Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Civil Engineering

Committee Chair/Advisor

Nigel Kaye

Committee Member

Abdul A Khan

Committee Member

Ashok Mishra

Committee Member

Nadarajah Ravichandran


A series of steady-state simulations have been conducted to investigate removal of dense gas from a simple square canyon formed between two square cross-section obstacles. Due to urbanization and industrialization, there always lies a high risk of exposure to harmful pollutants which can result from accidental release of toxic gasses. Those are often denser than the atmosphere. and can easily get trapped in between buildings in urban canopies. It is important to have full understanding of flushing mechanism of dense fluid inside urban canopies by steady turbulent flow because the exposure to these toxic dense gasses can be catastrophic. There have been several elaborate experimental investigations in this area. However, there are lots of scopes of computational investigation to fully understand and predict the flushing process. In this research, two different computational approaches have been investigated to study the flushing out behavior of dense gasses from a square canyon. Dense fluid is added uniformly through the base of the canyon at a steady rate. Over time a stratification develops in the canyon that eventually reaches a steady state. A wide range of parameter sets have been simulated and compared to the experimental results. The density of the inflow, its velocity, and the upstream surface roughness are systematically varied over the set of simulations run. A range of canyon stratifications are observed. In both computational approaches, the canyon has a two-layer stratification with a denser lower layer with a less dense upper layer. The flow over the canyon drives mixing across the interface between dense and ambient fluid. As the dense gas inflow rate is increased the lower dense layer thickens and the interface gets closer to the surface. In the RANS approach, three flow regimes were observed where the LES approach only exhibited regimes two. Also, simulated results from both approaches had lower mixing inside the canyon compared to the mixing in previous experiments. The simulation results indicate that the rate of inflow of dense fluid at the base of the canyon is a key parameter in the mixing process that has previously been neglected.



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