Session LK - Granular Flows IV.
ORAL session, Tuesday morning, November 23
Dauphine, New Orleans Hyatt Regency
Vertical vibrations are known to induce patterning instabilities in various fluid and fluid-like systems. Well known examples include the Faraday instability in viscous and nonviscous fluids and the patterned relief observed in dry granular systems. We study the instabilities of flat layers of granular material saturated with interstitial liquid and bounded above by an air interface. Increasing acceleration amplitude leads first to the accumulation of puddles of liquid on the surface as the grains compact, followed by a transition to a convection-driven heaping relief. This heaping phenomenon bears similarity to that observed in a granular system in a completely aqueous environment.^1 However, our system is quite different due to the air interface and because we study relatively thin layers of granular material, 20-50 diameters high, rather than hundreds of diameters in thickness. While the heaping relief we observe is generally disordered, under some conditions heaps arrange themselves into a robust and regular pattern. Heaps break up at higher drive accelerations, and the hilly relief gives way to cracking and violent breakup. We report on the phase portrait in critical acceleration versus frequency for the transitions to heaping and to cracking.
^1 V.G. Kozlov, A.A. Ivanova, and P. Evesque. Sand behavior in a cavity with incompressible liquid under vertical vibrations. Europhysics Lett. 42, 413-418 (1998).