ENGINEERING AND CFD
Towards Large-Eddy/Filtered-Density Function Simulations of Turbulent Sooting Flames
Principal Investigator:
Apl.-Prof. Dr. P. Gerlinger
Affiliation:
Institute of Combustion Technology, German Aerospace Center (DLR), Stuttgart (Germany)
Local Project ID:
pr87zi
HPC Platform used:
SuperMUC of LRZ
Date published:
Researchers at the Institute of Combustion Technology at the German Aerospace Center (DLR) use petascale HPC system SuperMUC at LRZ in Munich for the simulation of soot evolution in lifted, turbulent, ethylene-air jet flames. The scope of their work is to develop and analyze simulation techniques for turbulent combustion with focus on soot predictions. The long-term objective is to develop validated high fidelity simulation techniques for soot predictions in turbulent combustion systems such as aeroengines.
Combustion is one of the oldest heat and power generation technologies and continues to play an important role in covering the energy demand of the world. The intense use of combustion, however, has led to several environmental problems. One of them is the emission of soot. Soot and soot precursors are suspected to be carcinogenic. Furthermore, soot from aircraft engines is suspected to increase the amount of cirrus clouds at high altitudes and thus to influence the climate. From an engineering point of view, soot indicates incomplete and hence less efficient combustion.
Hence, continuous efforts are made to reduce soot emissions by improving existing and developing new combustion technologies. Computational models for predicting soot evolution play a key role here. Obtaining accurate soot predictions is, however, even today a formidable task. Technical combustion occurs typically in turbulent flows, which are extremely difficult to model. Additional complexity to the modelling problem is added through the presence of combustion in the turbulent flow. The chemical reaction rates and turbulent motion interact with each other and additional models are required for these processes. Finally, the chemical formation pathways of soot are not fully understood yet, which introduces a further modelling problem.
Figure 1: Instantaneous LES results for mixture fraction, temperature, PAH, and soot. (click to enlarge image)
Copyright: Institute of Combustion Technology, DLR, Stuttgart
Figure 2: Temperature distribution in flame (TPDF simulation): Average field (left-half) and Monte-Carlo-particle representation (right-half). (click to enlarge image)
Copyright: Institute of Combustion Technology, DLR, StuttgartResearch at the Institute of Combustion Technology at the German Aerospace Center (DLR) has focused so far on tackling each of these problems separately. For modelling the chemistry of soot formation a sectional model has been developed. Transported Probability Density Function (TPDF) methods and Large Eddy Simulation (LES) have been implemented for the modelling of turbulence-chemistry interaction and for resolving large scale turbulent motions, respectively.
The present project on the petascale System SuperMUC at LRZ strives to unify all these model approaches in a combined simulation technique. This is happening step wise, i.e. in a first step the performance of the TPDF method and the LES in conjunction with the sectional soot model are analyzed. To this end a turbulent, lifted ethylene-air flame is simulated, where comprehensive measurement data are available for model validation.
Due to the large number of unknowns, which are introduced by chemistry, and the extreme numerical stiffness of the problem, these simulations are computationally very expensive. Therefore high performance computers such as the petascale System SuperMUC at LRZ in Munich are required.
Scientific Contact:
Apl.-Prof. Dr. P. Gerlinger
Institute of Combustion Technology
German Aerospace Center (DLR)
Pfaffenwaldring 38-40, D-70569 Stuttgart/Germany
e-mail: Peter.Gerlinger[at]dlr.de
December 2016