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An objective perspective for classic flow classification criteria

type de publication      article dans une revue internationale avec comité de lecture
date de publication 2016
auteur(s) Martins Ramon Silva; Pereira Anselmo Soeiro; Mompean Gilmar; Thais Laurent; Thompson Roney L.
journal (abréviation) Comptes Rendus - Mecanique (Compt Rendus Mec)
volume (numéro) 344 (1)
  
pages 52 – 59
résumé Four classic criteria used to the classification of complex flows are discussed here. These criteria are useful to identify regions of the flow related to shear, elongation or rigid-body motion. These usual criteria, namely Q, δ, λ2 and λcr/λci, use the fluid's rate-of-rotation tensor, which is known to vary with respect to a reference frame. The advantages of using objective (invariant with respect to a general transformation on the reference frame) criteria are discussed in the present work. In this connection, we construct versions of classic criteria replacing standard vorticity, a non-objective quantity, by effective vorticity, a rate-of-rotation tensor with respect to the angular velocity of the eigenvectors of the strain-rate tensor. The classic criteria and their corresponding objective versions are applied to classify two complex flows: the transient ABC flow and the flow through the abrupt 4:1 contraction. It is shown that the objective versions of the criteria provide richer information on the kinematics of the flow.
mots clés ABC flow; Contraction; Flow classification; Objectivity; Vortex identification
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