High-Frequency Imaging of a Reacting Jet in Crossflow*

The Reacting Jet in Crossflow (RJICF) is a canonically important flowfield in chemically reacting flows. The high-frequency (typically over 10 kHz) shear layer instabilities are of particular significance, since their behavior governs the near field mixing and entrainment.  In this study, 10 kHz stereo PIV and OH-PLIF measurements were performed on a reacting hydrogen jet in a hot vitiated crossflow. By themselves, these measurements were not sufficient to resolve the high-frequency shear layer dynamics but were supplemented by 50 kHz OH* chemiluminescence. The signal intensity power spectrum indicates a peak frequency of these instabilities at 19 kHz, which lies in the dimensionless frequency range typical of non-reacting JICF studies. The spatial variation of the instability amplitude and phase was analyzed using Fourier analysis, and Proper Orthogonal Decomposition (POD) and Dynamic Mode Decomposition (DMD) were utilized to further isolate and understand the complex spatiotemporal dynamics. These methods succeeded in decoupling the lower-frequency jet flapping dynamics from the higher-frequency shear layer features, yielding new insight into the rich dynamics of the RJICF problem.