BI-STABLE FIRE FLOWS: ENGINEERED DESIGN AND ASSESSMENT WITH THE AID OF COMPUTATIONAL FLUID DYNAMICS

摘要

The aim of this study is to illustrate the capability and usefulness of Computational Fluid Dynamics in order to tailor engineered solutions where a complex flow pattern may be expected in Fire Safety Design. Among the possibilities of complex flow arising in a fire environment, the one represented by a so called "Bi-Stable Flow" is investigated. Particular attention is posed on the fields of force that generate such a flow, then the equations governing the motion and the models available to represent it are examined and discussed. Topics such as gravitational activity and turbulence action in the flow field then follow, leading to some choice or elimination of what computational fluid dynamics tools have to offer, at least at present time. Three types of bi-stable flow are then studied using computational fluid dynamics (CFD), with practical examples, representing potentially dangerous phenomena that could evolve during the dynamics of a fire. One type is a bi-stable flow induced by the Buoyancy Field, one type is a bi-stable flow induced by the Air entrainment Field, one type is a bi-stable flow induced by the Pressure wave Field. Examples include the "mushrooming effect" (hydrostatic atmospheric gradient combining with buoyancy thrust of a fire plume), the "trenching effect" (confinement of the air flow entrainment in a fire current), the "coughing effect" (pressure development through ceiling openings intended to vent a fire). So, the use of CFD tools helps sign a mark in view of an Optimal Design evolution in Fire Engineering skills.