Gretar Tryggvason

Direct numerical simulations of multiphase flows, where all continuum spatial and temporal scale are fully resolved for a large system undergoing unsteady motion, have advanced significantly over the last two decades or so. Such simulations have been used to examine a large number of multiphase systems and have resulted in a much improved understanding of their dynamics. The challenges now are at least twofold: How to simulate much more complex systems, and how to use the results to increase our ability to predict industrial scale flows. We first describe recent efforts to simulate three phase flows including bubbles and suspended particles as found in froth flotation used in mineral processing, where air bubbles are used to separate hydrophobic from hydrophilic particles. Here, the main challenge is to incorporate a moving contact line on freely moving solid particles. For predictions, we need coarse models that describe the dynamics of large-scale flows and currently most efforts to use the results of fully resolved simulations to improve coarse models relay on ideas going back several decades. Progress in data science is, however, posed to change that. In many cases the presence of a sharp phase boundary is the most important feature of the flow and we present formal ways to coarsen results from fully resolved simulations while preserving a sharp, but simplified phase boundary. We also discuss preliminary efforts to predict the evolution of the coarse flow using machine learning combined with trajectory modeling, where the conservation equations are augmented in such a way that the coarse flow evolves correctly.

Prof. Gretar Tryggvason is the Charles A. Miller, Jr. Distinguished Professor at the Johns Hopkins University and the head of the Department of Mechanical Engineering. He received his PhD from Brown University in 1985 and was on the faculty of the University of Michigan in Ann Arbor until 2000, when he moved to Worcester Polytechnic Institute as the head of the Department of Mechanical Engineering. Between 2010 and 2017 he was the Viola D. Hank professor at the University of Notre Dame and the chair of the Department of Aerospace and Mechanical Engineering. Prof. Tryggvason is well known for his contributions to computational fluid dynamics; particularly the development of methods for computations of multiphase flows and for pioneering direct numerical simulations of such flows. His various service activities include serving as the editor-in-chief of the Journal of Computational Physics 2002-2015 and currently the Chair of the Division of Fluid Dynamics of the American Physical Society. He is a fellow of APS, ASME and AAAS, and the recipient of several awards, including the 2012 ASME Fluids Engineering Award and the 2019 ASTFE Award.