Aviation Investigation Report A98H0003
1.16.9 Computer Fire Modelling
During this investigation, the analysis of the fire initiation and propagation was derived from a combination of sources, including detailed wreckage examination and reconstruction, laboratory burn test information, airflow patterns, the sequence of events, and the events timeline. Fire modelling was also used during the latter part of this analysis process.
In January 2002, the TSB contracted the Fire Safety Engineering Group (FSEG) at the University of Greenwich to conduct computational fluid dynamics (CFD) modelling using SMARTFIRE® software developed by the FSEG. The objective was to integrate information into a fire field model to study the potential effects of different variables on airflow and fire behaviour. The modelling helped to develop better insight into and understanding of the fire, and assisted in evaluating where the fire could have originated. This work also assisted in the interpretation of heat damage patterns by providing data on potential heat release and loss rate possibilities.
The CFD fire field model incorporated information such as the following:
- three-dimensional computer-aided design (CAD) exterior and interior aircraft geometry and construction details;
- material properties and associated fire burn test results;
- design and flight test airflow data; and
- atmospheric and flight profile information from the occurrence aircraft's FDR.
The modelling technology allowed investigators to conduct a series of full-scale virtual burns, using powerful computers to complete a multitude of complex calculations involving the interaction of processes, such as conduction, convection, and radiation. The computer processing of calculations for a single fire initiation scenario often took several days of continuous, uninterrupted, computational time. Subjects studied included potential odour and smoke migration paths, heat release, and complexities, such as heat loss rates to the outside atmosphere through the airframe. As full-scale aircraft fire testing was not an option, it would not have been possible to obtain information about in-flight fire initiation and propagation effects without the use of the fire modelling.
The CFD modelling substantiated the fire scenario presented in this report. When the model was run using the airflow flight test data, air was observed to be drawn into the cockpit interior in the area of the avionics CB panel, and to migrate through the cockpit into the avionics compartment as described in Section 1.16.3. The fire modelling also showed that initial fire propagation and growth characteristics were consistent with the fire scenario presented in this report. For the latter stages of the fire, only limited assessment was done of the information from the fire modelling because of the many permutations and combinations of possible events.
 Old Royal Naval College, Park Row, Greenwich, London, United Kingdom. The University of Greenwich Fire Safety Engineering Group was selected because of its internationally recognized expertise in fire field modelling using computational fluid dynamics (CFD) techniques for conduction, convection, and radiation calculations.
 CFD is a computational technology in which a computer model is created that represents a system or device under study. Sophisticated mathematical calculations, which typically include fluid flow physics, are applied to the virtual model to predict the dynamic outcome of heat transfer and how things flow (such as the flow of air and smoke from a fire).
 A deterministic undertaking that is based on the solution of mathematical equations to describe the physical behaviour of a fire, chemical behaviour of a fire, or both. Field models are based on an approach that divides the region of interest into a large number of small elemental volumes or cells. These cells are each systematically analyzed in increments to determine the changes in conditions for each cell, based in part on the changes occurring in adjacent cells, to calculate overall effect(s).
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