Research Project: Havayolu Kapanması Ve Yeniden Açılmasının Sayısal Modellenmesi
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Contributors
Funders
ID
TB.00456
Authors
Muradoğlu, Metin
Faculty Member
Publications
Effects of elastoviscoplastic properties of mucus on airway closure in healthy and pathological conditions
(American Physical Society, 2023) Erken, Oğuzhan; Muradoğlu, Metin; Izbassarov, D.; Romano, F.; Grotberg, J. B.; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Yes; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
Airway mucus is a complex material with both viscoelastic and viscoplastic properties that vary with healthy and pathological conditions of the lung. In this study, the effects of these conditions on airway closure are examined in a model problem, where an elastovis-coplastic (EVP) single liquid layer lines the inner wall of a rigid pipe and surrounds the air core. The EVP liquid layer is modelled using the Saramito-HB model. The parameters for the model are obtained for the mucus in healthy, asthma, chronic obstructive pulmonary disease (COPD), and cystic fibrosis (CF) conditions by fitting the rheological model to the experimental data. Then the liquid plug formation is studied by varying the Laplace number and undisturbed liquid film thickness. Airway closure is a surface-tension-driven phenomenon that occurs when the ratio of the pulmonary liquid layer thickness to the airway radius exceeds a certain threshold. In previous studies, it has been found that airway epithelial cells can be lethally or sublethally damaged due to the high peak of the wall stresses and stress gradients during the liquid plug formation. Here we demonstrate that these stresses are also related to the EVP features of the liquid layer. Yielded zones of the liquid layer are investigated for the different mucus conditions, and it is found that the liquid layer is in a chiefly unyielded state before the closure, which indicates that this phase is dominated by the elastic behavior and solvent viscosity. This is further confirmed by showing that the elastic coefficient is one of the most critical parameters determining whether the closure occurs. This parameter also largely affects the closure time. The wall stresses are also investigated for the pathological and healthy cases. Their peaks for COPD and CF are found to be the highest due to the viscoelastic extra stress contribution. Contrary to the Newtonian case, the wall stresses for COPD and CF do not smoothly relax after closure, as they rather remain effectively almost as high as the Newtonian peak. Moreover, the local normal wall stress gradients are smaller for the COPD and CF liquid layer due to their higher stiffness causing a smaller curvature at the capillary wave. The local tangential wall stress gradients are also shown to be smaller for these cases because of the slower accumulation of the liquid at the bulge.
Dynamics and interactions of parallel bubbles rising in a viscoelastic fluid under buoyancy
(Elsevier B.V., 2023) Muradoğlu, Metin; Naseer, Hafiz Usman; Ahmed, Z.; Izbassarov, D.; Department of Mechanical Engineering; Yes; College of Engineering
Three dimensional interface-resolved numerical simulations are performed to investigate interactions of two buoyancy-driven parallel bubbles rising in an otherwise quiescent viscoelastic fluid for a range of parameters. The flow equations are solved fully coupled with the FENE-P viscoelastic model equation using a front-tracking method and some new features of this complex flow field are reported for the first time. The flow parameters are varied around the baseline case for which a single bubble produces a negative wake. The surface tension, pressure, viscous and viscoelastic forces acting on the bubbles are computed and plotted as a function of time to demonstrate their evolution. The corresponding effects on bubble shapes, terminal velocities, flow field around the bubbles and the evolution of distance between their centers have been examined in detail. Effects of Weissenberg number, Galilei number, Eötvös number and the initial distance between bubbles are investigated. It is found that closely initialized parallel bubbles strongly interact via the negative wakes. Unlike the Newtonian fluid, a reversed flow is observed in between the parallel bubbles rising in a viscoelastic fluid. Long tails form behind the bubbles and they tilt towards each other due to wake interactions. We show that the total viscoelastic force acting on bubbles oscillates with a certain frequency and never attains a steady state value even when the bubbles reach a nearly steady motion. However, amplitude of resulting oscillations in bubble velocity is found to be much smaller. The steady distance between bubbles decreases with the Weissenberg number and the viscosity ratio while it increases with the Galilei number. The polymeric viscosity of the liquid is found to have a significant influence on the magnitude of repelling force acting on the bubbles and the direction of flow in between them. The Eötvös number is found to have a little impact on the distance between the bubbles at their steady-state motion for the range considered here. The normalized terminal velocity of bubbles increases rapidly as the Eötvös number becomes smaller than a critical value.
