Thesis (Ph.D.)--Syracuse University, 2008. / "Publication number: AAT 3333572."

Thesis (Ph.D.)--Drexel University, 2010. / Includes abstract and vita. Includes bibliographical references (leaves 108-117).

Thesis (Ph. D.)--Syracuse University, 2005. / "Publication number AAT 3177030."

<p> It is estimated that the rotor hub of a helicopter is responsible for up to 30% of the parasite drag of a helicopter. This is because the hub is a group of rotating bluff-body shapes exposed to high-velocity flow, which may produce hub revolution-dependent flow structures in the hub wake. These structures also interact with a helicopter&rsquo;s empennage and tail rotor, negatively impacting stability and performance. While some specific helicopter hubs have been studied, no study of a generalized hub shape has taken place. Because the hubs that have been studies are very geometrically complex, computational prediction of hub flow physics is not yet mature enough to be of use to industry. The objective of this study is to characterize the long-age wake of a geometrically simple configuration of canonical bluff bodies to model a helicopter hub. Three scale models were examined, each with four larger arms to represent rotor blade shanks and two smaller arms to represent scissor links. The models were identical in dimension, but one had a smoother arm profile and another had a variation in phase angle between the two sets of arms. The models were mounted in the Experimental Flow Physics Laboratory Large Water Tunnel, and tested at a hub diameter-based Reynolds number of 7.6 &times; 10⁵. Time-resolved velocity measurements were taken 14 hub radii downstream of one model, while phase-averaged velocity measurements were taken 7 hub radii downstream of the other two. Similar trends to previous works were observed, including two-per-hub revolution, four-per-hub revolution, and 6-per-hub revolution frequency content in the velocity spectra. This study therefore aids in the uncovering of fundamental flow physics of rotor hubs, creating a baseline case to which further parametric variations may be compared.</p><p>

<p> This work describes technical innovations to improve the data quality and volume for the Fast Plasma Investigation (FPI) on board the Magnetospheric Multiscale mission (MMS). A parametric study of wavelet compression has shown that plasma count data can be compressed to high compression ratios with a minimal effect on the integrated plasma moments. Different regions of the magnetosphere are analyzed for both electron and ion count data. The FPI trigger data, intended as a data ranking metric, has been adapted and corrected to a point where scientifically accurate pseudo moments can be generated and released to the research community, drastically increasing the availability of high time resolution data. This is possible due to a scaling system that tunes the dynamic range of the system per region, and the method of using a neural network to correct for exterior contamination effects, such as spacecraft potential. Finally, a map of detection angle bias has been generated that can be used to correct raw count for errors in look direction of incoming particles. This map was generated by statistically sampling particle flight paths through a charged spacecraft environment, validating against flight data. All three of these efforts lead toward the overarching goal of improving data quality and volume for the FPI suite, and future missions to come. </p><p>

<p> Flow separation is a common fluid dynamics phenomenon that occurs within supersonic nozzles while operating at off-design pressures. Typically, off-design pressures result in a shock formation that leads to a non-uniformity of the exiting flow and creates flow separation and flow recirculation. So far, no effective solution has been presented to eliminate flow separation and increase the total performance of the nozzle. The purpose of this work is to investigate whether a Gurney flap may beneficially affect the exiting flow pattern. For a better understanding of the Gurney flap effect, this investigation used a supersonic nozzle geometry based on a previous study by Lechevalier (2005). Results from the tested cases showed a poor effect of the flap at high free-stream Mach number and lower pressure ratio. Simulations of different flap heights along with different parameters showed a slight increase of thrust.</p><p>

<p> Given the increasing complexity of systems and the cost associated with test and evaluation of aerospace systems, more efficient methods are sought. Randomized test designs for aviation developmental test activities and other complex systems may not enable safe test conduct and may be prohibitively costly from a financial or time point of view. This research reviews Design of Experiments (DoE) test design approaches applicable to aerospace prototype test and evaluation activities. It proposes the use of Split Plot Optimal Designs to leverage advantages of DoE while satisfying requirements for limited randomization of the test runs. Through the use of case studies, the Split Plot Optimal Design approach is demonstrated to provide a 58% cost and schedule savings versus a One Factor At a Time approach, and 53% savings from the fully randomized Central Composite Design, while maintaining relevant statistical power. Through the use of Monte Carlo data simulation, the designs are evaluated for application to linear and quadratic models, with statistically significant results measured by Chi Squared and Kolmogorov-Smirnov tests. </p><p>

<p> Applications of sealant and adhesive technologies in aerospace industries require appropriate and reliable sealing materials and tools to provide suitable sealing. Due to a growing use of integral fuel tanks, which utilize the aircraft structure for fuel containment, this study focuses on nozzle geometry optimization of aircraft fuel tank sealant in order to develop and facilitate sealant approval process and to ensure the implementation of suitable fuel tank sealing. </p><p> Computational Fluid Dynamics (CFD) analyses were performed to study the sealant flow characterization and behavior using Star-CCM+ software. An empirical model was developed by the aid of Design of Experiments (DOE) techniques in order to develop a reliable mathematical model based on the collected data from numerical results. Scanning Electron Microscopy (SEM) was utilized to investigate the fracture/deformation of hollow glass microballoons and entrapped air bubbles within the cured sealant. </p><p> The results of this research concluded that the bent in nozzle geometry increases the sealant pressure drop throughout the nozzle. There is an optimized value for travel distance and cross sectional dimension and geometrical shape within the nozzle geometry that minimizes overall dynamic viscosity of the sealant.</p><p>

<p> The flight conditions of a hypersonic vehicle on an ascent trajectory are computed and Reynolds-averaged Navier-Stokes (RANS) simulations of the turbulent boundary layers are performed across a Mach number range of 0.3 up to 16 using the computational fluid dynamics (CFD) software, VULCAN. The boundary conditions and leading edge geometry are varied from the simple case of adiabatic and sharp to cooled and blunted to reveal the physics of how these effects impact the results of flat plate boundary layer methods as applied to practical aerospace systems. The law of the wall, the Van Driest transformation, and a shear stress preserving transformation's ability to collapse boundary layer velocity profiles under the conditions of variable wall boundary condition and leading edge geometry is explored. </p><p> Boundary layer related quantities examined include the boundary layer thickness, local skin friction coefficient, displacement thickness, momentum thickness, heat flux, and integrated loads. It is found that cooling the surface serves to increase the density of the boundary layer, making it thinner. This thinning of the boundary layer thickness increases the velocity gradients, thus increasing the shear stresses and the local skin friction coefficient. The effects on turbulent boundary layers of blunting the leading edge are explained by the difference in properties, particularly viscosity, caused by a detached bow shock instead of a Mach wave that comes off of a sharp nose plate. Heat flux into a vehicle is found to be insignificant at low speeds, but increases drastically as the Mach number rises into the supersonic and hypersonic regimes. It is observed that the integrated skin friction coefficient decreases as Mach number increases and the leading edge becomes blunted, however, it increases as more cooling is applied at the boundary. The integrated heat flux computed from a sharp leading edge geometry is greater compared to a blunted leading edge due to greater temperature gradients in the sharp nose case relative to the blunt nose case. </p><p> The shear stress preserving transformation, derived with the inclusion of a stress balance condition, is found to produce a better collapse of the velocity profile data than the Van Driest transformation and the incompressible law of the wall regardless of Mach number, boundary condition or leading edge geometry. The normalized untransformed velocity gradients are compared to the velocity gradients resulting from the Van Driest and shear stress preserving tranformation. It is shown that the velocity gradients from the shear stress preserving match the normalized untransformed velocity gradients more closely than the Van Driest velocity gradients do. The advantages, disadvantages, and limitations of each transformation are discussed.</p><p>

<p> Composite sandwich plates are widely used in aerospace, automobile and shipbuilding industries. Composite sandwich plates have many different types of failure modes. A comparative study of composite sandwich plates with different finite element modeling approaches for predicting buckling and wrinkling failure response is described in this thesis. The research considers composite sandwich plates with isotropic and anisotropic face-sheets with a thick core. Finite element solutions are obtained using Abaqus/CAE 2016 software by conventional shell element models and conventional shell/solid element models. This study investigates results obtained using finite element methods and compares them to experimental and analytical solutions for overall buckling and face-sheet wrinkling. Results of the study indicate that finite element methods provide an accurate and effective modeling approach for predicting both overall buckling and wrinkling response. </p><p> Furthermore, the study also explored buckling response of composite sandwich panels with different core thickness and face-sheet fiber angle orientation. The study found that the shell/solid element model provides an appropriate and effective modeling method to predict both overall buckling and local wrinkling behavior in composite sandwich plates.</p><p>