USMA Research Unit Affiliation

Civil and Mechanical Engineering

Date of Award

Summer 6-25-2010

Degree Type

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

Department

Mechanical Engineering

Abstract

One approach to small-scale fuel injection is to capitalize upon the benefits of electrohydrodynamics (EHD) and enhance fuel atomization. There are many potential advantages to EHD aided atomization for combustion, such as smaller droplets, wider spray cone, and the ability to control and tune the spray for improved performance. Electrohydrodynamic flows and sprays have drawn increasing interest in recent years, yet key questions regarding the complex interactions among electrostatic charge, electric fields, and the dynamics of atomizing liquids remain unanswered. The complex, multi-physics and multi-scale nature of EHD atomization processes limits both experimental and computational explorations.

In this work, novel, numerically sharp methods are developed and subsequently employed in high-fidelity direct numerical simulations of electrically charged liquid hydrocarbon jets. The level set approach is combined with the ghost fluid method (GFM) to accurately simulate primary atomization phenomena for this class of flows. Surface effects at the phase interface as well as bulk dynamics are modeled in an accurate and robust manner. The new methods are implemented within a conservative finite difference scheme of high-order accuracy that employs state-of-the-art interface transport techniques. This approach, validated using several cases with exact analytic solutions, demonstrates significant improvements in accuracy and efficiency compared to previous methods used for EHD simulations. As a final validation, the computational scheme is applied in direct numerical simulation of a charged and uncharged liquid kerosene jet. Then, a detailed numerical study of EHD atomization is conducted for a range of relevant dimensionless parameters to predict the onset of liquid break-up, identify characteristic modes of liquid disintegration, and report elucidating statistics such as drop size and spray dispersion. Because the methodologies developed and validated in this work open new, simulations-based avenues of exploration within a broader category of electrohydrodynamics, some perspectives on extensions or continuations of this work are offered in conclusion.

Modernization Priorities Supported

Next Gen Combat Vehicle, Future Verticle Lift

USMA Research Goals Supported

Develop the Faculty Professionally, Enhance the Reputation of USMA

First Advisor

John W. Daily

Second Advisor

Olivier B. Desjardins

Funder

Funding and sponsorship from the U.S. Army and U.S. Military Academy, as well as research funding provided by Army Research Office Contracts W911NF-08-C-0081 and W911NF-09-C-0157, is gratefully acknowledged.

Publisher

University of Colorado at Boulder

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