Aerospace Engineering Commons^™

Evaluation Of Preferential Vaporization Characteristics Of Isolated Single Droplet Combustion In A Converging Channel, Claire Elizabeth Dixon

Theses and Dissertations

Preferential vaporization of isolated single droplets was evaluated in this study. A previously verified lab-scale experiment using flow acceleration to counteract the effects of buoyancy in a converging channel with a decreasing cross section was utilized to investigate the single isolated droplet combustion. The previous experimentation revealed differences between results and values predicted by a one-dimensional numerical simulation. To investigate if the observed differences were the result of turbulent flow and the development of a boundary layer within the channel, a model was designed and analyzed in Ansys Fluent.

The developed Ansys simulation indicated that turbulent flow and growth of …

Actuation And Sensing Applications Of Piezoelectric Transducers, Connor Griffin

Theses and Dissertations

Piezoelectric materials, defined by their ability to display a charge across their surface in response to mechanical strain, are great for use in actuation and sensing applications. Actuation applications include acoustic devices, motors and vibration damping while sensing applications include pressure sensors, medical devices, energy harvesting and structural health monitoring (SHM). The use of piezoelectric actuation and sensing across the lifecycle of aerospace metals is currently an expanding field with use cases beginning with the manufacturing process and ending with SHM.

The research presented in this thesis had three goals: (i) to develop methods for implementation of piezoelectric actuation in …

Towards An Understanding Of The Thermodynamic Properties Of Crtao4: A Computational Perspective, Tanner B. Gordon

Theses and Dissertations

Materials that can withstand higher temperatures are paramount for next-generation aircraft design. Hypersonic capabilities and jet-turbine engines operate in extreme environments. Choosing materials that have high thermal stability and oxidation resistance for these applications can increase engine efficiency, reduce size, weight and power (SWaP), and increase the maneuverability of the aircraft. The mixed oxide CrTaO₄ has been experimentally observed to significantly contribute to oxidation resistance at high temperatures. However, and despite its significance, its properties remain largely unknown. This work explores the thermal properties of this material from a multi-scale approach, by obtaining an accurate description of the thermodynamics …

Design Of A Miniaturized Cubesat Tt&C Patch Antenna, Thomas A. Butterick

Theses and Dissertations

This effort explored the design of miniaturized rectangular microstrip patch antennas for application as a telemetry, tracking, and control (TT&C) on a CubeSat. The motivation for this research was the Grissom-P CubeSat mission planned by AFIT. The TT&C antenna selected for the mission exceeded the allotted size by over a factor of two. The studies performed included analyses of simply reducing aperture size, altering substrate permittivity, and layered approaches to antenna miniaturization. The primary approach to miniaturization was based on a virtually shorted patch antenna. Other approaches included an edge-shorted, slotted patch and the use of corner truncations for improved …

Magnetic Anomaly Mapping For Navigation, Luke T. Bergeron

Theses and Dissertations

Magnetic navigation (MagNav) has the potential to provide a global form of navigation that uses magnetic measurements of the Earth’s anomaly magnetic field and compares those measurements to a magnetic anomaly map in order to determine the user’s position. Widespread use of MagNav will require a database of fully-sampled, low-altitude magnetic anomaly maps. Existing magnetic anomaly map databases usually come from under- or poorly-sampled surveys. In this work, we provide an easy to follow MagNav anomaly map generation framework and set of survey collection metrics/requirements in an effort to help facilitate and standardize the creation of such a database. We …

Belief Space Planning For Alternative Navigation In Gnss-Denied Environments, Timothy I. Machin

Theses and Dissertations

Robust alternative navigation for autonomous agents becomes critical without reliable GNSS. Autonomous agents utilize measurement updates to constrain uncertainty. Belief space planning builds graph structures of beliefs within environments based on probable paths, agent and measurement models, and information of the environment. The Rapidly-exploring Random Alt-Nav Belief Graph (RRBANG) algorithm leverages stochastic filtering to implement a range of alt-nav measurement capabilities for robust navigation in GNSS-denied environments.

Robust Feature Matching For Visual-Based Aerial Navigation Using Registered Imagery, Luis Montenegro

Theses and Dissertations

This work leverages the SIFT detector along with known robust feature matching techniques for vision-aided sUAS navigation solutions. The proposed algorithm focuses on a sufficient number of features extracted, their quality and their distribution.

Atmospheric Polarization And Solar Position As Kalman Updates To A Navigation Solution, Thomas J. Wheeler

Theses and Dissertations

Simulation and physical testing of a sensor that measures relative position of the Sun and polarization of light in the atmosphere as a navigational aid in a Kalman filter.

Lunar Search And Rescue: The Next Step For Human Spaceflight Recovery, Benjamin J. Johnis

Theses and Dissertations

Humans return to the Moon in 2024 under the NASA Artemis mission. Commercial space explorations are rapidly expanding. The sudden increase of human spaceflight calls for increased emphasis on space rescue. These revelations drove an AFRL/AFIT capability gap assessment to provide specific proposals for a modern space rescue program guided by Transaction Cost Economics Theory. The mission analysis arms USSPACECOM and NASA to coordinate an interagency approach to Lunar Search and Rescue, positioning America to compete in the new space race. The strategic consequences of failing to act could fundamentally jeopardize American leadership in space.

Concept Of Operations Of Cislunar Mirror Satellites To Provide Augmented Lighting Of Dim Space-Based Objects, Alec E. Cook

Theses and Dissertations

The imaging and inspection of Resident Space Objects (RSOs) is an increasingly important mission as space-faring nations and commercial enterprises alike seek to develop means to repair and refuel spacecraft, as well as de-orbit RSOs to reduce orbital debris. Lighting conditions are not always advantageous for an imaging/inspection or repair/refuel spacecraft; therefore, the use of mirror spacecraft to reflect solar energy is proposed to illuminate dimly lit RSOs. The present research investigates the efficacy of space-based reflectors at examining spacecraft in the cislunar environment. Specific assessments include target spacecraft in geosynchronous Earth orbit and periodic orbits around selected Lagrange points, …

Experimental And Computational Bearing Strength Of Fiber Metal Laminate With And Without Film Adhesive, Christopher L. Bellanova Jr.

Theses and Dissertations

This research characterized the performance of a fiber metal laminate composed of carbon fiber and stainless steel without film adhesive and compared it to a similar, previously tested, fiber metal laminate including film adhesive. Removal of the adhesive layers reduced the localized thickness, simplified manufacturing, and allowed for a 20% increase in foil thickness. Quasi-static testing was conducted in double shear, single shear protruding, and single shear countersunk configurations. The results were compared to adhesive hybrid and control samples. To study the affects of bolt tension, samples at low torque in double shear were also tested. Progressive failure samples revealed …

Estimation Of Optimal Flight Trajectory In A Total Power Loss Scenario Using Proximal Policy Optimization, Eidahn Eliash

Theses and Dissertations

Recent research has been conducted in using deep reinforcement learning algorithms to generate closed form optimal control laws for helicopters in power loss scenarios. The control laws could allow for design of various cockpit visual pilot aids if proven successful. Such pilot aids are predicted to reduce pilot workload during execution of an emergency powerless landing, and to overall increase the probability of landing safely in such an event. The proposed topic discusses the use of the PPO algorithm in order to find an optimal control policy for a helicopter in a total power loss emergency landing scenario. The task …

Suitability Of Earth-Moon Triangular Lagrange Point Orbits For Space Situational Awareness, Eric P. Burkhart

Theses and Dissertations

The second space race is looming on the horizon, and the Moon is again at center stage. All major space fairing nations have plans for future Lunar exploration, but this time with plans to stay. NASA’s Artemis program plans to put humans back on the Moon in 2025 and establish a Lunar base on the South pole in the 2030s. Meanwhile, China has landed a rover on the far side of the moon with a communications relay satellite in a halo orbit around the L2 Lagrange point, and partnered with Russia to build a Lunar research station on the Lunar …

Gaseous Fuel Combustion In A Small Turbojet, Katherine A. Ashton

Theses and Dissertations

This project set out to test the suitability of natural gas as an aviation fuel by comparing how a small turbojet performed when run on traditional jet fuel versus methane. A JetCat P400, originally designed for jet fuel, was modified to run on methane. The modifications made did not succeed at getting the engine to run at normal operating speed on methane, but did get the engine to run at normal operating speeds using ethylene and ethane. It was determined a fuel and air mixing problem was hindering the engine performance when run on methane Future studies improving the fuel …

Overall Effectiveness Superposition Theory For A Film Cooled Leading Edge, Bailey W. Hopkins

Theses and Dissertations

Film cooling experimentation traditionally reports on the cooling performance of specialty-crafted cooling holes at various angles and array patterns. This is repeated across a variety of model geometries in an effort to provide as much information to the turbine blade designer. While this extensive database of cooling performance is helpful, its true value is found in the designer’s ability to effectively superpose the results on top of each other. One technique for predicting the performance of multiple coolant sources is film cooling superposition theory. This analytical model was employed classically by characterizing the adiabatic effectiveness across a model’s surface; however, …

Performance Analysis And Recommended Improvements Of A Cubesat Resistojet, Alexander M. Petrocelli

Theses and Dissertations

A small resistojet design was evaluated for its current performance and assessed for design and operational improvements. This resistojet is designed to operate on AFIT CubeSats with the intent of providing 100-200 mN of thrust at a specific impulse between 66-104 seconds. Using previously collected data and studies conducted on the design, analysis was performed to determine the current performance of this first-generation design. This provided a starting point for performance analysis over a variety of operational temperatures and pressures. This process was conducted for various heat exchanger path lengths of both the current design and two adapted path geometries. …

Investigation Of Hypersonic Near-Wake Relaminarization Over A 7 Degree Half-Angle Cone, Jesse L. Roberts

Theses and Dissertations

To investigate the potential for relaminarization in the near-wake of a 7-degree half-angle cone, a series of hypersonic wake experiments were conducted in the Air Force Research Laboratory Mach 6.1 Ludwieg tube. Relaminarization is a spatial phenomenon that occurs when a turbulent flow reverts to a laminar-like state at a downstream location, where turbulent fluctuations negligibly contribute to average flow properties. Although relaminarization has been documented in subsonic and supersonic flows, the current body of knowledge related to the occurrence of, and mechanisms that drive, relaminarization at hypersonic speeds is sparse. Measurements were obtained across a range of freestream unit …

Shock Induced Trailing Edge Separation Effect On F-16 Limit-Cycle Oscillation, Eric D. Stubblefield

Theses and Dissertations

No abstract provided.

Mechanical Properties And Performance Of A Novel Nano-Engineered Unitized Composite With Quasi-Isotropic Layup, Brian Matthew Pudlo

Theses and Dissertations

Carbon nanotubes (CNTs) exhibit outstanding mechanical, electrical, and thermal properties, but are a challenge to effectively implement into macroscopic composites for aerospace applications. This research investigates the mechanical properties and performance of a newly developed hybrid NanoStitch composite, alongside a control polymer matrix composite, at room temperature. Both composite material systems investigated in this work have quasi-isotropic layup. Monotonic tension-tofailure, tension-tension fatigue, and creep tests were performed to characterize the performance of the composites under cyclic and sustained loading. Experimental results obtained for the quasi-isotropic NanoStitch composite were compared to those obtained for the quasi-isotropic control composite. The properties and …

Debris Survivability Study For Mega-Constellation Architectures, Joseph C. Canoy

Theses and Dissertations

The analysis for the overall theoretical debris survivabilty of mega-constellation architectures, with an emphasis on space-based ballistic missile defense constellation (SB-BMD), is explored via three extensive different Monte Carlo simulations: preliminary analysis of low Earth Orbit (LEO) mega-constellation survivabilty following a fragmentation event within the constellation, analysis of LEO mega-constellation survivability with a fragmentation event occurring on a satellite performing a maneuver to insert itself within the constellation, and the analysis of LEO mega-constellation survivabilty after a fragmentation event resulting from the destruction of a missile. The LEO mega-constellations represent the SB-BMD constellation. The first two analysis sections will include …

Direct Collocation Methods For Comparison Of Aerothermodynamic Models Effect On Hypersonic Trajectory Optimization By The Process Of Continuation, Noor K. Khan

Theses and Dissertations

An algorithm was created to optimize trajectories of hypersonic glide vehicles with selected cost functions by applying the process of continuation to direct orthogonal collocation methods. The trajectory was optimized to maximize the range of launch position given a fixed terminal location. The hypersonic glide vehicle system dynamics were modeled with three-dimensional, three degree of freedom equations of motion assuming no thrust and a non-rotating Earth with the control as bank angle. Three aerothermodynamic models were compared when input as path constraints to calculate the stagnation point heating rate at the nose as well as integrated for heat load. Use …

Characterizing Jet Interaction Effects On A Cone In Mach 3.9 Flow, Titus J. Lee

Theses and Dissertations

Although jet interaction in the context of attitude control for aircraft and air weapons have been investigated for a variety of conditions and geometries, the knowledge base for their use with hypersonic vehicles is far more limited. The objective of the present investigation is to characterize the jet interaction effects in a Mach 3.9 freestream in the AFIT Small Supersonic Wind Tunnel using schlieren flow visualization and a 6-degree of freedom balance. A 7° aluminum cone was attached to the balance while air was injected through a stainless-steel tube, which was separately supported without any contact with the cone body …

Optimal Gyroid Infill For Space Launch, Jose R. Lopez Cordell

Theses and Dissertations

This research characterizes the optimal gyroid infill design for the 1st frequency response of composite sandwich panels. Structural performance may be improved by designing the gyroid infill within the sandwich panel to have a 1st mode resonance frequency above typical launch vehicle vibrations. Ensuring a component generates a natural frequency response above a designed threshold is mandatory for space launch systems to prevent damage. The gyroid, a Triply Periodic Minimal Surface (TPMS), has the potential to provide close to isotropic stiffness in the principal axes with a minimal amount of material, making it an attractive choice for this application. This …

Detonation Confinement In A Second-Generation Radial Rotating Engine, John T. Ursino

Theses and Dissertations

In recent years, Rotating Detonation Engines (RDEs) have been coupled with turbomachinery to harness the benefits of detonative combustion. A novel type of RDE, referred to as the disk or Radial RDE (RRDE), has been developed in pursuit of length and weight savings compared to a traditional annular flow RDE. This design includes a disk-shaped device within which reactants flow from the outer radius, detonate, and exit the inner radius. In this paper several modifications have been made to a previously tested RRDE to address issues that arose with the original design. The combustion chamber diameter has been increased to …

Development Of Novel Turbomachinery Manufacturing Methods, Timothy P. Winkler

Theses and Dissertations

Compact turbine engines are of increasing interest as a means of propulsion for small, lightweight, low cost, unmanned aerial systems. This study looks to leverage advancements in novel manufacturing technology to produce turbomachinery components while simultaneously reducing costs and manufacturing time. To determine the feasibility of drop-in replacements for stock components this study focused on several research areas. This included materials research on both polymer-reinforced and ceramic materials, specimen tensile testing to determine temperature-dependent material properties, finite element analysis of multiple candidate materials, design and fabrication of a spin test rig, and physical spin testing of manufactured components to predict …

Additively Manufactured Lenses For Modulating Guided Waves In Laminated Composites, Hajar Righi

Theses and Dissertations

Composite materials have increasingly been used as an alternative to metals and other isotropic materials for primary structural components in aerospace industries. Unlike traditional isotropic materials, composite materials are known to have complex internal microstructures. Therefore, it is essential to develop methods for the inspection, evaluation, and monitoring of composite materials. Ultrasonic-guided waves and, more precisely, Lamb waves have proven to be an efficient and accurate technique for the non-destructive testing. Since guided waves are dispersive and multimodal, it is important to develop a practical method to manipulate Lamb waves to achieve better structural health monitoring and non-destructive inspection results. …

Quasi 1d Modelling Of A Scramjet Engine Cycle Using Heiser-Pratt Approach, Asmaa Chakir

Theses and Dissertations

Scramjet engines are key for sustained hypersonic flights. Analytic models play a critical role in the preliminary design of a scramjet engine configuration. The objective of this research is to develop and validate a quasi-1D model for the scramjet engine encompassing inlet, isolator and combustor, to evaluate the impact of flight conditions and design parameters on the engine functionality. The model is developed assuming isentropic flow in the inlet with a single turn; modified Fanno-flow equations in the isolator that account for the area change of the core flow; and the combustor is modeled using Heiser-Pratt equations accounting for the …

Analysis Of Proposed Active Radiation Shielding Design Concept For Spacecraft, Claire Mechmann

Theses and Dissertations

A need exists to protect the crew of interplanetary spacecraft from lethal doses of Galactic Cosmic Radiation (GCR) and Solar Energetic Particles (SEPs). As plans progress to send humans beyond lower Earth orbit (LEO) and outside of Earth’s protective magnetosphere, agencies involved in this endeavor find themselves confronted with the obstacle of shielding the crew from this harmful radiation. A proposed active shielding concept design has been suggested, utilizing charged dielectric capacitors to deflect incoming charged particles. This analysis will examine the feasibility of the proposed design and offer potential materials useful for application. The results should prove informative for …

Stress-Based Topology Optimization Of Pi Preform-Bonded Composite Laminate Structure, Iwan Broodryk

Theses and Dissertations

The purpose of this work is to explore the stress-based topology optimization of structure that utilizes laminated composites and 3D woven Pi preform joints. Simple geometry, loading, and boundary conditions are considered. At a finite element level, an aggregate stress ratio is developed for Pi joint and acreage laminate elements. A basic descent method of moving asymptotes (BDMMA) algorithm is created to solve all optimization problems. Topology results for two different stress-based formulations and a compliance minimization problem are compared, followed by an in-depth analysis at a Pi joint and laminate level.

Accelerated Aging Of Adhesively Bonded Composite Joints For Use In Material Screening And Selection During Development: A Review And Case Study, Marie Danielle Flanigan

Theses and Dissertations

Adhesively bonded structures are used in many high-tech industries such as aerospace, automotive, and defense. The application of these joints using composite adherends has increased in recent years because of improved strength-to-weight ratio, design flexibility, and lower concern for corrosion. Quality acceptance of these structures largely depends on reliability and durability which includes influence of environmental service conditions on long-term behavior. Characterization of long-term behavior presents a difficult challenge to those involved in material selection and design due to the long service life of the joint compared to the development time available and complexity of the degradation mechanisms. Therefore, different …