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Published 2016 | public
Journal Article

Assessment of the constant non-unity Lewis number assumption in chemically-reacting flows


Accurate computation of molecular diffusion coefficients in chemically reacting flows can be an expensive procedure, and the use of constant non-unity Lewis numbers has been adopted often as a cheaper alternative. The goal of the current work is to explore the validity and the limitations of the constant non-unity Lewis number approach in the description of molecular mixing in laminar and turbulent flames. To carry out this analysis, three test cases have been selected, including a lean, highly unstable, premixed hydrogen/air flame, a lean turbulent premixed n-heptane/air flame, and a laminar ethylene/air coflow diffusion flame. For the hydrogen flame, both a laminar and a turbulent configuration have been considered. The three flames are characterised by Lewis numbers which are less than unity, greater than unity, and close to unity, respectively. For each flame, mixture-averaged transport simulations are carried out and used as reference data. The current analysis suggests that, for numerous combustion configurations, the constant non-unity Lewis number approximation leads to small errors when the set of Lewis numbers is chosen properly. For the selected test cases and our numerical framework, the reduction of computational cost is found to be minimal.

Additional Information

© 2016 Informa UK Limited. Received 4 September 2015; accepted 23 February 2016. This research was conducted with Government support under and awarded by the Department of Defense, Air Force Office of Scientific Research, National Defense Science and Engineering Graduate (NDSEG) Fellowship [32 CFR 168a]. The authors also gratefully acknowledge founding from the US Department of Energy – Basic Energy Sciences [DE-SC006591 under the supervision of Dr. Wade Sisk, and funding from Air Force Office of Scientific Research [FA9550-12-1-0472; FA9550-12-1-0144) under the supervision of Dr Chiping Li. This research used resources of the National Energy Research Scientific Computing Center, a Department of Energy Office of Science User Facility supported by the Office of Science of the U. Department of Energy [Contract No. DE-SC006591]. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation [grant number CTS-130006]. No potential conflict of interest was reported by the authors.

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