Numerical study of smoke movement in an inclined tunnel with wind effect

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Numerical study of smoke movement in an inclined tunnel with wind effect

 

Author: Cheung, Sheung Kwan
Title: Numerical study of smoke movement in an inclined tunnel with wind effect
Degree: M.Sc.
Year: 2010
Subject: Smoke prevention.
Tunnels -- Fires and fire prevention.
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiv, 54, [96] leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2551471
URI: http://theses.lib.polyu.edu.hk/handle/200/6922
Abstract: Previous works reported that the design and operation of tunnel ventilation system (TVS) can be affected by wind action at the tunnel portals. But these effects have not been discussed on the smoke management system (SMS) design for the inclined tunnels so far. The smoke movement pattern for a typical local road tunnel, as length of 100m x width of 9.90m x height of 5.85m was studied for different fire scenarios. Fire field model was used for the investigation. The software was used Fire Dynamic Simulator (FDS5). A better understanding of smoke movement would help the local tunnel authority to design better ventilation and smoke management control system for the inclined tunnel. As mentioned above, a preliminary study of wind effect on the road tunnel fire available in the computational fluid dynamics (CFD) model was reported. A t-square fire source of 5MW was used to simulate a typical private car fire, and different slopes of tunnel as 0°; 2.5° and 5.0° were considered on the simulation studies. The result showed that the fire environment inside the tunnel could be affected by the wind effect, and the positive and negative wind effect inside the tunnel could be produced by various wind directions at the tunnel portals. It is suggested that the wind effect should be considered on the SMS design for the inclined tunnel.
Moreover, to study the performance of longitudinal ventilation system design, critical air velocity with wind effect was investigated for different fire scenarios. Various t-square fires, as 5MW for private car; 30MW for bus and 100MW for heavy goods truck or gasoline puddle with different slope of tunnel were investigated. The simulation results of the present studies were compared with four existing empirical models. For the negative wind effect, additional air velocities of about 50% to 55% are required to oppose the negative wind pressure and prevent smoke backlayering inside the inclined tunnel. And for positive wind effect, no additional air velocities is required on the small heat release rate (HRR), e.g. 5MW, but the additional air velocities are required on the large HRR, e.g. 30MW and 100MW. As presented above, noted that strong turbulence air flow could be found at ceiling level near fire source with large HRR. This may be attributed to explain that smoke backlayering cannot be prevented, and additional air velocities are required for the case of positive wind effect and fire with large HRR. In addition, the problem also noted that current design approaches may not prevent the smoke backlayering for fire with large HRR.

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