A Numerical and Experimental Study of the Dispersion of a Dust Layer by a Rarefaction Wave
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In recent years, dynamics of dust lifting behind a passing shock wave have been studied extensively. Few studies have focused on the problem of dust lifting by a rarefaction wave. The aim of this study was to create a three-dimensional CFD model of previously conducted experiments. A second goal was to conduct own experiments of rarefaction wave-dust interaction and try to model these using CFD. The Eulerian-Eulerian approach was selected as the modelling technique with two different energy models studied; the segregated fluid temperature model and the segregated fluid isothermal model. The former provided a solution by solving the energy equation, while the latter kept a constant energy field. The results from the simulations were compared to results obtained using an exact Riemann solver, previous experiments and previous simulations. A ”smearing” of the head and tale of the waves was observed. Other than this, the simulation solving for the energy equation was in compliance with both the Riemann solution and previous experiments. The consequence of solving using the segregated fluid isothermal model was a too low speed of propagation of the rarefaction-, contact- and shock wave and ultimately a higher air velocity behind the rarefaction wave, which in turn led to a greater dust dispersion. Additionally, a simulation with a closed end geometry was run to investigate the effect of the reflected shock wave. The results indicated that the reflected shock wave and its accompanying flow of gas have a suppressing effect on dust dispersion caused by rarefaction waves. As a second part of the thesis experiments with a rarefaction wave interacting with a layer of particles were recorded with a high speed camera in two pressure chambers with different diameter using a solenoid valve to initiate depressurization. The particle layer showed similarities to a fluidized particle bed when exposed to the rarefaction wave. After the rarefaction wave arrived at the particle bed, the bed expanded upwards with visible bubbles forming and expanding inside, eventually breaking through the top of the bed and spouting dust further up the chamber. The height at which the bubbles broke through the particle bed surface was defined as breakthrough height. The breakthrough height was shown to increase with smaller pressure chamber diameter, smaller particle diameter and, at times, increasing pressure. A combination of smaller particle diameter, smaller pressure chamber diameter and higher initial pressure gave the highest amount of particle dispersion following the breakthrough.
PublisherThe University of Bergen
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