Collaborative Research: Measurements and Advanced Modeling of Dispersion in the Urban Environment

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This project addresses the challenging problem of the impact that density stratification has on contaminant dispersion in urban areas. Potential atmospheric hazards include toxic industrial chemical spills, intentional or accidental releases of nuclear, biological and chemical agents, and power plant accidents. Despite its importance, there is a lack of efficient approaches to the problem of determining the parameters necessary to predict the concentration statistics under stably stratified atmospheric conditions. This shortcoming arises because of several factors: i) scarcity of data due to the difficulty in conducting experimental campaigns for urban areas;ii) the variety of possible building configurations;iii) the multiscale nature of the flow over complex geometries. This gap will be bridged by combining laboratory experiments and numerical modeling as complementary techniques, with a multi-institution collaboration. The final goal is to progress towards a more complete understanding of the air pollution dispersion and micrometeorology in urban canopies in both neutral and density stratified conditions. Efforts will concentrate on four interrelated tasks: i) Set up of a novel water tunnel experiment involving urban geometry and density stratification. ii) Creation of an experimental database of density-stratified urban flow to characterize mean dispersion and fluctuations through the collection of long time series of turbulent velocity and scalar fields. iii) Development of a new high performance Lagrangian computational fluid dynamics code for three dimensional stratified flow. Parallel simulations will be performed on state of the art high performance computer clusters. iv) Development of theory and parameterizations to estimate the impact of stratification on concentration statistics. Intellectual Merit: The water tunnel data will be used to validate the results of a Lagrangian probability density function (PDF) numerical model specifically developed for urban environments. The analysis of the time series and the development of new parameterizations offer a unique potential for a significant improvement of our understanding of urban dispersion. These data will also be used to extend ongoing research on turbulence to stably stratified flows. Broader Impacts: This project will have a substantial impact on the development of parameterizations, models and theories necessary for improving capability to predict dispersion of hazardous materials in urban areas. Findings of this project will be presented beyond the traditional university audience through outreaching activities. George Mason University (GMU) organizes the Annual Conference on Atmospheric Transport and Dispersion, regularly attended by various stakeholders such as government agencies, emergency managers and commercial companies as well as international researchers, where the results of this research will be presented and discussed. The multidisciplinary character of this research will have a significant educational impact on the graduate students involved in the project as they work interactively on both experiments and theory. The participation of the students in the GMU conference will give them practical knowledge of the spectrum of research and operational environments related to their projects.