Master of Science, The Ohio State University, 2020, Aero/Astro Engineering

This thesis covers the intensive research effort to elucidate the role of elevated temperature in deposition. Several experimental campaigns were conducted in this pursuit. The testing explored high temperature deposition with 0-10 micron Arizona Road Dust (ARD) with the intent of creating a yield strength model that included temperature effects and could be incorporated into the existing OSU deposition model. Experimental work was first conducted in the impulse kiln facility where small amounts of the test dust were placed on ceramic targets and rapidly exposed to temperatures between 1200K and 1500K. Trends in the packing factor confirmed the existence of two threshold values (1350K and 1425K) that could be linked to strength characteristics of the dust when exposed to high temperatures. Using the information obtained from the kiln experiments, HTDF testing was conducted between 1325K and 1525K. Exit temperatures were set at 25K intervals in this region with a constant jet velocity of 150 m/s. The capture efficiency data showed this trend with temperature and indicated a softening temperature and melting temperature of 1362K and 1512K respectively. With these critical values in hand, the Ohio State University Molten Model was created to modify yield strength with particle velocity and temperature. The model was tested using CFD and showed a good capability for capturing particle temperature effects in deposition from an impinging particle-laden jet. A subsequent test campaign was conducted to explore the effect of varying surface temperature on deposition. Hastelloy coupons with Thermal Barrier Coatings (TBCs) were subjected to a constant jet at 1600K jet and 200 m/s while being cooled via a backside impingement jet. Surface temperatures between 1455K and 1125K were impacted with 0-10 micron ARD while an IR camera monitored the surface. Coupons with higher coolant flowrates (lower surface temperature) saw significantly lower deposition rates than the higher surf (open full item for complete abstract)

Committee: Jeffrey Bons Dr. (Advisor); Randall Mathison Dr. (Committee Member) Subjects: Aerospace Engineering

Master of Science in Mechanical Engineering, Cleveland State University, 2021, Washkewicz College of Engineering

Recent developments in aircraft propulsion electrification are motivated by economic and environmental factors such as lowering greenhouse gas emissions, reducing noise, and increasing fuel efficiency. This thesis focuses on a hybrid gas-electric propulsion concept combining a gas turbine jet engine with an electromechanical (EM) system. An optimal control system allows energy to be recovered from the gas turbine engine or injected into it from an electric storage unit. Energy extraction or injection can be obtained by selecting a performance weight in the optimization function that trades off fuel consumption with stored electrical energy utilization. The goal of this research is to validate the effectiveness and plausibility of the optimal controller during representative acceleration and deceleration maneuvers and at steady state. To accomplish this, the gas turbine engine dynamics are simulated using NASA's T-MATS package and used in a hardware co-simulation approach along with physical hardware representative of the EM system, namely motors, power converter, and an energy storage device. A time scaling methodology was used to reconcile the power levels of the physical EM system (in the order of a kilowatt) with those of the engine simulation (in the order of megawatts). Multiple steady state missions were represented within a full simulation environment and in the lab test environment that covered a wide range of fuel-electric optimization weights. In addition, a chop-burst study was conducted to ensure the readiness of the system to handle flight missions. Based upon captured data, specifically that of shaft torque, supercapacitor voltage, and fuel flow measurements, it was determined that the optimal control objective was met. An increase in fuel-electric optimization weight corresponded to a desired change in torque to the engine and voltage to the energy storage device.

Committee: Hanz Richter (Advisor); Jerzy Sawicki (Committee Member); Lili Dong (Committee Member) Subjects: Engineering; Mechanical Engineering

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

The goal of this work is to design and develop an injector with a novel porous injection technology (PIT) for dry low NOx combustor (DLN). One of the key factors that is essential for lowering NOx levels is the efficient mixing of fuel-air in both spatial and temporal domains. The porous injection technology has the potential to reduce the spatial and temporal gradients to a minimum. This novel injector design utilized different concepts such as lean premixing, micro-mixing and straight flow with bluff bodies' stabilization mechanism. The micro-mixer is a multi-injector block with nine injectors arranged in an equally spaced rectangular 3 by 3 array. Each injector in the multi-injector block has a porous tube through which fuel is injected. The porous tube is made of stainless steel with 30 µm porosity. Each porous tube is surrounded by eight smaller tubes through which compressed air is passed. The centerbody is mounted above the porous tube. The fuel and air mix in the annular space between the injector wall and the porous tube. The reacting and non-reacting flows of the micro-mixer under atmospheric conditions and a pressure drop of 4% were investigated as part of the injector development process. To evaluate the fuel-air mixing quality, two measurement techniques were used. The CO2 mixing technique - developed in-house, was used to quantify the spatial variations in the fuel mass fraction. Planar Laser Induced Fluorescence (PLIF) was used to obtain both spatial and temporal fuel mass fractions. The CO2 mixing measurements were used to validate the PLIF data for quantification. The RMS fluctuations in spatial and temporal domains were quantified from PLIF data. The length of the upper block was optimized and decided based on the mixing quality. Furthermore, Particle Image Velocimetry (PIV) measurements were conducted to study the injector's aerodynamics under the same operating conditions. The PIV measurements showed a Central Toroidal Recirculation Zone (CT (open full item for complete abstract)

Committee: San-Mou Jeng Ph.D. (Committee Chair); Jun Cai Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member); Bassam Mohammad Abdelnabi Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, The Ohio State University, 2005, Graduate School

Committee: Not Provided (Other) Subjects:

Master of Science, The Ohio State University, 2024, Aerospace Engineering

The role of quartz in gas turbine hot section deposition was investigated by varying both its size and percent concentration in Air Force Research Lab test dust (AFRL-02). The size distributions of quartz tested were 0 – 3 μm, 0 – 10 μm (baseline), and 10 – 20 μm while percent concentration ranged from 0% to 100%. The experiments replicated a gas turbine effusion cooling circuit with a flow temperature of 894K and plate surface temperature of 1144K. Aerosolized AFRL-02 dust was delivered to the test article, and capture efficiency, hole capture efficiency, blockage per gram, normalized deposit height, and effective area were recorded. A quartz size distribution of 0 – 3 μm showed the greatest deposition while 10 – 20 μm consistently deposited the least. Varying percent concentration of quartz had less obvious trends. While at a size distribution of 10 – 20 μm, increasing quartz concentration decreased deposition in all four assessment parameters. For a size distribution of 0 – 3 μm, increasing quartz concentration originally decreased deposition until greatly increasing it past a concentration of 68%. Quartz has been identified as a predominantly erosive mineral to deposits, but results suggest the size distribution contributes to deposition at a rate greater than or equal to percent concentration. The following study elucidates the effects of both size and concentration of quartz in a heterogenous mineral blend.

Committee: Jeffrey Bons (Advisor); Randall Mathison (Committee Member) Subjects: Aerospace Engineering

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

If gone undetected, volcanic ash in the atmosphere can have significant negative effects on the performance of air-breathing gas turbine engines. When ingested into the front of the engine, abrasion and erosion of key mechanical components can occur, accompanied by degradation of the materials located in the late-stages of the engine by ash that has become molten due to the high-temperature environment. These phenomena can lead to significant damage and premature failure in a fielded gas-turbine engine, thus the need to evaluate engine materials prior to their implementation arises. While volcanic ashes and turbine engine materials have been studied extensively in the literature, they have largely been studied independently, therefore no standardized volcanic ash media to be used in materials testing has been developed. In this work, a group of natural volcanic ash samples were evaluated using a variety of techniques to understand their chemical, physical, and thermal behavior. The information gathered in the characterization of the group of natural ash samples was then used to develop a synthetic volcanic ash media that has similar chemistry to and behaves like a natural ash when exposed to an environment like that in a late-stage gas turbine engine. The new synthetic ash media was compared to a natural ash, from Mt. Mazama in Oregon, USA. Specifically, its ability to melt and infiltrate the microstructural features of 7% yttria-stabilized zirconia thermal barrier coatings deposited on superalloy coupons was examined. It was shown via SEM analysis that when heated to 1200 °C, the synthetic ash melts and infiltrates the thermal barrier coating within a comparable time (<30 minutes) as Mt. Mazama ash, leading to the conclusion that it can be deemed an effective replacement for natural volcanic ash in materials testing. The development of this synthetic ash test media is meant to provide a solid starting point for future development of medias used (open full item for complete abstract)

Committee: Li Cao Ph.D. (Committee Chair); Matthew Hartshorne Ph.D. (Advisor); Donald Klosterman Ph.D. (Committee Member) Subjects: Aerospace Materials; Chemistry; Earth; Engineering; Geology; High Temperature Physics; Materials Science; Mineralogy

Master of Science, The Ohio State University, 2023, Mechanical Engineering

Airborne particulate ingestion into modern, high temperature aeronautical turbine engines can cause damage to internal components, including total engine failure. Volcanic ash interactions with turbine engines has been well studied, and current research in the field focuses on other mineral based test dusts that more closely emulate desert sand and other natural materials. This work focuses on AFRL test dust, the product of an Air Force program to formulate a dust that will create engine deposits that are similar in chemical composition to those deposits found in engines post service. This test dust contains quartz, gypsum, dolomite, aplite and salt, common minerals found in Earth's crust. Utilizing high temperature facilities at The Ohio State University, a testing campaign was developed to seek further understanding of any chemical synergies between these five minerals in an impinging jet configuration. The base AFRL recipe was altered in order to remove individual minerals or increase the quantity of given mineral in proportion to the others in order to compare deposition characteristics in the context of chemical composition when compared to the base mixture. Removing any single mineral does not noticeably change capture efficiencies of AFRL when compared to the control mixture. Capture efficiencies were driven by temperature much more than any given chemical manipulations as it was found that increasing temperature will increase the capture efficiency. At a certain point, deposits cool to a shiny, glassy finish and are incredibly hard. At these temperatures, chemical synergies are better interpreted through the lens of amorphous silica glass networks and alkali network modifiers than the previously proposed ratio of calcium to silicon, although these concepts are related as a silica glass network is heavily modified by the presence of calcium. These alkali network modifiers will decrease the viscosity of a partially or fully molten deposit, and lower viscositie (open full item for complete abstract)

Committee: Lian Duan (Committee Member); Jeffrey Bons (Advisor) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2023, Mechanical Engineering

This thesis aimed to improve the numerical framework of modeling particle deposition in environments relevant to the cooling passage of the gas turbine engines. The effort comprised three main parts: (i) Investigating forces affecting particle motions. (ii) Applying smoothing techniques to improve convergence for mesh morphing. (iii) Elucidating experimental results through numerical simulations and sensitizing the OSU deposition model to temperature. Forces affecting particle trajectories were examined with a focus on turbophoretic force and Saffman lift force. Stochastic models were employed to generate the fluctuating flow velocity for modeling the turbophoretic force. Concentration and axial distributions of deposition velocity, as well as deposition velocity versus particle relaxation time, were predicted by The Discrete Random Walk model (DRW) and variations of the Continuous Random Walk model (CRW). These predictions were compared with existing experiments and direct numerical simulation (DNS) using two different geometries. Special attention was given to the inconsistent directional vector that results from solving the Langevin equation in non-rectangular geometries using location-specific coordinate systems. To achieve more physical solutions, the Langevin equation in cylindrical coordinates was derived for the pipe flows. The effect of the Saffman lift force with two random walk models was also discussed. To improve the stability of mesh morphing for modeling deposit growth, smoothing techniques were employed to reduce the irregular surface resulting from the discreteness of numerical setup and the effect of the Saffman lift force. Three schemes, the mass-based method proposed by Forsyth et al, the inverse distance weighting method and the radial basis function method, were employed to model the growth of the deposit. Because the scale of real cooling passages in gas turbine engines makes it difficult to use a fine mesh, simulations using both a fine and (open full item for complete abstract)

Committee: Jeffrey Bons Dr. (Advisor); Lian Duan Dr. (Committee Member); Randall Mathison Dr. (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2022, Aerospace Engineering

Gas turbine engines are an essential technology in aviation and power generation. One of the challenges associated with increasing the efficiency of gas turbines is the thermal loading experienced by the engine components downstream of the combustors especially the high-pressure turbine blades. High temperatures and rotational velocities can cause blade failures in numerous ways such as creep or stress rupture. Technologies like film cooling are implemented in these components to lower the thermal loading and reduce the risk of failure. However, these introduce complexities into the flow which in turn increases the difficulty of predicting the performance of film cooled turbines. Accurately predicting the capabilities of these components is essential to prevent failure in gas turbine engines. Engineers use a combination of experiments and computational simulations to understand how these technologies perform and predict the operating conditions and lifespan of these components. A combined experimental and numerical program is performed on a single stage high-pressure turbine to increase understanding of film cooling in gas turbines and improve computational methods used to predict their performance. The turbine studied is a contemporary production model from Honeywell Aerospace with both cooled and uncooled turbine blades. The experimental work is performed at The Ohio State University Gas Turbine Laboratory Turbine Test Facility, a short duration facility operating at engine corrected conditions. The experiments capture heat flux, temperature, and pressure data across the entire blade, but this work will focus on the turbine blade tip data. Tip temperature data are captured using a high-speed infrared camera providing a unique data set unseen in the current literature. In addition to the experiments, transient conjugate heat transfer simulations of a single turbine passage are performed to recreate the experiments and give insight into the flow field in the tip (open full item for complete abstract)

Committee: Randall Mathison (Advisor); Sandip Mazumder (Committee Member); Michael Dunn (Committee Member); Jeffrey Bons (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Aerospace Engineering

Gas turbine performance is highly dependent on turbine inlet temperature, which often exceeds the working limitations of the materials involved. Film cooling is a widely used technology enabling highly efficient gas turbine cycles, where relatively cold air is injected as a film on the airfoil surfaces protecting the airfoils from the hot combustion gasses. Film cooled turbines exist in highly unsteady environments due to interactions between stationary and rotating components, and film cooling further complicates the flow. There is limited understanding of the unsteady nature of film cooling flows, resulting in limited ability to predict heat transfer and metal temperature on the components of a gas turbine. The goal of this work is to increase understanding of turbine cooling technology by examining time-accurate and time-averaged behaviors of the cooling flows. This dissertation incorporates experimental and computational analysis of pressure and heat transfer on an industry scale high-pressure turbine stage. Experimental measurements of pressure and heat transfer were performed on a turbine stage installed in the Turbine Test Facility at the Gas Turbine Laboratory. This facility is uniquely equipped to examine unsteady pressure and heat transfer on turbine stages operating at design corrected conditions. Heat transfer measurements are compared for multiple different cooling configurations on the rotating airfoils. Data are analyzed on time-averaged and time-resolved bases, and the results highlight cooling benefit differences among the various cooling hole shapes and coolant flow rates. Computational models of the turbine stage are also employed with steady and unsteady RANS modeling techniques. Experimental data are used for boundary conditions in the computational models as well as to evaluate the accuracy of the models. Comparisons of experimental and steady computations of film cooled turbines often result in poor agreement due to the complexity of film co (open full item for complete abstract)

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

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

As global warming becomes a cause of serious concern worldwide, stricter and stricter emission regulations are being imposed on gas turbine engines. Flameless combustion is a novel combustion technique that offers a significant reduction in NOx and CO emissions. The presence of a flameless flame is indicated by uniform temperature distribution in the combustor, which leads to simultaneous reductions in NOx and CO emissions. Nick Overman conducted tests on a swirl stabilized flameless burner in the GDPL lab at the University of Cincinnati. A well-distributed flameless flame was observed for an overall equivalence ratio of 0.36. But as the equivalence ratio was increased, the flame in the combustor switched to a diffusion flame, and non-uniform temperature distribution was observed, which led to an increase in NOx emissions. The work in this thesis aims to improve the operational range of flameless combustion by modifying the swirl stabilized setup used by Nick Overman to include a cavity upstream of the swirler. ANSYS Fluent is used to numerically investigate the performance of such a cavity-swirler setup. The k-epsilon realizable and Laminar Finite Rate model is used to model turbulence and combustion, respectively. Multiple cavity designs which lead to a final successful design are described in detail in this thesis. The final successful design consists of 8 fuel injectors surrounded by 24 air injectors introducing fresh reactants to the cavity. Modifications were then made to this design to include 8 injectors in the second stage of the swirler. The cavity injectors aligned at an angle to the cavity also possess a swirl angle to impart a tangential component of velocity to the reactants being introduced in the cavity. The performance of two designs, the Swirler Reduced air and Swirler Fuel cases, are investigated at different equivalence ratios. Parameters such as temperature, OH distribution, NOx, CO, CO2, H2O, and combustion efficiency are used to compare the tw (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Prashant Khare Ph.D. (Committee Member); Rodrigo Villalva Gomez Ph.D. (Committee Member) Subjects: Aerospace Materials

Doctor of Philosophy, The Ohio State University, 2021, Mechanical Engineering

Turbomachinery, like jet engines and industrial gas turbines in power plants, are very advanced and complex machines. Due to the complexity and cost of modern turbomachinery, there is active research in accurately predicting the physical system dynamics using computational models. Two big mechanisms that affect the structural response are the prestress effects from high rotational speeds and mistuning effects from tolerance deviations, wear, or damage. Understanding the role these two mechanisms play in the computational modeling of these systems is an important step toward a complete digital twin of an entire jet engine. There previously existed modeling methods that enabled each to be analyzed independently, but not simultaneously in an efficient manner. This will be one of the focus points of this dissertation. The other focus being an experimental investigation into exciting system resonances of a rotating bladed disk using air jets. These experiments will be used to validate the computational modeling method developed. This dissertation has three primary objectives. The first objective is to present reduced order modeling methods that allow for the efficient modeling of coupled systems and rotating systems, both with small or large mistuning. By efficiently including these mechanisms, more realistic boundary conditions can be used to help validate the reduced order models (ROMs) with experimental data. Both modeling methods create models a fraction of the size of the full model while retaining key dynamic characteristics of the full model. The second objective of this work is to show the capability of air jets in exciting synchronous and non-synchronous vibrations in a rotating bladed disk. Much previous research in this field focused on experiments with stationary systems. These tests can help isolate specific mechanisms that may be present in bladed disks, but may limit the applicability of the results to actual rotating systems. This work presents a method (open full item for complete abstract)

Committee: Kiran D'Souza (Advisor); Randall Mathison (Committee Member); Manoj Srinivasan (Committee Member); Herman Shen (Committee Member) Subjects: Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2021, Aero/Astro Engineering

The detrimental effects of deposition on gas turbine engine performance have become more pronounced as operation in climates with heavy concentrations of airborne particulate has increased over the past several decades. This has introduced relatively new and complex challenges for engine designers and maintenance teams who must account for and try to mitigate the host of negative consequences that can arise when particles accumulate on turbine hardware. The majority of deposition analysis is performed through experimental testing, whether it be in the full-scale engine environment or in a scaled-down facility. The cost involved with designing, manufacturing, and testing hardware can be exorbitant however, and thus computational models that can predict deposition behavior are an attractive and more affordable alternative. Over the past decade, a variety of models have been introduced to address this growing need. The aim of this work is two-fold and is addressed in two parts. The first goal is to improve the current state of deposition modeling by investigating the role that absolute pressure plays in the process. Experiments are first conducted in a High-Pressure Deposition Facility (HPDF) at the Aerospace Research Center (ARC) at the Ohio State University (OSU). Commercially available Arizona Road Dust (ARD) is delivered to an effusion cooling plate at a specified pressure ratio and flow temperature, and the absolute flow pressure is varied over a range of 14.77 atm to study the effect pressure has on the deposition levels and blockage of the effusion cooling holes. Two size distributions (0-3.5 and 0-10 µm) are investigated, and the results indicate that the deposition and blockage rates decrease monotonically as absolute pressure increases. This holds true for both sizes of dust, but the overall blockage rates are much higher for the 0-3.5 µm. The rate of decrease in hole blockage as pressure increases on the other hand is steeper for the 0-10 µm distributi (open full item for complete abstract)

Committee: Jeffrey Bons (Advisor); Randall Mathison (Committee Member); Sandip Mazumder (Committee Member) Subjects: Aerospace Engineering; Mechanical Engineering

Doctor of Philosophy, The Ohio State University, 2020, Mechanical Engineering

Gas turbine is an integrated part of modern aviation and power generation industry. The thermal efficiency of a gas turbine strongly depends on the turbine inlet temperature (TIT), and the turbine designers are continuously pushing the TIT to a higher value. Due to the increased freedom in additive manufacturing, the complex internal and external geometries of the turbine blade can be leveraged to utilize innovative cooling designs to address some of the shortcomings of current cooling technologies. The sweeping jet film cooling has shown some promise to be an effective method of cooling where the coolant can be brought very close to the blade surface due to its sweeping nature. A series of experiments were performed using a row of fluidic oscillators on a flat plate. Adiabatic cooling effectiveness, convective heat transfer coefficient, thermal field, and discharge coefficient were measured over a range of blowing ratios and freestream turbulence. Results were compared with a conventional shaped hole (777-hole), and the sweeping jet hole shows improved cooling performance in the lateral direction. Numerical simulation also confirmed that the sweeping jet creates two alternating vortices that do not have mutual interaction in time. When the jet sweeps to one side of the hole exit, it acts as a vortex generator as it interacts with the mainstream ow. This prevents the formation of the counter-rotating vortex pair (CRVP) and allows the coolant to spread in the lateral direction. The results obtained from the low speed at plate tests were utilized to design the sweeping jet film cooling hole for more representative turbine vane geometry. Experiments were performed in a low-speed linear cascade facility. Results showed that the sweeping jet hole has higher cooling effectiveness in the near hole region compared to the shaped hole at high blowing ratios. Next, a detailed experimental investigation of sweeping jet film cooling on the suction surface of a near engine scale (open full item for complete abstract)

Committee: Jeffrey Bons (Advisor); James Gregory (Committee Member); Randall Mathison (Committee Member); Ali Ameri (Committee Member) Subjects: Aerospace Engineering; Aerospace Materials; Engineering; Mechanical Engineering

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

The main objective of this research is to characterize the swirling flow in a gas fuel injector used in gas turbine engines. The experimental investigation conducted by implementing particle image velocimetry (PIV) measurements. The effect of confinement sizes are studied, as well as different Reynolds number effect. Unconfined swirling flow showed different flow characteristics than confined typical swirling flow. Unconfined flow features stronger axial jet spreads with short and thin recirculation zones, which is indicative of thin inner shear layer (ISL). The width of the vortex breakdown bubble was about the same size of the nozzle diameter in unconfined cases. Confining the swirling flow caused the width of vortex breakdown bubble to increase to become three times of the nozzle diameter with large confinement, and twice of the nozzle diameter in both medium and small confinements. In addition, the size and shape of inner recirculation zones significantly changed with confinements. Shear layer becomes thicker due the increased width of inner recirculation zones in confined cases. The axial velocity magnitude experienced reduction with confinements, indicating weaker axial jet spread. Furthermore, confinement forced the inlet jet to penetrate radially, which can be noticed by the increase radial velocity magnitude near the exit. In addition, increasing Reynolds number in confined flow induced greater radial jet dispersion. The large confinement had the lowest axial velocity magnitude and demonstrated a unique flow filed structure. Both medium and small confinements have similar axial and radial velocity values as well as similar flow characteristics. The axial centerline plots of axial velocity showed that the length of the reverse flow region or vortex breakdown are increased with confinements. The radial velocity profile, regardless of their considerably low magnitudes, illustrated non-monotonic behavior with increasing Reynolds number in all cases particula (open full item for complete abstract)

Committee: Ephraim Gutmark Ph.D. (Committee Chair); Mark Turner Sc.D. (Committee Member); Rodrigo Villalva Gomez Ph.D. (Committee Member) Subjects: Aerospace Materials

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

This research provides an experimental investigation into the behavior of naturally occurring, fuel-rich, unstable combustion of liquid fuel in a gas turbine combustor. Testing was done using an acoustically isolated single nozzle combustion test rig using liquid Jet-A fuel, capable of operating under unstable combustion conditions. A test matrix was established to identify operating conditions that incited high combustion instability in fuel-rich conditions. The pressure and flame intensity emissions were analyzed across the test matrix in both time and frequency domains. The Rayleigh Criterion was applied to identify the presence of thermo-acoustic instabilities using combustor pressure and flame emission fluctuations. The flame response was established to further characterize the flame dynamics using using the combustor velocity and flame emission fluctuations. Periodic flame structure and behavior was determined using a high speed camera and compared to the convection time delays calculated via flame emission measurements. The investigation concluded that for cases with sufficiently high pressure fluctuations, the Rayleigh Criterion identified thermo-acoustic instability in fuel-rich combustion. The high-speed video and flame emission measurements revealed the spatial and temporal characteristics of emissions in the OH*-band, indicating that it serves as the best approximation for heat release in a fuel-rich flame. Additionally, the high speed camera video and flame emission measurements indicated that CH*-band emissions convectively lag OH*-band emissions.

Committee: Jongguen Lee Ph.D. (Committee Chair); San-Mou Jeng Ph.D. (Committee Member); Kwanwoo Kim Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science in Mechanical Engineering (MSME), Wright State University, 2019, Mechanical Engineering

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 velocity deficit, elevated turbulence, and spanwise vorticity. Prior to application in a turbine flow environment, the concept was explored in a small developmental wind tunnel using a single device. The disturbance flowfield for different input settings was measured using hot-film anemometry and Particle Image Velocimetry. Insight was also garnered on how to improve later design iterations. With an array of devices installed upstream of a linear cascade of high-lift front-loaded turbine blades, settings were found which produced similar disturbances at varying frequencies that periodically impinged upon the leading-edge region. These settings were used to conduct an in-passage secondary flow study using high-speed Stereoscopic Particle Image Velocimetry. Results demonstrated the application of the periodic unsteadiness generator but found minor changes to the passage vortex. The vortex rotational strength decreased, and migration increased with increased perturbation frequency. Fourier analyses found the PV to be responsive at the actuation frequency with phase-locked ensemble-averaged data revealing that the disturbance periodically caused the PV to lose rotational strength. However, at the tested discrete frequencies, the vortex did not become locked (open full item for complete abstract)

Committee: Mitch Wolff Ph.D. (Advisor); Rolf Sondergaard Ph.D. (Committee Member); Christopher Marks Ph.D. (Committee Member) Subjects: Aerospace Engineering; Engineering; Experiments; Fluid Dynamics; Mechanical Engineering

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

A generic novel injector was designed for multi-Lean Direct Injection (M-LDI) combustors. One of the drawbacks of the conventional pressure swirl and prefilming type airblast atomizers is the difficulty of obtaining a uniform liquid sheet under all operating conditions. Micro-channels are needed inside the injector for uniformly distributing the fuel. The problem of non-uniformity is magnified in smaller sized injectors. The non-uniform liquid sheet causes local fuel rich/lean zones leading to higher NOx emissions. To overcome these problems, a novel fuel injector was designed to improve the fuel delivery by using a porous stainless-steel material with 30 µm porosity. The porous tube also acted as a prefilming surface. Liquid and gaseous fuels can be injected through the injector. The current study investigates the aerodynamics, spray quality, fuel-air mixing and emission characteristics of the novel injectors at 4% pressure drop and atmospheric conditions. The injectors have two configurations with different counter-rotating radial-radial swirlers. And the injector 1 has a SN of 0.75 and SN of injector 2 is 0.6. The characteristics of the novel injectors are also compared with a typical airblast injector having a peanut nozzle with flow number of 1. A Central Toroidal Recirculation Zone (CTRZ) and Corner Recirculation Zone (CRZ) are observed from the aerodynamics study. Spray measurements are carried out at various equivalence ratio conditions without a confinement. D10, D32 and D0.5 are investigated on Jet-A, GTL and blended fuels. There is no significant influence of fuel types on the spray behavior due to their similar physics properties. The porous injectors generate a fine spray with weighted SMD ~45 µm at equivalence ratio of 0.6. Gaseous Fuel-air mixing studies are carried out at different equivalence ratios with and without a confinement. A fully premixed mixing profile was obtained at 0.43” downstream of the injector exit. Flame characterization (open full item for complete abstract)

Committee: San-Mou Jeng Ph.D. (Committee Chair); Jun Cai Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member); Bassam Mohammad Abdelnabi Ph.D. (Committee Member) Subjects: Aerospace Materials

Master of Science, The Ohio State University, 2018, Aero/Astro Engineering

Sweeping jet impingement cooling was investigated in a gas turbine nozzle guide vane design with an engine-relevant Biot number of 0.3. Sweeping jets were created with fluidic oscillators and were compared to steady jets produced by cylindrical orifices (with length-to-diameter ratio of 1), the current state-of-the-art in engine designs. Experiments were performed in a low speed linear cascade with additively manufactured test pieces. The impingement cooling geometries were examined at multiple coolant mass flow rates and freestream turbulence intensities. The overall effectiveness of each cooling geometry was calculated using thermocouple measurements of the freestream and coolant temperatures, and infrared thermography measurements of the vane external surface temperature. A computational thermal inertia technique was used to determine the internal Nusselt numbers. The heat transfer provided by steady impinging jets produced a higher overall effectiveness and Nusselt number in the leading edge geometry. The sweeping jets provided more uniform heat transfer, reducing thermal gradients near the stagnation point. Pressure drop across each jet geometry was measured at a range of applicable mass flow rates. Fluidic oscillators were shown to create similar pressure drop to circular orifice holes when additive manufacturing abilities were fully incorporated in the nozzle guide vane internal cooling designs.

Committee: Jeffrey Bons (Advisor); Ali Ameri (Committee Member); James Gregory (Committee Member) Subjects: Aerospace Engineering

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

The thermal barrier coating is applied to the surfaces of the metal components of the gas turbine hot section, for example, a combustor liner, vanes, and rotating turbine blades. The coating contributes to increasing the operating temperature by providing a heat shield between the hot gas and the metallic substrate of the gas turbine engines. As well as increasing the service life of the gas turbine engine, the specific fuel consumption can also be improved with the increased overall pressure ratio. In particular, 6-9% wt. Yttria partially stabilized zirconia (7YSZ) ceramic coating has been widely used because of its excellent hardness, good erosion resistance, low thermal conductivity, and thermal expansion coefficient similar to Nickel based super-alloys. However, the experimental erosion resistance study of TBC by solid particle impact has not been extensively carried out within the operating range of the gas turbine. Through presented study, a preliminary design was conducted for the development of a new advanced high-temperature capable erosion test facility. The optimized length of the accelerating tunnel and design parameters were obtained using the combination of analytical and computational analysis. The performance of developed erosion test facility was validated with the predicted data and compared with the existing legacy erosion tunnel at the University of Cincinnati. This dissertation presents an experimental investigation of the effects of microstructures of topcoat of air plasma sprayed 7 wt\% YSZ thermal barrier coatings (APS 7YSZ TBCs) on erosion resistance at high temperature. A combination of air plasma sprayed YSZ TBCs with three different microstructures (porosities of 12.9 +- 0.5%, 19.5 +- 1.2%, and 3.7 +- 0.7%) was tested in the advanced high-temperature erosion test facility under gas turbine operating temperatures. Experiments were conducted to investigate erosion of TBCs over a range of temperatures between 537C and 980C, gas veloc (open full item for complete abstract)

Committee: Awatef Hamed Ph.D. (Committee Chair); San-Mou Jeng Ph.D. (Committee Member); Jongguen Lee Ph.D. (Committee Member); Robert W. Bruce Ph.D. (Committee Member) Subjects: Aerospace Materials