Equations for vertical distribution of temperature and velocity in a horizontal tunnel with a vertically longer rectangular shape under natural ventilation

Abstract

This study conducted a series of fire tests in a small-scale tunnel with a vertically elongated rectangular cross-section measuring 0.4 m in width and 0.5 m in height. The temperature and flow velocity within a quasi-steady, fire-driven smoke layer running along the center of the ceiling were measured up to a distance of 35 times the tunnel height from the fire source. Based on the observed velocity and temperature rise distributions within the smoke layer perpendicular to the tunnel ceiling, correlations were proposed to predict maximum temperature rise, maximum velocity, and smoke layer thickness at various distances from the fire source. The vertical distributions of velocity and temperature rise in the smoke layer are characterized by peak values and layer thickness across different distances from the fire source, with the layer thickness exhibiting a gradual exponential increase as the smoke moves further from the source. The vertical distribution shapes of velocity and temperature rise remain consistent regardless of the distance from the fire source, even in areas far from the source where the smoke layer thickness cannot be considered constant. Simple empirical equations were developed to represent the distributions of velocity and temperature rise within the smoke layer, specifically in a direction perpendicular to the tunnel ceiling. While acknowledging the challenges of scaling experimental results to full-scale tunnels, the applicability of the temperature distribution correlation to other tunnel models with different dimensions with different vertically elongated rectangular cross-section aspect ratios was confirmed through comparison with both small-scale and full-scale experimental data.