Experimental Studies Of A Small Scale Horizontal Axis Tidal Turbine

The research in this thesis focuses on the investigation of tidal turbines using a small scale horizontal axis tidal turbine and a 2D hydrofoil testing rig, combining experiments with simulations to provide comprehensive results and to better understand some of the variables that affect their performance. The experimental campaigns were carried out at the University of Victoria fluids research lab and the Sustainable Systems Design Lab (SSDL). The experimental testing rigs were re-designed by the author and are now fully automated, including a friendly graphical user interface for easy implementation. Particle image velocimetry (PIV) technique was used as the quantitative flow visualization method to obtain the time-averaged flow fields. This thesis presents three investigations. The first study aims to quantify the impacts of channel blockage, free surface effects and foundations on hydrokinetic turbine performance, using porous discs and an axial flow rotor. The results were used to cross-validate computational fluid dynamics (CFD) simulations. It was found that as wall blockage increases, thrust and power are incremented with and without the inclusion of free surface deformation. Discrepancies between simulations and experimental results on free surface effects compared to a slip wall were obtained and hence further research is recommended and the author gives some advice on how to proceed in this investigation.The second study determines the performance of four hydrofoil candidates over a range of low Reynolds number (Re), delivering useful information that can be applied to low Re energy conversion systems and, specifically in this case, to improve the performance of the small scale tidal turbine at the SSDL lab. The study combines the 2D hydrofoil test rig along with PIV measurements in order to experimentally obtain lift and drag coefficients. The experiments were carried out in the recirculating flume tank over the range of low Re expected for the small scale rotor rig, in order to provide more accurate results to improve rotor blade design. In addition, numerical simulations using XFOIL, a viscid-inviscid coupled method, were introduced to the study. These results were analysed against experiments to find the most suitable parameters for reliable performance prediction. The final results suggested that adding a numerical trip at a certain chordwise distance produced more reliable results.Finally, an experimental study on turbine rotor performance and tip vortex behavior was performed using again the rotor rig and PIV. Blade design and rotor performance were assessed, showing good agreement with Blade Element Momentum (BEM) simulations, particularly at predicting the tip speed ratio corresponding to the maximum power coefficient point. Regarding the wake structure, tip vortex locations (shed from the blade tips) were captured using PIV in the near wake region, showing evidence of wake expansion. The velocity and vorticity fields are also provided to contribute to the development and validation of CFD and potential flow codes.

The research detailed in this thesis was focused on developing an experimental testing system to characterize the non-dimensional performance coeffcients of horizontal axis kinetic turbines, including both wind turbines and tidal turbines. The testing rig was designed for use in a water tunnel with Particle Image Velocimetry (PIV) wake survey equipment to quantify the wake structures. Precision rotor torque measurement and speed control was included, along with the ability to yaw the rotor. The scale of the rotors were purposefully small, to enable rapid-prototyping techniques to be used to produce many different test rotors at low cost to furnish a large experimental dataset. The first part of this work introduces the mechanical design of the testing rig developed for measuring the output power of the scaled rotor models with consideration for the requirements imposed by the PIV wake measurements. The task was to design a rig to fit into an existing water tunnel facility with a cross sectional area of 45 by 45 cm, with a rotor support structure to minimize the flow disturbance while allowing for yawed inflow conditions. A rig with a nominal rotor diameter of 15 cm was designed and built. The size of the rotor was determined by studying the fluid similarities between wind and tidal turbines, and choosing the tip speed ratio as a scaling parameter. In order to maximize the local blade Reynolds number, and to obtain different tip speed ratios, the rig allows a rotational speed in the range of 500 to 1500 RPM with accurate rotor angular position measurements. Rotor torque measurements enable rotor mechanical power to be calculated from simulation results. Additionally, it is included in this section a description of the instrumentation for measurement and the data acquisition system. It was known from the outset that measurements obtained in the experiments would be subject to error due to blockage effects inherent to bounded testing facilities. Thus, the second part of this work was dedicated to developing a novel Computational Fluid Dynamics (CFD) methodology to post-process the experimental data acquired. This approach utilizes the velocity field data at the rotor plane obtained from the water tunnel PIV test data, and CFD simulations based on the actuator disk concept to account for blockage without the requirement for thrust data which would have been unreliable at the low forces encountered in the tests. Finally, the third part of this work describes the practical aspects of the laboratory project, including a description of the operational conditions for turbine testing. A set of preliminary measurements and results are presented, followed by conclusions and recommendations for future work. Unfortunately, the water tunnel PIV system was broken and thus unavailable for more than a year, so only mechanical measurements were possible with the rig during the course of this thesis work.

Hydropower is found to be one of the most reliable and inexpensive options for renewable energy which was now widely been adopted by many countries to substitute fossil fuel sources. This Brief highlights the impact of climate change on hydropower plants, especially on the turbine design, as turbines are responsible for optimal conversion and regular energy production. The vulnerability of turbines is analyzed with the help of Artificial Neural Networks, followed by Multi Criteria Decision Making methods for development of intelligent indices to represent the level of vulnerability of turbines due to the change in climate.

Aerodynamics of Wind Turbines is the established essential text for the fundamental solutions to efficient wind turbine design. Now in its second edition, it has been entirely updated and substantially extended to reflect advances in technology, research into rotor aerodynamics and the structural response of the wind turbine structure. Topics covered include increasing mass flow through the turbine, performance at low and high wind speeds, assessment of the extreme conditions under which the turbine will perform and the theory for calculating the lifetime of the turbine. The classical Blade Element Momentum method is also covered, as are eigenmodes and the dynamic behaviour of a turbine. The new material includes a description of the effects of the dynamics and how this can be modelled in an ?aeroelastic code?, which is widely used in the design and verification of modern wind turbines. Further, the description of how to calculate the vibration of the whole construction, as well as the time varying loads, has been substantially updated.

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.

Wind Turbines addresses all those professionally involved in research, development, manufacture and operation of wind turbines. It provides a cross-disciplinary overview of modern wind turbine technology and an orientation in the associated technical, economic and environmental fields. It is based on the author's experience gained over decades designing wind energy converters with a major industrial manufacturer and, more recently, in technical consulting and in the planning of large wind park installations, with special attention to economics. The second edition accounts for the emerging concerns over increasing numbers of installed wind turbines. In particular, an important new chapter has been added which deals with offshore wind utilisation. All advanced chapters have been extensively revised and in some cases considerably extended

Renewable Energies Offshore includes the papers presented in the 1st International Conference on Renewable Energies Offshore (RENEW2014), held in Lisbon, 24-26 November 2014. The conference is a consequence of the importance of the offshore renewable energies worldwide and an opportunity to contribute to the exchange of information on the dev