Experimental study of the influence of natural ventilation by shaft on the maximum ceiling temperature of buoyancy plume in tunnel fires

摘要

A series of model scale experiments were conducted to investigate the influence of natural ventilation by shaft on the maximum ceiling gas temperature. The shaft height and longitudinal fire source location from the shaft were changed to account for different natural ventilation strength. Results showed that the supplementary air flow induced by the stack effect due to the natural ventilation caused flame inclining to the downstream side of tunnel. And the inclination of the flame increased with the increasing of shaft height and the decreasing of distance from the shaft. Besides, as the air supplement flow can supply more oxygen for combustion, the fire mass loss rate increased with the induced air flow velocity. The higher shaft height (stronger stack effect), the smaller distance to the shaft, the larger mass loss rate was. Moreover, the inclination of flame and the increment of mass loss rate led to the change of ceiling gas temperature in tunnel. In consideration of the phenomenon of plug-holing and boundary layer separation for different conditions, an equivalent smoke exhaust velocity was defined to quantify the influence of smoke exhaust on the ceiling gas temperature. On this basis, the predictive correlations of the maximum ceiling gas temperature were put forward and further validated by comparing with the experimental data.