Investigation on the Dispersion Driven by a Condensed Phase Explosion in an Urban Environment
Speaker: Charline Fouchier, The von Karman Institute for Fluid Dynamics
Presentation
Abstract
Safety is a discipline which needs to constantly evolve with our society and techniques. Continuous improvements of our knowledge on dangerous phenomena linked to the industrial activities are critical to ensure the highest safety level possible. Examples of tragedies caused by explosively driven dispersion are numerous. Some of them include the dispersion of dangerous chemicals in the atmosphere, others are linked to dust dispersion serving as fuel to secondary dust explosions. The dispersion driven by an explosion can be accidental but also intentional. The explosion of a heterogeneous charge in an urban environment has various consequences. While the presence of building around the explosive will reduce considerably the impacts of projectiles and heat flux, it will have more complex effects on the blast propagation 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 fast first estimation of the risks linked to their activities. However, the existing models do not consider the effect of the urban environment.
The study aims to provide a quantitative experimental database on the dispersion driven by an explosion in an urban environment to validate recently developed simplified models. To achieve this goal, experimental techniques are developed and applied on heterogenous explosions inside a controlled reduced-scale urban environment. The challenge of the investigation, which brings its originality, consists in the characterization of the explosively driven dispersion from the beginning of the explosion to the atmospheric dispersion, which requires techniques applicable to large scales (the plume can reach 1 m3 in volume), to large ranges of velocities (from 0 up to 120 m/s) in extreme test conditions due to the use of explosives.
Flows visualizations are first used for a preliminary characterization of the plume dispersion. The analysis of the grey-scale dispersion images gives information about the plume displacement, volume and expansion velocity. Large Scale Particle Image Velocimetry (LS-PIV) and Mie-Scattering techniques are used to estimate the velocity and powder distribution fields of the dispersion. These techniques are first validated on the investigation of a large-scale jet - a well-known dispersion case. They are thereafter applied on the explosively driven dispersion. The plume is characterized in free field and inside a T-junction for different wind speeds, powder masses and explosion energies.
The study provides a strong experimental database on the dispersion driven by an explosion which leads to a better understanding of the phenomenon. Existing experimental techniques have been extended and validated for the large dynamic ranges involved in the explosively driven dispersion and can be used for further complex flows investigations.
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