Superheated steam similarity simulation on longitudinal distribution of maximum smoke temperature rise in tunnel fires

Physical simulation of smoke migration and temperature evolution is an important measure for studying tunnel fires. In this work, based on the similarity theory of fluid dynamics, the motion of superheated steam in the air is used to simulate the migration and heat transfer process of high-temperature smoke generated by tunnel fires. The similarity criteria and similarity scales between the motion of superheated steam and fire smoke are derived by the similarity transformation method. The migration pattern and temperature evolution of superheated steam under natural ventilation are investigated by using a self-built superheated steam experimental system. Then, fire tests are conducted on a combustion wind tunnel to verify the feasibility of this method. The results show that the similarity between fire smoke and superheated steam motions is demonstrated by considering geometric con-ditions, kinematic conditions and dynamic conditions. The maximum steam temperature rise increases as a power function of the buoyant flux and depends on the 5/3 power of the tunnel height. Moreover, the maximum ceiling steam temperature rise attenuates exponentially with the increasing distance from the steam source. Finally, the calculation model for predicting the longitudinal distribution pattern of the maximum smoke tem-perature rise beneath the tunnel ceiling is developed, which agrees well with the experimental results.