Computational Fluid Dynamics (CFD) are used to investigate two speech phenomena. The first phenomenon is the English bilabial plosive /pa/. Simulations are compared with microphone recordings and high speed video recordings to study the penetration rate and strength of the jet associated with the plosive /pa/. It is found that the dynamics in the first 10ms of the plosive are critical to penetration rate, and the static simulation was not able to capture this effect. However, the simulation is able to replicate the penetration rate after the initial 10ms. The second speech phenomenon is the English fricative /sh/. Here, the goal is to simulate the sound created during /sh/ to understand the flow mechanisms involved with the creation of this sound and to investigate the simulation design required to predict the sound adequately. A variety of simulation methods are tested, and the results are compared with previously published experimental results. It is found that all Reynolds-Averaged Navier-Stokes (RANS) simulations give bad results, and 2D Large Eddy Simulations (LES) also have poor results. The 3D LES simulations show the most promise, but still do not produce a closely matching spectra. It is found that the acoustic analogy matches the direct measurements fairly well in 3D simulations. The studies of /pa/ and /sh/ are compared and contrasted with each other. From the findings of the studies, and using theoretical considerations, arguments are made concerning which CFD methods are appropriate for speech research. The two studies are also considered for their direct applications to the field and future research directions which might be followed. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

The quasi-steady state-space models generally used to simulate the dynamics of underwater vehicles perform well in most steady flow scenarios, and are therefore acceptable for modeling today\'s fleet of endurance-focused autonomous underwater vehicles (AUVs). However, with their usage of numerous assumptions and simplifications, these models are not well suited to certain unsteady flow situations and for use in the development of AUVs capable of performing more extreme maneuvers. In the interest of better serving efforts to design a new generation of more maneuverable AUVs, a tool for simulating vehicle maneuvering within computational fluid dynamics (CFD) based environments has been developed. Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations are used in conjunction with a 6-degree-of-freedom (6-DoF) rigid-body kinematic model to provide a numerical test basin for vehicle maneuvering simulations. The accuracy of this approach is characterized through comparison with experimental measurements and quasi-steady state-space models. Three state-space models are considered: one model obtained from semi-empirical database regression (this is the method most commonly used in application) and two models populated with coefficients determined from the results of prescribed motion CFD simulations. CFD analyses focused on supporting the design of a general purpose AUV are also presented. / Ph. D.

This thesis seeks to investigate the predictive capabilities of Advanced turbulence models in the wake region of a wall-mounted cube. Dynamic Hybrid RANS/LES (DHRL), Hybrid RANS/LES (HRL) models, Nonlinear Explicit Algebraic Reynolds Stress Model (NEARSM), One- and Two-equation models, and numerical flux schemes will be compared against Direct Numerical Simulation (DNS) results to determine which model, or combination of models, produce the closest replication. The simulations were ran in Loci-Chem using both built-in features and modular code additions. The simulation results show the Shear Stress Transport (SST) model ran with NEARSM and Optimized Gradient REconstruction (OGRE) scheme gives better results than all other RANS and HRL models investigated herein. This result is matched only by SST with DHRL and OGRE. The best results were achieved using SST with NEARSM, DHRL, and OGRE. Thus, the NEARSM model shows potential to improve simulation results compared to simpler linear eddy-viscosity models.

Diesel and biodiesel combustion in a light duty compression ignition engine were simulated during a closed cycle, using a commercial computational fluid dynamics (CFD) code, CONVERGE. The corresponding computational domain was constructed for the engine based on combustion chamber geometry and compression ratio measurements. Submodels were calibrated for simulation. The results were able to capture the experimental pressure and apparent heat release rate trends for both fuels over a range of engine loads and fuel injection timings. NOx emissions trends were captured for diesel, while under-predicted for biodiesel. The NOx trends were also analyzed based on the thermal NO mechanism. A new modular tool in Matlab was developed for studying the residence time. It was found that high in-cylinder temperatures and their residence time are critical in NOx formation.

A method to efficiently introduce supersonic drag predictions from computational fluid dynamics (CFD) calculations in a combined aerodynamic-structural optimization of a High-Speed Civil Transport (HSCT) is presented. To achieve this goal, the method must alleviate the large computational burden associated with performing CFD analyses and reduce the numerical noise present in the analyses. This is accomplished through the use of response surface (RS) methodologies, a variation of the variable-complexity modeling (VCM) technique, and coarse grained parallel computing. Variable-complexity modeling allows one to take advantage of the information gained from inexpensive lower fidelity models while maintaining the accuracy of the more expensive high fidelity methods. The utility of the method is demonstrated on HSCT design problems of five, ten, fifteen, and twenty design variables. Motivation for including CFD predictions into the HSCT optimization comes from studies detailing the differences in supersonic aerodynamic predictions from linear theory, Euler, and parabolized Navier-Stokes (PNS) calculations for HSCT configurations. The effects of these differences in integrated forces and distributed loads on the aircraft performance and structural weight are investigated. These studies indicate that CFD drag solutions are required for accurate HSCT performance and weight estimates. Response surface models are also used to provide useful information to the designer with minimal computational effort. Investigations into design trade-offs and sensitivities to certain design variables, available at the cost of evaluating a simple quadratic polynomial, are presented. In addition, a novel and effective approach to visualizing high dimensional, highly constrained design spaces is enabled through the use of RS models. <i>NOTE: An updated copy of this ETD was added in July 2012 after there were patron reports of problems with the original file.</i> / Ph. D.

No description available.

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.

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.

published_or_final_version / Mechanical Engineering / Master / Master of Philosophy