Modeling dispersion in a street network for emergency response scenarios: the DIPLOS project

The accidental or deliberate release of hazardous airborne materials in densely populated areas is a contemporary threat that poses new scientific and modeling challenges. The dispersion modeling community is faced with the task of providing first responders with models that allow for a fast but accurate prediction of plume pathways, enabling to make informed decisions for evacuation and sheltering procedures. DIPLOS (Dispersion of Localised Releases in a Street Network) is a collaborative project between institutions in the UK and France that aims to develop and improve dispersion parameterizations in emergency response tools like the street-network based dispersion model SIRANE. The work builds on high-quality data sets of continuous and short-duration releases in urban arrays for different geometries and wind directions. Large-eddy simulation (LES) and direct numerical simulation (DNS) studies are complemented by extensive measurements and visualizations from boundary-layer wind-tunnel experiments. The aim is to quantify and parameterize the main exchange processes at intersections and in streets of finite extent. This includes studying and representing the effects of secondary sources, detrainment and re-entrainment, tall buildings and wind direction changes as well as developing empirical and theoretical methods to estimate concentration fluctuations in the short range. The presentation will highlight modeling challenges arising from the three-dimensionality of flow and dispersion features in the presence of buildings and will discuss improvements to the street-network modeling approach, facilitated by the analysis of the unique set of data from DIPLOS experiments and simulations.