Aerospace Engineering Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2737
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Item Hypersonic Application of Focused Schlieren and Deflectometry(2010) VanDercreek, Colin Paul; Yu, Kenneth H; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A non-intrusive diagnostic capability for determining the hypersonic shock and boundary layer structure was developed, installed, and successfully tested at the AEDC Hypervelocity Tunnel 9. This customized diagnostic involves a combination of a focused schlieren system, which relies on creating multiple virtual light sources using a Fresnel lens and a source grid, and a deflectometry system, which uses the focused schlieren and a photomultiplier tube. It was used for obtaining spatially resolved images of density gradients with a depth of focus less than one centimeter, while allowing high frequency measurements of density fluctuations. The diagnostic was applied in investigating the second-mode instability waves present in the boundary layer of a sharp-nosed cone submerged in a Mach 10 flow. The waves were successfully imaged and their frequencies were measured even though the flow density was below 0.01 kg/m^3 and the frequencies over 200 kHz. This adds a new capability to hypersonic testing.Item OPTIC FLOW BASED STATION-KEEPING AND WIND REJECTION FOR SMALL FLYING VEHICLES(2010) Patrick, Bryan; Humbert, James S.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Optic flow and Wide Field Integration (WFI) have shown potential for application to autonomous navigation of Unmanned Air Vehicles (UAVs). In this study the application of these same methods to other tasks, namely station-keeping and wind rejection, is examined. Theory surrounding optic flow, WFI and wind gust modeling is examined to provide a theoretical background. A controller based on a H∞ bounded formulation of the well known Linear Quadratic Regulator in designed to both mitigate wind disturbances and station-keep. The performance of this controller is assessed via simulation to determine both performance and trade-offs in implementation such as the method for optic flow calculation. Furthermore, flight tests are performed to examine the real world effectiveness of the controller. Finally, conclusions about potential improvement to implementation are drawn.Item SIMULATION AND MODELING OF AN ACOUSTICALLY FORCED MODEL ROCKET INJECTOR(2010) Gers, David; Yu, Ken; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)A numerical and experimental study was performed to assess the capability of the Loci-CHEM CFD solver in simulating dynamic interaction between hydrogen-oxygen turbulent diffusion flames and periodic pressure waves. Previous experimental studies involving a single-element shear-coaxial model injector revealed an unusual flame-acoustic interaction mechanism affecting combustion instability characteristics. To directly compare the simulation and experiments, various models in the present solver were examined and additional experiments conducted. A customized mesh and corresponding boundary conditions were designed and developed, closely approximating the experimental setup. Full 3-D simulations were conducted using a hybrid RANS/LES framework with appropriate chemistry and turbulence models. The results were compared for both reacting and non-reacting flows that were excited at various forcing frequencies representing both resonant and non-resonant behaviors. Although a good qualitative agreement was obtained for the most part, there was a significant discrepancy in simulating the flame-acoustic interaction behavior observed under non-resonant forcing conditions.Item Development of a reusable top-level control architecture for a robotic manipulator(2010) D'Amore, Nicholas; Akin, David; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The capabilities of a robotic system are strongly constrained by the capabilities of its control software. The development of this software represents a substantial fraction of the development effort of the overall system, due in part to the difficulty of reusing software written for previous robotic applications. A reusable software control architecture therefore has enormous potential to expedite the development and reduce the cost of this development process. This thesis presents a component-based reusable architecture for the top-level control of a robotic manipulator, developed within the Open Robot Control Software (Orocos) framework. This framework enables the development of software components that are applicable to a variety of robotic manipulators. The software is implemented on an existing manipulator platform as a demonstration of basic functionality. Simulations are conducted to verify adaptability to other kinematic arrangements.Item MANUFACTURING TECHNIQUES FOR TITANIUM ALUMINIDE BASED ALLOYS AND METAL MATRIX COMPOSITES(2010) Kothari, Kunal B; Wereley, Norman M; Radhakrishnan, Ramachandran; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Dual phase titanium aluminides composed vastly of gamma phase (TiAl) with moderate amounts of alpha2 phase (Ti3Al) have been considered for several high temperature aerospace and automobile applications. High specific strength coupled with exceptional high temperature performance in the areas of creep and oxidation resistance makes titanium aluminides "materials of choice" for next generation propulsion systems. Titanium aluminides are primarily being considered as potential replacements for Ni-based superalloys in gas turbine engine components with the aim of developing more efficient and leaner engines with high thrust-to-weight ratio. As titanium aluminides lack room temperature ductility, traditional manufacturing techniques such as casting, forging and rolling are more expensive to perform. To overcome this, research over the past decade has examined powder metallurgy techniques such as hot-isostatic pressing, sintering and hot-pressing to produce titanium aluminides parts. Enhancements in these powder metallurgy techniques has produced near-net shape parts of titanium aluminides possessing a homogeneous and refined microstructure and thereby exhibiting better mechanical performance. This study presents a novel powder metallurgy approach to consolidate titanium aluminide powders. Traditional powder consolidation processes require exposure to high temperatures over a lengthy duration. This exposure leads to grain growth in the consolidated part which adversely affects its mechanical properties. A rapid consolidation process called Plasma Pressure Compaction (P2C) has been introduced and utilized to consolidate titanium aluminide powders to produce titanium aluminide parts with minimal grain growth. The research also explores the role of small alloying additions of Nb and Cr to enhance ductility of the consolidated parts. The grain size of the consolidated parts is further reduced in the sub-micrometer range by milling the as-received powders. Finally, a metal matrix composite with TiAl matrix reinforced with TiB was developed by first blending the matrix and the reinforcement powders and then consolidating the powder blend.Item OPTIMAL CONTROL OF OBJECTS ON THE MICRO- AND NANO-SCALE BY ELECTROKINETIC AND ELECTROMAGNETIC MANIPULATION: FOR BIO-SAMPLE PREPARATION, QUANTUM INFORMATION DEVICES AND MAGNETIC DRUG DELIVERY(2010) Probst, Roland; Shapiro, Benjamin; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this thesis I show achievements for precision feedback control of objects inside micro-fluidic systems and for magnetically guided ferrofluids. Essentially, this is about doing flow control, but flow control on the microscale, and further even to nanoscale accuracy, to precisely and robustly manipulate micro and nano-objects (i.e. cells and quantum dots). Target applications include methods to miniaturize the operations of a biological laboratory (lab-on-a-chip), i.e. presenting pathogens to on-chip sensing cells or extracting cells from messy bio-samples such as saliva, urine, or blood; as well as non-biological applications such as deterministically placing quantum dots on photonic crystals to make multi-dot quantum information systems. The particles are steered by creating an electrokinetic fluid flow that carries all the particles from where they are to where they should be at each time step. The control loop comprises sensing, computation, and actuation to steer particles along trajectories. Particle locations are identified in real-time by an optical system and transferred to a control algorithm that then determines the electrode voltages necessary to create a flow field to carry all the particles to their next desired locations. The process repeats at the next time instant. I address following aspects of this technology. First I explain control and vision algorithms for steering single and multiple particles, and show extensions of these algorithms for steering in three dimensional (3D) spaces. Then I show algorithms for calculating power minimum paths for steering multiple particles in actuation constrained environments. With this microfluidic system I steer biological cells and nano particles (quantum dots) to nano meter precision. In the last part of the thesis I develop and experimentally demonstrate two dimensional (2D) manipulation of a single droplet of ferrofluid by feedback control of 4 external electromagnets, with a view towards enabling feedback control of magnetic drug delivery to reach deeper tumors in the long term. To this end, I developed and experimentally demonstrated an optimal control algorithm to effectively manipulate a single ferrofluid droplet by magnetic feedback control. This algorithm was explicitly designed to address the nonlinear and cross-coupled nature of dynamic magnetic actuation and to best exploit available electromagnetic forces for the applications of magnetic drug delivery.Item Computational Fluid Dynamic Solutions of Optimized Heat Shields Designed for Earth Entry(2010) Meeroff, Jamie Gabriel; Lewis, Mark J; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Computational fluid dynamic solutions are obtained for heat shields optimized aerothermodynamically using Newtonian impact theory. Aerodynamically, the low-order approach matches computational simulations within 10%. Benchmark Apollo 4 solutions show that predicted heat fluxes under-predict convective heating by 30% and over-predict radiative heating by 16% compared to computational results. Parametric studies display a power law reliance of convective heat flux on edge radius. A slender heat shield optimized for a single design point produces heat fluxes 1.8 times what was predicted using the Newtonian approach. Here, maximum heating decreases with the inverse cube of the base sharpness. Coupled vehicle/trajectory optimized designs are examined for lunar return (11 km/s) and Mars return (12.5 km/s) and show possible discrepancies for eccentric shapes using low-order empirical correlations. Ultimately, gains suggested by the low-order approach using complex geometries are not reflected in high-fidelity simulations. In some respects, the simpler shape is the ideal oneItem Propellant Injection Strategy for Suppressing Acoustic Combustion Instability(2010) Diao, Qina; Yu, Kenneth H.; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Shear-coaxial injector elements are often used in liquid-propellant-rocket thrust chambers, where combustion instabilities remain a significant problem. A conventional solution to the combustion instability problem relies on passive control techniques that use empirically-tested hardware such as acoustic baffles and tuned cavities. In addition to adding weight and decreasing engine performance, these devices are designd using trial-and-error empirical science, which does not provide the capability to predict the overall system stability characteristics in advance. In this thesis, two novel control strategies that are based on propellant fluid dynamics were investigated for mitigating acoustic instability involving shear-coaxial injector elements. The new control strategies would use a set of controlled injectors allowing local adjustment of propellant flow patterns for each operating condition, of which the instability could become a problem. One strategy relies on reducing the oxidizer-fuel density gradient by blending heavier methane to the main fuel hydrogen. Another strategy utilizes modifying the equivalence ratio to affect the acoustic impedance through the mixing and reaction rate changes. To provide the scientific basis, unit-physics experiments were conducted to explore the potential effectiveness of these strategies. Two different model combustors, simulating a single-element injector test and a double-element injector test, were designed and tested for flame-acoustic interaction. For these experiments, the Reynolds number of the central oxygen jet was kept between 4700 and 5500 making the injector flames sufficiently turbulent. A compression driver, mounted on one side of the combustor wall, provided controlled acoustic excitation to the injector flames, simulating the initial phase of flame-acoustic interaction. Acoustic excitation was applied either as a band-limited white noise forcing between 100 Hz and 5000 Hz or as a single-frequency, fixed-amplitude forcing at 1150 Hz which represented a frequency least amplified by any resonance. Effects of each control strategy on flame-acoustic interaction were assessed in terms of modifying the acoustic resonance characteristics subject to white-noise excitation and changes in flame brush thickness under single-frequency excitation. In the methane blending experiments, the methane mole fraction was varied between 0% and 63%. Under white noise excitation, up to 16% shift in a resonant frequency was observed but the acoustic pressure spectrum remained qualitatively similar. For the fixed frequency forcing, the spatial extent of flame-acoustic interaction was substantially reduced. In the other experiments, the equivalence ratio of the control injector was varied between 0 and infinity, causing up to 40% shift in a resonant frequency as well as changes in the acoustic pressure spectrum. These results open up the possibility of employing flow-based control to prevent combustion instabilities in liquid-fueled rockets.Item Design and Performance Prediction of Swashplateless Helicopter Rotors with Trailing Edge Flaps and Tabs(2010) Falls, Jaye; Chopra, Inderjit; Datta, Anubhav; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This work studies the design of trailing edge controls for swashplateless helicopter primary control, and examines the impact of those controls on the performance of the rotor. The objective is to develop a comprehensive aeroelastic analysis for swashplateless rotors in steady level flight. The two key issues to be solved for this swashplateless control concept are actuation of the trailing edge controls and evaluating the performance of the swashplateless rotor compared to conventionally controlled helicopters. Solving the first requires simultaneous minimization of trailing flap control angles and hinge moments to reduce actuation power. The second issue requires not only the accurate assessment of swashplateless rotor power, but also similar or improved performance compared to conventional rotors. The analysis consists of two major parts, the structural model and the aerodynamic model. The inertial contributions of the trailing edge flap and tab are derived and added to the system equations in the structural model. Two different aerodynamic models are used in the analysis, a quasi-steady thin airfoil theory that includes arbitrary hinge positions for the flap and the tab, and an unsteady lifting line model with airfoil table lookup based on wind tunnel test data and computational fluid dynamics simulation. The predicted swashplateless rotor power is sensitive to the pattern of trailed vorticity from the rotor blade. Trailed vortices are added at the inboard and outboard boundaries of the trailing edge flap, and the flap deflection is used to calculate an effective angle of attack for the calculation of the near and far wake. This wake model predicts the swashplateless rotor requires less main rotor power than the conventional UH-60A helicopter from hover to &mu = 0.25. As the forward flight speed increases, the swashplateless predicted power increases above the conventional rotor, and the rotor lift-to-drag ratio decreases below that of the conventional rotor.Item MODELING AND SIMULATION OF MIXING LAYER FLOWS FOR ROCKET ENGINE FILM COOLING(2010) Dellimore, Kiran Hamilton Jeffrey; Cadou, Christopher P; Trouvé, Arnaud; Aerospace Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Film cooling has been selected for the thermal protection of the composite nozzle extension of the J-2X engine which is currently being developed for the second stage of NASA's next generation launch vehicle, the Ares I rocket. However, several challenges remain in order to achieve effective film cooling of the nozzle extension and to ensure its safe operation. The extreme complexity of the flow (three-dimensional wakes, lateral flows, vorticity, and flow separation) makes predicting film cooling performance difficult. There is also a dearth of useful supersonic film cooling data available for engineers to use in engine design and a lack of maturity of CFD tools to quantitatively match supersonic film cooling data. This dissertation advances the state of the art in film cooling by presenting semi-empirical analytical models which improve the basic physical understanding and prediction of the effects of pressure gradients, compressibility and density gradients on film cooling effectiveness. These models are shown to correlate most experimental data well and to resolve several conflicts in the open literature. The core-to-coolant stream velocity ratio, R, and the Kays acceleration parameter, KP, are identified as the critical parameters needed to understand how pressure gradients influence film cooling performance. The convective Mach number, Mc, the total temperature ratio, Ω0, and the Mach number of the high speed stream, MHS, are shown to be important when explaining the effects of compressibility and density gradient on film cooling effectiveness. An advance in the simulation of film cooling flows is also presented through the development of a computationally inexpensive RANS methodology capable of correctly predicting film cooling performance under turbulent, subsonic conditions. The subsonic simulation results suggest that it in order to obtain accurate predictions using RANS it is essential to thoroughly characterize the turbulent states at the inlet of the coolant and core streams of the film cooling flow. The limitations of this approach are established using a Grid Convergence Index (GCI) Test and a demonstration of the extension of this RANS methodology to supersonic conditions is presented.