Every two weeks during the academic year, SAFL hosts prominent figures in environmental science and fluid mechanics. They come from all over the US and the world to share their insight and inspire us to tackle important questions in the field. These seminars are free and open to the public. Join us to learn about the latest research advancements and network with contacts in the field.

SAFL seminars are held on Tuesdays, from 3:00 to 4:15 p.m., either online or in the SAFL Auditorium. 

Fall 2021 Seminar Series

September 14th - Li Li, Penn State University

September 21st - Ellen Wohl, Colorado State University

October 5th - Michael Howland, Massachusetts Institute of Technology

October 19th - Teri Oehmke, University of New Hampshire

November 2nd - Doug Jerolmack, University of Pennsylvania

November 16th - Luca Brandt, KTH Royal Institute of Technology

November 30th - Eric D'Asaro, University of Washington

December 7th - Boya Xiong, University of Minnesota

We will record seminars and post them here when given permission by the speaker. To see if a recording is available, scroll down this page to "Past Seminars."

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Past Seminars

Shape and size effects of inertial particles in turbulent flow - Theresa B. Oehmke, University of New Hampshire

Theresa B. Oehmke, Postdoctoral Scholar, Department of Mechanical Engineering, University of New Hampshire

Abstract: Understanding how particles interact in turbulent flow is an important and open question with many industrial and natural applications. Using laboratory experiments, I investigate how particles within the inertial subrange of turbulence respond to their environment in terms of their kinematics (translation, orientation, tumbling, spinning) and dissolution rates. By first understanding how size influences motion, we can then determine how that motion should in turn impact dissolution. In this talk I will present methods and results for the 3D reconstruction of flat particle orientation that allows for examination of spinning vs tumbling rates. Then I will discuss how understanding of spinning and tumbling contributes to our knowledge of determining the impacts of shape and size on dissolution of in-house, custom made sugar particles.

Theresa Oehmke

About the speaker: Dr. Theresa B. Oehmke is a Postdoctoral Scholar in Mechanical Engineering at the University of New Hampshire. Dr. Oehmke earned a PhD in Environmental Engineering from UC Berkeley in 2021 and a Bachelor’s of Science in Environmental Engineering Science from Massachusetts Institute of Technology in 2015. Theresa does research related to Environmental Fluid Mechanics. Specifically, she is interested in the transport of particles and pollutants in turbulent flows. Prior research has included work with fibers, cuboids, and flat particles within the inertial subrange to study how size and shape influence particle motion and dissolution. Her research is funded by the National Science Foundation and she is also a recipient of the Make Our Planet Great Again (MOPGA) Fellowship and a two-time recipient of the STEM Chateaubriand Fellowship.

Wind farm optimization through collective control: The role of shear and stability in the atmospheric boundary layer - Michael F. Howland, MIT

Michael F. Howland, Assistant Professor, Department of Civil and Environmental Engineering, Massachusetts Institute of Technology

AbstractHistorically, control protocols have optimized the performance of individual wind turbines resulting in aerodynamic wakes which typically reduce total wind farm power production 10-20%. Wake steering, the intentional yaw misalignment of turbines in a wind farm to deflect energy deficit wake regions, has demonstrated potential as a wind farm control approach to increase collective power production. The potential for wake steering depends, in part, on the power reduction of yaw misaligned turbines. In the atmospheric boundary layer (ABL), the sheared wind speed and direction may change significantly over the rotor area, resulting in a relative inflow wind speed and angle of attack to the blade airfoil which depends on the radial and azimuthal positions. In order to predict the power production for an arbitrary yaw misaligned turbine based on the incident ABL velocity profiles, we develop a blade element model which accounts for wind speed and direction changes over the rotor area, and the model is validated using experimental data from a utility-scale wind farm. Leveraging aerodynamic wind farm models, we designed a physics- and data-driven wake steering control method to increase the power production of wind farms. The method was tested in a multi-turbine array at a utility-scale wind farm, where it statistically significantly increased the power production over standard operation. The analytic gradient-based power optimization methodology we developed can optimize the yaw misalignment angles for large wind farms on the order of seconds, enabling online real-time control. To improve wake steering control in transient ABL conditions, we developed a closed-loop wake steering control strategy, which is tested in large eddy simulations of the terrestrial diurnal cycle, altogether, the results indicate that closed-loop wake steering control can significantly increase wind farm power production over greedy operation provided that site-specific wind farm data is assimilated into the aerodynamic model.

Michael Howland

About the speaker: Michael F. Howland is an Assistant Professor of Civil and Environmental Engineering at MIT. He was a Postdoctoral Scholar at Caltech in the Department of Aerospace Engineering. He received his B.S. from Johns Hopkins University and his M.S. from Stanford University. He received his Ph.D. from Stanford University in the Department of Mechanical Engineering. His work is focused at the intersection of fluid mechanics, weather and climate modeling, uncertainty quantification, and optimization and control with an emphasis on renewable energy systems. He uses synergistic approaches including simulations, laboratory and field experiments, and modeling to understand the operation of renewable energy systems, with the goal of improving the efficiency, predictability, and reliability of low-carbon energy generation. He was the recipient of the Robert George Gerstmyer Award, the Creel Family Teaching Award, and the James F. Bell Award from Johns Hopkins University. At Stanford, he received the Tau Beta Pi scholarship, NSF Graduate Research Fellowship, a Stanford Graduate Fellowship, and was awarded as a Precourt Energy Institute Distinguished Student Lecturer.

Messy Rivers are Healthy Rivers: The Role of Spatial Heterogeneity in Sustaining River Ecosystems - Ellen Wohl, Colorado State University

Ellen Wohl, University Distinguished Professor, Department of Geosciences, Colorado State University

Abstract: Perceptions of river health are strongly influenced by expectations regarding a natural river. Many observers expect clear water, a slightly sinuous river with pools and riffles, and some riparian trees. River health, however, is much more complicated and multifaceted. The physical appearance of a river, for example, depends strongly on geomorphic context and river history. I use mountainous headwater rivers in Colorado to examine the influence of physical complexity on river health. Complexity can be described with respect to the stream bed, banks, cross-sectional form, and planform of the river and floodplain. The configuration of each of these components of a riverine system has implications for habitat abundance and diversity, sensitivity and resilience of the river to natural and human-induced disturbances, retention of water, sediment and nutrients, and connectivity within the riverine system and between the river and adjacent uplands. Many types of resource use simplify rivers to the point that the river undergoes a metamorphosis, or a thorough, sustained change in channel form and function. Loss of beaver dams and channel-spanning logjams in mountainous headwater rivers in Colorado, for example, has resulted in metamorphosis of physically complex, anastomosing channels that were highly connected to adjacent floodplains. These rivers have assumed an alternate stable state as single-thread channels with limited retention and resilience. Effective, sustainable river restoration involves (i) characterizing the magnitude of different forms of physical complexity naturally present in a particular river segment, (ii) understanding the effects of physical complexity on river ecosystem function, and (iii) assessing the degree to which this level of physical complexity can be restored or mimicked. An important part of this process may be educating stakeholders regarding the importance of physical complexity – messiness – in healthy rivers.

About the Speaker: Ellen Wohl received a B.S. in geology from Arizona State University and a Ph.D. in geosciences from the University of Arizona. She has been on the faculty at Colorado State University since 1989 and is now a University Distinguished Professor. Her research focuses on interactions between physical process and form and biota in river corridors.

The shallow and deep hypothesis: linking flow paths, biogeochemical reactions, and stream chemistry in the Critical Zone - Li Li, Penn State University

Li Li, Professor, Department of Civil and Environmental Engineering, Penn State University

Abstract: Hydrological flow and biogeochemical processes in the Critical Zone (CZ) are intimately coupled, yet their respective sciences have often progressed without as much integration. This lack of integration hinders mechanistic understanding and forecasting of earth surface and water response to human- and climate-induced perturbations. This talk will highlight insights gleaned from integrated hydro-biogeochemical measurements and modeling in the CZ. In particular, recent water chemistry data (carbon, nitrogen, and geogenic solutes) and hydro-biogeochemistry modeling has propelled the idea that shallow and deep flow paths connect waters of distinct chemistries at different subsurface depths to streams under variable flow conditions; and that the extent of shallow versus deep chemistry differences shape concentration-discharge relationship in streams. This idea underscores the importance of subsurface structure and vertical hydrological connectivity relative to the extensively studied horizontal connectivity and topography. Broadly, this hypothesis can potentially serve as a conceptual framework that links CZ subsurface structure to its hydrological and biogeochemical functioning under diverse climate, geology, and land cover conditions.

About the Speaker: Dr. Li Li is a professor in Environmental Engineering at Penn State University. Li received a bachelor and master’s degree in environmental chemistry from Nanjing University in China and a doctoral degree in environmental engineering and water resources from Princeton University. She worked at the Lawrence Berkeley National Laboratory as a postdoc and as a research scientist before joining faculty at Penn State University. Her group asks questions on how external drivers and internal structure regulate water flow paths and biogeochemical processes at the watershed scale under diverse climate, geology, and land use conditions. She is active in the Critical Zone community, and collaborates broadly with biogeochemists, hydrologists, ecologists, and geologists. She has been promoting woman scientists’ work via the Women Advancing River Research (WARR) seminar series.

SAFL Spring Awards Ceremony

SAFL is excited to host a virtual special awards ceremony on May 4th, 2021 that will celebrate students in the St. Anthony Falls Laboratory (SAFL) community. We are tremendously grateful to have such talented, dedicated students at SAFL, and it is a privilege to celebrate them with awards that honor not only them and their accomplishments, but the legacies of the people who have helped SAFL become what it is today.

We will be presenting the 2020 - 2021 Alvin G. Andersen Award, the Heinz G. Stefan Fellowship, and the Nels Nelson Memorial Fellowship. Family members will be present to speak about the award namesakes, the recipients will be introduced by their respective advisors, and the recipients will give remarks on their research.  We expect the event to last approximately an hour. 

2020 - 2021 Award Recipients:

Alvin G. Anderson Award - Kerry Callaghan, former PhD student from the Department of Earth and Environmental Sciences (advisor Andrew Wickert)
Heinz G. Stefan Fellowship - Lun Gao, PhD student from the Department of Civil, Environmental, and Geo- Engineering (advisor Ardeshir Ebtehaj)
Nels Nelson Memorial Fellowship - Yuanqing Liu, PhD student from the Department of Mechanical Engineering (advisor Lian Shen)

You can learn more about this year’s recipients in this linked program

Simulation and modeling of non-canonical turbulent flows - Junlin Yuan, Michigan State University

Junlin Yuan, Assistant Professor, Department of Mechanical Engineering, Michigan State University

Abstract: The bulk of wall turbulence research has focused, perhaps disproportionately, on canonical flows along smooth flat plates with uniform freestream conditions. However, in engineering and environmental applications, such as flow around hydraulic turbine blades, navy platforms and in rivers, we see a wide range of dynamically complicated flow fields, affected by surface roughness, curvature, freestream pressure gradients, and unsteadiness. The consequence is that existing descriptions and models of turbulence have limited utility to design practice. My long term goal is to build essential physics into models, to enable a consistent description for turbulence across a wide range of flow complexities. The first part of the talk will be focused on understanding and modeling for rough-walled, equilibrium turbulence or non-equilibrium ones subjected to longitudinal pressure gradients. Using data from direct and large-eddy simulations (DNS and LES), I will show that roughness significantly modifies turbulence under strong spatial or temporal accelerations. I will also show an example of machine-learned modeling of hydrodynamic drag from roughness with arbitrary topography.

The second part of the talk is on using DNS to better understand river hyporheic exchange, a phenomenon of turbulent flow bounded by rough, permeable walls. In our understanding of riverine systems, a gap of knowledge exists in how pore-scale heterogeneities affect multiscale hydrologic and biogeochemical processes. I will show that dynamics at the scale of sediment grains and small roughness formed by uppermost-layer grains—typically ignored in existing predictive approaches—can be important for exchanges across a flat bed. Specifically, pore-resolved DNS of flows bounded by beds modeled as closely packed spheres were carried out. Results showed that bed roughness induces deep, multiscale subsurface flow paths that yield residence time distribution with a power-law tail. The main driver appears to be the interfacial pressure variation generated by roughness, a mechanism fundamentally similar to the effect of bedforms. Future work will investigate (i) pore-scale dynamics in transient or spatially varying river flows, (ii) reactive solute transport affected by pore-scale dynamics, and (iii) potential link with reduced-order transport models used for water management practice.

About the Speaker: Dr. Junlin Yuan is an assistant professor in Department of Mechanical Engineering at Michigan State University. She obtained both MS and PhD degrees (2015) from Queen's University, Canada. Her PhD research focused on simulation (DNS and LES) and modeling of turbulent flows in the context of rough hydraulic turbine blades. At MSU, she continued to use large-scale simulations to identify the dynamics of wall-bounded turbulence with various complexities, and to develop physics-based, data-driven models. Topics include turbulence responses to acceleration/deceleration, wall roughness, wall permeability, curvature, and rotation. Applications cover engineering, environmental and bio-locomotive topics. Her research group is currently funded by ONR, NSF and the industry.

Straub Award Ceremony and Distinguished Lecture, featuring Dr. Tracy Mandel and Dr. Veronica Morales

Prior to our keynote presentation, we are excited to welcome and celebrate the most recent winner of the Lorenz G. Straub Award. Dr. Tracy Mandel completed her 2018 dissertation under Jeffrey Koseff at Stanford University. She will provide a brief remarks about her graduate thesis, titled Free-surface Dynamics in the Presence of Submerged Canopies. Dr. Mandel currently serves at University of New Hampshire as an Assistant Professor in Ocean Engineering and Mechanical Engineering. Her research group uses experimental and field approaches to study turbulent environmental flows, with a focus on coastal hydrodynamics. 

Keynote Presentation: Transport Phenomena Under Spatial Heterogeneity: Bridging the Pore and Darcy Scales

Veronica Morales, Assistant Professor Civil & Environmental Engineering, University of California Davis

Abstract: Solving the flow and mass transport through environmental porous media is central to many technological applications spanning groundwater remediation, oil recovery, and geotechnical engineering. Under spatial heterogeneity, the phenomena of flow and transport significantly differ from those in uniform media. The variability of natural pore-spaces gives rise to complex flow patterns and non-Gaussian velocity fluctuations that complicate predictions. Classic models for the field-scale omit this variability and use average system parameters to solve governing equations for flow and transport. Such types of models might acceptably capture the average time of arrival of a substance (e.g., a groundwater contaminant), but consistently fail to predict the often-observed early arrival and prolonged tailing in concentration signals. Capturing the variance and skewness of such concentration signals requires more information than is contained in average system descriptors. To this end, this talk will discuss work carried out to represent large-scale transport processes as the collective phenomena resulting from interactions between the pore-scale heterogeneity and the local-scale flow. The first part of the talk will discuss the rules of particle motion ascertained at the pore-scale that are efficiently upscaled with stochastic models to describe large-scale transport problems. We demonstrate how our model accurately captures the changeover from intense to weak spreading, which is poorly understood but crucial for problems in groundwater contamination. The second part of the talk focuses on flow distribution and recasts flow path resistance into a graph-theory problem. Through this work we learn where and why preferential pathways form and offer a simple metric to estimate the time of first arrival based on structural information of the porous medium alone.

About the Speaker: As a hydrogeologist, Veronica Morales’s research focuses on the physics of flow and reactive transport in porous media with a keen interest in understanding how particles move and interact in confined spaces. In 2017, Morales joined the faculty at the University of California, Davis where she was awarded the NSF-CAREER and the AGU Early Career Award. Previously, she was a postdoctoral associate at the Environmental Fluid Mechanics lab at ETH Zürich and the Soil Physics group at the SIMBIOS Centre. She holds a PhD in Biological & Environmental Engineering from Cornell University (2011), and dual Bachelor degrees in Environmental Science and Spanish Literature from the University of California, Santa Barbara (2004).

Transform Engineering for a Climate Changed Future – What Role for Reflexive Practice? Linda Shi, Cornell University

Linda Shi, Assistant Professor, Architecture Art Planning, Cornell University and Hanne van den Berg, Urban Adaptation Expert, European Environment Agency

Abstract: These are exciting times for civil and environmental engineers, who have an immense role to play in societal transformation under climate change. Cities, funders, public agencies, and policymakers are increasingly advocating infrastructure projects that mitigate flood risks, especially in the aftermath of disasters. Whether projects are green or grey, we are seeing a resurgence of infrastructure proposals that are large in scale and ambition after decades of more decentralized stormwater management. These projects, nevertheless, respond only to the physical vulnerabilities of place by shifting water from one site to another. Decades of social science research demonstrate that vulnerability to environmental hazards are socially constructed by laws, policies, and politics that together shape a household or communities’ ability to overcome the impacts of a disaster event. From this perspective, major infrastructure works are not only a technical, apolitical, value-neutral proposition, but a physical intervention that reflects and entrenches politics of inequality. In the United States, many have disproportionately benefitted wealthier, whiter, and otherwise more privileged groups, while socially vulnerable groups whose communities were disinvested and neglected for decades have had to relocate to make way for infrastructure - often leaving for other environmentally precarious sites. 

This double-header talk presents concepts of social and spatial justice, and how water management projects have contributed to inequitable social vulnerability to hydrological risks. We then share a case study of how flood management in Houston reflects the tensions in how traditional engineering practices have contributed to inequitable local flood risks, and how engineers there have grappled with questions of equity, justice, and fairness. We argue that engineers have an opportunity and a need to reflect on the epistemological roots of the profession, mainstream modes of analysis, and cultural attitudes towards change and more diverse ways of knowing. 

Transport of thermal energy by rain in thawing permafrost landscapes - Becca Neumann, University of Washington

Becca Neumann, Associate Professor, Civil & Environmental Engineering, University of Washington

Abstract: Northern high latitudes are expected to get warmer and wetter. There is consensus that warming will intensify permafrost thaw and increase wetland methane emissions, facilitating a positive climate feedback. However, the effects of increased precipitation are uncertain. At two different thawing wetland complexes in Alaska, we found that rain rapidly altered soil temperature, both within the permafrost plateau and within the thaw wetland. To a first approximation, rain has the same temperature as air, and when air and soil temperatures are mismatched, rainwater inputs can rapidly change subsurface soil temperatures through thermal conduction. At one site, we found that when wetland soils were warmed by spring rainfall, methane emissions increased by ~30%. The warm, deep soils early in the growing season likely enhanced both microbial and plant processes that increased emissions. At the other site, data showed rapid thaw of frozen soil within the permafrost plateau during a large rain event. This result indicates, but does not prove, that thermal transport by rain could be an important mechanism for thawing permafrost. The collective datasets clearly demonstrate the ability of rain to advect thermal energy into soils, and indicate that through this mechanism, rain notably affects the radiative forcing of thawing permafrost landscapes.

About the Speaker: Becca joined the Civil and Environmental Engineering Department at University of Washington in 2011 and is currently an associate professor. She leads the hydro-biogeochemistry research group, which investigates how hydrologic, chemical and biological processes interact in soils, aquifers and surface waters to control the movement and concentration of chemicals in air, water, plants and animals. The group harnesses knowledge and techniques from multiple disciplines to tackle societally relevant topics, such as food and water quality and global climate change. Prior to UW, Becca was a NOAA Climate and Global Change postdoctoral fellow at Harvard University and a Ph.D. student at the Massachusetts Institute of Technology. She worked as an environmental engineering consultant for EG&G Technical Services before graduate school, and received her B.S. in Civil and Environmental Engineering and B.A. in Art and Art History from Rice University. Outside of work, Becca enjoys hiking, skiing and rock climbing with her husband and two kids.

A scaling-law approach to liquid impact - Devaraj van der Meer, University of Twente

Devaraj van der Meer, Professor, University of Twente

Abstract: The impact of liquid masses onto solid substrates constitutes a research field of paramount importance for many applications. These range from the microscopic scale of, e.g., inkjet printing, to large-scale oceanic wave impacts onto maritime structures, and many of them have been active, but largely disconnected research topics for many decades. In this work, we investigate to what extent the many phenomena observed within this vast range of impact parameters can be captured and connected using simple scaling laws. With focus on determining the pressures occurring during impact, we formulate a framework that aims to incorporate the influence of gas compressibility, air cushioning, liquid compressibility, and surface instabilities. This approach leads to remarkable conclusions, e.g., why for droplets impacting at low and moderate speeds liquid compressibility is expected to play no significant role.

About the Speaker: Devaraj van der Meer studied theoretical high-energy physics in Leiden in the Netherlands and, after spending several beautiful years as a high-school and college physics teacher, obtained his PhD in 2004 in experimental granular physics, after a radical switch of topics. He is currently professor in the Physics of Fluid group at the University of Twente, also in the Netherlands, where he is working on a broad range of topics ranging from granular physics, via liquid impact problems, to mass and heat transfer. He is Applied Physics Chair, member of the Dutch Physics Council and is a Vidi and a Vici laureate within the Dutch Talent programme.