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The hydrodynamic and structural loading characteristics of straight and helical-bladed vertical axis tidal and current flow turbines

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Marsh, PJ (2015) The hydrodynamic and structural loading characteristics of straight and helical-bladed vertical axis tidal and current flow turbines. PhD thesis, University of Tasmania.

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Abstract

Vertical axis cross flow tidal and current flow turbines are proposed to generate electrical
energy from the ocean's kinetic energy, however little is known of their performance and
loading characteristics. In this work, fixed pitch straight and helical-bladed vertical axis
turbines were investigated using numerical simulation models to perform examinations of
the influence of geometrical layout and rotational rate on power output, torque fluctuations,
mounting forces, structural stress, and deflection magnitudes. These studies were conducted
to establish the relative merits of various turbine configurations, including variations in strut
section, strut-blade mounting tab design, strut location, as well as varying degrees of blade
helicity and section angle inclination. To establish performance and loading parameters,
transient Computational Fluid Dynamics (CFD) and Double Multiple Streamtube (DMS)
hydrodynamic simulation models were developed, which were then coupled with structural
models using beam theory and Finite Element Analysis (FEA) techniques. Extensive verification and validation of the hydrodynamic results against Experimental Fluid Dynamics
(EFD) results from literature for turbines of differing geometrical layouts was performed to
ensure simulation accuracy.
Simulation results show that numerical models can accurately simulate performance when
compared to EFD results if suitable modelling techniques are utilised. The results show
that significant differences in performance characteristics such as power output and mount-
ing force magnitudes occur for turbines with differing geometrical layouts. Straight-bladed
turbines were found to generate higher power output, torque fluctuation levels, mounting
forces, structural stress, and defection magnitudes than helical turbines of the same frontal
area, as a result of the blade inclination of the helical turbine to the inflow. The influence of
strut design on power output was also significant, with low-drag struts located at the blade
tips generating the highest power output when compared to turbines with high-drag struts
located at the quarter-span location. For both straight and helical turbines the highest
stress magnitudes were found at the blade-strut joints. Overall these results demonstrate
that straight-bladed turbines are better suited for harnessing tidal and current flow ocean
energy than helical-bladed turbines, as they generate higher power outputs whilst not incurring any significantly adverse structural penalties. These results are significant as previous numerical simulation and EFD works have concentrated on each configuration individually, with little known of their respective merits.
The numerical models developed as part of this work are capable of accurately capturing
the complex behaviour of vertical axis turbines for differing geometrical layouts, allowing for
future design investigations to be conducted without the need for EFD. The development of
these models, and the inclusion of suggested simulation guidelines in this work, has created
a useful design toolbox for future use that is suitable for turbine optimisation studies as well
as coupling with fatigue evaluations to ensure turbine longevity.

Item Type: Thesis (PhD)
Keywords: Vertical Axis Tidal Turbine, Hydrodynamics, Structural Loading
Copyright Information:

Copyright 2015 the Author

Additional Information:

Chapter 2 appears to be the equivalent of a pre-print version of an article published as: Marsh P., Ranmuthugala, D., Penesis, I., Thomas, G, 2016.The influence of turbulence model and two and three-dimensional domain selection on the simulated performance characteristics of vertical axis tidal turbines, Renewable energy, 105, 106-116

Chapter 3 appears to be the equivalent of a post-print version of an article published as: Marsh P., Ranmuthugala, D., Penesis, I., Thomas, G., 2015. Three-dimensional numerical simulations of straight-bladed vertical axis tidal turbines investigating power output, torque ripple and mounting forces, Renewable energy, 83, 67-77

Chapter 6 appears to be the equivalent of a post-print version of an article published as: Marsh P., Ranmuthugala, D., Penesis, I., Thomas, G., 2015. Numerical investigation of the influence of blade helicity on the performance characteristics of vertical axis tidal turbines, Renewable energy, 81, 926-935

Chapter 7 appears to be the equivalent of a post-print version of an article published as: Marsh P., Ranmuthugala, D., Penesis, I., Thomas, G., 2016. Numerical simulation of the loading characteristics of straight and helical-bladed vertical axis tidal turbines, Renewable energy, 94, 418-428

Date Deposited: 14 Nov 2016 00:08
Last Modified: 01 Nov 2017 16:00
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