Similar articles

Abstract: The construction of bifurcated tunnels is essential to advancing urban infrastructure systems, as they conserve land, reduce carbon emissions, and optimize traffic. However, the bifurcation structure of the parallel confluence section of such tunnels poses significant challenges in the design and operation of the tunnel ventilation system, in terms of both the internal and external environment. In this work, the flow and loss characteristics of parallel confluence sections are studied with numerical simulations and model experiments. The influences of the confluence ratio q and the confluence angle θ on the flow characteristics and loss mechanisms of the parallel confluence section are revealed theoretically. The results indicate that when q is small, the high-velocity airflow from the mainline entrains the low-speed airflow from the ramp, leading to flow separation at the upper connection between the parallel section and the gradual transition section; when q is large, the high-velocity airflow from the ramp entrains the low-speed airflow from the mainline, resulting in flow separation on the side of the confluence section adjacent to the mainline. Additionally, the mismatch between the airflow ratio Q and cross-sectional area ratio φ of the mainline tunnel and the ramp prior to confluence enhances the jet entrainment effect, increases the curvature of the streamline, expands the range of the flow separation area, and generates higher confluence loss coefficients |K₁₃| and |K₂₃| of the mainline and the ramp. For small q, K₁₃ and K₂₃ remain relatively constant with respect to θ, whereas for large q, both |K₁₃| and |K₂₃| decrease as θ increases. Finally, a semi-empirical formula is proposed to predict the loss coefficients for parallel bifurcated tunnels with confluence angles ranging from 5° to 15°. This study provides insights into the aerodynamic behaviour and loss mechanisms in bifurcated tunnels, offering guidelines for enhancing the efficiency of tunnel ventilation systems in tunnel-like underground infrastructure.

平行式汇流分岔隧道流动损失特性研究

[1]Abou-HaidarNI, DixonSL, 1992. Pressure losses in combining subsonic flows through branched ducts. Journal of Turbomachinery, 114(1):264-270.

[2]BassettMD, WinterboneDE, PearsonRJ, 2001. Calculation of steady flow pressure loss coefficients for pipe junctions. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 215(8):861-881.

[3]BlaisdellFW, MansonPW, 1963. Loss of Energy at Sharp-Edged Pipe Junctions in Water Conveyance Systems. Technical Bulletin 1283, US Department of Agriculture, USA.

[4]ChenT, ZhouD, LuZJ, et al., 2021. Study of the applicability and optimal arrangement of alternative jet fans in curved road tunnel complexes. Tunnelling and Underground Space Technology, 108:103721.

[5]ChenZE, ChenXF, KongXM, et al., 2024. Study on the flow characteristics and local loss characteristics of the confluence segment of bifurcate tunnel. Modern Tunnelling Technology, 61(3):53-60 (in Chinese).

[6]GaoZH, LiuMG, ZhaoPJ, et al., 2024. Influence of tunnel slope on the one-dimensional spread of smoke transportation and temperature distribution in tunnel fires. Tunnelling and Underground Space Technology, 146:105650.

[7]GardelAE, 1957. Les pertes de charge dans les ecoulements au travers de branchments en te. Bulletin Technique de la Suisse Romande, 83(9):123-130 (in French).

[8]HagerWH, 1984. An approximate treatment of flow in branches and bends. Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 198(1):63-69.

[9]ItōH, ImaiK, 1973. Energy losses at 90° pipe junctions. Journal of the Hydraulics Division, 99(9):1353-1368.

[10]JafariS, FarhaniehB, AfshinH, 2023. Numerical investigation of critical velocity in curved tunnels: parametric study and establishment of new model. Tunnelling and Underground Space Technology, 135:105021.

[11]KrólA, KrólM, 2021. Numerical investigation on fire accident and evacuation in a urban tunnel for different traffic conditions. Tunnelling and Underground Space Technology, 109:103751.

[12]LiL, LiYL, HuangJT, et al., 2001. Numerical simulation and experimental study on water flow in Y-type tube. Journal of Hydraulic Engineering, (3):49-53 (in Chinese).

[13]LiangCJY, NanS, ShaoXL, et al., 2021. Calculation method for air resistance coefficient of vehicles in tunnel with different traffic conditions. Journal of Building Engineering, 44:102971.

[14]LiuF, YinC, ChenJZ, et al., 2020. Numerical simulation study on the influence of intersection angle of confluence section on ventilation characteristics of freeway tunnel. Modern Tunnelling Technology, 57(S1):‍645-650 (in Chinese).

[15]MillerDS, 1971. Internal Flow: a Guide to Losses in Pipe and Duct Systems. British Hydromechanics Research Association, Cranfield, UK, p.303-360.

[16]MohamedMS, LarueJC, 1990. The decay power law in grid-generated turbulence. Journal of Fluid Mechanics, 219:195-214.

[17]OkaK, NozakiT, ItoH, 1996. Energy losses due to combination of flow at tees. JSME International Journal Series B Fluids and Thermal Engineering, 39(3):489-498.

[18]QinWJ, HuCG, GuoLP, et al., 2006. Effect of near-wall grid size on turbulent flow solutions. Transactions of Beijing Institute of Technology, 26(5):388-392 (in Chinese).

[19]ShiX, LüHX, ZhuDL, et al., 2013. Flow resistance and characteristics of PVC tee pipes. Transactions of the Chinese Society for Agricultural Machinery, 44(1):73-79 (in Chinese).

[20]ShihTH, LiouWW, ShabbirA, et al., 1995a. A new k-ϵ eddy viscosity model for high Reynolds number turbulent flows. Computers & Fluids, 24(3):227-238.

[21]ShihTH, ZhuJ, LumleyJL, 1995b. A new Reynolds stress algebraic equation model. Computer Methods in Applied Mechanics and Engineering, 125(1-4):287-302.

[22]TavoularisS, CorrsinS, 1981. Experiments in nearly homogeneous turbulent shear flow with a uniform mean temperature gradient. Part 2. The fine structure. Journal of Fluid Mechanics, 104:349-367.

[23]WangMN, DengT, YuL, 2024. Development and prospects of operation and disaster prevention ventilation technology in China’s traffic tunnels. Modern Tunnelling Technology, 61(2):152-166 (in Chinese).

[24]XuFQ, DuZG, ChenC, 2022. Distribution and development characteristics of urban road tunnels in China. Modern Tunnelling Technology, 59(6):35-41 (in Chinese).

[25]ZhangX, ZhangTT, HuangZY, et al., 2018. Local loss and flow characteristic of dividing flow in bifurcated tunnel. Journal of Zhejiang University (Engineering Science), 52(3):440-445 (in Chinese).

[26]ZhangX, ZhangTH, HouYG, et al., 2019. Local loss model of dividing flow in a bifurcate tunnel with a small angle. Journal of Zhejiang University-SCIENCE A (Applied Physics & Engineering), 20(1):21-35.

[27]ZhangX, GuoS, DangXY, et al., 2024. Experimental investigation on the influence of portal-blocking speed on fire behaviors in tunnel structure. Case Studies in Thermal Engineering, 53:103811.

[28]ZhuK, HuHP, ZhangX, et al., 2024. Influence of tunnel bifurcation form on the local ventilation resistance characteristics of dividing flow. Journal of China University of Metrology, 35(2):197-202 (in Chinese).