Large eddy simulation of thermal plume behavior in horizontally partitioned dual enclosure

Abstract

The fire induced flow characteristics through horizontal passage between two enclosures are investigated under natural and forced ventilation conditions. The physical model consists of upper and lower enclosures with door openings through which forced air enters the dual enclosure. Transient three-dimensional simulations are performed by Large Eddy Simulations (LES) using Fire Dynamic Simulator (FDS) code. The assisting and opposing behavior of forced air stream in enclosure fire are investigated by varying fire source locations. The flow characteristics through horizontal and vertical passages are found to be oscillatory and bidirectional. In natural ventilation conditions, heat source location and thermal buoyancy force change the flow characteristics in dual enclosures. Under forced ventilation conditions, ambient air stream significantly affects fire transport phenomena by aiding or opposing the thermal buoyancy force. At higher velocity inlets, ambient air diffuses heat from fire and reduces temperature gradients inside dual enclosure. The forced air stream dominates buoyancy force and drives hot gases to propagate in reverse direction. The critical ventilation velocity that prevents the spreading of thermal plume from doorway opening is identified. The model employed has been validated with the existing experimental results available in literature.