Characterization and prediction of ceiling temperature propagation of thermal plume in confined environment of common services tunnel

Common services tunnel is one of the successful applications for increase the resilience of urban utilities and infrastructure. In its isolated environment, the massive transport energy resources bring about a relatively high risk of thermal disaster. Characteristics of ceiling gas temperature is very important for early-phase detecting and controlling of the abnormal heat release. This paper presents a numerical investigation on the propagation of ceiling gas temperature of thermal plume in a common services tunnel, especially focuses on the influence of the isolated closed-end, which causes significant difference from the traffic tunnel. Results show that for the closed-end tunnel, due to the asymmetrical air supplementation, the vertical plume inclines to the closed side and thicker thermal layer accumulates in the closed area. Ceiling temperature profile behaves differently with different energy source locations, the influence strength of the closed end can be divided into the far-field and near-field region. In the near-field region, the restricted thermal plume flows back and is directly entrained into the thermal layer, thus the nearer to the closed end, the higher of the maximum ceiling temperature, T-max. While in the far-field region, the energy source is relatively farther away from the closed end, T-max becomes constant with different energy source locations, which is also indicated in previous full-scale experiments. Besides, predictive correlations of the maximum ceiling temperature are proposed for energy source in far-field and near-field region, respectively. And the applicability of the proposed correlations is validated by comparing to the previous works.