Lippert, Anja Charlotte (2016)
Direct Numerical Simulations of Thermocapillary Driven Motions
in Two-phase Flows.
Technische Universität Darmstadt
Dissertation, Erstveröffentlichung
Kurzbeschreibung (Abstract)
In this thesis, a code framework is created to allow further insight into thermocapillary driven flows through direct numerical simulation of two-phase flows. For the numerical simulations, the full Navier-Stokes equations and energy equation are solved in a Volume of Fluid framework. To this end, the underlying sets of equations for each phase are conditioned, volume averaged and added to obtain one set of equations valid within the whole physical domain, incorporating the corresponding jump conditions. The interface between the two phases is captured by piecewise linear reconstruction from the volume fraction field. Apart from providing a sharp interface, such a geometrical reconstruction allows a specific position to store interface values and generate additional information around the interface via subgrid-scale modeling. For the energy transport in temperature form, a novel algorithm avoids mixed quantities, as present in the one-field formulation. Based on cut-cell methods, the interface reconstruction is used to generate two grids on which phase specific, averaged, but not mixed, quantities are stored for each phase. The exchange between both phases takes place according to the jump condition at the reconstructed interface. Additionally, the interface values are stored at the plane barycenters. The thermal Marangoni forces are calculated directly from these interface temperatures by discretizing the interface gradient. To prevent artificial accelerations in the vicinity of the interface, the surface tension is applied via a balanced continuous surface force algorithm. A library of common macroscopic contact angle models and different contact line velocities is created to capture contact line dynamics. Based on the contact angle for each contact line cell, the surface tension and normal vectors are adapted such that the interface encloses this angle with the solid wall. Three algorithms are implemented for contact line pinning. The new developments are incorporated within the in-house code Free Surface 3D. They are thoroughly validated, in isolation as well as in combination. With this extended framework thermocapillary driven flows are investigated in applications relevant for industrial processes. These investigations include short-scale Marangoni flows in a film on an evenly heated horizontal wall with a structured surface. Simulations are performed to study the influence of film height, wall temperature, topography changes and the effect of gravity on flow characteristics like interface velocity, flow patterns and heat transport. Furthermore, the physical mechanisms and acting forces of a thermally actuated droplet on a inhomogeneously heated wall are investigated. The droplet motion is studied both in two and three dimensions, where a movement either towards the cold or the warm side can be observed. The last application concerns liquid bridges as a model of half-zone melting, where the effects of contact angle and contact line pinning on flow patterns are captured by the numerical simulation.
Typ des Eintrags: | Dissertation | ||||
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Erschienen: | 2016 | ||||
Autor(en): | Lippert, Anja Charlotte | ||||
Art des Eintrags: | Erstveröffentlichung | ||||
Titel: | Direct Numerical Simulations of Thermocapillary Driven Motions in Two-phase Flows | ||||
Sprache: | Englisch | ||||
Referenten: | Bothe, Dr. Dieter ; Stephan, Dr. Peter | ||||
Publikationsjahr: | 27 November 2016 | ||||
Ort: | Darmstadt | ||||
Datum der mündlichen Prüfung: | 15 Juli 2016 | ||||
URL / URN: | http://tuprints.ulb.tu-darmstadt.de/5817 | ||||
Kurzbeschreibung (Abstract): | In this thesis, a code framework is created to allow further insight into thermocapillary driven flows through direct numerical simulation of two-phase flows. For the numerical simulations, the full Navier-Stokes equations and energy equation are solved in a Volume of Fluid framework. To this end, the underlying sets of equations for each phase are conditioned, volume averaged and added to obtain one set of equations valid within the whole physical domain, incorporating the corresponding jump conditions. The interface between the two phases is captured by piecewise linear reconstruction from the volume fraction field. Apart from providing a sharp interface, such a geometrical reconstruction allows a specific position to store interface values and generate additional information around the interface via subgrid-scale modeling. For the energy transport in temperature form, a novel algorithm avoids mixed quantities, as present in the one-field formulation. Based on cut-cell methods, the interface reconstruction is used to generate two grids on which phase specific, averaged, but not mixed, quantities are stored for each phase. The exchange between both phases takes place according to the jump condition at the reconstructed interface. Additionally, the interface values are stored at the plane barycenters. The thermal Marangoni forces are calculated directly from these interface temperatures by discretizing the interface gradient. To prevent artificial accelerations in the vicinity of the interface, the surface tension is applied via a balanced continuous surface force algorithm. A library of common macroscopic contact angle models and different contact line velocities is created to capture contact line dynamics. Based on the contact angle for each contact line cell, the surface tension and normal vectors are adapted such that the interface encloses this angle with the solid wall. Three algorithms are implemented for contact line pinning. The new developments are incorporated within the in-house code Free Surface 3D. They are thoroughly validated, in isolation as well as in combination. With this extended framework thermocapillary driven flows are investigated in applications relevant for industrial processes. These investigations include short-scale Marangoni flows in a film on an evenly heated horizontal wall with a structured surface. Simulations are performed to study the influence of film height, wall temperature, topography changes and the effect of gravity on flow characteristics like interface velocity, flow patterns and heat transport. Furthermore, the physical mechanisms and acting forces of a thermally actuated droplet on a inhomogeneously heated wall are investigated. The droplet motion is studied both in two and three dimensions, where a movement either towards the cold or the warm side can be observed. The last application concerns liquid bridges as a model of half-zone melting, where the effects of contact angle and contact line pinning on flow patterns are captured by the numerical simulation. |
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Alternatives oder übersetztes Abstract: |
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URN: | urn:nbn:de:tuda-tuprints-58172 | ||||
Sachgruppe der Dewey Dezimalklassifikatin (DDC): | 600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften und Maschinenbau | ||||
Fachbereich(e)/-gebiet(e): | 04 Fachbereich Mathematik 04 Fachbereich Mathematik > Analysis 04 Fachbereich Mathematik > Analysis > Mathematische Modellierung und Analysis 04 Fachbereich Mathematik > Mathematische Modellierung und Analysis (MMA) |
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Hinterlegungsdatum: | 11 Dez 2016 20:55 | ||||
Letzte Änderung: | 07 Feb 2024 11:55 | ||||
PPN: | |||||
Referenten: | Bothe, Dr. Dieter ; Stephan, Dr. Peter | ||||
Datum der mündlichen Prüfung / Verteidigung / mdl. Prüfung: | 15 Juli 2016 | ||||
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