Analysis of a Horizontal-Axis Tidal Turbine Performance in the Presence of Regular and Irregular Waves Using Two Control Strategies

Stephanie Ordonez-Sanchez,Matthew Allmark,Catherine Lloyd,Ivan Santic,Kate Porter,Robert Ellis,Tim O’Doherty,Cameron Johnstone

doi:10.3390/en12030367

Stephanie Ordonez-Sanchez, Matthew Allmark + Show 6 more

Open Access

https://doi.org/10.3390/en12030367

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Abstract

The flow developed on a tidal site can be characterized by combinations of turbulence, shear flows, and waves. Horizontal-axis tidal turbines are therefore subjected to dynamic loadings that may compromise the working life of the rotor and drive train components. To this end, a series of experiments were carried out using a 0.9 m horizontal-axis tidal turbine in a tow tank facility. The experiments included two types of regular waveforms, one of them simulating an extreme wave case, the other simulating a more moderate wave case. The second regular wave was designed to match the peak period and significant wave height of an irregular wave which was also tested. Measurements of torque, thrust, and blade-bending moments were taken during the testing campaign. Speed and torque control strategies were implemented for a range of operational points to investigate the influence that a control mode had in the performance of a tidal stream turbine. The results showed similar average power and thrust values were not affected by the control strategy, nor the influence of either the regular or irregular wave cases. However, it was observed that using torque control resulted in an increase of thrust and blade root bending moment fluctuations per wave period. The increase in fluctuations was in the order of 40% when compared to the speed control cases.

Highlights

Achieving commercial and financial viability in the marine energy industry is challenging due to the complex and variant nature of the conditions seen by Horizontal-Axis Tidal Turbines (HATTs).Non-uniformity and unsteadiness occurring in the marine environment in the form of turbulence, sheared flows, surface waves, and tidal cycles mean that tidal turbines are subjected to a wide range of dynamic loading characteristics
The turbine was tested under two types of regular wave-tow cases and an irregular wave-tow test
It was found that when looking at average values, the control mode or the type of wave-tow case investigated did not affect the rotor thrust, rotor torque or blade root bending moment measurements when these where compared to tow-only conditions

Summary

Introduction

Achieving commercial and financial viability in the marine energy industry is challenging due to the complex and variant nature of the conditions seen by Horizontal-Axis Tidal Turbines (HATTs). Non-uniformity and unsteadiness occurring in the marine environment in the form of turbulence, sheared flows, surface waves, and tidal cycles mean that tidal turbines are subjected to a wide range of dynamic loading characteristics. The turbine components must be able to withstand the maximum forces induced by the hydrodynamics and be resistant to fatigue damage due to the cyclic nature of these loads. The high variability in the flow characteristics has implications for optimization of the device in terms of the sizing of components. Fluctuations in power production, resultant from the dynamic tidal resource, pose significant challenges for the power conditioning and control systems. It is imperative that the realistic loading characteristics are quantified and the way in which these interact with the turbine system are fully understood

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