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关键词：隧道火灾；数值模拟；排烟口数量；排烟口间距
Ventilation Design of a Tunnel Based on Fluent
ABSTRACT：In recent years, With the continuous development of science and technology and economy in China.Tunnel which is one of the three-dimensional transport is in rapid growth in both range and quantity.The tunnel has a special structure,so if its internal ventilation installation has not been reasonably designed,huge economic losses will be inevitable if a fire breaks out inside.
This paper used the method of numerical simulation to study the ventilation and smoke extraction in case that a fire broke out in a tunnel.
The length of tunnel was 2.2km in this paper. The length of its central was 1476m. It consisted of one tube. The tube had four-lane. The inner diameter of the tube was 9.9m. The height of the lane was 4.5m.The designed traffic volume was 2400 per hour. During normal operation of the tunnel,ventilation mode was using piston wind which produced by the entering traffic.When the tunnel was blocked or a fire broke out, the jet fans were started to complement the wind. In the same time, the exhaust ports were opened timely to discharge the contaminative gases.
It is assumed that a fire broke out in the downlink tube of the tunnel. In order to facilitate research,I chose to cut out 260m in the middle of the downlink tube for numerical simulation studies.It is assumed that it was a bus fire.The distance of the fire to the entrance of the intercepted tube is 50m. The size of the fire source was 8.0m×2.8m×3.0m, the scale of the fire was 20MW, the maximum temperature of the fire up to 700℃~800℃, the amount of smoke gas of the fire was 50m³/s.
In this paper,I have a simulated calculation to the original ventilation and smoke settings.Then I came up with the four schemes of the setting of exhaust ports. First of all, according to the requirements of each scheme established appropriate model in the Gambit software. Then,each model was imported to the Fluent for numerical simulation. Finally, I analyzed the numerical simulation results. The mainly contents of this paper as follows:
(1) Analyzing the ventilation effect for the original ventilation scheme.The distance of exhaust ports is 60m. If we opened two exhaust ports in the downstream of a fire source when a fire broke out, the total exhaust volume was 44.56m³/ s. The value is smaller than the smoke of the fire source that was 50m³/s. We abandoned this solution for it could not ensure the safety of the personnel inside the tunnel. If we opened three exhaust ports instead, the total exhaust volume was 51.36m³/s, this value was bigger than 50m³/s, and therefore the original plan need we opened three exhaust ports .
(2) Analyzing the ventilation effect for optimum proposal: we changed the distances between exhaust ports 60m to 50m or 40m. When the distance between the exhaust port is 50m,we open two exhaust ports exhaust volume was 44.32m³/s; three exhaust spacing 50m was 50.88m³/s; two exhaust spacing 40m was 44.32m³/s; three exhaust spacing 40m was 51.00m³/s; the open two exhaust ports on total exhaust volume was less than smoke production.We abandoned these two solutions for they could not ensure the safety of the personnel inside the tunnel.The two scheme open three smoke exhaust volume were greater than the total smoke production, and the gap between these quantities were small and could meet all the smoke generated 20MW fire requirements. When the distances of the exhaust ports were 40m, the number of the exhaust ports was the most of the schemes. When the distances of the exhaust ports were 50m, the number of the exhaust ports was moderate. According to the model,a fire occurred until the smoke gases were discharged.The maximum distance of the smoke gases spread as follow: when the distances of the exhaust ports were 40m, the smoke gases spread to 92m at the downstream of the fire. When the distances of the exhaust ports were 50m, the smoke gases spread to 112m at the downstream of the fire. When the distances of the exhaust ports were 60m, the smoke gases spread to 132m at the downstream of the fire.