Grantee Research Project Results
2002 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
EPA Project Officer: Aja, Hayley
Project Period: October 1, 2001 through September 30, 2007
Project Period Covered by this Report: October 1, 2001 through September 30, 2002
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 main objectives of this research project are to: (1) implement, test, and use the 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 co-located with point aerosol sensors to identify pathways and sources of aerosols.
Progress Summary:
Computational simulation tools and instruments are being developed and deployed to address potential exposure pathways in urban environments from airborne particles. Air pollution is affected critically 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, due to the complex ground topology typically found in cities. The goal of this year's research has been to implement and test a new generation physical model of turbulence to improve the state-of-the-art of computer simulations of flow and transport within urban environments and to undertake a series of field observations on airborne particles in southeastern Baltimore using a suite of air quality instruments. Measurements are taken at this location, in part, because a prevailing concept is that the downtown buildings direct particulates from the hazardous stacks in south Baltimore toward the eastern neighborhoods.
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 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 (Porte-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 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, the ability to handle complex geometries, and unsteady flows. However, 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 project has been to implement, test, and use this new model for simulating pollutant transport in urban environments.
Our modeling progress to date has been to: (1) implement the scale-dependent Lagrangian dynamic model in the JHU LES code; (2) perform validation tests on flat surfaces (the tests were successful); (3) simulate flow over patches with varying roughness scales (those tests have demonstrated the capability of the model to capture local variations in coefficient); and (4) implement the model in wind flow over a building topology. For this purpose, the JHU LES code was modified to allow prescription of complex geometry boundary conditions (to represent buildings, using the embedded boundary method), and the Lagrangian dynamic model was implemented in conjunction with these new boundary conditions.
Preliminary results for flow around a representative building shape (see Figure 1) confirm that physically realistic flow patterns are obtained (including the existence of the characteristic horse-shoe vortex around the base of the building, the separated wake, etc.). In terms of the ability of the dynamic model to predict spatially varying values of the coefficient, we present spatial distributions of the predicted coefficient field (see Figure 1). Interestingly, the coefficient increases almost five-fold in regions of rapid straining on the sides of the building where the flow is deflected in an irrotational fashion, whereas the coefficient is decreased along the shear layers downstream of the building. There are reasons to believe that these trends are physically realistic. As a comparison, simulations with the standard Smagorinsky model would impose a spatially uniform value of near 0.03, thus damping the shear layers too much and possibly not damping enough in the high-strain regions.
(a) | (b) |
Figure 1. (a) Lagrangian cs Distribution. The distribution is in an atmospheric boundary layer flow over a single building, along a representative horizontal plane. (b) Two Three-Dimensional Iso-surfaces of Lagrangian Dynamic Coefficient. These iso-surfaces show complex spatial structure.
We have improved the capabilities of the JHU lidar, which can be used to assess certain features of the LES simulations (e.g., ABL entrainment) and measure the transport patterns of aerosols. In this research project, aerosols and their chemical properties have been measured during the intensive summer 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 is extremely time consuming, as it requires 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.
Figure 2. Lidar Time Series of Relative Aerosol Concentration. Height range is z from 250m to 2200m (arbitrary units) demonstrating ABL entrainment.
Future Activities:
We will introduce transport equations for concentration of pollutants, test the predictions of flow around building shapes with available data, and generalize to the case of several buildings to approach the level of complexity typically found in urban environments. We also will 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, aerosols, lidar, light detection, ranging, Baltimore, Maryland, MD., 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/~ceafm/ Exit
http://www.jhu.edu/~dogee/mbp 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