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Numerical modelling of the extensional dynamics in elastoviscoplastic fluids
KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics.
KTH, Centres, SeRC - Swedish e-Science Research Centre. KTH, School of Engineering Sciences (SCI), Centres, Linné Flow Center, FLOW. KTH, School of Engineering Sciences (SCI), Engineering Mechanics, Fluid Mechanics and Engineering Acoustics. Department of Energy and Process Engineering, Norwegian University of Science and Technology (NTNU), Trondheim, Norway.ORCID iD: 0000-0002-4346-4732
(English)Manuscript (preprint) (Other academic)
Abstract [en]

The extensional dynamics of an elasto-viscoplastic (EVP) fluid is studied by means of numerical simulations closely modelling an experimental configuration.  Specifically, we track the interface between the EVP material and the Newtonian medium using an algebraic volume of fluid method (MTHINC-VOF) and employ a fully Eulerian immersed boundary method (IBM) to model the motion of the piston responsible of the extension of the material.

We investigate the role of different values of the yield stress, surface tension at the interface between the EVP material and the surrounding fluid, polymer viscosity ratio, and extension rates on the necking thickness of the material, extensional viscosity, and yielding of the material. 

 The results of the simulations reveal that when the yield stress of the EVP material is much larger than the viscous stresses, the material undergoes an elastic deformation, regardless of the selected values of extension rate, interfacial forces, and viscosity ratio. Moreover, increasing the ratio of the polymeric viscosity to the total viscosity of the system accelerates the EVP rupture due to the high stress concentration in the central part of the material sample. Specific and novel to our study, we show that interfacial forces cannot be ignored when the surface tension coefficient is such that a Capillary number based on the extensional rate is order 1. For large values of the surface tension coefficient, the EVP material fails sooner, with a clear deviation from the exponential reduction in the neck thickness.

National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-320570OAI: oai:DiVA.org:kth-320570DiVA, id: diva2:1706315
Note

QC 20221026

Available from: 2022-10-25 Created: 2022-10-25 Last updated: 2022-10-26Bibliographically approved
In thesis
1. Numerical study of interface dynamics and phase change
Open this publication in new window or tab >>Numerical study of interface dynamics and phase change
2022 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Multi-phase fluid flows are ubiquitous in natural phenomena and different industrial applications such as in food industry, the medical sector, heat exchangers, power generation systems, to name a few.  Understanding the underlining  physics of multi-phase flows  proved to be a challenging task due to presence of sophisticated dynamics, including the evolution of the interface between any pair of phases, thermodynamics and possibility of phase change, interactions between the fluid phases and a solid phase, etc.  Together with theoretical studies and experiments performed on a variety of multi-phase flow problems, numerical simulations have been employed by many researchers to scrutinise different aspects of the problem. During the last decades, a great many studies have been conducted aiming to provide more accurate numerical frameworks for investigating multi-phase flow problems.

Among the various complicated aspects of a multi-phase flow, the present thesis is focused on few characteristics of it the understanding of which requires more considerations and demands improvements in the numerical frameworks. First, we elaborate on the different interface tracking approaches suit the study of different multi-phase flows. In particular, a Volume of Fluid method, a compressible formulation of a diffuse interface approach, a Cahn-Hilliard phase field method, and an Immersed Boundary method are employed to study wetting phenomemna and fluxes at the interface. We have initially investigated biological-relevant membranes, extensional dynamics of a Elasto-viscoplastic material, and droplet spreading over rough surfaces.  In the second part of the thesis, we propose novel numerical methods and setups to investigate the phase change problems in both nanoscale and mesoscale. In particular, we developed a novel numerical method for the solidification problem, a pressure control setup for studying boiling at nanoscale, and a pressure based algorithm for modelling the boiling and evaporation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2022. p. 81
Series
TRITA-SCI-FOU ; 2022:55
National Category
Fluid Mechanics and Acoustics
Research subject
Engineering Mechanics
Identifiers
urn:nbn:se:kth:diva-320579 (URN)978-91-8040-393-1 (ISBN)
Public defence
2022-11-25, F3, Lindstedtsvägen 26 & 28, floor 2, No. 132, Floor 2, Stockhom, 13:00 (English)
Opponent
Supervisors
Note

QC 221026

Available from: 2022-10-26 Created: 2022-10-25 Last updated: 2022-11-09Bibliographically approved

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Shahmardi, ArminBrandt, Luca

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