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UID:2436@i2m.univ-amu.fr
DTSTART;TZID=Europe/Paris:20180706T110000
DTEND;TZID=Europe/Paris:20180706T120000
DTSTAMP:20180621T090000Z
URL:https://www.i2m.univ-amu.fr/evenements/rotating-rayleigh-benard-convec
 tion-probing-the-transition-to-the-rotation-dominated-regime/
SUMMARY: (...): Rotating Rayleigh-Benard convection: probing the transition
  to the rotation-dominated regime
DESCRIPTION:: Séminaire commun I2M (équipe ALEA-SI) / IRPHE (Seminar I2M 
 / IRPHE)-Most geo- and astrophysical flows are driven by strong thermal fo
 rcing and affected by high rotation. In these systems\, direct measurement
 s of the physical quantities are not possible due to their large scales\, 
 remoteness and complexity. A model containing the main physical constituen
 ts is rather beneficial. This approach is given by the problem of rotating
  Rayleigh-Benard convection (RRBC): a rotating fluid layer heated from bel
 ow and cooled from above. For large-scale systems\, the governing paramete
 rs of RRBC take extreme values\, leading to a regime of geostrophic turbul
 ence.-Background rotation causes different flow structures and heat transf
 er efficiencies in Rayleigh-Benard convection. Three main regimes are know
 n: rotation-unaffected (regime I)\, rotation-affected (regime II) and rota
 tion-dominated (regime III). Regimes I and II are easily accessible with e
 xperiments and numerical simulations (see right figure [1])\, thus they ha
 ve been extensively studied\, see for a recent review [2]. On the other ha
 nd\, access to regime III is more troublesome. Thus\, regime III and the t
 ransition to this regime are less explored. Approaching the geostrophic re
 gime of rotating convection\, where the flow is highly turbulent and at th
 e same time dominated by the Coriolis force\, typically requires dedicated
  setups with either extreme dimensions or troublesome working fluids (e.g.
 \, cryogenic helium). In this study\, we explore the possibilities of ente
 ring the geostrophic regime of rotating convection with classical experime
 ntal tools: a table-top conventional convection cell with a height of 0.2 
 m and water as the working fluid [3]\, see figure below. In order to exami
 ne our experimental measurements\, we compare the spatial vorticity autoco
 rrelations with the statistics from simulations of geostrophic convection 
 reported earlier [4]. Our findings show that we have indeed access to the 
 geostrophic convection regime and can observe the signatures of the typica
 l flow features reported in the aforementioned simulations. As a next step
  we explored the role of coherent flow structures on the transition to reg
 ime III in RRBC. There are two main hypotheses proposed for the driving me
 chanisms of the transition to regime III one of them directly related to f
 low coherency. These hypotheses are usually examined through different par
 ameters such as viscous and thermal boundary layers thicknesses and heat t
 ransfer efficiency [5\,6]. In this work\, we study regime III and these hy
 potheses from a new perspective: Lagrangian velocity and acceleration fluc
 tuations and autocorrelations of tracers from experiments. We have found t
 hat the transition to regime III coincides with three phenomena\; the vert
 ical motions are suppressed\, the vortical plumes penetrate further into t
 he bulk and the vortical plumes interact less with their surroundings. The
 se findings allow us to evaluate the available hypotheses and to understan
 d more about regime III [7].These regime transitions will be discussed in 
 this talk.-[1] R.J.A.M. Stevens\, H.J.H. Clercx and D. Lohse\, PRE 86\, 05
 6311 (2012).[2] R.J.A.M. Stevens\, H.J.H. Clercx and D. Lohse\, EJMB/F 40\
 , 41-49 (2013).[3] D. Nieves\, A.M. Rubio and K. Julien\, PoF 26\, 086602 
 (2014).[4] H. Rajaei\, R.P.J. Kunnen and H.J.H. Clercx\, PoF 29\, 045105 (
 2017).[5] E.M. King\, S. Stellmach\, J. Noir\, U. Hansen and J.M. Aurnou\,
  Nature 457\, 301-304 (2009).[6] K. Julien\, E. Knobloch\, A.M. Rubio and 
 G.M. Vasil\, PRL 109\, 254503 (2012).[7] H. Rajaei\, K.M.J. Alards\, R.P.J
 . Kunnen and H.J.H. Clercx\, submitted to JFM (2018).--http://www.tue.nl/e
 n/research/researchers/herman-clercx/-Accès IRPHE
CATEGORIES:Séminaire,Analyse Appliquée
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DTSTART:20180325T030000
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