Effects of ambient pressure on fire-induced buoyancy driven plume dispersion and re-entrainment behavior in a street canyon

Abstract

The present study investigated the effects of ambient pressure on fire-induced buoyancy driven plume dispersion and re-entrainment behavior in a street canyon. A series of numerical simulations were conducted adopting Fire Dynamics Simulator software with heat release rate, wind flow velocity and ambient pressure varying. The results show that the fire smoke diffusion characteristics can be divided into four regimes, i.e., buoyancy-dominated regime, transition regime, critical regime and wind-dominated regime. The ambient pressure can influence the smoke diffusion in the street canyon, and the smoke flow patterns under relatively larger ambient pressure are more susceptible to wind flow. The dimensionless ambient pressure P* was introduced to quantify the effect of ambient pressure on critical re-entrainment wind velocity, and a prediction model of critical re-entrainment wind velocity was proposed. Further, considering the influences of ambient pressure and entrainment coefficient, a uniform correlation was proposed to predict the temperature rise ΔT at different heights in the plume region. Besides, the critical Fr number was insensitive to the ambient atmospheric pressure. A good correlation for predicting the critical value of the Fr number was given based on the analyses in this paper.