Aerospace Engineering Commons^™

A Computational Fluid Dynamic Analysis Of Oxyacetylene Combustion Flow For Use In Material Response Boundary Conditions, Craig Meade

Theses and Dissertations--Mechanical Engineering

Oxyacetylene torches are used in the aerospace industry and research to test thermal protection system materials (TPS) due to their high flame temperatures and high heat flux capabilities. The purpose of this work is to determine a combustion model to accurately simulate the high temperature flow of an oxyacetylene torch. The flow conditions around a sample material can then be used as boundary conditions when modeling TPS material response. Two separate combustion models with equilibrium chemistry were investigated using ANSYS Fluent™; the Eddy-Dissipation Model, and the Partially Premixed model.The results of this study are compared to existing experiments for validation.

Stratospheric Glider Measurements Of Atmospheric Parameters, Anisa Haghighi

Theses and Dissertations--Mechanical Engineering

In June 2021 a series of high altitude flights were conducted in Spaceport America, NM, using a balloon launched Uncrewed Aircraft System (UAS) to assess its capability to conduct measurements of various atmospheric properties and study turbulence in the troposphere and lower stratosphere. This UAS descends using an automated flight trajectory. The instruments aboard included a NASA-developed infrasonic microphone to evaluate its remote turbulence detection capabilities and a five-hole probe capable of measuring the in situ wind vector. Also on board were temperature, humidity and wind profile sensors. This document focuses on the atmospheric properties measured at high altitudes, the …

Impact Of Spallation And Internal Radiation On Fibrous Ablative Materials, Raghava Sai Chaitanya Davuluri

Theses and Dissertations--Mechanical Engineering

Space vehicles are equipped with Thermal Protection Systems (TPS) that encounter high heat rates and protect the payload while entering a planetary atmosphere. For most missions that interest NASA, ablative materials are used as TPS. These materials undergo several mass and energy transfer mechanisms to absorb intense heat. The size and construction of the TPS are based on the composition of the planetary atmosphere and the impact of various ablative mechanisms on the flow field and the material. Therefore, it is essential to quantify the rates of different ablative phenomena to model TPS accurately. In this work, the impact of …

A Decoupled Engineering Methodology For Accurate Prediction Of Ablative Surface Boundary Conditions In Thermal Protection Systems, Justin Cooper

Theses and Dissertations--Mechanical Engineering

The main objective of the present work is to demonstrate a method for prediction of aerothermal environments in the engineering design of hypersonic vehicles as an alternative to the current heritage method. Flat plate and stagnation point boundary layer theory require multiple assumptions to establish the current engineering paradigm. Chief among these assumptions is the similarity between mass and heat transfer. Origins of these assumptions are demonstrated and their relationship to conservative engineering design is analyzed, as well as conditions where they possibly break down. An alternative approach for assessing aerothermal environments from the fluid domain is presented, which permits …

Formation Control With Bounded Controls And Collision Avoidance: Theory And Application To Quadrotor Unmanned Air Vehicles, Zachary S. Lippay

Theses and Dissertations--Mechanical Engineering

This dissertation presents new results on multi-agent formation control and applies the new control algorithms to quadrotor unmanned air vehicles. First, this dissertation presents a formation control algorithm for double-integrator agents, where the formation is time varying and the agents’ controls satisfy a priori bounds (e.g., the controls accommodate actuator saturation). The main analytic results provide sufficient conditions such that all agents converge to the desired time-varying relative positions with one another and the leader, and have a priori bounded controls (if applicable). We also present results from rotorcraft experiments that demonstrate the algorithm with time-varying formations and bounded controls. …

Numerical And Scaling Study On Application Of Inkjet Technology To Automotive Coating, Masoud Arabghahestani Dr.

Theses and Dissertations--Mechanical Engineering

A thorough literature review identified lack of precision control over quality of droplets generated by the currently available industrial sprayers and a growing need for higher quality droplets in the coating industry. Particularly, lack of knowledge and understanding in continuous inkjets (CIJ) and drop-on-demand (DOD) technologies is identified as significant. Motivated by these needs, this dissertation is dedicated to computational fluid dynamics (CFD) and scaling studies to improve existing inkjet technologies and develop new designs of efficient coating with single and/or multiple piezoelectric sensors to produce on-demand droplets. This dissertation study aims at developing a new DOD type coating technology, …

Formation Control With Collision Avoidance For Fixed-Wing Unmanned Air Vehicles With Speed Constraints, Christopher Heintz

Theses and Dissertations--Mechanical Engineering

Advances in the miniaturization of powerful electronic components and motors, the democratization of global navigation satellite systems (GNSS), and improvements in the performance, safety, and cost in lithium batteries has led to the proliferation of small and relatively inexpensive unmanned aerial vehicles (UAVs). Many of these UAVs are of the multi-rotor design, however, fixed-wing designs are often more efficient than rotary-wing aircraft, leading to a reduction in the power required for a UAV of a given mass to stay airborne. Autonomous cooperation between multiple UAVs would enable them to complete objectives that would be difficult or impossible for a single …

Kentucky Re-Entry Universal Payload System (Krups): Hypersonic Re-Entry Flight, John Daniel Schmidt

Theses and Dissertations--Mechanical Engineering

The Kentucky Re-entry Universal Payload System (KRUPS) is a small capsule designed as a technology testbed for re-entry experiments. For its first incarnation, KRUPS has been designed to test Thermal Protection Systems (TPS) and instruments in re-entry flights. Because of the unique environment a vehicle undergoes during re-entry, there is a high-demand for experimental data from re-entry experiments. KRUPS has been developed at the University of Kentucky (UK) over the past seven years to meet this demand. After completing sub-orbital campaigns, the first KRUPS hypersonic re-entry mission was attempted. The mission involved building three 11-inch diameter capsules each outfitted with …

In-Situ Characterization Of Burr Formation In Finish Machining Of Inconel 718, Hamzah M. Zannoun

Theses and Dissertations--Mechanical Engineering

One of the undesirable byproducts that occur during the machining process is the development of burrs, which are defined as rough excess material that forms around the geometric discontinuities of a part. Burrs are especially problematic because they have negative impacts across the triple bottom line: economic, environmental, societal. For one, they are expensive to remove because the deburring process is entirely manual and requires skill. Further, burr material is typically discarded which is adding to the already mounting waste generated from machining such as in coolant and chip disposal. Lastly, there are many societal implications, such as operator injury …

Experimental Investigation Of Roughness And Blowing Effects Over Ablator-Like Surfaces, Colby Borchetta

Theses and Dissertations--Mechanical Engineering

Two separate experiments using PIV were carried out to investigate the effects of
roughness and blowing over surfaces geometrically similar to ablation materials used for atmospheric re-entry. The first, water tunnel experiments, employed a dimpled surface similar to AVCOAT, while the second set was completed in a wind tunnel with a material similar to PICA. For the first set, the flow with blowing becomes destabilized, and more disorganized. The blowing disrupts the relatively simple vorticity shedding process and significantly modifies momentum transport via interaction of detached structures. Flow structure and their modifications were examined with a sPOD analysis. The focus …

Modeling Thin Layers In Material Response Solvers, Christen Setters

Theses and Dissertations--Mechanical Engineering

Thermal Protection Systems (TPS) are a necessary component for atmospheric entry. Most TPS contain thin layers of various materials such as ceramic coatings, pore sealers and bonding agents. When modeling TPS, these thin layers are often neglected due to the difference in scale between the TPS (centimeters) and the thin layers (micrometers). In this study, a volume-averaging flux-conservation method is implemented in the governing equations of a finite volume material response code. The model proposes the addition of a volume and area fraction coefficient which utilizes a weighted-averaging between the amount of thin layer and heat shield material in a …

Turbulence Suppression In An Axially Rotating Pipe, Alyn J. Smith

Theses and Dissertations--Mechanical Engineering

The phenomenon of turbulence suppression in a rotating pipe flow system has been well documented by past research and experimentation. Despite this, the methods that drive this phenomenon have not yet been effectively characterized, especially at higher Reynolds numbers. While many experiments have been performed to better understand swirling turbulent pipe flow, a difficulty that arises is how to test for high levels of rotation without reducing the Reynolds number. This thesis documents the design and construction of a new pressurized pipe flow system at the University of Kentucky aimed at achieving high Reynolds numbers without causing a reduction in …

Electromagnetic Formation Control Using Frequency Multiplexing, Zahra Abbasi

Theses and Dissertations--Mechanical Engineering

This dissertation addresses control of relative positions and orientations of formation flying satellites using magnetic interactions. Electromagnetic formation flight (EMFF) is implemented, in which each satellite is equipped with a set of electromagnetic coils to generate an electromagnetic field. Traditional EMFF technique applies DC magnetic fields which lead to a nonlinear and highly coupled formation dynamics that allow for only position or orientation control of the satellites. We present a new frequency multiplexing method, which is a technique that uses multi-frequency sinusoidal controls, to approximately decouple the formation dynamics and to provide enough controls for both position and orientation control. …

The Kentucky Re-Entry Universal Payload System (Krups): Orbital Flight, James Tyler Nichols

Theses and Dissertations--Mechanical Engineering

Due to the uniqueness of atmospheric entry environments, ground facilities cannot accurately replicate re-entry conditions. Consequently, scientists primarily rely on numerical models to predict these conditions and inform Thermal Protection System (TPS) designs. These models often lack flight validation, which is necessary for increasing their fidelity. Thus, there is a substantial need to obtain such data to advance modeling capabilities.

The Kentucky Re-entry Universal Payload System (KRUPS) is an adaptable test-bed for scientific experimentation with initial application to TPS. This vehicle was designed at the University of Kentucky to serve as an inexpensive means of obtaining validation data to enhance …

Measurements Of Wind Turbine Wake Evolution And Trajectory During Morning Boundary Layer Transition And Under Wake Steering Conditions Via Unmanned Aerial Vehicles, Stewart Nelson

Theses and Dissertations--Mechanical Engineering

In July of 2019, a flight campaign was conducted using semi-autonomous Unmanned Aerial Vehicles (UAVs) at the Port Alma Kruger Energy wind farm in Ontario, Canada, to study various aspects of wind turbine wake evolution. Horizontal transects across the wakes were measured using modified fixed-wing aircraft fitted with a five-hole probe to measure the wind velocity vector. Reference boundary layer conditions were measured by an octocopter with an assortment of mounted sensors flying vertical profiles upstream of the turbines. Three experiments were conducted during the campaign, which consisted of a study on wake behavior during the morning boundary layer transition, …

Attitude Control And Consensus On So(3) Using Sinusoids: Theory And Application To Small Satellites, Roshan Anandrao Chavan

Theses and Dissertations--Mechanical Engineering

We present and analyze kinematic-level and dynamic-level feedback control algorithms for single agent attitude control and multi-agent attitude consensus on SO(3). The kinematic-level algorithms yield attitude feedback controls that are piecewise-continuous sinusoidal angular velocities. The dynamic-level algorithms yield attitude feedback controls that are relative angles of rotational-mass actuators, which are continuous but only piecewise continuously differentiable sinusoids. Furthermore, the dynamic-level algorithms are designed to accommodate actuator stroke constraint. We present application of the dynamic-level control algorithms to attitude control and consensus of small-satellites.

A Computational Fluid-Structure Interaction Method For Simulating Supersonic Parachute Inflation, Jonathan Boustani

Theses and Dissertations--Mechanical Engineering

Following the successful landing of the Curiosity rover on the Martian surface in 2012, NASA/JPL conducted the low-density supersonic decelerator (LDSD) missions to develop large diameter parachutes to land the increasingly heavier payloads being sent to the Martian surface. Unexpectedly, both of the tested parachutes failed far below their design loads. It became clear that there was an inability to model and predict loads that occur during supersonic parachute inflation. In this dissertation, a new computational method that was developed to provide NASA with the capability to simulate supersonic parachute inflation is presented and validated. The method considers the loose …

Structural Optimization Of Space Transit Vehicle Concept, Hercules, James Philip Rogers

Theses and Dissertations--Mechanical Engineering

STRUCTURAL OPTIMIZATION OF SPACE TRANSIT VEHICLE CONCEPT, HERCULES:

A COMPARATIVE STUDY OF STRUCTURAL OPTIONS

Hercules is a vehicle concept developed by NASA Langley's Vehicle Analysis Branch to satisfy the need for sustainable transit between Earth, the moon, and Mars. Hercules features unprecedented abort capabilities and mission flexibility to aid in NASA's Mars campaign. By utilizing modern software to perform structural analysis and optimization for a large selection of stiffened panel concepts, beam concepts, and materials trends in the structural optimization emerge. These trends will be invaluable for the design of future spacecraft needed to fulfill similar roles.

The structural optimization …

Development Of Universal Solver For High Enthalpy Flows Through Ablative Materials, Umran Duzel

Theses and Dissertations--Mechanical Engineering

Atmospheric entry occurs at very high speeds which produces high temperature around the vehicle. Entry vehicles are thus equipped with Thermal Protection Systems which are usually made of ablative materials. This dissertation presents a new solver that models the atmospheric entry environment and the thermal protection systems. In this approach, both the external flow and the porous heat shield are solved using the same computational domain. The new solver uses the Volume Averaged Navier-Stokes Equations adapted for hypersonic non-equilibrium flow, and is thus valid for both domains. The code is verified using analytical problems, set of benchmarks and also a …

Influence Of Size Effects On Surface Generation During Finish Machining And Surface Integrity In Ti-6al-4v, Ian S. Brown

Theses and Dissertations--Mechanical Engineering

Finish machining is an essential manufacturing process that is used to enhance the mechanical characteristics of critical components. The deformation that occurs at the tool and workpiece interface in finish machining significantly affects a host of component properties, commonly referred to as “surface integrity” properties. Surface roughness is a machining deformation-affected characteristic that is of high relevance in contemporary manufacturing. However, over recent decades it has been made clear that the material properties of the deformed surface layers are relevant to component performance as well. Predicting the overall surface quality of a machined component is of great relevance to the …

Flame Stabilization Of A Premixed Jet In Vitiated Coflow, Tyler Owens

Theses and Dissertations--Mechanical Engineering

Premixed staged combustion in gas turbine engines can reduce emissions by lowering peak flame temperatures but can also lead to different stability characteristics when compared to traditional combustors. High pressure ratio and subsequently high temperatures can lead to conditions suitable for both autoignition and premixed flame propagation in an environment where spatial fuel/air variations are present.

An experimental facility which issues a premixed jet into a coflowing vitiated mixture was studied to examine the stability behavior, resulting in a lifted flame. The effective ignition delay observed flame was much greater than homogeneous ignition delay calculations for the same conditions. It …

Carbon Oxidation At The Atomic Level: A Computational Study On Oxidative Graphene Etching And Pitting Of Graphitic Carbon Surfaces, Simon Schmitt

Theses and Dissertations--Mechanical Engineering

In order to understand the oxidation of solid carbon materials by oxygen-containing gases, carbon oxidation has to be studied on the atomic level where the surface reactions occur. Graphene and graphite are etched by oxygen to form characteristic pits that are scattered across the material surface, and pitting in turn leads to microstructural changes that determine the macroscopic oxidation behavior. While this is a well-documented phenomenon, it is heretofore poorly understood due to the notorious difficulty of experiments and a lack of comprehensive computational studies. The main objective of the present work is the development of a computational framework from …

Single-Degree-Of-Freedom Experiments Demonstrating Electromagnetic Formation Flying For Small Satellite Swarms Using Piecewise-Sinusoidal Controls, Ajin Sunny

Theses and Dissertations--Mechanical Engineering

This thesis presents a decentralized electromagnetic formation flying (EMFF) control method using frequency-multiplexed sinusoidal control signals. We demonstrate the EMFF control approach in open-loop and closed-loop control experiments using a single-degree-of-freedom testbed with an electromagnetic actuation system (EAS). The EAS sense the relative position and velocity between satellites and implement a frequency-multiplexed sinusoidal control signal. We use a laser-rangefinder device to capture the relative position and an ARM-based microcontroller to implement the closed-loop control algorithm. We custom-design and build the EAS that implements the formation control in one dimension. The experimental results in this thesis demonstrate the feasibility of the …

Enhanced Surface Integrity With Thermally Stable Residual Stress Fields And Nanostructures In Cryogenic Processing Of Titanium Alloy Ti-6al-4v, James R. Caudill

Theses and Dissertations--Mechanical Engineering

Burnishing is a chipless finishing process used to improve surface integrity by severe plastic deformation (SPD) of surface asperities. As surface integrity in large measure defines the functional performance and fatigue life of aerospace alloys, burnishing is thus a means of increasing the fatigue life of critical components, such as turbine and compressor blades in gas turbine engines. Therefore, the primary objective of this dissertation is to characterize the burnishing-induced surface integrity of Ti-6Al-4V alloy in terms of the implemented processing parameters. As the impact of cooling mechanisms on surface integrity from SPD processing is largely unexplored, a particular emphasis …

Design Process For The Containment And Manipulation Of Liquids In Microgravity, Chris Meek

Theses and Dissertations--Mechanical Engineering

In order to enhance accessibility to microgravity research, the design process for experiments on the ISS must be streamlined and accessible to all scientific disciplines, not just aerospace engineers. Thus, a general design and analysis toolbox with accompanying best practices manual for microgravity liquid containment is proposed. The work presented in this thesis improves the design process by introducing a modular liquid tank design which can be filled, drained, or act as a passive liquid-gas separation device. It can also be pressurized, and used for aerosol spray. This tank can be modified to meet the design requirements of various experimental …

Wing-Tip Vortex Evolution In Turbulence, Hari Charan Ghimire

Theses and Dissertations--Mechanical Engineering

Planar and stereo particle image velocimetry measurements were conducted of a wing-tip vortex decaying in free-stream turbulence in order to understand the evolution of a vortex and its decay mechanism. The vortex decayed faster in the presence of turbulence. The decay of the circulation was found to be almost entirely due to a decrease in circulation of the vortex core, caused by the relative decrease in peak tangential velocity without a corresponding increase in core radius. These events were found to be connected with the stripping of core fluid from the vortex core. The increased rate of decay of the …

Multiphase Interaction In Low Density Volumetric Charring Ablators, Ali D. Omidy

Theses and Dissertations--Mechanical Engineering

The present thesis provides a description of historical and current modeling methods with recent discoveries within the ablation community. Several historical assumptions are challenged, namely the presence of water in Thermal Protection System (TPS) materials, presence of coking in TPS materials, non-uniform elemental production during pyrolysis reactions, and boundary layer gases, more specifically oxygen, interactions with the charred carbon interface.

The first topic assess the potential effect that water has when present within the ablator by examining the temperature prole histories of the recent flight case Mars Science Laboratory. The next topic uses experimental data to consider the instantaneous gas …

Thermo-Mechanical Coupling For Ablation, Rui Fu

Theses and Dissertations--Mechanical Engineering

In order to investigate the thermal stress and expansion as well as the associated strain effect on material properties caused by high temperature and large temperature gradient, a two-way thermo-mechanical coupling solver is developed. This solver integrates a new structural response module to the Kentucky Aerothermodynamics and Thermal response System (KATS) framework. The structural solver uses a finite volume approach to solve either hyperbolic equations for transient solid mechanics, or elliptic equations for static solid mechanics. Then, based on the same framework, a quasi-static approach is used to couple the structural response and thermal response to estimate the thermal expansion …

Intermittency Effects On The Universality Of Local Dissipation Scales In Turbulent Boundary Layer Flows With And Without Free-Stream Turbulence, Sabah Falih Habeeb Alhamdi

Theses and Dissertations--Mechanical Engineering

Measurements of the small-scale dissipation statistics of turbulent boundary layer flows with and without free-stream turbulence are reported for Re_τ ≈ 1000 (Re_θ ≈ 2000). The scaling of the dissipation scale distribution is examined in these two boundary conditions of external wall-bounded flow.

Results demonstrated that the local large-scale Reynolds number based on the measured longitudinal integral length-scale fails to properly normalize the dissipation scale distribution near the wall in these two free-stream conditions, due to the imperfect characterization of the upper bound of the inertial cascade by the integral length-scale. When a length-scale based on Townsend's …

Laminar And Turbulent Study Of Combustion In Stratified Environments Using Laser Based Measurements, Stephen William Grib

Theses and Dissertations--Mechanical Engineering

Practical gas turbine engine combustors create extremely non-uniform flowfields, which are highly stratified making it imperative that similar environments are well understood. Laser diagnostics were utilized in a variety of stratified environments, which led to temperature or chemical composition gradients, to better understand autoignition, extinction, and flame stability behavior. This work ranged from laminar and steady flames to turbulent flame studies in which time resolved measurements were used.

Edge flames, formed in the presence of species stratification, were studied by first developing a simple measurement technique which is capable of estimating an important quantity for edge flames, the advective heat …