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What is Compu tat ional Flu id Dynam ics
(CFD)?
Computational(having to do with mathematics & computation)
Fluid Dynamics (the dynamics of things that flow)
CFD is built upon fundamental physics equations: equations
of motion and conservation. CFD applications range fromnumerical weather prediction to vehicular aerodynamics design.
CFD applications are linked with advances in computing
software and hardware. CFD software is characterized by the
physical models in the software.
Fine-scale CFD applications closely match the true geometryof the physical objects and processes being modeled.
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Br ief Backg round
before electronic compu ters
Philosophical Interests in Fluid Flow
Newtons Physical Equations (1686)
Navier-Stokes Equations (1823)
V. BjerknesNotions of Numerical
Weather Prediction (1904)
L.F. RichardsonFirst Numerical
Weather Prediction (1922)
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Br ief Backg round
w i th elect ron ic compu ters
:Prog ress ion to A ir Quali ty Modeling
First Electronic Computers (1940s)
J. CharneyFirst Computer Numerical
Weather Prediction (April 1950) Numerical Modeling of Air Quality
Promoted by US EPA in 1970s and 1980s
CMAQ Evolves in the 1990s to Present CMAQ Continues to Evolve with Advancing
Computation Hardware and Software
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Challenge to Relate to
Human Exposure Assessment
Fou r Quest ions Model ing
Should Help Answer
How many people are exposed ? What is the level of each persons exposure?
What are the causes of exposure?
How can exposures be altered efficiently?
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Total Exposure Concentrat ions =
Local Sources + Regional Backg round
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Roadway Exposu res:
With in the Roadway or Neighborhood
Microenvi ronments
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Making Fine-Scale CFD
Application Routine
Computational resources. Today, industrial complexes
can be practically modeled by most workstations, while
complex urban areas can only be modeled by the cluster
systems.
Develop best-practice methods.
CFD codes have many options.
Develop user-friendly interfaces for general application.
Air quality modelers should be able to run routineapplications.
Interface CFD software with other models.
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Support /Col laborators
Wei Tang: National Research Council Post Docwith EPA, 2003-2005 (2.5 years)
Matt Freeman, Richard Spencer: EPA Scientific Visualization Centerunder EPA contract with Lockheed-Martin
Karl Kuehlert, Brian Bell, Walter Schwarz: EPA Cooperative Researchand Development Agreement with Fluent, Inc
Michael Lazaro: EPA Memorandum of Cooperation withArgonne National Laboratory
Department of Homeland Security: New York City Urban DispersionProgram
Army Research Laboratory MSRC Visualizationand Supercomputing Facility
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App l icat ion of
Fine-scale CFD Models
Develop databases to complement the
dearth of exposure measurements.
Support the development of HumanExposure Factors.
Support the development of subgrid
parameterization for CMAQ.
Interface with CMAQ
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Presen t CMAQ
Multi-scale Multi-pollutant
Various Chemical and Physical
Processes
Common Linkage of Meteorology,
Emissions, and Air Quality
Regional Applications > 10 km grid
Urban Applications > 1 km grid
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Example Fine-scale CFD
Think Inside the Box
A few example solutions follow:
While the example cases do not involve
thermal heating, methods have been
developed for adding heat fluxes to any gridface or volume.
Motion of objects can be added.
Particle physics can be added. Chemistry can be added.
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Fine-scale CFD Model ing o f
Urban Neighborhoods
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Example Wind Field
What is the direct ion o f the freestream w inds?
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Example: Winds from Southwest
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Surface Winds and w ith Plume
Concentrat ion wi th in Bui ld ing A rrays
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Plume Ini t iated from
Different Poin t Locat ion s
- bu t w ithin an Ident ic al Wind Field.
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Hor izon tal Planes
- Vert ical Veloc ity
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Area-averaged * Winds
Urban Canopy Parameterization
Wind speed Wind direction
*Area-averaged over same horizontal slice-plane shown in the previous slide.
Upstream Inlet: Blue
Upstream Inlet: Blue
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Automobi le
Microenvi ronments
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Model ing Urban Roadways
- Includ ing the Vehic le Effects
TKEGrid Resolution
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Modeling Urban Roadways
- Inc lud ing the Veh icle Effects
ConcentrationWind Velocity
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Disclaimer
The research presented here was performedunder the Memorandum of Understandingbetween the U.S. Environmental Protection
Agency (EPA) and the U.S. Department ofCommerce's National Oceanic andAtmospheric Administration (NOAA) andunder agreement number DW13921548. Thiswork constitutes a contribution to the NOAA
Air Quality Program. Although it has beenreviewed by EPA and NOAA and approvedfor publication, it does not necessarily reflecttheir policies or views
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