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VERSION:2.0
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SUMMARY:Virtual MEchanics GAthering -MEGA- Seminar: Coating flow instabili
 ties: to pearl or to whirl on fibers and sculpting draperies in limestone 
 caves
DTSTART:20201119T161500
DTEND:20201119T173000
DTSTAMP:20260916T050215Z
UID:6e6786566ef4b77aa634cc87b20fbb4bf926e9fce68ea51f28d45b78
CATEGORIES:Conferences - Seminars
DESCRIPTION:Shahab Eghbali & Pier Giuseppe Ledda (LFMI\, EPFL)\nAbstract 
 The study of the dynamics of coating flows is of undeniable interest owing
  to the wide presence in natural environments and the large number of appl
 ications in industrial and manufacturing processes. Here\, we bring two ex
 amples of coating flows showing the broad variety of patterns\, i.e.\, the
  destabilization of a gravity-driven viscous flow coating a vertical fiber
 \, and the draperies formation in the context of karst structures when the
  coating fluid flows below an inclined substrate.\n\nNumerous studies have
  focused on the transition of a liquid thread into a downward-traveling tr
 ain of beads along a fiber\, a phenomenon known as Rayleigh-Plateau instab
 ility\, in the limit of small Bond number\, where the surface tension domi
 nates over gravity. Here\, we explore the limit of large Bond number\, i.e
 . centimetric radial sized liquid column.  The experiments are carried ou
 t using highly viscous silicone oil to focus on inertialess flows. We obse
 rve the formation of a helical interface\, coiling around the thin fiber. 
 We address theoretically the physical mechanism underlying the observed in
 terface coiling by the linear stability analysis of a unidirectional flow 
 along a rigid eccentric fiber. The asymmetry of the drainage velocity\, ab
 ove a certain threshold\, induces coiling. Overall\, small fiber radius an
 d large eccentricity tend to promote the coiling of the interface\, while 
 small Bond numbers tend to preserve the axisymmetric interface. \n\nWe th
 en move to the study of the role of hydrodynamic instabilities in the morp
 hogenesis of typical draperies structures encountered among other speleoth
 ems in limestone caves. The problem is tackled using the lubrication appro
 ximation for the fluid film flowing under an inclined plane\, in the prese
 nce of substrate perturbations that grow according to a classical depositi
 on law. We generalize to the two-dimensional case the spatio-temporal anal
 ysis of the linear impulse response resulting from linear simulations. We 
 exploit the concepts of Riesz transform and monogenic signal\, the multi-d
 imensional complex continuation of a real signal\, to retrieve the asympto
 tic properties of the wavepacket. The isotropy of the pure hydrodynamic so
 lution is broken and the deposition process selects predominant streamwise
  structures on the substrate as the response is advected away. Furthermore
 \, the presence of an initial localized perturbation on the substrate prod
 uces a quasi-steady region characterized by streamwise structures both in 
 the fluid film and on the substrate. We suggest that these linear selectio
 n mechanisms contribute to the formation of draperies under inclined cave 
 ceilings.\n\nBio Shahab Eghbali did his bachelor's in Mechanical Engineer
 ing at the University of Tehran\, Iran\, in 2014. In the same year\, he jo
 ined EPFL to pursue his studies in the Master's program in the Institute o
 f Mechanical Engineering with the Aero-and-Hydrodynamics orientation. Sinc
 e 2018\, he is a doctoral assistant in the Laboratory of Fluid Mechanics a
 nd Instabilities (LFMI) where he is currently working on the instability o
 f complex interfacial flows.\n\nPG Ledda is a Ph.D. student at the Laborat
 ory of Fluid Mechanics and Instabilities at the EPFL. He obtained his B.sc
  and M.sc in Aerospace and Aeronautical Engineering at the University of P
 isa. He joined EPFL during his master thesis\, focused on the pattern char
 acterization when a porous bluff body is invested by an asymptotic flow. H
 e is now focused on the pattern formation in karst environments and the fl
 ow modelization using lubrication models. His main interests involve the f
 low control of aerodynamic flows by porosity variations and of thin films 
 by textured substrates.
LOCATION:Zoom: epfl.zoom.us/s/98393329833 Room Passcode: 349948 http://epf
 l.zoom.us/s/98393329833
STATUS:CONFIRMED
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