液体燃料表面脉动火焰蔓延机理数值研究

Numerical simulation of pulsating flame spread over liquid fuel surface

关键词:  火焰蔓延  热毛细效应  浮力效应  闪点温度  数值模拟

Key words:  Flame spread  Thermocapillary effect  Buoyancy effect  Flash point  Numerical simulation

摘要:

针对液体表面火焰蔓延提出了一种基于气液两相耦合的三维数值模拟模型，并针对低于闪点温度的液体燃料表面脉动火焰蔓延机理进行了数值研究。本文提出的数值方法成功捕捉到脉动火焰蔓延现象，预测的火焰蔓延脉动频率及传播速率与实验值吻合良好。本研究表明：火焰前锋后方存在显著横向对流流动，促进从慢速蔓延向快速蔓延的转变；气液两相中的回流区是成对出现的，即使在快速蔓延阶段火焰前锋下方仍然存在较小的气相回流区；火焰前锋前方的表面对流流动强度不是始终单调衰减的，在慢速蔓延阶段存在“双峰流动”特征；火焰前锋前方的液面温度是单调下降的，不存在温度“波谷”，温度“波谷”的发现是存在薄热边界层和实验手段无法分辨薄边界层中的温度梯度导致的。

Abstract:

A three-dimensional numerical model based on the coupling between gas and liquid phases was proposed for flame spread over liquid fuel. The proposed model was also used to investigate the mechanism of pulsating flame spread over liquid fuel below the flash point temperature. The pulsating flame spread was successfully captured and both the predicted pulsating frequency and spread rate are in good agreement with experimental data. The following findings were revealed in this study： significant transverse motions exist behind the flame front， facilitating the transition from the crawling stage to the jump stage； the recirculation cells are paired in both the liquid and gas phases and a small recirculation cell was also found under the flame front in the jump stage； the convective surface flow intensity in front of the flame front does not monotonically attenuate and a two-peak flow structure was found in crawling stage； fuel surface temperature monotonically decreases in front of flame front and the temperature valley was not predicted， and the existence of the temperature valley might be due to the fact that the liquid thermal boundary layer is too thin and the inability to resolve the temperature gradient by the current experimental technique.