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1. Schörner, Mario. The stability of gravity-driven viscous films over topography.

Degree: PhD, Ingenieurwissenschaften, 2018, Universität Bayreuth

The gravity-driven flow of a viscous film over an inclined surface is a fundamental problem in fluid mechanics. This type of flow serves as a model to catch the physics behind a wide range of technical and environmental processes which silently affect our lives. The most simplified case of this basic hydrodynamic configuration is the flow of a viscous film over an infinitely extended and perfectly flat substrate, which even has an exact analytical solution. However, in the real world, the substrates on which the films move are frequently rough  – either intentionally or accidentally. The great challenge arises that, in general, the flows over such inclined topographies cannot be calculated analytically from the Navier-Stokes equations. The interaction between the underlying topography and the fluid layer results in a complicated dynamical behavior and gives rise to, e.g., the formation of eddies in the troughs and resonant standing waves at the flow's free surface. As already small substrate defects can significantly affect the film flows, the requirement for predictable product and process properties in coating industries generated considerable interest in improving the understanding of the associated flow mechanisms. Since the interface between the liquid and the surrounding gas is a deformable boundary, waves can appear spontaneously at the free surface if a critical volume flux is exceeded. These waves are the reaction of the system to disturbances, like external forcing or ambient noise, and grow or shrink on their way downstream. Dependent on the volume flux, the perturbation's frequency, and the interaction between the fluid and the topography a complicated topology of stable (waves are damped) and unstable (waves are amplified) flow regimes appears. In medical and semiconductor industries, where uniformly thin coatings are essential, the formation of these waves gives rise to great difficulties in the manufacturing processes. As a pure analytical treatment of the vast majority of these hydrodynamic systems is impossible today, thorough experimental investigations and comprehensive computational modelings are inalienable to improve the understanding of the associated flow mechanisms. The present dissertation deals with the effects of different types of topographies on the free surface stability of gravity-driven viscous films. Comprehensive new experiments were combined with all existing analytical, numerical and experimental findings on this complex problem. That way, new flow phenomena were uncovered and attributed to the fundamental mechanisms which determine the flow dynamics. The aim of the present study was to characterize these results for the sake of unveiling a universally valid principle, being able to describe and unify all findings on the stability of gravity-driven viscous film flows. The first step in order to unveil whether the above-mentioned universal principle indeed exists was to investigate whether the flows over different topographies can exhibit the same stability behavior, or… Advisors/Committee Members: Aksel, Nuri (advisor).

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APA · Chicago · MLA · Vancouver · CSE | Export to Zotero / EndNote / Reference Manager

APA (6th Edition):

Schörner, M. (2018). The stability of gravity-driven viscous films over topography. (Doctoral Dissertation). Universität Bayreuth. Retrieved from https://epub.uni-bayreuth.de/3855/

Chicago Manual of Style (16th Edition):

Schörner, Mario. “The stability of gravity-driven viscous films over topography.” 2018. Doctoral Dissertation, Universität Bayreuth. Accessed January 15, 2019. https://epub.uni-bayreuth.de/3855/.

MLA Handbook (7th Edition):

Schörner, Mario. “The stability of gravity-driven viscous films over topography.” 2018. Web. 15 Jan 2019.

Vancouver:

Schörner M. The stability of gravity-driven viscous films over topography. [Internet] [Doctoral dissertation]. Universität Bayreuth; 2018. [cited 2019 Jan 15]. Available from: https://epub.uni-bayreuth.de/3855/.

Council of Science Editors:

Schörner M. The stability of gravity-driven viscous films over topography. [Doctoral Dissertation]. Universität Bayreuth; 2018. Available from: https://epub.uni-bayreuth.de/3855/

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