Effect of vertical density stratification on the buoyancy-induced flow at a doorway opening

Abstract

This study deals with the process of smoke filling in a compartment and the exhaust of smoke through a doorway located in a side of the enclosure. This configuration is a typical scenario of smoke propagation during a fire event in a compartment. This study focuses on the vertical temperature stratification in the smoke layer and its consequences on buoyancy flow induced at the doorway. From two theoretical approaches, considering or not considering the vertical temperature stratification in the smoke layer, this study highlights how vertical temperature stratification may modify the doorway flow. The first approach is a well-mixed description considering constant temperature and thus no thermal stratification in the smoke layer. The second one describes the vertical density stratification with multilayer approach. The results show that the vertical stratification is the consequence of the process of air entrainment within the plume. The consideration of temperature stratification in the smoke layer changes the prediction of the flow through the doorway. A sensitivity analysis points out how two variables (the initial buoyancy flux and the dimension of the enclosure) modify this influence. The discussion improves the understanding of the stratification in an enclosure and gives new insight into the predictions of smoke propagation for fire safety applications.