Comparative study between Conditional Moment Closure (CMC) and Conditional Source-term Estimation (CSE) applied to piloted jet flames

Abstract

Conditional Moment Closure (CMC) and Conditional Source-term Estimation (CSE) are investigated in a direct side-by-side comparison of the Sandia flames. The objective of the present study is to determine the strengths and weaknesses of each modelling approach given the same initial conditions and computational set-up. The predictions from both CMC and CSE are compared to detailed experimental data. In case of Sandia flame D, the CMC and CSE turbulent flow and mixing fields are similar near the nozzle exit, in agreement with the experimental data, with some differences farther downstream. The CMC and CSE conditional mass fractions for the major species are in good agreement with the experimental data downstream of the nozzle for lean mixtures. For fuel rich mixtures, an underprediction of the conditional mass fractions of methane and corresponding overestimation of the conditional mass fraction of water are observed at some axial locations. The CMC and CSE conditional mass fractions of the minor species and conditional temperature reproduce the general characteristics of the experimental profiles. However, major differences are observed for Sandia flame E. The discrepancies are attributed to the use of RANS and the boundary conditions set in CMC and some approximations made in the chemistry tables in CSE. Favre-averaged profiles are comparable in CMC and CSE. The computational time for each model is investigated and CSE appears to be faster. Further discussion on some of the strengths and weaknesses of each combustion model is also presented. Overall, both CMC and CSE are shown to produce results of comparable quality given the same numerical schemes, mesh, and boundary conditions.