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

PhD defense ECL

Sarah Clève

Vendredi 4 octobre 2019, ECL bât. W1 amphi 201

Sarah Clève

Microstreaming induced in the vicinity of an acoustically excited, nonspherically oscillating microbubbler

Le jury se compose de

Philippe Marmottant, Université Grenoble Alpes, Rapporteur
Robert Mettin, Georg-August-Universität Göttingen, Rapporteur
Caroline Derec, Université Paris Diderot, Examinatrice
Peter Spelt, Université de Lyon Claude Bernard, Examinateur
Philippe Blanc-Benon, Ecole Centrale de Lyon, Directeur de thèse
Claude Inserra, Université de Lyon Claude Bernard, Encadrant
Cyril Mauger, INSA de Lyon, Encadrant

Microbubbles find use in several domains, one of them being medical ultrasound applications. Different characteristics of those bubbles such as their acoustic esonance or their destructive effect during inertial cavitation can be exploited. Another phenomenon induced around acoustically excited bubbles is microstreaming, that means a relatively slow mean flow with respect to the fast bubble oscillations. Microstreaming and its associated shear stresses are commonly agreed to play a role in the permeabilization of cell membranes, a detailed understanding of the induced flows is however missing. To acquire basic physical knowledge, this work focuses on
the characterization of streaming induced around an air bubble in water, more precisely around a single acoustically trapped and excited, nonspherically oscillating bubble. The experimental part consists of two steps. First, the bubble dynamics, in particular the triggered shape mode and the orientation of the bubble have to be controlled. For this, the use of bubble coalescence proves to be an adequate method. In a second step, the microstreaming is recorded in parallel to bubble dynamics. This allows to correlate the obtained streaming patterns to the respective shape oscillations. The large number of obtained pattern types can be classified, in particular with respect to the mode number and bubble size. A close investigation of the bubble dynamics allows furthermore deducing the important physical mechanisms which lead to such a variety of streaming patterns. In order to confirm the experimental findings, an analytical model has been developed. It is based upon time-averaged second-order fluid mechanics equations and the experimentally obtained bubble dynamics serves as input parameters. Supplementary to the microstreaming work, this manuscript contains a short section on directed jetting of contrast agent microbubbles, which might appear at high acoustic driving. The impact of those microjets on cell membranes presents another mechanism made responsible for the permeabilization of cell membranes.

Agenda

  • Friday 4 October -

    Soutenance de thèse : Sarah Clève

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