Simulation on smoke re-circulation transition in an urban street canyon for different fire source locations with cross wind

Abstract

When a fire occurs inside an urban street canyon, the pollutant evolution is particular as a result of the fire-induced high buoyancy. Controlled by the competition of cross wind inertia force and fire plume buoyancy, the presence of fire smoke re-circulation in the street canyon has significant threat on human safety. Previous research mostly reported the re-circulation when fire locates in the center position, but the fire location variation effect has not been taken into consideration. In this paper, a street canyon model of 18 m wide and 18 m high is built with a constant heat release rate of 5 MW, while ten fire distances to the leeward building from 3 to 15 m are simulated. Results show that the smoke re-circulation is distinguished into three regimes for different fire locations. The re-circulation does not exist at the first regime, but it appears with its critical wind velocity slightly increases at the second regime, then the critical velocity increases sharply at the third regime. Besides, the flow patterns, and CO concentrations are presented and discussed as references to such re-circulation transition. Correlations are proposed to predict the critical wind velocity and the corresponding Froude Number for various fire locations.