Comparative analysis of methods for heat losses in turbulent premixed flames using physically-derived reduced-order manifolds
Comparative analysis of methods for heat losses in turbulent premixed flames using physically-derived reduced-order manifolds
Heat losses have the potential to substantially modify turbulent combustion processes, especially the formation of pollutants such as nitrogen oxides. The chemistry governing these species is strongly temperature sensitive, making heat losses critical for an accurate prediction. To account for the effects of heat loss in large eddy simulation (LES) using a precomputed reduced-order manifold approach, thermochemical states must be precomputed not only for adiabatic conditions but also over a range of reduced enthalpy states. However, there are a number of methods for producing reduced enthalpy states, which invoke different implicit assumptions. In this work, a set of a priori and a posteriori LES studies have been performed for turbulent premixed flames considering heat losses within a precomputed reduced-order manifold approach to determine the sensitivity to the method by which reduced enthalpy states are generated. Two general approaches are explored for generating these reduced enthalpy states and are compared in detail to assess any effects on turbulent flame structure and emissions. In the first approach, the enthalpy is reduced at the boundary of the one-dimensional (1D) premixed flame solution, resulting in a single enthalpy deficit for a single premixed flame solution. In the second approach, a variable heat loss source term is introduced into the 1D flame solutions by mimicking a real heat loss to reduce the post-flame enthalpy. The two approaches are compared in methane–air piloted turbulent premixed planar jet flames with different diluents that maintain a constant adiabatic flame temperature but experience different radiation heat losses. Both a priori and a posteriori results, as well as a chemical pathway analysis, indicate that the manner by which the heat loss is accounted for in the manifold is of secondary importance compared to other model uncertainties such as the chemical mechanism, except in situations where heat loss is unphysically fast compared to the flame time scale. A new theoretical framework to explain this insensitivity is also proposed, and its validity is briefly assessed.
large eddy simulation, nitrogen oxides, radiation, reduced-order manifolds, turbulent premixed flames
42-66
Nunno, A. Cody
e62d0330-7656-4f2b-9053-429fa816e2ca
Grenga, Temistocle
be0eba30-74b5-4134-87e7-3a2d6dd3836f
Mueller, Michael E.
de069534-2aa2-4382-a380-0f3fdbfc6526
22 June 2018
Nunno, A. Cody
e62d0330-7656-4f2b-9053-429fa816e2ca
Grenga, Temistocle
be0eba30-74b5-4134-87e7-3a2d6dd3836f
Mueller, Michael E.
de069534-2aa2-4382-a380-0f3fdbfc6526
Nunno, A. Cody, Grenga, Temistocle and Mueller, Michael E.
(2018)
Comparative analysis of methods for heat losses in turbulent premixed flames using physically-derived reduced-order manifolds.
Combustion Theory and Modelling, 23 (1), .
(doi:10.1080/13647830.2018.1479043).
Abstract
Heat losses have the potential to substantially modify turbulent combustion processes, especially the formation of pollutants such as nitrogen oxides. The chemistry governing these species is strongly temperature sensitive, making heat losses critical for an accurate prediction. To account for the effects of heat loss in large eddy simulation (LES) using a precomputed reduced-order manifold approach, thermochemical states must be precomputed not only for adiabatic conditions but also over a range of reduced enthalpy states. However, there are a number of methods for producing reduced enthalpy states, which invoke different implicit assumptions. In this work, a set of a priori and a posteriori LES studies have been performed for turbulent premixed flames considering heat losses within a precomputed reduced-order manifold approach to determine the sensitivity to the method by which reduced enthalpy states are generated. Two general approaches are explored for generating these reduced enthalpy states and are compared in detail to assess any effects on turbulent flame structure and emissions. In the first approach, the enthalpy is reduced at the boundary of the one-dimensional (1D) premixed flame solution, resulting in a single enthalpy deficit for a single premixed flame solution. In the second approach, a variable heat loss source term is introduced into the 1D flame solutions by mimicking a real heat loss to reduce the post-flame enthalpy. The two approaches are compared in methane–air piloted turbulent premixed planar jet flames with different diluents that maintain a constant adiabatic flame temperature but experience different radiation heat losses. Both a priori and a posteriori results, as well as a chemical pathway analysis, indicate that the manner by which the heat loss is accounted for in the manifold is of secondary importance compared to other model uncertainties such as the chemical mechanism, except in situations where heat loss is unphysically fast compared to the flame time scale. A new theoretical framework to explain this insensitivity is also proposed, and its validity is briefly assessed.
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Published date: 22 June 2018
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Funding Information:
The authors gratefully acknowledge funding from the U.S. Department of Energy, National Energy Technology Laboratory through the University Turbine Systems Research Program, award number DE-FE0011822 (Office of Fossil Energy). The simulations presented in this article were performed on computational resources supported by the Princeton Institute for Computational Science and Engineering (PICSciE) and the Princeton University Office of Information Technology's Research Computing Department.
Funding Information:
The authors gratefully acknowledge funding from the U.S. Department of Energy, National Energy Technology Laboratory through the University Turbine Systems Research Program, award number DE-FE0011822 (Office of Fossil Energy). The simulations presented in this article were performed on computational resources supported by the Princeton Institute for Computational Science and Engineering (PICSciE) and the Princeton University Office of Information Technology’s Research Computing Department.
Publisher Copyright:
© 2018, © 2018 Informa UK Limited, trading as Taylor & Francis Group.
Keywords:
large eddy simulation, nitrogen oxides, radiation, reduced-order manifolds, turbulent premixed flames
Identifiers
Local EPrints ID: 480927
URI: http://eprints.soton.ac.uk/id/eprint/480927
ISSN: 1364-7830
PURE UUID: 027f35bd-8ead-4c0f-a232-39c6944ca473
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Date deposited: 10 Aug 2023 16:59
Last modified: 18 Mar 2024 04:10
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Author:
A. Cody Nunno
Author:
Temistocle Grenga
Author:
Michael E. Mueller
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