Upward Flame Spread and Extinction over Wavy Solids

Laboratory scale experimental and modeling results of one-sided upward flame spread over wavy cellulosic paper samples are presented. The sinusoidal shaped samples with varying wavelength and amplitude are aligned perpendicular to the gravitational direction so the upward buoyant flow sees peaks and valleys along its flow path. Depending on the wave amplitude and wavelength, the flame can spread from sample peak to peak initially but may later sustain slow burning from isolated flamelets inside the sample valleys or become quenched. The degree of fuel burning completeness, pyrolysis front spread rate, and extinction limits (both local and overall) depend on the wavy parameters in a complex way as well as the ambient relative humidity. Flame spread over wavy samples thus has unique features not found in continuous flat samples nor in discrete samples. Video records of the experiments supplied in the paper present both the front and the side views of these interesting transient flame developments. A simplified two-dimensional numerical model was formulated and solved to show selected salient features of the complex fluid dynamics over wavy structure and the heat transfer and burning characteristics of the wavy samples.

本文呈现了单面向上火焰在波纹状纤维素纸试样上蔓延的实验室规模实验与建模结果。实验采用波长与振幅可变的正弦形试样，将其垂直于重力方向布置，使得向上的浮升流在流动路径中依次经过波峰与波谷。根据波纹振幅与波长的不同，火焰最初可在试样波峰间蔓延，但后续可能依托试样波谷内的孤立小火舌维持缓慢燃烧，亦或发生熄火。燃料燃烧完全度、热解前沿蔓延速率以及熄火极限（包括局部与整体）不仅受环境相对湿度影响，还与波纹参数存在复杂的依赖关系。因此，波纹试样上的火焰蔓延具备连续平面试样与离散试样均不具备的独特特性。本文附带的实验视频记录展示了这类有趣的瞬态火焰演化过程的正面与侧面视角。本文构建并求解了简化二维数值模型，用以阐释波纹结构上复杂流体动力学的若干显著特征，以及波纹试样的传热与燃烧特性。