*Technical Note* **Investigation of the Temperature Beneath Curved Tunnel Ceilings Induced by Fires with Natural Ventilation**

**Haowen Tao \*, Zhisheng Xu and Dongmei Zhou**

School of Civil Engineering, Central South University (CSU), Changsha 410075, China; zhshxu@csu.edu.cn (Z.X.); 204811140@csu.edu.cn (D.Z.)

**\*** Correspondence: hw.tao@csu.edu.cn; Tel.: +86-731-8265-5177

**Abstract:** The distribution characteristics of the temperature below ceilings in curved tunnel fires have not been quantitatively studied. A small-scale tunnel was constructed in this work to study the maximum temperature and longitudinal attenuation of the temperature below ceilings induced by fires in a curved tunnel with natural ventilation. Different tunnel turning radiuses and fire heat release rates were taken into account. The results show that the distribution characteristics of temperature below the tunnel ceiling is hardly affected by the tunnel turning radius in a scenario where the flame plume impinges on the ceiling (strong-plume-driven). The fire-induced maximum temperature and longitudinal attenuation of temperature in curved tunnels are comparable to those of straight tunnels. Improved correlations are proposed for the condition of a strong-plume-driven ceiling jet, and the measured value of the temperature of the experiment collapsed well. This work may enhance the understanding of temperature distributions in curved tunnel fires.

**Keywords:** curved tunnel fire; naturally ventilated tunnel; maximum temperature; longitudinal temperature attenuation
