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Full-Text Articles in Engineering
Preparation And Characterization Of Porous Pdms For Printed Electronics, Eyad Khalid M. Balbaid
Preparation And Characterization Of Porous Pdms For Printed Electronics, Eyad Khalid M. Balbaid
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Fabricating an elastomeric substrate with internal features could provide a novel structure with distinctive mechanical properties that allow them to stretch, bend and absorb the impact force. To date, polydimethylsiloxane (PDMS) is a great candidate as a substrate for flexible electronic applications, due to easy fabrication, high stability and low cost. In the current thesis, porous PDMS samples are fabricated and characterized based on the particle size and the fusion of salt and sugar treated micro-regions. The liquid PDMS is prepared by mixing the silicon elastomer base (Sylgard 184) and elastomer curing agent using volume ration 10:1. The salt and …
Design And Manipulation Of A Power-Generating System With High-Temperature Fuel Cells For Hypersonic Applications, Jack Randolph Chalker
Design And Manipulation Of A Power-Generating System With High-Temperature Fuel Cells For Hypersonic Applications, Jack Randolph Chalker
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Current hypersonic vehicles tend to be incapable of producing onboard power with traditional generators due to their use of supersonic combusting ramjets (scramjets). Because of this, they seek additional energy sources for supporting advanced electronics or other auxiliary power-dependent devices while requiring elaborate thermal management systems to combat temperatures exceeding 700ºC. The incorporation of Solid Oxide Fuel Cell (SOFCs) stacks is an efficient solution, capable of generating large quantities of power through the use of natural fuel sources at high temperatures. Developments in this thesis include the design, construction, and support of a system operating at hypersonic-environment conditions with a …
Design And Implementation Of Periodic Unsteadiness Generator For Turbine Secondary Flow Studies, Nathan James Fletcher
Design And Implementation Of Periodic Unsteadiness Generator For Turbine Secondary Flow Studies, Nathan James Fletcher
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A primary source of periodic unsteadiness in low-pressure turbines is the wakes shed from upstream blade rows due to the relative motion between adjacent stators and rotors. These periodic perturbations can affect boundary layer transition, secondary flow, and loss generation. In particular, for high-lift front-loaded blades, the secondary flowfield is characterized by strong three-dimensional vortical structures. It is important to understand how these flow features respond to periodic disturbances. A novel approach was taken to generate periodic unsteadiness which captures some of the physics of turbomachinery wakes. Using stationary pneumatic devices, pulsed jets were used to generate disturbances characterized by …
As-Manufactured Modeling Of A Mistuned Turbine Engine Compressor Evaluated Against Experimental Approaches, Daniel L. Gillaugh
As-Manufactured Modeling Of A Mistuned Turbine Engine Compressor Evaluated Against Experimental Approaches, Daniel L. Gillaugh
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As-manufactured rotors behave quite differently than nominal, as-designed rotors due to small geometric and material property deviations in the rotor, referred to as mistuning. Traditional integrally bladed rotor (IBR) modeling approaches assume each blade is identical. State-of-the-art IBR dynamic response predictions can be accomplished using asmanufactured models (AMM) generated via optical topography measurements and mesh morphing. As-manufactured models account for geometric deviations occurring through the machining process, material deviations and field wear, allowing each blade to respond differently. Rotor designs are intended to avoid resonance crossings throughout an engine’s operating range, but total avoidance is challenging. This has led to …
Aerodynamics Of Fan Blade Blending, Clint J. Knape
Aerodynamics Of Fan Blade Blending, Clint J. Knape
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Blending is a method of fan and compressor blade repair. The goal of the blending process is to remove stress concentration points such as cracks and nicks along the leading, trailing, or tip edges of the blade. The stressed areas are typically removed by grinding or cropping away the surrounding material. For integrally bladed rotor (IBR) disks, repairing a damaged blade is much more economical than replacing the entire disk. However, the change in shape of the blade will change the local aerodynamics and result in mistuning, both structurally and aerodynamically. In a worst case scenario, the change in the …
Analytical And Experimental Investigation Of Time-Variant Acceleration Fields, Justin A. Williams
Analytical And Experimental Investigation Of Time-Variant Acceleration Fields, Justin A. Williams
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Devices expected to operate in elevated or non-standard acceleration fields are often tested in similar conditions prior to deployment. Typically these tests only simulate steady-state acceleration fields in one direction. However, real acceleration fields often vary both directionally and temporally. Designing experiments to produce these conditions requires careful forethought and analysis in order to understand the emergent acceleration components that result from the methodology. An experiment was designed and executed on a horizontal centrifuge in which the radial acceleration varied sinusoidally between -10 < a_r < 10 g. Negative acceleration was achieved by rotating the test article relative to the radial acceleration vector using a servo motor. A model was developed that predicted the acceleration field at every point along the test article. The model provided important information such as the acceleration magnitude and direction anywhere on the test device at any point in time. This model was then used to optimize the velocity profile of the servo motor to minimize experimental artifacts.
Adaptive Identification Of Classification Decision Boundary Of Turbine Blade Mode Shape Under Geometric Uncertainty, Ian M. Boyd
Adaptive Identification Of Classification Decision Boundary Of Turbine Blade Mode Shape Under Geometric Uncertainty, Ian M. Boyd
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Integrally Bladed Rotors (IBR) of aircraft turbine engines suffer from fluctuations in the dynamic response that occurs due to blade to blade geometric deviations. The Stochastic Approach for Blade and Rotor Emulation (SABRE) framework has been used to enable a probabilistic study of mistuned blades in which a reduced order modeling technique is applied in conjunction with sets of surrogate models, called emulators, to make predictions of mistuned mode shapes. SABRE has proven useful for non-switching mode shapes. However, switching mode shapes have non-stationary or discontinuous response surfaces which reduce the accuracy of the surrogate models used in SABRE. To …
Rasters Vs Contours For Thin Wall Ultem 9085 Fdm Applications, Vausman Kota
Rasters Vs Contours For Thin Wall Ultem 9085 Fdm Applications, Vausman Kota
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Currently many components are additively manufactured via fused deposition modeling (FDM). However, FDM results in gaps between passes which produces a poor surface finish and porous material that is difficult to hold pressure. Commercial scale air systems require a pressure to be maintained within thin walled components with minimal post processing and clean up after fabrication. A design of experiments (DOE) was created to identify the optimal raster vs contour ratio for UTLEM 9085 CG fabricated using FDM at different build angles and wall thicknesses. A custom-built pressurized test system was developed, the leak rates were calculated and the surfaces …
Simulation, Experimentation, Control And Management Of A Novel Fuel Thermal System, Austin L. Tipton
Simulation, Experimentation, Control And Management Of A Novel Fuel Thermal System, Austin L. Tipton
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Modern aircraft experience increasing thermal loads from electronics, electromechanical actuators, and directed energy weapons. These aircraft also have a reduced ability to transfer thermal energy to the atmosphere due to the use of composite skins and a limited number of air intake ports. For aircraft that use fuel as a heatsink, these factors can cause the fuel at points of the system to exceed temperature limits, which can result in fuel coking, damage to subsystems, and even complete system failure. This thesis investigates the fuel thermal management shortcomings of contemporary aircraft systems and suggests a new methodology to extend performance. …
An Investigation On Spur Gear Rolling Contact Fatigue Crack Initiation And Crack Propagation Under Ehl Condition, Vignesh Dharmajan
An Investigation On Spur Gear Rolling Contact Fatigue Crack Initiation And Crack Propagation Under Ehl Condition, Vignesh Dharmajan
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Pitting is a rolling contact fatigue phenomenon commonly observed in mechanical rolling elements, such as gears and bearings. In case of gear contacts, pitting usually takes place in the dedendum region, where both sliding and contact load are high. In this study, a model is developed to predict surface breaking crack formation fatigue lives, including both nucleation and propagation stages, for spur gear contacts operating under mixed elastohydrodynamic lubrication (EHL) condition. The model utilizes a gear load distribution model for tooth contact Analysis. A mixed EHL formulation is implemented to evaluate the surface normal pressure and tangential shear, incorporating the …
Transmission Electron Microscopy Analysis Of Silicon-Doped Beta-Gallium Oxide Films Grown By Pulsed Laser Deposition, Cynthia Thomason Bowers
Transmission Electron Microscopy Analysis Of Silicon-Doped Beta-Gallium Oxide Films Grown By Pulsed Laser Deposition, Cynthia Thomason Bowers
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Due to the large band gap of β-Ga2O3 and recent improvements toward high quality native substrates and the ability to shallow dope epitaxial β-Ga2O3 it is an attractive material for applications in power electronic devices. Such devices require advances in the areas of thin film growth and carrier concentration control to deliver high mobility films appropriate for the device structures. Transmission electron microscopy (TEM) analysis can provide information concerning doping, crystal structure, and internal strain which will be valuable to assess the role of defects and impurities on the transport properties for feedback to optimize the bulk and epitaxial growth …
Using Cfd To Improve Off-Design Throughflow Analysis, Troy J. Lanchman
Using Cfd To Improve Off-Design Throughflow Analysis, Troy J. Lanchman
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In turbomachinery design, complex internal flows give rise to significant losses and blockage whose effects are difficult to properly analyze without detailed computational fluid dynamics (CFD) methods or experiments. In a typical design method, CFD is used in conjunction with simpler throughflow or cascade codes to hasten the process. However, the lesser physical accuracy of the design codes demands the inclusion of models to improve the accuracy of the throughflow codes. This thesis aims to use CFD data to generate improved loss and blockage models for a 2D compressor throughflow code by matching throughflow data to CFD data using optimizations. …
Unsteady Effects Of A Pulsed Blowing System On An Endwall Vortex, Molly Hope Donovan
Unsteady Effects Of A Pulsed Blowing System On An Endwall Vortex, Molly Hope Donovan
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The low-pressure turbine is an important component of a gas turbine engine, powering the low-pressure spool which provides the bulk of the thrust in medium- and high-bypass engines. It is also a significant fraction of the engine weight and complexity as it can comprise up to a third of the total engine weight. One way to drastically reduce the weight of the low-pressure turbine is to utilize high lift blades. To advance high-lift technology, the Air Force Research Laboratory (AFRL) designed the L2F blade profile, which was implemented in the linear cascade at AFRL/RQT’s low speed wind tunnel facility. The …
Development Of A Computer Program For Transient Heat Transfer Coefficient Studies, Sri Prithvi Samrat Samayamantula
Development Of A Computer Program For Transient Heat Transfer Coefficient Studies, Sri Prithvi Samrat Samayamantula
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At the present time, the magnitude of transient convective heat transfer is approximated using heat transfer coefficient correlations developed for steady state conditions. This is done by necessity, as transient heat transfer correlations are not readily available. There is a rare transient heat transfer correlation found in the literature, but the number of correlations available can be counted on one hand. In addition, the literature does provide some plots of Nusselt numbers for specific cases of transient convective heat transfer, but these are limited to the specific case for which they were developed. The work presented in this thesis is …
Power/Thermal Interaction Within An Adaptive Turbine Engine, Andrew K. Desomma
Power/Thermal Interaction Within An Adaptive Turbine Engine, Andrew K. Desomma
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Usually power take off (PTO) with a two-spool turbofan engine has been accomplished via the high pressure (HP) shaft and bleed air from the high-pressure compressor (HPC). The PTO is used to run various aircraft components such as generators and hydraulic pumps, which also produce waste heat. To better understand the coupled transient nature of balancing engine thrust, power take off and thermal management, a transient variable cycle three stream turbofan engine model has been developed to investigate the integrated behavior. The model incorporates many dynamic features including a third-stream heat exchanger as a heat sink for thermal management and …