分叉隧道合流段流动特征及局部损失特性研究

Study on the Flow Characteristics and Local Loss Characteristics of the Confluence Segment of Bifurcate Tunnel

进口匝道的存在导致隧道内空气出现合流现象,掌握合流段空气的流动特征和损失特性是分叉隧道通风设计的基础。针对夹角为5°~15°的分叉隧道,采用CFD方法和比尺模型试验研究合流比q和夹角θ对合流段空气流动和局部损失的影响。结果表明:随着q增大,主线局部损失系数ξ_(21)迅速减小,而匝道局部损失系数ξ_(31)则先迅速增大后趋于稳定。当合流前主线与匝道风量比Q大于两者截面积比φ时,ξ_(21)主要受流线弯曲的影响,ξ_(31)主要受射流增压作用的影响;当Q 21和ξ_(31)的主控因素则互换。在q较小时,ξ_(21)、ξ_(31)基本不随合流夹角θ变化;在q较大时,随着θ增大ξ_(21)基本保持不变,而ξ_(31)减小。提出了可准确预测夹角为5°~15°分叉隧道合流段局部损失系数的半经验公式,弥补了分叉隧道合流通风设计理论的不足。

Presence of entrance ramp will lead to air confluence in the tunnel,so understanding the flow characteristics and loss characteristics of air in the confluence segment is a prerequisite for ventilation design of a bifurcate tunnel.For a bifurcate tunnel with 5°~15°included angle,the CFD method and scale model are used in the experimental study on how the confluence ratio q and included angleθwill impact the air flow and local loss in the confluence segment.As the results indicate:As q increases,the local loss coefficientξ_(21) of the main line quickly decreases,while the local loss coefficientξ_(31) of the ramp first increases quickly and then stabilizes.Before confluence,if the air volume ratio Q between the main line and ramp is greater than the sectional area ratioφbetween them,ξ_(21) is mainly affected by the flow line bending,andξ_(31) is mainly affected by the jet flow pressurization;if Q<φ,the main controlling factors ofξ_(21) andξ_(31) are interchanged.If q is small,ξ_(21) andξ_(31) will essentially remain unchanged even when the confluence included angleθchanges;if q is big,then asθincreases,ξ_(21) essentially remains unchanged,whileξ_(31) decreases.A semi-empirical formula is proposed that can accurately predict the local loss coefficient of the confluence segment of a bifurcate tunnel with 5°~15°included angle.This formula fills the gap in the design theory for confluence ventilation of bifurcate tunnel.