RANS simulation of a turbulent premixed bluff body flame using conditional source-term estimation

Abstract

In the present work, simulations are performed in order to study a turbulent premixed flame stabilised behind a bluff body burner. Conditional Source-term Estimation (CSE) is the combustion model adopted for this purpose and it is coupled with a trajectory gene- rated low-dimensional manifold method for chemistry reduction: conditional-averaged chemical source terms are closed by conditional-averaged scalars, which are obtained by inverting an integral equation. Two regularisation methods are implemented. The optimal regularisation parameter is determined and a sensitivity analysis is performed related to the effect of the value of the regularisation parameter. In the present study, only small differences in the conditional and unconditional averages are noticed for values of the regularisation parameter located in the optimal range determined by the L-curve. Two-equation k–ε and Shear Stress Transport (SST) turbulence models are used to solve the flow field in either the reactive or non-reactive case. Different values of the constant in the standard k–ε model and of γ₂ in the SST k–ω model are tested. Mean axial velocity and progress variable profiles are compared with experimental data. It is found that SST k–ω gives better results for the velocity profile in both the reactive and non-reactive cases. A value of γ₂ equal to 0.65 provides best predictions in the reactive case. The progress variable prediction exhibits similar profiles in the case of CSE and the flamelet combustion model approach. Very good agreement is achieved between the CSE predictions and experimental data.

Keywords:

• conditional source-term estimation
• premixed
• turbulent
• combustion
• RANS

Acknowledgements

Financial support for this research was provided by Rolls-Royce Canada and MITACS/MPRIME. The authors would like to thank Mr Kariuki and Professor Mastorakos for providing the experimental data.