scholarly journals A Note on the Effects of Local Blockage and Dynamic Tuning on Tidal Turbine Performance

2020 ◽  
Vol 143 (1) ◽  
Author(s):  
Lei Chen ◽  
Paul A.J. Bonar ◽  
Christopher R. Vogel ◽  
Thomas A.A. Adcock
Keyword(s):  
Oscillatory Flow ◽  
Tidal Channels ◽  
Scale Theory ◽  
Dynamic Tuning ◽  
Tidal Turbines ◽  
Turbine Performance ◽  
Actuator Disc ◽  
Tidal Turbine ◽  
Tuning Strategy ◽  
Blade Element

Abstract Numerical simulations are used to explore the potential for local blockage effects and dynamic tuning strategies to enhance the performance of turbines in tidal channels. Full- and partial-width arrays of turbines, modeled using the volume-flux-constrained actuator disc and blade element momentum theories, are embedded within a two-dimensional channel with a naturally low ratio of drag to inertial forces. For steady flow, the local blockage effect observed by varying the cross-stream spacing between the turbines is found to agree very well with the predictions of the two-scale actuator disc theory of Nishino and Willden (2012, “The Efficiency of an Array of Tidal Turbines Partially Blocking a Wide Channel,” J. Fluid Mech., 708, pp. 596–606). For oscillatory flow, however, results show that, consistent with the findings of Bonar et al. (2019, “On the Arrangement of Tidal Turbines in Rough and Oscillatory Channel Flow,” J. Fluid Mech., 865, pp. 790–810), the shorter and more highly blocked arrays produce considerably more power than predicted by two-scale theory. Results also show that, consistent with the findings of Vennell (2016, “An Optimal Tuning Strategy for Tidal Turbines,” Proc. R. Soc. A, 472(2195), p. 20160047), the “dynamic” tuning strategy, in which the tuning of the turbines is varied over the tidal cycle, can only produce significantly more power than a temporally fixed turbine tuning if the array has a large number of turbine rows or a large local blockage ratio. For all cases considered, trends are consistent between the two turbine representations but the effects of local blockage and dynamic tuning are found to be much less significant for the more realistic tidal rotor than for the idealized actuator disc.

Local Blockage Effects for Idealised Turbines in Tidal Channels

2019 ◽  
Author(s):  
Lei Chen ◽  
Paul A. J. Bonar ◽  
Christopher R. Vogel ◽  
Thomas A. A. Adcock
Keyword(s):  
Oscillatory Flow ◽  
Numerical Models ◽  
Numerical Results ◽  
Tidal Channels ◽  
One Dimensional ◽  
Scale Theory ◽  
Actuator Disc ◽  
Tidal Turbine ◽  
The One ◽  
Turbine Arrays

Abstract In this paper, idealised analytical and numerical models are used to explore the potential for local blockage effects to enhance the performance of turbines in tidal channels. Arrays of turbines modelled using the volume-flux-constrained actuator disc and blade element momentum theories are embedded within one-dimensional analytical and two-dimensional numerical channel domains. The effects of local blockage on the performance of arrays comprising one and five rows of actuator discs and tidal rotors operating in steady and oscillatory channel flow are then examined. In the case of steady flow, numerical results are found to agree very well with the two-scale actuator disc theory of Nishino & Willden [1]. In the case of oscillatory flow, however, numerical results show that the shorter and more highly blocked arrays produce considerably more power than predicted by the one-dimensional two-scale theory. These results support the findings of Bonar et al. [2], who showed that under certain oscillatory flow conditions, the power produced by a partial-width tidal turbine array can be much greater than predicted by two-scale theory. The departure from theory is most noticeable in the case of five turbine rows, where the two-scale theory predicts that the maximum available power should decrease with increasing local blockage but the numerical model shows the maximum available power to increase. The effects of local blockage are found to be less pronounced for the more realistic tidal rotor than for the highly idealised actuator disc but for both models, the results show that in oscillatory flow, considerably more power is available to the shorter and more highly blocked turbine arrays.

scholarly journals Comparison of synthetic turbulence approaches for blade element momentum theory prediction of tidal turbine performance and loads

2020 ◽  
Vol 145 ◽  
pp. 408-418 ◽  
Author(s):  
Michael Togneri ◽  
Grégory Pinon ◽  
Clément Carlier ◽  
Camille Choma Bex ◽  
Ian Masters
Keyword(s):  
Blade Element Momentum Theory ◽  
Momentum Theory ◽  
Turbine Performance ◽  
Tidal Turbine ◽  
Blade Element

Centred and staggered arrangements of tidal turbines

2013 ◽  
Vol 739 ◽  
pp. 72-93 ◽  
Author(s):  
S. Draper ◽  
T. Nishino
Keyword(s):  
Average Power ◽  
Wind Farms ◽  
Fixed Number ◽  
Offshore Wind ◽  
Offshore Wind Farms ◽  
Pressure Equalization ◽  
Tidal Turbines ◽  
Actuator Disc ◽  
Staggered Arrangement ◽  
Tidal Turbine

AbstractIn this paper we extend linear momentum actuator disc theory to consider two rows of tidal turbines placed in a centred or staggered arrangement. The extensions assume a streamwise spacing between rows that is sufficient for pressure equalization, but is not too large for significant mixing of the upstream turbine wake before the second row. We first consider a given number of turbines in a tidal channel; in this case the average power for a staggered arrangement over two rows is found to be higher than that for a centred arrangement, but lower than can be obtained by placing all turbines side-by-side in one row (if all turbines have the same local resistance). Furthermore, staggered arrangements extract power more efficiently than centred arrangements, but less efficiently than a single row with the same number of turbines, and this has implications for ranking different arrangements of tidal turbines. We also use the extended actuator disc models (together with an argument of scale separation) to consider some example arrangements of tidal turbines in laterally unconfined flow. Specifically, it is shown that locally staggering a fixed number of turbines in an array to form a tidal farm generates less power than placing the same number of turbines side-by-side. However, if more than one row of turbines is adopted (perhaps to keep the farm spatially compact) then the optimum turbine spacing within a row increases significantly with addition of a second row. This trend suggests that multi-row tidal turbine farms would require wide turbine spacing within each row to maximize the power per turbine, similarly to existing offshore wind farms.

Design of a Tidal Turbine Array for the Bohai Strait, China

2018 ◽  
Author(s):  
Lei Chen ◽  
Paul A. J. Bonar ◽  
Thomas A. A. Adcock
Keyword(s):  
Design Strategies ◽  
Stream Power ◽  
Tidal Turbines ◽  
Actuator Disc ◽  
Tidal Turbine ◽  
Tidal Stream ◽  
Flow Through ◽  
Turbine Arrays ◽  
Theoretical Results ◽  
Bohai Strait

In this paper, we consider array design strategies to maximise the power available to turbines placed in the Bohai Strait, which is considered to be one of China’s most promising candidate sites for tidal stream power. The discontinuous Galerkin version of the open-source hydrodynamic model ADCIRC is used to simulate flow through the strait and tidal turbines are introduced using a sub-grid scale actuator disc model. New design algorithms based on key theoretical results are used to build large arrays, which are then compared in terms of both the collective power output and the power produced per turbine. The results of the analysis are used to draw general conclusions about the optimal design of tidal turbine arrays.

scholarly journals Cross-Flow Tidal Turbines with Highly Flexible Blades—Experimental Flow Field Investigations at Strong Fluid–Structure Interactions

Energies ◽  
2021 ◽  
Vol 14 (4) ◽  
pp. 797
Author(s):  
Stefan Hoerner ◽  
Iring Kösters ◽  
Laure Vignal ◽  
Olivier Cleynen ◽  
Shokoofeh Abbaszadeh ◽  
...  
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Cross Flow ◽  
Speed Ratio ◽  
Fluid Structure Interactions ◽  
Dimensional Parameter ◽  
Fluid Structure ◽  
Passive Flow Control ◽  
Tidal Turbines ◽  
Tidal Turbine

Oscillating hydrofoils were installed in a water tunnel as a surrogate model for a hydrokinetic cross-flow tidal turbine, enabling the study of the effect of flexible blades on the performance of those devices with high ecological potential. The study focuses on a single tip-speed ratio (equal to 2), the key non-dimensional parameter describing the operating point, and solidity (equal to 1.5), quantifying the robustness of the turbine shape. Both parameters are standard values for cross-flow tidal turbines. Those lead to highly dynamic characteristics in the flow field dominated by dynamic stall. The flow field is investigated at the blade level using high-speed particle image velocimetry measurements. Strong fluid–structure interactions lead to significant structural deformations and highly modified flow fields. The flexibility of the blades is shown to significantly reduce the duration of the periodic stall regime; this observation is achieved through systematic comparison of the flow field, with a quantitative evaluation of the degree of chaotic changes in the wake. In this manner, the study provides insights into the mechanisms of the passive flow control achieved through blade flexibility in cross-flow turbines.

scholarly journals Rotor Loading Characteristics of a Full-Scale Tidal Turbine

Energies ◽  
2019 ◽  
Vol 12 (6) ◽  
pp. 1035 ◽  
Author(s):  
Magnus Harrold ◽  
Pablo Ouro
Keyword(s):  
Turbulent Flows ◽  
Mechanical Loading ◽  
Full Scale ◽  
Design Stage ◽  
Flow Profile ◽  
Expected Return ◽  
Tidal Turbines ◽  
Theoretical Predictions ◽  
Tidal Turbine

Tidal turbines are subject to highly dynamic mechanical loading through operation in some of the most energetic waters. If these loads cannot be accurately quantified at the design stage, turbine developers run the risk of a major failure, or must choose to conservatively over-engineer the device at additional cost. Both of these scenarios have consequences on the expected return from the project. Despite an extensive amount of research on the mechanical loading of model scale tidal turbines, very little is known from full-scale devices operating in real sea conditions. This paper addresses this by reporting on the rotor loads measured on a 400 kW tidal turbine. The results obtained during ebb tidal conditions were found to agree well with theoretical predictions of rotor loading, but the measurements during flood were lower than expected. This is believed to be due to a disturbance in the approaching flood flow created by the turbine frame geometry, and, to a lesser extent, the non-typical vertical flow profile during this tidal phase. These findings outline the necessity to quantify the characteristics of the turbulent flows at sea sites during the entire tidal cycle to ensure the long-term integrity of the deployed tidal turbines.

scholarly journals The Importance of Fault Prediction in a Tidal Turbine. Misalignment and Cracks in the Shaft

Proceedings ◽  
2018 ◽  
Vol 2 (22) ◽  
pp. 1368
Author(s):  
Beatriz F. Cal ◽  
Pedro Fraga
Keyword(s):  
Failure Prediction ◽  
Ocean Currents ◽  
Fault Prediction ◽  
Early Failure ◽  
Tidal Turbines ◽  
Early Appearance ◽  
Rapid Changes ◽  
Tidal Turbine

This study is focused on the early failure prediction of underwater Tidal Turbines. These types of turbines undergo strong torques due to ocean currents which also causes rapid changes in direction and speed which subjected to important loads and misalignments. The main objective of this study is therefore to analyse the response to the constant vibration produced by those misalignments and early appearance of cracks in this shaft.

A French Application Case of Tidal Turbine Certification

2016 ◽  
Author(s):  
Stéphane Paboeuf ◽  
Laura-Mae Macadré ◽  
Pascal Yen Kai Sun
Keyword(s):  
Renewable Energy ◽  
Water Current ◽  
Support Structure ◽  
Design Assessment ◽  
Certification Scheme ◽  
Tidal Turbines ◽  
Marine Energy ◽  
Certification Procedure ◽  
Tidal Turbine

Tidal turbines are emerging technologies offering great potential for the harnessing of a renewable and predictable oceanic resource. However, exploitation at sea comes with significant design, installation, grid connection, and maintenance operations challenges. Consequently, guidelines and standards are required to ensure safety, quality, performance and accelerate tidal turbines development and commercialisation. Standardisation is also a necessity to support and improve safety and confidence of a wide range of Marine Renewable Energy (MRE) stakeholders such as designers, project operators, investors, insurers or final users. There are undergoing developments on guidelines, standards and certification systems within the International Electrotechnical Commission (IEC) Technical Committee TC 114 “Marine energy - Wave, tidal and other water current converters” and the IEC Renewable Energy “Marine Energy - Operational Management Committee” (IECRE ME – OMC). However, as the tidal energy concepts are only at the demonstration stage, only few guidelines and no dedicated certification scheme has been published so far within this organization, which guarantee an international, independent, non-governmental and consensus-based elaboration process. The aim of this paper is to present a proposal of certification methodology, developed by Bureau Veritas for the design assessment of current and tidal turbines, and its application to a French case study. This certification procedure was developed within the French research project Sabella D10 funded by ADEME and is published in the Bureau Veritas guideline NI603 “Current & Tidal Turbines”. The suggested certification procedure addresses prototype, component, type and project certification. Main objective, scope, intermediary steps to be completed and resulting certificates will be detailed for each certification scheme, as well as their interactions. This methodology will be illustrated by the case study on the Sabella D10 prototype, a French tidal turbine installed in 2015 in the Fromveur Passage, off Ushant Island. Sabella D10 is a 1 MW tidal turbine fully submerged laid on the seabed with a horizontal axis and 6 blades. It is the first French tidal turbine producing electricity and connected to the electrical network. The Sabella D10 case study will focus on prototype certification and computations performed for support structure and blades. The paper will describe the load cases that have been considered, the review procedure for the support structure and the blades design assessment, including description of a streamlined method for basic design and a detailed method for final design. In conclusion, the next steps will be introduced to continue the certification developments of tidal and current turbines.

scholarly journals Passive acoustic methods for tracking the 3D movements of small cetaceans around marine structures

2020 ◽  
Author(s):  
Douglas Gillespie ◽  
Laura Palmer ◽  
Jamie Macaulay ◽  
Carol Sparling ◽  
Gordon Hastie
Keyword(s):  
Marine Mammals ◽  
New Technologies ◽  
Three Dimensional ◽  
Tidal Energy ◽  
Time Of Arrival ◽  
Marine Animals ◽  
Tidal Turbines ◽  
Wide Range ◽  
Tidal Turbine ◽  
Passive Acoustic

AbstractA wide range of anthropogenic structures exist in the marine environment with the extent of these set to increase as the global offshore renewable energy industry grows. Many of these pose acute risks to marine wildlife; for example, tidal energy generators have the potential to injure or kill seals and small cetaceans through collisions with moving turbine parts. Information on fine scale behaviour of animals close to operational turbines is required to understand the likely impact of these new technologies. There are inherent challenges associated with measuring the underwater movements of marine animals which have, so far, limited data collection. Here, we describe the development and application of a system for monitoring the three-dimensional movements of cetaceans in the immediate vicinity of a subsea structure. The system comprises twelve hydrophones and software for the detection and localisation of vocal marine mammals. We present data demonstrating the systems practical performance during a deployment on an operational tidal turbine between October 2017 and October 2019. Three-dimensional locations of cetaceans were derived from the passive acoustic data using time of arrival differences on each hydrophone. Localisation accuracy was assessed with an artificial sound source at known locations and a refined method of error estimation is presented. Calibration trials show that the system can accurately localise sounds to 2m accuracy within 20m of the turbine but that localisations become highly inaccurate at distances greater than 35m. The system is currently being used to provide data on rates of encounters between cetaceans and the turbine and to provide high resolution tracking data for animals close to the turbine. These data can be used to inform stakeholders and regulators on the likely impact of tidal turbines on cetaceans.

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