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Modélisation et développement de diagnostics optiques pour la caractérisation de gouttes surfondues en écoulement ou en interaction avec un substrat sous-refroidi

Abstract : Icing phenomena that occur on aircraft in flight can be a major hazard in aeronautics. The main resulting safety problems are reduced visibility, pitot tube blockage and reduced aerodynamic performance. In this context, aircraft must be certified for various icing conditions likely to be encountered, particularly in relation to the presence of supercooled droplets with diameters greater than 50 µm in the atmosphere. The certification stages are carried out using standardised icing wind tunnel tests that make it possible to recreate aeronautical icing conditions close to those encountered in flight. The objectives of the work presented in this manuscript concern the implementation of a new optical technique based on Laser-Induced Fluorescence (LIF) for the characterization of supercooled droplets: temperature, detection of their states (i.e. liquid, solid or mixed), characterization of drops in mixed phase and dynamic of the solidification front in a droplet impacting a subcooled substrate. A first LIF technique, using two fluorescent tracers and three spectral bands of detection, allows to measure the temperature of supercooled droplets in flow as well as to estimate the fraction of ice contained in a population of droplets in flow. Measurements carried out in conditions similar to those encountered in aeronautics were performed in an icing wind tunnel of the DGA Essais-Propulseurs and showed the difficulty of reproducing real aeronautical icing conditions (droplets in thermal equilibrium with the carrier phase). A second technique based on Laser Induced Fluorescence Fast Imaging (PLIF) was developed to study the solidification of a droplet impacting a subcooled substrate. This new PLIF method provides, for the first time, access to the dynamics and morphology of the solidification front inside the droplet.The study focused on droplet impacts on a dry substrate and on a substrate covered with an ice layer. The second case allows to get rid of the phenomenon of water supercooling and thus of the random character of the solidification triggering. The measurements showed that the evolution of the solidification front and the characteristics of the tip formed by the droplet at the end of solidification were dependent on the nature of the substrate (thermal conductivity) and the angle of contact between the droplet and the substrate.
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https://hal.univ-lorraine.fr/tel-03021918
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Submitted on : Tuesday, November 24, 2020 - 3:24:23 PM
Last modification on : Monday, March 29, 2021 - 4:03:06 PM
Long-term archiving on: : Thursday, February 25, 2021 - 8:24:00 PM

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  • HAL Id : tel-03021918, version 1

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Mehdi Stiti. Modélisation et développement de diagnostics optiques pour la caractérisation de gouttes surfondues en écoulement ou en interaction avec un substrat sous-refroidi. Thermique [physics.class-ph]. Université de Lorraine, 2020. Français. ⟨NNT : 2020LORR0120⟩. ⟨tel-03021918⟩

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