Direct numerical simulations (DNS) are employed to investigate laminar boundary layer separation and its control by vortex generator jets (VGJs), i.e. by injecting fluid into the flow through an array of small holes. Particular focus is directed towards identifying some of the relevant physical mechanisms associated with VGJ control of low Reynolds number separation, as encountered in low-pressure turbine applications. In a comparison of selected controlled cases, pulsed VGJs are shown to be much more effective than steady VGJs, when the same momentum coefficient is used for the actuation. The formation and the dynamics of steady as well as unsteady flow structures are subsequently investigated in more detail. For steady VGJs, up to a certain "threshold" amplitude, angled injection is shown to be more effective than vertical injection, which is attributed to the fact that the generated longitudinal vortices remain closer to the wall while penetrating deeper into the boundary layer (in the spanwise direction). Beyond this "threshold" amplitude, however, vertical VGJ injection "suddenly" yields fully attached flow along the entire surface. This change in the global flow dynamics is explained by the formation of symmetric horseshoe-type vortices which are shown to augment the entrainment of high-momentum fluid from the free stream. For pulsed VGJs, the increased control effectiveness is attributed to the fact that hydrodynamic instabilities of the underlying flow can be exploited. When pulsing with frequencies to which the separated shear layer is naturally unstable, instability modes are shown to develop into large scale, spanwise coherent structures. These structures provide the necessary entrainment of high-momentum fluid to reattach the flow. In a series of additional simulations, the effects of varying the frequency as well as the duty cycle are investigated. While deviations from the "optimal" pulsing frequency are shown to result in increased separation losses, changes in the duty cycle have only a minor influence on the effectiveness of the control.

Thesis (Ph.D.)--Syracuse University, 2007. / "Publication number: AAT 3295539."

Thesis (Ph.D.)--Syracuse University, 2007. / "Publication number: AAT 3295513."

<p> Wind energy is a promising alternative to the depleting non-renewable sources. The height of the wind turbines becomes a constraint to their efficiency. Airborne wind turbine can reach much higher altitudes and produce higher power due to high wind velocity and energy density. The focus of this thesis is to design a shrouded airborne wind turbine, capable to generate 70 kW to propel a leisure boat with a capacity of 8-10 passengers. The idea of designing an airborne turbine is to take the advantage of higher velocities in the atmosphere. </p><p> The Solidworks model has been analyzed numerically using Computational Fluid Dynamics (CFD) software StarCCM+. The Unsteady Reynolds Averaged Navier Stokes Simulation (URANS) with K-&epsiv; turbulence model has been selected, to study the physical properties of the flow, with emphasis on the performance of the turbine and the increase in air velocity at the throat. The analysis has been done using two ambient velocities of 12 m/s and 6 m/s. At 12 m/s inlet velocity, the velocity of air at the turbine has been recorded as 16 m/s. The power generated by the turbine is 61 kW. At inlet velocity of 6 m/s, the velocity of air at turbine increased to 10 m/s. The power generated by turbine is 25 kW.</p>

abstract: The Magnetoplasmadynamic (MPD) thruster is an electromagnetic thruster that produces a higher specific impulse than conventional chemical rockets and greater thrust densities than electrostatic thrusters, but the well-known operational limit---referred to as ``onset"---imposes a severe limitation efficiency and lifetime. This phenomenon is associated with large fluctuations in operating voltage, high rates of electrode erosion, and three-dimensional instabilities in the plasma flow-field which cannot be adequately represented by two-dimensional, axisymmetric models. Simulations of the Princeton Benchmark Thruster (PBT) were conducted using the three-dimensional version of the magnetohydrodynamic (MHD) code, MACH. Validation of the numerical model is partially achieved by comparison to equivalent simulations conducted using the well-established two-dimensional, axisymmetric version of MACH. Comparisons with available experimental data was subsequently performed to further validate the model and gain insights into the physical processes of MPD acceleration. Thrust, plasma voltage, and plasma flow-field predictions were calculated for the PBT operating with applied currents in the range $6.5kA < J < 23.25kA$ and mass-flow rates of $1g/s$, $3g/s$, and $6g/s$. Comparisons of performance characteristics between the two versions of the code show excellent agreement, indicating that MACH3 can be expected to be as predictive as MACH2 has demonstrated over multiple applications to MPD thrusters. Predicted thrust for operating conditions within the range which exhibited no symptoms of the onset phenomenon experimentally also showed agreement between MACH3 and experiment well within the experimental uncertainty. At operating conditions beyond such values , however, there is a discrepancy---up to $\sim20\%$---which implies that certain significant physical processes associated with onset are not currently being modeled. Such processes are also evident in the experimental total voltage data, as is evident by the characteristic ``voltage hash", but not present in predicted plasma voltage. Additionally, analysis of the predicted plasma flow-field shows no breakdown in azimuthal symmetry, which is expected to be associated with onset. This implies that perhaps certain physical processes are modeled by neither MACH2 nor MACH3; the latter indicating that such phenomenon may not be inherently three dimensional and related to the plasma---as suggested by other efforts---but rather a consequence of electrode material processes which have not been incorporated into the current models. / Dissertation/Thesis / M.S. Aerospace Engineering 2011

<p> During approach and landing, the HL-20 follows a typical reusable launch vehicle (RLV) autoland trajectory: deep descent, followed by a parabolic flare, and final descent. The trajectory shape is determined by six independent parameters. An artificial neural network (ANN) is designed to generate the trajectory parameters for the HL-20 based on desired objectives using MATLAB&reg;&rsquo;s Neural Network Toolbox. This research examines three mission objectives: specifying flight time, specifying the final downrange position error, and specifying the average error between the desired angle of attack and actual angle of attack. The ANN successfully produces parameters that meet mission objectives and, in some cases, improve upon nominal errors. It is also demonstrated that the ANN structure and ANN training vectors have a profound impact on the success of the neural network.</p><p>

abstract: A design methodology for a new breed of launch vehicle capable of lofting small satellites to orbit is discussed. The growing need for such a rocket is great: the United States has no capabilities in place to quickly launch and reconstitute satellite constellations. A loss of just one satellite, natural or induced, could significantly degrade or entirely eliminate critical space-based assets which would need to be quickly replaced. Furthermore a rocket capable of meeting the requirements for operationally responsive space missions would be an ideal launch platform for small commercial satellites. The proposed architecture to alleviate this lack of an affordable dedicated small-satellite launch vehicle relies upon a combination of expendable medium-range military surplus solid rocket motor assets. The dissertation discusses in detail the current operational capabilities of these military boosters and provides an outline for necessary refurbishments required to successfully place a small payload in orbit. A custom 3DOF trajectory script is used to evaluate the performance of these designs. Concurrently, a parametric cost-mass-performance response surface methodology is employed as an optimization tool to minimize life cycle costs of the proposed vehicles. This optimization scheme is centered on reducing life cycle costs per payload mass delivered rather than raw performance increases. Lastly, a novel upper-stage engine configuration using Hydroxlammonium Nitrate (HAN) is introduced and experimentally static test fired to illustrate the inherent simplicity and high performance of this high density, nontoxic propellant. The motor was operated in both pulse and small duration tests using a newly developed proprietary mixture that is hypergolic with HAN upon contact. This new propellant is demonstrated as a favorable replacement for current space vehicles relying on the heritage use of hydrazine. The end result is a preliminary design of a vehicle built from demilitarized booster assets that complements, rather than replaces, traditional space launch vehicles. This dissertation proves that such capabilities exist and more importantly that the resulting architecture can serve as a viable platform for immediate and affordable access to low Earth orbit. / Dissertation/Thesis / Ph.D. Aerospace Engineering 2011

<p> In modern launch vehicle design the elastic dynamics of the vehicle are not considered in the control scheme of the vehicle due to the large size and large inertia of the vehicle. A few fleet of small nanosatellite spacecraft are coming online that do not require such large vehicles and could be aided by a cheaper, smaller launch vehicle. This paper lays out the ground work for developing a real-time controller that controls the vehicle to maintain tracking control while the vehicle experiences elastic loads. The launch vehicle is modeled as an inverted pendulum with the elastic dynamics of the vehicle observed as an extra moment applied to the vehicle. The controller actively reconstructs the bending modes of the vehicle and incorporates the elastic dynamics along with the angular position and rate of change of the angular position to create a dynamic inversion controller. The controller contains an inner loop traditional Proportional Integral Derivative (PID) controller along with an outer loop control that utilizes adaptive control to adjust the gains utilized in the PID inner loop based on the vibrations experienced. The controller was tested and shown to be more capable than a traditional PID controller in maintaining the course of the launch vehicle. The controller consists of an inner loop with a PID controller and an outer loop and utilizes dynamic inversion with gain scheduling that uses the predicted active vibrational mode to apply a gain to the error to properly control the vehicle</p><p>

<p> The design and development of any complex, safety-critical, human-machine interface is a complex and lengthy process. A major requirement of the development process is the human-in-the-loop evaluation of the design. A novel virtual environment was developed using passive haptics, hand tracking, and an immersive head mounted display to provide a new design evaluation tool for cockpit designers. Instead of requiring an expensive simulator to be designed and developed, the "Rapidly Reconfigurable Research Cockpit" (R3C) prototype can be used inside of an existing engineering mockup, allowing design evaluations to occur more rapidly and earlier in the design process. The R3C prototype uses a hand tracker to determine when the user is pressing a button on a non-functional geometrical mockup of an instrument (known as passive haptics). The user wears a virtual reality head mounted display that provides an immersive visual-virtual layer over the mockup, enabling the instruments to respond to the inputs read from the hand tracked movements of the user. The unique technical approach of the R3C prototype is described and compared to previous work. </p><p> Three human subject experiments were performed to evaluate the use of the R3C prototype. The first experiment validated the technical approach, finding that subjects could accurately and successfully target buttons in the R3C virtual environment. The second experiment focused on characterizing the effect of the passive haptics on the Fitts' throughput. Subjects performed a Fitts' ISO-9241 circle task in the virtual environment with and without the passive haptics. Passive haptics was found to have a significant effect on Fitts' throughput (<i>p</i> &lt; 0.01). The third experiment compared the performance of the R3C prototype as a design evaluation tool to a traditional touchscreen based simulator. Subjects were split into two groups to perform a design evaluation of two cockpit instruments, one group using the R3C simulator and the other the touchscreen simulator. It was found that tracking task and a response task had similar performance between simulators, but time pressured tasks performed worse in the R3C simulator. Subjective feedback about the designs being evaluated was analyzed from both groups. All major usability issues were identified by both groups. The R3C system provides a promising platform for design evaluation of a cockpit in the early stages of design.</p><p>

abstract: This paper addresses some aspects of the development of fully coupled thermal-structural reduced order modeling of planned hypersonic vehicles. A general framework for the construction of the structural and thermal basis is presented and demonstrated on a representative panel considered in prior investigations. The thermal reduced order model is first developed using basis functions derived from appropriate conduction eigenvalue problems. The modal amplitudes are the solution of the governing equation, which is nonlinear due to the presence of radiation and temperature dependent capacitance and conductance matrices, and the predicted displacement field is validated using published data. A structural reduced order model was developed by first selecting normal modes of the system and then constructing associated dual modes for the capturing of nonlinear inplane displacements. This isothermal model was validated by comparison with full finite element results (Nastran) in static and dynamic loading environments. The coupling of this nonlinear structural reduced order model with the thermal reduced order model is next considered. Displacement-induced thermal modes are constructed in order to account for the effect that structural deflections will have on the thermal problem. This coupling also requires the enrichment of the structural basis to model the elastic deformations that may be produced consistently with the thermal reduced order model. The validation of the combined structural-thermal reduced order model is carried out with pure mechanical loads, pure thermal loads, and combined mechanical-thermal excitations. Such comparisons are performed here on static solutions with temperature increases up to 2200F and pressures up to 3 psi for which the maximum displacements are of the order of 3 thicknesses. The reduced order model predicted results agree well with the full order finite element predictions in all of these various cases. A fully coupled analysis was performed in which the solution of the structural-thermal-aerodynamic reduced order model was carried out for 300 seconds and validated against a full order model. Finally, a reduced order model of a thin, aluminum beam is extended to include linear variations with local temperature of the elasticity tensor and coefficients of thermal expansion. / Dissertation/Thesis / Doctoral Dissertation Aerospace Engineering 2014