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ISSN Online: 2377-424X

ISBN CD: 1-56700-226-9

ISBN Online: 1-56700-225-0

International Heat Transfer Conference 13
August, 13-18, 2006, Sydney, Australia

NUMERICAL SIMULATION OF UNSTEADY BACKLAYERING IN TUNNEL FIRES

Get access (open in a dialog) DOI: 10.1615/IHTC13.p26.170
8 pages

Abstract

During a fire in a tunnel smoke and hot combustion products can spread against longitudinal ventilation, a phenomenon usually referred as “backayering”. This has a significant influence on evacuation and fire fighting. The minimum ventilated air velocity necessary to prevent backlayering is designated as “critical velocity”. This phenomenon has been recently observed in the large scale tests conducted in the Runehammar road tunnel (2003), where, during several heavy goods vehicle (HGV) fire simulations, backflow velocity oscillations and reversal where observed. The present work addresses this issue by the study of the influence of the fire heat release rate (HRR) curve slope on the smoke flow dynamics. Threedimensional simulations were carried out in a realistic tunnel model, with the ventilation fans represented as implicit momentum sources in the CFD calculations, and comparison with available experimental results showed good agreement. In addition, the results predict that a small variation of the HRR curve slope induces oscillations in the backlayer flow.