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

该项目解决了密度分层对城市地区污染物扩散的影响这一具有挑战性的问题。潜在的大气危害包括有毒工业化学品泄漏，核、生物和化学剂的故意或意外释放，以及发电厂事故。尽管它很重要，但在确定必要参数以预测稳定分层大气条件下的浓度统计数据这一问题上，缺乏有效的方法。这一缺陷是由以下几个因素造成的：1)由于难以在城市地区开展实验运动而缺乏数据；Ii)各种可能的建筑结构；Iii)复杂几何形状上流动的多尺度性质。这一差距将通过将实验室实验和数值模拟作为互补技术与多机构合作相结合来弥补。最终目标是在中性和密度分层条件下更全面地了解城市冠层的空气污染扩散和微气象学。工作将集中于四项相互关联的任务：1)建立一项涉及城市几何和密度分层的新型水洞实验。ii)建立密度分层城市流实验数据库，通过收集湍流速度和标量场的长时间序列来表征平均分散和波动。iii)开发了一种新的高性能拉格朗日三维分层流计算流体力学代码。并行模拟将在最先进的高性能计算机集群上进行。iv)发展理论和参数化，以估计分层对浓度统计的影响。智力优势：水洞数据将用于验证拉格朗日概率密度函数（PDF）数值模型的结果，该模型是专门为城市环境开发的。时间序列的分析和新的参数化的发展为我们对城市分散的理解提供了一个独特的潜力。这些数据还将用于将正在进行的湍流研究扩展到稳定分层流动。更广泛的影响：本项目将对参数化、模型和理论的发展产生重大影响，这些都是提高预测城市地区有害物质扩散能力所必需的。这个项目的发现将通过外展活动向传统的大学观众展示。乔治梅森大学（GMU）组织了大气运输和扩散年度会议，政府机构、应急管理人员、商业公司以及国际研究人员等各利益攸关方定期参加会议，会上将介绍和讨论这项研究的结果。这项研究的多学科特性将对参与项目的研究生产生重大的教育影响，因为他们在实验和理论上都是互动的。参加GMU会议的学生将获得与项目相关的研究范围和操作环境的实用知识。

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 projects 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.