Fluid Mechanics and Acoustics Laboratory - UMR 5509

LMFA - UMR 5509
Laboratoire de Mécanique des Fluides et d’Acoustique
Lyon
France


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Home > News > Thesis defense > 2016 thesis defense

PhD Defense

Aurore Loisy

Jeudi 15 septembre 2016 - 14h - amphi 201 - ECL

Aurore Loisy

Direct numerical simulation of bubbly flows: coupling with scalar transport and turbulence

Jury:

  • Jérémie BEC, Laboratoire Lagrange (Observatoire de la Côte d’Azur), Rapporteur
  • Alain CARTELLIER, LEGI (Université Grenoble Alpes)
  • Michel LANCE, LMFA
  • Dominique LEGENDRE, IMFT (Institut National Polytechnique de Toulouse), Rapporteur
  • Aurore NASO, LMFA, Co-directrice de thèse
  • Olivier POULIQUEN, IUSTI (Polytech Marseille)
  • Peter SPELT, LMFA, Co-directeur de thèse

Abstract:
This thesis is devoted to the study of homogeneous bubbly flows and their coupling with scalar transport and turbulence. It focuses on the effects of finite size, hydrodynamic interactions, and suspension microstructure, which are investigated using direct numerical simulations at the bubble scale. The dynamics of laminar buoyancy-driven bubbly suspensions is first revisited. More specifically, the effect of volume fraction on the bubble drift velocity is clarified by connecting numerical results to theory for dilute ordered systems, and similarities between perfectly ordered and free disordered suspensions are evidenced. The modeling of scalar mixing in laminar suspensions, as described by an effective diffusivity tensor, is then addressed. A rigorous framework for the computation of the effective diffusivity is provided, a semi-analytical correlation is proposed for ordered suspensions, and a crucial difference between ordered and disordered suspensions with respect to scalar transport is highlighted. Lastly, turbulence is included in the simulations, and its interaction with a finite-size bubble is characterized. The behavior of a bubble as large as the Taylor microscale is shown to share a number of common features with that of a microbubble, most notably, the flow sampled by the bubble is biased. A definition of the liquid flow seen by the bubble, as it enters in usual models for the added mass and the lift forces, is finally proposed.


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