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LES INVESTIGATION OF THE HYSTERESIS REGIME IN THE COLD MODEL OF A SWIRL BURNER

Muhamed Hadziabdic
Faculty of Engineering and Natural Sciences, International University of Sarajevo, Bosnia and Herzegovina; and Department of Applied Physics, Delft University of Technology, Prins Bernhardlaan 6, 2628 BWDelft, The Netherlands

R. Mullyadzhanov
Novosibirsk State University and Institute of Thermophysics SB RAS Pirogova St 2, 63090 Novosibirsk, Russia

K. Hanjalic
Department of Multi-scale Physics, Faculty of Applied Sciences, Delft University of Technology, The Netherlands and Novosibirsk State University, Russia

Résumé

We report on large-eddy simulation of flow in a cold replica of a non-premixed swirl burner in which hysteresis was detected when transiting from an attached long flame to a short lifted flame and vice versa (Hubner et al. 2003, Tummers et al. 2008). The unconfined highly swirling annular jet is generated by rotating the outer pipe of the annular air supply at 4000 rpm, while gas is fed through an inner annulus. The swirl number, controlled by the flow rate, range from 2.8 for the stable ("blue" flame) to 4.9 for the unstable ("yellow" flame). The air and fuel Reynolds numbers are 11250 and 2250 respectively for the maximum, to 6400 and 1300 for the minimum flow rate case. The LES results agree well with the available experimental data, reproducing notably different sizes and strengths of the central recirculation bubbles in the stable and unstable jets. It is shown that the flow undergoes different adjustments when approaching from different initial states to a state in the hysteresis region where both, the stable and unstable combustion regimes have been observed experimentally at the same swirl number of 3.26.