Study on distributions of airflow velocity and convective heat transfer coefficient characterizing duct ventilation in a construction tunnel

This paper explores the longitudinal distributions of airflow velocity and convective heat transfer coefficient (CHTC) characterizing duct ventilation in a construction tunnel of geothermal area. The effects of duct ventilation parameters (i)inlet airflow velocity u(in), (ii) duct diameter d*, and (iii) distance of nozzle from working face L-0*, are examined respectively. This work is carried out by numerical simulations with steady RANS (Reynolds-Averaged Navier-Stokes) equations for applications in tunnel airflow. Turbulence model SST k - omega (Shear-Stress Transport k-omega) combined with LRNM (Low-Reynolds Number Modelling) method are used concerning the Low-Reynolds Number effects in boundary layer region. The numerical models are validated by previous literatures, and checked for Reynolds number independence of flow field. The results show that, in a turbulent airflow forced by duct ventilation, the longitudinal distributions of surface-averaged CHTC (SCHTC) and mean airflow velocity (MAV) follow a piecewise-Gaussian-distribution law respectively. And those distributions largely depend on u(in) and d*, but not affected by L-0*, except for some raised in a region close to working face. These results can assist an optimal duct-ventilation design for cost-effective tunnel space cooling in a geothermal tunnel under construction.