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（4）假定隧道中一辆公共汽车发生自燃引起火灾，将隧道入口风速的变化规律通过UDF导入FLUENT中，进行数值模拟。
当入口风速变化时，由于火源的制约以及隧道内速度方向的影响导致火源右侧段温度范围的变化较快，温差大约达到35K左右。沿着Y轴的正方向发展，温度继续降低，315K至323k的温度段迅速降低到308K至315K段，且其温度影响范围远小于稳态时的该温度段。另一个较大的区别在于温度在308K至315K段在火源右侧的隧道三分之二段温度在Z轴正方向的影响增大。
通过本文对不同车型的热释放速率变化以及入口风速变化的数值模拟结果与在稳态下的数值模拟结果进行对比，使本论文的结果更加贴近实际情况，为今后研究隧道火灾时通风情况的学者或设计隧道通风的人员提供研究、设计方法以及结果作为参考。
关键词： 隧道火灾；数值模拟；车辆类型；热释放速率；入口风速
Optimization design of a tunnel ventilation based on UDF simulation
Abstract: With the continuous development of science and technology and the actual demand of various geographical location in China, tunnels in our country is in rapid growth in both quantity and range. Because the particularity of tunnel structure, the fire which happens in the tunnel will cause tremendous loss of lives and economic loss, if the design of the ventilation in the tunnel is unreasonable.
This paper used the method of numerical simulation to study the ventilation when the tunnel was on a fire. Assumed that there is an accident caused by a bus spontaneous combustion in the side hole of the tunnel when it was in normal operation. The bus is 11000mm long, 2500mm wide and 3000mm high. In order to study the ventilation of middle length of 150m segment of 20MW fire in the full-length 2880m tunnel side hole and to verify the original ventilation scheme is feasible. The tunnel in the normal operation period use piston wind which is generated by vehicles entering the tunnel. When the tunnel is in fire condition, the tunnel jet fans will be started for makeup air, and smoke outlets will be opened simultaneously to exhaust the poisonous gas timely.
• The main content of this paper is pided into two parts, one is to simulate the change of velocity and temperature in fire condition caused by three types of vehicles in the tunnel when the heat release rate with changes. The other is to simulate the change of velocity and temperature in fire condition caused by a bus spontaneous combustion when the velocity of tunnel entrance with changes.
(1) Assumed that there was a fire caused by a car spontaneous combustion in the tunnel, the change rules of cars’ heat release rate can be pided into three stages. When the time of x between 0s and 120s, the heat release rate is y=x/24; When the time of x between 120s and 730s, the heat release rate is y=5; When the time of x between 730s and 780s, the heat release rate is y=-x/10+78; The numerical simulation is according to the above formula.
Through the comparison between the actual situation and steady state, the following conclusions can be concluded that the velocity of the middle of the tunnel which is on the right side of the fire source decreased gradually along the positive direction of Y axis instead of being constant in a range. There are three various temperature range on the right side of the fire source which decreased along the increase of Z positive axis value. In addition, two temperature stages still existed in the 1/3 section of tunnel on the right side of the fire source and the temperature which was near to the roof of the tunnel was lower than the temperature which was near to the ground. The range of temperature between 310K to 319K had the larger influence on the right side of the fire source.
(2) Assumed that there was a fire caused by a truck spontaneous combustion in the tunnel, the change rules of trucks’ heat release rate can be pided into three stages. When the time of x between 0s and 150s, the heat release rate is y=x/15; When the time of x between 150s and 730s, the heat release rate is y=15; When the time of x between 730s and 780s, the heat release rate is y=-x/5+156; The numerical simulation is according to the above formula.
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