On the dynamics of sprays in complex gas turbine swirl injectors

Abstract

Coupling of spray with the coherent structures of highly turbulent flow has been a long-standing problem, especially in the context of liquid fuel delivery systems in gas turbine combustors. In this work, we analyze the evolution of the hydrodynamic topology and consequent spray-flow interactions in a dual swirl injector assembly. We have shown (using time-resolved particle image velocimetry) that the geometry of the swirl cup (exit flare angle and mixing length), as well as the flow orientation (counter vs. co) in the primary and secondary swirlers, ascertain the hydrodynamic transitions in the resultant flow field. Width of the recirculation zone $$ \left( {{\raise0.7ex\hbox{$r$} \!\mathord{\left/ {\vphantom {r {R_{o} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${R_{o} }$}}} \right) $$ is identified as the key length-scale used to ascertain the global characteristics of the flow field. For a given flare angle, reduction in length scale $$ \left( {{\raise0.7ex\hbox{$r$} \!\mathord{\left/ {\vphantom {r {R_{o} }}}\right.\kern-0pt} \!\lower0.7ex\hbox{${R_{o} }$}}} \right) $$ is witnessed with orientation switch from counter-rotation to co-rotation configuration. Proper orthogonal decomposition (POD) is implemented over instantaneous flow field data to extract energetic spatial flow structures and temporal modes. POD revealed the existence of distinct frequency bands depending on the relative dominance of the primary or secondary swirler flow fields. Dynamic mode decomposition (DMD) also has been carried out to delineate the evolution of dominant frequency values with respect to the experimental variables.