Theses and Dissertations at Montana State University (MSU)
Permanent URI for this collectionhttps://scholarworks.montana.edu/handle/1/733
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Item Numerical study of electric Reynolds number on electrohydrodynamic (EHD) assisted atomization(Montana State University - Bozeman, College of Engineering, 2016) Sheehy, Patrick John Harper; Chairperson, Graduate Committee: Mark OwkesIn today's modern world, nearly all industries utilize the benefits of fast, long distance transportation that burning fossil fuels deliver. However, fluctuating fuel prices has created interest in researching alternatives to fossil fuels. Bio-fuels are one of these alternatives, but they generally have a higher viscosity and water content than diesel. This means high pressures are required to atomize the fuel in the combustion chamber, thus bio-fuels are limited to larger or less efficient engines. A potential method to reduce the pressure requirements is to use Electrohydrodynamic (EHD) assisted atomization. EHD assisted atomization injects electrical charges into the liquid fuel before spraying, meaning the fuel has an electrical charge distribution before and after atomization. For many relevant engineering flows, including liquid fuel injection, the charge mobility timescale (time it takes the charges to relax to the fluid-gas boundary) is similar in magnitude to the charge convection timescale (relevant flow time), which leads to a non-trivial electric charge distribution. This distribution within the liquid fuel may enhance atomization, the extent to which is dependent on the ratios of the timescales which are known as the electric Reynolds number (Re subscript e). In this work, a computational approach for simulating two-phase EHD flows is used to investigate the amount Re subscript e influences the resulting atomization quality. The computational approach is second-order, conservative, and is used to consistently transport the phase interface along with the discontinuous electric charge density and momentum. The scheme sharply handles the discontinuous electric charge density, allowing robust and accurate simulations. In addition, this method is modified by a work distribution scheme to improve processor utilization on High Performance Computing (HPC) clusters. Using these methods, multiple three-dimensional test cases are simulated with varying Re subscript e values which highlight the effect of Re subscript e on the atomization efficiency of a liquid jet. Comparison of these cases shows the importance of Re subscript e on atomization and suggests that decreasing Re subscript e (increasing charge mobility) leads to larger concentrations of electric charge density, increased Coulomb force, and ultimately improved break-up during the atomization process.Item Heat transfer characteristics of small configuration hot-wires in low Reynolds number subsonic and supersonic air flows(Montana State University - Bozeman, College of Engineering, 1985) Hertel, Peter SeanItem Determining the biomechanical response of a filiform hair array : a low Reynolds number fluid-structure model(Montana State University - Bozeman, College of Letters & Science, 2009) Cummins, Breschine; Chairperson, Graduate Committee: Tomas GedeonA model system that has been the subject of many anatomical, developmental, functional, and theoretical studies over the last 30 years is the cercal sensory system of the cricket. This system is composed of two antenna-like appendages covered with hundreds of filiform mechanosensory hairs, and encodes information about the direction and dynamics of low-velocity air currents. The encoding is determined by the biomechanical properties of the mechanosensory hairs. These properties are poorly understood, primarily because accurate experimental measurements of the air-current-driven movements of the hairs are difficult to obtain, and adequate mathematical tools for modeling arbitrarily complex hair-to-hair interactions within the canopy have been absent. The study presented here solves fundamental problems in both of these areas. Previous studies have characterized the biomechanics of the filiform hairs, but only one study considered the fluid-mediated interaction of closely-packed hairs. A major goal of our work was to model the motion of a dense patch of thin filaments driven by bulk fluid flow, in a context that is immediately relevant to the cercal system. To understand the function of the sensory epithelium as a whole, we developed a numerical model based on a novel mathematical tool: the method of regularized unsteady Stokeslets. This method is generally applicable to low Reynolds number fluid flow in domains that are subject to periodic forcing along the boundary. The numerical scheme associated with our mathematical model is fast, scalable, accounts for the interaction between arbitrary arrangements of hairs. We measured the biomechanical stimulus-response properties of 19 filiform hairs, and used that data to fit parameters to our mathematical model. We demonstrate for the first time that one of the mechanical parameters controlling filiform hair motion depends on the frequency of the air stimulus. Our numerical simulations demonstrate that damped and synergistic hair interactions can occur between closely-packed hairs. Low frequency signals (< 50 Hz) are damped, and higher frequency signals (50-200 Hz) are amplified. We hypothesize that the characteristic dense patch of hairs at the proximal end of the cercus acts as a noise cancellation filter that removes low frequency components of ambient environmental stimuli.