Studies on flow dynamics and spray swirl interactions in gas turbine combustor

Abstract

Coupling of spray with the coherent structures of a highly turbulent flow has been a long-standing problem especially in the context of liquid fuel delivery systems in gas turbine combustors. The atomizer in a gas turbine combustor usually has one or more (radial/axial entry) air swirlers with a fuel nozzle being mounted centrally along the longitudinal axis of swirler. It is well known that swirling flows are highly three dimensional in nature and often induce multiple aerodynamically unstable modes whose frequencies are several orders of magnitude. The basic understanding of flow dynamics in gas turbine swirl cup is critical to achieving clean and efficient combustion in modern-day gas turbine combustors. In this work, we analyze the evolution of the hydrodynamic topology and consequent spray-flow interactions in a coaxial swirl injector assembly. The key results of the present work are discussed in four parts. In the first part, the global evolution and temporal dynamics of various vortex breakdown modes are discussed. Experiments are carried out for three sets of co annular flow Reynolds number and#119877;and#119890;and#119886;=4896,10545,17546. Furthermore, for each and#119877;and#119890;and#119886; condition, swirl number and#119878;and#119866; is varied independently from 0and#8804;and#119878;and#119866;and#8804;3. Three distinct forms of vortex breakdown namely, pre-vortex breakdown (PVB), central toroidal recirculation zone (CTRZ; axisymmetric toroidal bubble type breakdown) and sudden conical breakdown are explored in greater details. Energy ranked, and frequency resolved / ranked robust structure identification methods POD, DMD respectively is implemented over instantaneous time resolved PIV data sets to extract the dynamics of coherent structures associated with each vortex breakdown modes. The dominant structures obtained from POD analysis suggest the dominance of KH instability (axial + azimuthal; accounts ~ 80 % of total TKE) for both PVB and CTRZ while the remaining energy is contributed by shedding modes...