Regimes in turbulent non-premixed combustion
Final Report Abstract
In the scope of the project period, a novel regime diagram for turbulent non-premixed combustion was developed and tested. Unlike previous, purely statistical approaches to regime diagrams in turbulent combustion, the presented method relies on the instantaneous topology of the mixture fraction field. To answer the research questions, an extensive database of high fidelity reacting and nonreacting DNS was established over the course of the project. This database far exceeds the originally proposed cases. Furthermore, the cases were designed to be useful beyond the immediate scope of the project. DE analysis was applied to the mixture fraction fields and passive scalar fields of the various DNS cases. The underlying hypothesis of the DE-based regime diagram was tested rigorously. It was found that the DE parameters are highly useful in identifying and characterizing the local interaction between turbulence and combustion chemistry. It was shown that DE are sensible sub-units in the context of the investigation of the turbulent flame structure. Unlike conventional flame analysis which utilizes one-point quantities, the inherent ability provided by the DEs of a straight forward and well parametrized estimation of non-local effects in the presented conditions was instrumental. The advantages and applicability of DE analysis beyond the analysis performed in this project was demonstrated. Furthermore, nondimensional regime boundaries were obtained, which are independent of the non-dimensional numbers or fuel composition. The inherent differences of the combustion in the individual regimes was investigated and characterized. The investigation of the DE parameter statistics yielded the surprising result that the universality of the normalized statistics observed in inert flows is also present in the reacting cases and is consequently unaffected by the heat release. The characteristic scaling of the mean DE parameters, which was previously observed in inert flows, applies to the DEs obtained from mixture fraction fields of non-premixed flames as well. All originally posed objectives were reached and the research questions could be adequately answered. Besides the changed and expanded DNS setup, the proposed work program and research methods were applied. Furthermore, the presented findings enabled the formulation of a framework for the prediction of combustion regimes in CFD simulations of engineering applications utilizing non-premixed combustion. While the combustion modelling was beyond the original scope of the project, it allowed for a quantification of the impact of combustion conditions which are currently not considered in sate-of-the-art simulations. Therefore, the prediction results emphasize the importance of continuing the research of these conditions.
Publications
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“Corrections to the 4/5-law for decaying turbulence”. 69th Annual Meeting of the APS Division of Fluid Dynamics. 2016
J. Boschung, M. Gauding, F. Hennig, D. Denker, and H. Pitsch
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“Dissipation Element Analysis of Reacting-and Non-Reacting Flows.” 69th Annual Meeting of the APS Division of Fluid Dynamics. 2016
D. Denker, J. Boschung, F. Hennig, and H. Pitsch
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“Generalized higherorder Kolmogorov scales”. J. Fluid Mech. 794 (2016), pp. 233–251
J. Boschung, F. Hennig, M. Gauding, H. Pitsch, and N. Peters
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“Gradient Trajectory Analysis of Turbulence Induced Extinction Events”. Seventeenth International Conference on Numerical Combustion, May 6-8, Aachen, Germany. 2019
D. Denker, A. Attili, M. Bode, and H. Pitsch
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“Prediction of nonpremixed combustion regimes in a DI diesel engine in various operation points”. Proceedings of the 9th European Combustion Meeting, April 14-17, Lisbon, Portugal. 2019
D. Denker, K. Niemietz, A. Attili, M. Korkmaz, and H. Pitsch
