Granular Flows: Rheology and Booming Sand Dunes

Dr. Melany L. Hunt
Department of Mechanical Engineering
California Institute of Technology

Flows of dry particulate material as well as liquid-solid flows are ubiquitous in industrial and geophysical environments, such as debris flows, slurries, mining and milling operations, and sediment transport. This presentation overviews two ongoing studies at Caltech: the rheological measurements of granular flows, and field studies on booming sand dunes. Current rheological models often invoke the ideas and experiments of R.A. Bagnold from the 1950s. Although the Bagnold work has been cited extensively over the last fifty years, the rheological measurements are dictated by the design of the experimental facility and secondary flow effects. Currently we are engaged in new rheological measurements in the laboratory as well as experiments involving single particle collisions. The second topic involves the flow at the surface of a large sand dune, which may be accompanied by a loud booming sound that consists of a primary audible frequency plus harmonics. This booming phenomenon has fascinated and challenged explorers and researchers for centuries, and yet it remains a scientific mystery. Our recent field measurements contradict the prevailing theories, and may lead to a scientific explanation of the sound.