Research On Key Parameters Of Operating Ventil Ation In Curved Road Tunnels

With the development of the business of road tunnel, so many complicated road tunnels have been built, which make a higher request for the tunnel ventilation theory and system. Based on the two cueved tunnels-Ganhaizi tunnel and Tiezhaizi No 1 tunnel under construction, Computational Fluid Dynamic(CFD),experiment and Field measurement were carried out to study the tunnel ventilation theory and the key parameters of ventilation system systemically and carefully. The main results can be found below.The transient wall shear stress(WSS) is different from the corresponding steady one under the condition of unsteady flow in tunnels and pipeline. A pipeline is the research objective in this thesis and the ramp-up and ramp-down cases was run in this experiment. The results show that there are four stages for the change of transient WSS in ramp-up cases. It can be found the transient WSS increases rapidly and overshoots the steady value in stage 1, the transient WSS increases slowly and undershoot the steady value in stage 2, the transient WSS increases rapidly and overshoots the steady value again in stage 3 and in stage 4 the transient WSS is almost the same to the steady one. It also can be described three stages for the change of transient WSS in ramp-down cases. The transient WSS decreases significantly and is lower than the steady one in stage 1 and 2, and the transient WSS increases slowly and overshoot the steady one. The behavior of the transient WSS is caused by the flow inertia and turbulence delay, and the extent would change with the change of the acceleration or deceleration and the initial flow state.A three numerical method was carried out to analyze the ventilation resistance in curved tunnels. The results show that the influence of the air speed and the cross section shape on the resistant coefficient can be ignored. When the curved radius is less than 2000m, the coefficient would increase significantly with the decrease of the radius. When the radius is more than 2000m, the difference of the coefficient between the curved tunnel and the straight tunnel is small. A method was proposed in this thesis.A three dimensional unsteady numerical analysis using the moving mesh was used to study the traffic force in curved tunnels. The results show that the difference traffic force is too small when running on different lines. However, the difference of the traffic force due to in different curved tunnel is great. The traffic force increases with the decrease of the radius of the curved tunnel. A higher traffic speed would improve the traffic force significantly, but make the adverse impact on the effective drag coefficient of traffics. A longer traffic space would improve the effective drag coefficient of traffics.A three dimensional numerical analysis and field measurement were used to study the optimal location of jet fans in the two curved tunnel. It also can be found the pressure-rising coefficient would improve when moving the jet fans 0.5m from the centre line towards the convex wall; when moving the jet fans towards the concave wall, the pressure-rising coefficient would decrease significantly. The biggest pressure-rising coefficient is obtained when the fans are arranged according to the distance of 2.4m between the fans, the fans offset of 0.5m from the centre line towards the convex wall. The distance required for pressure to be fully recovered is approximately 90-120m in this study. The cross-sectional static pressure is biggest. Accordingly, the longitudinal distance of jet fans should be more than this value in curved tunnels.