Flow fields around an intruder immersed in a 2D dense granular layer

We investigated the granular flows around a cylindrical intruder immersed in a two dimensional disordered granular medium for initial packing fractions close to but below the jamming transition. We observed a gradual transition in the flow behavior during the penetration of the intruder within the granular medium. The average longitudinal displacement field induced by the intruder penetration is characterized by a long-range decay in the first stage of motion. However the decay becomes exponential at more advanced stages with more developed recirculation of grains around the intruder. This transition towards a localization of the average flow is associated with the gradual compression of the granular medium in front of the intruder and with the onset of recirculations, in relation with the dynamics of the cavity that forms behind the intruder.