Hypervelocity impacts generate a flash of light, known as an impact flash, and have plumes of ejecta that are complex, both temporally and spatially, composed of condensed phased particles, fragments, and gases. Recently, several hypervelocity impact experiments were conducted at the Johns Hopkins Hypervelocity Facility for Impact Research Experiments (HyFIRE) two-stage light gas gun facility for the purposes of studying the mechanisms responsible for impact flash in order to motivate a predictive flash model. Impacts of a spherical aluminum projectile and aluminum target at 2 km/s were performed with a range of chamber backfill pressures (10 – 500 Torr) and with two gas compositions (air and argon). Multiple sensing diagnostics were employed for the experiments, including radiometers, a time-integrated spectrometer, and high-speed cameras (both unfiltered and bandpass filtered at 486nm). A novel approach to extracting quantitative data from high-speed imagery is presented, including assessments of combustion localization within the impact cloud, temporal combustion extent, flash area, and flash expansion rate. The results from the high-speed imagery agree with previous findings by Simpson et al. (2023) regarding impact cloud structure and provide evidence of ablation particle jetting in the cloud. Overall, we find that the chamber backfill pressure and composition have significant effects on the temporal, spatial, and luminous evolution of the flash, and that this backfill has a large bearing on the presence and importance of combustion processes within the impact cloud. The coupling of aluminum fragment ablation and combustion with the overall impact flash signature will also be discussed. Finally, difficulties in the experimental setup are assessed and follow-on experiments are proposed to give further insight into impact flash emission mechanisms.
2025-04-09 09:00:00
