Abstract
This paper presents the results of numerical experiments on fire development and the backdraft phenomenon. The numerical model of fire development built with the use of Ansys Fluent was then validated based on literature data taken from real fire experiments. Some theoretical foundations of airflow and combustion modelling were added. Some features of the numerical model, which allowed for its high accuracy to be achieved, were widely discussed. Since large buoyancy forces were involved, to reproduce the decrease of the atmospheric pressure with height, a variable static pressure was applied using UDF (user-defined function).The results showed good accordance taking into account both the temperature profiles and the distribution of the airflow velocity. Once the model was validated, the research was extended to examine the backdraft phenomenon. The results revealed characteristic phases of the phenomenon and the occurrence of the gravity current as well, which were reported by empirical experiments.
Highlights
Due to a tight shell there are specific conditions for fire development in modern buildings
Weng carried out scaled model experiments and confirmed that the mass fraction of unburned fuel was the crucial parameter in determining backdraft occurrence
The first step was the validation of the built-up numerical model
Summary
Due to a tight shell there are specific conditions for fire development in modern buildings. The flames travel outside through the upper part of the newly formed opening andfresh air inflows through its lower part, forming a so-called gravity current Studies on this extremely dangerous backdraft phenomenon have been carried out for a long time. Fleischmann examined backdraft both by model tests and numerical research as well [7,8,9] He found that the mass fraction of the unburned fuel in a compartment greater than 15% was the necessary. Weng carried out scaled model experiments and confirmed that the mass fraction of unburned fuel was the crucial parameter in determining backdraft occurrence He determined the threshold value at the level of 9.8% [10]. The results, split into two parts, model validation and the backdraft phenomenon analysis, are presented in the third section, followed by the conclusions
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