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Articles 1 - 30 of 166
Full-Text Articles in Aerospace Engineering
Investigation And Control Of Görtler Vortices In High-Speed Flows, Omar Es-Sahli
Investigation And Control Of Görtler Vortices In High-Speed Flows, Omar Es-Sahli
Theses and Dissertations
High-amplitude freestream turbulence and surface roughness elements can excite a laminar boundary-layer flow sufficiently enough to cause streamwise-oriented vortices to develop. These vortices resemble elongated streaks having alternate spanwise variations of the streamwise velocity. Following the transient growth phase, the fully developed vortex structures downstream undergo an inviscid secondary instability mechanism and, ultimately, transition to turbulence. This mechanism becomes much more complicated in high-speed boundary layer flows due to compressibility and thermal effects, which become more significant for higher Mach numbers. In this research, we formulate and test an optimal control algorithm to suppress the growth rate of the aforementioned …
Quasi 1d Modelling Of A Scramjet Engine Cycle Using Heiser-Pratt Approach, Asmaa Chakir
Quasi 1d Modelling Of A Scramjet Engine Cycle Using Heiser-Pratt Approach, Asmaa Chakir
Theses and Dissertations
Scramjet engines are key for sustained hypersonic flights. Analytic models play a critical role in the preliminary design of a scramjet engine configuration. The objective of this research is to develop and validate a quasi-1D model for the scramjet engine encompassing inlet, isolator and combustor, to evaluate the impact of flight conditions and design parameters on the engine functionality. The model is developed assuming isentropic flow in the inlet with a single turn; modified Fanno-flow equations in the isolator that account for the area change of the core flow; and the combustor is modeled using Heiser-Pratt equations accounting for the …
Experiments To Mitigate Flow Recirculation In A Closed Anechoic Chamber Using Mesh Screens As Turbulence Suppressors, Tori Kay Wolverton
Experiments To Mitigate Flow Recirculation In A Closed Anechoic Chamber Using Mesh Screens As Turbulence Suppressors, Tori Kay Wolverton
Theses and Dissertations
The desire to gather acoustic data of a propeller in simulated hover without environmental effects is met with the challenge of recirculating flow in a closed anechoic chamber. Flow recirculation in an anechoic chamber is not ideal because the effects of it being ingested by the rotor cause unsteady loadings on the propeller. This unsteady loading causes vortex noise from the turbulence introduced by the recirculation of the flow. The aim is to study the acoustic signature of a propeller separate from external factors and engine noise. Two different propellers with three different screen combinations were tested in a closed …
Direct Simulation And Reduced-Order Modeling Of Premixed Flame Response To Acoustic Modulation, Zheng Qiao
Direct Simulation And Reduced-Order Modeling Of Premixed Flame Response To Acoustic Modulation, Zheng Qiao
Theses and Dissertations
This dissertation introduces a general, predictive and cost-efficient reduced-order modeling (ROM) technique for characterization of flame response under acoustic modulation. The model is built upon the kinematic flame model–G-equation to describe the flame topology and dynamics, and the novelties of the ROM lie in i) a procedure to create the compatible base flow that can reproduce the correct flame geometry and ii) the use of a physically-consistent acoustic modulation field for the characterization of flame response. This ROM addresses the significant limitations of the classical kinematic model, which is only applicable to simple flame configurations and relies on ad-hoc models …
Characterizing Wake Roll-Up And Vortex Structure For Delta Wing Configuations Featuring Flow Control Devices At Low Reynolds Number, Jeffrey M. Layng
Characterizing Wake Roll-Up And Vortex Structure For Delta Wing Configuations Featuring Flow Control Devices At Low Reynolds Number, Jeffrey M. Layng
Theses and Dissertations
Various configurations of a cropped delta wing featuring a NACA 0012 wing-section were evaluated experimentally at a Reynolds number of 5.0 x 105 in the Air Force Institute of Technology Low-Speed Wind Tunnel facility. The effects of active flow control (AFC) and passive boundary-layer fences (BLF) were shown to improve high angle of attack delta wing performance. The AFC BLFs were shown to replicate the performance enhancements found in passive BLFs without incurring a drag penalty. An experimental characterization of the wake region is presented to compare the wake roll-up and leading edge vortices for these baseline, passive BLF, …
Exploratory Measurement Of Recession Rates Of Low Temperature Ablators Subjected To Mach 6 Flow, Ross H. Kellet
Exploratory Measurement Of Recession Rates Of Low Temperature Ablators Subjected To Mach 6 Flow, Ross H. Kellet
Theses and Dissertations
The high speed/high-temperature effect of heat shield ablation was simulated in the low-enthalpy AFRL Mach 6 Ludwieg Tube using solid dry ice as a low-temperature sublimator. The experiments utilized both 21 half-angle cones and bi-conic models with a 7 ° half-angle leading edge followed by a 26° half-angle base contained within a cryogenic-cooled stainless steel holder. A method of fabricating dry ice test articles was developed using commercially procured dry ice and custom-made aluminum molds. Tests were performed at Mach 6.1 with a stagnation temperature of 490 K and stagnation pressures ranging from 40 - 500 psi. Unit Reynolds number …
Fluid-Structure Interaction Of Nrel 5-Mw Wind Turbine, Mohamed Sayed Elkady Abd-Elhay
Fluid-Structure Interaction Of Nrel 5-Mw Wind Turbine, Mohamed Sayed Elkady Abd-Elhay
Theses and Dissertations
Wind energy is considered one of the major sources of renewable energy. Nowadays, wind turbine blades could exceed 100 m to maximize the generated power and minimize produced energy cost. Due to the enormous size of the wind turbines, the blades are subjected to failure by aerodynamics loads or instability issues. Also, the gravitational and centrifugal loads affect the wind turbine design because of the huge mass of the blades. Accordingly, wind turbine simulation became efficient in blade design to reduce the cost of its manufacturing. The fluid-structure interaction (FSI) is considered an effective way to study the turbine's behavior …
Optimizing Design Parameters For Active Flow Control Boundary-Layer Fence Performance Enhancement On A Delta Wing, Nathan L. Tedder
Optimizing Design Parameters For Active Flow Control Boundary-Layer Fence Performance Enhancement On A Delta Wing, Nathan L. Tedder
Theses and Dissertations
Utilizing computational fluid dynamic (CFD) simulations, the presented study is able to further the investigation of replicating and improving upon the performance of a NACA 0012 cropped half-span delta-wing at high angles-of-attack with an active flow control fluidic fence via wall-normal, steady blowing from an optimized single chordwise slot located at z/b = 70%,. The data is generated using CREATE-AV Kestrel v10.1rc5 CFD software on the Department of Defense High Performance Computing systems. The flight regime is held constant at a Mach number of 0.18 and a Reynolds number (Re) of 5.0 x 105, based on the root …
Nebulizer-Based Systems To Improve Pharmaceutical Aerosol Delivery To The Lungs, Benjamin M. Spence
Nebulizer-Based Systems To Improve Pharmaceutical Aerosol Delivery To The Lungs, Benjamin M. Spence
Theses and Dissertations
Combining vibrating mesh nebulizers with additional new technologies leads to substantial improvements in pharmaceutical aerosol delivery to the lungs across therapeutic administration methods. In this dissertation, streamlined components, aerosol administration synchronization, and/or Excipient Enhanced Growth (EEG) technologies were utilized to develop and test several novel devices and aerosol delivery systems. The first focus of this work was to improve the poor delivery efficiency, e.g., 3.6% of nominal dose (Dugernier et al. 2017), of aerosolized medication administration to adult human subjects concurrent with high flow nasal cannula (HFNC) therapy, a form of continuous-flow non-invasive ventilation (NIV). The developed Low-Volume Mixer-Heater (LVMH) …
The Effect Of Passive And Active Boundary-Layer Fences On Delta Wing Performance At Low Reynolds Number, Anna C. Demoret
The Effect Of Passive And Active Boundary-Layer Fences On Delta Wing Performance At Low Reynolds Number, Anna C. Demoret
Theses and Dissertations
The effect of passive and active boundary-layer fences (BLFs) on performance is evaluated on a NACA 0012 delta wing (croot = 14in, ctip = 2.8in, Λ = 45°, b = 23.5in) at a Reynolds number (Re) of 5.0 x 105 based on the root chord. The performance improvements of a passive BLF are replicated and improved upon using an active flow control (AFC) fluidic fence created by a wall-normal steady-blowing jet from a slot. The application of a passive BLF at a spanwise location of 70% z/b resulted in an 8.7% increase in CLmax compared to …
Initial Stage Of Fluid-Structure Interaction Of A Celestial Icosahedron Shaped Vacuum Lighter Than Air Vehicle, Dustin P. Graves
Initial Stage Of Fluid-Structure Interaction Of A Celestial Icosahedron Shaped Vacuum Lighter Than Air Vehicle, Dustin P. Graves
Theses and Dissertations
The analysis of a celestial icosahedron geometry is considered as a potential design for a Vacuum Lighter than Air Vehicle (VLTAV). The goal of the analysis is ultimately to understand the initial fluid-structure interaction of the VLTAV and the surrounding airflow. Up to this point, previous research analyzed the celestial icosahedron VLTAV in relation to withstanding a symmetric sea-level pressure applied to the membrane of the structure. This scenario simulates an internal vacuum being applied in the worst-case atmospheric environmental condition. The next step in analysis is to determine the aerodynamic effects of the geometry. The experimental setup for obtaining …
Wall Model Large Eddy Simulation Of A Diffusing Serpentine Inlet Duct, Ryan J. Thompson
Wall Model Large Eddy Simulation Of A Diffusing Serpentine Inlet Duct, Ryan J. Thompson
Theses and Dissertations
The modeling focus on serpentine inlet ducts (S-duct), as with any inlet, is to quantify the total pressure recovery and ow distortion after the inlet, which directly impacts the performance of a turbine engine fed by the inlet. Accurate prediction of S-duct ow has yet to be achieved amongst the computational fluid dynamics (CFD) community to improve the reliance on modeling reducing costly testing. While direct numerical simulation of the turbulent ow in an S-duct is too cost prohibitive due to grid scaling with Reynolds number, wall-modeled large eddy simulation (WM-LES) serves as a tractable alternative. US3D, a hypersonic research …
Influence Of Leading Edge Oscillatory Blowing On Time-Accurate Dynamic Store Separation, Ryan G. Saunders
Influence Of Leading Edge Oscillatory Blowing On Time-Accurate Dynamic Store Separation, Ryan G. Saunders
Theses and Dissertations
The primary objective of this research is to support the static and dynamic characterization and the time-accurate dynamic load data acquisition of store separation from a cavity with leading edge oscillatory blowing. Developing an understanding of, and potentially controlling, pitch bifurcation of a store release is a motivation for this research. The apparatus and data acquisition system was used in a two-part experiment to collect both static and dynamic testing data in the AFIT low speed wind tunnel in speeds of 60, 100, and 120 mph, from Reynolds numbers varying from 5.5x104 to 4.6x105, depending on reference …
Investigation Of Endwall Vortex Manipulation In High Lift Turbines Caused By Active Endwall Forcing, Horatio J. Babcock
Investigation Of Endwall Vortex Manipulation In High Lift Turbines Caused By Active Endwall Forcing, Horatio J. Babcock
Theses and Dissertations
With the increased demand for lighter, more fuel efficient and smaller gas turbine engines, the impetus to reduce the weight and size of the turbine has become apparent. One approach to reduce this weight is to reduce the number of blades in the turbine. However, to maintain power output, each blade must be capable of supporting a greater amount of lift. While several high-lift turbine profiles have been detailed in literature, most of these profiles have increased endwall losses, despite their desirable mid-span characteristics. To mitigate this endwall loss, a number of active and passive flow approaches have been studied …
Tracking Shock Movement On The Surface Of An Oscillating, Straked Semispan Delta Wing, Justin A. Pung
Tracking Shock Movement On The Surface Of An Oscillating, Straked Semispan Delta Wing, Justin A. Pung
Theses and Dissertations
A recent research effort, sponsored by the Air Force Office of Scientific Research, numerically investigated the unsteady aerodynamic flow field around an oscillating, straked, delta wing. The study was centered on determining the importance of the unsteady aerodynamic forces acting as a driver for a nonlinear motion known as limit cycle oscillations. The current effort focused on creating a computational model to compare to the results of previous tests and modeling efforts and discover new information regarding the onset of LCO. The computational model was constructed using the Cartesian overset capabilities of the CREATE-AV™ fixed wing fluid dynamics solver Kestrel. …
Analytical Models And Control Design Approaches For A 6 Dof Motion Test Apparatus, Kyra L. Schmidt
Analytical Models And Control Design Approaches For A 6 Dof Motion Test Apparatus, Kyra L. Schmidt
Theses and Dissertations
Wind tunnels play an indispensable role in the process of aircraft design, providing a test bed to produce valuable, accurate data that can be extrapolated to actual flight conditions. Historically, time-averaged data has made up the bulk of wind tunnel research, but modern flight design necessitates the use of dynamic wind tunnel testing to provide time-accurate data for high frequency motion. This research explores the use of a 6 degree of freedom (DOF) motion test apparatus (MTA) in the form of a robotic arm to allow models inside a subsonic wind tunnel to track prescribed trajectories to obtain time-accurate force …
Thermochemical Non-Equilibrium Models For Weakly Ionized Hypersonic Flows With Application To Slender-Body Wakes, Matthew P. Clarey
Thermochemical Non-Equilibrium Models For Weakly Ionized Hypersonic Flows With Application To Slender-Body Wakes, Matthew P. Clarey
Theses and Dissertations
The current resurgence of interest in hypersonic technologies has warranted an inquiry into the commonly employed thermochemical non-equilibrium models within computational fluid dynamic (CFD) simulations. Additionally, research has historically focused on forebody flowfields, while studies of the complex wake structure have remained elusive. Although the forebody is of significance for vehicle analysis, the wake presents many exploitative characteristics. This dissertation aimed to address these two deficits. First, two three-temperature non-equilibrium models were developed, increasing the fidelity of hypersonic solutions above that of the legacy two-temperature model. The models were then investigated via zero-dimensional simulations, to detail the non-equilibrium processes, and …
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Wall-Modeled Large Eddy Simulation Of A Three-Dimensional Shock-Boundary Layer Interaction, Nicholas J. Marco
Theses and Dissertations
The direct simulation of turbulent flows is prohibitive at high Reynolds numbers; thus, methods such as RANS and LES are used. However, these methods still require a large number of cells near a solid boundary. To circumvent this issue, a Wall-Modeled Large Eddy Simulation (WM-LES) can be used. Of interest is how these wall models perform in comparison to a Wall-Resolved Large Eddy Simulation (WR-LES) and experimental results of a shock turbulent boundary layer interactions (STBLI) and specifically, whether equilibrium wall models are sufficient to resolve the oscillatory and hence non-equilibrium nature of these flows or whether a non-equilibrium model …
An Efficient Euler Method To Predict Shock Migration On A Straked Delta Wing Design, Dylan N. Hope
An Efficient Euler Method To Predict Shock Migration On A Straked Delta Wing Design, Dylan N. Hope
Theses and Dissertations
In support of the Air Force Office of Scientific Research, this project sought to identify the significance of nonlinear aerodynamic phenomena in regards to LCO of a straked delta wing design. Previous works include unsteady Navier-Stokes aeroelastic analysis of various wing designs and flight test of F-16 transonic LCO with interest focused on oscillatory SITES behavior. The research presented within this investigation further expanded the understanding of unsteady aerodynamics by performing aeroelastic analysis of a wing oscillated in pitch with an Euler-based, boundary layer coupled numerical method (ZEUS). The wing was tested for a multitude of LCO parameters such as …
Time-Dependent Validation Of Finite Element Strain Distribution Of A Plastically-Deformed Plate Via Digital Image Correlation, Kevin R. Knapp
Time-Dependent Validation Of Finite Element Strain Distribution Of A Plastically-Deformed Plate Via Digital Image Correlation, Kevin R. Knapp
Theses and Dissertations
Generation of residual stress is an essential step in the generation of Goodman data via Air Force Research Laboratory's vibration-based fatigue test. Conventional Goodman data is constructed through uniaxial fatigue testing at a rate of 40 Hz, while the vibration-based testing excites stresses at 1,600 Hz in a stress state that is similar to those seen in gas turbine engine airfoils. A pre-strain procedure is conducted to form residual tensile stress, which serves as a steady stress when the specimen is subjected to fully-reversed vibration-based fatigue loads. This steady tensile stress is desired at the fatigue zone of the test …
Investigation Of Dynamic Store Separation Out Of A Weapons Bay Cavity Utilizing A Low Speed Wind Tunnel, Andrew D. Bower
Investigation Of Dynamic Store Separation Out Of A Weapons Bay Cavity Utilizing A Low Speed Wind Tunnel, Andrew D. Bower
Theses and Dissertations
Characterizing mission store trajectories as they separate from a weapons bay cavity is highly relevant to the Air Force mission. The flow around a weapons bay is unsteady. The unsteady flow can cause a mission store separation trajectory to be unpredictable, and such is the case for what some have termed a pitch bifurcation. Traditional wind tunnel testing is incapable of detecting a bifurcation because traditional wind tunnel testing records time-averaged data. In this study, an experimental testing system was developed and refined in order to support the time-accurate characterization of dynamic mission store separation events. A Motion Test Apparatus …
Cavity Geometric Features And Entrainment Characterization Resulting From A Ballistically Induced Hydrodynamic Ram Event, Andrew J. Lingenfelter
Cavity Geometric Features And Entrainment Characterization Resulting From A Ballistically Induced Hydrodynamic Ram Event, Andrew J. Lingenfelter
Theses and Dissertations
Hydrodynamic Ram can cause damage to industrial and aircraft systems. The resulting transient spray increases the probability of fire. To better understand the driving mechanisms behind transient spray, internal, and external measurements of the cavity geometry, and entrained flow field were accomplished. Research determined cavity contraction and separation are pre-cursors to the initiation of the transient spray phases. The entrained flow measurement required development of a new and novel technique using a continuous wave laser and atomized water particles. The peak mass flow correlated well with cavity geometric features, such as cavity contraction. Using the mass flow, cavity diameter at …
Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope
Investigation Into Reynolds Number Effects On A Biomimetic Flapping Wing, Daniel K. Hope
Theses and Dissertations
This research investigated how the nature of the wing changed as a function of Reynolds number by measuring the forces produced by wings with varying characteristic lengths, tested at varying air densities. Increasing the wing span increased the overall weight of the wing, which reduced the 1st natural frequency; and did not result in an increase in vertical force over the baseline 50 mm wing. However; if the decrease in natural frequency was counteracted by increasing the thickness of the joint material in the linkage mechanism, vertical force production did increase over the baseline wing planform. Negligible forces and moments …
Design And Flight Test Of A Weapons-Cavity Acoustics And Separation Test Bed, Zachary Probst
Design And Flight Test Of A Weapons-Cavity Acoustics And Separation Test Bed, Zachary Probst
Theses and Dissertations
Two very important, and often detrimental, phenomena can occur when an open weapons bay, or more generally-a cavity, is exposed to high-velocity flow. First, a shear layer develops over the cavity, leading to large regions of difficult-to-predict flow. Second, dynamic pressure oscillations are generated within the cavity itself. These two issues can combine to have multiple harmful effects on weapons carriage and employment. This provided motivation for flight tests which quantify forces and moments on a store, mounted at various positions in the cavity, for a variety of flight conditions. Specifically, a low-cost, easily reconfigurable test bed for weapons-cavity research …
Force And Moment Measurements Applicable To A Flexible Weapons System, James B. Sellers
Force And Moment Measurements Applicable To A Flexible Weapons System, James B. Sellers
Theses and Dissertations
Continuing the development of the 6-DOF Motion Test Apparatus (MTA) for performing dynamic wind tunnel tests revealed the importance of a capable data acquisition (DAQ) system for collecting and analyzing data. Assembling and testing the DAQ system in conjunction with the MTA, AFIT Low-Speed Wind Tunnel, and a selection of high-performance sensors was the primary focus of this research. Specifically, acquiring time-accurate aerodynamic force and moment measurements on a variety of test models was of high importance. With the established real-time DAQ system hardware, a National Instruments (NI) LabVIEW program was created to acquire data from an ATI Nano25-E force …
Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania
Analysis Of Hypersonic Vehicle Wakes, Matthew A. Kania
Theses and Dissertations
As advancements are made with ballistic missiles, particularly in the area of hypersonic bodies, there is a growing need to advance the methods of detecting these new ballistic weapons. As a result, the National Air and Space Intelligence Center has asked the Air Force Institute of Technology to examine the wake region behind hypersonic bodies. A thorough understanding of the aerothermal phenomena and the chemical reactions occurring in the wake region will enable an advancement of tracking hypersonic bodies. This research examined the wake region behind a hypersonic body using computational fluid dynamics.
This study used Pointwise® to develop a …
Characterization Of A Robotic Manipulator For Dynamic Wind Tunnel Applications, James C. Lancaster
Characterization Of A Robotic Manipulator For Dynamic Wind Tunnel Applications, James C. Lancaster
Theses and Dissertations
The newly acquired 6-DOF Motion Test Apparatus (MTA) was installed to perform dynamic wind tunnel testing in the AFIT Low Speed Wind Tunnel. Several complex motions revealed that the overall performance of the test rig needed improvement especially during small motions. The motions exposed that further enhancements would need to be performed individually for each joint. This research effort focused on the improvement of the MTA wrist roll motor and controller using a pitch oscillation. The controller software was improved using position feedback because the MTA wrist roll motor and controller exhibited reduced signal bias and amplitude attenuation. The enhanced …
Influence Of Mach Number And Dynamic Pressure On Cavity Tones And Freedrop Trajectories, Justin D. Merrick
Influence Of Mach Number And Dynamic Pressure On Cavity Tones And Freedrop Trajectories, Justin D. Merrick
Theses and Dissertations
Weapons release at supersonic speeds from an internal weapons bay is a highly desirable capability. To ensure a successful release at multiple Mach numbers, the aerodynamic environment must be well-understood and repeatable, with a robust system for safe testing of store separation. For this reason, experimental methods were used to investigate the characteristics of a scaled WICS bay with a length-to-depth ratio of 4.5 at multiple Mach numbers and stagnation pressures. Three new nozzles were designed, manufactured, and characterized for the AFIT small supersonic tunnel, yielding freestream Mach numbers of 2.22, 1.84, and 1.43. In addition, a control valve was …
The Characterization Of Material Properties And Structural Dynamics Of The Manduca Sexta Forewing For Application To Flapping Wing Micro Air Vehicle Design, Ryan P. O'Hara
Theses and Dissertations
The Manduca Sexta species of moth serves as a source of biological inspiration for the future of micro air vehicle flapping flight. The ability of this species to hover in flapping flight has warranted investigation into the critical material, structural, and geometric properties of the forewing of this biological specimen. A rigorous morphological study of the Manduca Sexta forewing was conducted to characterize the physical and material properties of the biological forewing for the purpose of developing an advanced parametric three dimensional model finite element analysis (FEA) model. This FEA model was tuned to match the experimentally determined structural dynamics …
Novel Discretization Schemes For The Numerical Simulation Of Membrane Dynamics, Kyle F. Kolsti
Novel Discretization Schemes For The Numerical Simulation Of Membrane Dynamics, Kyle F. Kolsti
Theses and Dissertations
Motivated by the demands of simulating flapping wings of Micro Air Vehicles, novel numerical methods were developed and evaluated for the dynamic simulation of membranes. For linear membranes, a mixed-form time-continuous Galerkin method was employed using trilinear space-time elements, and the entire space-time domain was discretized and solved simultaneously. For geometrically nonlinear membranes, the model incorporated two new schemes that were independently developed and evaluated. Time marching was performed using quintic Hermite polynomials uniquely determined by end-point jerk constraints. The single-step, implicit scheme was significantly more accurate than the most common Newmark schemes. For a simple harmonic oscillator, the scheme …