This paper presents a numerical investigation into the phenomenon of flame spread over thin circular ducts in normal gravity and microgravity environments. Flame spread over such geometry is of significant interest due to its relevance in various practical applications, including tubes for flow purpose in medical system, fire safety in spacecrafts, ducts as well as wiring tubes. This study comprises of a comprehensive investigation of key parameters affecting flame spread rate, including fuel radius and opposed flow speed in normal gravity and microgravity environments. A 2-D axisymmetric flame spread model accounted for char and numerical simulations were performed which revealed valuable insights into the underlying mechanisms governing flame spread over such geometry. The results computed from the numerical model is compared with the experimentally observed flame spread rate to validate the numerical model which can be used to gain a comprehensive understanding of the underlying physical phenomena. As the radius of circular duct increases the flame spread rate increases both in normal gravity and microgravity environments. The conduction heat feedback and radiation heat gain coming from hot char through gas phase at inner core region are the two major mechanisms which controls the flame spread phenomena over the circular duct fuels. The flame spread rate at different flow ranging from quiescent (0 cm/s) to 30 cm/s is also evaluated and 21 % oxygen and found a non-monotonic increasing decreasing trend of flame spread rate at different opposed flow speed in both normal gravity and microgravity environments.

翻译：本文对常重力和微重力环境下薄圆管道上火焰蔓延现象进行了数值研究。由于此类几何结构在医疗系统流体管路、航天器防火安全、管道及线缆管等实际应用中具有重要关联性，该火焰蔓延问题备受关注。本研究系统考察了影响火焰蔓延速率的关键参数，包括常重力和微重力环境下的燃料半径与反向气流速度。建立了考虑炭层形成的二维轴对称火焰蔓延模型，通过数值模拟揭示了该几何结构下火焰蔓延的基本机理。将数值模型计算结果与实验观测的火焰蔓延速率进行对比验证，为深入理解相关物理现象提供了有效工具。研究表明，在常重力和微重力环境中，圆管道半径增大会导致火焰蔓延速率提高。内芯区域高温炭层通过气相传递的导热反馈和辐射热获取，是控制圆管道燃料火焰蔓延现象的两大主要机制。本文还评估了从静止（0 cm/s）至30 cm/s不同流速及21%氧气浓度下的火焰蔓延速率，发现常重力和微重力环境中反向气流速度对火焰蔓延速率呈现非单调的增减变化趋势。