Turbulent Ceiling-Jet Induced by Large-Scale Fires

Abstract

A fire which is sufficiently far from the walls of a compartment typically produces a hot rising plume which impinges on the ceiling to form a radial, outward moving ceiling-jet. A theory is developed to predict the major characteristics of this turbulent ceiling-jet flow in terms of the fire's heat release rate and distance below the ceiling. Two models of turbulent air entrainment into the ceiling-jet are considered. Comparison of theoretical results with data obtained during a program of large-scale experiments indicates that a simple entrainment model is adequate for a distance of up to several ceiling heights from the central axis of the fire. The analysis can also be applied to situations of a fire in a corner or adjacent to a plane wall.