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摘要
The effect of viscoelasticity on the interfacial dynamics of air displacing a viscoelastic fluid under the presence of gravity, i.e., the dip coating flows is examined. A stabilized finite element method coupled with a pseudo-solid domain mapping technique is used to carry out the computations. The fluid is modeled by the Finitely Extensible Non-linear Elastic Chilton-Ralison (FENE-CR) constitutive equation. Simulations at various Ca and Bo are performed in order to determine the limiting condition for dip coating where the flow characteristics become independent of Bo. For all values of Ca and Bo studied, the flow is characterized by recirculation near the interface. To this end the film thickness scaled with the capillary length, as a function of Wi, at low Ca and high Bo collapses onto a single curve, and agrees with the analytical expression for the film thickness in the low Wi limit. As the value of Ca is increased, the corresponding value of Bo that is required to collapse the results onto a single curve, i.e., the dip coating flow limit, is correspondingly higher. For a fixed Ca and Wi, increasing Bo results in a decrease in the film thickness, an increase in the size of the recirculation region and an increase in the strain rates subsequently leading to an increase in the normal stresses. We show that the interfacial dynamics in the dip coating flow are qualitatively similar to those observed in the Hele-Shaw flow. Specifically, at low Wi, film thinning occurs and as the value of Wi is increased, the formation of normal elastic stress boundary layers in the capillary transition region is observed. This is accompanied by a sharp increase in the film thickness and a compression of the air-liquid interface in the capillary transition region. Published by Elsevier B.V.
- 出版日期2011-7
