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Impact of numerics on the predictive capabilities of reacting flow LES

机译：数值对反应流LES的预测能力的影响

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Combustors in modern aerospace propulsion systems are highly optimized devices and further enhancements to their performance will require advanced predictive modeling techniques. The LES approach has potential to be such a technique, but demonstration of its true predictive capability remains a challenge. In this paper, a methodical study is performed to assess the impact of numerical error on the predictive capabilities of LES and to distinguish it from error arising from physical modeling. Four codes are employed to simulate the bluff body stabilized flame experiment of Volvo Flygmotor AB. The physical models (governing equations and sub-grid models) are kept identical between the codes so that the physical modeling error is the same. For the same reason, computational grids are also kept identical since the sub-grid models are grid dependent. Results indicate that all codes produce a very similar solution for the non-reacting flow in terms of large scale unsteady vortex shedding behavior, mean profiles and second order turbulence statistics, on a suitably refined grid. This solution is also very close to the experimentally observed behavior of the flow. In contrast, for the reacting case, solutions from the various codes exhibit significant differences when analyzed under the same metrics and with similar or even finer grid resolution than that used for the non-reacting case. These differences are large enough to change the macroscopic behavior of the flow, e.g. some codes predict symmetric vortex shedding while others predict asymmetric shedding and some codes show strong recirculation zones while others show stagnant regions behind the bluff body. It is also shown that none of the solutions truly predicts the experimentally observed flow. Given that the physical sub-grid models and computational grids are the same in all the simulations, the inconsistency between results points to a significant impact of numerical methods and, hence, numerical error. The need for mitigation of this impact is highlighted, along with the need for metrics detailing how LES should be applied to reacting flows. It is suggested that both of these issues should be the focus of future work. (C) 2015 The Combustion Institute.. Published by Elsevier Inc. All rights reserved.
机译：现代航空航天推进系统中的燃烧器是高度优化的设备，其性能的进一步增强将需要先进的预测建模技术。 LES方法有可能成为这样一种技术，但是要证明其真正的预测能力仍然是一个挑战。在本文中，进行了系统的研究，以评估数值误差对LES预测能力的影响，并将其与物理建模产生的误差区分开。四个代码用于模拟沃尔沃Flygmotor AB的钝体稳定火焰实验。编码之间的物理模型（控制方程和子网格模型）保持相同，因此物理建模误差相同。出于同样的原因，由于子网格模型与网格相关，因此计算网格也保持相同。结果表明，在适当精制的网格上，就大规模非稳态涡旋脱落行为，平均轮廓和二阶湍流统计而言，所有代码都为非反应流产生了非常相似的解决方案。该解决方案也非常接近流的实验观察到的行为。相反，对于发生反应的情况，当以相同的度量标准进行分析时，与未反应的情况相比，来自各种代码的解决方案表现出显着差异，并且网格分辨率相似甚至更好。这些差异足够大，以改变流的宏观行为，例如。一些代码预示着对称的涡旋脱落，而另一些代码预示着不对称的涡旋脱落，而一些代码则显示出强烈的回流区，而另一些代码则显示了阻流体后面的停滞区域。还表明，没有一种解决方案能够真正预测实验观察到的流量。假设在所有模拟中物理子网格模型和计算网格都是相同的，结果之间的不一致表明了数值方法的重大影响，因此也产生了数值误差。强调了减轻这种影响的需要，以及对详细说明应如何将LES应用到反应流中的度量的需求。建议将这两个问题都作为未来工作的重点。 （C）2015 The Combustion Institute。由Elsevier Inc.出版。保留所有权利。

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