Onset and Stability of Convection in Porous Media: Visualization by Magnetic Resonance Imaging

Using magnetic resonance imaging, we examine the onset and stability of porous media convection (PMC) in packings of solid spheres. Nominally, PMC resembles Rayleigh-Bénard convection, except that there should be no vertical vorticity. We find pinned defects in convection patterns for disordered sphere packings. Roll-like structures form in regularly packed media, with rapid relaxation to stable patterns within the expected stable range. The size of up flow regions decreases relative to down flow regions with increasing Rayleigh number, producing a novel time dependent state for Ra $/$Ra ${}_c>6\mathrm{}$.