Turbine design dependency to turbulence: An experimental study of three scaled tidal turbines

An experimental study is presented on the performance of a vertical axis wind turbine with variable blade geometry of the design developed by Austin Farrah. This is experimentally compared with the performance of a correspondingly sized Bach-type Savonius turbine using the same electrical generator and measurement instrumentation in a wind tunnel. Experiments were performed for Reynolds numbers, based on blade chord, in the range 5 × 103 to 1 × 105, and for blade settings between −40° and +40o. The study shows that for the tip speed ratios that have been investigated, the Farrah vertical axis wind turbine design can only marginally outperform a corresponding two-bladed Bach-type Savonius turbine and then only when its blades are set to 40° pitch angle. The presence of a small inner cylinder, which rotates with the turbine, does not enhance its performance due to the fact that it is immersed in an extensive column of relatively static air.

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Tidal Turbine Load Variability in Following and Opposing Irregular Wave Conditions

Volume 9: Ocean Renewable Energy ◽

10.1115/omae2020-18701 ◽

2020 ◽

Author(s):

Samuel Draycott ◽

Jeffrey Steynor ◽

Anup Nambiar ◽

Brian Sellar ◽

Vengatesan Venugopal

Keyword(s):

Wave Interaction ◽

Irregular Waves ◽

Current Direction ◽

Irregular Wave ◽

Tidal Turbines ◽

Wave Parameters ◽

Load Distributions ◽

Equivalent Wave ◽

Tidal Turbine ◽

Turbine Design

Abstract Waves induce large loads on tidal turbines, yet the effect of irregular waves, particularly those which oppose the current direction, have received little attention. Here we experimentally assess the loading resulting from 24 irregular combined wave-current cases, statistically presenting the load variability acting on a 1:15 scale tidal turbine. Comparisons are made between following and opposing conditions of equivalent wave parameters, and the effect of varying frequency and amplitude is assessed. Example load distributions are also shown, along with streamwise variation of significant wave height around the turbine. It is concluded that both opposing and following conditions must be assessed to effectively de-risk tidal turbine design: large differences are observed both in terms of the nature & magnitude of the resulting loads and the wave interaction with the surrounding flow field.

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Designing multi-rotor tidal turbine fences

International Marine Energy Journal ◽

10.36688/imej.1.61-70 ◽

2018 ◽

Vol 1 (1 (Aug)) ◽

pp. 61-70 ◽

Cited By ~ 3

Author(s):

C. R. Vogel ◽

R. H. J. Willden

Keyword(s):

Navier Stokes ◽

Disk Model ◽

Local Flow ◽

Cavitation Inception ◽

Tidal Turbines ◽

Solidity Ratio ◽

Flow Phenomena ◽

Tidal Turbine ◽

Turbine Design ◽

Confined Flows

An embedded Reynolds-Averaged Navier-Stokes blade element actuator disk model is used to investigate the hydrodynamic design of tidal turbines and their performance in a closely spaced cross-stream fence. Turbines designed for confined flows are found to require a larger blade solidity ratio than current turbine design practices imply in order to maximise power. Generally, maximum power can be increased by operating turbines in more confined flows than they were designed for, although this also requires the turbines to operate at a higher rotational speed, which may increase the likelihood of cavitation inception. In-array turbine performance differs from that predicted from single turbine analyses, with cross-fence variation in power and thrust developing between the inboard and outboard turbines. As turbine thrust increases the cross-fence variation increases, as the interference effects between adjacent turbines strengthen as turbine thrust increases, but it is observed that cross-stream variation can be mitigated through strategies such as pitch-to-feather power control. It was found that overall fence performance was maximised by using turbines designed for moderately constrained (blocked) flows, with greater blockage than that based solely on fence geometry, but lower blockage than that based solely on the turbine and local flow passage geometry to balance the multi-scale flow phenomena around tidal fences.

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Experimental study on the restoration from a tilt-azimuth series for improvement in resolution

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s042482010013955x ◽

1995 ◽

Vol 53 ◽

pp. 636-637

Author(s):

Norio Baba ◽

Norihiko Ichise ◽

Syunya Watanabe

Keyword(s):

Experimental Study ◽

Spherical Aberration ◽

Incident Beam ◽

Optical Parameters ◽

Beam Tilting ◽

Illumination Method ◽

Restoration Method ◽

Illumination Mode

The tilted beam illumination method is used to improve the resolution comparing with the axial illumination mode. Using this advantage, a restoration method of several tilted beam images covering the full azimuthal range was proposed by Saxton, and experimentally examined. To make this technique more reliable it seems that some practical problems still remain. In this report the restoration was attempted and the problems were considered. In our study, four problems were pointed out for the experiment of the restoration. (1) Accurate beam tilt adjustment to fit the incident beam to the coma-free axis for the symmetrical beam tilting over the full azimuthal range. (2) Accurate measurements of the optical parameters which are necessary to design the restoration filter. Even if the spherical aberration coefficient Cs is known with accuracy and the axial astigmatism is sufficiently compensated, at least the defocus value must be measured. (3) Accurate alignment of the tilt-azimuth series images.

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