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

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

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

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

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

Master of Science, The Ohio State University, 2015, Aero/Astro Engineering

A large number of physical continuous-time systems are controlled using digital controllers. These systems are often referred to as sample data systems or hybrid systems and they have become the norm for many real world applications. With this in mind, the impact of modeling uncertainties and time delay are considered. Maintaining stability in a system is of the upmost importance for any control system but the models which are used to develop the control laws which control the actual system are not perfect, being subject to a variety of uncertainties and errors. The goal of a robust control law is to guarantee the stability despite the uncertainty that may exist in the system while a nominal control law is designed with only single perfectly modeled design point in mind. Despite the drive toward hybrid systems in application, the focus in developing robust control methods for uncertain systems, especially as it applies to input-delayed sample data systems, has been more geared toward strictly continuous-times systems or strictly discrete-time systems. Here a methodology for designing robust digital controllers to stabilize uncertain continuous-time systems when subject to a given range of elemental uncertainty an input-delay is set forth. The inspiration for this research grew out of the challenges of implementing a distributed engine control system for gas turbine engines on aerospace vehicles. As a precursor to the development of the robust control methodology presented in this document, a study was conducted to better understand the impact of uncertainty and time delay on gas turbine engines with a vision toward implementing distributed engine control. Simulation results using linearized models of the GE T700 Turboshaft Engine and the NASA developed generic twin-spool engine model C-MAPSS40k suggest that the gas turbine engine is inherently robust in its ability to maintain stability but still no guarantee of its stability can be made using strictly nominal contr (open full item for complete abstract)

Committee: Rama Yedavalli Dr. (Advisor); Herman Shen Dr. (Committee Member) Subjects: Aerospace Engineering

Master of Science (MS), Wright State University, 2013, Mechanical Engineering

Molten carbonate fuel cells (MCFC) have a high operating temperature of approximately 650° C (1200° F) to achieve sufficient conductivity of its carbonate electrolyte. Therefore, a gas turbine engine coupled with a MCFC is desirable since the turbine engine can be used to provide hot gas to the cathode, and the cathode gas residue can be used to raise the temperature of the natural gas and water vapor mixture (fuel) before it enters the MCFC at the anode. Dynamic models of a hybrid power plant consisting of a gas turbine engine and a MCFC with their respective components were developed in MATLAB/Simulink to capture in real time the changes due to sudden fluctuations on power loads, air flows, etc., and to develop safe and efficient control of this system. The power plant is composed by a compressor, turbine, shaft, heat exchangers, heat recovery unit, an oxidizer and a molten carbonate fuel cell working synergistically able to achieve high operating efficiencies and power demands in the MW range. The project is a joint effort between Purdue University and Wright State University where the oxidizer and fuel cell models are developed by Purdue, and the rest of the components are developed by Wright State University.

Committee: Mitch Wolff Ph.D. (Advisor); James Menart Ph.D. (Committee Member); Scott Thomas Ph.D. (Committee Member) Subjects: Energy; Mechanical Engineering

Master of Science in Engineering (MSEgr), Wright State University, 2012, Electrical Engineering

In this thesis, a fault detection and isolation (FDI) method is developed for aircraft engines by utilizing nonlinear adaptive estimation techniques. Engine sensor faults, actuator faults and component faults are considered under one unified framework. The fault diagnosis architecture consists of a bank of nonlinear adaptive estimators. One of them is the fault detection estimator used for fault detection, and the remaining ones are fault isolation estimators employed to determine the particular fault type/location after fault detection. Each isolation estimator is designed based on the functional structure of a particular fault type under consideration. The FDI architecture has been integrated with the Commercial Modular Aero-Propulsion System Simulation (C-MAPSS) engine model developed by NASA researchers in recent years. Extensive simulation results and comparative studies are conducted to verify the effectiveness of the nonlinear FDI method.

Committee: Xiaodong Zhang PhD (Advisor); Kuldip Rattan PhD (Committee Member); Kefu Xue PhD (Committee Member) Subjects: Aerospace Engineering; Electrical Engineering

Doctor of Philosophy, The Ohio State University, 2009, Mechanical Engineering

As the demand for greater efficiency and reduced specific fuel consumption from gas turbine engines continues to increase, design tools must be improved to better handle complicated flow features such as vane inlet temperature distortions, film cooling, and disk purge flow. In order to understand the physics behind these features, a new generation of turbine experiments is needed to investigate these features of interest for a realistic environment.This dissertation presents for the first time measurements and analysis of the flow features of a high-pressure one and one-half stage turbine operating at design corrected conditions with vane and purge cooling as well as vane inlet temperature profile variation. It utilizes variation of cooling flow rates from independent circuits through the same geometry to identify the regions of cooling influence on the downstream blade row. The vane outer cooling circuit, which supplies the film cooling on the outer endwall of the vane and the trailing edge injection from the vane, has the largest influence on temperature and heat-flux levels for the uncooled blade. Purge cooling has a more localized effect, but it does reduce the Stanton Number deduced for the blade platform and on the pressure and suction surfaces of the blade airfoil. Flow from the vane inner cooling circuit is distributed through film cooling holes across the vane airfoil surface and inner endwall, and its injection is entirely designed with vane cooling in mind. As such, it only has a small influence on the temperature and heat-flux observed for the downstream blade row. In effect, the combined influence of these three cooling circuits can be observed for every instrumented surface of the blade. The influence of cooling on the pressure surface of the uncooled blade is much smaller than on the suction surface, but a local area of influence can be observed near the platform. This is also the first experimental program to investigate the influence of vane inlet (open full item for complete abstract)

Committee: Dr. Michael Dunn PhD (Advisor); Dr. Sandip Mazumder PhD (Committee Member); Dr. William Rich PhD (Committee Member); Dr. Mohammad Samimy PhD (Committee Member) Subjects: Fluid Dynamics; Mechanical Engineering

Master of Science (MS), Ohio University, 1998, Mechanical Engineering (Engineering)

Viability of stirling-based combined cycle distributed power generation

Committee: David Bayless (Advisor) Subjects: Engineering, Mechanical