Aerospace Engineering Commons^™

Developing Computational Models For Pulsed-Inductive Plasma Formation, Zachary Aaron Gill

Masters Theses

"Pulsed-inductive discharges are a common method of producing a plasma. They provide a mechanism for quickly and efficiently generating a large volume of plasma for rapid use and are seen in applications including propulsion, fusion power, and high-power lasers. However, some common designs see a delayed response time due to the plasma forming when the magnitude of the magnetic field in the device is at a minimum. New designs are difficult to evaluate due to the amount of time needed to construct a new geometry and the high monetary cost of changing the power generation circuit. To more quickly evaluate …

Mechanisms Of Lean Flame Extinction, Ian M. Lasky

Honors Undergraduate Theses

Lean flame blowout is investigated experimentally within a high-speed combustor to analyze the temporal extinction dynamics of turbulent premixed bluff body stabilized flames. The lean blowout process is induced through fuel flow reduction and captured temporally using simultaneous high-speed particle imaging velocimetry (PIV) and CH* chemiluminescence. The evolution of the flame structure, flow field, and the resulting strain rate along the flame are analyzed throughout extinction to distinguish the physical mechanisms of blowout. Flame-vortex dynamics are found to be the main driving mechanism of flame extinction; namely, a reduction of flame-generated vorticity coupled with an increase of downstream shear layer …

Optimal Sintering Temperature Of Ceria-Doped Scandia Stabilized Zirconia For Use In Solid Oxide Fuel Cells, Amanda K. Assuncao

Honors Undergraduate Theses

Carbon emissions are known to cause decay of the Ozone layer in addition to creating pollutant, poisonous air. This has become a growing concern among scientists and engineers across the globe; if this issue is not addressed, it is likely that the Earth will suffer catastrophic consequences. One of the main culprits of these harmful carbon emissions is fuel combustion. Between vehicles, power plants, airplanes, and ships, the world consumes an extraordinary amount of oil and fuel which all contributes to the emissions problem. Therefore, it is crucial to develop alternative energy sources that minimize the impact on the environment. …

Aviation Outreach Model And Gap Analysis: Examining Solutions To Address Workforce Shortages, Rebecca K. Lutte

Aviation Institute Faculty Publications

The purpose of this research is to examine aviation outreach programs to identify best practices and areas for improvement in the endeavor to recruit youth to the aviation industry. The research includes creation of a model of aviation outreach and development and application of an aviation outreach gap analysis design. Three programs are analyzed, Women in Aviation Girls in Aviation Day, Experimental Aviation Association Young Eagles, and Aircraft Owners and Pilots Association High School Aviation Initiative. Each program takes a unique approach to recruiting youth and the strengths and weaknesses, based on the aviation outreach model, are discussed. Results of …

Thermo-Mechanical Coupling For Ablation, Rui Fu

Theses and Dissertations--Mechanical and Aerospace 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 …

Wing-Tip Vortex Evolution In Turbulence, Hari Charan Ghimire

Theses and Dissertations--Mechanical and Aerospace 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 …

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 and Aerospace 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 and Aerospace 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 …

Verification And Validation Studies For The Kats Aerothermodynamics And Material Response Solver, Olivia Schroeder

Theses and Dissertations--Mechanical and Aerospace Engineering

Modeling the atmospheric entry of spacecraft is challenging because of the large number of physical phenomena that occur during the process. In order to study thermal protection systems, engineers rely on high fidelity solvers to provide accurate predictions of both the thermochemical environment surrounding the heat shield, and its material response. Therefore, it is necessary to guarantee that the numerical models are correctly implemented and thoroughly validated. In recent years, a high-fidelity modeling tool has been developed at the University of Kentucky for the purpose of studying atmospheric entry. The objective of this work is to verify and validate this …

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

Theses and Dissertations--Mechanical and Aerospace 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 …

Discrete-Time Adaptive Control Algorithms For Rejection Of Sinusoidal Disturbances, Mohammadreza Kamaldar

Theses and Dissertations--Mechanical and Aerospace Engineering

We present new adaptive control algorithms that address the problem of rejecting sinusoids with known frequencies that act on an unknown asymptotically stable linear time-invariant system. To achieve asymptotic disturbance rejection, adaptive control algorithms of this dissertation rely on limited or no system model information. These algorithms are developed in discrete time, meaning that the control computations use sampled-data measurements. We demonstrate the effectiveness of algorithms via analysis, numerical simulations, and experimental testings. We also present extensions to these algorithms that address systems with decentralized control architecture and systems subject to disturbances with unknown frequencies.

Analysis Of Heat Transfer On Turbulence Generating Ribs Using Dynamic Mode Decomposition, Michael Elmore

Electronic Theses and Dissertations

Ducts with turbulence-promoting ribs are common in heat transfer applications. This study uses a recent modal extraction technique called Dynamic Mode Decomposition (DMD) to determine mode shapes of the spatially and temporally complex flowfield inside a ribbed duct. One subject missing from current literature is a method of directly linking a mode to a certain engineering quantity of interest. Presented is a generalized methodology for producing such a link utilizing the data from the DMD analysis. Theory suggests exciting the modes which are identified may cause the flow to change in such a way to promote the quantity of interest, …

Influence Of Transverse Slot Jet On Premixed Flame Acceleration, Dylan Tarrant

Electronic Theses and Dissertations

This work aims to identify the key flow parameters that influence flame acceleration in a semi-confined square channel. A transverse fluidic jet was used as an active flow blockage mechanism and to introduce turbulence into the propagating flame. Three experimental parameters were used to examine the relative influence of (1) mixture reactivity defined here as system equivalence ratio (SER), (2) jet mixture composition (JMC), and the momentum ratio (MR) on the acceleration of laminar premixed methane flame. High-speed PIV and schlieren photography were utilized to characterize the instantaneous flow-field conditions throughout the flame-jet interaction. Using these diagnostic techniques, flame front …

Square-Root Consider Filters With Hyperbolic Householder Reflections, James S. Mccabe, Kyle J. De Mars

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Maintaining positive definiteness of a filter's error covariance estimate is of paramount importance to any stable and reliable estimation scheme. Two widely used methods for protecting a filter from loss of positive-definiteness are that of consider filtering and square-root filtering. Despite their widespread use in estimation applications, a filtering methodology that combines the two techniques has yet to be presented in a unified, streamlined architecture. This paper develops a new approach to square-root filtering using hyperbolic Householder reflections. A specialization of the method is considered to permit computationally efficient applications, and a numerical example pertaining to a ballistic reentry is …

Set-Theoretic Model Reference Adaptive Control Of A Generic Transport Model, Ehsan Arabi, Tansel Yucelen, Nhan T. Nguyen

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This paper illustrates an application of a recently developed set-theoretic model reference adaptive control architecture on a generic transport model developed by NASA. The set- theoretic model reference adaptive control allows the system error bound between the state of an uncertain dynamical system and the state of a given reference model to be less than a-priori, user-defined worst-case performance bound. Thus, it has the capability to enforce strict performance guarantees to the adaptively controlled uncertain dynamical systems. specifically, after designing set-theoretic adaptive controllers for both longitudinal and lateral-directional dynamics here, the efficacy of this architecture is illustrated on the NASA …

Linear Burn Rate Of Monopropellant For Multi-Mode Micropropulsion, Alex J. Mundahl, Steven P. Berg, Joshua L. Rovey

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Multi-mode micro propulsion is a technology that can enable rapidly composable small satellites with unprecedented mission flexibility. To maximize mission flexibility a multi-mode micro propulsion monopropellant must be shared between the chemical and electric propulsion modes. Previous research has identified a promising monopropellant that is both readily catalytically exothermically decomposed (chemical mode) and electro sprayable (electric mode). In this work the linear burn rate of this monopropellant is determined and used to aid the design of a microtube catalytic chemical thruster. Experiments with a pressurized fixed volume reactor are used to determine the linear burn rate. Benchmark experiments use a …

Boundary-Layer Separation Control Using Laser-Induced Air Breakdown, Alfram Bright, Nathan Tichenor, Kevin Kremeyer, Richard Wlezien

Mechanical and Aerospace Engineering Faculty Research & Creative Works

Modification of the flow separation characteristics of a laminar airfoil using a remotely located high-power laser was experimentally investigated in a low-speed, low-turbulence wind tunnel. A laminar airfoil model (chord length of 500 mm) was designed and fabricated to emulate the flight characteristics of a small aircraft. At 0 deg angle of attack, the airfoil model was determined to have an incipient laminar separation bubble on its lifting surface between 67 and 80% chord. A strong laser-induced breakdown was generated 2 mm upstream of the leading edge by focusing a collimated beam emitted from a 900 mW laser at 1064 …

The Effect Of Task Load, Automation Reliability, And Environment Complexity On Uav Supervisory Control Performance, Sarah M. Sherwood

Doctoral Dissertations and Master's Theses

Over the last decade, military unmanned aerial vehicles (UAVs) have experienced exponential growth and now comprise over 40% of military aircraft. However, since most military UAVs require multiple operators (usually an air vehicle operator, payload operator, and mission commander), the proliferation of UAVs has created a manpower burden within the U.S. military. Fortunately, simultaneous advances in UAV automation have enabled a switch from direct control to supervisory control; future UAV operators will no longer directly control a single UAV subsystem but, rather, will control multiple advanced, highly autonomous UAVs. However, research is needed to better understand operator performance in a …

Application Of Artificial Neural Networks For The Prediction Of Aluminium Agglomeration Processes, Tejasvi K, Y Pydi Setty, Vemana Venkateswara Rao, Kalyan Chakarvarthy

International Journal of Aviation, Aeronautics, and Aerospace

Aluminium is universal and vital constituent in composite propellants and typically used to improve performance. Aluminum agglomeration takes place on the burning surface of aluminized propellants, which leads to reduced combustion efficiency and 2P flow losses. To understand the processes and behaviour of aluminum agglomeration, particles size distribution of composite propellants were studied using a quench particle collection technique, at 2 to 8 MPa and varying quench distances from 5mm to 71mm. To predict the agglomerate diameter of metallized/ultra-fine aluminium of composite propellants, a new artificial neural network (ANN) model was derived. Five Layered Feed Forward Back Propagation Neural Network …

Innovative Dodecacopter Design – Bulgarian Knight, Svetoslav Zabunov, Garo Mardirossian

International Journal of Aviation, Aeronautics, and Aerospace

The current article aims at introducing a novel dodecacopter multirotor design called Bulgarian Knight. The aircraft implements a number of innovations and characteristics that give it an advantage over other contemporary multi-copters. Some of its novel characteristics are the mounting of the rotors under the fuselage by use of pusher propellers. Further, the design implements twelve rotors positioned in an optimal geometric coverage.