Alan H HuberPhysical Scientist; PhD, QEP

NOAA, ASMD, in partnership with the US EPA, National Exposure Research Laboratory, RTP, NC, USA

THE 5TH ANNUAL CMAS CONFERENCE, Chapel Hill, NC October 18, 2006

A FRAMEWORK FOR FINE-SCALE COMPUTATIONAL FLUID DYNAMICS

AIR QUALITY MODELING AND ANALYSIS

What is Computational Fluid Dynamics (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 from numerical 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 geometry of the physical objects and processes being modeled.

Brief Background– before electronic computers

• Philosophical Interests in Fluid Flow

• Newton’s Physical Equations (1686)

• Navier-Stokes Equations (1823)

• V. Bjerknes – Notions of Numerical Weather Prediction (1904)

• L.F. Richardson – First Numerical Weather Prediction (1922)

Brief Background– with electronic computers

:Progression to Air Quality Modeling• First Electronic Computers (1940’s)• J. Charney – First Computer Numerical

Weather Prediction (April 1950)• Numerical Modeling of Air Quality

Promoted by US EPA in 1970’s and 1980’s• CMAQ Evolves in the 1990’s to Present • CMAQ Continues to Evolve with Advancing

Computation Hardware and Software

Challenge to Relate to Human Exposure Assessment

– Four Questions Modeling Should Help Answer

• How many people are exposed ?• What is the level of each person’s exposure?• What are the causes of exposure? • How can exposures be altered efficiently?

Total Exposure Concentrations = Local Sources + Regional Background

Urban Exposures: Beyond the Lamp Post

Roadway Exposures: Within the Roadway or Neighborhood

Microenvironments

Human Exposure

• A human is only exposed to what can possibly contact his body.

• Air quality concentrations need to be linked to temporal and spatial scales associated with profiles of human exposure relevant to supporting health risk assessments

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 routine applications.

• Interface CFD software with other models.

Support/Collaborators• Wei Tang: National Research Council Post Doc

with EPA, 2003-2005 (2.5 years)

• Matt Freeman, Richard Spencer: EPA Scientific Visualization Center under EPA contract with Lockheed-Martin

• Karl Kuehlert, Brian Bell, Walter Schwarz: EPA Cooperative Research and Development Agreement with Fluent, Inc

• Michael Lazaro: EPA Memorandum of Cooperation withArgonne National Laboratory

• Department of Homeland Security: New York City Urban Dispersion Program

• Army Research Laboratory MSRC Visualization and Supercomputing Facility

Application of Fine-scale CFD Models

• Develop databases to complement the dearth of exposure measurements.

• Support the development of Human Exposure Factors.

• Support the development of subgrid parameterization for CMAQ.

• Interface with CMAQ

Present 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

Potential for Interfacing CMAQ CFD with Fine-scale CFD Models

• Increasing computational capacities make it possible to extend CMAQ to spatially fine-scales. Finer temporal scale may be more difficult.

• Interface CMAQ when needed with a separate fine-scale (subgrid) model.

• Pass information between separate CMAQ and

fine-scale model.

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 grid face or volume.

• Motion of objects can be added.• Particle physics can be added.• Chemistry can be added.

Fine-scale CFD Modeling of Urban Neighborhoods

Example Wind FieldWhat is the direction of the freestream winds?

Example: Winds from Southwest

Surface Winds and with Plume Concentration within Building Arrays

Plume Initiated from Different Point Locations

- but within an Identical Wind Field.

Horizontal Planes - Vertical Velocity

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

Automobile Microenvironments

Modeling Urban Roadways - Including the Vehicle Effects

TKE Grid Resolution

Modeling Urban Roadways - Including the Vehicle Effects

Concentration Wind Velocity

SUMMARY STATEMENT

• CMAQ-like air quality modeling systems may evolve to support the critical needs for modeling human exposures to air pollutants.

• Continued advances in computing hardware and software make it possible and increasingly more practical to consider extending present CMAQ air quality models to increasingly finer scales.

• Fine-scale CFD should be interfaced with CMAQ

• Fine-scale CFD should support CMAQ parameterizations

• Fine-scale CFD models can also be applied independent of larger scale grid models to support the development of human exposure factors and the human exposure profiles that are dominated by local source emissions.

Disclaimer

• The research presented here was performed under the Memorandum of Understanding between the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Commerce's National Oceanic and Atmospheric Administration (NOAA) and under agreement number DW13921548. This work constitutes a contribution to the NOAA Air Quality Program. Although it has been reviewed by EPA and NOAA and approved for publication, it does not necessarily reflect their policies or views