Law and prediction model of smoke backflow distances under fire of railway tunnel

Taking shiziyang tunnel as background, the numerical simulation was carried on different fire source power, ventilation wind velocity and different slope tunnel model. The change law of backflow distances of smoke of the tunnel was analyzed, and the data of imitation was fitted. The result indicates that the relations between backflow distances of smoke and natural logarithm of different to ventilation wind velocity, different fire source power are changing in line with straight line, increasing or decreasing. The impact from slope on backflow distances of smoke has something to do with ventilation wind velocity, on which there is a critical point, under the same situation, while ventilation wind velocity is greater than critical point, backflow distances of smoke are longer, in contrast, the smaller it is, the shorter the distance is. And then, relational expression between backflow distances of smoke and relevant parameters was obtained through dimensional analysis, backflow distances of smoke model was built by combining its change law and backflow distances of smoke formula is built through fitting data. The formulas´ rationality and advantage are analyzed.