Study on the Flow Characteristics and Local Loss Characteristics of the Confluence Segment of Bifurcate Tunnel
Presence of entrance ramp will lead to air confluence in the tunnel,so understanding the flow characteris-tics and loss characteristics of air in the confluence segment is a prerequisite for ventilation design of a bifurcate tun-nel.For a bifurcate tunnel with 5°～15°included angle,the CFD method and scale model are used in the experimen-tal study on how the confluence ratio q and included angle θ will impact the air flow and local loss in the confluence segment.As the results indicate:As q increases,the local loss coefficient ξ21 of the main line quickly decreases,while the local loss coefficient ξ31 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 ratio φ between them,ξ21 is mainly affected by the flow line bending,and ξ31 is mainly affected by the jet flow pressurization;if Q<φ,the main control-ling factors of ξ21 and ξ31 are interchanged.If q is small,ξ21 and ξ31 will essentially remain unchanged even when the confluence included angle θ changes;if q is big,then as θ increases,ξ21 essentially remains unchanged,while ξ31 de-creases.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.
Bifurcate tunnelConfluence segmentCFDScale model testLocal lossPrediction model
NETL
NSTL
万方数据
