Study on smoke temperature profile in bifurcated tunnel fires with various bifurcation angles under natural ventilation

Abstract

A 1:10 small-scale bifurcated tunnel including main tunnel and branch tunnel was built, and the bifurcation angle was set to 60°. 21 tests with 7 possible fire locations were carried out in the small-scale tunnel under natural ventilation. Furthermore, 32 numerical simulation cases with 8 bifurcation angles were simulated by CFD. The results indicated that: 1) the maximum ceiling temperature in the bifurcated tunnel was independent of the fire location and bifurcation angle. Only when the fire was in the bifurcation area, the maximum smoke temperature rise was slightly higher than that located in other areas of the main tunnel. 2) the longitudinal temperature attenuation of the upstream and downstream from fire source in the main tunnel was independent of the bifurcation angle. 3) If the bifurcation angle varied between 20° and 160°, when the bifurcation angle ≤ 90°, the variation of bifurcation angle had a significant effect on the longitudinal temperature distribution in the branch tunnel. However, when the bifurcation angle > 90°, the longitudinal temperature distribution in the branch tunnel almost did not vary with the change of the bifurcation angle. A prediction model for the longitudinal temperature in the branch tunnel was established by considered the effect of bifurcation angle.