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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. 

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. 

Swirl combustion is one of the most efficient approach to efficient combustion processes and therefore, it has received great interest particularly from aerospace industry. Swirl combustion has been studied in the past both experimentally and computationally. However, in spite of the extended studies, the swirl combustion is still not well understood and therefore, further studies are required. One of the open questions in the swirl combustion is the effect of the swirl number on the combustion efficiency and instabilities. Over decades, extensive experimental and computational studies of swirl combustion have been performed. The experimental studies of swirl combustion are quite challenging due to the unsteady nature of the combustion process. To overcome these challenges, computational studies have been used in the study of turbulent combustion. The present study concerns the effect of the swirl number on the combustion efficiency and flame stability. The combustion efficiency is assessed based on the temperature developed inside the combustion chamber and NOx levels. The effect of air/fuel blowing ratio on the combustion efficiency and instability is also investigated in this research. The computations are carried out using the large-eddy simulation (LES) approach along with the flamelet combustion model. The analysis reveals the unsteady nature of the flame and thus, its departure from the core of the combustor. The analysis also reveals the presence of a region of high level of temperature, NO and2CO , inside the combustor 

In this paper, a novel model reference adaptive control (MRAC) architecture for nonlinear, time-varying, hybrid dynamical systems is applied for the first time to design the control system of a multi-rotor unmanned aerial vehicle (UAV). The proposed control system is specifically designed to address problems of practical interests involving autonomous UAVs transporting unknown, unsteady payloads and subject to instantaneous variations both in their state and in their dynamics. These variations can be due, for instance, to the payload’s dynamics, impacts between the payload and its casing, and sudden payload dropping and pickup. The proposed hybrid MRAC architecture improves the UAV’s trajectory tracking performance over classical MRAC also in the presence of motor failures. The applicability of the proposed framework is validated numerically through the first use of the high-fidelity simulation environment PyChrono for autonomous UAV control system testing. 

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. 

Swirl combustion is encountered in many engineering applications since it provides efficient fuel burning. Experimental studies of turbulent swirl combustion poses challenges due to unsteady nature of the combustion phenomenon. Therefore, computational approaches are a promising alternative for the numerical studies of supersonic combustion. The present studies concerns the computational studies of swirl combustion, particularly the effect of the injection scheme on the combustion efficiency and flame stability. Therefore, the effect of the air-fuel ratio on the combustion efficiency and flame stability is subject of investigation. The combustion efficiency is assessed based on the temperature developed inside the swirl combustor. The computations are carried out using the large-eddy simulation (LES) approach along with the flamelet combustion model. The analysis reveals the unsteady nature of the flame and thus, its departure from the core of the combustor. The analysis also reveals the presence of a region of high level of temperature, NO and2CO , inside the combustor. 

Computational studies of transient three-dimensional flapping wing are carried out using the large eddy simulation (LES) approach. The studies concern the understanding of the effect of flapping motion on the aerodynamic performance and aeroacoustics noise of a finite NACA0012 wing. The flapping motion of the wing generates trailing-edge vortices whose magnitude and scale vary in time. The near-field flow is associated with periodic flow separation and reattachments, which cause a time-dependent aerodynamic coefficients. 

The aeroelastic phenomenon plays a critical role in the aerodynamic performance and stability of fixed wing aircrafts. Aeroelastic phenomena may cause flow separation and large deformations of the wing, and implicitly high stresses into the structure. The computational study of aeroelasticity, in high-speed fixed wing, requires fully-coupled aeroelastic algorithms. Therefore, in the present research we propose a CFD based approach using the large-eddy simulation approach along with a finite-element method for the computations of the structural deformations. The analysis is performed for subsonic and transonic flows with Mach number . The analysis reveals that the elastic deformations of the wing and stresses in the wing increase with the Mach number. 

The aeroelastic phenomena of fixed-wing aircraft in transonic and supersonic flight regimes plays a critical role in the design of high-speed aircraft. The present research concerns the development of computationally efficient and accurate methods for the computation of aeroelastic systems containing transonic and supersonic flows. Therefore, we propose a fully- coupled, time-marching aeroelastic approach utilizing an URANS model. The computational studies are carried out to assess the effect of the freestream Mach number and angle of attack on the structural dynamics and stresses developed in the wing structure. The studies are carried out for a range of Mach numbers, 𝑴∞ = 𝟎. 𝟖 – 𝟏. 𝟒, and angles of attack, 𝜶 = {𝟐°, 𝟒°, 𝟔°}. The analysis reveals that the aeroelastic deformation of the wing and induced stress in the wing structure increase with the freestream Mach number.