PhD Thesis Defence Presentations - Dionisis Pettas
Abstract (Περίληψη)
The gravity-driven film flow over a flat inclined surface is a fundamental problem in fluid mechanics. This flow appears in many significant industrial, environmental and biomedical processes. Although this flow is a classic problem in fluid mechanics, nevertheless, in the real world, the substrates on which the films move exhibit some kind of roughness, either accidentally or intentionally. The interaction between the underlying topography and the fluid layer triggers a complicated dynamical behavior that favors the formation of eddies inside the bottom undulations and resonant standing waves at the free surface of the flow. Even the small fluctuations of the substrate can significantly affect the shape of the free surface. Besides the topological variations, the rheology of the material can affect the fluid flow since the liquids involved are often polymer solutions which generally exhibit non-Newtonian properties. Moreover, a fully wetting state cannot always be achieved. Recent studies indicate that the wetting state of the substrate depends both on its geometrical and liquid properties, while air inclusions can be formed during the coating process of these surfaces resulting in products of inferior quality. Regarding the calculation of the critical parameters for the onset of interfacial instabilities, the existing literature is mainly limited to the Newtonian case. However, the polymeric properties may affect the stability of the flow significantly. Due to the widespread usage of polymer solutions in industrial applications, the understanding of the mechanisms leading to the stabilization/destabilization of the flow is of the utmost importance, while the latter gives the potential for instability control through the development of appropriately tailored substrates.
Speakers Short CV (Σύντομο Βιογραφικό Ομιλητή)
Education
2015: M. Sc. in Chemical Engineering, Department of Chemical Engineering University of Patras
2012: B. Sc. in Physics, Department of Physics, University of Patras
Journal Publications
[1] Pettas, D., Karapetsas, G., Dimakopoulos, Y. and Tsamopoulos, J. "On the origin of extrusion instabilities: Linear stability analysis of the viscoelastic die swell", J. Non-Newtonian Fluid Mech., 224, 61-77 (2015), doi:10.1016/j.jnnfm.2015.07.011.
[2] Pettas, D., Karapetsas, G., Dimakopoulos, Y. and Tsamopoulos, J. "On the degree of wetting of a slit by a liquid Flowing Along an Incline plane", J. Fluid Mech., 820, 45-41 (2017), doi:10.1017/jfm.2017.190.
[3] Pettas, D., Karapetsas, G., Dimakopoulos, Y. and Tsamopoulos, J. "Viscoelastic film flows over an inclined substrate with sinusoidal topography. I. Steady state", Phys. Rev. Fluids, 4, 20 (2019), doi:10.1103/PhysRevFluids.4.083303. (Editor’s Suggestion)
[4] Pettas, D., Karapetsas, G., Dimakopoulos, Y. and Tsamopoulos, J. "Viscoelastic film flows over an inclined substrate with sinusoidal topography. II. Linear stability analysis", Phys. Rev. Fluids, 4, 8 (2019), doi:10.1103/PhysRevFluids.4.083304. (Editor’s Suggestion)
[5] Pettas, D., Dimakopoulos, Y. and Tsamopoulos, J. "Steady flow of a viscoelastic film over an inclined plane featuring periodic slits", J. Non-Newtonian Fluid Mech., (2019), (submitted for publication).
Conference Presentations
[1] "Linear stability analysis during the extrusion of a viscoelastic liquid from a planar die", with G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 9th PanHellenic conference on Fluid-Flow Phenomena, Athens, GREECE, December 12-13, 2014
[2] "Linear stability analysis of viscoelastic fluid extrusion through a planar die", with G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 10th Annual European Rheology Conference, Annual European Rheology Conference 2015, Nantes, FRANCE, April 14-17, 2015.
[3] "Investigation of the flow stability during extrusion of a viscoelastic fluid from a planar die" with G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 10th PanHellenic Scientific Conference in Chemical Engineering, Patras, GREECE, June 4-6, 2015.
[4] "Steady Film Flow Over 2D topography with Air Inclusion" with St. Varchanis, Y. Dimakopoulos, and J. Tsamopoulos, International Conference on Multiphase Flow 2016, Firenze, ITALY, May 22-27, 2016.
[5] "Partial wetting of 2D topography by a viscoelastic Film" with Y. Dimakopoulos and J. Tsamopoulos, Annual European Rheology Conference 2017, Copenhagen, DENMARK, April 3-6, 2017.
[6] "Linear Stability analysis of a Newtonian Film Flowing Over a Substrate with topographical Features" with G. Karapetsas, Y. Dimakopoulos, and J. Tsamopoulos, 70th Annual Meeting of APS Division of Fluid Dynamics, Denver, USA, November, 19-21, 2017.
[7] "Stability Analysis of Viscoelastic Fluid Over a Structured Topography." with G. Karapetsas, Y. Dimakopoulos, and J. Tsamopoulos, 12th European Fluid Mechanics Conference, Vienna, AUSTRIA, September 9-13, 2018.
[8] "Linear stability of viscoelastic Film Flow Over Structured Surfaces." with G. Karapetsas, Y. Dimakopoulos, and J. Tsamopoulos, 71th Annual Meeting of APS Division of Fluid Dynamics, Atlanta, USA, November, 18-20, 2018.
[9] "Stability of a Viscoelastic Film Flowing Over a Substrate with Sinusoidal Corrugations" with G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 12th PanHellenic Scientific Conference in Chemical Engineering, Athens, GREECE, May 29-31, 2019.
[10] "Non-linear analysis of extrusion instabilities in polymer melt processing” with S. Varchanis, Y. Dimakopoulos and J. Tsamopoulos, 91st Society of Rheology meeting in North Carolina, USA, October, 21-25, 2019.
[11] "Numerical simulation of a viscoelastic film flowing over a substrate with periodic rectangular trenches” with A. Marousis, G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 5th Workshop for Graduates and Post-Docs in Chemical Engineering Sciences in Patras, GREECE, 6 November, 2019
[12] "Flow stability of a liquid film partially wetting a substrate with rectangular trenches” with G. Karapetsas, Y. Dimakopoulos and J. Tsamopoulos, 72nd Annual Meeting of APS Division of Fluid Dynamics, Seattle, USA, November, 23-26, 1019.