Main flow characteristics in a lean premixed swirl stabilized gas turbine combustor – Numerical computations

Abstract

Main swirling flow characteristics are numerically investigated in a typical lean premixed swirl stabilized combustor. The combustor under investigation has been reported previously in the literature for experimentally determining both the combustion instabilities frequency and amplitude with no reference to the detailed flow dynamics inside. It is described in details in the present work. Both realizable Kepsilon 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 shown. Also a corner 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, 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=0.6) to determine the effect of swirl on flow characteristics. The high swirl experimental case of S=0.6 resulted in wider central recirculation zone, shorter corner 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. However, further numerical and experimental investigations need to be done in order to gain more insight of the flow dynamics inside the combustor.