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SUMMARY:MEchanics GAthering -MEGA- Seminar: Talk1 - Instability driven rel
 axation of an anticyclone\; Talk2 - Pattern formation of a thin film flowi
 ng under an inclined plane
DTSTART:20191114T161500
DTEND:20191114T173000
DTSTAMP:20260415T122304Z
UID:ad626ed19fc8b5978e5afcf063d2811a1d88d50ca0e6ba90911ca846
CATEGORIES:Conferences - Seminars
DESCRIPTION:Eunok Yim & Pier Giuseppe Ledda\, LFMI​\, EPFL\nInstabilit
 y driven relaxation of an anticyclone\, by Eunok Yim\nWe study the nonlin
 ear evolution of the centrifugal instability appearing in a columnar antic
 yclone using a semi-linear approach to model the transient unsteady flow e
 volution in a self-consistent manner. For anticyclones in a homogeneous vi
 scous flow\, the fastest growing instability is without oscillation in tim
 e but with a finite axial wavenumber. Hence\, the self-consistent model is
  developed around the spatially averaged time dependent meanflow and the f
 luctuation\, which reduces the problem from 2D nonlinear to 1D semi-linear
 . The two linear meanflow and fluctuation equations are coupled via the Re
 ynolds stress of the fluctuations.\nAt a given rotation ratio between the 
 vortex angular velocity and the background rotation\, only the most linear
 ly unstable mode is considered for Reynolds numbers Re=800 and 2000 define
 d with the maximum angular velocity and the radius of the vortex.  For bo
 th values of Re\, the model predicts well the nonlinear evolution of the m
 eanflow and the fluctuation amplitude. Higher harmonics are non-negligible
  only at the highest value of Re. The results show that the angular moment
 um of the meanflow is homogenized to a stable state via the action of the 
 Reynolds stresses of the fluctuation. \n\nPattern formation of a thin fil
 m flowing under an inclined plane\, by Pier Giuseppe Ledda\nWe discuss th
 e pattern formation of a thin film flowing under an inclined planar substr
 ate\, combining theoretical\, experimental and numerical results. The phen
 omenon is related to the Rayleigh-Taylor instability\, in which one heavie
 r fluid is placed above a lighter one. When an upper wall and the substrat
 e inclination are considered\, a variety of patterns are observed. The nat
 ural and forced dynamics of the flat film to spanwise perturbations and th
 e resulting non-linear structures are studied\; in both cases\, spanwise-p
 eriodic\, streamwise-aligned structures\, called rivulets\, arise. The imp
 ulse response of a flat film is numerically and experimentally studied. We
  analyze the linear response\, which does not show any preferential direct
 ion\; a weakly non-linear model highlights however the selection of the st
 reamwise structures. The fully non-linear evolution leads to a steady patt
 ern characterized by fully saturated rivulets\, the profile of which is an
 alyzed in detail. A secondary stability analysis reveals the presence of a
  range of parameters in which only rivulets are observed\, in agreement wi
 th the experimental observations. Outside of this range\, lenses appear on
  the rivulets\, which may eventually drip.
LOCATION:MED 2 2423 https://plan.epfl.ch/?room==MED%202%202423
STATUS:CONFIRMED
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