Transient heat transfer analysis of airflow in a thermal water-bearing tunnel considering airflow turbulence and surrounding rock seepage effects

In deep tunnels traversing fractured water-rich strata, surface water descend, heats up at depth, and then rises into the tunnel, resulting in a ‘thermal water-bearing’ tunnel. This paper investigates the transient temperature evolution of such tunnels through laboratory-scale model experiment and numerical simulation, considering the convective heat transfer of thermal water in the surrounding rock. The experimental model was designed using similarity criteria derived from the equation analysis method. The 3D numerical model simulates the interaction between thermal water-saturated surrounding rock and tunnel airflow. The thermal field of the surrounding rock accounts for the coupling effects of the flow field, which follows Darcy's law. The tunnel airflow is governed by the RANS (Reynolds-Averaged Navier-Stokes) equations and the k−ω turbulence model, combined with the LRNM (Low-Reynolds Number Modeling) method for near-wall treatment. This approach is coupled with the energy balance equation to calculate the airflow temperature. The numerical model is validated using monitoring data from experimental measurements of grouted tunnel wall and airflow temperatures. Finally, parameter studies are conducted for both ungrouted and grouted tunnels, demonstrating the effectiveness of grouting in controlling airflow temperature by blocking thermal water.