Master of Science in Mechanical Engineering (MSME), Wright State University, 2024, Mechanical Engineering

An approach for the architecture optimization of emulator embedded neural networks is proposed. While the emulator embedded neural network has been shown to provide accurate predictions with suitable emulators, there is still a challenge regarding how to select the optimal hyperparameters of network architectures, such as, the number of neurons, layers, types of activation functions, etc. The selection of hyperparameters greatly affects the performance of the neural network model training both in terms of accuracy and efficiency. To address this challenge, this study proposes an algorithm that tests a range of hyperparameters and selects the best performing set. The algorithm compares network architectures using average cross-validation error and architecture size. Additionally, the algorithm implements Bayesian optimization to accelerate the hyperparameter selection process and leverages a database of benchmark analytical problems to better define the hyperparameter search space. The proposed method is demonstrated using analytical examples, an aerospace fracture mechanics design study, and a representative aerospace vehicle design study. It was found that the proposed algorithm was able to successfully select well-performing architectures from within the chosen search spaces. In comparison to the popular grid search algorithm, it found architectures of similar sizes and performance while testing less than half of the total number of architectures. The proposed algorithm was able to successfully avoid large architectures when the accuracy benefits were minimal compared to smaller architectures, saving both time and computational efficiency. The potential benefits of the algorithm when applied to aerospace design application are an increased confidence in the selected architecture, identification of best fit architectures with less dependence on experts' knowledge and experience, and reduction in time and computational efficiency when selecting an architecture.

Master of Science in Mechanical Engineering (MSME), Wright State University, 2024, Mechanical Engineering

In the constant search for more efficient engines, one approach to gain performance is to reduce the weight of the low pressure turbine (LPT) module. This module can account for up to 30% of the total engine weight [1], and a reduction in LPT weight results in clear gains to engine performance and a reduction in engine cost. High lift airfoils accomplish this weight reduction by each blade extracting a larger amount of work from the flow and thus requiring fewer blades to drive the compressor when compared to conventional blades. However, high lift LPT blades, quantified by a high Zweifel loading coefficient Zw>1.15, encounter increasing loss at low Reynolds numbers. Named Reynolds lapse, this effect is problematic if the engine must operate at high altitude cruise conditions such as the case with unmanned air vehicles. The two airfoils of this study, the L2FHW and the L3FHW, were designed to be front loaded and to demonstrate favorable low Reynolds number loss characteristics. Both airfoils were tested in the Transonic Turbine Cascade (TTC) at the Air Force Research Laboratory Building 18 Test Cell 21. The TTC is capable of high Mach number and low Reynolds number flow via independent control of each. Each airfoil was tested across a broad range of Mach numbers: exit Mach 0.78 down to 0.2 and exit Reynolds numbers from 23,000 to 201,000. Across each condition an exit total pressure traverse yielded the loss coefficient of the cascade at that condition. It was found that across all design exit Mach conditions, 0.78, both airfoils experience fully attached flow and nearly flat loss behavior. This strongly aligns with the design level predictions made. At conditions beyond expected operating conditions, the L2FHW displayed resistance to un-reattaching separations at all conditions down to exit Mach 0.2 Reynolds number 23,300. The L3FHW showed un-reattaching separations at only the most extreme condition tested, exit Mach 0.2 and Reynolds number 25,300. (open full item for complete abstract)

Master of Science, Miami University, 2024, Mechanical and Manufacturing Engineering

Wire electrical discharge machining (WEDM) enables production of complex parts with tight tolerances, although maintaining dimensional accuracy in corners and tapers remains challenging due to wire deflection and vibration. This study optimizes WEDM parameters for achieving high-accuracy in machining complex geometrical parts and taper cuts in 6061 Aluminum alloy using Excetek W350G WEDM machine with a copper wire electrode. Parameters including Wire Tension, Pulse On-Time, Pulse Off-Time, Wire Feed Rate, Open Circuit Voltage, and Flashing Pressure were varied using L18 Taguchi Orthogonal Array and response graph method to identify optimal cutting conditions. Results indicated feature-specific optimization is crucial, as different geometrical features (rectangular fins, triangular fins, gears) exhibited varying critical parameters. Key findings highlighted the importance of Wire Tension and Pulse On-Time in maintaining cutting accuracy, although at varying levels for specific features. Response graphs demonstrated effects of major WEDM parameters on corner and profile accuracies, whereas Taguchi analysis provided optimum settings of parameters for each feature and taper cutting. Validation experiments for rectangular fins showed significant improvement in the dimensional error for the fin length and taper angle. These advancements will enhance precision, efficiency, and versatility of WEDM processes in machining complex profiles, and corners, contributing to precision manufacturing.

Master of Science (M.S.), University of Dayton, 2024, Aerospace Engineering

Traditional conceptual-level aerodynamic analysis is limited to empirical and/or inviscid models due to considerations of computational cost and complexity. There is a distinct desire to incorporate higher-fidelity analysis into the conceptual-design process as early as possible. This work seeks to enable the use of high-fidelity data by developing and applying multi-fidelity surrogate models that can efficiently predict the underlying response of a system with high accuracy. To that end, a novel form of the multi-fidelity polynomial chaos expansion (PCE) method is introduced, extending the surrogate modeling technique to accept three distinct fidelities of input. The PCE implementation is evaluated for a series of analytical test functions, showing excellent accuracy in creating multi-fidelity surrogate models. Aerodynamic analysis of a generic hypersonic vehicle (GHV) is performed using three codes of increasing fidelity: CBAERO (panel code), Cart3D (Euler), and FUN3D (RANS). The multi-fidelity PCE technique is used to model the aerodynamic responses of the GHV over a broad, five-dimensional input domain defined by Mach number, dynamic pressure, angle of attack, and left and right control surface settings. Mono-, bi-, and tri-fidelity PCE surrogates are generated and evaluated against a high-fidelity “truth” database to assess the global error of the surrogates focusing on the prediction of lift, drag, and pitching moment coefficients. Both monofidelity and multi-fidelity surrogates show excellent predictive capabilities. Multi-fidelity PCE models show significant promise, generating aerodynamic databases anchored to RANS fidelity at a fraction of the cost of direct evaluation.

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

An experimental investigation into the wave sources responsible for the noise generation mechanisms of supersonic jet noise and their mitigation using MVG nozzles is presented. Flow field measurements using PIV revealed that MVGs mitigate noise through two mechanisms; they generate internal oblique shock waves that weakens the shock cell, and they substantially increase the shear layer mixing and its entrainment of ambient fluid which reduces the length scales and velocities of the convecting coherent structures. In addition, time-resolved Schlieren visualizations were spectrally analyzed to decompose and reconstruct the hydrodynamic waves in the flow field and the generation process of the acoustic wave emission directly from the jet providing insights into the noise generation mechanism and their suppression by inducing the peak wave instabilities to shift to larger wavenumber values to reduce their acoustic emission efficiencies, which were confirmed by acoustic measurements. The findings from this investigation show direct visualization of the acoustic wave emission from the sources in the flow field. These waves have downstream components that are emitted from the modulation of the shear layer inducing spatial coherence of the turbulent vortical structures. This modulation is induced by the passing of the upstream acoustic waves along the shear layer from all shock cells synchronized as a phased array with regions of constructive and destructive interference patterns which steers the emitted acoustic radiation beams. The intense acoustic beam perturbs the shear layer and induces the formation of the internal trapped waves with phase velocities propagating upstream of the supersonic jet flow. Based on these findings, new noise generation mechanisms are proposed that cover various aspects of the physical mechanisms of jet noise components for the turbulent mixing noise, the broadband shock associated noise and the screech resonance tone, along with reduction and (open full item for complete abstract)

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

The integration of AI in autonomous vehicles has been rapidly expanding and has the potential to raise concerns about non-compliant or malicious actors. Predicting movements or strategies of these actors could provide a substantial advantage in the mitigation of such threats. In a simulated asteroids style game, capture of these actors closely resembles pursuit evasion problems in differential games. In this work, multiple evader control methods are mapped by an adaptable fuzzy modified potential field avoidance method trained via genetic algorithm. Evader routes are integrated and optimal interception points are determined by numerical methods or a fuzzy logic approach. Time delayed mines are then placed at the interception point to eliminate the evader. The fuzzy modified potential field has also been separately trained to produce highly effective avoidance within congested asteroid environments.

MS, University of Cincinnati, 0, Engineering and Applied Science: Aerospace Engineering

This study underlines the impact of the flow structures on the internal flow field through shape-transitioning ducts with global favorable pressure gradients and local adverse pressure gradients, local to the shape-transitioning geometries. Results are evaluated for convergence apropos of acquisition frequency. This thesis presents preliminary results of flow structure measurement by introducing the structures with a cylindrical bluff body in the cross flow. Structure transport through the two duct configurations studied includes the free jet of a convergent nozzle and through a shape-transitioning nozzle. Particle Image Velocimetry (PIV) was employed in data acquisition considering its substantial spatiotemporal resolution necessary. Findings show that the free jet results are characterized by high-velocity jets, detached velocity deficit region at the tailing edge of the cylinder, and strong velocity gradients due to the shear layers formed between the wake, the jets, and the ambient. On the contrary, flow through the shape transitioning or favorable pressure gradient (FPG) nozzle reflects a well-behaved flow with a low-velocity region attached to the cylinder in most cases. The outcome difference primarily stems from the velocity experienced at the cylinder in each case. An examination of convergence, considering the acquiring frequency of the flow field data, unveiled a weighty impact of acquisition frequency on the results of turbulent flow fields. The ensemble average of the results based on the mathematical computation using analytical methods in the time domain revealed an overall comparable trend in results with notable distinctions in the near wake region. Convergence dependence of results on flow essence emerged with a comparison of the running averages at a point within and outside the wake. In conclusion, it was established that a smaller subset of image pairs drawn from a universal set is ample for effectively capturing the physics of the flow fiel (open full item for complete abstract)

Doctor of Philosophy in Engineering, Cleveland State University, 2024, Washkewicz College of Engineering

Nonlinear hereditary inelastic deformation behavior can occur in many materials utilized at elevated service temperatures. This behavior can include creep, rate sensitivity, and plasticity. Accurate assessments of nonlinear stress and deformation behavior are important in predicting the operational life and overall performance of critical engineering systems. Inelastic constitutive models have been developed and deployed to meet these assessment needs. The models must predict nonlinear behavior under complex thermomechanical load paths. This includes capturing phenomena such as Bauschinger's effect, cyclic softening and hardening, stress relaxation, and ratcheting when present in high-temperature applications. This dissertation provides a literature review that details the development of inelastic constitutive modeling as it relates to polycrystalline materials. This review distinguishes between inelastic constitutive models that account for nonlinear behavior at the microstructural level, time independent classic plasticity models, and time-dependent unified models. Emphasis is placed on understanding the underlying theoretical framework for unified viscoplasticity models where creep and classical plasticity behavior are considered the result of applied boundary conditions instead of separable rates representing distinct physical mechanisms. This review also discusses recent topics in constitutive modeling that offer new techniques that bridge the gap between the microstructure and the continuum. Focus has been given to material science models that physically explain nonlinear behavior at the microstructural level. An understanding of material microstructure is always necessary in developing accurate multiaxial continuum-level constitutive models that characterize the responses of engineering components modeled with continuum-level perspective. Many forms of inelastic constitutive models are presented that include differential formulation (open full item for complete abstract)

Master of Science in Engineering Mechanics, Cleveland State University, 2024, Washkewicz College of Engineering

This paper presents a computational finite element analysis (FEA) focused on the utilization of shape memory alloy (SMA) interfaces as thermal expansion compensators for ductile positive coefficient of thermal expansion (CTE) materials such as Aluminum 6061-T6. The investigation delves into the efficacy of superelastic, one-way, and two-way shape memory effects in mitigating thermal expansion-induced stresses within engineering structures utilizing beam components. The research examines critical structural factors in a fixed beam system such as thermally induced internal stresses and buckling resilience at varying thermal loads. Computational simulation software from ANSYS Mechanical was calibrated to fit previous data from the literature on commercially available NiTi-based SMA properties. Comparing noninterface and SMA-interfaced beam structures, this study demonstrates the potential of SMAs to mitigate thermally induced stresses, thereby enhancing the structural integrity and longevity of engineering structures in thermal gradient environments. Furthermore, this paper proposes potential industries where the implementation of SMA interfaces could prove advantageous over current thermal compensating practices, including aerospace, optical, and civil engineering. This paper also introduces employing two-way shape memory alloys (TWSMAs) in thermal compensation by using computational and numerical analysis to showcase that TWSMAs response can be trained to perform similarly to materials with a negative thermal coefficient. By leveraging the unique property of trained TSMAs of the bidirectional shape memory effect, the aim was to demonstrate a second stress-free thermal state at an elevated temperature to increase the structure's buckling resilience. This research underscores the practical feasibility and performance of SMA interfaces as thermal expansion compensators, setting the stage for further exploration of advanced SMA technologies.

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Aerospace Engineering

A significant challenge to engine design is the development of combustion systems that meet increasingly strict efficiency, performance, and emissions demands. This pursuit often prompts using conditions at the limits of capability, dictating the need to expand the envelope of robust and reliable operation. The use of nanosecond-pulsed high-frequency discharges (NPHFDs) for ignition has attracted considerable attention because of their ability to produce active radicals and excited species, ultrafast gas heating effects, and unique hydrodynamic behavior. These characteristics are why NPHFDs have proven effective in extending ignition limits and reducing ignition times in quiescent, low-speed, and high-speed turbulent environments. Despite these observations, the community will benefit from additional research on NPHFDs to better understand their kinetics, hydrodynamics, and operational strengths and weaknesses compared to conventional exciter systems. The work within this dissertation provides insight into these topics, starting with results from a two-photon laser-induced fluorescence campaign that reports the spatio-temporal evolution of oxygen atom fluorescence produced from a nanosecond discharge. Results indicated that the evolution of the oxygen atom (O-atom) signal was heavily influenced by the discharge-induced flow field. This work was followed by an exploration of the unique hydrodynamics related to a train of nanosecond discharges, namely, discharge-induced jetting motion and the experimental conditions that maximize/minimize its influence. Overall, the jetting motion was bolstered by larger inter-electrode distances, higher pulse repetition frequencies (shorter inter-pulse times), and larger bursts of pulses. Increasing the bulk flow velocity did not eliminate the jetting motion but reoriented it in the bulk flow direction such that its spanwise magnitude decreased. With the unique attributes of NPHFDs known, a comparison between an NPHFD exciter system (open full item for complete abstract)

MS, Kent State University, 2024, College of Aeronautics and Engineering

Understanding thermal performance is essential to optimizing system performance, reducing damage, and enhancing overall reliability and safety, especially in high-powered heat generating applications. In the growing eVTOL (electric Vertical Take-Off and Landing) ecosystem, being able to provide a means to quantify and characterize the thermal performance of new propulsion platforms has resorted to complex, numerical solutions via commercial software. One reason for this is how thermal performance is affected by a phenomenon called thermal soak. Thermal soak is the sudden increase of internal component temperature due to terminating any forced convective cooling from a heat-producing system (i.e., landing and shutting down after hovering.) A more accessible thermal soak model was developed and explored with the aim of better understanding heat transfer properties of electric/hybrid motors under VTOL power conditions. The purpose of this thesis is to discover if thermal soak as a lumped parameter 2nd order system can be reliably modeled with defined damping ratios, natural frequencies, and initial conditions that are functions of system thermal parameters. Comparisons between the thermal soak model and experimental data from a multitude of eVTOL motor and propeller configurations at different power and ambient conditions exhibit this. The importance of this model lies in its predictive capability for evaluating thermal soak effects on mechanical components, especially in the initial stages of design or for developing generalized rules-of-thumb for new thermal systems. This contributes to the framework of an eHETR (eVTOL Hybrid Electro-Thermal Rotorcraft) model capable of simulating high-power (>100kW) electric/hybrid rotary-wing propulsion systems and the heat generation experienced during rotorcraft flight.

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Engineering

The development of next generation aircraft is trending towards more interconnected and highly multidisciplinary systems. To better support the design of these systems, an alternative approach to design is needed beyond traditional methods. An automated design approach by means of multidisciplinary design, analysis, and optimization (MDAO) offers the potential to enable aircraft concepts traditional designers may not have considered. However, the selection of objective function for optimization remains an ambiguous choice by the designer. To remove ambiguity from the choice of objective function, a universal measure of performance in the form of exergy and its destruction can be used. Through the quantity of exergy, typically disparate systems such as the force-based approach of aerodynamics can be compared in a one-to-one fashion to the energetic-based approach of a thermal or propulsion system. In this thesis, a high-fidelity approach for aerodynamic and thermo-mechanical exergy destruction evaluation and sensitivity analysis is provided to enable gradient-based design optimization. To arrive at the exergy destruction equations, a formal development of the entropy balance equation from the concavity property of entropy is presented. From the balance equations, the exergy destruction equations can be derived for arbitrary thermal and fluid processes. The aerodynamic exergy destruction functional is implemented in FUN3D and a rigorous verification effort is conducted demonstrating good functional agreement with test cases. Additionally, the discrete adjoint is implemented and demonstrates discrete agreement with complex-step derivatives. A series of trade studies are then conducted on the Generic Hypersonic Vehicle (GHV) to identify performance metrics of the vehicle. The thermal exergy destruction functional is implemented in MAST along with a series of verification cases for the functional and discrete adjoint demonstrating discrete agreement. A series of therm (open full item for complete abstract)

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Engineering

With the increasing interest in electric vertical takeoff and landing air vehicles and small-scale Unmanned Air Vehicles, many novel design concepts favor the fixed-pitch-propeller as the primary propulsion system due to its simplicity and reliability. This expands the application scenario of the fixed-pitch propeller from axial forward flight to edgewise flight conditions. The current study investigated the changes in its performance when operating at higher incidence angle conditions as well as the proximity effects of the propellers in these conditions. It is hypothesized that the propeller performance under various conditions and proximities can be reasonably predicted by modeling the changes in the inflow angle of the propeller. This hypothesis was tested using three major steps. First, a relationship between inflow angle, propeller inclination angle, and advance ratio was established using a series of experimental investigations. Second, this relationship was used to predict the performance of two propellers in tandem configuration with various horizontal and vertical offset distances. Third, the same model was used to predict the ceiling effect of the propeller at different incidence angles and advance ratios. All experiments were conducted at the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) Laboratory under its open jet configuration. Force-based experiments, flow visualization as well as phase-locked Particle Image Velocimetry (PIV) experiments were conducted for all investigations. The changes in propeller performance at various flight conditions were quantified and several normalization methods were successfully employed indicating the predictability of various propeller forces and moments. A novel propeller axial thrust prediction model was proposed considering the propeller performance as a summation of propeller-like components and wing-like component, with an overall error of less than 8.3%. Flow visualization and PIV results confirmed the (open full item for complete abstract)

Doctor of Philosophy (Ph.D.), University of Dayton, 2024, Engineering

Event-based pixel sensors asynchronously report changes in log-intensity in microsecond-order resolution. Its exceptional speed, cost effectiveness, and sparse event stream makes it an attractive imaging modality for particle tracking velocimetry. In this work, we propose a causal Kalman filter-based particle event velocimetry (KF-PEV). Using the Kalman filter model to track the events generated by the particles seeded in the flow medium, KF-PEV yields the linear least squares estimate of the particle track velocities corresponding to the flow vector field. KF-PEV processes events in a computationally efficient and streaming manner (i.e.~causal and iteratively updating). Our simulation-based benchmarking study with synthetic particle event data confirms that the proposed KF-PEV outperforms the conventional frame-based (FB) particle image/tracking velocimetry (PIV/PTV) as well as the state-of-the-art event-based (EB) particle velocimetry methods. In a real-world water tunnel event-based sensor data experiment performed on what we believe to be the widest field view ever reported, KF-PEV accurately predicted the expected flow field of the SD7003 wing, including details such as the lower velocity in the wake and the flow separation around the underside of an angled wing.

Master of Science (M.S.), University of Dayton, 2024, Aerospace Engineering

Recent advancements in battery technology have led to an increase in the development of electric Vertical Takeoff and Landing (eVTOL) vehicles, typically using electrically-powered propellers to generate both lift and thrust. These vehicles typically operate in low-altitude, and limited-space conditions in urban environments. Unsteady flows from building wakes or atmospheric boundary layer effects raise concern to the stability of eVTOL-capable aircraft under normal operating conditions and during transition from vertical to forward flight and vice-versa in population dense areas. Although all types of unsteady flows have been studied for decades, little has been published on the influence of unsteady flow on a propeller-wing system. Understanding of this system is crucial to ensuring the safety of not only the passengers of these VTOL aircraft, but also the safety of the public. Investigation into powered wing response to streamwise gust encounters was conducted through various propeller locations, angles of attack, reduced frequencies, and thrust levels. All experiments were run at the University of Dayton Low Speed Wind Tunnel (UD-LSWT) in its open-jet configuration. The shuttering system downstream of the test section consists of a set of rotating louvers that change angle to effectively change the blockage ratio of the wind tunnel. Different louver angles and actuation frequencies provide different velocities and reduced frequencies. Particle Image Velocimetry (PIV) was conducted on the freestream flow during actuation of the louvers to spatially characterize the angle of attack variation throughout the test section. The results from PIV were used to determine the optimal testing location and wing size for the test article. The wing was designed to be modular, accepting a number of different propeller Distribution Statement A: Approved for Public Release; Distribution is Unlimited. PA# AFRL-2024-2083 4 locations. Four total configurations were considered – (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Aerospace Engineering

Thrust vectoring (TV) is the ability to manipulate the directivity of the primary jet to provide a cross-stream force off the primary jet axis. TV can enable desirable flight regimes such as hyper-maneuverability and short/vertical take-off and landing. Modern conventional TV methods utilize a physical mechanism to mechanically deflect the jet flow and change the thrust direction. This method is both heavy and mechanically complex, especially for an axisymmetric jet. A novel approach to TV is explored in this paper by investigating localized arc filament plasma actuators' (LAFPAs) ability to impart a TV force on a subsonic, axisymmetric jet by attaching the flow to a radially expanding surface (termed “reaction surface”), at the jet exit. LAFPAs will be used to asymmetrically control the entrainment of the jet to provide a deflection of the jet via the conservation of momentum. The deflected jet will then attach to the reaction surface via the Coanda effect. The jet flow was interrogated at baseline and excited cases with a static pressure array located 0.75 jet diameters downstream of the actuators at 70% of the chord of the reaction surface and with cross-stream particle image velocimetry (PIV) located 3 jet diameters downstream of the actuators. Two jet Mach (Mj) values were assessed, Mj = 0.48 and 0.9. The results show that the LAFPAs create a repeatable and significant asymmetric pressure profile trend with respect to excitation frequency. In general, low excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force towards the active actuators, while high excitation frequencies provide an asymmetric azimuthal pressure profile that corresponds to a vectored thrust force away from the active actuators. Cross-stream PIV flow field measurements show that the asymmetry in the azimuthal pressure profile is not as significant as would be desirable for thrust-vectoring applications. However, the PIV results do show (open full item for complete abstract)

Doctor of Philosophy, The Ohio State University, 2024, Aerospace Engineering

A major challenge in the development of high-speed flight vehicles is understanding, managing, and controlling the impact of an extreme operating environment. Fluid-structural interactions (FSI) are an important and challenging concern due to need for optimal weight and multi-functional structures, juxtaposed with the possibility of catastrophic failure and degradation of vehicle performance. Conditions where strong coupling arises between compliant structures and multi-scale fluid dynamic features characteristic to the flight environment, such as turbulence, shock motions, and flow separation, are not sufficiently understood. This challenges \emph{a priori} model fidelity selection for accurate and efficient prediction of FSI, directly impacting development of high-speed vehicles. This dissertation seeks to address these open questions through studying the interaction between a high-speed, separating turbulent flow field and a compliant cantilever plate. The main features of the flow are separation at the end of the plate and reattachment on the downstream floor, which are modulated by shear layer instabilities and interaction with the cavity underneath the plate. Wall-resolved large eddy simulations (LES) are applied to capture interaction with the multi-scale flow field. Companions predictions are also made with unsteady Reynolds-averaged Navier-Stokes (URANS) and local piston theory (LPT) in order to contextualize the significance of interaction with the inherent flow unsteadiness. The interaction with the flow field is first examined through prescribed oscillations of the cantilever. The flow response to varying amplitude motions in the first bending mode as well as combined bending-torsional motion is explored. Here, the oscillation frequency is set to align with the characteristic low-frequency unsteadiness in the underside recirculation region. Then, the potential for energy transfer between high-frequency structural modes to the shear layer (open full item for complete abstract)

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Real world operational environments for uncrewed aerial systems are inherently dynamic and full of uncertainties. This presents significant challenges to the safety and reliability of autonomous precision landing systems for UAVs. This study focused on evaluating and improving upon the existing ArduPilot precision landing system. ATARI testing identified brittle areas within the precision landing architecture. The precision landing failsafe interacts with other failsafes, including the critical battery failsafe, which created a state where the ground station could not land the UAV. Motion capture testing demonstrated a testing method to obtain a measure of ground truth and assess UAV performance. Analysis showed precision landing performed within requirements and much better than GPS. Results also identified room for improvement in the relative position estimation. In response to the identified brittle behavior, new flight modes were created to successfully decouple precision landing from the LAND and RTL flight modes. Now there is the option to normal RTL or LAND while precision landing is enabled, preserving precision landing strictness. GCS can force the UAV to land in the event of precision landing failsafe. A fuzzy logic based risk assessment algorithm was developed and successfully tested with logged data from a real precision landing flight. This will be valuable in future integration with a new failsafe which to make real time go/no-go decisions to continue precision landing. This research not only underscores the high performance of ArduPilot's precision landing system, but added critical safety improvements and laid the foundation for further enhancements to UAV precision landing and operational reliability.

PhD, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Continuous control and monitoring of the gas turbine combustor wall is essential for preventing combustor liner from overheating which may significantly damage structural integrity and reduce overall lifespan. In the past half century combustor outlet temperature has risen from 1100 to 1850 K. The continuous increase of severity of operating conditions inside combustor demands for a temperature determination method whose operation and accuracy are not affected by ever rising temperature. Conventional methods such as thermocouples and thermographic phosphor are not only intrusive, but their operation is also either restricted by an upper temperature limit (thermocouple) or measurement accuracy significantly decreases with increasing temperature beyond a certain threshold (thermographic phosphor). In this paper a multi-wavelength pyrometry system is developed which provides a fast, minimally intrusive temperature determination of the combustor wall. This method does not require any prior knowledge of exact emissivity but of the functional relationship between emissivity and wavelength over the spectral region of interest. One of major problems of wall temperature measurement using a pyrometry in combustor is that the emission from the combustor wall is interfered by the emissions from molecular radicals existing in the flame such as CH* (~431nm), OH* (~308nm), CO2* (400-600 nm) in the visible range and major species such as H2O (1.4,1.9,2.7,6.3 um) and CO2 (2.7,4.3,15 um) in the infrared region. In this report, a combustor that is made of stainless steel and runs on natural gas and the spectrum of flame emission is measured to identify a proper wavelength range (650-800 nm) over which there exists minimal or no interference from flame emission with thermal radiation. Thermal radiation is measured within the mentioned spectral range with a spectrometer and camera assembly from the target spot on the combustor wall with temperatures ranging from 1000 to 1300K. Thermal (open full item for complete abstract)

Master of Science, The Ohio State University, 2024, Aerospace Engineering

The role of quartz in gas turbine hot section deposition was investigated by varying both its size and percent concentration in Air Force Research Lab test dust (AFRL-02). The size distributions of quartz tested were 0 – 3 μm, 0 – 10 μm (baseline), and 10 – 20 μm while percent concentration ranged from 0% to 100%. The experiments replicated a gas turbine effusion cooling circuit with a flow temperature of 894K and plate surface temperature of 1144K. Aerosolized AFRL-02 dust was delivered to the test article, and capture efficiency, hole capture efficiency, blockage per gram, normalized deposit height, and effective area were recorded. A quartz size distribution of 0 – 3 μm showed the greatest deposition while 10 – 20 μm consistently deposited the least. Varying percent concentration of quartz had less obvious trends. While at a size distribution of 10 – 20 μm, increasing quartz concentration decreased deposition in all four assessment parameters. For a size distribution of 0 – 3 μm, increasing quartz concentration originally decreased deposition until greatly increasing it past a concentration of 68%. Quartz has been identified as a predominantly erosive mineral to deposits, but results suggest the size distribution contributes to deposition at a rate greater than or equal to percent concentration. The following study elucidates the effects of both size and concentration of quartz in a heterogenous mineral blend.