Particles in supersonic plumes and turbulence

Abstract: As a manned lander descends onto the surface of Mars, millions of people hundreds of millions of miles away on Earth watch the event as transmitted with a breathtaking time delay. We are aware that the final approach will be dusty, with a significant number of particles kicked up that will impede surface visibility. This scenario is reminiscent of the challenges faced during lunar exploration. While particles pose significant challenges for planetary exploration, they are also prevalent in environmental flows and industrial processes across a wide range of flow and particle loading regimes.

In this talk we will focus on two ongoing efforts on particle-laden flows. The first part will focus on the inhomogeneous distribution of small inertial particles as they interact with a turbulent flow. High particle concentration regions, or clusters, affect the modulation of the host turbulent flow and can lead to additional fluctuations of temperature or wave propagation in the particle-fluid mixture. We will present our new vertical particle-laden channel flow facility, the world longest to our knowledge, along with a novel data analysis tool for time-resolved particle-fields that significantly reduces the computational cost. We will share results of cluster size and lifetime statistics. The second part of the talk will focus on particle-laden flows resulting from the impingement of a supersonic plume onto a granular surface, as seen in rocket-powered planetary descents. In this case, subsonic, supersonic, and even rarefied flow regimes coexist, and particle loadings vary from dilute to very dense due to soil fluidization and erosion. We will share our results on flow and particle measurements from a Mach 5 thruster in a vacuum facility for varying jet expansion ratios and mass flow. Using a novel millimeter wave interferometer, we were able to measure, for the first time, the temporal evolution of ejecta concentration in optically opaque particle-flow mixtures.

Bio: Laura Villafañe is an Assistant Professor in the Department of Aerospace Engineering at the University of Illinois at Urbana-Champaign. Her research focuses on particle-laden flows, turbulent and separated flows, and on the development of non-intrusive diagnostics and data analysis tools. She holds a B.Sc./M.Sc. degree in Aerospace Engineering from the Polytechnic University of Madrid, and completed her Ph.D at the von Karman Institute for Fluid Dynamics, Belgium. Prior to joining UIUC she was a Postdoctoral Fellow and Research Engineer at the Center for Turbulence Research at Stanford University. Laura is the recipient of two NASA Early-Stage-Innovation Awards.