This paper describes a new approach that uses a small-scale rig, high-speed optical diagnostics, and the Krylov-based dynamic mode decomposition data analysis technique to elucidate the mechanisms that drive tangential combustion instabilities in full-scale combustors, e.g., liquid rocket engines. The developed rig uses a single injector to supply gaseous reactants whose mean flow direction is perpendicular to the excited, transverse, acoustic oscillations with frequencies equivalent to those encountered in full-scale engines. The strongly coupled fluid mechanics, combustion dynamics, and acoustic oscillations were studied using synchronized, high-speed (10 kHz) particle image velocimetry; OH-planar laser induced fluorescence; chemiluminescence; and dynamic pressure measurements. Each dataset was analyzed with the dynamic mode decomposition method to determine the approximate, complex frequencies and mode shapes of the system’s least-stable modes. The results of this analysis suggest that the fluid dynamics are heavily influenced by shear layer instabilities and helical vortices, signs of which appear in multiple modes with a similar convective velocity. From the fluorescence data, a 168 Hz mode identified near the observed combustion instability frequency suggests a linkage between the transverse acoustic oscillations and the oscillations of the vortex breakdown bubble. This study also suggested that a better description of the driving mechanism might be obtained in the future by simultaneously analyzing all the measured datasets by the dynamic mode decomposition.
Development and Dynamical Analysis of Laboratory Facility Exhibiting Full-Scale Combustion Instability Characteristics
AIAA Journal ; 55 , 12 ; 4314-4329
2017-12-01
Article (Journal)
Electronic Resource
English
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