Tag Archives: Horizontal axis

Shape design and numerical analysis on a 1 MW tidal current turbine for the south-western coast of Korea


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Patrick Mark Singh and Young-Do Choi, Renewable Energy – August 2014

Abstract

The study concentrates on the shape design and numerical analysis of a 1 MW horizontal axis tidal current turbine (HATCT), which can be applied near the southwest regions of Korea. On the basis of actual tidal current conditions of south-western region of Korea, configuration design of 1 MW class turbine rotor blade is carried out by blade element momentum theory (BEMT). The hydrodynamic performance including the lift and drag forces, is conducted with the variation of the angle of attack using an open source code of X-Foil. The optimized blade geometry is used for Computational Fluid Dynamics (CFD) analysis with hexahedral numerical grids. This study focuses on developing a new hydrofoil and designing a blade with relatively shorter chord length in contrast to a typical TCT blade. Therefore, after a thorough study of two common hydrofoils, (S814 and DU-91-W2-250, which show good performance for rough conditions), a new hydrofoil, MNU26, is developed. The new hydrofoil has a 26% thickness that can be applied throughout the blade length, giving good structural strength. Power coefficient, pressure and velocity distributions are investigated according to Tip Speed Ratio by CFD analysis. As cavitation analysis is also an important part of the study, it is investigated for all the three hydrofoils. Due to the shorter chord length of the new turbine blade in contrast to a typical TCT blade design, a Fluid Structure Interaction (FSI) analysis is also done. Concrete conclusions have been made after comparing the three hydrofoils, considering their performance, efficiency, occurrence of cavitation and structural feasibility.

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Shaping array design of marine current energy converters through scaled experimental analysis


A.S. Bahaj and L.E. Myers – Energy, August 2013

Abstract

Marine current energy converters or tidal turbines represent an emerging renewable energy technology that can provide a predictable supply of electricity. Single devices are in operation around the world with aspirations to deploy farms or arrays of multiple devices.

We present an experimental study that has characterised the downstream wake flow around a 1/15th-scale turbine in a large circulating water channel and a series of experiments involving static actuator disks at 1/120th-scale allowing simulation of multiple-device layouts.

Our analysis demonstrates that the near wake is highly turbulent with structures generated by the rotor and support structure. This region of flow may prove difficult to numerically simulate with a high degree of accuracy. In the far wake the performance of static actuator disks can be matched to mechanical rotors reducing scale and cost facilitating replication of complex array geometries. Here the ambient turbulence and geometric properties of the device/channel drive the wake recovery towards free stream conditions.

Devices operating downstream of others will be subject to a non-steady flow field making comparative performance difficult. We discuss the possibility of unequal device specification and rated power within an array (unlike wind farms) providing a more representative measure of array performance.

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Marine current energy resource assessment and design of a marine current turbine for Fiji


Jai N. Goundar and M. Rafiuddin Ahmed – Renewable Energy, July 2013

Abstract

Pacific Island Countries (PICs) have a huge potential for renewable energy to cater for their energy needs. Marine current energy is a reliable and clean energy source. Many marine current streams are available in Fiji’s waters and large amount of marine current energy can be extracted using turbines. Horizontal axis marine current turbine (HAMCT) can be used to extract marine current energy to electrical energy for commercial use. For designing a HAMCT, marine current resource assessment needs to done. A potential site was identified and resource assessment was done for 3 months. Continue reading

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The effect of surface waves on the performance characteristics of a model tidal turbine


L. Luznik, K.A. Flack, E.E. Lust, and K. Taylor – Renewable Energy, November, 2013

Abstract

Scale model tests were conducted on a three bladed horizontal axis tidal turbine in a large tow tank facility at the United States Naval Academy. Performance characteristics are presented for a turbine towed at a constant carriage speed for cases with and without surface waves. Intermediate waves were modeled that are representative of swells typically found on the continental shelf of the United States eastern seaboard. The oscillatory wave velocity present in the water column results in significant variations in measured turbine torque and rotational speed as a function of wave phase. This in turn produces cyclic variations in tip speed ratio and power coefficient. The power coefficient over the entire wave phase did not show a difference from the experiments without waves for a range of tip speed ratios, as reported in previous studies. The waves limited the lower range of tip speed ratios at which the turbine could operate. These results highlight the impact of surface waves on turbine design and performance, and the importance of understanding the site-specific wave conditions.

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Flume tank characterization of marine current turbine blade behaviour under current and wave loading


B. Gaurier, P. Davies, A. Deuff, G. Germain – Renewable Energy, November, 2013

Abstract

The long term reliability of tidal turbines is critical if these structures are to be cost-effective. Optimized design requires a combination of material durability models and structural analyses which must be based on realistic loading conditions.

This paper presents results from a series of flume tank measurements on strain gauged scaled turbine blades, aimed at studying these conditions. A detailed series of tests on a 3-blade horizontal axis turbine with 400 mm long blades is presented. The influence of both current and wave-current interactions on measured strains is studied. These tests show that wave-current interactions can cause large additional loading amplitudes compared to currents alone, which must be considered in the fatigue analysis of these systems.

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2002–2012: 10 Years of Research Progress in Horizontal-Axis Marine Current Turbines


Kai-Wern Ng, Wei-Haur Lam, and Khai-Ching Ng – Energies, March, 2013

Abstract

Research in marine current energy, including tidal and ocean currents, has undergone significant growth in the past decade. The horizontal-axis marine current turbine is one of the machines used to harness marine current energy, which appears to be the most technologically and economically viable one at this stage. A number of large-scale marine current turbines rated at more than 1 MW have been deployed around the World. Parallel to the development of industry, academic research on horizontal-axis marine current turbines has also shown positive growth. This paper reviews previous research on horizontal-axis marine current turbines and provides a concise overview for future researchers who might be interested in horizontal-axis marine current turbines. The review covers several main aspects, such as: energy assessment, turbine design, wakes, generators, novel modifications and environmental impact. Future trends for research on horizontal-axis marine current turbines are also discussed.

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Interactions between tidal turbine wakes: experimental study of a group of three-bladed rotors


T. Stallard, R. Collings, T. Feng and J. Whelan – Phil. Trans. R. Soc. A, 2013

Abstract

It is well known that a wake will develop downstream of a tidal stream turbine owing to extraction of axial momentum across the rotor plane. To select a suitable layout for an array of horizontal axis tidal stream turbines, it is important to understand the extent and structure of the wakes of each turbine. Studies of wind turbines and isolated tidal stream turbines have shown that the velocity reduction in the wake of a single device is a function of the rotor operating state (specifically thrust), and that the rate of recovery of wake velocity is dependent on mixing between the wake and the surrounding flow. For an unbounded flow, the velocity of the surrounding flow is similar to that of the incident flow. However, the velocity of the surrounding flow will be increased by the presence of bounding surfaces formed by the bed and free surface, and by the wake of adjacent devices. This paper presents the results of an experimental study investigating the influence of such bounding surfaces on the structure of the wake of tidal stream turbines.

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