Unsteady Hydrodynamics Of Tidal Turbine Blades
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Modelling the Unsteady Hydrodynamic Response of Lightly Loaded Tidal Turbines
| Author | : Bao Ngoc Ha Tran |
| Publisher | : |
| Total Pages | : 358 |
| Release | : 2017 |
| Genre | : Hydraulic turbines |
| ISBN | : |
CFD Analysis of Unsteady Hydrodynamic Loading on Horizontal Axis Tidal Turbine (HATT) Blades
| Author | : Xue Wang |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2015 |
| Genre | : |
| ISBN | : |
Horizontal Axis Tidal Turbines (HATTs) can experience amplified, time varying hydrodynamic loads during operation due to dynamic stall. Elevated hydrodynamic loads impose high structural loads on turbine blades, thus appreciably shortening machine service life. An improved characterization of the unsteady hydrodynamic loads on tidal turbine blades is therefore necessary to enable more reliable predictions of their fatigue life and to avoid premature failures. This thesis reports on a Computational Fluid Dynamics (CFD) analysis of the unsteady blade loading of a scale-model HATT taking dynamic stall into account. Numerical simulations are performed both in two-dimensional (2-D) and three-dimensional (3-D) using the commercial CFD solver ANSYS Fluent.After a brief description of the theories and methods involved, the behaviour of flow at low Reynolds number around a NACA-0012 aerofoil pitching in a sinusoidal pattern that induces dynamic stall is studied firstly to validate the numerical method and the choice of turbulence models. Then full 3-D computations of a rotating scale-model HATT rotor are presented for steady and periodic unsteady inflow situations, respectively. The reliability of the 3-D numerical method is evaluated by comparing the blade loads, especially the out-of-plane blade-root bending moment (defined as being about an axis normal to the rotor axis), with measurement data obtained from experimental tests conducted at the University of Strathclyde's Kelvin Hydrodynamics Laboratory towing tank. Analyses in the steady velocity study are documented for a broad range of rotor speeds and flow velocities. Furthermore, investigations of 3-D flow separation and scale effects on blade loads are also performed.The periodic unsteady velocity study aims to examine the out-of-plane blade-root bending moment response to harmonic axial motion, deemed representative of the free-stream velocity perturbations induced by the unsteady flow. Parametric tests on oscillatory frequencies and amplitudes are carried out in order to analyse the HATT blade hydrodynamic behaviour under different flow patterns. Detailed flow field data is analysed to understand 3-D dynamic stall from a modelling perspective.It is concluded that the results by the present study provide significant insights into the flow physics occurring around the HATT rotor blades under various flow conditions. The CFD method can be used for designing more advanced HATT rotors, it also can be used to fine tune the computationally faster lower order Blade Element Momentum (BEM) methods for parametric design studies where experimental data is not available, particularly at the challenging rotor operating conditions involving flow separation and dynamically varying hydrodynamic behaviours.
An Experimental Investigation of Turbulence and Unsteady Loading on Tidal Turbines
| Author | : Ian Angus Milne |
| Publisher | : |
| Total Pages | : 228 |
| Release | : 2013 |
| Genre | : Hydraulic turbines |
| ISBN | : |
This research addresses the need for an improved characterisation of the onset flow turbulence and the unsteady hydrodynamic blade loads on tidal turbines for the purposes of predicting fatigue life. A new, extensive set of parameters which characterise the magnitudes of the turbulent fluctuations, the anisotropy and the scales of the turbulence at a tidal energy site have been presented. A novel application of rapid distortion theory estimated the velocity fluctuations to be amplified by 15% due to the presence of the turbine. The turbulence was also predicted to be well correlated over the outer span of a turbine blade at the frequencies of interest. Together, these results enabled a set of non-dimensional parameters describing the turbulence induced forcing on a turbine blade to be established. A model-scale horizontal-axis turbine was used to investigate the unsteady blade load response in a still-water towing tank. A set of wind tunnel tests of the S814 foil were also conducted and used to demonstrate that the lift on the blades could have been degraded by 10% at the relatively low Reynolds numbers at which the turbine was tested, relative to full-scale. This was owing to dominant laminar separation bubbles. Single frequency planar oscillations of the turbine were used to quantify the contribution of hydrodynamic unsteadiness to the blade-root bending moment. For attached flow, the unsteady bending moment was found to amplify the steady loads by up to 15 %. The total hydrodynamic added mass was up to 2.7 times larger than from non-circulatory forcing and decreased with frequency. Dynamic inflow theory and a returning wake model were able to provide qualitative predictions of these results at low frequencies. At low tip-speed ratios, phenomena consistent with delayed separation and dynamic stall were characterised and the unsteady loading was up to 25% larger than the steady load. Linear superposition of the single frequency responses was also demonstrated to offer a reliable technique to model the response to a multi-frequency forcing and to a large eddy.
An Unsteady Hydrodynamic Model for Tidal Current Turbines
| Author | : Tom Ruaridh McCombes |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2014 |
| Genre | : |
| ISBN | : |
Due to concerns about the impacts of carbon emissions on the environment, the security of supply of electricity and the likelihood of achieving "peak-oil" in the near future, governments have legislated to reduce reliance on fossil fuels. An attractive alternative is power obtained from tidal currents, and the coast of the British Isles is especially hydraulically active. Tidal energy converters typically resemble wind turbines however, unlike wind turbines, they are expected to operate in an environment which is singularly hostile, and will also be expected to generate power in non-ideal operating conditions. This thesis is concerned with the ability to model individual and groups of tidal devices including their mutual interactions. The ability to capture unsteady inflow conditions at realistic array spacing requires preservation of turbine wakes over a sufficiently large range at spatial resolutions and over time durations which are not feasible using standard computational fluid dynamics software. This thesis has combined methodologies developed for helicopter wake modelling with techniques used in naval architecture for modelling thick maritime propellers into a computational tool. The particular formulation of the Navier-Stokes equations employed allows the determination of the unsteady pressure and force distributions on a turbine rotor due to the effects of a neighbouring device, even if it is operating some significant distance upstream. The constituents of the method of this thesis are developed and applied to "proof-of-principle" studies. These include flow past static and oscillating 2-D aerofoils and past a 3-D wing, wind turbine and tidal turbine configuration. The results from these studies demonstrate that the model is convergent and capable of capturing the time dependant forces on these devices, and by comparison with analytical or experimental results, or via inter-model comparison begins the process of calibration and validation of the model. The method is then applied to flow past groups of turbines in various array configurations, and a coaxial, contra-rotating device. The outcome of this work is a decision making tool which can be used to improve success and reduce risk in tidal power array planning, optimise device configurations and is translatable back into rotorcraft or naval architecture usage.
The Effect of Unsteady Sea Conditions on Tidal Stream Turbine Loads and Durability
| Author | : Thomas Mikael Nevalainen |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
This thesis explores the effect that the unsteady hydrodynamics of the marine climate has on the load generation and subsequent durability of horizontal axis tidal stream turbines (TSTs). This is achieved through several campaigns of numerical modelling where the methodologies adopted were chosen on the principle of maximising the computational effi ciency, allowing for time-domain durability calculations to be performed.The inflow was modelled by a variety of engineering wave models coupled with the underlying current profi€les and the rotor loads were resolved using blade element momentum theory (BEMT). The rotor loads were then fed to a six degree of freedom drive train model to analyse the stresses and the fatigue damage in the system.In order to inform on the input-output relationships of a turbine's operating conditions and the generated loads, a sensitivity analysis was performed on the BEMT model to show each input parameter's influence on the loading. The results showed that the rotor radius, blade pitch, signifi€cant wave height, inflow velocity and shear current steepness were the dominant factors in regards to the loading. Furthermore,an investigation on the internal contact stresses in the turbine's main bearing found that simplifying the turbine loading problem down to a one-dimensional phenomenon gave a signi€ficant underestimation in the internal loads.It is concluded that to accurately model the internal loads on a TST, the full spatial range of the rotor loads including the o‚-axis components, must be incorporated in the structural modelling to avoid under prediction of the stresses and the related over predictions of the resulting fatigue life. The standard fatigue analysis techniques used in this work were also identifi€ed as possibly being unsuitable for the highly dynamic marine climate and suggestions on how to address this issue are provided.
Wind Energy Handbook
| Author | : Tony Burton |
| Publisher | : John Wiley & Sons |
| Total Pages | : 784 |
| Release | : 2011-06-13 |
| Genre | : Technology & Engineering |
| ISBN | : 0470699752 |
Named as one of Choice's Outstanding Academic Titles of 2012 Every year, Choice subject editors recognise the most significant print and electronic works reviewed in Choice during the previous calendar year. Appearing annually in Choice's January issue, this prestigious list of publications reflects the best in scholarly titles and attracts extraordinary attention from the academic library community. The authoritative reference on wind energy, now fully revised and updated to include offshore wind power A decade on from its first release, the Wind Energy Handbook, Second Edition, reflects the advances in technology underpinning the continued expansion of the global wind power sector. Harnessing their collective industrial and academic expertise, the authors provide a comprehensive introduction to wind turbine design and wind farm planning for onshore and offshore wind-powered electricity generation. The major change since the first edition is the addition of a new chapter on offshore wind turbines and offshore wind farm development. Opening with a survey of the present state of offshore wind farm development, the chapter goes on to consider resource assessment and array losses. Then wave loading on support structures is examined in depth, including wind and wave load combinations and descriptions of applicable wave theories. After sections covering optimum machine size and offshore turbine reliability, the different types of support structure deployed to date are described in turn, with emphasis on monopiles, including fatigue analysis in the frequency domain. Final sections examine the assessment of environmental impacts and the design of the power collection and transmission cable network. New coverage features: turbulence models updated to reflect the latest design standards, including an introduction to the Mann turbulence model extended treatment of horizontal axis wind turbines aerodynamics, now including a survey of wind turbine aerofoils, dynamic stall and computational fluid dynamics developments in turbine design codes techniques for extrapolating extreme loads from simulation results an introduction to the NREL cost model comparison of options for variable speed operation in-depth treatment of individual blade pitch control grid code requirements and the principles governing the connection of large wind farms to transmission networks four pages of full-colour pictures that illustrate blade manufacture, turbine construction and offshore support structure installation Firmly established as an essential reference, Wind Energy Handbook, Second Edition will prove a real asset to engineers, turbine designers and wind energy consultants both in industry and research. Advanced engineering students and new entrants to the wind energy sector will also find it an invaluable resource.
