TU Darmstadt / ULB / TUbiblio

Numerical Simulation of Shear Driven Wetting

Rettenmaier, Daniel (2019):
Numerical Simulation of Shear Driven Wetting.
Darmstadt, Technische Universität, [Online-Edition: https://tuprints.ulb.tu-darmstadt.de/8510],
[Ph.D. Thesis]

Abstract

In this thesis, a simulation framework is built that is able to accurately predict forced wetting on complex geometry in turbulent shear flow. To optimize functionalities and to increase the safety of industrial applications such as in printing, coating or the exterior water management of vehicles it is necessary to properly understand the motion of drops and rivulets in shear flow. For this purpose, the specific interplay of multi-phase flows, three-phase contact line dynamics, and turbulent flow fields on a multitude of length and time scales are to be modeled and discretized in such a way that complex geometries are representable. The sensitivity of the drop and rivulet motion on small length scales is the main motivation of this study since a detailed description of wetting phenomena on large-scale applications is necessary but not affordable. To develop the required simplifying models, all necessary models for a detailed description of the complex physical interplay are implemented and validated in the present study.

The numerical framework is based on the Volume of Fluid method within OpenFOAM to describe the multi-phase flow. To simulate wetting, a variety of models regarding the surface tension and the contact line dynamics, including the contact angle hysteresis, have been implemented and validated successfully. One of two elaborate turbulence models has been chosen because of its compatibility with the multi-phase flow description. This hybrid turbulence model is based on a Reynolds Average Navier Stokes method and a Large Eddy Simulation method, which provides a flexible compromise between accuracy and computational resources. Furthermore, to cope with the multitude of length scales, the high-performance techniques Adaptive Mesh Refinement and Dynamic Load Balancing have been significantly enhanced within this work to ensure a stable and efficient as well as highly parallelizable computation. All incorporated models have been implemented based on an unstructured mesh, which allows for the representation of complex geometries.

In particular, the key scenarios of wetting found in the exterior water management of vehicles have been simulated and compared with well-defined experiments. Simulations of drop impact, as well as drop and rivulet motion on inclined plates, match with a variety of experimental setups in literature. Critical characteristics, such as the incipient motion of drops, the cornering of the drop tails and the meandering of rivulets also match experimental findings very well. Moreover, in shear flow, the simulation of the incipient motion of drops is in accordance with experiments and a developed theoretical model. Finally, the interaction of a moving drop in turbulent shear flow with a microchannel further confirms the predictive capabilities of the numerical framework even for complex geometries.

Item Type: Ph.D. Thesis
Erschienen: 2019
Creators: Rettenmaier, Daniel
Title: Numerical Simulation of Shear Driven Wetting
Language: English
Abstract:

In this thesis, a simulation framework is built that is able to accurately predict forced wetting on complex geometry in turbulent shear flow. To optimize functionalities and to increase the safety of industrial applications such as in printing, coating or the exterior water management of vehicles it is necessary to properly understand the motion of drops and rivulets in shear flow. For this purpose, the specific interplay of multi-phase flows, three-phase contact line dynamics, and turbulent flow fields on a multitude of length and time scales are to be modeled and discretized in such a way that complex geometries are representable. The sensitivity of the drop and rivulet motion on small length scales is the main motivation of this study since a detailed description of wetting phenomena on large-scale applications is necessary but not affordable. To develop the required simplifying models, all necessary models for a detailed description of the complex physical interplay are implemented and validated in the present study.

The numerical framework is based on the Volume of Fluid method within OpenFOAM to describe the multi-phase flow. To simulate wetting, a variety of models regarding the surface tension and the contact line dynamics, including the contact angle hysteresis, have been implemented and validated successfully. One of two elaborate turbulence models has been chosen because of its compatibility with the multi-phase flow description. This hybrid turbulence model is based on a Reynolds Average Navier Stokes method and a Large Eddy Simulation method, which provides a flexible compromise between accuracy and computational resources. Furthermore, to cope with the multitude of length scales, the high-performance techniques Adaptive Mesh Refinement and Dynamic Load Balancing have been significantly enhanced within this work to ensure a stable and efficient as well as highly parallelizable computation. All incorporated models have been implemented based on an unstructured mesh, which allows for the representation of complex geometries.

In particular, the key scenarios of wetting found in the exterior water management of vehicles have been simulated and compared with well-defined experiments. Simulations of drop impact, as well as drop and rivulet motion on inclined plates, match with a variety of experimental setups in literature. Critical characteristics, such as the incipient motion of drops, the cornering of the drop tails and the meandering of rivulets also match experimental findings very well. Moreover, in shear flow, the simulation of the incipient motion of drops is in accordance with experiments and a developed theoretical model. Finally, the interaction of a moving drop in turbulent shear flow with a microchannel further confirms the predictive capabilities of the numerical framework even for complex geometries.

Place of Publication: Darmstadt
Divisions: 16 Department of Mechanical Engineering
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA)
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA) > Modelling and simulation of turbulent flows
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA) > Flow control and unsteady aerodynamics
Exzellenzinitiative
Exzellenzinitiative > Graduate Schools
Exzellenzinitiative > Graduate Schools > Graduate School of Computational Engineering (CE)
16 Department of Mechanical Engineering > Fluid Mechanics and Aerodynamics (SLA) > Dynamics of drops and sprays
Date Deposited: 25 Aug 2019 19:55
Official URL: https://tuprints.ulb.tu-darmstadt.de/8510
URN: urn:nbn:de:tuda-tuprints-85100
Referees: Tropea, Prof. Dr. Cameron and Bothe, Prof. Dr. Dieter
Refereed / Verteidigung / mdl. Prüfung: 16 January 2019
Alternative Abstract:
Alternative abstract Language
Das Ziel der vorliegenden Dissertation ist die numerische Simulation von Benetzung in turbulenter Scherströmung und bei komplexen geometrischen Verhältnissen. Zur Optimierung der Funktionalität und der Sicherheit industrieller Anwendungen wie z.B. im Druck, bei Beschichtungen oder bei Verschmutzungen am Fahrzeug soll die Bewegung von Tropfen und Rinnsalen in Scherströmung vollständig verstanden werden. Dabei müssen der Mehrphasen-Strömung, der dynamischen Drei-Phasen Kontaktlinie, der turbulenten Strömung und einer Vielzahl von Längen- und Zeitskalen bei der Modellierung und Diskretisierung so Rechnung getragen werden, dass auch komplexe Geometrien abgebildet werden können. Die hohe Sensitivität bezgl. der Prozesse auf kleinen Skalen auf die Tropfen und Rinnsalbewegung motiviert diese Arbeit, da in der großskaligen Anwendung eine detaillierte Beschreibung der kleinen Skalen notwendig wäre, aber nicht möglich ist. Um vereinfachende Modelle zu entwickeln, wurde in dieser Arbeit ein Strömungslöser implementiert, in dem alle notwendigen Modelle für eine detaillierte Beschreibung der vielfältigen physikalischen Effekte eingebunden sind. In OpenFOAM wird die Mehrphasenströmung mithilfe der Volume of Fluid Methode beschrieben. An diese Methode wurde eine Reihe von Modellen für die Oberflächenspannung, die Kontaktliniendynamik und die Kontaktwinkel-Hysterese gekoppelt, mit experimentellen Daten validiert und die vielversprechendste Kombination ausgewählt. Diese Modelle bilden die Basis für eine akkurate Simulation der Benetzung. Hinsichtlich der Kompatibilität der Turbulenzmodelle mit der verwendeten Mehrphasenströmungsmethodik wurde ein Hybridmodell ausgewählt, welches dynamisch und lokal die Turbulenzmodellierung der günstigen aber ungenauen Reynolds Average Navier Stokes Methode und der teuren aber genauen Large Eddy Simulations Methode blendet. Um eine Vielzahl an zugrundeliegenden Längenskalen parallel und ressourcenschonend auflösen zu können, wurde die adaptive Gitterverfeinerung und dynamische Lastverteilung in OpenFOAM signifikant verbessert. Alle genannten Methoden sind so implementiert, dass eine Darstellung komplexer Geometrien mit Hilfe der unstrukturierten Gitterrepresentätion möglich ist. Simulationen der Schlüsselszenarien von Tropfenaufprall und Tropfen- und Rinnsalbewegung am Auto werden im Rahmen dieser Arbeit mit wohl-definierten Experimenten verglichen. Tropfen- und Rinnsalbewegung auf geneigten Ebenen stimmen mit den Simulationen dieser Arbeit überein. Dabei werden die charakteristische Startbewegung der Tropfen, die Hinterkante bewegter Tropfen, sowie das Mäandern von Rinnsalen hervorragend getroffen. Auch in Scherströmung lässt sich die Startbewegung eines Tropfens vorhersagen, wobei die Ergebnisse der Experimente, Simulation und eines hier präsentierten theoretischen Modells sehr gut übereinstimmen. Die Interaktion der Tropfenbewegung in turbulenter Scherströmung mit komplexer Geometrie bestätigt in einer abschließenden Untersuchung die hervorragenden prädiktiven Eigenschaften der ausgewählten Modelle und Methoden.German
Export:
Suche nach Titel in: TUfind oder in Google

Optionen (nur für Redakteure)

View Item View Item