Date of Graduation

12-2025

Document Type

Thesis

Degree Name

Master of Science in Mechanical Engineering (MSME)

Degree Level

Graduate

Department

Mechanical Engineering

Advisor/Mentor

Walters, Dibbon

Committee Member

Leylek, James

Second Committee Member

Millett, Paul

Keywords

hydrokinetic turbines; oscillating foil energy harvester; renewable energy; vertical axis hydrokinetic turbine

Abstract

This thesis presents a computational investigation of optimal kinematic operating parameters governing various hydrokinetic turbines (HKT) systems for the use of power generation within river and tidal environments. Two separate studies are performed. The first study investigates optimal cycle parameters for simple and complex kinematic modes governing the motion of oscillating foil energy harvesters (OFEH). An iterative gradient-ascent optimization method is used to search for local efficiency optima based on an initial set of kinematic parameters. To search the operational space for up to eight degrees of freedom (DOF), a maximin space filling condition was implemented to efficiently compute initial kinematic parameter sets. Multiple kinematic profiles were found, with some existing only when higher kinematic modes are considered. Results show that inclusion of higher OFEH kinematic modes can lead to improved cycle efficiency as well as multiple unique operating conditions. The second study performs a comparative study between three different vertical axis hydrokinetic turbine (VAHT) configurations by establishing a local performance map around kinematic operating conditions found through a precursor optimization process. Simulations are performed on a conventional Darrieus turbine, an OFEH with circular foil motion, and a Wollongong turbine with 2, 3, and 4-foil configurations. The latter is a hybrid turbine whose foils rotate one half-period about its axis every full cycle and remains largely unexplored in literature. Turbine performance is evaluated based on maximum cycle-averaged efficiency and its sensitivity to changes in kinematic operating conditions. It is found that the Wollongong turbine produced consistently high efficiency and was largely insensitive to changes in operating conditions compared to the configurations investigated. The Wollongong turbine and OFEH both show favorable startup characteristics and a peak operation below a tip speed ratio of one. For both studies, the efficiency of each HKT is assessed based on unsteady computational fluid dynamics (CFD) simulations performed with the CFD solver flowPsi.

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