The main objective of this study is to clarify effects of flame straining on flame structures and heat release rate (HRR) of swirling flames. This is achieved by analyzing results of direct numerical simulations (DNS) of hydrogen—air turbulent swirling premixed flames considering two swirl number and two equivalence ratio cases. Statistical characteristics of HRR are investigated by examining the mean HRR conditioned on a reaction progress variable and the total HRR in the computational domain. Conditional means of the HRR show that the magnitude of the HRR in reaction zones is smaller for higher swirl number cases than that for lower swirl number cases. A direct comparison between strained laminar and swirling flames shows the influence of the strain rate on the flame structure and the progress of elementary reactions. As strain rate increases in a laminar flame, the peak of the HRR by an exothermic reaction H 2 + OH → H 2 O + H shifts toward the burnt side, implying active production of H in the burnt side. The HRR of the above reaction also shows an increasing tendency in a laminar flame under the strain rates greater than 10 6 s − 1 . The strain–flame interaction with this tendency affects the HRR on highly strained flame surfaces of the swirling flames. It is also clarified that the local HRR intensity is dominated not only by strain rate but also by diffusion of H from the burnt to unburnt side.

中文翻译：

---

旋流氢气-空气预混火焰中放热速率对火焰应变的响应

本研究的主要目的是阐明火焰应变对旋转火焰的火焰结构和放热率 (HRR) 的影响。这是通过分析考虑两个涡流数和两个当量比情况的氢气-空气湍流旋流预混火焰的直接数值模拟 (DNS) 结果来实现的。通过检查以反应进程变量为条件的平均 HRR 和计算域中的总 HRR，研究了 HRR 的统计特征。HRR 的条件均值表明，较高旋流数情况下反应区中 HRR 的大小小于较低旋流数情况下的 HRR。应变层流火焰和旋流火焰之间的直接比较显示了应变速率对火焰结构和基本反应进程的影响。随着层流火焰中应变速率的增加，放热反应 H 2 + OH → H 2 O + H 产生的 HRR 峰值向燃烧侧移动，这意味着在燃烧侧积极产生 H。上述反应的 HRR 在应变速率大于 10 6 s - 1 的层流火焰中也显示出增加的趋势。具有这种趋势的应变-火焰相互作用会影响旋流火焰的高度应变火焰表面上的 HRR。还澄清了局部 HRR 强度不仅受应变速率的支配，而且还受 H 从燃烧侧向未燃烧侧的扩散支配。上述反应的 HRR 在应变速率大于 10 6 s - 1 的层流火焰中也显示出增加的趋势。具有这种趋势的应变-火焰相互作用会影响旋流火焰的高度应变火焰表面上的 HRR。还澄清了局部 HRR 强度不仅受应变速率的支配，而且还受 H 从燃烧侧向未燃烧侧的扩散支配。上述反应的 HRR 在应变速率大于 10 6 s - 1 的层流火焰中也显示出增加的趋势。具有这种趋势的应变-火焰相互作用会影响旋流火焰的高度应变火焰表面上的 HRR。还澄清了局部 HRR 强度不仅受应变速率的支配，而且还受 H 从燃烧侧向未燃烧侧的扩散支配。