Unstrained and strained flamelets for LES of premixed combustion
Combustion Theory and Modelling
Taylor & Francis
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Langella, I., & Swaminathan, S. (2016). Unstrained and strained flamelets for LES of premixed combustion. Combustion Theory and Modelling, 20 410-440. https://doi.org/10.1080/13647830.2016.1140230
The unstrained and strained flamelet closures for filtered reaction rate in large eddy simulation (LES) of premixed flames are studied. The required sub-grid scale (SGS) PDF in these closures is presumed using the Beta function. The relative performances of these closures are assessed by comparing numerical results from large eddy simulations of piloted Bunsen flames of stoichiometric methane–air mixture with experimental measurements. The strained flamelets closure is observed to underestimate the burn rate and thus the reactive scalars mass fractions are under-predicted with an over-prediction of fuel mass fraction compared with the unstrained flamelet closure. The physical reasons for this relative behaviour are discussed. The results of unstrained flamelet closure compare well with experimental data. The SGS variance of the progress variable required for the presumed PDF is obtained by solving its transport equation. An order of magnitude analysis of this equation suggests that the commonly used algebraic model obtained by balancing source and sink in this transport equation does not hold. This algebraic model is shown to underestimate the SGS variance substantially and the implications of this variance model for the filtered reaction rate closures are highlighted.
SGS variance, dynamic model, SDR
The authors express their gratitude to EPSRC, Siemens and Rolls-Royce for their support. This work is funded by the grant numbered EP/I027556/1.
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External DOI: https://doi.org/10.1080/13647830.2016.1140230
This record's URL: https://www.repository.cam.ac.uk/handle/1810/253205