Experimental and numerical studies on the buoyancy-driven smoke movement in inclined short tunnel fires under natural ventilation

Abstract

The paper focuses on the smoke flow movement in inclined short tunnel fires. Small-scale tunnel fire tests and numerical simulations are implemented by considering the tunnel inclination, heat release rate (HRR), tunnel height and upward distance from fire source to upward opening. The comprehensive impacts of tunnel inclination, HRR and upward length on the smoke back-layering flow and the influencing mechanism are emphasized. It is found that as the upward distance and tunnel inclination increase, the back-layering length decreases, and at the meantime, the decrease rate is affected by the HRR. Specifically, under a certain tunnel inclination, as the upward distance increases, the back-layering length decreases faster as HRR becomes greater. Besides, as the tunnel inclination increases, the decrease rate of the back-layering length against the upward distance also becomes greater under a larger HRR. Meanwhile, it is found that when the fire is located near the upward opening, back-layering length becomes longer as HRR increases, however, the increase trend levels off as the tunnel becomes steeper. This leads to the results that the back-layering length may increase, level off and decrease with HRRs. Based on these findings, a prediction correlation for the back-layering length is established considering multi-factors (tunnel inclination, upward length, HRR and tunnel height). Furthermore, the verification is implemented by comparing the calculated back-layering length and test and numerical simulation results, showing an acceptable prediction.