The present work analyses theoretically and numerically fire plumes evolving in a two-layer stratified environment. The ambient fluid consists of a lower cold (heavy) layer and an upper warm (light) layer with a sharp interface. The fire plume is controlled by the fire heat release rate Q. Depending on the density interface location, the temperatures of the layers and on the fire source conditions, the fire plume can rise indefinitely or can be captured by the density stratification. To determine a criterion between these two situations, a theoretical model is proposed. With this model, it is found that the trapping/escaping criterion of the fire plume is determined in terms of a stratification parameter \(\varLambda > 0.88\). This stratification parameter \(\varLambda\) is a function of the fire heat release, the density interface location and the ambient stratification. The model also allows the plume height to be determined analytically. The comparison with the numerical data shows an excellent agreement. Finally, for practical purposes, we propose a simplified correlation to estimate the height of the trapped plume as a function of the interface height, the temperatures of the layers and the fire heat release rate.

本工作从理论和数值上分析了在两层分层环境中演化出的火羽。环境流体由较低的冷（重）层和较高的热（轻）层组成，并具有锋利的界面。火羽由火的放热率Q控制。根据密度界面的位置，层的温度以及火源的条件，火羽可能会无限期上升或被密度分层捕获。为了确定这两种情况之间的标准，提出了一种理论模型。通过该模型，发现火烟的捕获/逃逸标准是根据分层参数\（\ varLambda> 0.88 \）来确定的。此分层参数\（\ varLambda \）是火的热释放，密度界面位置和环境分层的函数。该模型还允许通过分析确定羽流高度。与数值数据的比较显示出极好的一致性。最后，出于实际目的，我们提出了一种简化的相关性，以估计捕集的羽流的高度与界面高度，层的温度和火的放热率之间的函数关系。