Numerical studies on density jump in a long corridor fire

Many long corridors are built in underground public transport interchanges in downtown of big cities. Smoke control systems have to be installed in these long corridors. A density jump might occur when the smoke flowing under the ceiling hits a smoke barrier. High mass flow rates are then resulted due to additional air entrainment. In this paper, characteristic of density jump at smoke barrier in long corridors, which are induced by horizontal smoke movement underneath the ceiling, will be studied by Computational Fluid Dynamics (CFD). Three fire scenarios LF1, LF2 and LF3 with 3 MW, 5 MW and 10 MW fires are selected in a long corridor with two smoke barriers to study the characteristic of density jump. Predicted results by CFD are discussed and compared with the analytical expressions about density jump. As the Froude number under normal fire condition is relatively low, other scenarios HF1–HF3 with higher Froude number were carried out. All CFD results further confirm that density jump occurs when smoke flowing in a long corridor strikes the smoke barrier. Air entrainment would be increased and this phenomenon should be included in fire hazard assessment of long corridor.

► Smoke density jump in a long corridor was studied by computational fluid dynamics.
► Results confirm that density jump occurs when smoke strikes the smoke barrier.
► Air entrainment increases and this should be included in fire hazard assessment.
► There are challenges on grid sizes and free boundary conditions in using CFD.
► Extended computing domain was proposed to improve the 2-dimensional simulations.