Rafika Ben Haj Slama PhD Defense

Title: Flows generated by a focused ultrasound wave in a liquid medium: Acoustic streaming and solid particles flow.
Summary: The present thesis relates to flows generated by focused ultrasound in homogeneous liquid and in liquid charged with particles. Experimental work in water, using Particle Image Velocimetry (PIV) optical technique and CFD (Computational Fluid Dynamics) numerical modeling using Fluent simulation tool, allow as to study involved hydrodynamic and acoustic phenomena : the fluid acoustic streaming and ultrasound radiation force acting on solid particles. This work is provided in the general context of sono-thrombolysis technique (blood clot destruction by ultrasonic cavitation) optimization, where issues related to thrombolytic agents mixing enhancement and to the risk of clot fragments release in the circulation, arise.
Firstly, this work allowed to evaluate the PIV technique for flow measurement in the particular case of high intensity focused ultrasound field presence, where radiation force is likely to influence the seeding particles movement. Indeed, numerical and experimental results comparison has shown that only 5µm-diameter particles are suitable for streaming measurement. In a second time, we managed to characterize the acoustic streaming in an infinite liquid medium and to compare it with a circular free jet flow. Results related to this characterization showed that the streaming flow, even if it presents structural differences compared to this conventional jet, it has important common characteristics, in particular, related to a self-similarity zone existence. Furthermore, an analysis of radiation force effect on suspended solid particles was carried out. In that, we managed to determine a critical diameter above which solid particles flow is dominated by the ultrasound radiation force rather than the streaming drag force.
Time: 14H30
Place: Salle de conférence du bâtiment INSERM au 151 Cours Albert Thomas, 69003 Lyon