超大断面水平隧道纵向通风临界风速CFD分析

首先介绍了临界风速研究的基本思路及国内外主要研究成果.结合国内某长大公路隧道设计,建立一长300m、水力高度10.64m的水平隧道模型,通过CFD模拟确定超大断面隧道临界风速的影响因子及相应的准则关联式.模拟表明:与火灾热释放速率相比,环境温度的影响可以忽略不计;与Atkinson(模型试验)及Buxton(大尺度试验)相似,临界风速随热释放速率的变化分为两个区域,与低热释放速率时不同,一旦热释放速率超过40MW,临界风速的变化明显趋于缓慢.

CFD Analysis on Critical Velocity of Longitudinal Ventilation for Super Large Horizontal Tunnel

The longitudinal air velocity required to prevent back-layering is often called the "critical velocity".So far its values for various tunnels have been obtained mainly from sets of equations derived by applying Froude number preservation,combined with some experimental data.In virtue of the discrepancies between the Kennedy model and Atkinson experimental data, the study addressed the problem of critical ventilation in large cross sectional horizontal tunnel.Especially the leveling-off of critical velocity for large values of heat release rate was analyzed.The CFD results implied that within the variation of the ambient temperature studied,the ambient temperature has negligible effect on the critical velocity.It was also shown clearly that there are two regimes of variation of critical velocity against fire heat release rate.At low heat release rates,the critical velocity varies just like Kennedy model,however once the heat release rate surpasses 40MW,the critical velocity becomes independent of fire heat release rate.Furthermore the study used dimensionless velocity and dimensionless heat release rate with the tunnel hydraulic height as the characteristic length in the data analysis.And a good agreement has been obtained with the results of both reduced-scale tunnel and the full-scale colliery tunnel.