Researchers from the University of Western Australia (UWA) have developed a new way of calculating turbulence intensities on wind and tidal turbines with greater accuracy.
As countries across the globe continue to seek out cleaner and more sustainable electricity generation, there has been a growing interest in wind and tidal power. However, many people may not be aware that wind and tidal turbines are fatigue sensitive devices, with the unsteady (turbulent) upstream flow being a major contributor to blade fatigue.
Early generation turbine blades were falling well short of their 20-25 year design life due to a lack of knowledge of turbulence and its effect on the blade loads. As a result, large safety factors are routinely adopted in design, affecting the cost-competitiveness of the industry.
According to Dr Ian Milne, UWA Research Fellow, the research was motivated by this and aims to reduce the uncertainties associated with turbulence-induced turbine loads.
Dr Milne’s PhD research at the University of Auckland, completed in 2014, was undertaken in collaboration with leading international tidal turbine companies and consultancies and analysed new field measurements of the turbulence within a proposed tidal energy site in Scotland (pictured).
Using an extensive dataset acquired by the metocean consultancy Partrac Ltd in 2009 on behalf of leading turbine manufacturer Andritz Hydro Hammerfest (AHH) and ScottishPower Renewables, the research provided the industry with essential new insights into the properties of turbulence in rapid tidal flows and identified important differences between tidal and atmospheric turbulent flows.
More recently, Dr Milne’s research at UWA, in collaboration with Imperial College London and tidal turbine companies, is focused on developing new methodologies to explicitly account for the changes in the turbulence when it encounters a turbine rotor.
Installation of the AHH tidal turbine for the MeyGen project (image supplied).
Dr Milne said that the standard method adopted by industry to compute the fatigue loads assumes that the turbulence remains unchanged as it encounters a turbine rotor.
“However, this approach neglects the effect of distortion and unsteady blockage which can amplify or attenuate the turbulence and therefore the fatigue loads,” he explained.
“To address this shortcoming, through new research we have developed a theory to account for turbulence distortion and unsteady pressure which can be included in standard analyses.”
The new theory developed by the researchers is expected to help turbine designers more accurately predict the fatigue of equipment and improve the efficiency in generating wind and tidal power.
The theory allows for both the distortion of the turbulent field as well as for the unsteady pressure field imposed by the turbine and is applicable for both below-rated and above-rated turbine operations.
The research also drew on recent technological advances (such as LIDAR and Acoustic Doppler Current Profilers) to obtain field measurements from the flow immediately upstream of the turbine, which have been used to verify the theoretical model.
“Ultimately, these research programmes are intended to provide the renewables industry with a means of obtaining more reliable estimates of the fatigue loads and consequentially reduce the conservativeness employed in design,” Dr Milne commented.
