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Investigation of the Pollutant Dispersion Driven by a Condensed-Phase Explosion in an Urban Environment

par Fouchier, Charline
Président du jury Degrez, Gérard
Promoteur Parente, Alessandro
Publication Non publié, 2020-09-11

Thèse de doctorat

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Résumé :

Understanding and predicting the consequences of dangerous phenomena linked to the industrial activity is critical to ensure the highest safety level possible. Explosions represent a high risk of fatalities and economic loss and even though the phenomenon is studied in the literature, accidents still occur.The explosion in air of a heterogeneous charge (i.e. an explosive charge surrounded or mixed with a gaseous, solid, or liquid pollutant) has various consequences. While the presence of buildings around the explosion will reduce considerably the impact of most of them, it will affect in more complex ways the propagation of the pressure released, also called bast wave, and the pollutant dispersion. Simplified models to characterize the blast propagation and the dispersion following an explosion are necessary tools for industries to access a first estimation of the risks related to their activities. However, the existing models do not take into account the effect of the urban environment.The global objective of the project is to improve the understanding of the blast propagation and the dispersion inside an urban environment by generating a quantitative database. In parallel to the project, simplified models are being developed by the Commissariat à l’Energie Atomique et aux Energies Alternatives (CEA) Gramat (center from the Direction des Applications Militaires (DAM)) and will be validated by the generated experimental database. To achieve this goal, experimental techniques are developed and applied to a controlled reduced-scale urban environment, and a CFD approach is used to facilitate the understanding of the blast experimental results. The challenges associated with the creation of a new experimental system led to innovative solutions in response to technical issues. The main originality of the project is the investigation of explosively driven dispersion under a controlled atmospheric boundary layer, which represents a novelty in the area from the author's knowledge. Existing experimental techniques have been extended and validated for the large dynamic ranges involved in the explosive dispersion. The research is separated into two parts: the investigation of the blast, and the investigation of the dispersion driven by an explosion, both inside an urban environment in a 1:200 reduced scale.In the first part, the blast propagation has been first investigated in free field to characterize the energy, the geometry, and the repeatability of each studied explosives. Then the blast has been studied inside four selected typical urban configurations. To help the understanding of the blast path, a numerical model has been developed in OpenFoam to simulate the propagation and a good overlap between the experimental and numerical results has been observed. The second part of the research focuses on the investigation of the explosively driven dispersion. Micro-sized talc particles have been added around the explosives to simulate the pollutant dispersion. Large-Scale Particle Image Velocimetry (LS-PIV) and Mie-Scattering techniques have been first investigated and validated on a supersonic jet. They have been thereafter applied to the explosively driven dispersion. Three atmospheric conditions, two masses of talc, and two diameters of powder have been investigated, both in free field and inside a T-junction.The experimental techniques used to characterize the explosion of a heterogeneous charge show promising results. They are powerful tools to investigate complex large-scale and large dynamic range flows.