AEM Seminar: Friday, February 28th - Prof R. Jason Hearst, Department of Energy & Process Engineering, Norwegian University of Science & Technology (NTNU)

[Molly Schmitz]

University of Minnesota

Aerospace Engineering and Mechanics
Spring 2025 Seminar Series

Friday, December 6, 2024

209 Akerman Hall

2:30pm-4:30pm

AEM Seminar:  

The complex role of turbulence: Vanishing tip vortices, scattering waves, and enhanced gas transfer

Abstract:

We will discuss three areas where recent advances in experimental turbulence measurements have led to new insights. First, time-resolved volumetric measurements of the wake of a model wind turbine are used to investigate the often-observed phenomenon whereby ortices “vanish” rapidly downstream of a wind turbine. Moving to air-water interfacial flows, we investigate the interaction between surface waves and sub-surface turbulence, with a particular focus on enstrophy enhancement and wave scattering. Our results demonstrate that sub-surface turbulence can increase the rate of environmentally significant gas exchange (e.g., O₂, CO₂) across the air-water interface by up to 45%. The talk will also showcase recent advances in flow measurements, including the use of quantifiable laser-induced fluorescence to map O₂ concentration in water while simultaneously capturing the velocity field and surface topology. Additionally, we introduce a novel co-flowing air-water facility equipped with active turbulence grids in each phase, allowing for independent control of turbulence in the air and water.

 

Bio:

Jason Hearst is a Professor at the Norwegian University of Science and Technology (NTNU) in Trondheim, Norway. His primary research activities are centred around the generation of bespoke turbulent flows using active turbulence generating grids and investigating how turbulence influences other canonical and environmental fluids problems. His team is primarily funded via the European Research Council (Starting Grant, GLITR), Marie Skłodowska-Curie Actions (Post-doctoral fellow, Dr. Yi Hui Tee, InMyWaves) and the Research Council of Norway (FRIPRO, WallMix; Knowledge Building Project, reSail).  Jason Hearst earned his PhD in 2015 from the University of Toronto Institute for Aerospace Studies (Canada), and then worked as a post-doctoral researcher at the University of Southampton (UK) with Prof. Bharath Ganapathisubramani. He moved to NTNU in 2017 as an Associate Professor and was promoted to Professor in 2023. He has been on sabbatical since August 2024, first at the University of Oxford and now from January 2025 he is at the University of Toronto.

*Refreshments to follow 

Molly Schmitz (She/Her/Hers)

Graduate Program Coordinator & Executive Accounts Specialist

Department of Aerospace Engineering & Mechanics

University of Minnesota - Twin Cities

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[Molly Schmitz]

University of Minnesota

Aerospace Engineering and Mechanics
Spring 2025 Seminar Series

Friday, March 7, 2025

209 Akerman Hall

2:30pm-4:30pm

AEM Seminar:  

Ejecta clouds by plume impingement on granular surfaces, a challenge to planetary landings

Abstract:

As a manned heavy lander descends onto the natural surface of a planetary body or the Moon, the plumes of the thrusters required for deceleration impinge on the regolith eroding craters underneath the vehicle and lifting dense clouds of ejecta. Surface distance sensing and visibility, lander stability, and ejecta impacts in nearby infrastructure and vehicle sensors, are some of the risks caused by plume-surface interactions (PSI) whose assessment is critical for mission design. However, no empirical or engineering models are available that can reliably relate plume and soil properties to surface erosion or ejecta, numerical simulations of PSI are challenged by the extreme range of particle loadings and flow regimes that need modeling, and flight or ground test data from experiments reproducing the relevant physics have been impeded by the opacity of the dense particle cloud.
We present ongoing work on sub-scale PSI experiments using a Mach 5 jet impinging on a bed of 103 μm mean diameter glass microspheres under vacuum conditions. A novel mm-wave interferometric technique has been developed that circumvents the problem of optical opacity to enable high temporal resolution spatial ejecta concentration measurements when used in a tomographic setup. It leverages commercially available automotive frequency modulated
continuous-wave (FMCW) radars and passive reflectors, providing a cost effective and portable diagnostic to measure volume fraction in optically opaque dispersed multiphase flows. We combine distinct flow and particle diagnostics, including mm-wave techniques, NO Planar Laser Induced Fluorescence, high-speed pressure measurements and lateral cloud imaging, planar particle tracking velocimetry and post-test three-dimensional crater reconstruction, to interpret erosion phenomenology and the role of varying parameters such as jet expansion ratio, mass flow, and nozzle to surface distance. We will also discuss ongoing efforts to merge simplified particle trajectory models and sparse experimental data to reconstruct the 4D ejecta cloud evolution and estimate erosion rates as well as far field effects.

 

Bio:

Laura Villafañe is an Assistant Professor in the Department of Aerospace Engineering at the University of Illinois at Urbana-Champaign. Her research explores a wide range of fluid dynamic problems, with particular interest on turbulent and particle-laden flows, and on the development of data analysis tools and non-intrusive diagnostics, including non-conventional flow diagnostics such as Magnetic Resonance Imaging. She graduated on Aerospace Engineering at the
Polytechnic University of Madrid, completed her Ph.D at the von Karman Institute for Fluid Dynamics, Belgium, and was a Postdoctoral Fellow and Research Engineer at the Center for Turbulence Research at Stanford University prior to joining the faculty at UIUC in 2019. She is the recipient of three NASA Early-Stage-Innovation Awards for plume-surface interactions and parachute fluid and structural mechanics. Laura was elected Young Observer to the US National Committee for Theoretical and Applied Mechanics in 2024, and AIAA Associate Fellow Class of 2025.

*Refreshments to follow 

Molly Schmitz (She/Her/Hers)