수직벽 화재 자연대류에 의한 난류 경계층 열유동 특성 해석

Abstract

The analysis of characteristics of turbulent flow and thermal boundary layer for natural convection caused by fire along vertical wall is performed. The 4m-high vertical copper plate is heated and kept at a uniform surface temperature of <TEX>$60^{\circ}C$</TEX> and the surrounding fluid (air) is kept at <TEX>$16.5^{\circ}C$</TEX>. The flow and temperature is solved by large eddy simulation(LES) of FDS code(Ver.6), in which the viscous-sublayer flow is calculated by Werner-Wengle wall function. The whole analyzed domain is assumed as turbulent region to apply wall function even through the laminar flow is transient to the turbulent flow between <TEX>$10^9$</TEX><<TEX>$Gr_z$</TEX><<TEX>$10^{10}$</TEX> in experiments. The various grids from <TEX>$7{\times}7{\times}128$</TEX> to <TEX>$18{\times}18{\times}128$</TEX> are applied to investigate the sensitivity of wall function to <TEX>$x^+$</TEX> value in LES simulation. The mean velocity and temperature profiles in the turbulent boundary layer are compared with experimental data by Tsuji & Nagano and the results from other LES simulation in which the viscous-sublayer flow is directly solved with many grids. The relationship between heat transfer rate(<TEX>$Nu_z$</TEX>) and <TEX>$Gr_zPr$</TEX> is investigated and calculated heat transfer rates are compared with theoretical equation and experimental data.