A41C-0630
High Resolution Simulations of a Hot Thermal Plume Interacting with two Buildings
The interaction of a moving atmosphere with a group of buildings is a highly nonlinear in time and space process that typically produces areas of vortex shedding and flow separation. The introduction of a hot thermal plume, crudely representing hot gases produced after detonation of a terrorist device, into this environment leads to additional interactions that make it relatively difficult to predict the movement of the plume. To help understand whether prediction is even possible in this type of environment, high-resolution simulations have been conducted in which a thermal plume was introduced into a flow field found upstream of two buildings. Even under this relatively simple setting, sensitivity simulations reveal the need for extremely high resolution, about 10 cm, to be able to accurately depict the interaction of the plume with the two buildings. In this presentation, results from simulations employing increasingly higher resolution will be shown to explain why such high resolution is required. Additionally, results from simulations in which the building are not present will also be shown to help illustrate that without the buildings being present the movement of the thermal plume is relatively easy to predict.
A41C-0631
Radioactive Dispersive Device (RDD) Bomb Modeling in Cities for Emergency Response Using the QUIC Model
The Quick Urban and Industrial Complex (QUIC) dispersion modeling system was developed as a rapid dispersion analysis tool to examine concentration and deposition patterns from a variety of chemical, biological, and radiological release sources. One of the model's modules produces an approximated three-dimensional wind field around buildings using an empirical diagnostic approach. A second module calculates the contaminant transport and dispersion using an urbanized Lagrangian random-walk dispersion model, incorporating gradient diffusion and non-local mixing to produce building-induced turbulence. QUIC's GUI includes a city builder for creating building domains, a meteorology builder to specify wind profiles, and a source GUI for location(s), geometry, type, and amount of release. Recent code improvements include the ability to release, track, and deposit particles of multiple size distribution, an explosive release accompanied by a buoyant plume, and a post-processing Depositional calculator, which sums deposition on horizontal and vertical surfaces, as a function of particle size bins. Los Alamos National Laboratory and the U.S. Environmental Protection Agency have worked to formulate hypothetical RDD urban releases with the objective of a pre-emptive prediction of contaminant air concentrations, their dispersion, and subsequent surface contaminant deposition, and relate these concentrations to the Protective Action Guides for emergency response and clean-up concentration metrics, with provided examples. We will discuss model development, applications, and direction for further research.
A41C-0632
Mesoscale Ensembles of Urban Canopy Parameterizations Applied to the Coastal Environment: Impacts on Urban Dispersion
The application of high-resolution mesoscale ensembles utilizing different urban canopy parameterization (UCP) characterizations is used to investigate the impact on urban dispersion in the coastal environment. Using the Coupled Ocean Atmosphere Mesoscale Prediction System* (COAMPS®) developed by the Naval Research Laboratory (NRL), model parameters and urban/land surface morphologies are perturbed within two parameterizations: the multi-level UCP originally developed by Brown and Williams (1998) and the WRF Kusaka UCP. Results will be shown for COAMPS® configured with 5-nests centered on New York City (Manhattan) with highest horizontal resolution of 0.444 km and COAMPS® configured with 4-nests centered on Tokyo, Japan with highest resolution of 1.67 km. The impact of the urban canopy layer on mesoscale plume transport, as well as its development and evolution, will be shown using COAMPS® simulations with the embedded passive tracer model. Model tracer releases occurring both within and above the urban canopy will be compared to assess the impact of coastal urban boundary layer structure on plume transport.
A41C-0633
Chemical Dense Gas Modeling in Cities
Many industrial facilities have on-site storage of chemicals and are within a few kilometers of residential population. Chemicals are transported around the country via trains and trucks and often go through populated areas on their journey. Many of the chemicals, like chlorine and phosgene, are toxic and when released into the air are heavier-than-air dense gases that hug the ground and result in high airborne concentrations at breathing level. There is considerable concern about the vulnerability of these stored and transported chemicals to terrorist attack and the impact a release could have on highly-populated urban areas. There is the possibility that the impacts of a dense gas release within a city would be exacerbated since the buildings might act to trap the toxic cloud at street level and channel it over a large area down side streets. However, no one is quite sure what will happen for a release in cities since there is a dearth of experimental data. There are a number of fast-running dense gas models used in the air pollution and emergency response community, but there are none that account for the complex flow fields and turbulence generated by buildings. As part of this presentation, we will discuss current knowledge regarding dense gas releases around buildings and other obstacles. We will present information from wind tunnel and field experiments, as well as computational fluid dynamics modeling. We will also discuss new fast response modeling efforts which are trying to account for dense gas transport and dispersion in cities.
A41C-0634
The Effects of Plume Buoyancy and Momentum on the Flow Structure and Dispersion in the Vicinity of an Idealized Building
Numerical simulations of buoyant and neutral plume dispersion in the vicinity of a cubical building were performed using a commercially available CFD code and the RNG k-e turbulence model. It was observed that when a release occurred inside the cavity region the size and shape of the cavity region were affected by both plume buoyancy and source momentum. Conversely, the effects of plume buoyancy on the concentration profiles within the cavity were noticeably different from those caused by momentum. Increased plume buoyancy resulted in greater fractions of plume being captured inside the recirculation cavity. Contrarily, greater plume momentum resulted in smaller plume fractions captured inside the building cavity. Plumes released immediately downwind of a cubical building considerably altered the flow field and dispersion characteristics of the entire cavity recirculation region. The buoyancy effects on the flow structure observed during this study should be considered in impact assessments where accurate predictions of short-term, near-field concentration fluctuations near source releases are required. This will become even more relevant if a sustainable-energy hydrogen-fuel infrastructure develops in the upcoming years.
A41C-0635
An Urban Boundary Layer and Dispersion Parameterization for the LLNL NARAC Modeling System: Preliminary Tests with the Joint Urban 2003 Field Project Data Set
The Lawrence Livermore National Laboratory (LLNL) National Atmospheric Release Advisory Center (NARAC) modeling system addresses the transport and dispersion of toxic and hazardous materials from a variety of source types and accounts for a wide range of physical processes. To provide real-time forecasts for emergency response applications, NARAC runs ADAPT, a diagnostic meteorological model, to generate gridded non- divergent wind, turbulence, and other meteorological fields. These are then used by NARAC's Lagrangian dispersion model, LODI, to predict the dispersion patterns. This paper describes modifications to the algorithm used to generate the boundary layer wind and turbulence profiles within ADAPT to parameterize urban scale effects on the urban boundary layer (UBL) wind and turbulence profiles. The UBL consists of four sublayers including the urban canopy layer (UCL), the roughness sublayer, the inertial sublayer, and the "outer" layer. The key surface parameters describing roughness effects (displacement height, roughness length, mean building height and the average fractional frontal area) are obtained from building data corresponding to the urban core of Oklahoma City, where the Joint Urban 2003 Field Project took place. Given these parameters, a reference wind speed, surface heat flux, and UBL height, the mean wind and turbulence profiles can be generated. Within the UCL, the mean wind is parameterized by an exponential profile based on a "canopy" model, whereas above the UCL, the wind is given by the Monin-Obukhov (MO) similarity profile that accounts for stability effects; the UCL and MO profiles are matched at the canopy top to ensure the continuity of the profile. Meteorological observations and tracer sampling data from the Joint Urban 2003 Field Project are used to assess the new approach. In particular, the ability of the parameterization to reconstruct the urban vertical profiles of wind and turbulence are evaluated. The impact on the fate and transport of a contaminant released in an urban area is also examined. This work was performed under the auspices of the US Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48. The Department of Homeland Security sponsored the production of this material under the Department of Energy contract for the management and operation of Lawrence Livermore National Laboratory. UCRL-ABS-234357
A41C-0636
Comparisons of Urban Transport and Dispersion Model Predictions to Field Trial Data
For the past 3 years our group at IDA has been involved in validation efforts associated with several Urban Transport and Dispersion (T&D) modeling systems. Models under study include MESO/RUSTIC, QUIC-URB/QUIC-PLUME, CT-Analyst, and four sub-models within HPAC, the Urban Canopy Model, Micro-Swift/Spray, the Urban Dispersion Model, and the Urban Windfield Module. Our main efforts have centered on supplying sponsors, and the T&D community as a whole, credible, protocol-driven comparisons of model predictions and field trial observations. I will review our most recent Urban T&D comparison work, with particular attention paid to comparisons of QUIC-URB/QUIC-PLUME predictions to the 29 continuous SF6 releases carried out during the Joint Urban 2003 (JU2003) field experiment in Oklahoma City.
A41C-0637
Numerical Model for Atmospheric Contaminant Clouds from Nuclear Explosions
Our numerical approach includes fluid mechanical model which is the combination of a compressible GEODYN code and a Low Mach code (LMC). The first one is an explicit code and it is intended to simulate early stages of nuclear explosions up to 15 s. The second one is an implicit code based on a pressure projection method and it is intended to simulate subsequent cloud rise events up to few hours. We perform series of cloud rise scenarios ranging from idealized bubble rise problem to realistic air bursts. We analyze effects of compressible dynamics and different turbulent parameterizations on the cloud evolution. It is found that in a realistic configuration interaction of a reflected shock wave from the ground with a fireball affects significantly cloud evolution in contrast to idealized bubble rise simulations. We show that by providing initial source from compressible GEODYN code, later times flow evolution can be successfully simulated with fast and efficient LMC code. Finally, we develop formalism for tracer particles and their fallout and present some preliminary results. This work was performed in part under the auspices of the U.S. Department of Energy by University of California, Lawrence Livermore National Laboratory under Contract W-7405-Eng-48.