Current emissions targets have created a strong need for introducing more renewable
energy sources into the energy mixture. The oscillating-foil turbine (OFT) has
gained interest in recent years for renewable energy extraction. Experimental and
numerical studies on the OFT experience different levels of wall confinement than
what may be experienced at a natural site. Walls in close proximity will direct the
flow at the turbine, causing a greater perceived velocity by the turbine, and thus a
higher theoretical performance. This work aims to increase understanding of flow
confinement on the fully-passive OFT. This is motivated by (1) enabling comparison
between turbine performance operating at different confinement levels, and (2)
potentially providing a means to enhance performance by designing a turbine which
uses confinement to its advantage.
The experiments were performed using a NACA0015 foil with an aspect ratio of
7.5 in a water tunnel equipped with adjustable lateral walls. The foil was undergoing
passive oscillations in pitch and heave degrees of freedom. The kinematic parameters
of the foil oscillations and its energy harvesting performance were measured at eight
blockage ratios, ranging from 22% to 60%, for two structural configurations of the
turbine.
Quantitative flow imaging was performed using particle image velocimetry (PIV),
at three confinement levels, to observe the timing of the leading-edge vortex (LEV)
formation and shedding throughout the foil oscillation cycle. Loading on the foil was
related to the flow structure by calculating the moments of vorticity with respect to
the pitching axis of the foil.
The results showed that the efficiency and the power coefficient increased with
increasing confinement. This was expected due to the higher incident velocity on the
foil in the presence of the confining walls. At the highest level of confinement, the
close proximity of the foil to the walls during parts of the oscillation cycle resulted in
a change in the phase lag between the pitching and the heaving components of the
foil motion. In turn, this shift in the kinematic parameters led to a sharp decrease in
the energy-extraction performance of the turbine. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/14086 |
| Date | 05 August 2022 |
| Creators | Mann, Sierra |
| Contributors | Oshkai, Peter, Dumas, Guy |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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