Study on large eddy simulation of lateral inlet/outlet under bending outflow

Due to the influence of topography and geology in actual engineering projects, water tunnels often have horizontal bends. These bends result in non-uniform inflow conditions, complicating the turbulence characteristics at the inlet and outlet compared to straight- line tunnels. This study employs Large Eddy Simulation to analyze a real engineering problem. The calculated results are compared with experimental data, revealing close agreement in flow velocity and probability density distribution. The findings show that under outflow conditions, the flow-split ratios for each channel are 0.64, 0.81, 1.26, and 1.29, indicating a highly non-uniform horizontal velocity distribution. In the vertical direction, the main flow occurred primarily in the lower middle section, and the vertical Reynolds shear stress in the diffusion segment exhibits a distinctive pattern with alternating positive and negative peaks. This phenomenon is primarily attributed to flow separation in the upper middle area and wall shearing near the bottom. The recirculation region′s height in the two middle channels was found to be greater than that in the side channels, indicating that trash racks in the central channels are more susceptible to reverse flow velocities. Additionally, flow separation near the trash rack gives rise to a three-axis vortex, while two energy-concentrated pulsations occur in the upper middle section and near the bottom. Moreover, under bending flow conditions, turbulence intensities in different channels increase by 11%, 25%, 29%, and 3%, respectively, compared to those in uniform flow situations. Consequently, the unfavorable flow regime and high turbulence intensity associated with bending flow pose a threat to the trash rack. © 2024 International Research and Training Center on Erosion and Sedimentation and China Water and Power Press. All rights reserved.