Master of Science (M.S.), University of Dayton, 2024, Mechanical Engineering

This work discusses the experimental testing of a nominal six-inch diameter single airstream rotating detonation engine that utilizes a hollow core to split the airstream into two separate flow paths and causes the test article to self-balance. Hydrogen and air were selected as the fuel/oxidizer combination for this test. The hollow core is designed to mimic a venturi nozzle, enabling the collection of pressure and temperature at the throat of nozzle to determine the mass flow rate through each flow path. Two Laval nozzles with varying contraction ratios, 7.5 and 11, and three fuel rings of varying injection are experimentally examined and their impact on the operability of the self-balancing RDE is investigated. This work highlights the calculation and determination of the mass flow split between the flow paths during cold flow and hot flow conditions, the operating map across six experimental configurations, and the impact of fuel injection penetration and momentum flux on the operability of the test article.

Committee: Matthew Fotia (Advisor); Taber Wanstall (Committee Member); Carson Running (Committee Member) Subjects: Mechanical Engineering

Master of Science (MS), Ohio University, 2024, Chemical Engineering (Engineering and Technology)

The objective of this research is to continue development of the flowtube, a new type of test equipment developed at the ICMT. Baseline testing is commonly used to validate models and ensure understanding of the electrochemical system. Baseline mass transfer experiments were performed using a rotating cylinder electrode (RCE). Baseline corrosion experiments were completed using an RCE as well as a rotating disk electrode (RDE). Mass transfer within the RDE system was also successfully modeled using computational fluid dynamics (CFD) software Ansys Fluent. Experimental and simulated results were validated using well known and accepted correlations. Validation of the CFD simulations is vital because no physical prototype for the flowtube currently exists to compare with the CFD results. The RDE simulations will serve as a baseline to prove that Fluent is capable of performing accurate mass transfer calculations and potentially future corrosion simulations. Current testing apparatuses for flowing environments tend to be large and/or difficult to use in a small-scale lab. To combat this, the flowtube cell can create a controlled single phase flow regime in a glass cell or autoclave and can test 3 samples at one time in its most recent revision. A new revision is currently being created, so the flowtube was modeled using CFD in order to determine how design alterations will affect the flowing environment within the glass cell. The flowtube hydrodynamics have been successfully modeled using Ansys Fluent. This model can illustrate fluid flow in the glass cell around the flowtube apparatus in both steady state and transient conditions. This model will continue to be expanded upon in the future to reflect the design considerations for the next prototype version. Design considerations and their impact on the hydrodynamics of the flowtube system were analyzed through this research.

Committee: Srdjan Nesic (Advisor); Marc Singer (Committee Member); Bruce Brown (Committee Member); Rebecca Barlag (Committee Member) Subjects: Chemical Engineering; Engineering; Fluid Dynamics

PhD, University of Cincinnati, 2004, Engineering : Environmental Engineering

Biofiltration has developed into a promising technology for the abatement of volatile organic compounds (VOCs), odors, and hazardous air pollutants in waste gas streams. Many factors, however, are still creating an environment for greater innovation as well as new products for biofiltration processes. Rotating drum biofilters (RDBs) are such an innovation. The objectives of this investigation are to develop and understand RDBs and consequently to design and operate RDBs properly. Three RDBs, a single-layer RDB, a multi-layer RDB, and a hybrid RDB, were developed and evaluated at various design and operation conditions in this investigation. Spongy medium that was used to support the biofilms was mounted on a cylindrical drum frame that was rotated at a preset speed. Diethyl ether, toluene, and hexane were chosen as the model VOC. Results showed that the RDBs were readily started up and removed VOCs with high water solubility and a low value of Henry' constant efficiently with more than 6 month duration without any biomass control measures. The single-layer and hybrid RDBs usually reach the lowest and highest VOC removal efficiency. VOC removal efficiency decreased with increased VOC loading rate and decreased gas empty contact time (EBCT). Nitrate in the liquid phase of the RDBs can be rate-limiting for diethyl ether removal. With increased drum rotating speed, the change in VOC removal efficiency depends on VOC properties, VOC loading rate, drum rotating speed value, and biofilter configurations. The microbial community structure along medium depth are almost identical for each of the RDBs , however, the structure changes with the operation conditions and biofilter configuration. Review of the biomass accumulation rates among different layers reveals four biomass accumulation patterns which represent different removal mechanisms: surface biofiltration, in-depth biofiltration, shallow biofiltration, and reverse biofiltration. The dominant biomass accumulation patter (open full item for complete abstract)

Committee: Dr. Makram Suidan (Advisor) Subjects: Engineering, Environmental

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

In recent years, rotating detonation combustors (RDCs) have come to the forefront of combustion research with their potential to revolutionize gas turbine combustion. The technology promises to drastically increase combustion efficiency, reduce combustor complexity/sizing, and achieve significant pressure rise across the combustor. A form of pressure gain combustion, rotating detonation combustors utilize detonative combustion to achieve combustion of reactants in a continuous but inherently unstable process. A detonation cell anchors within the combustor chamber and continuously rotates around the thrust axis, combusting fresh reactants as the wave travels, at supersonic velocities. This work explores a novel concept for an RDC which utilizes two separate air and fuel flows. Referred to as the pilot and core flows, a combusted core flow undergoes secondary combustion through a rotating detonation combustor acting as a pilot flameholder to impart additional energy. This approach hopes to not only improve the RDC operation space, but also to demonstrate the viability of an RDC as a device to detonatively combust reactants in two separate high-temperature flows. While the pilot flow is electrically heated, the core flow is heated via combustion to achieve higher temperatures, with the reduced oxygen content considered. This work focuses on the design and initial testing of a facility constructed to serve as a platform for investigating combustors with conditions beyond traditionally available laboratory flows. The facility, known as the Center Hill Detonation Laboratory (CDL) is located at the University of Cincinnati's Center Hill Research Facility, a satellite campus of the University of Cincinnati built for advanced research experiments. At the core of the facility's capabilities are the ability to provide multiple sources of high air mass flows, electric air heating, and a gaseous pre-burner system that can provide elevated core flow temperatures. Crucia (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member) Subjects: Aerospace Engineering

MS, University of Cincinnati, 2024, Engineering and Applied Science: Aerospace Engineering

Detonation combustion based propulsion systems, although not currently in use, hold the promise of many benefits over the deflagration combustion that used in existing air and space travel. These benefits include increased thermodynamic efficiency, which leads to more work done for less fuel, and simpler designs, which can result in reduced weight and cost per propulsion system. There are two main categories of detonation combustors, pulse detonation combustors (PDC) and rotating detonation combustors (RDC). In much of the literature, PDC and RDC are frequently used interchangeable with pulse detonation engine (PDE) and rotating detonation engine (RDE), a convention that will be continued here. Both of these detonation systems were used as part of this thesis project. This project consisted of two parts. The first was an experimental study on the impact of a magnetic field on a detonation wave in a PDC type device. Magnetic fields that were calculated to be between approximately 0.25 T and 0.35 T were used. This portion of the project found little to no significant changes in the flow properties of pressure and velocity at similar conditions when a magnetic field was present as opposed to when no magnetic field was present. These results, while not new, informed the study's predictions for the next portion of the project and suggested that the operation of a PDC would be roughly unchanged in the presence of a magnetic field. In the next portion of the project, the magnetic field was transferred over to an RDC. This allowed for the main goal of this thesis, the measurement of the current induced by the interaction between the detonation wave and magnetic field, to be completed. It has been suggested that it might be possible to use this current to generate electrical energy from the RDC while it is operating. This electrical energy could then be used as a supplemental source of electrical power as needed on an air or spacecraft. To measure this curre (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Daniel Cuppoletti Ph.D. (Committee Member); Shaaban Abdallah Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Sciences (Engineering), Case Western Reserve University, 2024, EMC - Aerospace Engineering

In icing conditions, ice accretes on aircraft components which impacts performance and stability. Researchers simulate icing in wind tunnels to understand icing physics and to develop methods of mitigating its effects. This research investigates the capabilities of the Adaptive Icing Tunnel (AIT), a small-scale tunnel designed to conduct economical and quicker tests. A test plan is developed to characterize the temperature in the AIT including objectives, instrumentation, methodology, and test matrices. Four drop sizing methods are developed that use scaling physics, LEWICE, a cloud droplet probe (CDP), and a rotating multi-cylinder. For specified ice shapes, the scaling and LEWICE methods result in average differences between the calculated and actual MVDs of 24.5% and 71.9% respectively. Methodologies and test plans are developed to use the CDP and the rotating multi-cylinder. The test plans designed will be used during the initial aerothermal and icing cloud characterizations of the AIT.

Committee: Paul Barnhart (Advisor); Chirag Kharangate (Committee Member); Majid Rashidi (Committee Member); Ru-Ching Chen (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

MS, University of Cincinnati, 2023, Engineering and Applied Science: Aerospace Engineering

This thesis studies the effect of equivalence ratio and mass flow rates on the near-field acoustic properties of a Rotating Detonation Engine. Two experiments were carried out to study this. Experiment one had mainly cases with no detonation and cases with unstable detonation, while experiment two had all stable detonations. The acoustic modes of the combustor used in experiment one were explored and the correlation between the acoustic modes and the peak frequencies were examined. This study shows a clear trend in acoustics with change in equivalence ratio. These trends also differ with detonation modes. Unstable detonations and stable detonations saw highest amplitude and frequency around stoichiometry equivalence values while test cases without detonations did not follow this trend. Instead, amplitude continued to increase as equivalence ratio increased. These results helped to build on the existing information about the acoustics of rotating detonation engines.

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Paul Orkwis Ph.D. (Committee Member); Jeffrey Kastner Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science (M.S.), University of Dayton, 2022, Aerospace Engineering

Rotating detonation engines (RDEs) have continued to gain interest in the combustion research industry as a promising form of pressure gain combustion (PGC). The RDE has the potential for better performance than existing turbo-engines with its simplicity of design and manufacturing, lack of moving parts, increased power density, lower entropy, and high thermodynamic efficiency. The large pressure rise, or gain, in PGC can be used to produce increased thrust or extract shaft work. A lot of progress has been made in the last decade, however, there are still many challenges to overcome with RDEs. In particular, there are many complications with the feed mechanics of an RDE that influences the overall RDE performance. The goal of this study is to evaluate if changing the taper of the RDE channel impacts the feed mechanics and operation of the RDE. Current RDE research has mainly focused on two types of RDE designs – the radial and axial configuration. These configurations relate to the direction air and fuel are injected into the system. For this study, the reactants were fed axially. An existing axial RDE test rig in AFRL is utilized in this investigation, with new components made for the outer body, center body, and the inner and outer air injector plates of each configuration. In this research, three different configurations are tested. One design with no taper, which serves as the baseline. The other additional two configurations feature either a 15-degree taper inward or a 30-degree taper outward. Each of the three design configurations held certain constants in order to be able to make fair comparisons with the data. All designs have a channel length of 4.5 inches and the centerline of each profile starts at the same radial location. The designs have a nominal 0.9-inch channel width and all channel area ratios were held constant across all three designs. Each design configuration is tested across a wide range of equivalence ratios and mass flows. Pressure an (open full item for complete abstract)

Committee: Matthew Fotia Ph.D. (Committee Chair); Christopher Stevens Ph.D. (Committee Member); Frederick Schauer Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Master of Science (M.S.), University of Dayton, 2022, Aerospace Engineering

Rotating Detonation Engines (RDEs) and pressure gain combustion (PGC) present a pathway to increased performance and fuel savings due to improved thermal efficiency and power density. RDEs utilize detonations to combust reactants, which provides higher thermal efficiencies than deflagration combustion. This increase in efficiency comes from increases in total pressure achieved across the detonation front, whereas deflagrations produce losses in total pressure. However, high thermal loads have limited uncooled and conventionally manufactured RDE test duration. Currently there is a need to develop novel cooling schemes that minimize the associated performance penalty, provide adequate cooling to extend test duration, and characterize changes in RDE performance and operability. This investigation was aimed at quantifying film cooling when applied to the unsteady and adverse pressure gradient of a RDE. Two film cooled outer-body combustion liners were manufactured and tested using a H2-air operated 6-inch RDE with an aerospike plug nozzle, heat sink center-body, and a 0.64 inch detonation channel width. Additionally, a control liner without holes was manufactured and tested. The two film cooled liners varied film pressure drop to characterize changes in RDE operability, temperature response, and cooling manifold pressure unsteadiness. All liners used approximately equivalent total flow area, as well as diameter weighted axial and circumferential spacing to allow comparison. The combustion air injection area ratio was set to 0.33, and the nozzle area ratio set to 1.0 and 0.66 relative to the channel area. Combustion air manifold pressures, cooling air manifold pressures, cooling air temperature, combustion liner temperature, operating mode, detonation stability, and detonation wave speed were analyzed for an array of combustion air mass flow rates, equivalence ratios, cooling air mass flow rates, and liner geometries. A high-speed camera was utilized to confirm operating (open full item for complete abstract)

Committee: Matthew Fotia (Committee Chair); Frederick Schauer (Committee Member); Adam Holley (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

MS, University of Cincinnati, 2021, Engineering and Applied Science: Mechanical Engineering

In recent years, intelligent data-driven techniques for health identification and diagnostics of rotating machines, have started to gain increasing attention for optimizing maintenance practices, enhancing operational safety, and reducing unnecessary costs. Specifically, deep learning methodologies have been popularly developed because of their ability to automatically extract meaningful features from raw measurement data. Owing to this, they are suitable for industrial applications, where feature engineering knowledge and domain expertise might be limited. Despite their effective development, a major drawback of traditional approaches lies in the general assumption that the training and test dataset are acquired from similar distributions, i.e., same mechanical system/component under identical conditions. However, in real-world applications, the diagnostic model developed using labeled train data (referred as source domain) can be applied on a different (but related) unlabeled test data (referred as target domain). In such scenarios, where there exists a distributional shift, the generalization ability of the model is seriously affected leading to poor fault diagnosis performance. This cross-domain diagnostic issue is further enhanced in harsh practical conditions with environmental noise and reduced data availability. To minimize the distributional gaps and improve the model's generalization process, a domain adaptation methodology within the deep learning framework has been proposed in this study. Multiple convolutional operations coupled with maximum mean discrepancy metric, facilitate automatic extraction of domain-invariant features for promising diagnostic performance across domains. For further enhancing the model's robustness and maintaining high levels of generalization, noisy condition labels are introduced during the model training process. Using the proposed approach, promising results can be obtained even with strong noise interference in testing da (open full item for complete abstract)

Committee: Jay Lee Ph.D. (Committee Chair); Jay Kim Ph.D. (Committee Member); Manish Kumar Ph.D. (Committee Member) Subjects: Mechanical Engineering

MS, University of Cincinnati, 2020, Engineering and Applied Science: Aerospace Engineering

The combustor and exhaust dynamics of four different RDC configurations are studied via visualization using a mid-infrared camera that acquires frames at multiple exposure times. In one-wave operation significant swirl is imparted on fresh reactants by the rotation of the detonation wave, while counter-rotation de-swirls reactants. Significant pre-burning of fresh reactants was also found regardless of operational mode. At higher-flow rates, waves exhibit a distinct double-lobed shape, similar to the cell structure seen in detonation theory, but much larger in width, indicating that this may be one wave about to split into two. There are extensive regions of unburnt reactants that exist near the outer wall indicating poor mixing of reactants. The extent of the unburnt reactants is seen to have an effect on the shape of the exhaust by dictating whether it is angled outward, straight, or angled inward. Spatial partial orthogonal decomposition performed on the combustor showed that the inclination of fresh reactants was in fact a distinct flow feature. SPOD also showed multiple swirling structures in the exhaust during one-wave modes. These structures were noticeably absent in counter-rotating propagation. A newly designed flow-through RDC is manufactured and tested in order to characterize its operating map. A mixture of hydrogen and air at varying air mass flow rates and equivalence ratios are tested. The combustor was unable to light off or operated as a deflagration at all tests at 0.2 kg/s, and a majority of tests at 0.3 kg/s, indicating that the bulk velocity of the air may have been too low. Detonations were seen only at a small handful of conditions, only at 0.4 and 0.5 kg/s of air. The rest of the test cases operated as transition points, where they saw switches between deflagration and detonation throughout the test. These existed just below stoichiometric, all the way to rich conditions. Interesting was the transition from detonation to deflagration which (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Daniel Cuppoletti Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, The Ohio State University, 2021, Mechanical Engineering

This document presents the development and implementation of a new generation of double-sided heat-flux gauges at The Ohio State University Gas Turbine Laboratory (GTL) along with heat transfer measurements for film-cooled airfoils in a single-stage high-pressure transonic turbine operating at design corrected conditions. Double-sided heat flux gauges are a critical part of turbine cooling studies, and the new generation improves upon the durability and stability of previous designs, while also introducing high-density layouts that provide better spatial resolution. These new customizable high-density double-sided heat flux gauges allow for multiple heat transfer measurements in a small geometric area such as immediately downstream of a row of cooling holes on an airfoil. Two high-density designs are utilized: Type A consists of 9 gauges laid out within a 5 mm by 2.6 mm (0.20 inch by 0.10 inch) area on the pressure surface of an airfoil, and Type B consists of 7 gauges located at points of predicted interest on the suction surface. At the same time, improvements to the manufacturing and installation processes for single gauges increased the survival rate of the gauges from 47% to 84%. Both individual and high-density heat flux gauges are installed on the blades of a transonic turbine experiment for the second build of the High-Pressure Turbine Innovative Cooling program (HPTIC2). Run in a short duration facility, the single-stage high-pressure turbine operated at design-corrected conditions (matching corrected speed, flow function, and pressure ratio) with forward and aft purge flow and film-cooled blades. Gauges are placed at repeated locations across different cooling schemes in a rainbow rotor configuration. Airfoil film-cooling schemes include round, fan, and advanced shaped cooling holes in addition to uncooled airfoils. Both the pressure and suction surfaces of the airfoils are instrumented at multiple wetted distance locations and percent spans from roughly (open full item for complete abstract)

Committee: Randall Mathison PhD (Advisor); Michael Dunn PhD (Committee Member) Subjects: Aerospace Engineering; Engineering; Experiments; Mechanical Engineering

Master of Science, The Ohio State University, 2020, Welding Engineering

Aluminum gas metal arc welding (GMAW) uses inert shielding gas to minimize weld pool oxidation and reduce susceptibility to porosity and lack of fusion defects. For aluminum shipbuilding, Naval requirements highly recommend the use of helium – argon mixtures or 100% (pure) helium shielding gas to provide a broader heat field and ensure proper weld fusion, particularly at the weld toes. Pure argon shielding gas can be used but it has proven to be susceptible to lack of fusion and porosity defects, particularly in thick sections that pose a large heat sink where argon's lower thermal conductivity promotes a narrower arc heat field and poorer weld penetration. The continued use of helium is a concern because it's a finite resource that costs approximately 5 times argon. In this study, the rotating electrode pulsed gas metal arc welding (REP-GMAW) process was investigated as a way to solve the argon shielding fusion problem, mitigate helium consumption, and provide shipbuilding cost savings. The target application was horizontal and vertical erection butt joints made from 5083 aluminum plate. An advanced REP-GMAW torch was used that permitted the evaluation of a range of electrode spin diameters and frequencies. Compared to torch weaving at a couple hertz, the arc heat field and bead shape can be more effectively changed since the rotation speeds can be up to 5,000 rotations per minute (~83 hertz). A series of bead on plate tests were used to evaluate the relationship between ER5183 electrode rotation parameters and arc power on constant deposit area bead shape. These tests were compared to stringer beads (no oscillation) that were made with argon, helium, and helium-argon shielding gases. Preferred rotating electrode parameter relationships were developed with pure argon for producing weld beads that had underbead fusion profiles that were equivalent to helium-based weld deposits. For preferred deposit sizes for groove welding, preferred bead shape welds were (open full item for complete abstract)

Committee: Dennis Harwig Dr. (Advisor); Boyd Panton Dr. (Committee Member) Subjects: Engineering

Doctor of Philosophy, University of Akron, 2020, Mechanical Engineering

In this research, an innovative surface engineering process, ultrasonic nanocrystal surface modification (UNSM), was used to process a 7075-T651 aluminum alloy. It was observed that UNSM led to better surface finish, higher surface hardness, and the generation of an oxide layer on the surface of this alloy, in addition to beneficial compressive residual stresses in the near-surface region. Rotating–bending fatigue tests showed that UNSM processing significantly improved the fatigue performance of 7075-T651 aluminum alloy in both the low-cycle fatigue regimes and high-cycle fatigue regimes. Besides, the oxides that formed in the surface layer after UNSM treatment were found to prevent pitting corrosion of 7075-T651 aluminum alloy in a 3.5 wt% NaCl solution. Therefore, the fatigue performance of the UNSM-treated samples did not deteriorate after corrosion in a 3.5 wt% NaCl solution. These results demonstrate that UNSM is a robust surface modification method that can improve the rotating–bending fatigue resistance and pre-corrosion fatigue resistance of the 7075-T651 aluminum alloy. Furthermore, the fatigue life extension of the pre-damaged 7075-T651 aluminum alloy through UNSM treatment was investigated for the first time. It was found that the fatigue life of 7075-T651 aluminum alloy deteriorates after being immersed in a corrosion solution. However, UNSM treatment significantly recovered the fatigue life of the pre-corroded samples. Removal of corroded surface layer, the introduction of work-hardened surface region and compressive residual stress by UNSM treatment played a compelling role in the restoration of fatigue life of the pre-damaged sample. This result indicated that UNSM is a feasible method for rejuvenation of corrosion-damaged 7075-T651 aluminum alloy. UNSM also showed its powerful effectiveness to rejuvenate pre-fatigued 7075-T651aluminum alloy.

Committee: Yalin Dong (Advisor); Chang Ye (Committee Member); Guo-Xiang Wang (Committee Member); Qixin Zhou (Committee Member); En Cheng (Committee Member) Subjects: Mechanical Engineering

Doctor of Engineering, University of Dayton, 2020, Mechanical Engineering

The mixing industry has long depended on scaled down experimental methods combined with computational analysis to determine rotating mixer designs for customer applications. Most industrial mixing companies have the capabilities in-house to perform these experiments and the analysis to show customers the benefits of proposed designs. Experimental methods center around the calculation of power draw of the mixing unit, determined from a simple torque cell to determine power draw, and the blend time, shown through acid-base neutralization, which are both fairly simple to calculate from an scaled down rig and apply it to either customer designs or in the development of new mixers. The computational analysis centers around research done by mixing forefathers who developed methodology to calculate time dependent mixing parameters, like blend time, through steady state analysis due to restrictions in computational capacity. This is possible because the majority of the mixing can be observed from studying the macro-scale interactions. The impellers and baffles in a tank drive large scale motion which blends two different species or temperatures together to create a uniform mixture. Similar to rotating mixers, there are two main parameters used when analyzing static mixers. Similar to power draw for rotating mixers, static mixers are driven by the pressure drop across the mixer. The second parameter that is used to determine the effectiveness of a static mixer is the coefficient of variation, a statistical measurement of the degree of uniformity. This looks at a two-dimensional plane located downstream from the mixer outlet and determines the effectiveness of the mixer. This has been used for decades to provide the target for customer designs, but it provides a limited picture of the process. The snap shot on a two-dimensional plane provides a small window into what is happening in the entire process. The coefficient of variation also is merely a statistical paramete (open full item for complete abstract)

Committee: Markus Rumpfkeil Ph.D. (Advisor); Kevin Myers D.Sc. (Committee Member); Eric Janz (Committee Member); John Thomas Ph.D. (Committee Member); Robert Wilkens Ph.D. P.E. (Committee Member) Subjects: Chemical Engineering; Engineering; Mechanical Engineering

Master of Science in Materials Science and Engineering (MSMSE), Wright State University, 2020, Materials Science and Engineering

Rotating Detonation Engines (RDE) are being explored as a possible way to get better fuel efficiency for turbine engines than is otherwise possible. The walls of the RDE are subjected to cyclic thermal and mechanical shock loading at rates of approximately 3 KHz, with gas temperatures as high as 2976 K. This project performed testing with Inconel 625 and 304 stainless steel coupons in an RDE outer body to attempt to measure material ablation rates. Significant microstructural changes were observed to include grain growth in both alloys, carbide formation and grain boundary melting in Inconel, and formation of delta ferrite in the stainless steel. The testing performed in this study was unable to generate a wear rate for either material. The Inconel coupons exhibited threshold behavior, with no measurable material loss below a critical temperature, and near instantaneous melting and failure above that temperature. The 304 survived the most aggressive test conditions the facility could produce without measurable ablation. Longer duration testing is required in order to determine a damage rate for these materials under a detonative environment.

Committee: H. Daniel Young Ph.D. (Advisor); Raghavan Srinivasan Ph.D., P.E. (Committee Member); Christopher Stevens Ph.D. (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Materials Science; Metallurgy

Doctor of Philosophy, The Ohio State University, 2020, Chemistry

Electrochemical reduction of CO2 (CO2RR) is a promising route to convert CO2 to value-added chemicals such as carbon monoxide, formic acid, methanol, and others. Efficient conversion of CO2 using renewable sources of electricity can potentially mitigate the rising CO2 concentration in the atmosphere in addition to alleviating our dependence on fossil fuels to generate chemicals. Most of the CO2RR studies to date focus on designing novel catalysts to improve the reaction activity and selectivity for real-world applications. However, being able to quickly and accurately evaluate the performance of newly-designed catalysts and to rapidly screen catalyst candidates remain an essential part of the catalyst discovery process. Traditional product analysis routine includes sample pre-concentration (e.g. using long electrolysis time), sample preparation, instrument detection (e.g. GC or NMR) and/or instrument availability. This time-consuming routine heavily impedes the efficient evaluation and screening of newly-designed CO2RR catalysts. It also limits our ability to investigate the catalyst degradation mechanism within a short time frame like minutes. In this work, a rotating ring-disc electrode (RRDE)-based method was proposed and demonstrated to be able to shorten the total product analysis time from several hours (even days) to less than 1 minute. Small CO2RR product molecules such as H2, CO, HCOOH and their mixtures were proved to be quantified successfully on an RRDE assembly based on their electrochemical fingerprints. During CO2RR, OH- is always generated concurrently with reduction products. The accumulation of OH- near the catalyst surface during CO2RR remains a critical issue since the local pH can easily be over 3 pH units higher than the bulk during electrolysis and thus directly affects the CO2RR activity and selectivity. To systematically investigate the role of local pH on CO2RR selectivity and consequently the reaction pathway, in this work, an RR (open full item for complete abstract)

Committee: Anne Co (Advisor) Subjects: Analytical Chemistry; Chemistry

MS, University of Cincinnati, 2019, Engineering and Applied Science: Aerospace Engineering

RDC: Several variants of rotating detonation combustors are investigated in order to determine the impacts of mass flowrate, equivalence ratios, and geometry on the detonation front itself. High speed OH* chemiluminesence imaging is taken of the detonation front through a quartz outerbody. These images are then run through several imaging algorithms in order to draw quantitative information from the photographs. It was found that as the mass flowrate is increased, the intensity of the detonation front is increased as well. Increasing the air mass flowrate also increased the wave height which is consistent with previous literature. The low and high extremes of equivalence ratios resulted in less stable and less intense operation. Pulsejet: Several pulsejets are investigated in order to determine the effects of geometrical variation on the pressure, ionization, thrust, and temperature inside of the pulsejet. Two combustors, three tailpipes, and two flarings are interchanged to provide twelve different geometries. Data are collected from four pairs of axially distributed pressure and ionization sensors, three thermocouples, and one load cell and is analyzed to characterize its operation. A wavelet decomposition is utilized to assess the impact of structural vibrations upon the dynamic load cell measurements. The analysis indicates that the addition of a flaring significantly increases thrust and temperature of the engine. Furthermore, each combustor sizing has a preferred tailpipe length associated with it. Excessive deviation from this condition (especially shorter lengths of tailpipes) may result in a pulsejet than cannot operate unassisted (without forced air or fuel injection).

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

PhD, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering

Recent years have witnessed a notable increase in endeavors resorted to investigating unsteady combustion/pressure processes that offer a prospective increase in stagnation pressure due to a more efficient combustion of fuel. One such pressure gain combustion (PGC) concept is a rotating detonation combustor (RDC). RDCs make use of a rotating detonation wave that travels circumferentially about a hollow or annular chamber at kilohertz frequencies, continually combusting the supplied reactants without the need for more than one initial ignition event. Due to its simplicity in design, which can be integrated into existing systems' architecture, and the lack of moving mechanical components, RDCs are at the forefront of PGC research. The current dissertation deals with the basic mechanics of these combustors. Specifically, the diverse modes of detonative operation in annular and hollow combustor configurations are experimentally studied, and the variables dictating these modes are extracted. The question of what exactly constitutes a rotating detonation combustor is answered, by “converting” a conventional atmospheric deflagrative hollow combustor into an RDC. Further, based on this demonstration, the numerous kinships between RDC operation and decades of observations pertaining to high frequency combustion instabilities in rocket engines are presented and discussed. It is argued that most of the poorly understood phenomena of high frequency instabilities can be explained by detonation-based physics. Finally, evidence is presented that suggests rotating detonations to be type of near-limit detonation behavior. The findings of this study are proposed to be useful for the three different communities of RDC research, rocket engine instabilities and fundamental detonation physics.

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Mark Turner Sc.D. (Committee Member) Subjects: Aerospace Materials

MS, University of Cincinnati, 2018, Engineering and Applied Science: Aerospace Engineering

The effects of an azimuthally-grooved wall on rotation detonation combustors are investigated for hydrogen-air mixtures. Cause for this investigation came from the narrow range of operating points at which a detonative can operate with a stable, one wave mode. Using previous detonation research for linear detonations, the corrugated design was chosen and implemented into an RDC. Different air flow rates were tested, with equivalence ratios varying between 0.5 and 2 for three different channel widths and two outer-wall geometries — smooth (conventional) and corrugated with triangular obstacles on the outer wall — to compare the two operations. RDC operation with the corrugated wall produced sustained detonation propagation even at very small channel widths (3.18mm-6.35mm) where the smooth geometry failed across different flow rates. The reasons for this difference in operation are further investigated using shadowgraph imaging and reacting two-dimensional numerical simulations, leading to the conclusion that the reflected shock waves and strong vortices, both stemming from the presence of the obstacles, improved the propensity of detonation sustenance within the combustor. The obtained results appear to be in line with the findings from fundamental detonation studies, where similar obstacles tended to produce and sustain the detonations, at otherwise near-limit failure conditions. This presents a promising venue for obtaining rotating detonations in otherwise inoperable conditions of flow rates and mixture reactivity. Furthermore, within the detonative combustion community there has been more investigation into counter rotating modes. Analysis of both geometries show the existence of this mode, however the mode appears to be more pronounced in the conventional, smooth, geometry than the grooved design.

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Shaaban Abdallah Ph.D. (Committee Member); Prashant Khare (Committee Member) Subjects: Aerospace Materials