Introduction to Blowing and Drifting Snow Processes and Their Representation in Numerical Models

In this seminar I will explore and contrast several different modeling techniques for disperse multiphase flows, focusing on where each method is most applicable and what kinds of considerations need to be made in different geophysical settings. Disperse multiphase flows are characterized by flows involving at least two phases. Usually one phase is a continuous phase like water or air, but could be any gaseous or liquid phase. The other phase or phases are dispersed phases like water drops, sand, or ash, as long as the phase is not continuously connected in space. Several important geophysical phenomena can be classified as dispersed multiphase flows, including clouds, blowing snow and sand, sediment transport in rivers and oceans, and volcanic ash ejection and powder snow avalanches. This diverse set of phenomena requires a robust set of simulations techniques to address different scales and unique physical phenomena. Broadly speaking there are two classes of dispersed multiphase flow simulations, Euler-Euler and Euler-Lagrange, which differ in how they treat the dispersed phase, either as a fluid or as particles. Beyond representations of the disperse phase, models also differ in what interactions between and amongst the phases are represented explicitly, from one way coupled models all the way up to four-way coupled simulations. These two modeling choices (Euler- Euler vs Euler-Lagrange and degree of coupling) are largely dependent on what physical phenomenon is being modeled, with particular sensitivity to particle mass loading, boundary conditions, and computational considerations.