Abstract:
The generation of electricity from ocean waves using oscillating water column
(OWC) wave energy converters is currently uneconomic due to the high
capital cost and low efficiencies of such devices. The bidirectional air turbines
utilised in OWCS are one of the
principal sources of inefficiency and
a significant increase in their performance would improve the prospects of
commercial scale wave power generation.
The
ability of computational fluid dynamics (CFD) to predict the performance of both Wells
and impulse type bidirectional turbines for use in OWCS
was examined by comparison with experimental results taken from the literature.
A design process was then undertaken for a datum impulse turbine and
a novel high-efficiency impulse turbine arrangement. Numerical performance
predictions are presented with a comparison against experimental data from
a large-scale oscillating-flow test rig.
An automated design and aerodynamic optimisation system was subsequently
developed for application to this novel impulse turbine design. The optimiser
employs a hybridised genetic algorithm along with Kriging meta¬models to
significantly decrease the number of expensive calls to the 3D-CFD code used
to evaluate the objective function. Comparisons to a number of state of the
art
optimisation algorithms from the literature on some mathematical test
functions indicated that the optimiser had equivalent or better performance
for most problems.
A parameter study was carried out to investigate the effect of various turbine
in
design variables, before undertaking a 14-variable global design optimisation.
A 5-variable
optimisation exercise was then performed to investigate the effi-
ciency gains that could be achieved by using three-dimensional rotor blades.
Substantial
gains in performance were attained and the predicted levels of
efficiency are significantly higher than those previously reported in the literature
for other bidirectional
impulse turbine designs.
