Influence of tunnel bifurcation form on the local ventilation resistance characteristics of dividing flow
Aims:With the improvement of urban construction level and intensity,there are more and more bifurcated tunnels with ramps.In response to the difficulty of ventilation design in bifurcated tunnels,it is urgent to explore the influence of tunnel bifurcation form on the local ventilation resistance characteristics of dividing flow.Methods:By building a 1/13 scale bifurcated tunnel ventilation test platform that synchronously met the similarity of resistance and pressure and a three-dimensional CFD model of bifurcated tunnel,the flow characteristics and local loss coefficient of different bifurcated forms of bifurcated tunnels were studied.And the influence of the tunnel bifurcated forms such as the diversion structure and the deceleration lane on the local loss coefficient was further analyzed.Results:The results showed that the local loss coefficient of the main line and ramp decreased first and then increased with the increase of the diversion ratio,and reached the minimum when the diversion ratio was 0.4.Compared with directional bifurcated tunnels,there was little difference in the local loss coefficient of the main line,but there was an obvious difference in the local loss coefficient of the ramp.When the diversion ratio was small,the local loss of the ramp of the parallel bifurcated tunnel was greater.And when the diversion ratio was large,it was the opposite.The addition of the deceleration lane would reduce the local loss coefficient of the ramp when the diversion ratio was small,but would increase the local loss coefficient of the main line when the diversion ratio was large.Conclusions:The research results can provide reference for the ventilation design of bifurcated tunnels.
local losstunnel engineeringbifurcationcomputational fluid dynamics simulationsscale testparallel ramp
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