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1. PLIF and PIV on a 15 kHz Supersonic Co-Axial Injector

   Solomon, JT; Noah, H; Lockyer, R (June 2024, AIAA Aviation 2024)

   AIAA (Ed.)

   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. 

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2. PLIF Exploration of an Active Co-Axial Injector in Crossflow From a Rectangular CD Nozzle

   https://doi.org/10.2514/6.2025-3321  

   Solomon, John T; Lockyer, Rhys; Tubbs, Lauryn; Connel, Russell (July 2025, American Institute of Aeronautics and Astronautics)

   AIAA (Ed.)

   The mixing characteristics of an active coaxial injector in crossflow configurations are explored in this paper. A miniature rectangular CD nozzle generates crossflow for the injector for subsonic and supersonic test conditions. The flowfield of the active injection system consists of an actuation air jet at the inner core of the coaxial nozzle (1mm ID) that provides large mean and fluctuating velocity profiles in the shear layers of a fluid stream injected surrounding the core through an annular nozzle with ID=1.5 mm and OD=1.96 mm. The baseline flowfield of the annular stream in various crossflow conditions was studied first without actuation. The injector's active and passive actuation modes of operation are then evaluated and compared across multiple crossflow conditions with the baseline data. In the active mode, the annular stream is actuated by a pulsed jet operating at 17 kHz. In steady mode, the actuation jet is a steady coaxial underexpanded jet. Measurements using planar laser-induced fluorescence (PLIF) indicate that the active coaxial injection approach using high-frequency pulsed jets at the core significantly improves mixing of the acetone-seeded annular stream in supersonic crossflow conditions compared to the steady and baseline test cases. Data suggests that such a system has the potential to be evaluated further for real-life flow mixing and control applications, such as supersonic and hypersonic combustors. 

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3. Planar Laser-Induced Fluorescence (PLIF) Studies on a High-frequency Pulsed CoAxial Injector Flowfield

   John T Solomon, Rhys Lockyer (December 2022, Proceedings of the 9th International and 49th National Conference on Fluid Mechanics and Fluid Power (FMFP) December 14-16, 2022, IIT Roorkee, Roorkee-247667, Uttarakhand, India)

   Effective mixing in supersonic and hypersonic flow conditions is critical for developing next-generation high-speed air-breathing transport systems. Efficient fuel mixing with fast-moving air leads to a better economy and fewer pollutants. Ultimately the mixing is a molecular diffusion problem. However, the macroscopic phenomena, such as entrainment and vorticity dynamics resulting from the shear layer instabilities of the mixing fluids, play a significant role in the overall efficiency of the process. This paper studies a novel, coaxial injector system integrated with a high-frequency microjet actuator operating at 15.5 kHz for improving mixing in extreme flow conditions. This co-flow system consists of a highfrequency supersonic actuation air jet at the inner core 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 high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a steady co-axial configuration operating at the same input pressure. This paper reports the flow mixing characteristics of the injection system captured using planar laser-induced fluorescence (PLIF). 

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4. High-Frequency Pulsed Coaxial Injectors for High-Speed Flow Mixing and Control

   https://doi.org/10.2514/1.J062369  

   Solomon, John T; Lockyer, Rhys; Jones, Tailor; Kreth, Phillip (December 2023, AIAA Journal)

   AIAA (Ed.)

   Efficient and controlled mixing of fuel with fast-moving air is a challenging physical problem relevant to hypersonic systems. Although mixing happens at the molecular level through diffusion, the macroscopic phenomenon such as entrainment and vorticity dynamics resulting from the shear layer instabilities of the mixing fluids play a significant role in the overall efficiency of the process. With a focus on improving mixing at extreme flow conditions, this paper presents a fundamental study of a novel, high-speed, pulsed coflow system integrated with ultrahigh-frequency actuators (11–20 kHz). This injection system consists of a supersonic actuation air jet at the inner core that provides large mean and fluctuating velocity profiles in the shear layers of a fluid stream injected surrounding the core through an annular nozzle, with pulsing occurring at a designated frequency. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a steady coaxial configuration operating at the same input pressure. Experiments also indicate a strong connection between the frequency and unsteady amplitude of the actuation jet to the supersonic flow mixing phenomenon. This paper reports the design details of the injector assembly and flow mixing characteristics captured using phase-locked microschlieren and planar laser-induced fluorescence techniques. 

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5. High-Frequency Pulsed Co-axial Injectors for High-Speed Flow Mixing and Control

   https://doi.org/10.2514/6.2022-3926  

   Solomon, John T.; Kreth, Phillip A.; Lockyer, Rhys; Jones, Tailor (June 2022, AIAA Aviation Meeting Chicago 2022)

   Efficient and controlled mixing of fuel with fast-moving air is a challenging physical problem relevant to hypersonic systems. Although mixing happens at the molecular level through diffusion, the macroscopic phenomena such as entrainment and vorticity dynamics resulting from the shear layer instabilities of the mixing fluids play a significant role in the overall efficiency of the process. With a focus on improving mixing at extreme flow conditions, this paper presents a fundamental study of a novel, high-speed, pulsed co-flow system integrated with ultra-high frequency actuators that operates at 11-20 kHz. This injection system consists of a supersonic actuation air jet at the inner core that provides large mean and fluctuating velocity profiles in the shear layers of a fluid stream injected surrounding the core through an annular nozzle, with pulsing occurring at a designated frequency. The high-frequency streamwise vortices and shockwaves tailored to the mean flow significantly enhanced supersonic flow mixing between the fluids compared to a steady co-axial configuration operating at the same input pressure. Experiments also indicate a strong connection between the frequency and unsteady amplitude of the actuation jet to the supersonic flow mixing phenomena. This paper reports the design details of the injector assembly and flow mixing characteristics captured using phase-locked microschlieren and planar laser-induced fluorescence (PLIF) techniques. 

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