View Video Presentation: https://doi.org/10.2514/6.2022-2372.vid

Femtosecond laser activation and sensing of hydroxyl (FLASH) is employed for seedless velocimetry measurements in the turbulent, reacting environment of a rotating detonation combustor (RDC) exhaust. This technique, which is a subset of hydroxyl tagging velocimetry (HTV), is first demonstrated in an H2-air Hencken calibration burner to characterize its utility in reacting environments. H2O molecules are dissociated by the focusing of a near-infrared femtosecond laser, producing a superequilibrium concentration of Hydroxyl (OH) radicals beyond the naturally occurring amount in the flame. The OH radicals are excited by a 1 MHz rate planar laser-induced fluorescence (PLIF) system, allowing the excess OH radicals to be tracked through the exhaust for periods up to 10 microseconds before the signal decays to the natural background level. Time-resolved velocity and flow-angle measurements and their uncertainty are quantified within the RDC exhaust. Such measurements can be used to optimize post-combustion devices as well so to compare with ultrafast-laser-based temperature measurements to develop and a more complete understanding of the highly transient thermodynamic state within the exit flow of combustors with high levels of turbulence and/or detonative thermochemical conditions.