Prediction of characteristics of enclosed turbulentjet flames

Abstract

This paper reports on a study of flow and mixing of enclosed turbulent flames. It is shown that important conclusions concerning characteristic features of flow and mixing can be derived from rather simple considerations. The flow of enclosed turbulent jet flames is divided into four separate regions: an entrance region, a developed turbulent jet flow region, a pressure-increase region, and a post-jet-flow region. A general similarity parameter B, which is introduced for the jet-flow region, is closelyrelated to the Thring-Newby and the Craya-Curtet similarity parameters. However, it differs from these in being related to the cross-sectional area of the enclosure at the axial position of maximum recirculation. A theory is developed for the recirculation of downstream materials into the jet-flow region.It is based on the pressure increase in the post-jet-flow region. Three unique functions of B are established for unswirled jets, on the basis of this theory and experimental data: the recirculation velocity at the axial position of maximum recirculation, the axial position of maximum recirculation, and the maximum recirculation. The influence of weak and moderate swirls on the recirculation characteristics is taken into consideration by the swirl number S, proposed by Kerr and Fraser. It is shown that increased swirl moves the axial position of maximum recirculation toward the entrance. The maximum recirculation, however, remains a unique function of B. Expressions are derived for various characteristics of mixing within the jet-flow region. The theoretical results are verified by experimental data, taken mainly from literature.