Research Project: Damlacık Buharlaşmasının Ara-Yüz Çözümlü Doğrudan Simülasyonu
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Contributors
Funders
ID
TB.00862
Authors
Muradoğlu, Metin
Faculty Member
Publications
Non-Newtonian and surfactant effects on the liquid plug rupture in an airway reopening model
(Cambridge University Press, 2025) Muradoğlu, Metin; Hao, Renjie; Izbassarov, Daulet; Grotberg, James B.; Lacassagne, Tom; Bahrani, S. Amir; Romano, Francesco; Department of Mechanical Engineering; Yes; College of Engineering
Elastoviscoplastic effects on liquid plug propagation and rupture occurring in airways are studied computationally using the Oldroyd-B and Saramito-Herschel-Bulkley models. The relevant parameters are selected from physiological values representative of the eighth-to-tenth generation branches of a typical adult lung. The respiration pushes the liquid plug, depositing a trailing film thicker than the leading film. As a result, the liquid plug gets drained and eventually ruptures. We model airway reopening considering a rigid axisymmetric tube whose inner surface is coated by a thin non-Newtonian liquid film. A critical elastic behaviour is revealed: for low Weissenberg number (subcritical), the viscoelastic stress is released in the liquid plug, while for high Weissenberg number (supercritical), the stretched polymeric chains release their stresses in the trailing film, giving rise to (i) hoop stress that increases the film thickness and (ii) axial stress that leads to a speed-up of the liquid plug. Under supercritical conditions, we also identify a resonance that amplifies the elastic stresses. A mechanical analogy is proposed to elucidate the resonance phenomenon. The occurrence of the resonance is robust upon a variation of Weissenberg number, Laplace number, reference solvent-to-total dynamic viscosity ratio, the surfactant elastoviscoplastic mucus. Our simulations confirm that a presence of surfactants do not significantly affect the results, except for the expected delay of airway reopening due to air-mucus surface contamination. Such a novel elastocapillary mechanism increases the risk of epithelial cell damage regardless of the occurrence of plug rupture.
Computational investigation of deformable droplet evaporation under forced convection
(Elsevier, 2026) Salimnezhad, Faraz; Muradoğlu, Metin; Salimnezhad, Faraz; Department of Mechanical Engineering; Graduate School of Sciences and Engineering; Yes; College of Engineering; GRADUATE SCHOOL OF SCIENCES AND ENGINEERING
Evaporation of a deformable droplet under convection is investigated and performance of the classical and Abramzon–Sirignano (A–S) models is evaluated. Using the Immersed Boundary/Front-Tracking (IB/FT) method, interface-resolved simulations are performed to examine droplet evaporation dynamics over a wide range of Reynolds (20 ≤ R e ≤ 200), Weber (0 . 65 ≤ W e ≤ 9), and mass transfer (1 ≤ B M ≤ 15) numbers. It is shown that flow in the wake region is greatly influenced by the Stefan flow as higher evaporation rates leads to an earlier flow separation and a larger recirculation zone behind the droplet. Under strong convection, the models fail to capture the evaporation rate especially in the wake region, which leads to significant discrepancies compared to interface-resolved simulations. Droplet deformation greatly influences the flow field around the droplet and generally enhances evaporation but the evaporation rate remains well correlated with the surface area. The A–S model exhibits a reasonably good performance for a nearly spherical droplet but its performance deteriorates significantly and generally underpredicts evaporation rate as droplet deformation increases. The A–S model is overall found to outperform the classical model in the presence of significant convection.
