Boundary Integral Formulation of Electric Fields in Level Set Simulations of Charged Droplets

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76922/1/AIAA-2005-4665-176.pd

Simulation of Charge and Mass Distributions of Indium Droplets Created by Field Emission

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77396/1/AIAA-2006-3560-440.pd

UNLV Graduate Wind Quintet & UNLV New Horizons Band & UNLV Community

Program listing performers and works performed

Field emission electric propulsion thruster modeling and simulation.

Electric propulsion allows space rockets a much greater range of capabilities with mass efficiencies that are 1.3 to 30 times greater than chemical propulsion. Field emission electric propulsion (FEEP) thrusters provide a specific design that possesses extremely high efficiency and small impulse bits. Depending on mass flow rate, these thrusters can emit both ions and droplets. To date, fundamental experimental work has been limited in FEEP. In particular, detailed individual droplet mechanics have yet to be understood. In this thesis, theoretical and computational investigations are conducted to examine the physical characteristics associated with droplet dynamics relevant to FEEP applications. Both asymptotic analysis and numerical simulations, based on a new approach combining level set and boundary element methods, were used to simulate 2D-planar and 2D-axisymmetric probability density functions of the droplets produced for a given geometry and electrode potential. The combined algorithm allows the simulation of electrostatically-driven liquids up to and after detachment. Second order accuracy in space is achieved using a volume of fluid correction. The simulations indicate that in general, (i) lowering surface tension, viscosity, and potential, or (ii) enlarging electrode rings, and needle tips reduce operational mass efficiency. Among these factors, surface tension and electrostatic potential have the largest impact. A probability density function for the mass to charge ratio (MTCR) of detached droplets is computed, with a peak around 4,000 atoms per electron. High impedance surfaces, strong electric fields, and large liquid surface tension result in a lower MTCR ratio, which governs FEEP droplet evolution via the charge on detached droplets and their corresponding acceleration. Due to the slow mass flow along a FEEP needle, viscosity is of less importance in altering the droplet velocities. The width of the needle, the composition of the propellant, the current and the mass efficiency are interrelated. The numerical simulations indicate that more electric power per Newton of thrust on a narrow needle with a thin, high surface tension fluid layer gives better performance.Ph.D.Aerospace engineeringApplied SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/126313/2/3238104.pd

Analytical exact solutions for unsteady collisionless plume flows in a vacuum

This paper presents a set of gaskinetic solutions to the problem of unsteady collisionless round plume development: startup and development to a steady flow; steady flow; and shutting down from a steady flow. This can find applications in studying similar transient plume flows from space propulsion devices. Different from many past studies, here we consider the general situation that the average exit gas speed can be larger than zero, and detailed geometry of the nozzle exit radius is included. A fundamental space velocity time relation is adopted in this study and it plays a crucial role to obtain the complete flowfield properties of density, velocity, pressure and temperature. This study reveals that there are some internal complementary relations on density and momentum among these three processes. The results involve complex integrations involving factors of time, geometry, and specific speed ratio. Several numerical simulations with the direct simulation Monte Carlo method validate these analytical exact results

Differential Expression of Genes in Cells Cultured from Juxtacanalicular Trabecular Meshwork and Schlemm's Canal

Purpose: The purpose of this study was to distinguish differences in gene expression between cells cultured from the juxtacanalicular trabecular meshwork (JCTM) and those from Schlemm's canal (SC), to gain clues to differences between those cell types, and to add to our baseline knowledge of gene expression differences in these cell types for later comparison between cells from nonprimary open-angle glaucoma (POAG) and POAG outflow tissues. Methods: A set of JCTM and SC cells was cultured from each of 2 donor eyes by an explant method, grown to passage 3, and frozen in liquid nitrogen. The cells were thawed, total RNA was extracted, and the probes made from total RNAs were hybridized to MICROMAX human cDNA microarray slides in 2 separate trials. Differentially expressed genes were analyzed using PubMed, Prosite, and IPA software, and the expression of several of the genes including intercellular adhesion molecule-1 (ICAM-1), tenascin, and β-spectrin was assessed by immunofluorescence. Results: Schlemm's canal cells differentially expressed ICAM-1, spectrin, complement, fibulin-1, and several genes consistent with an endothelial origin in both arrays, while the JCTM cells more often overexpressed genes consistent with contractile, matrix function, and neural character. At the same time, many genes highly expressed in the first array were not highly overexpressed in the second. One highly overexpressed gene in the JCTM in both arrays, that for heparan sulfate 3-O-sulfotransferase-1 precursor, is thought to be somewhat unique, and could affect the glycosaminoglycan functionality in the extracellular matrix (ECM). Conclusions: We found generally good agreement between the 2 array trials, but some contradictions as well. Many of the genes overexpressed in each cell type had been described in earlier work, but several were new. Tables of genes, grouped by cellular function, and the complete datasets are provided for the development of new hypotheses