Multiphase flows are ubiquitous in the world around us. Above us, the dynamics of clouds are governed by the interaction of air, water vapor, droplets, and ice crystals. Around us, geophysical mass flows such as snow avalanches, mudslides, debris flows, and volcanic eruptions present significant natural hazards. Below us, sediment transport processes in rivers, lakes, and oceans affect the health of freshwater, estuarine, and benthic ecosystems, while magma flows shape the evolution of Earth’s crust. A common feature shared by the above environmental multiphase flows is the enormous range of length scales to which they give rise, from droplets and clay particles of micrometer size to atmospheric weather systems and ocean currents exceeding thousands of kilometers. The resulting multiscale nature renders the exploration of environmental multiphase flows by laboratory experiments, numerical simulations, field observations and remote sensing highly challenging.

This program will address common organizing principles across the entire spectrum of density ratios and volume fractions of multiphase flows, based on recent progress in experimental laboratory investigations, high-resolution computer simulations and novel approaches to field observations and in situ measurements. The goal is to bridge the gap between information at the microscale and continuum descriptions for the macroscale by promoting the development of upscaling strategies that will enable predictions of large-scale flow phenomena at environmental and geophysical scales.