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Fluid Dynamics Seminar
Monday, Mar. 28, 2011,
4:00 PM
Cullimor Hall, Room 611
New Jersey Institute of Technology
CFD analysis of free surface flow of viscoplastic materials in human airways
Parsa Zamankhan
Department of Bio-Medical Engineering, University of Michigan
Abstract
Liquid plugs can be formed through installation of liquids into liquid-lined conduits or through Rayleigh instability of the coating liquids in such conduits (Halpern and Grotberg 1992). In addition, the spaces between consecutive gas bubbles in Taylor flow (Shao, Gavriilidis et al. 2009) are filled by liquid plugs. The formation of plugs through Rayleigh instability occurs in respiratory airways of human beings and animals, blocking the lower generations of the lung from inhaling \ Oxygen and exhaling Co2 (Bian, Tai et al. 2010). The blocked airways can be re-opened by introducing a critical pressure difference across the two menisci. The reopening procedure, however, can injure epithelial cells that cover the inner side of the respiratory walls. The motion of the plug due to the pressure difference induces stresses along the wall which can lead to lethal damage of epithelial cells. The inner side of the respiratory airways is covered by mucus which is a non-Newtonian fluid with a yield stress. The developed liquid plugs in the airway through the closure process therefore consist of non-Newtonian materials with a yield stress. This would lead to some major differences compared to Newtonian plugs during the propagation. In this presentation the results of a CFD analysis on the steady displacement of liquid plugs in 2D channels are discussed. The yield stress behavior of mucus was approximated by the Bingham fluid Equation (Oldroyd 1947; Oldroyd 1947). The Bingham fluid Equation was implemented via Papanastasiou’s regularized constitutive equation (Papanastasiou 1987). The governing equations were solved by a mixed discontinuous finite-element formulation and the free surface was resolved by the method of spines (Kistler and Scriven 1984). The computational results show that the yield stress modifies the plug profile through increasing the film thickness and suppression of the capillary waves along the leading meniscus. The magnitude of the induced shear stress along the wall is also elevated by the yield stress. This would enhance the potential of epithelial cell injury during the reopening process.
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