Numerical investigation of air flow field evolution and leakage patterns in large-scale goaf areas

Understanding the evolution of air flow fields and leakage patterns in large-scale goaf areas is crucial for preventing spontaneous combustion of residual coal and ensuring mining safety. Current understanding of air leakage evolution in interconnected goaf areas remains insufficient for effective hazard control. This study aims to investigate the characteristics of air flow fields and establish prevention strategies for large-scale goaf areas. Fast Lagrangian analysis of continua in 3 dimensions (FLAC3D) numerical simulations were employed to analyze the fracturing and stress distribution of overlying strata, establishing a three-dimensional porosity model. The spatiotemporal evolution of air leakage flow fields was then simulated using FLUENT computational fluid dynamics software. Results indicated that stress distribution in the large goaf area was concentrated in the central region, exhibiting a “saddle-shaped” fracture pattern with a maximum stress of 35.4 MPa. The void ratio distribution displayed an elliptical pattern, with the lowest value of 0.097 in the compacted central goaf area, increasing to 0.34 at the boundary. Measurements of the air leakage field revealed inlet and outlet flow rates of 242.63 and 232.62 m3/min, respectively. The coupled hazardous zones were primarily concentrated around air leakage sources and their adjacent goaf areas, extending 336.42 m horizontally and 224.21 m vertically, encompassing a total area of 17 433.04 m2. Based on these findings, a three-zone prevention strategy was developed, providing new insights into spontaneous combustion control for large-scale goaf areas.