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Microbubbles and Microparticles are Not Faithful Tracers of Turbulent Acceleration

type de publication      article dans une revue internationale avec comité de lecture
date de publication 2016
auteur(s) Mathai Varghese; Calzavarini Enrico; Brons Jon; Sun Chao; Lohse Detlef
journal (abréviation) Physical Review Letters (Phys. Rev. Lett.)
volume (numéro) 117 (2)
numéro de papier 024501
  
résumé We report on the Lagrangian statistics of acceleration of small (sub-Kolmogorov) bubbles and tracer particles with Stokes number St 1 in turbulent flow. At a decreasing Reynolds number, the bubble accelerations show deviations from that of tracer particles; i.e., they deviate from the Heisenberg-Yaglom prediction and show a quicker decorrelation despite their small size and minute St. Using direct numerical simulations, we show that these effects arise due the drift of these particles through the turbulent flow. We theoretically predict this gravity-driven effect for developed isotropic turbulence, with the ratio of Stokes to Froude number or equivalently the particle drift velocity governing the enhancement of acceleration variance and the reductions in correlation time and intermittency. Our predictions are in good agreement with experimental and numerical results. The present findings are relevant to a range of scenarios encompassing tiny bubbles and droplets that drift through the turbulent oceans and the atmosphere. They also question the common usage of microbubbles and microdroplets as tracers in turbulence research.
mots clés Correlation time; De correlations; Isotropic turbulence; Lagrangian statistics; Micro-particles; Numerical results; Particle drift velocity; Turbulence research
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