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Theses

Fragmentation aérodynamique d’une goutte liquide induite par une onde de choc plane

Abstract : This thesis proposed a groundbreaking description of the shock-induced aerodynamic fragmentation of a water droplet at the transition of the Rayleigh-Taylor Piercing and the Shear-Induced Entrainment regimes. An experimental facility consisting of a shock tube and high-speed imaging diagnostics is used to investigate the fragmentation processes. Experimental results are supported with numerical simulations performed with the open-source code ECOGEN dedicated to multiphase compressible flows. The shock wave effect on the droplet is assessed by a theoretical modelling based on geometrical acoustics which allows for the description of the wave spatio-temporal dynamics and enables to predict the time-dependent location of the highest energy density. Pressure fields are determined using numerical simulations. It appears that the water tensile rupture is reached for a shock wave Mach number of 1.7 from which bubble cloud cavitation may occur by causing signification changes in the fragmentation dynamics. As regards to the interfacial dynamics, both experiments and numerical simulations show the development of a transverse azimutal modulation resulting in the periodic ligament structure at the droplet surface. Contrary to the modulation growth, its initiation seems to be independent of the capillary effects as revealed by a Fourier analysis of the 3-D numerical results. The ligament dynamics is a cyclic process driven by the vortex shedding process in the wake of the droplet. Four cycles have been observed before the residual droplet core breaks up owing to the growth of an air cavity inside the droplet that acts as weak spot, and thus facilitating the droplet split-off.
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Submitted on : Friday, March 12, 2021 - 1:36:11 PM
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Luc Biasiori-Poulanges. Fragmentation aérodynamique d’une goutte liquide induite par une onde de choc plane. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2021. Français. ⟨NNT : 2021ESMA0002⟩. ⟨tel-03167765⟩

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