Master of Science / Department of Mechanical and Nuclear Engineering / Byron W. Jones / Airline cabins represent an indoor environment in which the spread of particles or contaminants is of interest due to the large number of passengers and distances they travel. In fact, hundreds of millions of passengers travel each year spending extended periods in close proximity to one another. This close proximity causes concern about the spread of disease and contaminants amongst passengers. These passengers move from region to region of the world increasing the potential for worldwide epidemics. In an effort to understand the aircraft cabin environment and the dispersion of fine particles, an experimental study was conducted. The cabin used for the experiments is a simulated Boeing 767-300 with eleven rows, each comprised of seven seats. The particles release occurred in a short burst in all the seats across the second row simultaneously. This design focused on the longitudinal dispersion of particles throughout the cabin. The particles from this release had corrected aerodynamic diameters between 0.87 and 1.70 micrometers. The collection and analysis of data took place based on five criteria. The first analysis focused on the total particle counts at 27 locations throughout the cabin. The second analysis made use of a reference location for each of the tests and presents the exposure in each of those locations as a fraction of the reference during the same test. The third analysis centers its attention on the transient behavior as the particles were counted at various locations. The forth and fifth types of data analysis focus on the time required for each tested location to reach either 100 total particle counts or ten percent of the total seen at that location during that test. The tests show the regions close to the source experience higher levels of exposure, less time to reach the time limits, and higher levels of variation from test to test. The locations farther from the source show lower exposure levels, longer times to reach the limits, and less variation from test to test. This indicates the variations close to the source stem from the chaotic nature of the airflow rather than from irregularities of the dispersion system. The data agree well with previous work and suggest further studies would improve the understanding of the aircraft cabin environment and the spread of airborne particles and contaminants.

Master of Science / Department of Mechanical and Nuclear Engineering / Mohammad H. Hosni / Millions of people travel by commercial aircraft each year. The close proximity of passengers aboard an airplane leads to one of the primary reasons that air quality in an aircraft cabin is of interest. In recent years there have been multiple reported instances of people contracting illnesses after being aboard an aircraft for an extended period of time. In order to better understand air quality in an aircraft cabin, an experimental study of particulate transport in a half cabin model of a Boeing 767 was performed. In the study, both 3[Mu]m and 10[Mu]m particles were tested separately by injecting them into the cabin through a vertical tube, 609.6 mm (24 in) above the floor, at a single location on the centerline of the half cabin test section. Resulting particulate concentrations were measured at five locations along the centerline of the half cabin test section. It was found that for the 3[Mu]m particles, the normalized concentration was about one for all of the locations except directly above the injection site. Therefore, the concentrations were approximately the same as the well-mixed concentration, where the well-mixed concentration is the concentration in the test cabin if the test cabin is uniformly mixed. For the same test conditions, the normalized concentrations for the 10[Mu]m particles were well below one, around 0.1. Several more concentration measurements using the 10[Mu]m particles were taken at the same five locations, both on and off the centerline, and for different particle injection and cabin pressure conditions. The concentration results using a diffuser cone to inject the 10[Mu]m particles into the test cabin and a neutral cabin pressure were higher than the results found using the straight injection tube, but they were not very repeatable. After pressurizing the cabin to slightly above ambient pressure and using the diffuser cone, the resulting average normalized particle concentrations along the centerline were found to be between 0.4 and 1.5 and repeatable within the estimated measurement uncertainty. Therefore, it appears that the 3[Mu]m particles follow the airflow in the test cabin well, but it is not clear if the 10[Mu]m particles do as well.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / Zhongquan Zheng / In this study, a vortex particle method is used to simulate incompressible vortical flows, specifically aircraft wake vortices. This is particularly suitable for a wake vortex system that is slowly varying in the axial direction and has a high Reynolds number and low Mach number. The flow field, in the form of vorticity, is employed as the source in the far-field acoustic calculation using a vortex sound formula that enables computation of acoustic signals radiated from an approximated incompressible flow field. In a two-dimensional vortex system, the stretching effect in the axial direction is neglected. The purpose of this study is to focus on vortex core behaviors. A numerical simulation is performed in a more realistic wake consisting of a counter-rotating vortex pair with inviscid ground effects and shear flows. A Kirchhoff spinning-core vortex model is thus used as a starting point. In a vortex system with multiple vortices, such as a complicated aircraft vortex wake vortices, the sound emission frequency of the unsteady vortex core is subjected to change because of interactions between multiple vortices. The behaviors of the influence, indicated by the ratio between the core size and the distance of the vortices, are investigated as well as the underlining vortex core dynamic mechanisms. Cases of co-rotating vortices and a multiple-vortex system composed of two counter-rotating vortex pairs are studied for applications to aircraft wake vortex sound. In three-dimensional vortices, sinusoidal instabilities, which occur in the axial direction at various length scales, result in significant flow structure changes in these vortices, and thus influence their radiated acoustic signals. Cases of vortex rings and a pair of counter-rotating vortices are studied when they are undergoing both long-wave and short-wave instabilities. Both inviscid and viscous interactions are considered and the effects of turbulence are simulated using sub-grid-scale models. A higher peak frequency than the Kirchhoff frequency appears due to the straining field caused by mutual perturbation, under both long-wave and short-wave instabilities. Vortices with the initial core vorticity of the Gaussian distribution and the elliptic distribution are also studied.

Doctor of Philosophy / Department of Industrial & Manufacturing Systems Engineering / Zhijian Pei / Titanium alloy is one of the most important materials used in major segments of industries such as aerospace, automobile, sporting goods, medical and chemical. Market survey has stated that the titanium shipment in the USA has increased significantly in last two decades, indicating its increased usage. Industries are always under tremendous pressure to meet the ever-increasing demand to lower cost and improve quality of the products manufactured from titanium alloy. Similar to titanium alloys, silicon carbide and dental ceramics are two important materials used in many applications. Rotary ultrasonic machining (RUM) is a non-traditional machining process that combines the material removal mechanisms of diamond grinding and ultrasonic machining. It comprises of a tool mounted on a rotary spindle attached to a piezo-electric transducer to produce the rotary and ultrasonic motion. No study has been reported on RUM of titanium alloy, silicon carbide and dental ceramics. The goal of this research was to provide new knowledge of machining these hard-to-machine materials with RUM for further improvements in the machining cost and surface quality. A thorough research has been conducted based on the feasibility study, effects of tool variables, effects of machining variables and wheel wear mechanisms while RUM of titanium alloy. The effects of machining variables (such as spindle speed, feed rate, ultrasonic vibration power) and tool variables (grit size, diamond grain concentration, bond type) have been studied on the output variables (such as cutting force, material removal rate, surface roughness, chipping size) and the wheel wear mechanisms for titanium alloy. Feasibility of machining silicon carbide and dental ceramics is also conducted along with a designed experimental study.