Development and Dynamical Analysis of Laboratory Facility Exhibiting Full-Scale Combustion Instability Characteristics

Abstract

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.