A Hele-Shaw system was used by University of Chicago MRSEC researchers, Sidney Nagel and Heinrich Jaeger and their research groups, to explore the zero-surface-tension properties of granular "fluids."Â’ Theoretically, it was determined by Paul Wiegmann, also at the University of Chicago, that fluid fingering in the zero-surface-tension limit should lead to singular cusp structure locally and fractal geometry globally.Â’ Granular flow provides the first experimental evidence for the coexistence of these two singular features and shows how the local cusps evolve into a global fractal. Â’ Summer REU student, Aaron Patterson from Morehouse College, conducted the preliminary experiments for this study.
The fugure shows patterns of fingers at an overpressure of 0.20 atm.Â’ In general, the patterns are sharper at low pressure and smoother at high pressure.Â’ This is opposite to what happens in Newtonian fluids.Â’ Work made possible throughÂ’ the NSF MRSEC program, DMR-0213745.
