Effect of blockage-induced near wake flow on fire properties in a longitudinally ventilated tunnel

摘要

Effect of blockage-induced near wake flow on fire properties in a longitudinally ventilated tunnel was studied. Numerical simulation was conducted in a tunnel under longitudinal ventilation velocity in the range of 1.0-4.0 m/s. Vehicular blockage was positioned in the upstream of the fire source, with four kinds of blockage ratios (0.24, 0.40, 0.56, 0.72). Temperature contours were used to describe the fire plume region in the tunnel with longitudinal ventilation. It is found that the fire flame goes five stages and transits leaning direction from downstream to upstream of the fire with increasing blockage ratio and ventilation velocity, behaving differently from that in just a longitudinally ventilated tunnel without vehicular blockage. With the increasing ventilation velocity and blockage ratio, the vertical temperature 5 m downstream of the fire decreases and temperature difference in the vertical direction gradually weakens. However, in the upstream 2.5 m from the fire, after the temperature tending to be uniform in the vertical direction, it is high in the middle height and low at the top and bottom. At ventilation velocity larger than 2.5 m/s, the temperature beneath the tunnel ceiling decreases with the increasing blockage ratio downstream of the fire, while there is increase in the upstream. A new expression with the factor blockage ratio included is proposed to predict the maximum temperature beneath the tunnel ceiling, showing good agreement with simulation data.