The radical intensity ratio of the diatomic carbon to methylidyne was characterized at initial pressures up to 10 bar using certified gasoline of 93% octane. This gasoline was selected due to its availability as a common fuel. The characterization of the radical intensity ratio of gasoline at elevated pressures enabled the creation of a calibration map of the equivalence ratio at engine relevant conditions. The proposed calibration map acts as a feedback loop for a combustor. It allows for the location of local rich and lean zones. The local information acquired can be used as an optimization parameter for injection and ignition timings, and future combustor designs. The calibration map is applicable at low and high engine loads to characterize a combustors behavior at all points in its operation map. Very little emphasis has been placed on the radical intensity ratio of unsteady flames, flames at high pressure, and liquid fuels. The current work performed the measurement on an unsteady flame ignited at different initial pressures employing a constant volume combustion chamber and liquid gasoline as the fuel source. The chamber can sustain a pressure rise of 200 bar and allows for homogenous fuel to air mixtures. The results produced a viable calibration map from 1 to 10 bar. The intensity ratio at initial pressures above 5 bar behaved adversely in comparison to the lower pressure tests. The acquired ratios at the higher initial pressures are viable as individual calibration curves, but created an unexpected calibration map. The data shows promise in creating a calibration map that is useful for practical combustors.

Propulsion systems continue to be influenced by the efficiency of combustion systems. One approach to substantially improve combustion efficiency is through pressure gain combustion or detonation-based engines. Additionally, detonations are being used as a high-energy ignition device by taking advantage of the rapid heat release that a detonation naturally exhibits. One method to utilize the power of detonations is through using a pulse detonation device to ignite an ethylene-fueled supersonic flame-holder, where the conditions are challenging due to the low temperatures, pressures, and residence times. In this study, we investigate the transient mechanisms of detonation wave diffraction through a geometric area expansion and contraction for pressure amplification. The sudden area expansion causes detonation diffraction, which results in complex interactions between deflagration fronts and reflected shock waves. Two expansion ratios are explored to tailor the detonation energy deposition and re-initiation location. High-speed broadband chemiluminescence and schlieren illustrate the gas dynamic mechanisms of the decoupling and re-initiation process through an optically accessible test section. Pressure and velocity measurements are also acquired simultaneously. The results show that the detonation is subcritical as it enters the expansion, causing it to decouple. The re-initiation mechanism is shown to be a coalescence of transverse waves or reflection off the back wall depending on the expansion ratio and length of the expansion chamber.

Stationary power generating gas turbines are held to strict emissions standards that limit efficiency and power output. Dry low NOx combustors are being designed to limit NOx emissions while simultaneously improving efficiency. Axially staged combustors are leveraged to reduce emissions by staging heat release into separate stages. This is done by splitting some fuel and air to a downstream axial stage that is closer to the combustor exit. In this stage, the residence time is decreased allowing for optimal turbine inlet temperatures with improved emissions. The current thesis focuses on the downstream reacting jet-in-crossflow at power generating gas turbine relevant conditions. The experimental facility consists of a headend burner which provides a vitiated crossflow at various conditions for the axial stage. The headend burner consists of a concentric dump style combustor that is used to stabilize a lean methane-air flame. Downstream of the vitiator is the test section which consists of 3 optical viewing ports for imaging diagnostics and an interchangeable injector plate to study different jet geometries. The current work investigates a 4 mm diffusion jet, a 0.5 in fully premixed jet, 0.5 in partially premixed jet, and a 0.5 in fully premixed jet. Particle Image Velocimetry (PIV) is utilized to obtain flow-field characteristics, and CH* chemiluminescence is used to visualize flame behavior. Additionally, a Horiba gas analyzer is used to obtain emissions measurements for various run conditions. Various flames are observed for the different conditions ran, and emissions measurements show axially staging benefits at full load gas turbine conditions.

During the life cycle of aircraft, external structures are under constant attack from environmental degradation in the form of corrosion. Corrosive defects consist of multiple types of surface and subsurface damage that are often undetectable due to surface coatings or insulation leading to loss in structural integrity. Non-destructive techniques for corrosion detection typically require the removal of paint. Detection of corrosion under insulation (CUI) is highly valuable for cost and time effectiveness. Although techniques have been developed for detection of CUI, not many of these satisfy the criteria for portability and hangar operation. To address this, multiple techniques were investigated yielding Pulsed Eddy Current Thermography (PECT) as a promising technique to pursue a proof of concept. Through multiphysics simulation using COMSOL, case studies were developed to understand and predict the temperature responses of aircraft materials when altering the current, lift off, and defect size and to design the coil for optimal non-destructive detection capabilities. Initial studies were conducted on various samples including coated and uncoated Aluminum, Carbon steel, Zinc-galvanized carbon steel with different types of corrosion. A novel in-house MATLAB© code was developed for post-processing of the corroded samples. Initially, defect localizations through edge heating or from dissipation were captured through IR thermography. To address issues with non-uniformity of heating that decrease the accuracy and precision of this technique, the thermal change with respect to time was analyzed through each frame and decomposed using Fourier transform from the time domain to a frequency domain. Manufactured corroded defects made through salt fog and acid baths, such as pitting voids, were detected under insulation of 125 microns with diameters ranging from 0.5 - 1 mm for all material systems. These results show the high potential of PECT for aerospace on-field applications providing location and shape for defects under insulation.

Naval propulsion is a critical component for every vessel, and it is the subject of this thesis, specifically bio-inspired propulsion. Numerical modeling is used as a tool to understand the relationship between mechanical undulation and the hydrodynamic response. Through three stages, the research presented here examines and refines tools for understanding fundamentals of undulating propulsion. Those three objectives are: to verify and validate the proposed numerical models against existing experiments, establishing a baseline of fidelity; to examine the causal linkage between fluid-boundary interactions and undulating propulsion; and to create a moment based method for characterizing generalized undulating propulsive mechanisms. First, a verification and validation effort is performed for three representative experiments which exhibit key characteristics of undulating propulsion. As a part of these validation efforts, uncertainty quantification is used to highlight and guide appropriate regions for CFD application. Second, parametric studies are performed on a simplified undulating bodies to generate an understanding of how localized mechanical deformations from a generic swimming motion, shape the unsteady fluid dynamics of the system. Finally, to quantify the performance and efficiency of various swimming motions, a moment based approach is developed which examines wake profiles and computes efficiency metrics. The sum total of these three efforts provides a unified, coherent understanding of common forms of undulating propulsion and can propel future work in the field.

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, in this case, heat transfer. This theory is tested by contouring the walls of the duct by the extracted mode shapes. The test procedure is taken from an industrial perspective. An initial, unmodified geometry provides a baseline for comparison to later contoured models. The initial case is run as a steady-state Reynolds-Averaged Navier-Stokes model. Large-Eddy Simulation generates the necessary data for the DMD analysis. Several mode shapes extracted from the flow are applied to the duct walls and run again in the RANS model, then compared to the baseline, and their relative performance examined.

This study describes three-dimensional (3D) quantitative visualization of density field in a supersonic flow around a cone spike. A measurement of the density gradient is conducted within a supersonic wind tunnel facility at the Propulsion and Energy Research Laboratory at the University of Central Florida utilizing Structured Light-Field Focusing Schlieren (SLLF). In conventional schlieren and Shadowgraph techniques, it is widely known that a complicated optical system is needed and yet visualizable area depends on an effective diameter of lenses and mirrors. Unlike these techniques, SLLF is yet one of the same family as schlieren photography, it is capable of non-intrusive turbulent flow measurement with relatively low cost and easy-to-setup instruments. In this technique, cross-sectional area in the flow field that is parallel to flows can be observed while other schlieren methods measure density gradients in line-of-sight, meaning that it measures integrated density distribution caused by discontinuous flow parameters. To reconstruct a 3D model of shock structure, two-dimensional (2D) images are pictured to process in MATLAB. The ultimate goal of this study is to introduce a novel technique of SLLF and quantitative 3D shock structures generated around a cone spike to reveal the interaction between free-stream flow and the high-pressure region.

Modelling flow and acoustics in a constricted duct at low Mach numbers is important for investigating many physiological phenomena such as phonation, generation of arterial murmurs, and pulmonary conditions involving airway obstruction. The objective of this study is to validate computational fluid dynamics (CFD) and computational aero-acoustics (CAA) simulations in a constricted tube at low Mach numbers. Different turbulence models were employed to simulate the flow field. Models included Reynolds Average Navier-Stokes (RANS), Detached eddy simulation (DES) and Large eddy simulation (LES). The models were validated by comparing study results with laser doppler anemometry (LDA) velocity measurements. The comparison showed that experimental data agreed best with the LES model results. Although RANS Reynolds stress transport (RST) model showed good agreement with mean velocity measurements, it was unable to capture velocity fluctuations. RANS shear stress transport (SST) k-ω model and DES models were unable to predict the location of high fluctuating flow region accurately. CAA simulation was performed in parallel with LES using Acoustic Perturbation Equation (APE) based hybrid CAA method. CAA simulation results agreed well with measured wall sound pressure spectra. The APE acoustic sources were found in jet core breakdown region downstream of the constriction, which was also characterized by high flow fluctuations. Proper Orthogonal Decomposition (POD) is used to study the coherent flow structures at the different frequencies corresponding to the peaks of the measured sound pressure spectra. The study results will help enhance our understanding of sound generation mechanisms in constricted tubes including biomedical applications.

This thesis focuses on the development of a flexible, physics-based life prediction approach for steels under complex conditions. Low alloy steels continue to be the materials of choice for large turbomachinery structures experiencing high temperatures for long durations. There has been significant advancement in the research of modern alloys; furthermore, these materials are continue to be utilized in boilers, heat exchanger tubes, and throttle valve bodies in both turbomachinery and pressure-vessel/piping applications. The material 2.25Cr-1Mo is studied in the present work. The resistance of this alloy to deformation and damage under creep and/or fatigue at elevated temperatures make it appropriate for structures required to endure decades of service. Also, this material displays an excellent balance of ductility, corrosion resistance, and creep strength under aggressive operating conditions. Both creep-fatigue (CF) and thermomechanical fatigue (TMF) have been the limiting factor for most turbine components fabricated from various alloys; therefore, a life prediction approach is constructed for simulating fatigue life for cases where the material is experiencing mechanical loading with thermal cycling. Flexibility is imparted to the model through its ability to emphasize the dominant damage mechanism which may vary among alloys. A material database is developed to improve and compare the model with experimental data. This database contains low cycle fatigue (LCF), creep fatigue (CF), and thermomechanical fatigue (TMF) experiments. Parameters for the model are obtained with regression fits with the support of a broad experimental database. Additionally, the cumulative damage approach, better known as Miner's rule, is used in this study as the fundamental method to combine damage mechanisms. Life predictions are obtained by the usage of a non-interacting creep-plasticity constitutive model capable of simulating not only the temperature- and rate-dependence.

Aerospace vehicles often experience triboelectric charging while traversing the atmosphere. Triboelectric charging occurs when a material come into frictional contact with a different material. Aerospace vehicles triboelectrically charge due to frictional contact with dust and ice crystals suspended in the atmosphere. Launch vehicles traversing ice clouds in low-pressure atmosphere are especially prone to electrostatic discharge events (i.e. sparks). These conditions are hazardous and affect the vehicle's launch commit criteria. In 2010, engineers from an ARES-I rocket launch reported concerns with triboelectric charging over their self-destruct system antenna. This concern was addressed by putting the antenna through harsh conditions in a laboratory environment. The need for laboratory testing could have been avoided if there was a mathematical model to predict these events. These discharge events can typically be predicted by the Classical Paschen's Law, which relates discharge voltage to pressure, material and distance between the charged and ground surfaces (i.e. electrodes). However, the Classical Paschen's Law does not capture any aerodynamic considerations such as large bulk flow and compressibility effects. It became apparent that a new model would be needed to predict a discharge voltage with aerodynamic considerations. This research focused on defining a theoretical model and providing experimental data to validate the model. The hypothesis of this work is that charged ions are removed too quickly for enough charge to build up and result in an electrostatic discharge at the voltage that is predicted by the Classical Paschen's Law. The wind tunnel testing for this experiment was conducted at the Center for Advanced Turbomachinery & Energy Research (CATER) facility. A charged electrode was exposed to flows at Mach numbers 1.5 to 3.5. It was found that the supersonic flow suppressed the electrostatic discharge events. The voltage required for an electrostatic discharge at supersonic conditions increased by a factor of three. The modified Paschen's Law can help in defining the launch commit criteria of aerospace vehicles.