Date of Award


Degree Type


Degree Name

Doctor of Philosophy (PhD)


Mechanical Engineering

First Advisor

Carlos M Corvalan

Second Advisor

Paul E Sojka

Committee Member 1

Osvaldo H Campanella

Committee Member 2

Stephen D Heister


The free-surface dynamics of drop coalescence and that of impinging liquid jets have both fundamental interest and practical importance in processes ranging from crop spraying and the processing of food emulsions to the atomization of fuel and pro- pellants in combustion and propulsion engines. These processes frequently involve the use of complex fluids -- shear-thinning or viscoelastic non-Newtonian liquids, which often contain surfactants either as additives or as contaminants. This Thesis reports high-fidelity simulations of unsteady free-surface flows of complex fluids. The objec- tive is to advance the understanding of the free-surface dynamics of drop coalescence and liquid jet impingement when viscous, surfactant and shear-thinning e↵ects are important. Simulations in this Thesis enabled, for the first time, a comprehensive nu- merical analysis of the coalescence of surfactant-laden drops after the merging drops make contact. The analysis reveals how interfacial (Marangoni) stresses induced by uneven accumulation of surfactant control the rate at which the drops coalesce by modulating the pull of surface tension on the tiny meniscus bridge joining the drops. Simulations also enabled the analysis of the unsteady free-surface dynamics of im- pinging viscous and shear-thinning liquid jets. Results demonstrate that viscous and shear-thinning stresses profoundly a↵ects the impingement dynamics -- in particu- lar the velocity and thickness of the resulting radially expanding liquid sheet -- by modifying the pressure developed in the impact region.