Separation and Pattern Formation in Fluid-immersed Granular Mixtures

Michael Swift

School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK

We shall describe a range of separation phenomena that occur in binary granular mixtures subjected to vibration in the presence of a fluid. Under vertical vibration, a fine bronze-glass mixture in air spontaneously segregates into glass-rich and bronze-rich "phases" that are extremely pure. Similar behaviour is also observed for mixtures of larger glass and bronze particles submerged in water. Under horizontal vibration, the mixtures segregate into stripes aligned perpendicular to the axis of vibration. To aid our understanding, we have developed numerical simulations that are able to capture many of the key features observed experimentally. From both experiment and simulation, we conclude that these strong separation effects result from the coupling between the granular motion and that of the fluid driven thorough the bed by vibration.