Abstract Multi-regime turbulent combustion modelling remains challenging and is explored with occurrence of local extinction in this study. A partially premixed model based on unstrained premixed flamelets is used in this work to investigate a piloted jet flame configuration with inhomogeneous inlets. Three different cases are simulated, which differ in the bulk mean velocity that amounts respectively to about 50%, 70% and 90% of the blow off velocity measured experimentally. As the jet velocity approaches the blow off limit, local extinctions start to occur along the flame surface and thus these flames are challenging from a modelling prospective. Two different numerical approaches, involving scaled and unscaled progress variable respectively, are compared to elucidate their abilities and limitations to predict local extinctions and to deal with the three-stream problem at the pilot/coflow interface. The key modelling details for such predictions are indicated and discussed. LES results are systematically compared to two sets of experimental measurements available in the literature for the three flames. The differences observed in the two experimental datasets are also discussed with the help of LES results. Although both approaches show promising agreement for the flame statistics, the scaled progress variable approach better predicts the local extinctions. The unscaled approach shows to naturally handle the three-stream problem without additional treatment for the pilot/coflow interface, which is required for the scaled approach. Furthermore, computed scalar dissipation rate of mixture fraction is compared with the measurements showing good agreement for the conditions investigated. This further suggests that local extinctions can be predicted using unstrained flamelets if the correct scalar mixing and its dissipation are captured.

中文翻译：

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使用非应变小火焰预测具有非均匀入口的自控喷射火焰的局部消光

摘要 多机制湍流燃烧建模仍然具有挑战性，并在本研究中随着局部消光的发生而进行了探索。在这项工作中使用基于无应变预混小火焰的部分预混模型来研究具有不均匀入口的先导喷射火焰配置。模拟了三种不同的情况，它们的体积平均速度不同，分别相当于实验测得的吹散速度的 50%、70% 和 90%。随着射流速度接近吹气极限，沿火焰表面开始发生局部消光，因此从建模的角度来看，这些火焰具有挑战性。两种不同的数值方法，分别涉及缩放和未缩放的进度变量，进行比较，以阐明它们在预测局部灭绝和处理引导/协流界面处的三流问题方面的能力和局限性。指出并讨论了此类预测的关键建模细节。LES 结果与文献中关于三种火焰的两组实验测量值进行了系统比较。在 LES 结果的帮助下还讨论了在两个实验数据集中观察到的差异。尽管两种方法都显示出对火焰统计数据有希望的一致性，但缩放进度变量方法可以更好地预测局部灭绝。非标度方法表明可以自然地处理三流问题，而无需对标度方法所需的先导/协流接口进行额外处理。此外，将计算出的混合分数的标量耗散率与测量结果进行比较，结果表明所研究的条件具有良好的一致性。这进一步表明，如果正确的标量混合及其耗散被捕获，则可以使用无应变的火焰来预测局部灭绝。