Prediction of airflow rate and analysis of driving forces for natural ventilation in underground corridors

Natural ventilation in relatively enclosed underground spaces has aroused people’s interest due to the poor air quality and high energy consumption of mechanical ventilation. Small-scale experiments and numerical simulation are utilized to investigate the influence of thermal and wind conditions on the ventilation characteristics of underground corridors. The non-dimensional flow rate is calculated, which can be used to evaluate ventilation performance and predict airflow rate. The interaction of driving forces is quantitatively analyzed based on the Archimedes number and the critical non-dimensional flow rate. The results reveal that incoming wind counteracts buoyancy partly in shear ventilation, while the wind promotes buoyancy-driven ventilation in cross ventilation. The air change rate decreases under different driving force modes, from the purely buoyancy-driven to the combined-force-driven to the purely wind-driven, for shear ventilation with the wind speed of 1 ∼ 3 m/s. For cross ventilation, the descending order is the combined-force-driven, the purely wind-driven, and the purely buoyancy-driven. When driven by wind, non-dimensional flow rate remains constant with a value of 0.025 for shear ventilation and 0.68 for cross ventilation in the corridors with the opening ratio less than 12 %. When driven by combined force, Q* is not a constant value but rather varies with wind speed. Especially when the wind speed exceeds 1.5 m/s, the buoyancy can be ignored in cross ventilation. The findings of this study can serve as a basis for ventilation design and the prediction of ventilation rate in underground corridors.