Off-campus UMass Amherst users: To download campus access dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.

Non-UMass Amherst users: Please talk to your librarian about requesting this dissertation through interlibrary loan.

Dissertations that have an embargo placed on them will not be available to anyone until the embargo expires.

Document Type

Campus-Only Access for One (1) Year

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Mechanical Engineering

Year Degree Awarded

2016

Month Degree Awarded

May

First Advisor

Prof. David P. Schmidt

Abstract

Sprays are encountered regularly in many industrial and military applications including inkjets, cooling processes, evaporation processes, catalyzation, coatings, and propulsion chambers. Spray atomization phenomena of Newtonian fluids have received significant academic and industrial research attention, however, the effect of non-Newtonian rheologies on spray formation and downstream droplet behavior has not been as heavily investigated. The aim of this work is to elucidate the effect of non-Newtonian and viscoelastic rheological effects on droplet behavior in the context of secondary atomization and droplet collisions.

This study utilizes finite volume computational fluid dynamics (CFD) to recreate droplet fluid physics in a numerical setting to a high accuracy. Droplet collision systems comprised of Newtonian, viscoelastic and shear-thinning rheologies are simulated using a Lagrangian moving-mesh interface tracking method (MMIT). This interface tracking approach provides increased surface curvature accuracy on relatively coarse meshes compared to many Eulerian multiphase methods. Modeling assumptions and interface mesh treatments are validated using existing analytical and experimental comparisons showing good agreement. Interpolation error due to cell deformation is minimized with local topological mesh adaptation and a global element quality optimization algorithm. The fully three dimensional computational study investigates the effect of these non-Newtonian and viscoelastic rheologies on a droplet collision. Here, simulated fluid ligaments exhibit increased stability with greater relative elasticity. By applying the similar simulation techniques to collisions of shear thinning droplets, a simple reduced order viscosity model has been produced, valid within a certain range of Weber number values.

Another important atomization phenomenon, secondary breakup, is simulated using a volume of fluids (VOF) based interface capturing method applied to a centroid tracking moving mesh. Here, an axisymmetric CFD study of the wind induced break up of both Newtonian and non-Newtonian droplets is presented with comparisons with experimentally observed results. The numerical implementation is further verified by displaying accurate recreation of rapid micro-scale bubble collapse processes and subsequent jet ejection observed in controlled laboratory settings. The presented simulation results show capability in prediction of both the transient deformation morphology and the time scales in which droplet disintegration occurs.

Share

COinS