外立面作用下水平湍流浮力射流火焰的附壁研究

Study on fire attachment of horizontal turbulent buoyant jet on a facade wall

用防火板模拟建筑外立面,设计了可控流速和开口尺寸的气体燃烧器产生水平湍流浮力射流火焰,系统研究了外立面抑制火焰卷吸所导致的水平湍流浮力射流火焰附壁规律。将火焰流场演变分为两个阶段:(1)出口到流场水平动量衰减为零(等价点)的阶段;(2)火焰附壁或不附壁的阶段。其中,火焰附壁与否很大程度上取决于等价点到出口的水平距离LE。通过分析,我们发现雷诺应力是导致流场水平动量衰减和火焰附壁的主要原因。由此,我们基于普朗特混合长度理论推导了雷诺应力的近似表达式并结合动量控制方程,获得了LE与修正弗洛德数Fr*的线性关系,从理论上解释了出口宽高比n(n=B/H,B是开口宽度;H是开口高度)越大,火焰越容易附壁的现象,并确定了不同开口及流速条件下,火焰附壁的临界条件。

In this work, we designed a gas burner that can produce different kinds of opening size and gas velocity to study horizontal turbulent buoyant jet flame attachment due to the limited entrainment by the facade wall. By the analysis, we divided the flame spread into two stages： （1） fire spread from the opening to the equilibrium point （the position at which the momentum in the horizontal direction decays to zero） ; （2） fire spread after the equilibrium point with the existing facade （fire attachment or not）. Fire attachment mainly depends on the horizontal separation L~ between the equilibrium point and opening. It was found that the decay of horizontal momentum and fire attachment is mainly attributable to Reynolds stress. We presented an approximate derivation of Reynolds stress term using Prandtl＇s mixing length theory, and then by the momentum governing equation, a linear correlation between LE was derived and a modified Fr＊ was acquired. From that, it was interpreted that fire attachment will occur more easily when the ratio of the opening n （n=B/H , B is the opening width; is the opening height） becomes larger. The critical condition of fire attachment can be identified by the analysis.