不同送风断面面积对临界风速的影响分析

Analysis of the impact of the different air supply cross-sectional areas on the critical velocity

临界风速是隧道通风排烟设计的关键参数,为研究不同送风断面面积对临界风速的影响,采用1∶20隧道模型和12种不同火源功率,设计5种送风断面（分别为全断面送风、3/4断面送风、1/2断面送风、1/3断面送风和1/4断面送风）,通过理论分析、数值模拟及部分模型试验研究了不同送风断面面积对临界风速的影响。结果表明,在不同火源功率下,送风断面面积越大,临界风速越小,两者成反比关系。在不同送风断面面积下,当无量纲火源功率低于0. 2时,临界速度逐渐增大;当无量纲火源功率高于0. 2时,临界风速几乎保持不变,其大小与火源功率无关。对数据结果进行拟合,得到了不同送风断面面积的隧道火灾临界风速模型,并与试验结果取得了较好的一致性。

Through a numerical simulation and the partial model tests, the given paper has made an exploration of the impact of the different air supply cross-sectional areas on the critical velocity, which is the key parameter of the tunnel ventilation and smoke exhaust design. For this purpose, the paper has designed 5 kinds of air supply sections, including a full section air supply project in an 1：20 ratio tunnel model at 12 different heat-releasing rates, with a 3/4, 1/2, 1/3, and 1/4 sections of air supplies. Accord- ing to the - theorem and the similarity ttleory, the paper has also made an analysis of the related factors that influence the critical velocity and derived the dimensionless relationship among the critical velocity, the air supply section area and the heat release rate, with FDS 6. 1 being used for numerical simulation. The re- sults of our analysis demonstrate that, under the different heat release rates, the larger the crosssection area, the smaller the criti- cal velocity would be, thus, implying that there exists an inverse relation between the two factors. What is more, the ratio of the critical velocity tends to increase linearly with the reduction of the crosssectional area of the air supply, whose increase ratio can be actually almost the same as that of the reduction. Therefore, under the different air supply cross-sectional areas, in case the di- mensionless heat release rate is lower than 0. 2, the critical speed would be gradually increasing. For example, when the dimension- less heat releasing rate is greater than 0. 2, the critical velocity would be almost invariable with its size being independent of the heat release rate. Knitting the results of the data, it would be possible to gain the formula of the critical velocities of the tunnel fires with the different cross-sectional areas of the air supply, whose correlation coefficient should be equal to 0. 991 3. Thus, the critical velocity model we have worked out turns to be well in accord with the experimental results. Hence, the model we have developed is in a position to provide a valuable reference for the design of ventilation and smoke exhausting system in the highway tunnel.