Seminars

WARREN LECTURE SERIES

Luciano Castillo, Don Kay and Clay Cash Foundation Engineering Chair in Wind Energy and Professor, National Wind Resource Center, Department of Mechanical Engineering, Texas Tech University.

During the first portion of this seminar, extensive PIV data collected from a scaled down 3 blade, 3 x 5 turbine array is shown. In order to understand how large scale motions play a role in providing mean kinetic energy (MKE) to the array, low dimensional tools based on a proper orthogonal decomposition (POD) are used to analyze the spatially developing velocity field inside the scaled array. From this analysis, modal decomposition of the Reynolds stresses and fluxes of the MKE are constructed. Thus, from these modal expansions it is established that low order modes have large contributions to Reynolds shear stress regardless of analysis domain.  In addition, it will be shown that mean kinetic energy transport resulting from Reynolds shear stress typically serves to bring energy into the array while transport terms associated with Reynolds wall-normal stress typically removes energy from the array. Furthermore, it will be shown that the sum of the first 13 modes for the mean fluxes contributes 75% of the total Reynolds shear stress in the domain.

The concept of coherent transfers of energy is employed here as means to uncover the scales responsible for the entrainment of mean kinetic energy into the array. The major contributions to the MKE entrainment are achieved by large-scale motions associated with sums of the Reynolds shear stress, (idiosyncratic) modes (see figure 1). Thus, the sum of the first 9 modes yield 54% of the total energy entrainment, with scales given by L ~ 13D associated with this sum. It is expected that given a longer experimental setup, the lengths of these large-scale contributions would have been observed to be even bigger. Moreover, a major result from the modal length-scale analysis is that large scale motions or the idiosyncratic modes contain most of the MKE and that the low mode numbers are associated with the small scales. These high order POD modes in the inhomogeneous flow direction (x-coordinate) correspond to the Fourier-like modes and decay as 1/n where n is the mode number (see fig. 1 right). This observation is consistent with studies of wall-bounded flows by Baltzer& Adrian (PoF, 2011).  

From these results, it is clear that scales of the order of the total wind farm size are those which are critical in determining how much power can be extracted from the atmospheric boundary layer. In addition, during this seminar it will be shown that dispersive stresses are also important in the energy entrainment and dissipation in wind arrays with complex topography and where proximity between turbines exists.  

During the second part of the seminar, preliminary PIV results from scaled down experiments of 2 blades versus 3 blades arrays subject to similar conditions in a wind tunnel will be presented. Of primary importance from this data are the differences which exist in the entrainment patterns between 2 and 3 bladed turbine arrays. Finally, a prototype of a wind farm will be shown as means for future collaborations between UMN and TTU. In general, this seminar will stress the importance of understanding turbulence in wind energy. 

Gustavo Gioia, Professor, Okinawa Institute of Science and Technology, Okinawa, Japan

Two aspects of wall-bounded turbulent flows have been the subject of extensive, disjunct research efforts: average properties such as the frictional drag and the mean-velocity profile (MVP), and the energy spectrum of the turbulent fluctuations. In this talk we seek to establish a link between the MVP of a turbulent pipe flow and the energy spectrum of the turbulent fluctuations in the flow. The idea is to use this hitherto missing ``spectral link'' to help us shed new light on the MVP by building on the well-known structure of the energy spectrum. We start with a brief review of the energy spectrum. Next, we carry out a spectral analysis to identify the eddies that dominate the production of shear stress via momentum transfer. This analysis allows us to express the MVP as a functional of the spectrum. Each part of the MVP turns out to be related to a specific spectral range: the buffer layer to the dissipative range, the log layer to the inertial range, and the wake to the energetic range. The parameters of the spectrum set the thickness of the viscous layer, the amplitude of the buffer layer, and the amplitude of the wake. In the last part of the talk, we compare the three canonical wall--bounded flows: pipe flow, channel flow, and boundary layer flow. We show that the disparities among the MVPs of the three canonical flows can be traced to corresponding disparities among the attendant energy spectra. I will try to explain all the salient concepts from scratch; even if you are an undergraduate student, do not be intimidated! This research was carried out in collaboration with Pinaki Chakraborty, Carlo Zuniga, Nigel Goldenfeld, and Nicholas Guttenberg.

Dr. George Christodoulou
Professor, and Director, Applied Hydraulics Laboratory,
National Technical University of Athens, Greece

The behavior of jets denser than ambient has drawn considerable attention in recent years, due to its theoretical complexity and practical importance related to the disposal of heavy effluents into the water environment, notably brines from desalination plants. The seminar addresses two main issues:

(a) The jet geometrical characteristics and dilutions achieved. Experimental results are presented for the geometrical characteristics of dense jets issuing upwards at an angle as well as for the concentration distributions within the jet. Also, a simple integral model for the description of such jets is proposed, as well as approximate estimates of their main characteristics, with comparison to the experimental findings.

(b) The development of the density current after impingement of the dense jet on the  bottom. Experimental results and theoretical analysis are presented for the spreading of the density current on either a horizontal or a sloping bottom.
 

Program
3:00 p.m. Refreshments
3:30 Welcome and Awards Presentation – Miki Hondzo, Professor of Civil Engineering and Associate Director of Research and Development, St. Anthony Falls Laboratory
3:45 Award Remarks and Seminar Presentations – Mohammad Ebtehaj and Andrew Erickson, Ph.D. candidates in Civil Engineering, St. Anthony Falls Laboratory
4:30 Question and Answer

Aqueous Pollutant Capture with Enhanced Filtration

Andrew Erickson,
Ph.D. candidate in Civil Engineering, St. Anthony Falls Laboratory,
College of Science and Engineering, University of Minnesota

A recent nationwide study reports that many stormwater pollutants such as phosphorus, cadmium, copper, zinc, and nitrogen are approximately 45% dissolved. Very few stormwater treatment practices can consistently capture dissolved pollutants over the life-cycle of a treatment practice, and therefore a large portion of the pollutant load is entering our impaired water bodies untreated. This presentation will discuss proven techniques for capturing dissolved pollutants and examine field applications of these techniques.

On Estimation of Hydrometeorological Signals with Sparse Prior

Mohammad Ebtehaj,
Ph.D. candidate in Civil Engineering, St. Anthony Falls Laboratory,
College of Science and Engineering, University of Minnesota

The past decades have witnessed a remarkable emergence of new sources of multi-scale multi-sensor geophysical data such as precipitation, soil moisture, cloud cover, and vegetation. For precipitation, these data include global spaceborne active and passive sensors, regional ground-based weather surveillance radars, and local rain gauges. Optimal integration and resolution enhancement of these multi-sensor data promise a posteriori estimates of precipitation fluxes with increased accuracy to be used for more accurate prediction of hydro-geomorphological events, such as floods and landslides. To this end, new methodologies are presented that capitalize on an important but overlooked property of precipitation, namely that of “sparsity”. “Sparsity” refers to the fact that when a signal is projected onto an appropriate domain (say, the gradient space) only a few of the projection coefficients are non-zero. Given the ubiquity of sparsity in many hydro-climatic processes, I intend to advance and redefine the conventional data fusion and assimilation techniques in hydrometeorological applications. 

Program
3:00 p.m. Refreshments
3:30 Welcome – Miki Hondzo, Professor of Civil Engineering and Associate Director of Research and Development, St. Anthony Falls Laboratory
3:35 Award Presentation – Alwin Young, alumnus
3:45 Award Remarks and Seminar Presentation – Daniel Zielinski, Ph.D. candidate in Civil Engineering, St. Anthony Falls Laboratory
4:30 Question and Answer
5:00 p.m. Adjourn

Daniel Zielinski
Ph.D. candidate in Civil Engineering, St. Anthony Falls Laboratory,
College of Science and Engineering, University of Minnesota

Barriers to fish movement have long been part of fisheries management and the control of invasive fishes in particular. Various barrier types have been developed, mostly with mixed success. Non-physical behavioral barriers, ones that rely on sensory stimuli to modify fish behavior, have gained interest in recent years. One such barrier, that we are investigating are bubble curtains, which generate distinct hydrodynamic and acoustic fields that may be exploited to deter passage of invasive fish species. This technology is particularly useful at sites where other barrier technologies are either too expensive or do not function. In this study, the invasive common carp, Cyprinus carpio L., was used as a model species to test the efficacy of the bubble curtain to inhibit movement, because this species, like many other ostariophysians, has a well developed sense of hearing. Behavioral laboratory trials revealed a 72% and 80% reduction in the number of times common carp crossed the bubble curtain in up- and down-stream directions, respectively. Sound appeared to be the dominant stimulus for common carp, as complementary acoustic measurements

showed that a simple bubble curtain generated a sound field with a maximum sound pressure level of 120-130dB (re 1μPa) at 150Hz, well above the carp hearing minimum threshold. Based on the behavioral laboratory trials, a full scale bubble curtain prototype is being developed for installation in the field. The bubble curtain’s potential role as an effective watershed management tool will be discussed in comparison to other barrier technologies will be discussed.

Lorenz G. Straub Award Recipient:
Mariano Ignacio Cantero, Consejo Nacional de Investigaciones Cientificas y Técnicas, Instituto Balseiro, Río Negro, Argentina

2007 Award-Winning Ph.D. Thesis: Modeling and Large Scale Simulation of Thermohaline and Particulate Density Currents

Program
3:00 p.m. Refreshments
3:30 Welcome – Straub Award Presentation
3:40 Recipient Remarks – Dr. Mariano Ignacio Cantero, Consejo Nacional de Investigaciones Cientificas y Técnicas, Instituto Balseiro, Río Negro, Argentina
3:50 Keynote Presentation – The Looming Crisis in Air Traffic Capacity: Can Vortex Dynamics Help? – Dr. Fazle Hussain, Cullen Distinguished Professor and Director, Institute of Fluid Dynamics and Turbulence, Department of Mechanical Engineering, University of Houston
4:50 Question and Answer
5:00 p.m. Adjourn

Fazle Hussain,
Cullen Distinguished Professor and Director,
Institute of Fluid Dynamics and Turbulence,
Department of Mechanical Engineering, University of Houston

The air traffic capacity is projected to be tripled by 2025, demanding a tripling of runways at major airports of the world.  Safe aircraft separation to avoid wake hazard is not only already a challenge during takeoffs and landings, but will become a major problem also during cruise in the crowded skies.  We propose a method of breaking up the trailing vortices and inducing their rapid decay so that separation between aircraft can be significantly reduced. We study via direct numerical simulation the evolution of a vortex column embedded in fine-scale turbulence, and then explore three potential mechanisms for core perturbation growth:

1. Centrifugal instability due to vortex circulation overshoot,
2. Kelvin wave growth due to resonance with the external turbulence, and 
3. Transient growth of perturbations in the normal-mode stable vortex.

We show that transient growth of bending waves can produce orders of magnitude growth in core turbulence and hence possible breakup of trailing vortices – particularly at Reynolds numbers relevant to aircraft.

Dr. Trisha Moore
Research Associate, St. Anthony Falls Laboratory,
College of Science and Engineering, University of Minnesota

Urban runoff has been cited as one of the leading causes of surface water degradation in both freshwaters and coastal estuaries.  Recognition of the issues associated with runoff-borne nutrient pollution has spurred the proliferation of stormwater control measures (SCMs) designed to reduce pollutant loads from urban runoff.  Among the most common SCMs are stormwater ponds, the design of which is intended to regulate peak runoff rates and remove solids from runoff.  Although not as common as ponds, constructed stormwater wetlands are gaining in popularity, particularly in developing urban areas draining to nutrient-sensitive coastal areas where stormwater nitrogen loads are regulated.  Since the primary functions for which SCMs such as ponds and wetlands are designed are peak flow control and pollutant removal, performance metrics generally focus on hydrologic and water quality aspects of these systems.  However, as constructed ecosystems, both ponds and wetlands may provide a range of other societal benefits, or ecosystem services, such as habitat provision and biodiversity maintenance, green house gas regulation, and opportunities for recreational, educational, and aesthetic experiences.  While often acknowledged, rarely are such ancillary benefits quantified, much less integrated into assessments to compare SCMs on the basis of the suite of ecosystem services they provide.  The costs of creating SCMs to provide such benefits present an additional assessment metrics, and one of prime importance to developers, municipalities, and others involved in the construction and maintenance of these systems.  While direct monetary costs are relatively well constrained, environmental costs incurred through stormwater management, such as greenhouse gas emissions, are only now being explored.  

In this seminar, I will present an assessment framework for quantifying ecosystem service provision by constructed stormwater ponds and wetlands.  Of particular focus here are carbon sequestration and biodiversity maintenance.  Differences in ecosystem service provision by ponds and wetlands, as well as design features found to improve service provision, will be highlighted.  A model developed to predict carbon emissions through the construction and maintenance of these systems will also be presented.

Dr. Xiaolei Yang
Research Associate, St. Anthony Falls Laboratory,
College of Science and Engineering, University of Minnesota

The performance of a wind farm can be improved significantly by optimizing the placement of wind turbines. In our work, we use the CURVIB-LES solver with turbine rotors parametrized by the actuator disk or actuator line model to study the arrangement of wind turbines in a wind farm. One fundamental step for optimizing wind-turbine placement is the understanding and modeling of the different effects of streamwise and spanwise spacing. These effects are first studied using LES with actuator disk model. Then an improved roughness height model is proposed to take into account of the different effects of the streamwise and spanwise spacing. In order to study the placement of turbines on complex terrains, a wall model which aims to capture the separation of boundary layer is also discussed.

Dr. Ray Hozalski
Professor of Civil Engineering,
University of Minnesota

Bioretention cells are increasingly popular in low-impact development as a means to sustainably mitigate the environmental problems associated with stormwater runoff. Yet, much remains to be known regarding the removal and ultimate fate of pollutants such as toxic metals and petroleum hydrocarbons in bioretention cells. In this presentation, I will discuss the results of field sampling and laboratory experiments performed to evaluate the effectiveness of bioretention systems at treating petroleum hydrocarbon-contaminated stormwater. For the field sampling, 75 soil samples were collected from 58 raingardens and 4 upland (i.e., control) sites in the Minneapolis, Minnesota area, representing a range of raingarden ages and catchment land uses. Total petroleum hydrocarbon (TPH) concentrations in the samples were quantified, as were 16S rRNA genes for Bacteria and two functional genes (phenol hydrolase or PHE and naphthalene dioxygenase or NAH) that encode for enzymes used in the degradation of petroleum hydrocarbons. TPH levels in all of the raingarden soil samples were low (< 3 µg/kg) and not significantly different from one another. All soil samples contained substantial quantities of 16S rRNA, PHE, and NAH genes, suggesting that bacteria in the soils have the capacity to biodegrade petroleum hydrocarbons (which was confirmed by batch experiments). Furthermore, the number of copies of Bacteria 16S rRNA genes and functional genes were greater in the raingardens planted with deeply-rooted natives and cultivars than in raingardens containing simply turf grass or mulch (p<0.036), suggesting that planted raingardens may be better able to assimilate TPH inputs. Next, laboratory-scale bioretention cells were constructed inside sealed glass columns. The columns were periodically spiked with 14C-naphthalene over a 5-month period and the fate of this representative hydrocarbon and the influence of vegetation on naphthalene fate was studied. Three column setups were used: one planted with a legume (Purple Prairie Clover, Dalea purpureum), one with grass (Blue-Joint Grass, Calamagrostis canadensis), and one unplanted (i.e., control). Overall naphthalene removal efficiency was 93% for the planted columns and 78% for the control column. Adsorption to soil was the dominant naphthalene removal mechanism (56-73% of added naphthalene), although degradation (i.e., mineralization, 12-18%) and plant uptake (2-23%) were also important. Volatilization was negligible (<0.04%). Significant enrichment of naphthalene-degrading bacteria occurred over time due to contaminant exposure and plant growth as evidenced by increased biodegradation activity and increased NAH gene concentrations in the bioretention media. Overall, this research suggests that bioretention is a viable solution for sustainable petroleum hydrocarbon removal from stormwater, and that vegetation can enhance overall performance and stimulate biodegradation.

Dr. Saeed Moghimi,
Leibniz Institute for Baltic Sea Research, Rostock, Germany

In this research, a state-of-the-art parallel programming tools have been utilized to develop a coupled wave and circulation modeling framework which takes into account  most of the important physical interaction mechanisms (e.g.surface waves turbulence effects, surface rollers, bottom boundary layer , etc.). The dynamically coupled system includes a three-dimensional coastal circulation model, the General Estuarine Transport Model (GETM), and a third generation wind wave model, the Simulating Wave Near-shore (SWAN). The coupled system components have been connected by model coupling toolkit (MCT) which is the coupler engine of the Community Climate System Model (CCSM). This model provides a high operational flexibility by combining several MPI models to operate simultaneously with different number of processes by different domain decompositions. The main goal of the research was to include the effects of surface waves in deep and shallow parts of the ocean contributing to momentum and energy exchange between the atmosphere and ocean. One of the main concerns was dedicated to implementation of the Vortex Force (VF) and dissipated wave momentum as driving forces together with the Generalized Lagrangian Method (GLM) as wave averaging operator following Ardhuin, 2008. This approach would enable us to perform an efficient simulation of three-dimensional structure of hydrodynamics of wave-current interaction in the surf zone and coastal waters. The coupled modeling system was validated against both the laboratory- and field-scale. Later the developed  Modeling  approach  will be  employed  to investigate climate change and  on going transformation processes due to surface wave and current interactions in the framework of RADOST (Regional Adaptation Strategies for the German Baltic Coast) project as well as setting up a high resolution test case to study three dimensional structure of highly variable tidal environment in the Wadden Sea.