Diffusion Characteristics and Influencing Factors for Large-Hole Natural Gas Pipeline Leakage in Utility Tunnels

This study investigates the large-hole leakage in natural gas pipelines within utility tunnels. In contrast to most previous studies that focused on small-hole leaks, ANSYS Fluent software is used to systematically examine the effects of different leakage locations, pipeline operating pressures, and inlet air velocities on the diffusion characteristics of methane under large-hole leakage conditions. Results indicate that the leak location has minimal effect on the maximum methane concentration, while it significantly influences the diffusion range. Specifically, the closer the leak is to the exhaust vent, the smaller the diffusion range, resulting in a decrease in average methane concentration within the tunnel. At a fixed location, methane concentration exhibits a nonlinear distribution with peak fluctuations depending on the leak location. Pipeline pressure has little effect on the maximum methane concentration or overall diffusion area, but it significantly affects high-concentration zones. When the pipeline pressure is below 3 MPa, increasing the pressure greatly expands these high-concentration zones. Incoming wind velocity substantially affects the maximum methane concentration, though it has less impact on the overall diffusion area; however, it notably accelerates the diffusion rate. As wind speed increases, methane concentration decreases at the air entrance, shows minor fluctuations in the central region, and increases near the exhaust vent. This study provides valuable reference material for the safe operation of natural gas pipelines in utility tunnels and establishes a basis for designing hazardous gas control systems and disaster warning mechanisms.