ETD Search Results: instcode:osu

1. Balla, Joseph V. Pressure-Sensitive Paint for Detection of Boundary Layer Transition.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► A polymer/ceramic pressure-sensitive paint (PSP) system was evaluated to detect the laminar… (more)

Subjects: Aerospace Engineering

Keywords: Pressure-sensitive paint, boundary-layer, transition

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2. Barker, Brett Jordan. Simulation of Coal Ash Deposition on Modern Turbine Nozzle Guide Vanes.

Degree: MS, Aero/Astro Engineering, 2010, Ohio State University

► A numerical study of the physical mechanisms associated with the deposition of… (more)

Subjects: Engineering

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3. Bhattacharyya, Sampriti. Reliability Analysis and Controls for Accelerator Driven Systems Based On Project X.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► Nuclear energy has tremendous potential as a reliable source of cheap, clean… (more)

▼ Nuclear energy has tremendous potential as a reliable source of cheap, clean energy. The key impediments to expanded use of nuclear energy are safety (Chernobyl and Fukushima), proliferation (Iran, N. Korea); and disposal of waste which remains dangerously radioactive for thousands of years. Presently nuclear waste is stored and managed by the power plant itself as an interim solution, with the intent of eventually transporting it for long term storage. However political, social, and environmental issues places barrier on selection of any such site, for example rejection of the Yucca Mountain Repository proposal. New generations of reactors are designed to generate less waste, alleviating but not solving the problem. In our research we discuss a new option: Accelerator Driven Subcritical System (ADSS) or simply Accelerator Driven Systems (ADS), a reactor that consumes rather than produce waste. In this case a proton accelerator is used to produce external neutrons and cause fission of actinide rich conventional radioactive waste. ADS can also use abundant (compared to uranium 235) natural isotopes, uranium 238 and thorium and produce waste with very little contamination of long-lived radioactive isotopes as its fuel. This kind of reactor is subcritical, passively safe, and since the fuel used is non-fissile and unsuitable for weapon grade, it is also free of proliferation risks. ADS research is ongoing around the world, particular in China, India, and the European Union. One of the major challenges, and the one studies in this work, is building a proton accelerator with unprecedented efficiency, intensity, and reliability. Here in the US, an accelerator called Project X is under development at Fermi National Accelerator Laboratory (Illinois) which is intended primarily for basic research, but it also meets the intensity and efficiency requirements for ADS. The reliability required by ADS is >99% whereas present accelerators have around 85%. In our research we start with a systematic study of accelerator reliability using Project X as a test bed. We use commercial software called Availability Workbench by Isograph to build the reliability block diagrams of the accelerator systems. Reliability modeling is not trivial because the components interdependencies are pretty complex; further it is a challenge to model such a large system. Here we discuss about the various modeling techniques and validate our methodology by modeling some of the subsystems of the Spallation Neutron Source (SNS), a proton linac at Oak Ridge National Laboratory. SNS is the only linac which has a reliability study performed for the whole system using a spreadsheet. Being a proton linac, it is similar to Project X in many respects. Reliability analysis and modeling helped us to understand the shortcoming of the design and identify the weak components. To improve system availability, which is of main concern to ADS, automated controls and repair is highly desired. One of the biggest sources of downtime in a linac is beam tuning, which can take several hours and presently done manually. Since that is unacceptable for ADS, we explore automated beam tuning methods. We develop beam models in State Space Method so that traditional control techniques can be applied. Further we discuss the use of χ^2 Minimization Technique for actual beam control. Our tests are done in simulated scale down versions of a linac, and further research is needed to validate the actual implementation of our concept. Advisors/Committee Members: Yedavalli, Rama K.

Subjects: Aerospace Engineering; Energy; Engineering; Nuclear Engineering; Nuclear Physics; Particle Physics

Keywords: Accelerator Driven Systems, Thorium Reactor, Project X, beam modeling, controls

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4. Bilwakesh, Kashi Ramamurthi. Thermal decomposition of hydrogen peroxide vapor at elevated temperatures behind incident and reflected shock waves.

Degree: PhD, Aero/Astro Engineering, 1969, Ohio State University

Advisors/Committee Members: Edse, Rudolph.

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5. Boehler, Michael David. Transient Aerothermodynamics of Flow Initialization for a Flat Plate Film Cooling Experiment in a Medium Duration Blowdown Wind Tunnel Facility.

Degree: MS, Aero/Astro Engineering, 2010, Ohio State University

► The magnitude of the temperature increase as a result of compression heating… (more)

Subjects: Mechanical engineering

Keywords: film cooling; blowdown; flat plate; compression heating; ingestion

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6. Bonilla, Carlos Humberto. The Effect of Film Cooling on Nozzle Guide Vane Ash Deposition.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► An accelerated deposition test facility was used to study the relationship between… (more)

Subjects: Aerospace Engineering; Aerospace Materials; Engineering

Keywords: Deposition; film cooling; ash deposition; nozzle guide vane; deposit; heat transfer; turbine deposition; engine deposition

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7. Culler, Adam John. Coupled Fluid-Thermal-Structural Modeling and Analysis of Hypersonic Flight Vehicle Structures.

Degree: PhD, Aero/Astro Engineering, 2010, Ohio State University

► This dissertation describes coupled fluid-thermal-structural modeling and analysis of a semi-infinite insulated… (more)

▼ This dissertation describes coupled fluid-thermal-structural modeling and analysis of a semi-infinite insulated metallic panel and a blade-stiffened carbon-carbon skin panel for aerothermoelasticity and forced response prediction in hypersonic flow. The United States Air Force' goals of affordable, reusable platforms capable of sustained hypersonic flight and responsive access to space depend on the ability to predict the response, the degradation, and ultimately the life of structures under combined, extreme aerodynamic heating and fluctuating pressure loads. However, the necessary modeling and prediction capabilities are severely limited in current commercial software due to the inability to seamlessly address multi-coupled, multi-scale fluid-thermal-structural interactions. Moreover, because of the complexity and expense of coupled computational methods, the capability is needed to define the necessary level of coupling a priori. The aim of this dissertation is to develop coupled fluid-thermal-structural analysis methodology for response prediction in combined, extreme environments. Furthermore, it seeks to identify key characteristics (e.g., trajectories, operating conditions, and structural configurations) that determine the level of coupling needed for different situations. An additional focus is the targeted use of simplified temporal coupling strategies for reducing the computational expense of hypersonic aerothermoelasticity and forced response prediction over long durations. First, in order to efficiently study the effects of fluid-thermal-structural coupling, an approximate hypersonic aerodynamics model is developed. The approximate model is verified and validated by comparison to aerodynamic pressure and heating data from hypersonic wind tunnel experiments and computational fluid dynamics solutions of the Navier-Stokes equations. Next, thermal and structural models of the panels are developed. The insulated metallic panel is modeled using the two-dimensional heat equation with a finite difference solution and von Karman plate theory with an assumed modes solution. Thermal and structural models of the carbon-carbon skin panel are developed using commercial finite element software. Partitioned fluid-thermal-structural solution strategies are developed and used to systematically study the impact of multiple physical coupling mechanisms and simplified temporal coupling procedures. The aerothermoelastic behavior of the insulated metallic panel is found to be dependent on mutual coupling of aerodynamic heating and structural deformation. Additionally, it is determined that simplified temporal coupling procedures offer substantial reductions in computational expense, with negligible loss of accuracy, for aerothermoelastic analysis over long-duration hypersonic trajectories. Quasi-static and transient dynamic structural responses of the carbon-carbon skin panel are investigated. It is found that the level of coupling needed for quasi-static response prediction depends largely on the in-plane structural boundary conditions, since greater resistance to thermal expansion results in larger deformations. Including these deformations in the aerodynamic heating analysis results in: nonuniform skin temperatures, asymmetric deformation, and elevated stresses. Predictions of panel failure and mode (static stress or snap-through) are found to be dependent on: trajectory, degree of coupling, and stiffness of in-plane boundary conditions. Additionally, it is determined that dynamic response predictions are sensitive to: mutual coupling of aerodynamic heating and structural deformation and temporal coupling of thermal and structural solutions. The degree of coupling needed for accurate dynamic response prediction increases with increasing fluctuating pressure levels and aerodynamic heating rates. Advisors/Committee Members: McNamara, Jack.

Subjects: Aerospace materials; Design; Engineering; Mechanical engineering

Keywords: hypersonic, structures, multi-disciplinary, fluid-thermal-structural, coupled, thermal effects, aerothermoelasticity

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8. Devarakonda, Nagini. Eco-inspired Robust Control Design for Linear Dynamical Systems with Applications.

Degree: PhD, Aero/Astro Engineering, 2011, Ohio State University

► Recently, the idea of using Ecological Sign Stability approach for designing robust… (more)

▼ Recently, the idea of using Ecological Sign Stability approach for designing robust controllers for engineering systems has attracted attention with promising results. In this work, continued research on this topic is presented. It is well known that, in the field of control systems, key to a good controller design is the choice of the appropriate nominal system. Since it is assumed that the perturbations are about this nominal, the extent of allowed perturbation to maintain the stability and/or performance very much depends on this ‘nominal’ system. Therefore, it is evident that this nominal system must have superior robustness properties. Incorporating certain robustness measures proposed in the literature, control design techniques have been realized in state space framework. However, the variety of controllers in state space framework is not as large as that of robust control design methods in frequency domain. Even these very few methods tend to be complex and demand some specific structure to the real parameter uncertainty (such as matching conditions). Overall, the success of all these methods for application to complex aerospace systems is still a subject of debate. Hence, there is still significant interest in designing robust controllers which can perform better than the existing controllers. Addressing these issues, current research proposes that the stability robustness measures for parameter perturbation are considerably improved if the ‘nominal’ system is taken (or driven) to be a ‘sign stable’ system. Motivated by this observation, a new method for designing a robust controller for linear uncertain state space systems is proposed. The novelty of this research lies in the incorporation of ecological principles in order to design robust controllers for engineering systems. It is observed that an ecological perspective gives better understanding of the dynamics of the open and closed loop system (nominal) matrices. One of the attractive features of this controller is that the robustness measure, enters the control design in an explicit manner. The result of implementing controllers inspired by ecological principles simplifies the control algorithm and for certain dynamic systems, greatly reduces computational effort required in the synthesis of the controller. Accurate synthesis of the control algorithms results in ‘most robust’ nominal system (closed loop system). Variations of this control design method that address different categories of uncertainty are presented. The resulting control design methods are illustrated with application to aircraft and spacecraft flight control and aircraft turbine engine control. Advisors/Committee Members: Yedavalli, Rama K.

Subjects: Aerospace Engineering

Keywords: Robust Control; Linear Uncertain Systems; Ecology; Sign Stability; Aircraft Control; Spacecraft Control; Aircraft Engine Control

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9. Fang, Shuo. Application of Fast-Responding Pressure-Sensitive Paint to a Hemispherical Dome in Unsteady Transonic Flow.

Degree: MS, Aero/Astro Engineering, 2010, Ohio State University

► The current work focuses on the application of fast-responding polymer/ceramic pressure-sensitive paint… (more)

▼ The current work focuses on the application of fast-responding polymer/ceramic pressure-sensitive paint (PSP) as an advanced surface pressure measurement technique for the study of unsteady flow fields in large-scale wind tunnels. Three different PSP experimental methods are demonstrated to resolve the surface pressure distribution over a hemispherical dome placed in subsonic flow with freestream Mach number of 0.6 and a total pressure of 71.8 kPa, where the Reynolds Number based on dome diameter (0.254 m) is 2.4 x 106. At this flow condition, a predominant shear layer oscillating at 400 Hz over the test model is observed. Three different PSP methods were employed to study this phenomenon: phase-averaged, real-time, and single-shot. In the phase-averaging technique, LED arrays are phase-locked to the shear layer frequency so that the strobed illumination freezes the motion of the oscillating fluid in one instant and the camera shutter stays open long enough to average the fluid motion over many cycles. In the real-time approach, a high-speed camera was used to capture the shear layer frequency at a shutter speed of 10 kHz without any averaging of the images. In the lifetime-based single-shot approach, the PSP information was acquired from one single laser pulse, which was also able to provide instantaneous surface pressures with high spatial resolution. An assessment of the three test methods is presented, with the advantage and disadvantage of each technique evaluated through example. To study the unsteady fluid dynamic problem in this work using PSP, it is important to demonstrate that the PSP formulation has the capability to accurately resolve the unsteady pressure changes. The response time of the polymer/ceramic PSP was characterized with a dynamic calibration technique using a loudspeaker. The quantitative point-measurement results show that the amplitude response of the PSP behaved like a 4th order dynamic system, with a frequency response of 3700 Hz. The dynamic calibration setup and results are presented. Advisors/Committee Members: Gregory, James.

Subjects: Aerospace Engineering

Keywords: pressure-sensitive paint; paint; aerodynamics; hemisphere; hemispherical dome; phase-averaging; real-time; lifetime

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10. Jedrey, Richard M. Development of a Discretized Model for the Restricted Three-Body Problem.

Degree: MS, Aero/Astro Engineering, 2011, Ohio State University

► Spacecraft trajectory design is a science that requires high precision with little… (more)

▼ Spacecraft trajectory design is a science that requires high precision with little error. One of the most classic trajectory design problems is the restricted three-body problem. Two methods to develop the trajectory of a spacecraft under the influence of two celestial bodies are through the use of the equations of motion, and the patched-conic approximation. Popular tools such as MATLAB can be used to solve the equations of motion if great care is taken when selecting an ODE solver since the results are dramatically different between different solvers. As a result, these tools aren’t very robust and can create significant errors, so a different approach must be used for generalized scenarios when an exact solution for comparison is unavailable. The patched-conic approximation can be easily used in a program such as MATLAB, but its exclusion of one of the two celestial bodies at every point in the trajectory creates drawbacks and significant errors. To avoid the errors that exist when using the patched-conic approach, research was put into the development of a simple model that could propagate a spacecraft’s trajectory under the effect of two celestial bodies while being robust enough to code and solve in a widely available program such as MATLAB. This model acts as a modification to the patched-conic approach. Throughout the trajectory the effect of the primary celestial body of the system on the spacecraft was calculated, as in the patched-conic approach, however unlike the patched-conic approach this effect is not ignored when the spacecraft reaches the secondary body’s sphere of influence. Furthermore, the effect of the secondary body was also considered even when the spacecraft is outside the secondary body’s sphere of influence. Then, by applying a weighted average to the spacecraft’s radius and velocity components respective to each celestial body, an updated state would be created that would allow the model to accurately propagate the trajectory. This would be compared to a numerically generated ‘exact’ solution to determine the errors. Algorithms that propagate the spacecraft’s trajectory out with respect to both celestial bodies were created and tested, including the propagation of the secondary celestial body’s orbit itself. A scheme based on the geometry was used in an attempt to combine the spacecraft’s states with respect to both celestial bodies using a weighted average. This scheme was tested at multiple points throughout the trajectory using a variety of weights, but no attempts were met with any success. However, the routines propagating the trajectories of the celestial bodies and spacecraft were proven to work correctly, and an initial foundation in creating a scheme to combine the spacecraft’s state has been laid out. Advisors/Committee Members: Oz, Hayrani.

Subjects: Aerospace Engineering; Engineering

Keywords: orbital mechanics; spacecraft trajectories; three-body problem; three-body model; n-body problem; n-body model; discretized spacecraft

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11. Jensen, Christopher Douglas. Global Pressure and Temperature Surface Measurements on a NACA 0012 Airfoil in Oscillatory Compressible Flow at Low Reduced Frequencies.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► A co-axial contra-rotating helicopter in forward flight has stall mechanisms that are… (more)

▼ A co-axial contra-rotating helicopter in forward flight has stall mechanisms that are intrinsically different from those on a traditional helicopter. Traditional helicopters need a cyclic pitch mechanism to balance the rotor lift about each rotation, which leads to dynamic stall from the rapid oscillations in pitch. Co-axial contra-rotating helicopters, which have a fixed pitch about each cycle, encounter a sinusoidal oscillation in Mach number with the mean velocity seen as the rotational velocity while the half amplitude is equal to the forward flight speed. The fluid dynamic mechanism limiting the forward flight speed is entirely different from that of traditional dynamic stall studies. This work sets out to design, create, and study the application of an oscillatory compressible flow field on a NACA 0012 airfoil in order to experimentally model this flow situation. A few different pressure-sensitive paints and imaging techniques were developed for investigation of this oscillatory effect. Ultimately a fast-acting bi-luminophore pressure- and temperature-sensitive paint was chosen for the investigation which uses a polymer-ceramic basecoat and a mixture of luminescent elements. These measurements were made using a two-camera, single-shot, intensity-based pressure-sensitive paint technique. Temperature-corrected pressure measurements were made and accounted for the intrinsic temperature sensitivity of pressure-sensitive paint. This dual-luminophore technique allows for accurate unsteady pressure measurements in a non-uniform and varying temperature environment; however, due to inadequate unsteady surface pressure tap measurements the pressure results were limited to the steady runs. This work involved the design and creation of a modification to Ohio State’s 6” x 22” Transonic Wind Tunnel to enable oscillations of the freestream Mach number. The current configuration produces Mach number oscillations between 0.44 and 0.64 for a Reynolds number range of 17 – 43 million per meter at frequencies up to 21 Hz. Unsteady shock location measurements were made at angles of attack of 9, 10 and 11 degrees and frequencies of 2.1, 9.5, 15.25 and 21 Hz on the NACA 0012 airfoil. Detailed measurements of the shock movement were made with these advanced measurement techniques in order to investigate unsteady effects of the oscillatory freestream flow. Unsteady effects were pronounced for a reduced frequency of 0.037 which is below the typical quasi steady to unsteady threshold of 0.05. Coefficient of pressure measurements for the steady runs were validated with historical data. It was found that the coefficient of lift measurements were in very good agreement, while the coefficient moment had significant errors. Furthermore, the PSP measurements were compared with particle image velocimetry data of other researchers in order to form a comparison of the on- and off-body fluid dynamics at a frequency of 9.5 Hz and angles of attack of 9 and 10 degrees. The single-shot pressure-sensitive paint technique was able to measure buffeting, which was found to be highly three dimensional over the span of the airfoil. Similar shock location unsteadiness due to buffeting was also measured in the forced oscillation cases at lower Mach numbers than steady runs, causing aperiodic behavior at certain azimuth locations with higher Mach numbers. Advisors/Committee Members: Gregory, James.

Subjects: Aerospace Engineering

Keywords: PSP; TSP; pressure sensitive paint; aerodynamics; Mach oscillation; freestream oscillation; NACA 0012

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12. Kecskemety, Krista Marie. Assessing the Influence of Wake Dynamics on the Performance and Aeroelastic Behavior of Wind Turbines.

Degree: PhD, Aero/Astro Engineering, 2012, Ohio State University

► While wind turbine farms are currently rapidly expanding, there are numerous technological… (more)

▼ While wind turbine farms are currently rapidly expanding, there are numerous technological challenges that must be overcome before wind energy represents a significant contributor to energy generation in the United States. One of the primary challenges is accurately accounting for the aerodynamic environment. This dissertation is focused on improving the aerodynamic modeling through the incorporation of wake effects. A comprehensive verification and validation of the NREL FAST code, which has been enhanced to include a Free Vortex Wake (FVW) model was conducted. The verification and validation is carried out through a comparison of wake geometry, blade lift distribution, wind turbine power and force and moment coefficients using a combination of Computational Fluid Dynamics (CFD) and experimental data. The results are also compared against Blade Element Momentum Theory (BEM), and results from an extensive experimental campaign by NREL on the prediction capabilities of wind turbine modeling tools. Results indicate that the enhanced aeroelastic code generally provides improved predictions. However, in several notable cases the predictions are only marginally improved, or even worse, than those generated using Blade Element Momentum Theory aerodynamics. After verification and validation of the model, the impact of including the free vortex wake model in the presence of turbulent flow was also examined. The inclusion of turbulence created large differences between BEM and FVW in predictions of rotor loading and power, however the amplitude of the turbulence did not have a large impact on the difference between the FVW and BEM. In addition to loading and power predictions, the structural response (tip deflections and root bending moments) of the wind turbine is investigated in the presence of turbulent inflow. The results indicate that the turbulence intensity and spectral model have a significant effect on the importance of the wake dynamics in modeling the tip deflections and root moments. From the dissertation results, it is concluded that modeling of the aerodynamic environment remains incomplete, even after inclusion of wake effects. One important aspect identified for future improvements is modeling of the unsteady aerodynamic lift characteristics of the rotor. Advisors/Committee Members: McNamara, Jack.

Subjects: Aerospace Engineering

Keywords: Wind Turbine; Vortex Wake; Aeroelasticity

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13. Kumar, Pradeep. Development of a Single-shot Lifetime PSP Measurement Technique for Rotating Surfaces.

Degree: MS, Aero/Astro Engineering, 2010, Ohio State University

► In this work, the viability of using pressure-sensitive paints as a pressure… (more)

Subjects: Mechanical engineering

Keywords: PSP, single-shot, lifetime, measurements, rotating surfaces, rotorcraft

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14. Litvay, Robyn Olson. Development and Validation of a New Air Carrier Block Time Prediction Model and Methodology.

Degree: PhD, Aero/Astro Engineering, 2012, Ohio State University

► Commercial airline operations rely on predicted block times as the foundation for… (more)

▼ Commercial airline operations rely on predicted block times as the foundation for critical, successive decisions that include fuel purchasing, crew scheduling, and airport facility usage planning. Small inaccuracies in the predicted block times have the potential to result in huge financial losses, and, with profit margins for airline operations currently almost nonexistent, potentially negate any possible profit. Although optimization techniques have resulted in many models targeting airline operations, the challenge of accurately predicting and quantifying variables months in advance remains elusive. The objective of this work is the development of an airline block time prediction model and methodology that is practical, easily implemented, and easily updated. Research was accomplished, and actual U.S., domestic, flight data from a major airline was utilized, to develop a model to predict airline block times with increased accuracy and smaller variance in the actual times from the predicted times. This reduction in variance represents tens of millions of dollars (U.S.) per year in operational cost savings for an individual airline. A new methodology for block time prediction is constructed using a regression model as the base, as it has both deterministic and probabilistic components, and historic block time distributions. The estimation of the block times for commercial, domestic, airline operations requires a probabilistic, general model that can be easily customized for a specific airline’s network. As individual block times vary by season, by day, and by time of day, the challenge is to make general, long-term estimations representing the average, actual block times while minimizing the variation. Predictions of block times for the third quarter months of July and August of 2011 were calculated using this new model. The resulting, actual block times were obtained from the Research and Innovative Technology Administration, Bureau of Transportation Statistics (Airline On-time Performance Data, 2008-2011) for comparison and analysis. Future block times are shown to be predicted with greater accuracy, without exception and network-wide, for a major, U.S., domestic airline. Advisors/Committee Members: Benzakein, Meyer.

Subjects: Engineering; Industrial Engineering; Operations Research; Statistics; Systems Design; Transportation; Transportation Planning

Keywords: Airline Block Time; Air Carrier Operations; Block Time Prediction; Block Time Estimation

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15. Li, Wenfei. Fault Diagnostics Study for Linear Uncertain Systems Using Dynamic Threshold with Application to Propulsion System.

Degree: PhD, Aero/Astro Engineering, 2010, Ohio State University

► Fault detection and isolation plays a critical role in aircraft engines and… (more)

▼ Fault detection and isolation plays a critical role in aircraft engines and the performance of their control systems. A great amount of research on model-based fault detection and isolation of aircraft engines has been studied since the 1970s. Model-based fault detection and isolation methods rely on the accuracy of the model. Model uncertainty, disturbances and noise, etc., all have a great impact on the fault detection and isolation design results. A challenge in the fault detection applications is the design of a scheme which can distinguish between model uncertainties, disturbances and the occurrence of faults. Most of the current approaches use a constant detection threshold. Currently, there are no useful guidelines for constant optimal threshold selection. In the absence of faults, a predetermined constant threshold would lead to more false alarms and missed detections under modeling uncertainties. Hence a technique to accommodate uncertainties and disturbances in the model, help in reducing false alarms and missed detections is essential for the enhancement of aircraft engine operations. In this work, a dynamic threshold algorithm is developed for aircraft engine fault detection and isolation that accommodates parametric uncertainties and disturbances. The algorithm takes the parametric uncertainties into consideration and proposes a dynamic threshold that makes use of the bounds on the parametric uncertainties which can thus distinguish an actual fault from the model uncertainties. First we design Kalman filters or unknown input observers based on the linearized engine model about a given nominal operating point, but the filters or observers use the measurements from the nonlinear engine model which includes uncertainty description. Using the robustness analysis of parametric uncertain systems, we generate upper-bound and lower-bound time response trajectories of the dynamic threshold. The extent of parametric uncertainties is assumed to be such that the perturbed eigenvalues reside in a set of distinct circular regions. A set of "structured" Kalman filters or unknown input observers are used for engine sensor or actuator fault diagnosis design. The residuals are errors between measured outputs and estimated outputs from a set of Kalman filters or a set of unknown input observers. With the dynamic threshold design approach, the residual crossing the upper bound or lower bound of the dynamic threshold indicates the occurrence of fault. Application to an aircraft turbofan engine model illustrates the performance of the proposed method. Advisors/Committee Members: Yedavalli, Rama.

Subjects: Engineering

Keywords: aircraft engine; dynamic threshold; fault diagnostics; FDI; linear uncertain system

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16. Neer, Michael Earnest. An investigation of spontaneous ignitions in flowing hydrogen air mixtures.

Degree: PhD, Aero/Astro Engineering, 1972, Ohio State University

Advisors/Committee Members: Edse, Rudolph.

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17. Packard, Nathan Owen. Active Flow Separation Control of a Laminar Airfoil at Low Reynolds Number.

Degree: PhD, Aero/Astro Engineering, 2012, Ohio State University

► Detailed investigation of the NACA 643-618 is obtained at a Reynolds number… (more)

▼ Detailed investigation of the NACA 643-618 is obtained at a Reynolds number of 6.4x104 and angle of attack sweep of -5° < α < 25°. The baseline flow is characterized by four distinct regimes depending on angle of attack, each exhibiting unique flow behavior. Active flow control is exploited from a row of discrete holes located at five percent chord on the upper surface of the airfoil. Steady normal blowing is employed at four representative angles; blowing ratio is optimized by maximizing the lift coefficient with minimal power requirement. The range of effectiveness of pulsed actuation with varying frequency, duty cycle and blowing ratio is explored. Pulsed blowing successfully reduces separation over a wide range of reduced frequency (0.1-1), blowing ratio (0.5–2), and duty cycle (0.6–50%). A phase-locked investigation, by way of particle image velocimetry, at ten degrees angle of attack illuminates physical mechanisms responsible for separation control of pulsed actuation at a low frequency and duty cycle. Temporal resolution of large structure formation and wake shedding is obtained, revealing a key mechanism for separation control. The Kelvin-Helmholtz instability is identified as responsible for the formation of smaller structures in the separation region which produce favorable momentum transfer, assisting in further thinning the separation region and then fully attaching the boundary layer. Closed-loop separation control of an oscillating NACA 643-618 airfoil at Re = 6.4x104 is investigated in an effort to autonomously minimize control effort while maximizing aerodynamic performance. High response sensing of unsteady flow with on-surface hot-film sensors placed at zero, twenty, and forty percent chord monitors the airfoil performance and determines the necessity of active flow control. Open-loop characterization identified the use of the forty percent sensor as the actuation trigger. Further, the sensor at twenty percent chord is used to distinguish between pre- and post- leading edge stall; this demarcation enables the utilization of optimal blowing parameters for each circumstance. The range of effectiveness of the employed control algorithm is explored, charting the practicality of the closed-loop control algorithm. To further understand the physical mechanisms inherent in the control process, the transients of the aerodynamic response to flow control are investigated. The on-surface hot-film sensor placed at the leading edge is monitored to understand the time delays and response times associated with the initialization of pulsed normal blowing. The effects of angle of attack and pitch rate on these models are investigated. Black-box models are developed to quantify this response. The sensors at twenty and forty percent chord are also monitored for a further understanding of the transient phenomena. Advisors/Committee Members: Bons, Jeffrey.

Subjects: Aerospace Engineering; Fluid Dynamics

Keywords: active flow control, experimental fluid dynamics, closed-loop control

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18. Saluru, Deepak Chaitanya. Active Fault Tolerant Model Predictive Control of a Turbofan Engine using C-MAPSS40k.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► Aircraft engine control is a crucial component for the safe and stable… (more)

Subjects: Aerospace Engineering

Keywords: C-MAPSS40k; engine control; fault tolerant control; model predictive control; optimal control

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19. Snyder, Michael Phillip. Design of a Lunar Rover Utilizing Hydrogen-Oxygen Fuel Cell Technologies.

Degree: MS, Aero/Astro Engineering, 2011, Ohio State University

► Future exploration of the solar system will depend on new designs and… (more)

Subjects: Aerospace Engineering

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20. Speth, Rachelle Lea. Parametric Study of the Effects of the Flapping Mode Excitation on the Near Field Structures of a Mach 1.3 Cold Jet.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► This effort investigates numerical and physical parameters influencing an ideally-expanded Mach 1.3… (more)

▼ This effort investigates numerical and physical parameters influencing an ideally-expanded Mach 1.3 jet excited by the m=+/-1 flapping mode. The excitation is imposed by eight Localized Arc Filament Plasma Actuators (LAFPA) placed around the periphery of the circular nozzle exit. The devices are modeled with a proven surface heating approach. The reference case considers the most amplified (jet column mode) frequency corresponding to a Strouhal number of 0.3, based on the diameter of the nozzle and the jet velocity, with an actuator-imposed temperature of 1500K and a duty cycle of 20%. Relative to this reference, the effects of changing frequency, duty cycle and actuator model temperature are explored. In some cases, e.g., actuator temperature, experimental data is not available, but for frequency, there is. The results are analyzed with several different quantitative and qualitative metrics, including time-averaged centerline decay and jet half width as well as phase-averaged coherent structures. Raising the frequency affects the dynamics in several ways. The number of vortical features observed in the phase-averaged data increases and the rate of decay of the centerline velocity is reduced. Furthermore, the alternating vortex ring interactions observed in the reference case are not distinct but are rather replaced by smaller structures, trends which are also observed in experiment. The flow mixes the fastest around the jet column mode (St~0.22). The higher duty cycles exhibits strengthened coherent structures and slightly higher jet growth along the flapping plane, but the overall dynamics remain the same. The response of the jet is relatively insensitive to actuator temperature model within reasonable limits. The latter two studies, with different duty cycles and actuator temperatures, are consistent with previous analyses demonstrating that instability manipulation, rather than heat deposition is the primary mechanism of control. Advisors/Committee Members: Gaitonde, Datta.

Subjects: Aerospace Engineering; Engineering; Mechanical Engineering

Keywords: supersonic jets; Large Eddy Simulation; plasma actuators

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21. Thake, Michael Patrick Jr. Investigation of a Laminar Airfoil with Flow Control and the Effect of Reynolds Number.

Degree: MS, Aero/Astro Engineering, 2011, Ohio State University

► Wind tunnel tests are performed on a NACA 643-618 airfoil at Reynolds… (more)

▼ Wind tunnel tests are performed on a NACA 643-618 airfoil at Reynolds numbers of 6.4x104, 1.8x105, 1.0x106, and 4.0x106 in order study several aspects of a laminar airfoil. Studies of flow control, separation bubbles and the effect of Reynolds number are the major topics of this effort. The tools used for investigation are surface pressure measurements, wake surveys, particle image velocimetry, hot-film anemometry, surface-oil flow visualization, and infrared imaging in order to view the problem from many angles. Preliminary testing at a Reynolds number of 64,000 determined that four distinct flow regimes exist with respect to angle of attack: weak laminar separation, moderate laminar separation, laminar separation bubble, and strong leading edge laminar separation. A portion of the study investigates the cause of such dynamic flow physics. Attempts are then made to employ flow control to induce or imitate the laminar separation bubble. By creating the laminar separation bubbles, significant lift increase and drag reduction are realized over a broader range of angles of attack. Normal blowing, suction, and zigzag tape are used, which are all well-characterized devices and have the potential to enhance lift and reduce drag. Lift is increased significantly and separation is delayed in three of the four regions as a result of control, where the region of no change is when the laminar separation bubble is already in effect. It is observed that the optimal flow control device changes between regimes because different flow physics are required to induce a change. Studies of Reynolds number scaling found that the lift increased and drag decreased as Reynolds number increased. It is important to note that the laminar separation bubble becomes naturally effective at most angles of attack by a Reynolds number of 180,000. Therefore, the value of flow control diminishes except in regions where strong leading edge separation is the limiting element of the airfoil. This research suggests that the laminar airfoil can be controlled in an energy efficient manner such that high performance is gained across all flight regimes with straightforward actuation. Advisors/Committee Members: Bons, Jeffrey.

Subjects: Aerospace Engineering; Engineering

Keywords: laminar airfoil; aerodynamics; flow control; Reynolds number; separation

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22. Vesel, Richard W. Jr. Aero-Structural Optimization of a 5 MW Wind Turbine Rotor.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► A 5 MW wind turbine rotor blade based on the NREL 5… (more)

Subjects: Aerospace Engineering

Keywords: wind turbine optimization; bend-twist coupling; airfoil optimization; genetic algorithms; aerostructural optimization

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23. Webb, Joshua J. The Effect of Particle Size and Film Cooling on Nozzle Guide Vane Deposition.

Degree: MS, Aero/Astro Engineering, 2011, Ohio State University

► A thesis is presented that investigates the effect of particle Stokes number… (more)

Subjects: Aerospace Engineering; Alternative Energy; Engineering; Experiments

Keywords: Deposition; Film Cooling; Roughness; Stokes Number

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24. Wertz, John Nicholas. An Energy-Based Experimental-Analytical Torsional Fatigue Life-Prediction Method.

Degree: MS, Aero/Astro Engineering, 2010, Ohio State University

► An energy-based cycle-dependent fatigue life prediction framework for the calculation of torsional… (more)

Subjects: Aerospace materials; Engineering; Experiments; Mechanical engineering; Mechanics

Keywords: energy-based torsional fatigue life-prediction shear method

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25. Yugulis, Kevin Lee. High Subsonic Cavity Flow Control Using Plasma Actuators.

Degree: MS, Aero/Astro Engineering, 2012, Ohio State University

► Localized arc filament plasma actuators have been used to control pressure fluctuations… (more)

▼ Localized arc filament plasma actuators have been used to control pressure fluctuations in a cavity with a length to depth ratio of 4.86. The rear wall of the cavity is inclined 30° above the horizontal plane and the cavity length is 61.7 mm, measured from the leading edge of the cavity to the mid-plane of the ramp. Five actuators have been uniformly distributed along the span of the wind tunnel at 1 mm upstream to the cavity leading edge. Experiments were conducted at Mach 0.6 and a Reynolds number of approximately 2x105 based on cavity depth. Forcing was conducted quasi-two-dimensionally and three-dimensionally. With this Mach number and geometry, the cavity was strongly resonating at the 2nd Rossiter mode corresponding to a frequency of 2.5 kHz. Time-resolved pressure measurements were used to assess the effectiveness of the actuators. Forcing quasi-two-dimensionally was found to be very effective, achieving a reduction in peak tone magnitude of over 20 dB and a reduction in broadband SPL of up to 5 dB. In general, the results for forcing in this manner were extremely sensitive to forcing frequency. The most effective forcing frequency was found at approximately 3300 Hz. Forcing was also conducted in several three-dimensional configurations. Overall certain three-dimensional configurations were found to be more effective than the quasi-two-dimensional forcing, and significantly less sensitive to frequency. Particle image velocimetry was used to understand how the forcing affected the shear layer. Interesting vortex dynamics such as possible vortex merging was observed, the details of which help to understand why certain frequencies are more effective than others. It was determined that the vortices in the shear layer are significantly weaker under three-dimensional forcing compared to quasi-two-dimensional forcing. This could help to explain the overall increase in effectiveness seen with three-dimensional forcing. ~ Advisors/Committee Members: Samimy, Mo.

Subjects: Aerospace Engineering

Keywords: aerodynamics; plasma actuators; cavity flow; active flow control

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