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We present analytical and numerical results on localized fluidization withina granular layer subjected to a local injection of fluid. As the injection rateincreases the three different regimes previously reported in the literature arerecovered: homogeneous expansion of the bed, fluidized cavity in whichfluidization starts developing above the injection area, and finally thechimney of fluidized grains when the fluidization zone reaches the freesurface. The analytical approach is at the continuum scale, based on Darcy'slaw and Therzaghi's effective stress principle. It provides a good descriptionof the phenomenon as long as the porosity of the granular assembly remainsrelatively homogeneous, i.e. for small injection rates. The numerical approachis at the particle scale based on the coupled DEM-PFV method. It tackles themore heterogeneous situations which occur at larger injection rates. Theresults from both methods are in qualitative agreement with data publishedindependently. A more quantitative agreement is achieved by the numericalmodel. A direct link is evidenced between the occurrence of the differentregimes of fluidization and the injection aperture. While narrow apertures letthe three different regimes be distinguished clearly, larger apertures tend toproduce a single homogeneous fluidization regime. In the former case, it isfound that the transition between the cavity regime and the chimney regime foran increasing injection rate coincides with a peak in the evolution of inletpressure. Finally, the occurrence of the different regimes is defined in termsof the normalized flux and aperture.

Localized fluidization in granular materials: Theoretical and numerical study