Grantee Research Project Results
2003 Progress Report: Large Eddy Simulation of Dispersion in Urban Areas
EPA Grant Number: R828771C004Subproject: this is subproject number 004 , established and managed by the Center Director under grant R828771
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: Center for the Study of Childhood Asthma in the Urban Environment
Center Director: Hansel, Nadia
Title: Large Eddy Simulation of Dispersion in Urban Areas
Investigators: Parlange, Marc , Helble, Joseph J. , Ondov, John M. , Meneveau, Charles
Current Investigators: Parlange, Marc , Meneveau, Charles
Institution: The Johns Hopkins University , University of Connecticut , University of Maryland - College Park
Current Institution: The Johns Hopkins University
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2007
Project Period Covered by this Report: October 1, 2002 through September 30, 2003
Project Amount: Refer to main center abstract for funding details.
RFA: Hazardous Substance Research Centers - HSRC (2001) Recipients Lists
Research Category: Hazardous Waste/Remediation , Land and Waste Management
Objective:
The overall objectives of this research project are to: (1) implement, test, and use new generation subgrid-scale models for simulating pollutant transport in urban environments in the Johns Hopkins University (JHU) Large Eddy Simulation (LES) code; and (2) measure aerosol profiles in the atmospheric boundary layer with the JHU lidar in eastern Baltimore collocated with point-aerosol sensors to identify pathways and sources of aerosols. The specific objectives for Year 2 of this research project are to: (1) use the new model to perform realistic high-resolution simulations of Atmospheric Boundary Layer (ABL) flow over heterogeneous surfaces; (2) formulate a parameterization for heterogeneous surfaces that would allow transport models with coarse resolutions to correctly parameterize the effect of subgrid scale variations in surface roughness; (3) add scalar equations to the code so it can simulate non-neutral ABLs and the transport of passive scalars such as particulate matter; (4) further the development of the subgrid scale model of the code so it can be more faithful to the physics of ABL flow under strongly convective or strongly stable atmospheric conditions; and (5) complete our field campaign with colleagues at the University of Maryland (J. Ondov), including JHU lidar measurements in south Baltimore to study sources and pathways of aerosols from the hazardous stacks in south Baltimore.
Progress Summary:
To address potential exposure pathways in urban environments from airborne particles, both computational simulation tools and instruments are being developed and deployed. Air pollution is critically affected by wind that transports pollutants from the emitter to other locations. Computer simulations of air movement and pollutant transport in the urban environments are especially challenging because of the complex ground topology typically found in cities. The previous progress report described the implementation and testing of a new generation physical model of turbulence to improve on the state-of-the-art of computer simulations of flow and transport within urban environments.
The major fundamental issue in developing improved computer simulations is the parameterization of unresolved small-scale turbulent motions (vortices and eddies smaller than the computer mesh size). Classical parameterizations rely on adjustable parameters (e.g., the Smagorinsky coefficient, cs) that can only be tuned in a fairly ad hoc fashion. This state of affairs has greatly limited the predictive powers of computer modeling of atmospheric turbulent phenomena. A major breakthrough occurred in the 1990s in the field of computer simulation of turbulent flows, when Germano, et al. (1991) recognized that one could use the turbulent eddy dynamics that are being computed to determine numerical values of unknown model parameters. These same parameters could then be used for modeling the unknown scales of motion, under the assumption of scale invariance. This new approach, the "dynamic model," already has been applied with success to a number of fairly simple flow conditions, mainly in engineering flow applications. Our group has been involved in generalizing this new paradigm to atmospheric flows, and our prior work has shown how to relax the basic assumption of scale invariance (Porté-Agel, Meneveau, and Parlange, 2000). The approach is based on a statistical analysis of the resolved motions during the computations (i.e., the resulting fields must be averaged over directions of statistical homogeneity).
For applications to urban environments, the geometries are too complex to allow finding such directions of statistical homogeneity; in fact, such directions rarely exist. Hence, a more general form of the dynamic model is needed. The Lagrangian dynamic model (Meneveau, Lund, and Cabot, 1996) provides a workable alternative, because it evaluates the statistical averages "on the fly" by following fluid particles during the simulation. The parameter thus obtained is a function of position and time. We will denote it as cs(x,t). The main advantages of the Lagrangian approach are: applicability to flows with no homogeneous directions, preservation of Galilean invariance, computation of a local cs at every point, and the ability to handle complex geometries and unsteady flows. Although quite successful in complex engineering flows, this model has not yet been applied and tested in the context of atmospheric flows where the length scales are quite different. One of the objectives of our research has been to implement, test, and use this new model for simulating pollutant transport in urban environments.
Our modeling progress last year included the: (1) implementation of the Lagrangian dynamic model in the JHU LES code; (2) performance of validation tests on flat surfaces (the tests were successful); and (3) implementation of the model in wind flow over a building. For the last step, the JHU-LES code was modified to allow prescription of complex geometry boundary conditions (to represent buildings, using the immersed boundary method), and the Lagrangian dynamic model was implemented in conjunction with these new boundary conditions. Also, in the context of another project (funded by the National Science Foundation), we simulated flow over patches with varying roughness scales (those tests have demonstrated the capability of the model to capture local variations in coefficient). We developed and successfully tested a parameterization for heterogeneous surfaces that yields an "equivalent surface roughness," representing the aggregate effect of the different patches; this is needed for this U.S. Environmental Protection Agency (EPA) project when variations in surface characteristics occur at a scale smaller than at the grid scale. A related development this year has been to include the transport of active (heat) and passive (pollutants) scalars to the model to allow the simulation of pollutant transport under nonneutral conditions. Last year's report demonstrated the ability of the JHU-LES code to reproduce some flow patterns around buildings, and to predict spatially varying values of the subgrid scale coefficient. One problem that remained was the high computational cost of the scale-dependent formulation proposed by Porté-Agel, et al. (2000) when used with Lagrangian averaging. Therefore, we are developing a new scale-dependent approach appropriate and computationally affordable when a Lagrangian averaging scheme is used in complex terrain.
Because some simulations of pollutant transport in urban areas might not always have the luxury of resolving all the topographic and surface features, especially when long-range transport from industrial to urban areas is attempted, a proper parameterization of subgrid scale features is needed. Such a parameterization was proposed for heterogeneous surfaces. This analytic parameterization yields an "equivalent surface roughness," representing the aggregate effect of the different patches. Our testing of the parameterization over simple patches was successful; as a next step, testing will be performed for complex patch layouts (see Figure 1).
Another development in the code was the inclusion of scalar equation to simulate the transport of active (heat) and passive (pollutants) scalars. A whole diurnal cycle can now be simulated and diurnal variations of the dynamic Smagorinsky coefficient is obtained without ad hoc parameter adjustments.
Figure 1. An Example of a Complex Patch Layout That Will be Simulated, a Total of Three Simulations for Complex Layouts Will be Performed
On the experimental side, we have vastly improved the capabilities of the JHU lidar that can be used to assess certain features of the LES simulations (e.g., ABL entrainment) and measure the transport patterns of aerosols. Specifically, we now can monitor all three wavelengths (1064, 532, 355 nm), we have a simplified technique to align the lidar, and the region of incomplete overlap between the laser and the telescope is now 100 m. In this research project, and in the context of another EPA-funded project (Principal Investigator Ondov, U.S. EPA Baltimore Supersite), aerosols and their chemical properties were measured during the intensive summer of 2002 measurement campaigns at the JHU Bay View Hospital to assess sources of particulates in that community. We have taken advantage of the related nature of the experimental work in using the eastern field site for safety concerns. The operation and maintenance of a lidar are extremely time consuming, requiring the use of safety spotters at all times. An example of lidar aerosol profiles obtained during the Canadian forest fire event of July 7 is presented in Figure 2. Boundary layer structures—strong downdrafts—are clearly evident, bringing large amounts of upper atmosphere (Canadian smoke) into the urban atmosphere. Additional air quality and meteorological data were collected, and will be analyzed to answer questions regarding aerosols pathways in the Baltimore environment as the next steps in this project.
Figure 2. Lidar Time Series of Relative Aerosol Concentration for a Height Range z From 250 m to 2,200 m (Arbitrary Units) Demonstrating ABL Entrainment
Future Activities:
We will: (1) test the predictions of flow around building shapes with available data, and generalize the case of several buildings to approach the level of complexity typically found in urban environments; and (2) analyze the field data collected at the eastern Baltimore site to identify Baltimore city and long-distance sources of aerosols and their movement from point sensors and lidar measurements.
Journal Articles:
No journal articles submitted with this report: View all 23 publications for this subprojectSupplemental Keywords:
large eddy simulation, LES, aerosols, light detection and ranging, lidar, environmental engineering, air pollution, metal transport, particulate matter, PM, aerosol composition, aerosol dynamics, aerosol particles, air quality models, air sampling, air toxics, airborne aerosols, airborne particulate matter, airborne urban contaminants, ambient aerosol, ambient air quality, ambient particle health effects, combustion kinetics, combustion byproducts, contaminant cycling, contaminant dynamics, contaminant transport, environmental health effects, epidemiology, exposure, hazardous air pollutants, HAPs, hazardous substance contamination, hazardous waste incinerators, human exposure, human health effects, human health risk, plume dispersion, respiratory impact, technical outreach, technology transfer, urban air, urban environment, waste combustion., RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, Air, particulate matter, Health Risk Assessment, Risk Assessments, Physical Processes, Ecology and Ecosystems, ambient aerosol, ambient air quality, urban air, air toxics, epidemiology, human health effects, contaminant transport, air quality models, airborne particulate matter, contaminant cycling, exposure, air pollution, air sampling, environmental health effects, large eddy simulations, hazardous waste incinerators, human exposure, respiratory impact, airborne aerosols, aerosol composition, ambient particle health effects, PM, urban environment, aersol particles, aerosols, human health risk, hazardous substance contaminationRelevant Websites:
http://www.jhu.edu/hsrc Exit
http://www.jhu.edu/~dogee/mbp/ Exit
http://pegasus.me.jhu.edu/~meneveau/ Exit
http://www.jhu.edu/~ceafm/ Exit
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
R828771 Center for the Study of Childhood Asthma in the Urban Environment Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R828771C001 Co-Contaminant Effects on Risk Assessment and Remediation Activities Involving Urban Sediments and Soils: Phase II
R828771C002 The Fate and Potential Bioavailability of Airborne Urban
Contaminants
R828771C003 Geochemistry, Biochemistry, and Surface/Groundwater Interactions
for As, Cr, Ni, Zn, and Cd with Applications to Contaminated Waterfronts
R828771C004 Large Eddy Simulation of Dispersion in Urban Areas
R828771C005 Speciation of chromium in environmental media using capillary
electrophoresis with multiple wavlength UV/visible detection
R828771C006 Zero-Valent Metal Treatment of Halogenated Vapor-Phase Contaminants in SVE Offgas
R828771C007 The Center for Hazardous Substances in Urban Environments (CHSUE) Outreach Program
R828771C008 New Jersey Institute of Technology Outreach Program for EPA Region II
R828771C009 Urban Environmental Issues: Hartford Technology Transfer and Outreach
R828771C010 University of Maryland Outreach Component
R828771C011 Environmental Assessment and GIS System Development of Brownfield Sites in Baltimore
R828771C012 Solubilization of Particulate-Bound Ni(II) and Zn(II)
R828771C013 Seasonal Controls of Arsenic Transport Across the Groundwater-Surface Water Interface at a Closed Landfill Site
R828771C014 Research Needs in the EPA Regions Covered by the Center for Hazardous Substances in Urban Environments
R828771C015 Transport of Hazardous Substances Between Brownfields and the Surrounding Urban Atmosphere
The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.
Project Research Results
3 journal articles for this subproject
Main Center: R828771
108 publications for this center
20 journal articles for this center