Abstract
Fast and accurate predictions of the flow and transport of materials in urban and complex terrain areas are challenging because of the heterogeneity of buildings and land features of different shapes and sizes connected by canyons and channels, which results in complex patterns of turbulence that can enhance material concentrations in certain regions. To address this challenge, we have developed an efficient three-dimensional computational fluid dynamics (CFD) code called Aeolus that is based on first principles for predicting transport and dispersion of materials in complex terrain and urban areas. The model can be run in a very efficient Reynolds average Navier–Stokes (RANS) mode or a detailed large eddy simulation (LES) mode. The RANS version of Aeolus was previously validated against field data for tracer gas and radiological dispersal releases. As a part of this work, we have validated the Aeolus model in LES mode against two different sets of data: (1) turbulence quantities measured in complex terrain at Askervein Hill; and (2) wind and tracer data from the Joint Urban 2003 field campaign for urban topography. As a third set-up, we have applied Aeolus to simulate cloud rise dynamics for buoyant plumes from high-temperature explosions. For all three cases, Aeolus LES predictions compare well to observations and other models. These results indicate that Aeolus LES can be used to accurately simulate turbulent flow and transport for a wide range of applications and scales.
Highlights
More than half of the world’s population lives in urban areas and the danger from an accidental or deliberate release of hazardous materials can be significant
The Reynolds average Navier–Stokes (RANS) version of Aeolus is used as an operational model in the National Atmospheric Release Advisory Center (NARAC) at Lawrence Livermore National Laboratory (LLNL) for quickly simulating the impacts of airborne hazardous materials in urban areas
We found that 48.9%, 84.7%, and 91.5% of the simulated points fall within FAC2, FAC5, complex urban areas which are consistent with the values suggested in Ha and FAC10, respectively, indicating excellent performance for predicting dispersion in urban areas which are consistent with the values suggested in Hanna and Chang
Summary
More than half of the world’s population lives in urban areas and the danger from an accidental or deliberate release of hazardous materials can be significant. Most fast-response models rely on empirical algorithms based on idealized building configurations This makes it difficult to generalize the accuracy of these models for flow fields in highly heterogeneous urban terrain without many validation exercises [6]. Computational fluid dynamics (CFD) models have been used to compute the flow field in urban areas and complex topography Comparison of these results with field measurements shows that these models work well in most regions [7,8,9,10,11,12,13]. Based on work carried out by Gowardhan (2008) and Gowardhan et al (2011), we have developed a new fast-response operational dispersion modeling system called Aeolus, which can predict the flow and transport of airborne contaminants in urban areas and complex terrain [9,11]. This test was a high-altitude air burst with an explosive yield of 11 kilotons and a height of burst (HOB) of 1836 m above ground level (AGL)
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