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ELSHAMY, OMAR MEXPERIMENTAL INVESTIGATIONS OF STEADY AND DYNAMIC BEHAVIOR OF TRANSVERSE LIQUID JETS
PhD, University of Cincinnati, 2007, Engineering : Aerospace Engineering
The injection of a liquid jet into a crossflow of air provides a means of higher penetration and rapidly mixing liquid fuel and air for combustion applications. The structure of the spray, formed is investigated. To attain this goal, the problem is divided into the following tasks which involve: (1) characterize the penetration, breakup, atomization, mixing, and breakup of liquid jet injected into crossflow at conditions relevant to real engine conditions, (2) establish an understanding of the structure of that transverse jet near the injection point, and (3) study the dynamics behavior of the transverse jet and propose new method to control the transverse liquid jet in crossflow. Two breakup modes have been observed, column and surface breakup. The agreement between the breakup map developed in the present study with the existing ones is quite good. The agreement between the PIV and LDV measurements was good and within 10% accuracy. PIV probe has been proven as a good tool to capture the aero-structure of spray generated by liquid jet in cross flows by comparing its results with the corresponding LDV results. Droplet velocity exhibits a minimum in the spray core. As the momentum ratio increases, the transverse location as well as the droplet velocity of the spray core increase, while the droplet velocity at the outer periphery decreases. Elevating the ambient pressure slightly decreases the penetration and decreases the spray spread. At higher ambient pressure, shorter axial distance is required for the droplet to follow the air flow. Mechanically exciting the transverse liquid jet can have a significant effect on the mixing, spreading, and penetration of the liquid jet in crossflow. The penetration of the jet may increase by more than 40 % while the spread of the jet by 100 % at an axial location of about ten diameters downstream of the injection point. The optimum excitation Strouhal number is about 0.0047, at which homogenous droplet average velocity distribution and maximum interaction between the liquid jet and the crossflow are observed. Novel correlations that describe the outer and inner boundaries of the dynamic jet are developed.

Committee:

Dr. San-Mou Jeng (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Dynamic Jet; PIV; LDV; Crossflow; Atomozation; LPP; Excitation; Modulation

Scharlemann, Carsten AInvestigation of thrust mechanisms in a water fed pulsed plasma thruster
Doctor of Philosophy, The Ohio State University, 2003, Aeronautical and Astronautical Engineering
Analytic models predict the possibility of extending the range of performance parameters of Pulsed Plasma Thrusters (PPT) by using propellants other than the traditionally used Teflon. A theoretical and experimental effort was initiated at The Ohio State University to investigate the use of alternative propellants for PPT. Analytical and numerical calculations (MACH2) indeed indicate a significant broadening of the obtainable range of specific impulse and thrust-to-power ratios when alternative propellants such as lithium or water are utilized. Consequently, in an effort to investigate changes in physical phenomena and thruster performance experimentally, a hybrid thruster was designed and built, facilitating the use of alternatively water or Teflon. The thruster design includes a unique water propellant feed system, allowing the supply of the water propellant without detrimentally affecting the inherent simplicity of the PPT system. ii The thruster operation and performance was investigated by several different diagnostic methods, including current and voltage measurements, Langmuir probes, and magnetic field probes. Furthermore, impact pressure measurements in the plume of the thruster allowed new insight into the plume structure and the accurate evaluation of impulse bits. Employment of the diagnostic methods for Teflon and water propellant enabled the unambigous identification of propellant related effects such as reduced electron temperature and higher exhaust velocites in the case of water propellant. The electromagnetic nature of the water thruster was clearly identified. For 30 J discharge energy, the water thruster requires only 5% of the mass bit of a Teflon thruster to produce an impulse bit 30% of the magnitude of the Teflon thruster, suggesting greatly increased propellant efficiencies. In agreement with the plasma diagnostic results, a specific impulse for the water thruster of up to 8000 s and efficiencies of up to 16% were evaluated.

Committee:

Thomas York (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Electric Propulsion; Pulsed Plasma Thruster; Water; Teflon; Plasma diagnostic; Langmuir probe; Magnetic field probe; Pressure probe; Space propulsion; Analyitic model; MACH2

SARAF, ADITYAROBUST FLIGHT CONTROL FOR COORDINATED TURNS
MS, University of Cincinnati, 2003, Engineering : Aerospace Engineering
In this thesis, the coupled, six-degree-of-freedom, motion equations for a fighter-type aircraft are derived and linearized for a typical subsonic cruise condition involving a coordinated turn at a steady turn rate. Because of the nonzero turn rate and the nonzero roll angle required for it, the equations of motion are coupled and therefore cannot be treated as decoupled longitudinal and lateral motions, particularly for relatively large turn rates. The linearized, coupled motion equations are then used to design a robust linear feedback controller for a particular turn rate using the LQG/LTR design technique. The robust controller is applied to the dynamics at other, considerably different turn rates, demonstrating its robustness. Although a sufficient condition for robust stability is violated over part of the frequency range, less conservative analysis of the closed loop system using structured singular value shows that the controller-plant system is robust to operating point changes.

Committee:

Dr. Bruce Walker (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

linear feedback controller; LQG/LTR design; motion equations for fighter-type aircraft; aircraft controller

LAKHAMRAJU, RAGHAVA RAJULIQUID JET BREAKUP STUDIES IN SUBSONIC AIRSTREAM AT ELEVATED TEMPERATURES
MS, University of Cincinnati, 2005, Engineering : Aerospace Engineering
An experimental study has been performed to study the nature of breakup and penetration of liquid jets injected transversely into subsonic cross airstreams at elevated temperatures relevant to practical applications in gas turbine combustion. Two liquids (Water and Jet-A) and two injection diameters (D = 0.3 mm, 0.5 mm) have been employed in the current investigations. Liquid-to-air momentum flux ratio (q - varied from 1 to 50) and Aerodynamic Weber number (We - altered from 50 to 950) were the principal liquid jet operating conditions. The temperatures of the liquid jet and the airstream (up to 505 K) have been increased in turns to obtain a wide range of data. Pulsed shadowgraphy technique was used to study the liquid jet breakup and penetration. Two modes of breakup have been noticed: Column breakup and Surface breakup. A breakup map has been worked out to note the conditions for the commencement of surface breakup and the transition zone slope is in good agreement with the breakup maps suggested in earlier studies. A correlation has been developed to predict the jet penetration with q, D, streamwise distance and temperature of the airstream.

Committee:

Dr. San-Mou Jeng (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

liquid jet; breakup; subsonic; penetration

PERRINO, MICHAELThe Design and Implementation of an Acoustic Flow Resistance Apparatus for Manufacturing Process Control
MS, University of Cincinnati, 2008, Engineering : Aerospace Engineering
This thesis presents the theory and application of flow resistance measurements in the development of acoustic liners. The principal focus of the thesis is on the design and development of a flow resistance measurement apparatus that is used in a factory environment to assist in the development and manufacturing process control of honeycomb, embedded with Mesh-Cap septa, used in double layer acoustic liners. The operating environment as well as stringent accuracy and reliability requirements require an apparatus that is ergonomic, user friendly, and robust. The theoretical basis of the flow resistance measurement and its application to acoustic liners is described in detail. The apparatus hardware and software requirements are studied to assure the final design meets or exceeds all the design criteria. The statistics used in the measurement process and in process control theory are also described in detail.

Committee:

Asif Syed (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Acoustic Flow Resistance Process Control

KING, AARON HENRYTHE EFFECT OF DEPTH ON A THREE-DIMENSIONAL RECTANGULAR CAVITY IN SUBSONIC FLOW
MS, University of Cincinnati, 2001, Engineering : Aerospace Engineering
A cavity was inserted into a 20 m/s subsonic flow. The flow had a freestream turbulence level of 0.5%. The cavity had an aspect ratio of 2.0 and was capable of reaching depths from 0.0 to 2.35L. Velocity and turbulence measurements were acquired in the shear layer over the cavity and upstream of the cavity in the approaching boundary layer using hotwire anemometry. These measurements showed that the approaching boundary layer approximated a universal fully turbulent boundary layer. The hotwire was also used to acquire energy spectra in the boundary and free shear layers as well as in the freestream in order to examine the frequency content of the flow. Finally condenser microphones were installed into the cavity and used to acquire energy spectra by measuring the unsteady pressure inside the cavity at various locations. Significant effort was made to identify the causes for each mode. The author has found evidence to suggest that tones generated by the cavity can be driven either acoustically or fluid dynamically. However, acoustics appear to dominate in the current cavity geometry and the current flow speed. The data acquired agrees well with past experiments. However, several new trends were noted that the author has not found mentioned in past work. First, shear layer velocity and turbulence profiles indicate the presence of a recirculation region at the upstream cavity lip. Second, relative sound pressure levels indicate that the total energy inside the cavity decreases as depth increases from D/L = 0.5 to 2.1. This loss of energy coincides with an increase in energy in the shear and boundary layers at the same depths. However, at cavity depths greater than D/L = 2.1 the trend reverses itself as a second vortex cell begins to form beneath the primary vortex.

Committee:

Dr. Peter Disimile (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

unsteady pressure; cavity; subsonic flow

GANGWAR, ASHUTOSHSource Term Modeling of Rectangular Flow Cavities
MS, University of Cincinnati, 2001, Engineering : Aerospace Engineering
The presence of small cavities has an effect on the primary fluid flow and should be modeled properly. The goal of this research is to develop a source term module that models the effect of these cavities for gas-path only simulations. In this approach the unsteady effect of the cavity in the solution is modeled by adding source terms to the right hand side of the Navier-Stokes equation without actually having to resolve the complex cavity geometry. This idea increases considerably the numerical efficiency of the scheme by avoiding the computation of small-scale fluid dynamic structures and complex geometric details of the cavity. Unsteady flow phenomena governing both subsonic and supersonic cavity oscillations were studied. The exact cycle for both cases has been presented and compared with those presented by other researchers. These unsteady solutions have been used to determine deterministic source terms. Source terms were then inserted in steady solutions and used to demonstrate that they can be used to model accurately cavity unsteadiness. Also two methods to model these source terms were briefly reviewed.

Committee:

Dr.Paul Orkwis (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

CFD/CAVITY; SUPERSONIC; AEROSPACE

Basu, DebashisHybrid Methodologies for Multiscale Separated Turbulent Flow Simulations
PhD, University of Cincinnati, 2006, Engineering : Aerospace Engineering
The goal of the present research is to develop and assess multiscale and hybrid turbulence models in simulation of separated turbulent flows at high Reynolds numbers in terms of grid refinement and CPU resources required for a certain level of spectral resolution of the separated flow. These investigated multiscale turbulence models include the DES (Detached Eddy Simulation), hybrid RANS (Reynolds-Averaged Navier Stokes) /LES (Large Eddy Simulation) and PANS (Partially Averaged Navier-Stokes) closure models. These techniques adapt a turbulence model, that function as a RANS model in regions where the grids are highly stretched and the high Reynolds number boundary layer is attached, to function as a sub-grid scale LES type model where the grid is nearly isotropic in the separated flow regions. This accomplished by reducing the turbulence eddy viscosity to promote resolution of more turbulence scales in these regions while still reverting to the original RANS behavior in attached flow and near wall regions. The sensitivity of the computed results to multiscale closure model parameters are compared for three developed formulations of the DES model, one variant of hybrid RANS/LES model, a proposed adaptation of the PANS model and the original multiscale SST-DES model for a number of problems involving unsteady separated high Reynolds number flow. The flow configurations include transonic flow over open cavity, subsonic flow over a back facing step and flow over wall-mounted hump. Simulation predictions are compared with experimental data and also equivalent LES simulations. Simulated results show that these models perform better when there is a distinct demarcation between the attached and separated regions and unsteady shear layers dominate the flow. Computed results show that multiscale methods based on the modification of the turbulent kinetic energy dissipation rate provide the most accurate results and the computed results for the unsteady spectra amplitude and frequency are significantly influenced by the model parameters and the grids. These models provide a useful tool for predicting complex 3-D separated unsteady flows over an expansive dynamic range at high Reynolds number and are comparable to LES predictions at (1/6)th - (1/10)th the corresponding LES CPU resources.

Committee:

Dr. Awatef Haned (Advisor)

Subjects:

Engineering, Aerospace

Bennett, David W.Numerical investigation of compressible vortices using the quasi-cylindrical approximation
Doctor of Philosophy, The Ohio State University, 2007, Aeronautical and Astronautical Engineering
To obtain a better understanding of compressible vortex dynamics, a numerical investigation of laminar, compressible vortices was conducted using the quasi-cylindrical approximation. The goal was to determine if the phenomena of vortex breakdown would occur. Vortex breakdown is an important and unsolved problem in the field of fluid dynamics. The results show that two possible flow regimes can occur for a potential vortex with a constant edge axial velocity. The first is a vortex that decays in a manner similar to the incompressible vortices examined by Batchelor. The centerline axial velocity decay is driven by the edge axial velocity. Far downstream, the axial velocity profile is nearly constant with the tangential and radial velocities approaching zero. The second flow regime occurs when the edge axial velocity is sufficiently small and vortex breakdown occurs. For a given Mach number, the critical value of edge axial velocity for breakdown was determined. For a set value of the edge axial velocity, the stream wise distance to obtain vortex breakdown was a strong function of the Mach number. As the Mach number increased, the distance to vortex breakdown was decreased.

Committee:

Richard Bodonyi (Advisor)

Subjects:

Engineering, Aerospace

Yuan, XinModel-based feedback control of subsonic cavity flows - control design
Doctor of Philosophy, The Ohio State University, 2006, Electrical Engineering
In this dissertation, we present and discuss development, implementation, and experimental results of reduced-order model based feedback control of subsonic cavity flows. Model based feedback control of subsonic flows have been studied and implemented by the flow control group at the Collaborative Center of Control Science (CCCS) at the Ohio State University (OSU). The team, composed of researchers from the departments of Electrical Engineering and Mechanical Engineering at the Ohio State, the Air Force Research Laboratory, and NASA Glenn Research Center, possesses synergistic capabilities in all of the required multidisciplinary areas of experimental data acquisition, computational flow simulation, low dimensional modeling, controller design, and experimental validation. The goal of the CCCS effort is to develop tools and methodologies for the use of closed-loop aerodynamic flow control to manipulate the flow over maneuvering air vehicles. The problem chosen for the initial study by the CCCS flow team is control of the resonant noise generated by subsonic flow past an open cavity. This phenomenon is characterized by a strong coupling between the flow dynamics and the flow-induced acoustic field that can lead to self-sustained resonance. Two approaches towards model development have been studied in this dissertation. One aims at representing the physical properties of the system by dynamical models in transfer function forms, referred to as the physics-based linear model in this dissertation. The other approach we have followed is based on proper orthogonal decomposition (POD) and Galerkin projection methods involving the flow governing equations, which is referred to as the nonlinear model or Galerkin model in the dissertation. Each model mentioned above can be further divided into two types: model derived from numerical simulation data and model derived from real time experimental data. Different types of feedback controllers have been designed for corresponding flow models. Closed-loop system performance has been evaluated by both numerical simulation and experimental implementation as well. These results confirm that model based feedback control represents a promising approach to flow control even in its current infancy state.

Committee:

Hitay Ozbay Andrea Serrani (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

model-based; feedback control; flow control

HILLEREAU, NICOLASSUPPRESSION CHARACTERISTICS OF ACOUSTIC LINERS WITH POROUS HONEYCOMB
MS, University of Cincinnati, 2004, Engineering : Aerospace Engineering
This thesis presents an investigation of the acoustic suppression by single layer liners. The purpose of this project was to study the influence of the porosity on the acoustic reduction and the width of the frequency band of the reduction. Tests were conducted on liner samples. The porous honeycomb core was simulated by means of porous partitions whose impedance was varied between zero (no partition) and infinity (impervious partitions). In addition to the resistance of the porous partitions, variation in the face sheet resistance was also included in the test matrix. A wave tube test apparatus was designed, fabricated and set up. It used an array of 16 transducers to measure the acoustic field along the duct. This allowed measuring of the acoustic attenuation data for the different liner configurations. The acoustic attenuation data showed that the porous honeycomb and the variation in the face sheet resistance have a significant impact on the acoustic attenuation performance of the liner. The results is a clear improvement of the noise suppression for the high frequencies (>3400Hz) with a corresponding reduction in suppression at lower frequencies (<2500Hz). A new approach is now to use a Flow Duct to test flat panels of acoustic liners under a grazing air flow to simulate the engine operating conditions. For further research a flow duct apparatus has been designed and fabricated. Flat panels of acoustic liners will be tested in this apparatus under grazing flow conditions that simulate conditions under engine operating conditions. The design details of this apparatus are also included in this thesis.

Committee:

Dr. Ephraim Gutmark (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Acoustic liner; Suppression characteristics; Porous honeycomb

OPALSKI, ANTHONY BENEDICTEXPERIMENTAL INVESTIGATION OF RAPID FLOW TRANSIENTS IN AN INLET/COMPRESSOR SYSTEM, INDUCED BY SHORT-DURATION ACOUSTIC AND ENTROPY DISTURBANCES
PhD, University of Cincinnati, 2002, Engineering : Aerospace Engineering
Highly sophisticated and extensively tested computational fluid dynamics codes are available to simulate the operation of inlet and compressor systems in high-speed air-breathing propulsion devices. In contrast, the methods used to couple these codes during the simulation of an unsteady flow transient are in a significantly less advanced state. In engineering practice the computations are typically performed separately for each device, while representing the adjacent component through a boundary condition. Unfortunately, the lack of experimentally validated compressor face boundary conditions leaves the accuracy of these models open to doubt. From the viewpoint of inlet computations, the compressor face boundary condition amounts to an approximate description of the manner in which upstream moving acoustic waves are induced by the arrival of downstream moving acoustic and entropy (temperature) disturbances to the compressor. This dissertation presents the results of an experimental investigation involving such rapid flow transients in a facility that combined a constant area circular inlet with a single-stage axial-flow compressor. Inlet Mach numbers ranged from 0.15 to 0.45. The experiment employed an impulse method, in which short-duration, large amplitude acoustic and entropy pulses were generated within the inlet utilizing an exploding wire technique. The incident acoustic pulse, its reflection from the compressor and the acoustic wave transmitted across the compressor were tracked by fast response pressure transducers, while entropy pulses were detected by dual-element hotfilm probes. Frequency domain analysis of the data yielded transfer functions that may be thought of as non-dimensional frequency-resolved reflection, transmission and induction coefficients. Transfer functions have been demonstrated to be suitable for the prediction of transients induced by small amplitude, incident acoustic and entropy pulses, thereby representing a powerful method for extending the results of the single experiment to a wide array of situations. The experimental results show that the amplitudes of both the reflections, and the upstream-moving acoustic waves induced by the incident entropy waves, increase with increasing axial Mach numbers. None of the currently customary compressor-face boundary conditions can predict the data obtained in this study, strongly suggesting that conventional practices concerning outflow boundary conditions during unsteady flow transients are in need of reassessment.

Committee:

Dr. Miklos Sajben (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

acoustic pulse; entropy pulse; compressor face boundary condition

SAID, HAZEMA NEW METHOD FOR THE SOLUTION OF THE INCOMPRESSIBLE NAVIER-STOKES EQUATIONS
PhD, University of Cincinnati, 2001, Engineering : Aerospace Engineering
Numerical Solution of the incompressible Navier-Stokes (INS) equations in primitive variables requires special care to ensure that the resulting flow field will satisfy the discrete governing equations (DGE). However, these equations are not satisfied by the existing solution methods, thus requiring the need to develop a new method. A new method is developed in this work to solve the INS equations in primitive variables. The method uses the velocity and pressure gradients as dependent variables compared to velocity and pressure that are used by all other primitive variables methods. These new dependent variables require additional constraint to be determined. The condition of irrotationality of the gradient of the pressure is employed to give the necessary equations to close the problem. Thus the flow field is represented by a new set of equations that when solved together produces a solution that satisfies the DGE. of the present method are summarized as follows: (1) it eliminates the compatability condition of the pressure equation typical of all pressure-based techniques, (2) it satisfies the discrete continuity and momentum equations. (3) Boundary conditions are physically known for all the dependent variables. (4) It eliminates the inversion of the implicit operator typical of the implicit primitive variables formulation, (5) Robust, stable and more accurate computational codes can be developed. Numerical results are obtained for the driven cavity problem, using both the explicit and the implicit forms of the method. Results are obtained for Reynolds numbers of 100, 400 and 1000. These results show that the present method produces a stable solution and that the resulting flow field does satisfy the DGE to machine zero.

Committee:

Dr. Shaaban Abdallah (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

incompressible flow; navier-stokes equations; implicit; explicit

Wang, FeIA Numerical and Experimental Study of the Thermodynamically Consistent Nonlinear Viscoelastic Response of an Expoxy Polymer in the Glassy Regime
MS, University of Cincinnati, 2006, Engineering : Aerospace Engineering
The mechanical behavior of polymers in the glassy state is complex and several models have been developed to describe a variety of phenomena. A thermodynamically consistent nonlinear viscoelastic constitutive theory is considered to capture the wide range of behaviors observed in glassy polymers, including phenomena like yield, stress relaxation, nonlinear stress–strain behavior under complex loading histories and others. The Helmholtz free energy potential for an isotropic, thermorheologically simple, viscoelastic material is constructed, and quantities such as the stress and entropy are determined from the Helmholtz potential using Continuum Mechanics. The objective of the present study is to evaluate the thermomechanical response of an epoxy polymer with this constitutive theory focusing on the transition from the rubbery to the glassy regime and calculating all necessary parameters for the loading portion in the glassy regime. The nonlinear viscoelastic formulation is written in Matlab and correlated with experimental results.

Committee:

Dr. Jandro Abot (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

polymer; viscoelasticity

Das, KaushikNumerical Simulations of Icing in Turbomachinery
PhD, University of Cincinnati, 2006, Engineering : Aerospace Engineering
Safety concerns over aircraft icing and the high experimental cost of testing have spurred global interest in numerical simulations of the ice accretion process. Extensive experimental and computational studies have been carried out to understand the icing on external surfaces. No parallel initiatives were reported for icing on engine components. However, the supercooled water droplets in moist atmosphere that are ingested into the engine can impinge on the component surfaces and freeze to form ice deposits. Ice accretion could block the engine passage causing reduced airflow. It raises safety and performance concerns such as mechanical damage from ice shedding as well as slow acceleration leading to compressor stall. The current research aims at developing a computational methodology for prediction of icing phenomena on turbofan compression system.Numerical simulation of ice accretion in aircraft engines is highly challenging because of the complex 3-D unsteady turbomachinery flow and the effects of rotation on droplet trajectories. The aim of the present research focuses on (i) Developing a computational methodology for ice accretion in rotating turbomachinery components (ii) Investigate the effect of inter-phase heat exchange (iii) Characterize droplet impingement pattern and ice accretion at different operating conditions. The simulations of droplet trajectories are based on a Eulerian-Lagrangian approach for the continuous and discrete phases. The governing equations are solved in the rotating blade frame of reference. The flow field is computed by solving the 3-D solution of the compressible Reynolds Averaged Navier Stokes (RANS) equations. One-way interaction models simulate the effects of aerodynamic forces and the energy exchange between the flow and the droplets. The methodology is implemented in the code TURBODROP and applied to the flow field and droplet trajectories in NASA Roto-67r and NASA-GE E3 booster rotor.The results highlight the variation of impingement location and temperature with droplet size. It also illustrates the effect of rotor speed on droplet temperature rise. The computed droplet impingement statistics and flow properties are used to calculate ice shapes. It was found that the mass of accreted ice and maximum thickness is highly sensitive to rotor speed and radial location.

Committee:

Dr. Awatef Hamed (Advisor)

Subjects:

Engineering, Aerospace

MA, XIANGNUMERICAL SOLUTIONS FOR DIRECT AND INDIRECT (DESIGN) TURBOMACHINERY PROBLEMS
MS, University of Cincinnati, 2006, Engineering : Aerospace Engineering
Quasi three-dimensional blade-to-blade, and hub to tip stream surfaces are traditionally used for analysis and design of turbomachinery components. In this study, the Euler equations have been reformulated for numerical solutions of the direct and the indirect (design) turbomachinery problem on the blade-to-blade surface. The governing equations are reformulated to derive a second order elliptic equation for the streamlines of the flow, thus eliminating the need for computational grids. In addition, the predicted streamlines automatically satisfy the continuity equation, resulting in a very efficient technique. The applications of the method to solve the direct and design problems are presented. The method is efficient, robust and accurate.

Committee:

Dr. Shaaban Abdallah (Advisor)

Subjects:

Engineering, Aerospace

Claypool, Ian RandolphA theoretical and numerical study of the use of grid embedded axial magnetic fields to reduce charge exchange ion induced grid erosion in electrostatic ion thrusters
Doctor of Philosophy, The Ohio State University, 2007, Aeronautical and Astronautical Engineering
Decay of ion thruster grids due to impact by charge exchange ions is the main life limiting factor in ion propulsion systems. Any system which can reduce the number or energy of ions impacting the grids will add to the life expectancy at current power levels. One possible technique for reducing damage from charge exchange ions would involve the incorporation in the grids of axial aligned embedded magnetic fields. These fields, generated by currents running around the grid apertures would form mini magnetic nozzles guiding beam ions through the aperture while diverting charge exchange ions from directly impacting the grids. A simple computational simulation of the environment within a single set of ion thruster grids has been created for use in evaluating the response of single charge exchange ions to many different grid geometries and field arrangements. This effort involved the development of the ionLite code which simulates the grid geometries, fields, and ion beam charge distribution while allowing individual charge exchange ions to be created at any point and their trajectories and eventual fates to be determined. Using this code the use of auxiliary magnetic fields was examined. This analysis shows that energy transfer to a simulated accelerator grid from charge exchange ions can be reduced by approximately 20%, but only at vary large magnitude magnetic field strengths (order of 100 T). It was found that for the configurations investigated the optimum performance resulted when the applied magnetic field was just enough to cause the particle Larmor radius to be approximately equal to the grid aperture radius. The use of lower mass propellants such as Neon or Helium allow for this benefit at fields on the order of 20 T. The potential impact of the embedded magnetic fields is shown to be very sensitive to grid geometry, and therefore it is probable that a different configuration could provide even greater reduction in kinetic energy transfer at moderate field levels.

Committee:

Thomas York (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Ion Propulsion; Charge Exchange Ions; Ion Thruster Grid Erosion; Charged Particle Simulations; Particle in Cell Code

MAY, CAMERONHIGH ANGLE OF ATTACK FLIGHT CONTROL OF DELTA WING AIRCRAFT USING VORTEX ACTUATORS
MS, University of Cincinnati, 2005, Engineering : Aerospace Engineering
The overall objective of this work was to develop an active fluidic control system that can effectively manipulate the vortex breakdown location over a highly swept delta wing. By moving the vortex breakdown fore or aft, a pitching moment can be induced on the delta wing without the use of any conventional control surfaces. The active control system can be incorporated into a feedback loop to input a desired pitching moment based on the real-time measured surface pressure. The type of active fluidic control system shown to be the most effective at delaying vortex breakdown was the along-core injection technique. In the previous studies using this technique, the control was an open loop system, that is, the flow field was observed and measured and then injection conditions were changed manually. The process was repeated until optimal conditions were observed. In order to move this technique closer to practical application, two important steps must be taken. The fist step is to close the control loop so that input changes can be instantly made according to the changing flow field. The second step is to simplify and optimize the control system. One advantage this control system has over conventional control surfaces is its simplicity. Conventional control surfaces employ complex and costly combinations of hydraulic and electronic components whereas the along-core injection system requires only solenoid actuators and a source of compressed air. Compressed air is readily available in the form of compressor bleed on most gas turbine engines. Other advantages of this system include elimination of drag due to deployed control surfaces and reduced radar vulnerability. A 60° delta wing model with a maximum span of 15.5 inches and a root chord of 13.5 inches was mounted in a subsonic wind tunnel. The wing is equipped with six control jets with variable azimuthal and pitch angles on the top surface approximately beneath the vortex core. A thorough optimization process was completed measuring static pressure to determine vortex breakdown location. Other variables in addition to azimuthal and pitch angles were injection momentum, frequency, and duty cycle. Measuring dynamic pressure, that is pressure fluctuation due to vortex shedding and pulsed injection, was also necessary to the development of a control algorithm. Dynamic pressure was measured at four chord-wise locations with uniform and randomly modulated duty cycles in order to ascertain duty cycle sensitivity on the systems overall effectiveness.

Committee:

Ephraim Gutmark (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Delta Wing; Flight Control; Flow Control; Vortex Breakdown

YODER, DENNIS ALLENALGEBRAIC REYNOLDS STRESS MODELING OF PLANAR MIXING LAYER FLOWS
PhD, University of Cincinnati, 2005, Engineering : Aerospace Engineering
This work investigates the ability of algebraic Reynolds stress models to predict planar mixing layer flows, including effects caused by increasing compressibility such as the reduction in mixing layer growth rate and disproportionate reduction in individual turbulent stresses which causes an increase in turbulence anisotropy. To achieve these results a new algebraic Reynolds stress model is developed from first principles with careful consideration for incorporating additional correlation terms which arise in compressible flows. A new explicit solution procedure for the Reynolds stresses is also developed using an appropriate three-term tensor basis representation for compressible flows. This new solution procedure is moderately more complicated than existing explicit solution procedures for incompressible algebraic stress models since it requires the solution of a quartic, rather than cubic, equation for one of the tensor basis coefficients. Special consideration must also be given to the treatment of specific degenerate cases which are self-correcting in the incompressible formulation. For two-dimensional incompressible flow, the new solution procedure properly reduces to that used in existing explicit algebraic stress models. The new algebraic stress model has been calibrated against detailed experimental data for a benchmark incompressible mixing layer. To aid in this calibration an automated numerical optimization procedure was developed. This calibration yielded a new set of coefficients for the pressure-strain correlation tensor that improves the predicted incompressible mixing layer growth rate and turbulent stresses. Recent experimental data and direct numerical simulations of compressible mixing layers indicate that the observed changes in mixing layer growth rate and turbulence anisotropy are caused by reduced pressure fluctuations. This reduced communication results in changes to the turbulent length scale and pressure-strain correlation tensor. Compressibility corrections based upon these physical mechanisms as well as explicit dilatational corrections have been examined. None of these corrections adequately predicts all of the observed changes in compressible mixing layers. However, this work shows that by combining the turbulent length scale correction with a reformulated correction factor to the pressure-strain correlation tensor better agreement with the mixing layer growth rate is achieved and simultaneous changes in the Reynolds stresses are demonstrated.

Committee:

Dr. Paul Orkwis (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

turbulence; turbulence modeling; compressible flow; mixing layer; optimization

Hileman, James IsaacLarge-scale structures and noise generation in high-speed jets
Doctor of Philosophy, The Ohio State University, 2004, Mechanical Engineering
This work examines the relationship between the dynamics of large-scale turbulence structures and the acoustic far-field of high Reynolds number, high-speed jets. Three Mach numbers were examined: 0.9, 1.3 and 2.0. The Mach 1.3 jet was also modified with delta tabs. A novel microphone array / algorithm was developed, tested and then used to locate sources of individual sound waves in space and time. Noise source distributions were compared to and correlated with flow visualization images that were examined with Proper Orthogonal Decomposition (POD). Time and frequency-domain analyses showed the acoustics of Mach 0.9 and 1.3 jets differed from the Mach 2.0 jet due to Mach wave emission in the latter case. Differences associated with turbulence structure scale were observed within the acoustic measurements. The addition of delta tabs led to streamwise vorticity production and the regulation and augmentation of spanwise vorticity. These modifications led to an upstream shift in the noise production regions of the jet and a shift away from the delta tab location. The regions of noise generation coincided with the location where the sides of the mixing layer merge (Mach 0.9, 1.3, 2.0, single-tab, quad-tab jets) or were dramatically altered (bifurcating region of the dual-tab jet). The streamwise vortices were not a strong, direct acoustic source for frequencies on the order of the peak jet radiation at the angle of maximum sound emission. The Mach 1.3 jet was analyzed for periods of noise generation (NG) and relative quiet (RQ) using simultaneously acquired flow and noise source localization data. POD modes were used to reconstruct cross-stream images and a series of crudely phase-locked streamwise images for the two cases. Both image planes showed the lower order POD modes that possess larger scale structures are important to the RQ while the higher order modes with relatively smaller scales dominate the NG. Within the phase-locked NG streamwise images, a series of robust structures form approximately one convective time scale before noise emission and then rapidly disintegrate as fluid is entrained to the jet’s core. The observed NG process bares many similarities to the breakdown of an instability wave.

Committee:

Mo Samimy (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

Jet noise; Jet exhaust; Large-scale structure; Large structure; Coherent structure; Turbulence mixing noise; Mach wave radiation; Mach wave emission; Delta tab; Streamwise vorticity; Proper Orthogonal Decomposition; Mexican hat wavelet; Microphone array

Marriott, Darin WilliamMagnetoplasmadynamic thruster behavior at the hundred megawatt level
Doctor of Philosophy, The Ohio State University, 2003, Aeronautical and Astronautical Engineering
Characteristic measurements were made of a hundred megawatt modified helium inverse pinch switch and compared against numerical modeling and theoretically expected behavior. Thruster voltage was measured for currents between three and three hundred kilo amps and for mass flow rates between 0.96 and 40 grams per second. From that, characteristic voltage, power, and resistance curves were generated. Electron temperature measurements made inside the plasma flow were found to be between three and thirty electron volts. General expected behavior, such as decreasing resistance with increasing mass flow rate, were confirmed. The quasi steady assumption was studied between 1.5 and 1.7 milliseconds and found to be appropriate. A theoretical model, based on normal MPD thrust behavior, was used to estimate fall voltages and pumping coefficients. An empirical model for thruster voltage was then created to estimate the behavior of voltage as a function of the similarity parameter. The two models were then put together and found to be self consistent with the experimental data. Total temperatures, specific impulses, and efficiencies for assumed isentropic nozzle expansion were then calculated.

Committee:

Gerald Gregorek (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

MPD Thruster; Gigawatt; Pulseline

Calhoun, Sean M.Six Degree-of-Freedom Modeling of an Uninhabited Aerial Vehicle
Master of Science (MS), Ohio University, 2006, Electrical Engineering & Computer Science (Engineering and Technology)

Developing a six degree-of-freedom (6-DOF) aircraft model has many practical purposes, especially in these times of rapidly growing Uninhabited Air Vehicle (UAV) technologies. This thesis covers some of the various topics involved in the development of such a model. The research performed was conducted at the Avionics Engineering Center, utilizing the Brumby R/C aircraft. Topics include a brief overview of the instrumentation system, techniques for inertia estimation, and system identification using the Ordinary Least Squares (OLS) method. Finally, the design and development of a Matlab/SIMULINK model will be covered, which will illustrate the accuracy and validity of the 6-DOF model.

Committee:

Douglas Lawrence (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

UAV; Unmanned Vehicle; 6-DOF Model; System Identification; Brumby

NITTALA, GANESH KUMARCOMPOSITE BEAM WITH WARPAGE FOR EXPLICIT FINITE ELEMENT SIMULATION
MS, University of Cincinnati, 2003, Engineering : Aerospace Engineering
This study presents the warpage analysis in thin-walled beams of arbitrary open cross section subjected to dynamic loads. Strength analysis has also been conducted for laminated composite beams under static loading conditions. The beam has seven displacement degrees of freedom at each node and the element formulation is based on Vlasov theory of thin-walled beams. Coupling between the force and moment resultants, and the transverse shear deformation have been accounted in the development of laminated composite beam theory. Hellinger-Reissner mixed variational principle is used in element formulation, with an augmented Lagrangian to impose the constraint condition on the rotational degree of freedom. A lumped mass matrix for the beam element has been derived, and central difference scheme is used for explicit time integration. The convergence of 2-node and 3-node thin-walled beam finite elements is studied and the results presented. An eigenvalue analysis is also performed using the lumped mass matrix. Several examples of dynamic loading are studied, and the time history results are compared with implicit time integration results obtained using 3D shell models in ANSYS. Results are also presented for various laminate stacking sequences.

Committee:

Dr. Ala Tabiei (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

thin-wall beam; composite; Vlasov; laminated; explicit finite element

LUKOVIC, BOJANMODELING UNSTEADINESS IN STEADY SIMULATIONS WITH NEURAL NETWORK GENERATED LUMPED DETERMINISTIC SOURCE TERMS
PhD, University of Cincinnati, 2002, Engineering : Aerospace Engineering
The lumped deterministic source term - neural network (LDST-NN) approach has been developed to obtain quasi-time-average solutions of cavity flows that include unsteady cavity effects in steady-state computations without the cavity. The results obtained with the LDST-NN based steady calculations are compared to the time average of fully unsteady solutions via the shear force acting on the cavity walls. Two orders of magnitude less computational time is required to obtain a quasi-time average simulation relative to time accurate simulations; a substantial savings. The estimated error, based on the calculated drag force, in these simulations is between 4% and 15 % as compared to fully unsteady calculations, which is satisfactory for many design purposes. This should be compared to the 40% to 154% errors obtained by neglecting the cavity completely for these same cases. As such, the modified neural network-based LDST model is a viable tool for representing unsteady cavity effects. The LDST-NN quasi-time averaged solution was able to capture global unsteady effects correctly. The LDSTs were found to correlate directly with observed sound pressure level trends and provide an additional means of assessing unsteadiness. The LDSTs were found to reach a maximum near the cavity/main flow interface but also extended well into the field; indicating that boundary condition representations alone would be inadequate for capturing unsteady effects. Deterministic source terms were computed from unsteady simulations and modeled with a neural network for use in steady simulations sans cavity to capture the entire time average effect of the cavity. This was demonstrated for the entire range of Mach numbers, length-to-depth ratios and various translational velocities of the cavity wall. The results of the study showed that modeling flow over cavities is possible with steady simulations that include source terms provided by a neural network. This method permits a considerable reduction in CPU time and is attractive for large scale simulations since it includes the effects of the unsteady phenomena without computing the unsteady flow inside the cavity.

Committee:

Dr. Paul Orkwis (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

UNSTEADY FLOW MODELING; CAVITY FLOW; LUMPED DETERMINISTIC SOURCE TERMS; NEURAL NETWORK

HOLTZCLAW, JOHN DAVIDCHARACTERIZATION OF LIGHT SICKLE ERYTHROCYTES DERIVED FROM DENSE ERYTHROCYTES IN VITRO
PhD, University of Cincinnati, 2001, Engineering : Engineering Mechanics
Over the past twenty years, studies investigating sickle cell pathophysiology have primarily focused on the dehydration process. Although this has lead to some significant insight into the sickling process and new therapeutic treatments, we still lack a fundamental understanding of the disease. Recent in vitro and in vivo studies have identified older, low-density (ρ<1.087 g/cc) sickle red blood cells (SS RBC) that are resistant to dehydration mediated by valinomycin or the Ca-activated K channel. We hypothesize that these light cells most likely derive from dense SS RBC that become rehydrated. To study rehydration, we subjected dense SSRBC (ρ>1.107 g/cc) to either oxygenated incubation or in vitro fast oxy/deoxy cycling using a dual channel, fast cycle apparatus (FCA) to simulate in vivo oxy/deoxy conditions. After oxy incubation or oxy/deoxy cycling, the number of light cells, (ρ<1.087 g/cc), was assessed. There was some light cell generation during static incubation at 37°C (3.0 +/- 2.2%, n=41). Fast oxy/deoxy cycling increased light cell formation (5.4 +/- 2.4%, n=41, p< 10 -11 ). These results support the hypothesis that rehydrated SS RBCs derive from dense cells. The rehydrated cells were K depleted (K + = 20 +/- 14 mmol/KgHb, n=5), Na + loaded (Na + = 394 +/- 106 mmol/KgHb, n=12), and had high levels of externalized phosphatidylserine, particularly in the presence of calcium. The presence of 1.5 mM external Ca ++ inhibited the formation of rehydrated SS RBC by 38% (p<0.01, n=7) during oxy/deoxy cycling. This inhibitory Ca ++ effect was prevented by the presence of 1 μM charybdotoxin (p<0.01, n=5), implying a competing dehydration effect from the Ca-activated K channel. Pre-incubation of the dense SS RBC with 45 μM DIDS, or the presence of 1 mM bumetanide, inhibited the generation of light cells during fast oxy/deoxy cycling by 39% (p<0.004, n=7) and 45% (p<0.002, n=8), respectively. These results support the hypothesis that the sickling-induced pathway, previously implicated in SS RBC dehydration, may be involved in the rehydration of dense, K depleted cells. 1 mM bumetanide also inhibited light cell generation during oxy incubation (p<0.05, n=9) suggesting a novel, bumetanide sensitive pathway in SS RBC rehydration.

Committee:

Dr. David L. Butler (Advisor)

Subjects:

Engineering, Aerospace

Keywords:

sickle cell; erythrocyte rehydration; cation transfer; red blood cells; oxy/deoxy cycling

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