Open Access

ARTICLE

Study on Flame Shape and Induced Wind Velocity in Inclined Tunnel Fires with One Portal Sealed

Shengzhong Zhao¹, Daiyan Chen¹, Han Zhang^1,2,*, Junhao Yu¹, Lin Xu¹, Zhaoyi Zhuang¹, Fei Wang^1,*
1 School of Thermal Engineering, Shandong Jianzhu University, Jinan, 250101, China
2 School of Architectural Engineering, Zaozhuang Vocational College of Science and Technology, Zaozhuang, 277599, China
* Corresponding Author: Han Zhang. Email: ; Fei Wang. Email:
(This article belongs to the Special Issue: Heat Transfer in Built Environments)

Frontiers in Heat and Mass Transfer https://doi.org/10.32604/fhmt.2025.071910

Received 15 August 2025; Accepted 04 November 2025; Published online 02 December 2025

Abstract

A sealed portal could significantly alter the flame shape and smoke flow characteristics in inclined tunnel fires. In inclined tunnels, two typical sealing conditions could be defined, namely the upper portal sealed and the lower portal sealed. In this study, the effects of tunnel slope on flame shape, flame length, along with smoke mass flow rate and induced velocity at the tunnel portal, are numerically investigated. The results show that, in all scenarios, flames initially rise vertically but tilt toward the sealed portal during the quasi-steady stage, with the largest tilt angle observed in tunnels sealed at the lower portal. The slope significantly affects the flame tilt angle. The flame tilt angle in tunnels with the lower portal sealed varies irregularly with the slope, while it decreases as the slope increases in tunnels with the upper portal sealed. Subsequently, the smoke mass flow rate and induced velocity at the tunnel portal are analyzed in detail. Drawing on the obtained data, the flame length prediction models for impinging flames and non-impinging flames under different sealing conditions are developed, along with dimensionless models for smoke mass flow rate and induced wind velocity. These findings provide a theoretical foundation for the formulation of fire rescue strategies and emergency evacuation plans in inclined tunnels with one portal sealed.

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Keywords

Inclined tunnel fire; flame shape; mass flow rate; induced air velocity

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