Centre de documentation
scientifique

Visualization of two-phase flow dynamics: Techniques for droplet interactions, interfaces, and material transport / Grzegorz Karol Karch (2017)  

Public Titre : Visualization of two-phase flow dynamics: Techniques for droplet interactions, interfaces, and material transport Type de document : Thèse/HDR Auteurs : Grzegorz Karol Karch, Auteur ; Thomas Ertl, Directeur de thèse ; H. Theisel, Directeur de thèse Editeur : Stuttgart : University of Stuttgart Année de publication : 2017 Importance : 180 p. Format : 21 x 30 cm Note générale : Bibliography Von der Fakultät Informatik, Elektrotechnik und Informationstechnik und dem Stuttgart Research Centre for Simulation Technology der Universität Stuttgart zur Erlangung der Würde eines Doktors der Naturwissenschaften (Dr. rer. nat.), genehmigte Abhandlung Langues : Anglais (eng) Descripteur : [Termes IGN] analyse visuelle [Termes IGN] mécanique des fluides [Termes IGN] visualisation 4D Index. décimale : THESE Thèses et HDR Résumé : (auteur) Computational visualization allows scientists and engineers to better understand simulation data and gain insights into the studied natural processes. Particularly in the field of computational fluid dynamics, interactive visual presentation is essential in the investigation of physical phenomena related to gases and liquids. To ensure effective analysis, flow visualization techniques must adapt to the advancements in the field of fluid dynamics that benefits substantially from the growing computational power of both commodity desktops and supercomputers on the one hand, and steadily expanding knowledge about fluid physics on the other. A prominent example of these advances can be found in the research of two-phase flow with liquid droplets and jets, where high performance computation and sophisticated algorithms for phase tracking enable well resolved and physically accurate simulations of liquid dynamics. Yet, the field of two-phase flow has remained largely unexplored in visualization research so far, leaving the scientists and engineers with a number of challenges when analyzing the data. These include the difficulty in tracking and investigating topological events in large droplet groups, high complexity of droplet dynamics due to the involved interfaces, and a limited choice of high quality interactive methods for the analysis of related transport phenomena. It is therefore the aim of this thesis to address these challenges by providing a multi-scale approach for the visual investigation of two-phase flow, with the focus on the analysis of droplet interaction, fluid interfaces, and material transport. To address the problem of analyzing highly complex two-phase flow simulations with droplet groups and jets, a linked-view approach with three-dimensional and abstract space-time graph representation of droplet dynamics is proposed. The interactive brushing and linking allows for general exploration of topological events as well as detailed inspection of dynamics in terms of oscillations and rotations of droplets. Another approach further examines the separation of liquid phases by segmenting liquid volumes according to their topological changes in future time. For visualization, boundary surfaces of these volume segments are extracted that reveal intricate details of droplet topology dynamics. Additionally, within this framework, visualization of advected particles corresponding to arbitrarily selected segment provides useful insights into the spatio-temporal evolution of the segment. The analysis of interfaces is necessary to understand the interplay of interface dynamics and the dynamics of droplet interactions. A commonly used technique for interface tracking in the volume of fluid-based simulations is the piecewise linear approximation which, although accurate, can affect the quality of the simulation results. To study the influence of the interface reconstruction on the phase tracking procedure, a visualization method is presented that extracts the interfaces by means of the first-order Taylor approximation, and provides several derived quantities that help assess the simulation results in relation to the interface reconstruction quality. The liquid interface is further investigated from the physical standpoint with an approach based on quantities derived from velocity and surface tension gradients. The developed method supports examination of surface tension forces and their impact on the interface instability, as well as detailed analysis of interface deformation characteristics. A line of research important for engineering applications is the analysis of electric fields on droplet interfaces. It is, however, complicated by higher-order elements used in the simulations to preserve field discontinuities. A visualization method has been developed that correctly visualizes these discontinuities at material boundaries. Additionally, the employed space-time representation of the droplet-insulator contact line reveals characteristics of electric field dynamics. The dynamics of droplets are often examined assuming single-phase flow, for instance when the internal material transport is of interest. From the visualization perspective, this allows for adaption of traditional vector field visualization techniques to the investigation of the studied phenomena. As one such concept, dye based visualization is proposed that extends the transport analysis to advection-diffusion problems, therefore revealing true transport behavior. The employed high quality advection preserves fine details of the dye, while the implementation on graphics processing units ensures interactive visualization. Several streamline-based concepts are applied in space-time representation of 2D unsteady flow. By interpreting time as the third spatial dimension, many 3D streamline-based visualization techniques can be applied to investigate 2D unsteady flow. The introduced vortex core ribbons support the examination of vortical flow behavior by revealing rotation near the core lines. For the study of topological structures, a method has been developed that extracts separatrices implicitly as boundaries of regions with different flow behavior, and therefore avoids potentially complicated explicit extraction of various topological structures. All proposed techniques constitute a novel multi-scale approach for visual analysis of two-phase flow. The analysis of droplet interactions is addressed with visualization of the phenomena leading to breakups and with detailed visual inspection of these breakups. On the interface level, techniques for the interface analysis give insights into the simulation quality, mechanisms behind topology changes, as well as the behavior of electrically charged droplets. Further down the scale, the dye-based visualization, streamline-based concepts for space-time analysis, and the implicit extraction of flow topology allow for the investigation of droplet internal transport as well as general single-phase flow scenarios. The applicability of the proposed methods extends, in a varying degree, beyond the use in two-phase flow. Their usability is demonstrated on data from simulations based on Navier-Stokes equations that exemplify practical problems in the research of fluid dynamics. Note de contenu : Introduction 1 - Fundamentals and State of the Art 2 - Visualization of Interactions in Droplet Groups 3 - Visualization of Liquid Interface Dynamics 4 - Visualization Approaches for Material Transport Conclusion Numéro de notice : 21572 Affiliation des auteurs : non IGN Nature : Thèse étrangère Note de thèse : Doktor thesis : Sciences naturelles : Stuttgart : 2017 En ligne : https://elib.uni-stuttgart.de/handle/11682/9701 Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=90563