索雷特扩散与辐射热损失对超贫氢空气混合物中浮力火焰核演化的影响
Effects of Soret Diffusion and Radiative Heat Loss on the Evolution of Buoyant Flame Kernels in Ultra-Lean Hydrogen-Air Mixture
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中文总结 AI 辅助
本研究采用数值方法，探究索雷特扩散与辐射热损失对超贫氢空气混合物中浮力火焰核演化的影响，明确二者对火焰核生长、轨迹及破碎的作用规律。
中文摘要 AI 辅助
地面重力下的超贫氢火焰受优先扩散、热扩散、热损失与自诱导对流之间的耦合相互作用支配。本研究采用详细化学反应机理与低马赫数公式，对静止的6体积分数H₂-空气混合物中的燃烧进行数值研究，考虑了完整的计算方案，分别启用和禁用索雷特扩散与光学薄辐射热损失。采用一维球对称计算分离点火后初始火焰核的生长过程，同时采用二维平面与轴对称模拟描述火焰核后续的浮力上升、变形与破碎过程。在分析的时间区间内，球对称火焰前锋半径遵循R_f²≈Kt的规律，而非恒速膨胀。索雷特扩散提高了有效生长系数K，而辐射则降低了该系数。轴对称模拟对实验测得的前沿点轨迹的再现效果远优于平面公式。索雷特扩散产生更大、上升更快的火焰核，并维持更接近圆形的上冠，而辐射对轨迹的影响较弱，但加剧了相对横向扁平化。所有情况下，环形涡都会拉伸火焰段并引发局部熄火与破碎；索雷特扩散延迟了破碎，而辐射则加速了破碎，二者对破碎时间的综合效应几乎相互抵消。结果表明，索雷特输运与辐射主要改变火焰核的生长及对涡诱导熄火的抗性，而定性的破碎路径仍受流体动力学控制。
英文摘要
Ultra-lean hydrogen flames under terrestrial gravity are governed by a coupled interaction among preferential diffusion, thermal diffusion, heat loss, and self-induced convection. This study numerically examines combustion in a quiescent 6~vol.\% H$_2$--air mixture using detailed chemistry and a low-Mach-number formulation. A complete calculations set was considered, with Soret diffusion and optically thin radiative heat loss independently enabled and disabled. One-dimensional spherical calculations were used to isolate the initial post-ignition flame kernel growth, while two-dimensional planar and axisymmetric simulations described its subsequent buoyant rise, deformation, and breakup. Over the analyzed interval, the spherical flame-front radius followed $R_f^2\approx Kt$ rather than constant-speed expansion. Soret diffusion increased the effective growth coefficient $K$, whereas radiation reduced it. The axisymmetric calculations reproduced the experimentally measured leading-point trajectory substantially better than the planar formulation. Soret diffusion produced larger, faster-rising kernels and maintained a more nearly circular upper cap, whereas radiation had a weaker effect on trajectory but increased relative lateral flattening. In all cases, a toroidal vortex stretched the flame segment and caused local extinction and fragmentation. Soret diffusion delayed breakup, while radiation advanced it; their combined effect on breakup time was nearly compensating. The results show that Soret transport and radiation primarily alter kernel growth and resistance to vortex-induced extinction, while the qualitative breakup pathway remains hydrodynamically controlled.
