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Abstract This paper presents experimental studies on a novel active high-frequency coaxial injector system designed for enhanced flow mixing and control at extreme flow velocity conditions. The flow dynamics and mixing characteristics of the system operating at 15kHz were captured using planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) techniques and compared against its steady and baseline modes. In pulsed mode, this active injection system delivers a pulsed supersonic actuation air jet at the inner core of the coaxial nozzle that provides large mean and fluctuating velocity profiles in the shear layers of an acetone-seeded fluid stream injected surrounding the core through an annular nozzle. The instantaneous velocity, vorticity and acetone concentration fields of the injector are discussed. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a classical steady coaxial configuration operating at the same input pressure. The paper analyses the dynamic and diffusion characteristics of this active coaxial injection system, which may have potential for supersonic mixing applications. 

With a focus on improving mixing at extreme flow velocity conditions, this paper presents planar laser-induced fluorescence (PLIF) and particle image velocimetry (PIV) studies on the flowfield of a high-speed, pulsed co-flow system integrated with a high-frequency actuator operating at 15 kHz. This active injection system delivers a supersonic pulsed actuation air jet at the inner core of the co-axial nozzle that provides large mean and fluctuating velocity profiles in the shear layers of a fluid stream injected surrounding the core through an annular nozzle. The instantaneous velocity, vorticity, and acetone concentration fields of the injector in three distinct modes of operation – pulsed actuation, steady actuation, and without actuation -are presented. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to the steady co-axial configuration operating at the same input pressure. The study analyzes the mixing and dynamic characteristics of this active co-axial injection system, which has the potential for supersonic mixing applications. 

This study meticulously probes the evolution of engineering undergraduates' attitudes and skills related to renewable energy and sustainability over two years at two institutions in the Southeastern United States. Data were intensively collected in two phases – fall 2022 and spring 2024 – amassing over 250 initial and upwards of 200 follow-up responses. This rigorous effort culminated in over 150 complete and matched datasets subjected to detailed examination. A bespoke, five-part survey was employed to capture the complex spectrum of students' attitudes. Our analytical approach incorporated ANOVA; these results indicated minimal group variances across most survey dimensions, hence suggesting a uniformity in perceptions. Paired sample tests brought to light a minor, but statistically significant increase in sustainability-related knowledge. The educational methods employed included hands-on projects, seminars, and group assignments focused on various aspects of renewable energy and sustainability. These incremental yet impactful changes highlight the potential of precise educational strategies to effectively mold student perspectives towards sustainability. By integrating solid statistical techniques and delving into the broader educational implications, this study provides valuable insights into the refinement of a sustainability-centered engineering curricula.