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Vidali Cristina

Vidali Cristina

PhD student - project CIFRE
LMFA and Air Liquide Paris Research & Development Center.
Subject : "Atmospheric heavy gas dispersion in complex environment"
Supervisor : Pietro Salizzoni & Louis Gostiaux

Understanding the physics of atmospheric dispersion of heavy gases plays a key role in evaluation and management of risks associated to accidental releases in complex environment.
Heavy gases dispersion is influenced by reduced dilution with ambient air and stagnation close to ground level with serious consequences in health and environmental impact. Their presence may produce favorable conditions to asphyxia, explosion and fire in urban areas or industrial sites.
The aim of this study is to investigate, experimentally and numerically, the dynamics of a heavy gas release trough measurements in air wind tunnel. In particular, we will identify local stratification influence on mixing between air and heavy gas, and on the multi-scale spectral distribution on turbulent kinetic energy. To that purpose, we analyse the emission in simple configurations such as elevated point source and linear source placed within a turbulent boundary layer. In the experiments, we perform simultaneous velocity and concentration measurement respectively with the Flame Ionization Detector (FID) and the X-Probe Hot Wire Anemometry (HWA).
The information provided by the dataset allows us to evaluate turbulent mass flux for both horizontal and vertical velocity and to analyse the statistics up to fourth moments of the concentration and velocity Probability Density Functions (PDFs). Furthermore, we examine dependence of flux Richardson number (Ri*) and turbulent Schmidt number (Sct) in heavy gas case. We perform CFD Reynolds Averaged Navier Stokes (RANS) simulations in 3D by means of ANSYS software FLUENT in order to compare and validate the mathematical model with our experimental results.