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A priori investigation of subgrid correlation of mixture fraction and progress variable in partially premixed flames

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Chen, ZX 
Ruan, S 
Langella, I 
Swaminathan, N 


Subgrid correlation of mixture fraction, Z, and progress variable, c, is investigated using Direct Numerical Simulation (DNS) data of a hydrogen lifted jet flame. Joint subgrid behaviour of these two scalars are obtained using a Gaussian-type filter for a broad range of filter sizes. Joint probability density function (JPDF) constructed using single-snapshot DNS data is compared qualitatively with that computed using two independent β-PDFs and a copula method. Strong negative correlation observed at different streamwise locations in the flame is well captured by the copula method. The subgrid contribution to the Z-c correlation becomes important if the filter is of the size of laminar flame thickness or larger. A priori assessment for the filtered reaction rate using flamelet approach with independent β-PDFs and correlated JPDF is then performed. The comparison with the DNS data shows that both models provide reasonably good results for a range of filter sizes. However, the reaction rate computed using copula JPDF is found to have a better agreement with the DNS data for large filter sizes because the subgrid Z-c correlation effect is included.



DNS, partially premixed flame, subgrid correlation, LES, copula

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Combustion Theory and Modelling

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Informa UK Limited
Engineering and Physical Sciences Research Council (EP/I027556/1)
European Commission Horizon 2020 (H2020) Industrial Leadership (IL) (686332)
Engineering and Physical Sciences Research Council (EP/K025791/1)