have investigated the effect of fluid elasticity on the interfacial dynamics in the back of the coater via a combined numerical/experimental study. The simulations are performed based on pseudo-solid domain mapping DEVSS/SUPG finite element method utilizing the Finitely Extensible Non-linear Elastic Chilton-Ralison (FENE-CR) constitutive equation.  The experimental studies have been performed in an eccentric cylinder geometry for both a viscous Newtonian fluid and a series of elastic Boger fluids. Specifically, we have observed, stable two-dimensional interfaces in the back of coater that get sharper and migrate toward the front of the coater with an increase in Capillary and Weissenberg numbers. Qualitatively similar behavior has been observed in the numerical simulations. Overall, it has been shown that fluid elasticity has a very significant influence on the interfacial dynamics of this class of flows, namely elasticity leads to an increase in both the film thickness and air-fluid interface sharpness and subsequently to flow instability.