| Περίληψη: |
Borehole gas extraction is a key measure for preventing and controlling gas hazards in underground coal mines. During negative-pressure-driven multi-borehole extraction, abrupt changes in flow direction and local adverse pressure gradients can induce flow separation within the boreholes and manifold, thereby increasing flow resistance and reducing extraction efficiency. However, current research has not yet clearly elucidated the formation mechanism of flow-separation zones during the multi-borehole converging-flow process. Therefore, based on actual underground borehole-layout parameters, this study established a three-dimensional numerical model of multi-borehole gas-extraction convergence and used Fluent to simulate the gas-flow characteristics under extraction negative pressures ranging from 10 to 30 kPa. The results show that, during multi-borehole gas extraction, the gas-flow direction changes at the convergence locations, where low-velocity separation zones form under the combined effects of boundary-layer separation and adverse pressure gradients. These separation zones exhibit strong spatial correspondence with low-pressure regions. As the extraction negative pressure increases from 10 to 30 kPa, the maximum gas velocity rises from 1.4208 to 1.9070 m/s, indicating enhanced axial gas-transport capacity. However, higher extraction negative pressure also intensifies the velocity gradient, pressure gradient, and turbulent effects. With increasing negative pressure, the separation-zone area ratio first increases and then decreases, reaching a peak of 0.1985 at 20 kPa, while its overall variation remains limited. Thus, negative pressure primarily regulates the local flow intensity within the separation zones rather than significantly altering their structure. These findings provide a theoretical basis for optimizing negative-pressure regulation and improving the transport efficiency of gas extraction. [ABSTRACT FROM AUTHOR] |