The characterisation of the hydrodynamic loads on tidal turbines due to turbulence

I.A. Milne, A.H. Day, R.N. Sharma, R.G.J. Flay

Research output: Contribution to journalArticle

18 Citations (Scopus)

Abstract

An improved characterisation of the hydrodynamic blade loads due to onset turbulence is essential in order to mitigate premature failures, reduce excessive levels of conservativeness and ultimately ensure the commercial viability of tidal turbines. The literature focussing on the turbulence in fast flowing tidal streams and of the unsteady loads that are subsequently imparted to rotors has previously been very limited. However, increased activity in the tidal energy community has led to new investigations and insights which are reported in this paper.

It has been found that through the use of acoustic Doppler-based sensors, the streamwise turbulence intensities generally tend to a value of approximately 6–8% at the mid-depth of proposed tidal energy sites. Evidence that the anisotropic structure and scales of the turbulence are more consistent with open-channel-based models than atmospheric-based correlations has also been found. Rapid distortion theory has been applied to estimate that the standard deviation of the streamwise turbulent velocity fluctuations in the onset free-stream flow may be amplified significantly by 15% due to the presence of a turbine. The turbulent fluctuations have also been predicted to remain well correlated over the outer span of the blades at the rotational frequency of the rotor.

Recent model-scale experiments have enabled the unsteady hydrodynamic loading to be isolated from the steady-flow loading. For cases where the boundary layer remains primarily attached across the blades, this has enabled linear transfer functions to be developed and applied to model the response to a multi-frequency forcing. It has also been found that phenomena consistent with delayed separation and dynamic stall can result in a blade root bending moment that exceeds the steady value by 25%, and this needs to be taken into account in design to reduce the probability of failure.
LanguageEnglish
Pages851-864
Number of pages14
JournalRenewable and Sustainable Energy Reviews
Volume56
Early online date22 Dec 2015
DOIs
Publication statusPublished - 1 Apr 2016

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Turbulence
Turbines
Hydrodynamics
Rotors
Stream flow
Steady flow
Bending moments
Turbomachine blades
Transfer functions
Boundary layers
Acoustics
Sensors
Experiments

Keywords

  • tidal turbine
  • turbulence
  • unsteady hydrodynamics
  • model-scale testing

Cite this

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title = "The characterisation of the hydrodynamic loads on tidal turbines due to turbulence",
abstract = "An improved characterisation of the hydrodynamic blade loads due to onset turbulence is essential in order to mitigate premature failures, reduce excessive levels of conservativeness and ultimately ensure the commercial viability of tidal turbines. The literature focussing on the turbulence in fast flowing tidal streams and of the unsteady loads that are subsequently imparted to rotors has previously been very limited. However, increased activity in the tidal energy community has led to new investigations and insights which are reported in this paper.It has been found that through the use of acoustic Doppler-based sensors, the streamwise turbulence intensities generally tend to a value of approximately 6–8{\%} at the mid-depth of proposed tidal energy sites. Evidence that the anisotropic structure and scales of the turbulence are more consistent with open-channel-based models than atmospheric-based correlations has also been found. Rapid distortion theory has been applied to estimate that the standard deviation of the streamwise turbulent velocity fluctuations in the onset free-stream flow may be amplified significantly by 15{\%} due to the presence of a turbine. The turbulent fluctuations have also been predicted to remain well correlated over the outer span of the blades at the rotational frequency of the rotor.Recent model-scale experiments have enabled the unsteady hydrodynamic loading to be isolated from the steady-flow loading. For cases where the boundary layer remains primarily attached across the blades, this has enabled linear transfer functions to be developed and applied to model the response to a multi-frequency forcing. It has also been found that phenomena consistent with delayed separation and dynamic stall can result in a blade root bending moment that exceeds the steady value by 25{\%}, and this needs to be taken into account in design to reduce the probability of failure.",
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The characterisation of the hydrodynamic loads on tidal turbines due to turbulence. / Milne, I.A.; Day, A.H.; Sharma, R.N.; Flay, R.G.J.

In: Renewable and Sustainable Energy Reviews , Vol. 56, 01.04.2016, p. 851-864.

Research output: Contribution to journalArticle

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AU - Day, A.H.

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