Effects of confinement on premixed turbulent swirling flame using large Eddy simulation

Abstract

This paper utilises large eddy simulation (LES) to study swirling reacting flows by comparison with experimental observations. The purpose is to provide further insights in engineering designs, as well as to improve modelling. A reduced-scale swirl burner has been developed for the experiments. Comparison of particle image velocimetry (PIV) measurements with LES results using finite rate chemistry shows that LES captures all the salient features of an unconfined flame including velocity and temperature distributions. However, when the flame is confined within a cylindrical combustor, the simulated flame shape is initially not consistent with experimental observation. Investigations show that the discrepancy is caused by the often practised assumption of adiabatic wall temperature. With the use of an assumed wall temperature distribution guided by laboratory observation, results of LES are consistent with experiments. Although the latter LES approach requires more computational resources, the improvement is found to be justified.

Keywords:

• premixed combustion
• swirl flame
• LES
• confinement
• finite rate chemistry

Acknowledgements

This work was supported by the Research Grant Council of Hong Kong Special Administrative Region (Grant No. PolyU 5105/08E and B-Q10H) and the Research Committee of The Hong Kong Polytechnic University (Grant No. G-U294). The Lawrence Berkeley National Laboratory effort was supported by the US Department of Energy, Office of Fossil Energy under Contract No. DE-AC03-76F00098. The authors also wish to thank Mr. Gary Hubbard, Mr. Ken Hom and Dr. David Littlejohn for their support in carrying out the experiments at LBNL, and also the personnel at the mechanical workshop for constructing the burner.