The finger-like branching pattern that occurs when a less viscous fluid displaces a more viscous one confined between two parallel plates, the so-called Hele-Shaw geometry, has been studied widely and with various normal fluids. Shown is the granular analog of a Hele-Shaw experiment, where we can investigate whether a granular material behaves as a fluid with zero surface tension.
In collaboration with the group of Heinrich Jaeger, we have been studying the properties of granular media. Despite their ubiquity and the simplicity with which the can be described, we understand very little about how these materials (e.g., sand) behave. In these studies we enter a new area of physics in which we are studying a statistical system of many particles but where the temperature is totally irrelevant. Thus, these systems are unavoidably always out of equilibrium, and we must come up with new concepts in order to understand and predict their properties.
“Impact dynamics of granular jets with non-circular cross-sections,” Xiang Cheng, L. Gordillo, W. W. Zhang, H. M. Jaeger, and S. R. Nagel submitted (2013). arXiv:1307.6810
"Still water: dead zones and collimated ejecta from the impact of granlar jets," Jake Ellowitz, Herve Turlier, Nicholas Guttenberg, Wendy W. Zhang, Sidney R. Nagel, arXiv:1304.4671 (2013).
“Formation of air bubbles during compaction of a granular pack,” X. Cheng, R. Smith, H. M. Jaeger, and S. R. Nagel, Phys. of Fluids 20, 123305 (2008).
“Toward the zero surface tension limit in granular fingering instability,” X. Cheng, L. Xu, A. Patterson, H. M. Jaeger and S. R. Nagel Nature Physics 4, 234 (2008).
“Granular Jets as a Classical Analog of RHIC Collisions,” X. Cheng, H. Jaeger and S. Nagel RHIC News (online publication) http://www.bnl.gov/rhic/news/011508/ (January 15, 2008).
“Granular Flow in a Rapidly Rotated System with Fixed Walls,” E. I. Corwin, Phys. Rev. E 77, 031308 1-8 (2008).
“Collective behavior in a granular jet: Emergence of a liquid with zero surface-tension,” X. Cheng, G. Varas, D. Citron, H. M. Jaeger, and S. R. Nagel, Phys. Rev. Lett. 99, 188001 (2007).
“Clustering instability in a freely falling granular jet,” M. E, Möbius, Phys. Rev. E 74, 051304 1-9 (2006).
“Three-dimensional Shear in Granular Flow,” X. Cheng, J. B. Lechman, A. Fernandez- Barbero, G. S. Grest, H. M. Jaeger, G. S. Karczmar, M. E. Möbius, and S. R. Nagel, Phys. Rev. Lett. 96, 038001 1-4 (2006).
“The Effect of Air on Granular Size Separation in a Vibrated Granular Bed,” M. E. Möbius, X. Cheng, P. Eshuis, G. S. Karczmar, S. R. Nagel, and H. M. Jaeger, Phys. Rev. E 72, 011304 1-13 (2005).
“The Behavior of Granular Materials under Cyclic Shear,” N. W. Mueggenburg, Phys. Rev. E 71, 031301 1-10 (2005).
“Stress transmission through three-dimensional granular crystals with stacking faults,” M. J. Spannuth, N. W. Mueggenburg, H. M. Jaeger, S. R. Nagel, Granular Matter 6, 215- 219 (2004).
“Intruders in the dust: Air-driven granular size separation,” M. E. Möbius, X. Cheng, G. S. Karczmar, S. R. Nagel, and H. M. Jaeger, Phys. Rev. Lett. 93, 198001 (2004).