CFD Investigation of Balcony Spill Plumes in Atria

摘要

Smoke management in buildings during fire events often uses mechanical ventilation systems to maintain smoke layer elevation above a safe evacuation path. Design of these systems requires accurate correlations for the smoke production rate of the buoyant fire plume.One design issue is the smoke production rate of fire plumes which spill out from a fire compartment,under a balcony and up through an atrium or other large volume.Current engineering correlations for these balcony spill plumes are based on a combination of one-tenth scale test data and theoretical analysis.Questions have arisen over the suitability of these correlations for real-scale designs. A combined program of full-scale experimentation and CFD modeling is being conducted to analyze the accuracy of these correlations. rnA full-scale experimental facility was constructed with a 5 m by 5 m by 15 m fire compartment connected to a four-story atrium.Propane fires in the compartment produce balcony spill plumes which form steady-state smoke layers in the atrium. Experimental variables include fire size, compartment opening width,balcony depth and compartment fascia depth.A variable exhaust system was used to achieve various smoke layer heights for each of 100 compartment configurations. Temperature,smoke obscuration and gas concentrations were measured in the compartment, atrium and exhaust system. rnThe experimental data was used to determine the atrium smoke layer elevation and balcony spill plume smoke production rate for each configuration and fire size.Comparison of this data with zone model results and design correlations for atrium smoke management systems will be performed to evaluate their accuracy. rnA CFD model of the experimental facility was implemented using the Fire Dynamics Simulator software(Version 3).Large-eddy simulations of the flow were performed with a constant radiative fraction and an infinitely fast mixture fraction combustion model.A grid sensitivity analysis was performed to optimize the grid design.The CFD model will be validated using the experimental data. The validated model will then be used to extend the experimental results to atrium heights greater than four stories.This model will also be used to compare balcony plume entrainment rates with values available in the literature for buoyant line plumes.