A three-month long program devoted to fluid-mediated particle transport in geophysical flows will take place at the Kavli Institute for Theoretical Physics in Santa Barbara, California, between September 23 and December 20, 2013. This program will provide an opportunity to develop a consensus regarding the important issues that must be addressed and the key questions to be answered in order to advance the understanding of natural fluid-particle flows. Associated with the program are two focus weeks and a concluding conference.
There are many elements of natural fluid-particle flows that are poorly understood. Examples are the in-fluence of the unsteady mean and fluctuating velocities on particles in a turbulent flow over a range of particle concentration and ratios of particle-fluid mass density; the nature of the inter-actions between particles and between the particles and fluid at the surface of a particle bed; and the mechanisms by which large-scale features develop on the bed in systems driven by water and the wind. Within the three-month program, two focus weeks and a concluding conference will take place that will involve researchers not attending the program. One focus week will be devoted to the interactions of particles with fluid turblence, the other will concentrate on mechanisms of erosion and deposition at the bed. The concluding confence, "Particle-Laden Flows in Nature", will take place during the last week of the program and attempt to provide an overview of the state of understanding of its subject.
Particle-laden flows occur naturally and in many industrial processes. They are not so well understood as flows involving only a fluid. This is because the interaction between the fluid and the particles and those between particles in the fluid are complicated and not easy to describe mathematically. It is important to try to achieve such descriptions in order to predict phenomena such as dune formation by wind-blown sand, underwater avalanches that threaten pipeline and communications cables, avalanches of powder and granular snow, and flows of ash and hot gases or rocks in molten lava during volcanic eruptions.
Particle-laden flows on Earth involve a liquid or a gas and include wind-blown sand, near-shore sediment transport, and powder snow avalanches; consequently, they cover a wide range of concentrations and particle/fluid density ratios. Recent progress in the study of granular materials, improvements in field instrumentation, and the increased capabilities of large-scale computer simulations have led to a better quantitative understanding of particle transport by a turbulent fluid, the interaction between transported grains and the bed, the development of surface feature on the bed, and their subsequent motion and interaction. A three-month program Fluid-Mediated Particle Transport in Geophysical Flows took place at the Kavli Institute for Theoretical Physics in Santa Barbara, California, in the fall of 2013 to advance the understanding of such flows. The program involved geologists, physicists and engineers who do field studies, laboratory experiments, theoretical modeling, and numerical computation on particle-fluid flow in Nature. Such flows have both common and unique features. All of them involve turbulent fluid flow modulated by dilute concentrations of particles through much of their body, important interactions between particles and particles and the fluid in denser concentration near and at the bed, and mobile beds that may be eroded, deposited upon, and deformed. The program at the Kavli Institute served to create a common culture between researchers with diverse backgrounds and to characterize the issues that remain before the description and prediction of natural fluid-particles flow become possible. A similar program is scheduled at the Max Planck Institute for Complex Systems in Dresden, Germany, in the spring of 2016.
