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This is a ‘sandwich thesis’ consisting of a publication that I contributed to during my M.Sc. work. The thesis begins with an introduction section in Chapter 1 that discusses the relevant physical concepts to the work performed in the publication. These topics include, polymers in section 1.1, fluid dynamics in section 1.2, and capillary effects in section 1.3. Chapter 2 contains an experimental technique section that maps out the experiments performed in the manuscript. The manuscript, Chapter 3, details the capillary driven levelling of thin polymer step that is supported by an immiscible polymer film and the dissipation of the capillary energy of the system. We find that the dissipation mechanism depends strongly on the viscosity ratio between the top and the bottom films. We developed a model of the energy dissipation that agrees well with the experimental results. / Thesis / Master of Science (MSc)

When a droplet is placed on a soft material, surface tension forces from the droplet are able to deform the substrate. This thesis explores the effect of substrate stiffness on energy dissipation as a droplet is slid along a soft material. We find behaviour is characterised by two regimes separated by the lengthscale of the deformation in the substrate. For films approximately the lengthscale of the deformation, dissipation increases with thickness. As the thickness becomes much larger than the size of deformation, there is a plateau in dissipation. This result agrees with the model we use to understand energy dissipation in these systems. / Thesis / Master of Science (MSc)

This work seeks to analyze the transient characteristics of a high-speed inlet with a variable-geometry, rotating cowl. The inlet analyzed is a mixed compression inlet with a compression ramp, sidewalls and a rotating cowl. The analysis is conducted at nominally Mach 4.0 wind tunnel conditions. Advanced Computational Fluid Dynamics techniques such as transient solutions to the Unsteady Reynolds-averaged Navier-Stokes equations and relative mesh motion are used to predict and investigate the unstart and restart processes of the inlet as well as the associated hysteresis. Good agreement in the quasi-steady limit with a traditional analysis approach was obtained. However, the new model allows for more detailed, time-accurate information regarding the fully transient features of the unstart, restart, and hysteresis to be obtained that could not be captured by the traditional, quasi-steady analysis. It is found that the development of separated flow regions at the shock impingement points as well as in the corner regions play a principal role in the unstart process of the inlet. Also, the hysteresis that exists when the inlet progresses from the unstarted to restarted condition is captured by the time-accurate computations. In this case, the hysteresis manifests itself as a requirement of a much smaller cowl angle to restart the inlet than was required to unstart it. This process is shown to be driven primarily by the viscous, separated flow that sets up ahead of the inlet when it is unstarted. In addition, the effect of cowl rotation rate is assessed and is generally found to be small; however, definite trends are observed. Finally, a rigorous assessment of the computational errors and uncertainties of the Variable-Cowl Model indicated that Computation Fluid Dynamics is a valid tool for analyzing the transient response of a high-speed inlet in the presence of unstart, restart and hysteresis phenomena. The current work thus extends the state of knowledge of inlet unstart and restart to include transient computations of contraction ratio unstart/restart in a variable-geometry inlet. / Doctor of Philosophy / Flight at high speeds requires efficient engine operation and performance. As the vehicle traverses through its flight profile, the engine will undergo changes in operating conditions. At high speeds, these changes can lead to significant performance loss and can be detrimental to the vehicle. It is, therefore, important to develop tools for predicting characteristics of the engine and its response to disturbances. Computational Fluid Dynamics is a common method of computing the fluid flow through the engine. However, traditionally, CFD has been applied to predict the static performance of an engine. This work seeks to advance the state of the art by applying CFD to predict the transient response of the engine to changes in operating conditions brought about by a variable geometry inlet with rotating components.

The supersonic jet plumes that exhaust from the engines of tactical aircraft produce intense noise signatures that expose the Navy personnel working on the deck of aircraft carriers to dangerously high levels of noise that often results in hearing damage. Reducing the noise radiated by these supersonic plumes is of interest to the Department of Defense and is the primary motivation of this research. Fundamentally, jet noise reduction is achieved by manipulating the nozzle boundary condition to produce changes in the turbulence development and decrease the acoustic efficiency of coherent structures. The research presented here focuses on a novel jet noise reduction technique involving a centered thermal non-uniformity that alters the base flow by introducing a temperature-driven centerline velocity deficit into a perfectly expanded Mach 1.5 jet. The results indicate $2 pm 0.5$ dB reductions in peak narrowband spectral sound pressure levels upstream of peak directivity directions for the non-uniform jet compared to a thermally uniform baseline, even for static thrust matched conditions. This reduction is hypothesized to be related to perturbations induced by the thermal non-uniformity that convect inside the irrotational core and reduce the correlation length scales of turbulence at locations far downstream. This hypothesis was evaluated by studying the coherent turbulence via its convective hydrodynamic footprint in the near-field. An indirect investigation of the near-field using a far-field-informed model of the wavenumber-frequency spectra indicate a reduction in the energy contained in the tail of the wavenumber spectra amplitude, suggesting a reduction in the size of large scale structures. A direct evaluation of the spatio-temporal behavior of the near-field was performed using temporally resolved schlieren images. Space-time correlations of the frequency-filtered near-field identified high frequency acoustic waves radiated by compactly coherent turbulent structures and low frequency Mach waves produced by large scale instabilities. In the thermally non-uniform case these features and their sources were found to be decorrelated at downstream regions. These results provide strong evidence that a centered thermal non-uniformity reduces the radiated noise compared to a uniform baseline by shortening the correlation length scales of coherent structures in regions far from the nozzle exhaust. / Doctor of Philosophy / A more complete understanding of the intense noise sources present in supersonic jet plumes is of value to both government and industry, and is a necessary step towards optimizing noise reduction techniques. Tactical aircraft that operate on the deck of aircraft carriers expose Navy personnel to dangerously high levels of noise that often results in permanent hearing damage. Supersonic jet noise reduction is also of relevance to the recent efforts to revitalize supersonic air transport over land. For supersonic air transport to become a reality, the noise produced by these future aircraft during takeoff and landing must meet the increasingly stringent community noise requirements. Fundamental jet noise research is needed to guide the design of future engine architectures for these aircraft to ensure their commercial success. The research presented herein examines a novel noise reduction technique that involves a centered thermal non-uniformity consisting of a heated jet plume with a spot of locally cooler, slower moving air concentrated along the centerline of a Mach 1.5 jet. This temperature driven velocity deficit is shown to reduce the radiated noise by up to 2.5 dB at peak frequencies and at angles just outside of the peak directivity direction. The cause of the noise reduction is hypothesized be related to a reduction in the size of the coherent structures that radiate a majority of the noise produced by turbulent jets. This hypothesis is evaluated by examining the 'footprint' of the coherent structures in the ambient field directly outside of the jet shear layer in an area called the near-field. An indirect investigation of the near-field using a far-field informed analytic model suggests a reduction in the size of large scale structures. A direct evaluation of the space time structure of the near-field was performed using temporally resolved schlieren images. Statistical processing of the density gradient provided by the schlieren images revealed acoustically intense structures known as Mach waves and high frequency acoustic waves. These features and their sources, large scale instabilities and compactly coherent turbulence, were found to be decorrelated by the introduction of the thermal non-uniformity. These results provide strong evidence that the centered thermal non-uniformity produces a noise benefit by reducing the size of the turbulent structures.

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Energy usage in buildings has become a major topic of research in the past decade, driven by the increased cost of energy. Designing buildings to use less energy has become more important, and the ability to analyze buildings before construction can save money in design changes. Computational fluid dynamics (CFD) has been explored as a means of analyzing energy usage and thermal comfort in buildings. Existing research has been focused on simple buildings without much application to real buildings. The current study attempts to expand the research to entire buildings by modeling two existing buildings designed for energy efficient heating and cooling. The first is the Viipuri Municipal Library (Russia) and the second is the Margaret Esherick House (PA). The commercial code FLUENT is used to perform simulations to study the effect of varying atmospheric conditions and configurations of openings. Three heating simulations for the library showed only small difference in results with atmospheric condition or configuration changes. A colder atmospheric temperature led to colder temperatures in parts of the building. Moving the inlet only slightly changed the temperatures in parts of the building. The cooling simulations for the library had more drastic changes in the openings. All three cases showed the building cooled quickly, but the velocity in the building was above recommended ranges given by ASHRAE Standard 55. Two cooling simulations on the Esherick house differed only by the addition of a solar heat load. The case with the solar heat load showed slightly higher temperatures and less mixing within the house. The final simulation modeled a fire in two fireplaces in the house and showed stratified air with large temperature gradients. / Master of Science

The primary motivation for this dissertation is to address the problem of aircraft engine degradation due to ingestion of non-aqueous particulates such as sand, dust, and ash. This dissertation introduces high fidelity Lagrangian particle models to account for the rotational effects of particles in complex turbulent flows. Part of the focus of the research is to provide novel techniques to model particle-surface collision induced rotation as well as develop correlations for forces and torques on non-spherical particles. Particulates in nature have a tendency to damage turbomachinery components through a number of mechanisms which include erosion and adhesion and will lead to engine failure. The trajectory, size, velocity, chemical composition and shape of the particles play an important role in predicting the damage occurring in the engine. An aircraft engine consists of a cold section, comprising of an inlet and compressor, and a hot section consisting of the combustion chamber and turbine. The particulates enter through the inlet and impact against the components within the compressor eroding away the surfaces as well as causing the particles to fracture into smaller sizes. On entering the hot section, the particles encounter drastic phase changes leading to change in their intrinsic properties. Some of these particles may also adhere to the blade surfaces blocking cooling ports. In this report we focus on particle interaction with the cold sections of aviation gas turbine engines, and so we do not study any of the phenomena that occur due to the heating of particles. To predict how particles will interact with the engine components it is first important to understand the trajectory of particles. For flow into the inlets and early stages of the compressor, particle trajectory is dominated by a two factors: particle aerodynamics and rebounds from surface collisions. Near-wall aerodynamics also play an important role in particle impact and surface erosion. The particle trajectories show the adverse effects of the near wall aerodynamic effects just before collision. The particle velocities are influenced significantly by these effects, and in order to predict particle rebound properties and erosion accurately, these effects have to be taken into account. One important, but often neglected aspect of particle trajectory is accurate prediction of particle rotation. The primary source of the angular velocity of the particles is through particle collisions with walls. However, few models of particle-wall impact introduce rotation. Several studies indicate that the particle angular velocity plays a significant role on their trajectories even in simple geometries such as curved pipes. The research in this dissertation introduces a collision-induced particle rotation model that improves the prediction of particle trajectories after rebound. The improved collision model compares well to experimental data provided in literature and its importance is demonstrated in a simple pipe bend. There have been several experimental studies from past literature, that have developed lift and drag correlations for rotating particles. However, from the literature we also see that these correlations are very specific to the particle shape, Reynolds Number and their orientation relative to the oncoming flow. Real particles are non-spherical, and almost all existing models for particles consider only spheres. Non-spherical particles have different values of aerodynamic lift, drag, and torque compared to their spherical counterparts. As a means to explore and quantify the effect of particle shape, and orientation on the aerodynamic forces and torques on non-spherical particles, we developed a CFD framework that has the ability to measure the lift and drag on arbitrarily shaped non-spherical particles by rotating a single particle in space in an airstream. On changing parameters such as the air velocity, rotation rate, orientation we can tabulate the lift and drag forces and torques on the particle. These correlations can be implemented into Lagrangian particle models to improve the predictions of particle trajectories due to rotation induced lift and drag. The importance of particle rotation is demonstrated by injecting particles into a high pressure compressor section of a gas turbine engine and comparing erosion profiles and impact locations between particles with and without the rotation models. The research presented in this dissertation aims to improve the prediction of particle trajectories by considering non-ideal parameters such as the aerodynamic effects on non-spherical particles and the influence of rotation on particle motion. Particle-surface collisions play a significant role in particle trajectories and so the first step in improving these predictions is to gain a better understanding of particle rebound phenomena. / Doctor of Philosophy / Aircraft engines suffer significant damage due to ingestion of solid particles such as sand, dust, and ash. The primary motivation for this dissertation is to investigate these phenomena and provide a better understanding of particle physics. These particles have a tendency to damage turbomachinery components through a number of mechanisms which include erosion and adhesion which will lead to engine failure. The trajectory, size, velocity, chemical composition and shape of the particles play an important role in predicting the damage occurring in the engine. An aircraft engine consists of a cold section, comprising of an inlet and compressor, and a hot section consisting of the combustion chamber and turbine. The particles enter through the inlet and impact against the components within the compressor eroding away the surfaces as well as causing the particles to fracture into smaller sizes. On entering the hot section, the particles encounter drastic phase changes leading to change in their intrinsic properties. Some of these particles may also adhere to the blade surfaces blocking cooling ports. In this report we focus on particle interaction with the cold sections of aviation gas turbine engines, and so we do not study any of the phenomena that occur due to the heating of particles. To predict how particles will damage the engine components it is first important to understand the trajectory of particles. For flow into the inlets and early stages of the compressor, particle trajectory is dominated by two factors: particle aerodynamics and rebounds from surface collisions. One important, but often neglected aspect of particle trajectory is accurate prediction of particle rotation. The primary source of particle rotation is through particle collisions with walls. However, few models of particle-wall impact introduce rotation and so the research in this dissertation introduces a collision-induced particle rotation model that improves the prediction of particle trajectories after rebound. The improved collision model compares well to experimental data provided. Real sand particles are oddly shaped particles and not perfect spheres. These non-spherical particles behave differently in air when compared to their spherical counterparts. The aerodynamic lift, drag, and torque are the driving factors for this difference in behavior. As a means to explore and quantify the effect of particle shape, and orientation on the aerodynamic forces and torques on non-spherical particles, we developed a CFD framework that has the ability to measure the lift and drag on arbitrarily shaped non-spherical particles by rotating a single particle in space in an airstream. On changing parameters such as the air velocity, particle rotation rate, and orientation we can tabulate the lift and drag forces and torques on the particle. These correlations can be implemented into to improve the predictions of particle motion in an aircraft engine. The importance of particle rotation is demonstrated by injecting particles into a high pressure compressor section of a gas turbine engine and comparing erosion profiles and impact locations between particles with and without the rotation models.

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