On the importance of the heat release rate in numerical simulations of fires in mechanically ventilated air‐tight enclosures

Abstract

A fire in a compartment with limited ventilation can cause a significant pressure rise, up to hundreds of Pascal. This is important in practice, as the pressure rise can cause damage or hinder evacuation, but also from the perspective of fire safety science. From the energy balance, taking into account the interaction between compartment pressure, fire dynamics and mechanical ventilation, the importance of the net heat gained per unit time in the gas phase is well recognized. This leads to the need to accurately quantify the heat release rate inside the compartment as a function of time. It is explained that scaling of the transient phenomena is not straightforward. The paper then focuses on numerical simulations, in particular on CFD in the gas phase. An overview is presented of different existing approaches for turbulent combustion modelling in turbulent buoyancy-driven flames with low values of scalar dissipation rate, typical for fire flames. A dynamic approach for modelling turbulent combustion, and the coupling with radiation modelling, is briefly discussed. Extinction and re-ignition are discussed extensively, in the context of reduced ventilation conditions. Finally, low-frequency oscillatory behaviour in mechanically ventilated air-tight compartments is addressed. It is argued that CFD simulations are a very valuable tool to gain further insight in this phenomenon. Suggestions for future research are formulated.