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Consequences of Urban Stability Conditions for Computational Fluid Dynamics Simulations of Urban Dispersion

The validity of omitting stability considerations when simulating transport and dispersion in the urban environment is explored using observations from the Joint URBAN 2003 field experiment and computational fluid dynamics simulations of that experiment. Four releases of sulfur hexafluoride, during two daytime and two nighttime intensive observing periods, are
simulated using the building resolving computational fluid dynamics model, FEM3MP to solve
the Reynolds Averaged Navier-Stokes equations with two options of turbulence parameterizations. One option omits stability effects but has a superior turbulence
parameterization using a non-linear eddy viscosity (NEV) approach, while the other considers buoyancy effects with a simple linear eddy viscosity (LEV) approach for turbulence
parameterization. Model performance metrics are calculated by comparison with observed winds and tracer data in the downtown area, and with observed winds and turbulence kinetic energy (TKE) profiles at a location immediately downwind of the central business district (CBD) in the
area we label as the urban shadow. Model predictions of winds, concentrations, profiles of wind
speed, wind direction, and friction velocity are generally consistent with and compare reasonably
well with the field observations. Simulations using the NEV turbulence parameterization generally exhibit better agreement with observations.

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Date Of Record Release 2009-06-16 15:27:19
Description The validity of omitting stability considerations when simulating transport and dispersion in the urban environment is explored using observations from the Joint URBAN 2003 field experiment and computational fluid dynamics simulations of that experiment. Four releases of sulfur hexafluoride, during two daytime and two nighttime intensive observing periods, are
simulated using the building resolving computational fluid dynamics model, FEM3MP to solve
the Reynolds Averaged Navier-Stokes equations with two options of turbulence parameterizations. One option omits stability effects but has a superior turbulence
parameterization using a non-linear eddy viscosity (NEV) approach, while the other considers buoyancy effects with a simple linear eddy viscosity (LEV) approach for turbulence
parameterization. Model performance metrics are calculated by comparison with observed winds and tracer data in the downtown area, and with observed winds and turbulence kinetic energy (TKE) profiles at a location immediately downwind of the central business district (CBD) in the
area we label as the urban shadow. Model predictions of winds, concentrations, profiles of wind
speed, wind direction, and friction velocity are generally consistent with and compare reasonably
well with the field observations. Simulations using the NEV turbulence parameterization generally exhibit better agreement with observations.
Classification
Resource Type
Format
Subject
Keyword Emergency response, Atmospheric releases, Urban environments, Winds, Simulations, Sulfur hexafluoride, Models, Reynolds Averaged Navier-Stokes equations, Turbulence parameterizations, Non-linear eddy viscosity (NEV), Turbulence kinetic energy (TKE), Central business district (CBD), Velocity, Fluid dynamics
Selector Stith
Date Of Record Creation 2009-06-16 15:15:05
Education Level
Date Last Modified 2010-04-09 17:03:28
Creator J.K. Lundquist, S.T. Chan
Language English
Date Record Checked: 2009-06-16 00:00:00 (W3C-DTF)

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