German VARAS (Physique)
When air is injected at the bottom of an immersed granular layer, it crosses the system by percolating or fracturing. It thus forms several paths that reach the free surface of the layer at different locations. In this thesis, we study this process experimentally (for a three and two dimensional setup), numerically and theoretically. First, we focus on the dynamics of the air invading the medium at short and long time scale, when injecting a continuous air flow. At long time, the typical size of the region explored by the air can be accounted for by a diffusion-like process . We also investigate the effect of gravity by tilting the experimental cell. We contrast the results with numerical simulations for the injection of a fixed volume of air, and characterize the morphology of the invasion zone. We show that the typical height and width of the region explored by the air does not depend on the injected volume only, but also on a dimensionless parameter c which accounts for the relative effects of the gravity and capillarity . Finally, when increasing the water height above the granular layer, successive grain advection and deposition form a crater consisting of two dunes growing and moving apart one from the other. We observe that the typical size of the crater increases logarithmically with time, independently of the gas emission process .
 G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 011302 (2011).
 G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 83, 061302 (2011).
 G.Varas, V. Vidal and J.-C. Géminard, Phys. Rev. E. 79, 021301 (2009).
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