Ventilation and heat exchange characteristics in high geotemperature tunnels considering buoyancy-driven flow and groundwater flow

Abstract Recently, an increasing number of tunnels were constructed in high-geotemperature regions and threatened with heat hazards, leading to an urgent required to analyze heat exchange characteristics and manage underground environment in these tunnels. To obtain the actual airflow and temperature field of high-temperature tunnel, a full coupled three-dimensional model incorporated with buoyancy flow was established describing the dynamic heat transfer process. The influence of buoyancy flow on temperature field in the radial and longitudinal direction of tunnel has been investigated respectively. Accounting for the buoyant effect is crucial to heat conduction and convection within tunnel, and it cannot be ignored in predicting air temperature with a large temperature difference tunnel. Additionally, this study highlights the significant effect of the presence and magnitude of groundwater flow on temperature variations and heat transfer of tunnel. When the magnitude of groundwater flow is larger than 0.01 m/d, the groundwater condition will significantly influence the temperature distribution of surrounding rock and airflow. The groundwater flow increases the temperature difference of tunnel and induces a clearer buoyancy effect inside the tunnel. As the groundwater flow direction angle increases from 0° to 90°, the influence of groundwater on heat transfer of tunnel increases first and then stabilizes. The longer the length of the seepage region is, the larger the average temperature at tunnel exit is, and the slower the temperature decreases with time. Furthermore, an orthogonal test was performed to investigate the influence degree of major factors on heat exchange of tunnel through range analysis. This study supplements the existing numerical model and research, making it more accurate to predict the thermal environment of tunnel, and guides optimization of tunnel design.