Theses and Dissertations - Department of Aerospace Engineering and Mechanics
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Browsing Theses and Dissertations - Department of Aerospace Engineering and Mechanics by Author "Baker, John"
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Item Borescopic Laser Doppler Velocimetry probe(University of Alabama Libraries, 2013) O'Brien, Kory Thomas; Olcmen, Semih M.; University of Alabama TuscaloosaA miniature fiber-optic, single-velocity-component Laser Doppler Velocimetry (LDV) probe for measurement in cramped spaces, where access is very limited, has been designed, constructed, and tested. The probe design allows the main probe dimensions to be small (7mm in diameter). In addition, the proposed back-scatter collection scheme allows the main section to be as long as needed to access remote locations. The laser beams are first collimated by passing them through two separate collimating lenses. The collimated light then passes through 1 mm holes machined into a right angle prism-mirror and are focused to form the measurement probe volume using the focusing lens placed at the end of the probe extension tube. The light scattered by the particles in the flow is collected back by the focusing lens and is collimated. The collimated light then reflects off the right-angle mirror by 90 degrees, passes through the receiving lens, and is focused to the receiving fiber terminator. The receiving fiber-optic cable transmits the collected light to the photo-multiplier tube which then converts the signal into an electrical signal for further processing of the data. The probe working principle was proven in two types of jet flows.Item Computational analysis of diffuser performance for the Subsonic Aerodynamic Research Laboratory wind tunnel(University of Alabama Libraries, 2012) King, Christopher David; Olcmen, Semih M.; University of Alabama TuscaloosaThe Air Force has expressed interest in improving the efficiency of the Subsonic Aerodynamic Research Laboratory (SARL) wind tunnel. In a previous analysis of losses throughout the tunnel, it was found that approximately thirty percent of pressure losses through the tunnel occurred at the exit of the tunnel (Britcher, 2011). The use of alternative diffuser geometries in reducing pressure losses at the exit of the tunnel and the computation of their efficiency improvement with respect to the original tunnel geometry and with respect to each other for the SARL wind tunnel are the focus of this research. Three different diffuser geometries were evaluated numerically using both the SolidWorks Flow Simulation add-on, and ANSYS FLUENT. For each of these geometries, a scaled down model was manufactured to be used for experimental validation in future work. Both the full size and small scale numerical models were evaluated with an inlet velocity of sixty meters per second. As the nature of the flow at this point in the wind tunnel is not known, both a uniform and fully developed turbulent flow profiles were evaluated for each design, both for the small scale models and the full size models, to determine pressure losses with respect to the varying flow types entering the diffusers. This research seeks to determine the effects of these different geometries on the flow downstream of the exit, and the possible energy savings associated with each design. In addition, it seeks to compare the numerical results obtained from both SolidWorks Flow Simulation and ANSYS FLUENT.Item Design for a low-cost k-band communication satellite constellation(University of Alabama Libraries, 2020-12) Strickland, Peyton Daniel; Olcmen, Semih M.; University of Alabama TuscaloosaThe feasibility of using a low-cost K-band communication satellite constellation in low-Earth orbit to provide continuous global coverage to ground terminal restricted aerospace vehicles was investigated. A phased array K-band transceiver pointing nadir, steerable ±45° in azimuth and elevation, and laser communication units for satellite-to-satellite cross link capability, were assumed for the payload. The figure of merit was the average percent coverage of the entire surface of the globe and the space surrounding the globe, up to 1000 km, with a goal of achieving 100% coverage, continuously. The results indicate that continuous global coverage is not feasible with a heritage phased array K-band transceiver with a range of 2000 km and 72 satellites; however, a hypothetical phased array K-band transceiver with a range of 2975 km was able to provide continuous global communication. The low-cost goal was not realized. The estimated cost of the constellation with the hypothetical transceiver is $4.861 B due to the large command and data handling and power requirements associated with the K-band transceiver. With the enormous costs associated with this project, despite using commercially available products, further analysis of the proposed satellite constellation is not recommended.Item Design of a dual-expander aerospike nozzle rocket engine(University of Alabama Libraries, 2016) McVay, Eric Stephen; Branam, Richard D.; University of Alabama TuscaloosaThe University of Alabama’s Aerospace Engineering and Mechanics Department is developing a computational dual-expander aerospike nozzle (DEAN) upper stage rocket engine to demonstrate the engine’s performance capabilities and to establish a model by which the DEAN can be built. This research expands the base model developed by the Air Force Institute of Technology to more accurately represent the physics involved in both the fluid flow and geometrical properties of the engine. The DEAN engine was modeled using NASA’s Numerical Propulsion System Simulation (NPSS) and Chemical Equilibrium with Applications (CEA) software. The methodology implemented in this research was validated by modeling the RL-10A-3-3A upper stage engine in NPSS and comparing resulting outputs with NASA’s ROCket Engine Transient Simulator (ROCETS) analysis. The DEAN uses liquid oxygen and liquid hydrogen as its propellant and is being designed to produce a thrust of 30,000 [lbf] and a specific impulse of at least 465.5 [s], at an oxidizer-to-fuel ratio of 5.88, while also remaining within the size envelope of the RL-10B-2 upper stage engine. The performance and size objectives were established to meet the National Aeronautics and Space Administration’s (NASA) Advanced Upper Stage Engine Program (AUSEP) need for an upper stage rocket engine to replace the aging RL-10 series engines that have been in production since the 1960s. Results indicate that optimal performance for the feasible solution space examined in this research occurs at an expansion ratio of 30, a throat area of 23 [in2], and a characteristic length, L*, of 90 [in]. The optimal DEAN design point was shown to achieve a thrust of more than 5,000 [lbf] greater than the RL-10B-2, a Isp of 1.8 [s] greater, and a significantly reduced size envelope.Item Development of a multiphysics model for precision thermal controls of an active hydrogen maser(University of Alabama Libraries, 2020) McKelvy, James Andrew; Lemmon, Andrew; University of Alabama TuscaloosaThe active hydrogen maser atomic frequency standard is widely used in modern radio science astronautics research due to its outstanding short-term frequency stability. Short-term frequency stability is critical to radio science applications because the accuracy and resolution of spacecraft range and Doppler measurements are directly associated with the stability of the communication system’s timing reference. Due to the design of the hydrogen maser and the sensitivity of the hydrogen ground state hyperfine transition, the achievable frequency stability of the hydrogen maser is degraded by temperature fluctuations in its operating environment. This temperature sensitivity results from the influence of Doppler shifts, cavity pulling, and wall shifts associated with the temperature of the maser microwave cavity. Modern hydrogen masers are designed to compensate for temperature sensitivity through the use of a precision thermal control system. This thesis details the development of a reduced-order multiphysics model of a precision thermal control system intended to mimic the internal regulated thermodynamics of a hydrogen maser. The developed electro-thermal model includes individual components representing the thermal plant, temperature sensors, and the associated temperature controller. The model is tuned to agree with empirical measurements from a simplified vacuum testbed, and it is empirically validated in both the time and frequency domains. The validated model is also leveraged to analyze the performance of the precision thermal control system within the Microchip MHM-2010 hydrogen maser. Analysis of this controller demonstrates that while the existing design meets performance specifications, there exists room for improvement in both the dynamic and steady-state tracking performance of this system. Overall, the proposed methodology presents a powerful approach for analyzing and improving the performance of a precision thermal control system.Item Drag measurements across patterned surfaces in a low Reynolds number Couette flow facility(University of Alabama Libraries, 2009) Johnson, Tyler Jay; Lang, Amy W.; University of Alabama TuscaloosaUnderstanding fluid dynamic drag, and its reduction, has always been a topic of primary concern. Direct drag measurements can be difficult to obtain with low viscosity fluids such as air or water. For this study a new low Reynolds number Couette facility was constructed to investigate surface drag. In this facility, mineral oil was used as the working fluid to increase the shear stress across the surface of the experimental models. A mounted conveyor creates a flow within a Plexiglas tank. The experimental model of a flat or patterned surface was suspended above the moving belt. The experimental plate was attached to linear bearings on a slide system that connects to a force gauge used to measure the drag. Within the gap between the model and moving belt a Couette flow with a linear velocity profile was created. Digital particle image velocimetry was used to confirm the velocity profile. A patterned surface, in this case consisting of 2-D cavities, was embedded into a large portion of a Plexiglas plate. First, the drag across a flat plate of the same size was measured and compared to theoretical values for laminar Couette flow. These results were found to be within 5% of predicted values following CD = 2/Re. The drag for a 2-D embedded square cavity model was then measured and compared to the flat plate results. A drag reduction of up to 20% was found for the lateral rib model at Re ~ 10 or less, with increasing drag reduction as the Re decreases. Lower drag reduction was found up to Re ~ 50, where the difference becomes negligible. Finally, the flow over the 2-D cavities was modeled with a partial slip at the bottom wall. Modeled average partial slip velocities were calculated from the drag measurements and reached values of 10-22% of the belt speed for Re < 10.Item Experimental study of a circular jet under the effect of secondary jets(University of Alabama Libraries, 2013) Laldinpuii Kurup, Arathi; Olcmen, Semih M.; University of Alabama TuscaloosaThe present study investigates the interaction between two jets: a primary round jet and secondary jets formed by a manipulated co-annular jet. Secondary jets were formed by a combination of a co-annular jet issuing from a nozzle with convex surfaces and fluid injection into the co-annular jet perpendicular to the primary jet axis. Experiments reported here were carried out using a two-component Laser-Doppler-Velocimetry system to determine the effects of the secondary jet on the primary jet. Mean velocity and Reynolds stress measurements were made along and across the primary jet centerline with and without the presence of the secondary jet. It was observed that fluid injection into the spacing between the inner jet pipe and the outer jet surface highly affects the characteristics of the mixing region. Fluid injection perpendicular to the co-annular jet transforms the co-annular jet into two separate jets positioned at 180 degrees apart from each other. As compared to the primary jet only case, the interaction of the secondary jets with the primary jet results in a planar primary jet showing faster centerline velocity reduction. The spreading of the jet was also seen to be twice the values observed with the primary jet alone at each x/d location. The Reynolds number for the primary jet was about 16000.Item Experimental study on the effects of nose geometry on drag over axisymmetric bodies in supersonic flow(University of Alabama Libraries, 2014) Brooker, Brian Tyler; Olcmen, Semih M.; University of Alabama TuscaloosaA new nose shape that was determined using the penetration mechanics to have the least penetration drag has been tested in the supersonic wind tunnel of the University of Alabama to determine the aerodynamic characteristics of this nose shape. The aerodynamic drag measured on the new nose shape and on four additional nose shapes are compared to each other. The results show that the new nose shape has the least aerodynamic drag. The measurements were made at Mach numbers ranging from 1.85 to 3.1. This study also required the maintenance of several components of the University of Alabama's 6-inch by 6-inch supersonic wind tunnel and modification of the existing data acquisition programs. These repairs and modifications included the repair and recalibration of the supersonic wind tunnel, repair of the four component force balance, and the modification of the tunnel's control program.Item Exploring the Use of an Echo State Network in Modeling Turbulent Jet Behavior(University of Alabama Libraries, 2021) Sapkota, Pradeep; Baker, John; University of Alabama TuscaloosaThis work investigates the use of an Echo State Network (ESN) to predict turbulent jet flow behavior. ESNs are a particular class of Recurrent Neural Networks (RNNs) that have been shown to model transient chaotic systems while avoiding some of the difficulties associated with training other types of recurrent neural networks. It is a large, random, fixed recurrent neural network in which each neuron receives a non-linear input signal, and the weights of the input and hidden neurons are fixed randomly. An extensive literature review is performed regarding the history of turbulent jet modeling and the use of an ESN to model turbulent flow analogs. In an initial investigation, a turbulent free jet issuing from a circular tube into a quiescent medium was modeled using an ESN. ESN training was achieved using a validated LES dataset obtained from commercially available CFD software. A separate LES dataset was used to evaluate how well the ESN predicted flow field behavior. A hyperparameter search was undertaken to enhance the ESN's ability to model the turbulent flow field under consideration. The ESN model proved capable of reproducing instantaneous vortical structures and centerline velocity behavior relative to LES model data and previously published experimental data. In a second investigation, two cases of heated turbulent jets discharging from a nozzle to a cold surrounding were studied using an ESN. LES of the jets were carried out in commercial CFD software, and the data obtained from LES were used for training and testing the ESN. Detailed comparisons of the mean velocity profiles and the mean temperature profiles along the streamwise and radial directions were provided, along with turbulence quantities. ESN showed a good agreement with LES simulation and the experiment data. The coherent structure of the jet was investigated by the visualization of the isosurface of the Q criterion. ESN was shown to be efficient in capturing the vortex rings at the vicinity of the nozzle. The ESN also proved capable of capturing mean turbulent kinetic energy distribution for different temperature gradient values. In the third and final investigation, the model problem was a variable density jet originating from a cylindrical tube that passed through a weakly restricted co-flow of low-speed air streams. ESN training and testing were carried out with the help of a validated LES dataset obtained from commercial CFD software. Compared to LES model data and previously published experimental data, the ESN model was able to reproduce turbulent flow field statistics. The ESN model correctly reproduced the profile shapes of radial shear stresses. The vortical evolution for the Helium jet was studied with the ESN model, and the ESN model captured the vortex rings formed at the jet exit and the large-scale structures downstream of the jet. Based on the study, it was concluded that the ESN model has the potential to model turbulent flow fields effectively.Item Impact of a biologically-inspired tail assembly on drag reduction for lighter-than-air near-space platforms(University of Alabama Libraries, 2010) Cottingham, Jason Lambert; Baker, John; University of Alabama TuscaloosaThe near space region is a vastly underused region of our atmosphere due to the extreme conditions present but makes up approximately 75% of the usable atmosphere. Although there are no weather patterns like rain, storms and clouds, the winds that are present at high altitudes are very challenging to overcome. Many have researched and designed high altitude platforms for exploration, but few have succeeded in experimental aircraft tests at altitude. Due to the low density, temperature and pressure in this region, fixed wing flight is almost impossible but lighter than air technology can be utilized to help overcome some of those challenges. Long endurance flight in the near space region is beginning to be heavily researched due to the many advantages of the capability from civilian uses to military uses. With the ever present winds in the near space region, lighter than air technology used in conjunction with its station keeping ability becomes an almost unconquerable task. This research focuses on using the adaptations of nature to help solve the power requirement challenge surrounding high altitude/long endurance flight. With the use of a biologically inspired tail, the drag on an airship can be decreased, and thus the power required for station keeping abilities. Using computational modeling, a complete environmental model was created to represent the aspects of the atmosphere that directly affect airship flight. A model of a basic shaped airship and an airship fitted with a tail inspired by avian flight were created to be used in the environmental model. The approach used in this research in one approach that could be used to significantly reduce the drag on a high altitude airship and help enable the creation of viable near space vehicles.Item Intake flow analysis of a pulsed detonation engine(University of Alabama Libraries, 2014) Strafaccia, Joshua Amadeus; Olcmen, Semih M.; University of Alabama TuscaloosaA CFD program is converted and modified to explore unsteady flow within the intake system of a pulse detonation engine (PDE). Using a quasi-one-dimensional approach the program provides insight into the unsteady nature of localized equivalence ratios to include their effects on PDE performance. The original FORTRAN program is converted into the MATLAB architecture, taking full advantage of user availability and post processing convenience. The converted program was validated against the original program and modified to include a primitive intake manifold system with a single fuel injector located approximately 10 feet upstream of the primary intake valve. Constant fuel mass flow rate at the injector end creates local variations in equivalence ratio throughout the PDE that may have significant impact on overall engine performance. The results of the current thesis research suggest that performance effects of up to 21% can be attributed to non-uniform fuel distribution throughout the detonation process and are most prevalent at lower frequencies and fill ratios.Item An investigation of the flow control mechanisms of shortfin mako skin(University of Alabama Libraries, 2015) Wheelus, Jennifer; Lang, Amy W.; University of Alabama TuscaloosaThe skin of fast-swimming sharks is proposed to have mechanisms to reduce drag and delay flow separation. The shortfin mako Isurus oxyrinchus is one of the fastest and most agile ocean predators and would benefit from minimizing its pressure drag by controlling flow separation. The skin of shortfin makos is covered in teeth-like denticles with lengths on the order of 0.2 mm. Recent biological studies have shown the bristling angle of these denticles to exceed 50° in locations likely to experience separation first. It is proposed that the reversing flow that occurs near the onset of separation activates denticle bristling. Once activated, the scales would impede the development of a more global separation event over the shark by stopping the reversing flow from travelling further upstream and causing interactions within the boundary layer that allow it to stay attached longer. Real shark skin samples are exposed to reversing flow and the interactions with the scales are documented with a specialized camera setup. The camera setup provides high magnification while still providing a large enough depth of field to visualize scale movement. It is shown that reversing flow indeed interacts with the scales and causes bristling in flank region specimens. Because it is not possible to test at the swimming speeds of the real mako in the University of Alabama water tunnel, a biomimetic scale array model is used in the experiment to study the boundary layer, Re stress, and cavity structures over the shark skin. It is shown that the introduction of the scales in the turbulent boundary layer yields a positive benefit in the flow by brings higher momentum fluid toward the surface. An examination of the cavity structures shows cavity vortices in most cases, with the notable exception being the first cavity in the turbulent boundary layer case which shows no average core vortex and instead shows an outward trend of fluid motion toward the boundary layer above. These results indicate the possibility of shortfin mako scales to control flow separation.Item Multidimensional complex systems – transition distributions as a resilience measure(University of Alabama Libraries, 2019) Shah, Shivank Kirit; Baker, John; University of Alabama TuscaloosaComplex networks can be observed in many areas ranging from ecological and biological to technical systems. Complex systems have many interacting components which make their dynamics non-linear. This makes it difficult to calculate important properties of the system such as resilience. The resilience of a system is how persistent the system is against external perturbations. Node centrality determines the importance that a node plays in the effective working of a network. The effect node centrality plays on the transition taking place was explored. Resilience has been defined based on the fraction of nodes that needs to be removed before the system fails. The fraction of nodes to be removed have been calculated statistically by calculating the centroid of the transition distribution. The logic used for defining resilience this way was that if the system transitions into the unwanted lower equilibrium state after a small perturbation it has a lower resilience than the system which transitions to that state after greater perturbation. The values of resilience obtained from the transition distribution agree with the trend in resilience shown by the effective control parameter, β_eff. It was concluded that the node centrality plays an important part in the transition distribution and hence it is important to identify the important or the most central nodes in the system also known as ‘hubs’. The current work proposes to lay a foundation to predict the dynamics of the same complex network with the help of Artificial Neural Networks. The recurrent Artificial Neural Networks have been trained using the data obtained by solving the set of non-linear ordinary differential equations which describe the spatial and temporal dynamics of the system. These equations have been solved numerically by a self-developed solver based on the Runge Kutta 4 algorithm. The architecture chosen for the neural network was the Simple Recurrent Neural Network. The Levenberg-Marquardt algorithm was used for training the neural network.Item Multivariable optimization of liquid rocket engines using Particle Swarm algorithms(University of Alabama Libraries, 2013) Jones, Daniel; Baker, John; University of Alabama TuscaloosaLiquid rocket engines are highly reliable, controllable, and efficient compared to other conventional forms of rocket propulsion. As such, they have seen wide use in the space industry and have become the standard propulsion system for launch vehicles, orbit insertion, and orbital maneuvering. Though these systems are well understood, historical optimization techniques are often inadequate due to the highly non-linear nature of the engine performance problem. In this thesis, a Particle Swarm Optimization (PSO) variant was applied to maximize the specific impulse of a finite-area combustion chamber (FAC) equilibrium flow rocket performance model by controlling the engine's oxidizer-to-fuel ratio and de Laval nozzle expansion and contraction ratios. In addition to the PSO-controlled parameters, engine performance was calculated based on propellant chemistry, combustion chamber pressure, and ambient pressure, which are provided as inputs to the program. The performance code was validated by comparison with NASA's Chemical Equilibrium with Applications (CEA) and the commercially available Rocket Propulsion Analysis (RPA) tool. Similarly, the PSO algorithm was validated by comparison with brute-force optimization, which calculates all possible solutions and subsequently determines which is the optimum. Particle Swarm Optimization was shown to be an effective optimizer capable of quick and reliable convergence for complex functions of multiple non-linear variables.Item On the Use of Echo State Networks in Various Configurations to Predict the Dynamics of Adversarial Swarms(University of Alabama Libraries, 2021) Gupta, Soham; Baker, John; University of Alabama TuscaloosaAdversarial (competitive) swarms consist of two or more systems (each system consisting of a collection of individuals, interconnected agents) where the goals of each group are conflicting. This work aims to use an Echo State Network to predict the individual behavior of agents in two adversarial swarms and thereby develop an improved understanding of the dynamics of such systems. The current study was divided into three phases. An agent-based Adversarial swarm model was initially developed comprising of two competing swarms, the Attackers, and the Defenders, respectively. The Defender aimed to protect a point of interest in unbounded 2D Euclidean space called the Goal. In contrast, the Attacker’s main task was to intercept the Goal while continually trying to evade the Defenders, which get attracted to it when they are in a certain vicinity of the Goal. The simulation was considered Semi-Hybrid as agent compromise, and goal compromise criteria were modeled to introduce realism as real-world engineering applications. The final system state was studied for all the varied number of agents making up each swarm. The effectiveness of the Semi-Hybrid approach was validated by using Multiscale Entropy, which revealed a greater degree of randomness for the Defenders than Attackers. In the second investigation, two configurations were used to evaluate the use of Echo State Networks for predicting group dynamics for each swarm. Configuration 1 employed a single ESN, i.e., the patio-temporal data for all agents of an Adversarial Swarm model was used input. In configuration 2, two separate ESNs, in parallel, were used to predict Defender and Attacker swarm dynamics. It was concluded that the parallel ESN configuration was more effective in achieving qualitatively similar predictions of the dynamics for the Adversarial Swarms. In the final investigation, an instance of an ESN in a massively parallel framework was trained on individual spatio-temporal data of every agent. The optimal hyperparameters obtained for every individual agent in the framework showed considerable variance that implied every agent in the Adversarial swarm reacted uniquely when a uniform stimulus was applied and thus reaffirmed the concept of individuality of agents in a swarm.Item A study of trailing-edge scalloping on flat plate-membrane airfoil performance(University of Alabama Libraries, 2009) Hicks, Travis; Hubner, James Paul; University of Alabama TuscaloosaThe objective of this investigation was to study how membrane scalloping affects the aerodynamic performance of flat, membrane wings at low Reynolds numbers. The onset of membrane vibration was also studied to determine its effects on the aerodynamic performance. This study was performed to improve the efficiency of MAVs (micro air vehicles). The removal of some of the membrane at the trailing edge of the airfoil, which has the highest amplitude of vibration, could significantly decrease the drag without overly affecting the lift. The plates studied were all flat plates with moderate aspect ratio and a repeating cell structure of latex membranes. This allowed the effects of the membrane to be studied with minimal effects from the tip vortices as long as the data was acquired behind the center cell. The onset of membrane vibration was studied using hot-wire anemometry, and the amplitude and frequency of membrane vibration were measured directly using a laser vibrometer. Through a momentum deficit analysis, local drag coefficients were obtained. These results were compared to direct measurements of lift and drag from external balance testing to determine the aerodynamic efficiency. Results showed that the shape of the latex cell has a greater impact on lift than the amount of scalloping and that the amount of scalloping has a greater affect on drag than the cell shape. These effects could allow batten-reinforced membrane wings for MAVs to be more efficient with proper membrane scalloping.Item Thrust measurement of the busek bht 20 microhall effect thruster(University of Alabama Libraries, 2020-12) Burleson, Connor; Branam, Richard; University of Alabama TuscaloosaThe research presented herein documents the process, data analysis, and results of testing a low power micro-hall effect thruster suitable for various mission objectives such as orbital maneuvers, momentum dumping, and precision pointing for microsatellites. The BHT 20 is a low power micro-hall effect thruster capable of generating thrust at the µN thrust level. The research presents high thrust level measurements between 1242 to 3193 µN for thruster conditions between 14.5 to 35.7 W at 413 to 474 µg/s argon flow rates with errors between 3.46 to 11.6%. Also, the discharge voltage and current operating envelope is characterized at the above conditions. Thruster operation was considered suboptimal due to unoptimized high flow rate to thruster power operating conditions. Overall, the research was considered a success by operating the BHT 20 at higher discharge voltages and obtaining thrust measurements at the respective test conditions. Results and recommendations to improve testing are included.