الفهرس 
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Abstract
In the present work, flame vortex interaction in lean premixed swirl stabilized combustors is investigated numerically using computational fluid dynamics. Flame vortex interaction is found to playa crucial role in combustion instabilities which hindered the design and development oflean premixed combustors. Main swirling flow characteristics are first investigated. The combustor used in the study has been reported previously in the literature. Both realizable K-epsilon and Detached eddy simulation (DES) turbulence models have been used to investigate the flow characteristics inside the combustor. The resultant governing equations have been solved by means of couple pressure based finite volume methodology. ANSYS-Fluent 12 commercial package has been used in the study. Using realizable K-epsilon, a central recirculation zone which is necessary for flame stabilization and efficient combustion has been detected. Also a
comer recirculation zone has been detected due to flow separation near combustor dump plane. Using DES, Worm like small scale coherent turbulent structures have been noticed over the vortex break down region followed by a large scale, full length, and columnar precessing vortex core along the pipe center line in consistent to previous findings. Results of the current moderate swirl case (S=0.45) have been qualitatively compared with an experimental high swirl case (S=O.6) to determine the effect of swirl on flow characteristics. The high swirl experimental case of S=O.6 resulted in wider central recirculation zone, shorter comer recirculation zone, faster flow reattachment to the wall
and slower decay of tangential velocity in comparison of current moderate swirl case of S=0.45. Both acoustics and flame vortex interactions are then numerically investigated. The aim of the work is to demonstrate numerically the role of flame vortex interaction as one of the main driving mechanisms of instabilities. Shear stress K-omega (SST K-w) model has <been used for turbulence closure due to its better capabilities in swirling flow problems over the realizable K-epsilon model near the wall. In addition, finite rate/eddy dissipation model has been used for chemical kinetics. A quarter wave mode, the fundamental acoustic
mode in the combustor premixed section, has been captured successfully. Using the present numerical frame, periodic reactants pocket/vortex shedding, ignition and heat release has been captured. Periodic heat release rate is found to drive periodic pressure waves which propagate upstream the combustor causing more perturbations in the inlet flow. The unstable shear layer downstream the center body leads to more vortex shedding hence closing the loop. Pictures of overall flame behavior show good agreement comparing with the reported experimental findings. However, further numerical and experimental investigations need to be done in order to gain more insight of both the flow and flame dynamics inside the combustor.