Experimental study of the effects of a thermal plume entrainment mode on the flow structure: Application to fire

The aim of this work is to experimentally simulate two heat sources of fire, one placed at ground level, the other at a height above the ground, in order to determine the effect of source air entrainment on the resulting flow structure. The development of a free thermal plume was examined by generating a plume produced from an electrically heated disk at a constant temperature. We first studied the behavior of a thermal plume induced by a disk embedded in a horizontal plate placed at the level of the ground. This configuration ensured a regular lateral entrainment of air to the plume. The analysis of the average fields as well as the axial evolution of velocity and temperature showed an important widening of the profiles that encouraged a faster spread of the plume. We then determined the structure of the thermal plume generated by the same source placed at a height above the ground, ensuring simultaneous vertical and lateral entrainment of air into the resulting plume.Results obtained reveal a vertical elongation of the average profiles that limits the lateral extension of the plume flow. Comparison of the plumes produced from the two configurations showed that the flow structure is strongly influenced by the nature of the source of air entrainment. An additional vertical contribution of air entrainment caused the location of the maximum axial velocity above the source to be raised, with the flow rate and the thermal flux absorbed by the air experiencing a relative increase of the order of 14% and 34%, respectively.