曲线隧道火灾烟气控制临界风速的研究

文章以双螺旋隧道实际工程为研究对象,采用数值计算方法对半径为600 m的曲线隧道在火灾工况下临界风速及火灾烟气的流动规律进行了深入研究和分析。结果表明,采用的数值计算方法对Memorial隧道火灾试验进行计算的结果吻合较好。当曲线隧道内发生规模为10 MW火灾时,火灾烟气控制的临界风速为2.5 m/s。降低曲线隧道通风速度,隧道内均出现明显的烟气回流现象,烟气回流层长度和厚度均随着通风速度的降低显著地增加。随着通风速度的提高,火焰的偏转角增大,拱顶最高温度升高。在火灾下游火源点附近断面烟气分布表现出不对称性,之后断面表现出明显的烟气分层分布。

河道截流戗堤下游回流长度研究

基于沿水深方向积分的平面二维水流动量方程,在采用合理的假定条件下,推导出含渗漏因素的戗堤下游回流区长度计算公式。研究结果表明,戗堤下游回流区长度不仅与坝长、水深、糙率、河宽缩窄比等因素有关,而且与戗堤自身的渗流量有关,回流区长度与渗漏量成反比。

几个典型隧道火灾问题研究进展

由于隧道数量的增加和隧道火灾造成的人员伤亡和财产损失巨大,隧道消防安全的研究一直是个热点问题。鉴于目前隧道火灾基础理论方面所开展的研究尚需深入细化,本文分析总结了几个隧道火灾基础问题的研究进展情况,主要包括隧道火灾的最高温度、火焰长度计算及隧道内温度衰减、火灾烟气回流和临界风速模型的演化等,较系统地总结了目前隧道火灾的几个主要研究方面的成果,指出了以往研究的一些不足之处。分析结果表明:目前对隧道火灾的研究主要集中于隧道内温度场特性、隧道内纵向风火灾发展的影响以及对隧道火灾烟气控制的研究。然而在隧道火灾基础理论方面所开展的研究还不够系统,因此要有效利用已有的可靠数据,对交通隧道火灾进行更加基础性和系统性地研究。需要进一步研究的内容包括:1)目前隧道火焰长度模型主要用于自由燃烧及机械通风影响下的隧道火灾,对于采用自然通风或横向通风的隧道,其火焰长度模型还有待进一步研究。2)当前的烟气回流模型多是通过小尺寸实验或较小火源功率实验进行验证,对于火源功率较大时烟气回流距离的函数关系是否仍然成立尚需进一步验证。3)由于限制风速较临界风速在控制烟气回流的同时可保持烟气层的稳定,更有利于火灾扑救和人员疏散,但目前关于限制风速的计算模型还未被提出,其与隧道几何尺寸的定量关系还需进一步研究。4)国内外对隧道火灾的研究主要是基于小尺寸模型,虽然得到了不少结论,澄清了很多现象,但是缺乏大规模火灾实验数据的验证,还要进行更多大尺寸或全尺寸实验来验证这些理论。5)对于UTLT类隧道的烟气蔓延与控制目前只进行了一些小尺寸实验研究,不能很好地指导该类隧道的防火设计,亟需进一步的理论研究和大尺寸实验验证。

Comparison on Hydraulic Characteristics Between Orifice Plate and Plug

Orifice plate energy dissipater as well as plug energy dissipater, as a kind of effective energy dissipater with characteristics of simple structure, convenient construction and high energy dissipation ratio, has become welcomed more and more by hydraulics researchers. The two kinds of energy dissipaters with sudden reduction and sudden enlargement forms are similar in energy dissipation mechanism, but there are differences in energy dissipation characteristics and cavitation characteristics. In the present paper, the differences between orifice plate and plug in energy loss coefficient, relating to their energy dissipation ratio, in the backflow region length, relating to their energy loss coefficient, and in the lowest wall pressure coefficient, relating to their cavitations risk, were analyzed by numerical simulations and physical experiment, and their features in above three aspects were also revealed. The results of research in the present paper demonstrate that the backflow region length of orifice plate is longer than that of plug at the same contraction ratio, the lowest wall pressure coefficient of plug is smaller than that of orifice plate at the same contraction ratio, and the energy loss coefficient of orifice plate is bigger than that of plug, which illustrates that plug is superior to orifice plate in resistance cavitation damage at the same contraction ratio.